Three-dimensional local grid refinement for block-centered finite-difference groundwater models using iteratively coupled shared nodes: A new method of interpolation and analysis of errors

USGS Publications Warehouse

Mehl, S.; Hill, M.C.

2004-01-01

This paper describes work that extends to three dimensions the two-dimensional local-grid refinement method for block-centered finite-difference groundwater models of Mehl and Hill [Development and evaluation of a local grid refinement method for block-centered finite-difference groundwater models using shared nodes. Adv Water Resour 2002;25(5):497-511]. In this approach, the (parent) finite-difference grid is discretized more finely within a (child) sub-region. The grid refinement method sequentially solves each grid and uses specified flux (parent) and specified head (child) boundary conditions to couple the grids. Iteration achieves convergence between heads and fluxes of both grids. Of most concern is how to interpolate heads onto the boundary of the child grid such that the physics of the parent-grid flow is retained in three dimensions. We develop a new two-step, "cage-shell" interpolation method based on the solution of the flow equation on the boundary of the child between nodes shared with the parent grid. Error analysis using a test case indicates that the shared-node local grid refinement method with cage-shell boundary head interpolation is accurate and robust, and the resulting code is used to investigate three-dimensional local grid refinement of stream-aquifer interactions. Results reveal that (1) the parent and child grids interact to shift the true head and flux solution to a different solution where the heads and fluxes of both grids are in equilibrium, (2) the locally refined model provided a solution for both heads and fluxes in the region of the refinement that was more accurate than a model without refinement only if iterations are performed so that both heads and fluxes are in equilibrium, and (3) the accuracy of the coupling is limited by the parent-grid size - A coarse parent grid limits correct representation of the hydraulics in the feedback from the child grid.

Geostatistical applications in ground-water modeling in south-central Kansas

USGS Publications Warehouse

Ma, T.-S.; Sophocleous, M.; Yu, Y.-S.

1999-01-01

This paper emphasizes the supportive role of geostatistics in applying ground-water models. Field data of 1994 ground-water level, bedrock, and saltwater-freshwater interface elevations in south-central Kansas were collected and analyzed using the geostatistical approach. Ordinary kriging was adopted to estimate initial conditions for ground-water levels and topography of the Permian bedrock at the nodes of a finite difference grid used in a three-dimensional numerical model. Cokriging was used to estimate initial conditions for the saltwater-freshwater interface. An assessment of uncertainties in the estimated data is presented. The kriged and cokriged estimation variances were analyzed to evaluate the adequacy of data employed in the modeling. Although water levels and bedrock elevations are well described by spherical semivariogram models, additional data are required for better cokriging estimation of the interface data. The geostatistically analyzed data were employed in a numerical model of the Siefkes site in the project area. Results indicate that the computed chloride concentrations and ground-water drawdowns reproduced the observed data satisfactorily.This paper emphasizes the supportive role of geostatistics in applying ground-water models. Field data of 1994 ground-water level, bedrock, and saltwater-freshwater interface elevations in south-central Kansas were collected and analyzed using the geostatistical approach. Ordinary kriging was adopted to estimate initial conditions for ground-water levels and topography of the Permian bedrock at the nodes of a finite difference grid used in a three-dimensional numerical model. Cokriging was used to estimate initial conditions for the saltwater-freshwater interface. An assessment of uncertainties in the estimated data is presented. The kriged and cokriged estimation variances were analyzed to evaluate the adequacy of data employed in the modeling. Although water levels and bedrock elevations are well described by spherical semivariogram models, additional data are required for better cokriging estimation of the interface data. The geostatistically analyzed data were employed in a numerical model of the Siefkes site in the project area. Results indicate that the computed chloride concentrations and ground-water drawdowns reproduced the observed data satisfactorily.

A simulation-optimization model for effective water resources management in the coastal zone

NASA Astrophysics Data System (ADS)

Spanoudaki, Katerina; Kampanis, Nikolaos

2015-04-01

Coastal areas are the most densely-populated areas in the world. Consequently water demand is high, posing great pressure on fresh water resources. Climatic change and its direct impacts on meteorological variables (e.g. precipitation) and indirect impact on sea level rise, as well as anthropogenic pressures (e.g. groundwater abstraction), are strong drivers causing groundwater salinisation and subsequently affecting coastal wetlands salinity with adverse effects on the corresponding ecosystems. Coastal zones are a difficult hydrologic environment to represent with a mathematical model due to the large number of contributing hydrologic processes and variable-density flow conditions. Simulation of sea level rise and tidal effects on aquifer salinisation and accurate prediction of interactions between coastal waters, groundwater and neighbouring wetlands requires the use of integrated surface water-groundwater mathematical models. In the past few decades several computer codes have been developed to simulate coupled surface and groundwater flow. However, most integrated surface water-groundwater models are based on the assumption of constant fluid density and therefore their applicability to coastal regions is questionable. Thus, most of the existing codes are not well-suited to represent surface water-groundwater interactions in coastal areas. To this end, the 3D integrated surface water-groundwater model IRENE (Spanoudaki et al., 2009; Spanoudaki, 2010) has been modified in order to simulate surface water-groundwater flow and salinity interactions in the coastal zone. IRENE, in its original form, couples the 3D shallow water equations to the equations describing 3D saturated groundwater flow of constant density. A semi-implicit finite difference scheme is used to solve the surface water flow equations, while a fully implicit finite difference scheme is used for the groundwater equations. Pollution interactions are simulated by coupling the advection-diffusion equation describing the fate and transport of contaminants introduced in a 3D turbulent flow field to the partial differential equation describing the fate and transport of contaminants in 3D transient groundwater flow systems. The model has been further developed to include the effects of density variations on surface water and groundwater flow, while the already built-in solute transport capabilities are used to simulate salinity interactions. The refined model is based on the finite volume method using a cell-centred structured grid, providing thus flexibility and accuracy in simulating irregular boundary geometries. For addressing water resources management problems, simulation models are usually externally coupled with optimisation-based management models. However this usually requires a very large number of iterations between the optimisation and simulation models in order to obtain the optimal management solution. As an alternative approach, for improved computational efficiency, an Artificial Neural Network (ANN) is trained as an approximate simulator of IRENE. The trained ANN is then linked to a Genetic Algorithm (GA) based optimisation model for managing salinisation problems in the coastal zone. The linked simulation-optimisation model is applied to a hypothetical study area for performance evaluation. Acknowledgement The work presented in this paper has been funded by the Greek State Scholarships Foundation (IKY), Fellowships of Excellence for Postdoctoral Studies (Siemens Program), 'A simulation-optimization model for assessing the best practices for the protection of surface water and groundwater in the coastal zone', (2013 - 2015). References Spanoudaki, K., Stamou, A.I. and Nanou-Giannarou, A. (2009). Development and verification of a 3-D integrated surface water-groundwater model. Journal of Hydrology, 375 (3-4), 410-427. Spanoudaki, K. (2010). Integrated numerical modelling of surface water groundwater systems (in Greek). Ph.D. Thesis, National Technical University of Athens, Greece.

A finite-element model for simulation of two-dimensional steady-state ground-water flow in confined aquifers

USGS Publications Warehouse

Kuniansky, E.L.

1990-01-01

A computer program based on the Galerkin finite-element method was developed to simulate two-dimensional steady-state ground-water flow in either isotropic or anisotropic confined aquifers. The program may also be used for unconfined aquifers of constant saturated thickness. Constant head, constant flux, and head-dependent flux boundary conditions can be specified in order to approximate a variety of natural conditions, such as a river or lake boundary, and pumping well. The computer program was developed for the preliminary simulation of ground-water flow in the Edwards-Trinity Regional aquifer system as part of the Regional Aquifer-Systems Analysis Program. Results of the program compare well to analytical solutions and simulations .from published finite-difference models. A concise discussion of the Galerkin method is presented along with a description of the program. Provided in the Supplemental Data section are a listing of the computer program, definitions of selected program variables, and several examples of data input and output used in verifying the accuracy of the program.

MODFLOW-2000, The U.S. Geological Survey Modular Ground-Water Model -- GMG Linear Equation Solver Package Documentation

USGS Publications Warehouse

Wilson, John D.; Naff, Richard L.

2004-01-01

A geometric multigrid solver (GMG), based in the preconditioned conjugate gradient algorithm, has been developed for solving systems of equations resulting from applying the cell-centered finite difference algorithm to flow in porous media. This solver has been adapted to the U.S. Geological Survey ground-water flow model MODFLOW-2000. The documentation herein is a description of the solver and the adaptation to MODFLOW-2000.

Fractal scaling analysis of groundwater dynamics in confined aquifers

NASA Astrophysics Data System (ADS)

Tu, Tongbi; Ercan, Ali; Kavvas, M. Levent

2017-10-01

Groundwater closely interacts with surface water and even climate systems in most hydroclimatic settings. Fractal scaling analysis of groundwater dynamics is of significance in modeling hydrological processes by considering potential temporal long-range dependence and scaling crossovers in the groundwater level fluctuations. In this study, it is demonstrated that the groundwater level fluctuations in confined aquifer wells with long observations exhibit site-specific fractal scaling behavior. Detrended fluctuation analysis (DFA) was utilized to quantify the monofractality, and multifractal detrended fluctuation analysis (MF-DFA) and multiscale multifractal analysis (MMA) were employed to examine the multifractal behavior. The DFA results indicated that fractals exist in groundwater level time series, and it was shown that the estimated Hurst exponent is closely dependent on the length and specific time interval of the time series. The MF-DFA and MMA analyses showed that different levels of multifractality exist, which may be partially due to a broad probability density distribution with infinite moments. Furthermore, it is demonstrated that the underlying distribution of groundwater level fluctuations exhibits either non-Gaussian characteristics, which may be fitted by the Lévy stable distribution, or Gaussian characteristics depending on the site characteristics. However, fractional Brownian motion (fBm), which has been identified as an appropriate model to characterize groundwater level fluctuation, is Gaussian with finite moments. Therefore, fBm may be inadequate for the description of physical processes with infinite moments, such as the groundwater level fluctuations in this study. It is concluded that there is a need for generalized governing equations of groundwater flow processes that can model both the long-memory behavior and the Brownian finite-memory behavior.

MODFLOW Ground-Water Model - User Guide to the Subsidence and Aquifer-System Compaction Package (SUB-WT) for Water-Table Aquifers

USGS Publications Warehouse

Leake, S.A.; Galloway, D.L.

2007-01-01

A new computer program was developed to simulate vertical compaction in models of regional ground-water flow. The program simulates ground-water storage changes and compaction in discontinuous interbeds or in extensive confining units, accounting for stress-dependent changes in storage properties. The new program is a package for MODFLOW, the U.S. Geological Survey modular finite-difference ground-water flow model. Several features of the program make it useful for application in shallow, unconfined flow systems. Geostatic stress can be treated as a function of water-table elevation, and compaction is a function of computed changes in effective stress at the bottom of a model layer. Thickness of compressible sediments in an unconfined model layer can vary in proportion to saturated thickness.

Hydrogeology of well-field areas near Tampa, Florida; Phase I, development and documentation of a two-dimensional finite-difference model for simulation of steady-state ground-water flow

USGS Publications Warehouse

Hutchinson, C.B.; Johnson, Dale M.; Gerhart, James M.

1981-01-01

A two-dimensional finite-difference model was developed for simulation of steady-state ground-water flow in the Floridan aquifer throughout a 932-square-mile area, which contains nine municipal well fields. The overlying surficial aquifer contains a constant-head water table and is coupled to the Floridan aquifer by a leakage term that represents flow through a confining layer separating the two aquifers. Under the steady-state condition, all storage terms are set to zero. Utilization of the head-controlled flux condition allows head and flow to vary at the model-grid boundaries. Procedures are described to calibrate the model, test its sensitivity to input-parameter errors, and verify its accuracy for predictive purposes. Also included are attachments that describe setting up and running the model. An example model-interrogation run shows anticipated drawdowns that should result from pumping at the newly constructed Cross Bar Ranch and Morris Bridge well fields. (USGS)

A comparison of analog and digital modeling techniques for simulating three-dimensional ground-water flow on Long Island, New York

USGS Publications Warehouse

Reilly, Thomas E.; Harbaugh, Arlen W.

1980-01-01

A three-dimensional electric-analog model of the Long Island, NY , groundwater system constructed by the U.S. Geological Survey in the early 1970 's was used as the basis for developing a digital, three-dimensional finite-difference model. The digital model was needed to provide faster modifications and more rapid solutions to water-management questions. Results generated by the two models are depicted as potentiometric-surface maps of the upper glacial and Magothy aquifers. Results compare favorably for all parts of Long Island except the northwestern part, where hydrologic discontinuities are most prevalent and which the two models represent somewhat differently. The mathematical and hydrologic principles used in development of ground-water models, and the procedures for calibration and acceptance, are presented in nontechnical terms. (USGS)

MODFLOW-2000, The U.S. Geological Survey Modular Ground-Water Model - User Guide to Modularization Concepts and the Ground-Water Flow Process

USGS Publications Warehouse

Harbaugh, Arlen W.; Banta, Edward R.; Hill, Mary C.; McDonald, Michael G.

2000-01-01

MODFLOW is a computer program that numerically solves the three-dimensional ground-water flow equation for a porous medium by using a finite-difference method. Although MODFLOW was designed to be easily enhanced, the design was oriented toward additions to the ground-water flow equation. Frequently there is a need to solve additional equations; for example, transport equations and equations for estimating parameter values that produce the closest match between model-calculated heads and flows and measured values. This report documents a new version of MODFLOW, called MODFLOW-2000, which is designed to accommodate the solution of equations in addition to the ground-water flow equation. This report is a user's manual. It contains an overview of the old and added design concepts, documents one new package, and contains input instructions for using the model to solve the ground-water flow equation.

Ground-water flow in the New Jersey Coastal Plain

USGS Publications Warehouse

Martin, Mary

1998-01-01

Ground-water flow in 10 aquifers and 9 intervening confining units of the New Jersey Coastal Plain was simulated as part of the Regional Aquifer System Analysis. Data on aquifer and confining unit characteristics and on pumpage and water levels from 1918 through 1980 were incorporated into a multilayer finite-difference model. The report describes the conceptual hydrogeologic model of the unstressed flow systems, the methods and approach used in simulating flow, and the results of the simulations.

Documentation of a finite-element two-layer model for simulation of ground-water flow

USGS Publications Warehouse

Mallory, Michael J.

1979-01-01

This report documents a finite-element model for simulation of ground-water flow in a two-aquifer system where the two aquifers are coupled by a leakage term that represents flow through a confining layer separating the two aquifers. The model was developed by Timothy J. Durbin (U.S. Geological Survey) for use in ground-water investigations in southern California. The documentation assumes that the reader is familiar with the physics of ground-water flow, numerical methods of solving partial-differential equations, and the FORTRAN IV computer language. It was prepared as part of the investigations made by the U.S. Geological Survey in cooperation with the San Bernardino Valley Municipal Water District. (Kosco-USGS)

MODEL -- BIOPLUME III VERSION 1.0 - SEPTEMBER 1997 (SUBSURFACE PROTECTION AND REMEDIATION DIVISION, NRMRL)

EPA Science Inventory

BIOPLUME III is a 2D, finite difference model for simulating the natural attenuation of organic contaminants in groundwater due to the processes of advection, dispersion, sorption, and biodegradation. Biotransformation processes are potentially important in the restoration of aq...

A modification of the finite-difference model for simulation of two dimensional ground-water flow to include surface-ground water relationships

USGS Publications Warehouse

Ozbilgin, M.M.; Dickerman, D.C.

1984-01-01

The two-dimensional finite-difference model for simulation of groundwater flow was modified to enable simulation of surface-water/groundwater interactions during periods of low streamflow. Changes were made to the program code in order to calculate surface-water heads for, and flow either to or from, contiguous surface-water bodies; and to allow for more convenient data input. Methods of data input and output were modified and entries (RSORT and HDRIVER) were added to the COEF and CHECKI subroutines to calculate surface-water heads. A new subroutine CALC was added to the program which initiates surface-water calculations. If CALC is not specified as a simulation option, the program runs the original version. The subroutines which solve the ground-water flow equations were not changed. Recharge, evapotranspiration, surface-water inflow, number of wells, pumping rate, and pumping duration can be varied for any time period. The Manning formula was used to relate stream depth and discharge in surface-water streams. Interactions between surface water and ground water are represented by the leakage term in the ground-water flow and surface-water mass balance equations. Documentation includes a flow chart, data deck instructions, input data, output summary, and program listing. Numerical results from the modified program are in good agreement with published analytical results. (USGS)

A Martian global groundwater model

NASA Technical Reports Server (NTRS)

Howard, Alan D.

1991-01-01

A global groundwater flow model was constructed for Mars to study hydrologic response under a variety of scenarios, improving and extending earlier simple cross sectional models. The model is capable of treating both steady state and transient flow as well as permeability that is anisotropic in the horizontal dimensions. A single near surface confining layer may be included (representing in these simulations a coherent permafrost layer). Furthermore, in unconfined flow, locations of complete saturation and seepage are determined. The flow model assumes that groundwater gradients are sufficiently low that DuPuit conditions are satisfied and the flow component perpendicular to the ground surface is negligible. The flow equations were solved using a finite difference method employing 10 deg spacing of latitude and longitude.

Composite use of numerical groundwater flow modeling and geoinformatics techniques for monitoring Indus Basin aquifer, Pakistan.

PubMed

Ahmad, Zulfiqar; Ashraf, Arshad; Fryar, Alan; Akhter, Gulraiz

2011-02-01

The integration of the Geographic Information System (GIS) with groundwater modeling and satellite remote sensing capabilities has provided an efficient way of analyzing and monitoring groundwater behavior and its associated land conditions. A 3-dimensional finite element model (Feflow) has been used for regional groundwater flow modeling of Upper Chaj Doab in Indus Basin, Pakistan. The approach of using GIS techniques that partially fulfill the data requirements and define the parameters of existing hydrologic models was adopted. The numerical groundwater flow model is developed to configure the groundwater equipotential surface, hydraulic head gradient, and estimation of the groundwater budget of the aquifer. GIS is used for spatial database development, integration with a remote sensing, and numerical groundwater flow modeling capabilities. The thematic layers of soils, land use, hydrology, infrastructure, and climate were developed using GIS. The Arcview GIS software is used as additive tool to develop supportive data for numerical groundwater flow modeling and integration and presentation of image processing and modeling results. The groundwater flow model was calibrated to simulate future changes in piezometric heads from the period 2006 to 2020. Different scenarios were developed to study the impact of extreme climatic conditions (drought/flood) and variable groundwater abstraction on the regional groundwater system. The model results indicated a significant response in watertable due to external influential factors. The developed model provides an effective tool for evaluating better management options for monitoring future groundwater development in the study area.

3D Modeling of the Deep Groundwater System at Mount Shasta, California, Using Finite Difference and Inverse Modeling in Combination with Magnetotellurics

NASA Astrophysics Data System (ADS)

Webb, C. H.; Foglia, L.; Fogg, G. E.; McClain, J.

2017-12-01

Precipitation in mountainous systems is responsible for much of the world's freshwater supply. Volcanic mountains in particular may have the capacity to store large amounts of groundwater, due to the relatively high permeability of volcanic rocks as compared to fractured crystalline rocks. These qualities make volcanic aquifers likely candidates for laterally extensive deep groundwater systems. However, the depth extent of these aquifers is not well understood and has been little studied, due to the dearth of well data in most mountain systems. When determining a water budget, especially for mountainous regions, it is necessary to understand the extent of the entire system, including the deep components. Mount Shasta of the California cascade volcanoes is one potential case of a deep groundwater system with the capacity to store significant amounts of water. In order to develop a conceptual model of the role of deep and regional groundwater flow in the Mt. Shasta groundwater system, the region was modeled using MODFLOW_2005, the finite difference flow model developed by USGS. The model was constrained using SRTM topography data, spring flow rates, PRISM precipitation rates, and well log levels. Geologic cross sections and gravity data were referenced in order to create a realistic estimate of the aquifer's structure down to 6km in depth. The aquifer stratigraphy was then represented by using 6 layers with 2-4 zones of hydraulic conductivity per layer to account for both vertical and lateral differences in lithology as well as decreasing permeability with depth. These hydraulic conductivity parameters of the model were varied using inverse modeling (UCODE_2014) to determine which layers and zones could support flow and still produce results consistent with existing well logs. Depth of flow was also corroborated with resistivity data collected in Shasta Valley using magnetotelluric (MT) soundings. Depths with comparatively low electrical resistivity were assumed to be aquifer units, and zones with high resistivity were assumed to be aquitards. By performing MT soundings in multiple locations and dividing the model into zones, this model tests both the maximum depth of flow as well as how that depth varies with lithology and geographical location.

Effect of Pumping on Groundwater Levels: A Case Study

NASA Astrophysics Data System (ADS)

Sindhu, G.; Vijayachandran, Lekshmi

2018-03-01

Groundwater is a major source for drinking and domestic purposes. Nowadays, extensive pumping has become a major issue of concern since pumping has led to rapid decline in the groundwater table, thus imposing landward gradient, leading to saline water intrusion especially in coastal areas. Groundwater pumping has seen its utmost effect on coastal aquifer systems, where the sea-ward gradient gets disturbed due to anthropogenic influences. Hence, a groundwater flow modelling of an aquifer system is essential for understanding the various hydro-geologic conditions, which can be used to study the responses of the aquifer system with regard to various pumping scenarios. Besides, a model helps to predict the water levels for the future period with respect to changing environment. In this study, a finite element groundwater flow model of a coastal aquifer system at Aakulam, Trivandrum district is developed, calibrated and simulated using the software Finite Element subsurface Flow system (FEFLOW 6.2).This simulated model is then used to predict the groundwater levels for a future 5 year period during pre monsoon and post monsoon season.

Effect of Pumping on Groundwater Levels: A Case Study

NASA Astrophysics Data System (ADS)

Sindhu, G.; Vijayachandran, Lekshmi

2018-06-01

Groundwater is a major source for drinking and domestic purposes. Nowadays, extensive pumping has become a major issue of concern since pumping has led to rapid decline in the groundwater table, thus imposing landward gradient, leading to saline water intrusion especially in coastal areas. Groundwater pumping has seen its utmost effect on coastal aquifer systems, where the sea-ward gradient gets disturbed due to anthropogenic influences. Hence, a groundwater flow modelling of an aquifer system is essential for understanding the various hydro-geologic conditions, which can be used to study the responses of the aquifer system with regard to various pumping scenarios. Besides, a model helps to predict the water levels for the future period with respect to changing environment. In this study, a finite element groundwater flow model of a coastal aquifer system at Aakulam, Trivandrum district is developed, calibrated and simulated using the software Finite Element subsurface Flow system (FEFLOW 6.2).This simulated model is then used to predict the groundwater levels for a future 5 year period during pre monsoon and post monsoon season.

Digital-computer model of ground-water flow in Tooele Valley, Utah

USGS Publications Warehouse

Razem, Allan C.; Bartholoma, Scott D.

1980-01-01

A two-dimensional, finite-difference digital-computer model was used to simulate the ground-water flow in the principal artesian aquifer in Tooele Valley, Utah. The parameters used in the model were obtained through field measurements and tests, from historical records, and by trial-and-error adjustments. The model was calibrated against observed water-level changes that occurred during 1941-50, 1951-60, 1961-66, 1967-73, and 1974-78. The reliability of the predictions is good in most parts of the valley, as is shown by the ability of the model to match historical water-level changes.

Hydrogeology of well-field areas near Tampa, Florida; Phase 2, development and documentation of a quasi-three-dimensional finite-difference model for simulation of steady-state ground-water flow

USGS Publications Warehouse

Hutchinson, C.B.

1984-01-01

This report describes a quasi-three-dimensional finite-difference model for simulation of steady-state ground-water flow in the Floridan aquifer over a 932-square-mile area that contains 10 municipal well fields. The over-lying surficial aquifer contains a water table and is coupled to the Floridan aquifer by leakage term that represents flow through a confining layer separating the two aquifers. Under the steady-state condition, all storage terms are set to zero. Use of the head-controlled flux condition allows simulated head and flow changes to occur in the Floridan aquifer at the model boundaries. Procedures used to calibrate the model, test its sensitivity to input-parameter errors, and validate its accuracy for predictive purposes are described. Also included are attachments that describe setting up and running the model. Example model-interrogation runs show anticipated drawdowns under high, average, and low recharge conditions with 10 well fields pumping simultaneously at the maximum annual permitted rates totaling 186.9 million gallons per day. (USGS)

Experimental and numerical modelling of surface water-groundwater flow and pollution interactions under tidal forcing

NASA Astrophysics Data System (ADS)

Spanoudaki, Katerina; Bockelmann-Evans, Bettina; Schaefer, Florian; Kampanis, Nikolaos; Nanou-Giannarou, Aikaterini; Stamou, Anastasios; Falconer, Roger

2015-04-01

Surface water and groundwater are integral components of the hydrologic continuum and the interaction between them affects both their quantity and quality. However, surface water and groundwater are often considered as two separate systems and are analysed independently. This separation is partly due to the different time scales, which apply in surface water and groundwater flows and partly due to the difficulties in measuring and modelling their interactions (Winter et al., 1998). Coastal areas in particular are a difficult hydrologic environment to represent with a mathematical model due to the large number of contributing hydrologic processes. Accurate prediction of interactions between coastal waters, groundwater and neighbouring wetlands, for example, requires the use of integrated surface water-groundwater models. In the past few decades a large number of mathematical models and field methods have been developed in order to quantify the interaction between groundwater and hydraulically connected surface water bodies. Field studies may provide the best data (Hughes, 1995) but are usually expensive and involve too many parameters. In addition, the interpretation of field measurements and linking with modelling tools often proves to be difficult. In contrast, experimental studies are less expensive and provide controlled data. However, experimental studies of surface water-groundwater interaction are less frequently encountered in the literature than filed studies (e.g. Ebrahimi et al., 2007; Kuan et al., 2012; Sparks et al., 2013). To this end, an experimental model has been constructed at the Hyder Hydraulics Laboratory at Cardiff University to enable measurements to be made of groundwater transport through a sand embankment between a tidal water body such as an estuary and a non-tidal water body such as a wetland. The transport behaviour of a conservative tracer was studied for a constant water level on the wetland side of the embankment, while running a continuous tide on the coastal side. The integrated surface water-groundwater numerical model IRENE (Spanoudaki et al., 2009, Spanoudaki, 2010) was also used in the study, with the numerical model predictions being compared with experimental results, which provide a valuable database for model calibration and validation. IRENE couples the 3D, non-steady state Navier-Stokes equations, after Reynolds averaging and with the assumption of hydrostatic pressure distribution, to the equations describing 3D saturated groundwater flow of constant density. The model uses the finite volume method with a cell-centered structured grid providing thus flexibility and accuracy in simulating irregular boundary geometries. A semi-implicit finite difference scheme is used to solve the surface water flow equations, while a fully implicit finite difference scheme is used for the groundwater equations. Pollution interactions are simulated by coupling the advection-diffusion equation describing the fate and transport of contaminants introduced in a 3D turbulent flow field to the partial differential equation describing the fate and transport of contaminants in 3D transient groundwater flow systems. References Ebrahimi, K., Falconer, R.A. and Lin B. (2007). Flow and solute fluxes in integrated wetland and coastal systems. Environmental Modelling and Software, 22 (9), 1337-1348. Hughes, S.A. (1995). Physical Modelling and Laboratory Techniques in Coastal Engineering. World Scientific Publishing Co. Pte. Ltd., Singapore. Kuan, W.K., Jin, G., Xin, P., Robinson, C. Gibbes, B. and Li. L. (2012). Tidal influence on seawater intrusion in unconfined coastal aquifers. Water Resources Research, 48 (2), doi:10.1029/2011WR010678. Spanoudaki, K., Stamou, A.I. and Nanou-Giannarou, A. (2009). Development and verification of a 3-D integrated surface water-groundwater model. Journal of Hydrology, 375 (3-4), 410-427. Spanoudaki, K. (2010). Integrated numerical modelling of surface water groundwater systems (in Greek). Ph.D. Thesis, National Technical University of Athens, Greece. Sparks, T. D., Bockelmann-Evans, B. N. and Falconer, R. A. (2013). Laboratory Validation of an Integrated Surface Water- Groundwater Model. Journal of Water Resource and Protection, 5, 377-394. Winter, T.C., Harvey, J.W., Franke, O.L. and Alley, W.M., 1998. Groundwater and surface water - A single resource. USGS, Circular 1139.

A Modular Three-Dimensional Finite-Difference Ground-Water Flow Model

USGS Publications Warehouse

McDonald, Michael G.; Harbaugh, Arlen W.; Guo, Weixing; Lu, Guoping

1988-01-01

This report presents a finite-difference model and its associated modular computer program. The model simulates flow in three dimensions. The report includes detailed explanations of physical and mathematical concepts on which the model is based and an explanation of how those concepts are incorporated in the modular structure of the computer program. The modular structure consists of a Main Program and a series of highly independent subroutines called 'modules.' The modules are grouped into 'packages.' Each package deals with a specific feature of the hydrologic system which is to be simulated, such as flow from rivers or flow into drains, or with a specific method of solving linear equations which describe the flow system, such as the Strongly Implicit Procedure or Slice-Successive Overrelaxation. The division of the program into modules permits the user to examine specific hydrologic features of the model independently. This also facilita development of additional capabilities because new packages can be added to the program without modifying the existing packages. The input and output systems of the computer program are also designed to permit maximum flexibility. Ground-water flow within the aquifer is simulated using a block-centered finite-difference approach. Layers can be simulated as confined, unconfined, or a combination of confined and unconfined. Flow associated with external stresses, such as wells, areal recharge, evapotranspiration, drains, and streams, can also be simulated. The finite-difference equations can be solved using either the Strongly Implicit Procedure or Slice-Successive Overrelaxation. The program is written in FORTRAN 77 and will run without modification on most computers that have a FORTRAN 77 compiler. For each program ,module, this report includes a narrative description, a flow chart, a list of variables, and a module listing.

Application of Harmony Search algorithm to the solution of groundwater management models

NASA Astrophysics Data System (ADS)

Tamer Ayvaz, M.

2009-06-01

This study proposes a groundwater resources management model in which the solution is performed through a combined simulation-optimization model. A modular three-dimensional finite difference groundwater flow model, MODFLOW is used as the simulation model. This model is then combined with a Harmony Search (HS) optimization algorithm which is based on the musical process of searching for a perfect state of harmony. The performance of the proposed HS based management model is tested on three separate groundwater management problems: (i) maximization of total pumping from an aquifer (steady-state); (ii) minimization of the total pumping cost to satisfy the given demand (steady-state); and (iii) minimization of the pumping cost to satisfy the given demand for multiple management periods (transient). The sensitivity of HS algorithm is evaluated by performing a sensitivity analysis which aims to determine the impact of related solution parameters on convergence behavior. The results show that HS yields nearly same or better solutions than the previous solution methods and may be used to solve management problems in groundwater modeling.

1r2dinv: A finite-difference model for inverse analysis of two dimensional linear or radial groundwater flow

USGS Publications Warehouse

Bohling, Geoffrey C.; Butler, J.J.

2001-01-01

We have developed a program for inverse analysis of two-dimensional linear or radial groundwater flow problems. The program, 1r2dinv, uses standard finite difference techniques to solve the groundwater flow equation for a horizontal or vertical plane with heterogeneous properties. In radial mode, the program simulates flow to a well in a vertical plane, transforming the radial flow equation into an equivalent problem in Cartesian coordinates. The physical parameters in the model are horizontal or x-direction hydraulic conductivity, anisotropy ratio (vertical to horizontal conductivity in a vertical model, y-direction to x-direction in a horizontal model), and specific storage. The program allows the user to specify arbitrary and independent zonations of these three parameters and also to specify which zonal parameter values are known and which are unknown. The Levenberg-Marquardt algorithm is used to estimate parameters from observed head values. Particularly powerful features of the program are the ability to perform simultaneous analysis of heads from different tests and the inclusion of the wellbore in the radial mode. These capabilities allow the program to be used for analysis of suites of well tests, such as multilevel slug tests or pumping tests in a tomographic format. The combination of information from tests stressing different vertical levels in an aquifer provides the means for accurately estimating vertical variations in conductivity, a factor profoundly influencing contaminant transport in the subsurface. ?? 2001 Elsevier Science Ltd. All rights reserved.

Application of the conjugate-gradient method to ground-water models

USGS Publications Warehouse

Manteuffel, T.A.; Grove, D.B.; Konikow, Leonard F.

1984-01-01

The conjugate-gradient method can solve efficiently and accurately finite-difference approximations to the ground-water flow equation. An aquifer-simulation model using the conjugate-gradient method was applied to a problem of ground-water flow in an alluvial aquifer at the Rocky Mountain Arsenal, Denver, Colorado. For this application, the accuracy and efficiency of the conjugate-gradient method compared favorably with other available methods for steady-state flow. However, its efficiency relative to other available methods depends on the nature of the specific problem. The main advantage of the conjugate-gradient method is that it does not require the use of iteration parameters, thereby eliminating this partly subjective procedure. (USGS)

Semianalytical computation of path lines for finite-difference models

USGS Publications Warehouse

Pollock, D.W.

1988-01-01

A semianalytical particle tracking method was developed for use with velocities generated from block-centered finite-difference ground-water flow models. Based on the assumption that each directional velocity component varies linearly within a grid cell in its own coordinate directions, the method allows an analytical expression to be obtained describing the flow path within an individual grid cell. Given the intitial position of a particle anywhere in a cell, the coordinates of any other point along its path line within the cell, and the time of travel between them, can be computed directly. For steady-state systems, the exit point for a particle entering a cell at any arbitrary location can be computed in a single step. By following the particle as it moves from cell to cell, this method can be used to trace the path of a particle through any multidimensional flow field generated from a block-centered finite-difference flow model. -Author

The Mississippi Embayment Regional Aquifer Study (MERAS): Documentation of a Groundwater-Flow Model Constructed to Assess Water Availability in the Mississippi Embayment

USGS Publications Warehouse

Clark, Brian R.; Hart, Rheannon M.

2009-01-01

The Mississippi Embayment Regional Aquifer Study (MERAS) was conducted with support from the Groundwater Resources Program of the U.S. Geological Survey Office of Groundwater. This report documents the construction and calibration of a finite-difference groundwater model for use as a tool to quantify groundwater availability within the Mississippi embayment. To approximate the differential equation, the MERAS model was constructed with the U.S. Geological Survey's modular three-dimensional finite-difference code, MODFLOW-2005; the preconditioned conjugate gradient solver within MODFLOW-2005 was used for the numerical solution technique. The model area boundary is approximately 78,000 square miles and includes eight States with approximately 6,900 miles of simulated streams, 70,000 well locations, and 10 primary hydrogeologic units. The finite-difference grid consists of 414 rows, 397 columns, and 13 layers. Each model cell is 1 square mile with varying thickness by cell and by layer. The simulation period extends from January 1, 1870, to April 1, 2007, for a total of 137 years and 69 stress periods. The first stress period is simulated as steady state to represent predevelopment conditions. Areal recharge is applied throughout the MERAS model area using the MODFLOW-2005 Recharge Package. Irrigation, municipal, and industrial wells are simulated using the Multi-Node Well Package. There are 43 streams simulated by the MERAS model. Each stream or river in the model area was simulated using the Streamflow-Routing Package. The perimeter of the model area and the base of the flow system are represented as no-flow boundaries. The downgradient limit of each model layer is a no-flow boundary, which approximates the extent of water with less than 10,000 milligrams per liter of dissolved solids. The MERAS model was calibrated by making manual changes to parameter values and examining residuals for hydraulic heads and streamflow. Additional calibration was achieved through alternate use of UCODE-2005 and PEST. Simulated heads were compared to 55,786 hydraulic-head measurements from 3,245 wells in the MERAS model area. Values of root mean square error between simulated and observed hydraulic heads of all observations ranged from 8.33 feet in 1919 to 47.65 feet in 1951, though only six root mean square error values are greater than 40 feet for the entire simulation period. Simulated streamflow generally is lower than measured streamflow for streams with streamflow less than 1,000 cubic feet per second, and greater than measured streamflow for streams with streamflow more than 1,000 cubic feet per second. Simulated streamflow is underpredicted for 18 observations and overpredicted for 10 observations in the model. These differences in streamflow illustrate the large uncertainty in model inputs such as predevelopment recharge, overland flow, pumpage (from stream and aquifer), precipitation, and observation weights. The groundwater-flow budget indicates changes in flow into (inflows) and out of (outflows) the model area during the pregroundwater-irrigation period (pre-1870) to 2007. Total flow (sum of inflows or outflows) through the model ranged from about 600 million gallons per day prior to development to 18,197 million gallons per day near the end of the simulation. The pumpage from wells represents the largest outflow components with a net rate of 18,197 million gallons per day near the end of the model simulation in 2006. Groundwater outflows are offset primarily by inflow from aquifer storage and recharge.

Modelling of groundwater quality using bicarbonate chemical parameter in Netravathi and Gurpur river confluence, India

NASA Astrophysics Data System (ADS)

Sylus, K. J.; H., Ramesh

2018-04-01

In the coastal aquifer, seawater intrusion considered the major problem which contaminates freshwater and reduces its quality for domestic use. In order to find seawater intrusion, the groundwater quality analysis for the different chemical parameter was considered as the basic method to find out contamination. This analysis was carried out as per Bureau of Indian standards (2012) and World Health Organisations (1996). In this study, Bicarbonate parameter was considered for groundwater quality analysis which ranges the permissible limit in between 200-600 mg/l. The groundwater system was modelled using Groundwater modelling software (GMS) in which the FEMWATER package used for flow and transport. The FEMWATER package works in the principle of finite element method. The base input data of model include elevation, Groundwater head, First bottom and second bottom of the study area. The modelling results show the spatial occurrence of contamination in the study area of Netravathi and Gurpur river confluence at the various time period. Further, the results of the modelling also show that the contamination occurs up to a distance of 519m towards the freshwater zone of the study area.

MT3DMS: Model use, calibration, and validation

USGS Publications Warehouse

Zheng, C.; Hill, Mary C.; Cao, G.; Ma, R.

2012-01-01

MT3DMS is a three-dimensional multi-species solute transport model for solving advection, dispersion, and chemical reactions of contaminants in saturated groundwater flow systems. MT3DMS interfaces directly with the U.S. Geological Survey finite-difference groundwater flow model MODFLOW for the flow solution and supports the hydrologic and discretization features of MODFLOW. MT3DMS contains multiple transport solution techniques in one code, which can often be important, including in model calibration. Since its first release in 1990 as MT3D for single-species mass transport modeling, MT3DMS has been widely used in research projects and practical field applications. This article provides a brief introduction to MT3DMS and presents recommendations about calibration and validation procedures for field applications of MT3DMS. The examples presented suggest the need to consider alternative processes as models are calibrated and suggest opportunities and difficulties associated with using groundwater age in transport model calibration.

Modeling dissolution and volatilization of LNAPL sources migrating on the groundwater table.

PubMed

Kim, Jeongkon; Corapcioglu, M Yavuz

2003-08-01

A vertically averaged two-dimensional model was developed to describe areal spreading and migration of light nonaqueous-phase liquids (LNAPLs) introduced into the subsurface by spills or leaks from underground storage tanks. The NAPL transport model was coupled with two-dimensional contaminant transport models to predict contamination of soil gas and groundwater resulting from a LNAPL migrating on the water table. Numerical solutions were obtained by using the finite-difference method. Simulations and sensitivity analyses were conducted with a LNAPL of pure benzene to study LNAPL migration and groundwater contamination. The model was applied to subsurface contamination by jet fuel. Results indicated that LNAPL migration were affected mostly by volatilization. The generation and movement of the dissolved plume was affected by the geology of the site and the free-product plume. Most of the spilled mass remained as a free LNAPL phase 20 years after the spill. The migration of LNAPL for such a long period resulted in the contamination of both groundwater and a large volume of soil.

Linkage Of A Finite Element Flow Model With A Soil Moisture Model: Challanges Under Semiarid Conditions

NASA Astrophysics Data System (ADS)

Roediger, T.; Siebert, C.; Krause, P.

2008-12-01

The arid to semiarid Middle East is a region of extreme growth of population. Hence, the rare and over- expoitated water resources in that region have to be more protected against antropogenic and geogenic pollution. One way to help solving that complex issue is to develop an intelligent and integrated strategy to manage all available water resources, which is the aim of the multilateral SMART-project in the Lower Jordan Valley. To generate such an IWRM, all water resources (groundwater, surface runoff, waste water) of the valley and its shoulders have to be quanti- and qualitatively evaluated. The strategy of SMART is to upscale knowledge, extracted from local catchment areas to the project scale, which covers the area between Sea of Galilee, Jerusalem, Dead Sea and Amman. The study areas of the here presented sub-project are the Wadis Qilt (Palestine) and Al Arab (Jordan). The aim of the sub-project is to evaluate natural resources on catchment scale by combining hydrochemical and hydraulical methods to develop a high precision model. Concerning the quantification of the system, two seperated models will be linked: a numerical finite element flow-model for the groundwater passage and a new devolped hydrological model JAMS, which is excellently prepared for humid conditions. The power of JAMS is the highly accurate assessment of soil moisture balance and consequently of surface runoff and groundwater recharge. However, the empirical equations and input parameters have to be adjusted onto the conditions of the semiarid Wadi Al Arab and the arid Wadi Qilt. After the adaption of JAMS, the spatially and temporarily differentiated calculation of runoff and groundwater recharge is possible. Beside climatic gradients, the key issue is, to correctly evaluate the evapotranspiration in respect to the different classes of landuse. In the study area Wadi Al Arab, the groundwater recharge was calculated as area-indicated output parameter of JAMS. This output was used to be the spatial differentiated input parameter of the numerical flow model. The advantage is the direct comparability of the finite-element meshs of JAMS and FeFlow. However, the individual definitions of values (recharge, base flow, exfiltration of JAMS, infiltration of FeFlow, etc.) of both models have to be linked by an interface between both systems. One of the biggest challenges is the temporal discretization of recharge between leaving soilcrust and entering groundwater table. In fact, the target was to evaluate the effects of retardation of the unsaturated zone in dependence to the hydraulic parameters of the entire groundwater reservoir.

MODFLOW-LGR-Modifications to the streamflow-routing package (SFR2) to route streamflow through locally refined grids

USGS Publications Warehouse

Mehl, Steffen W.; Hill, Mary C.

2011-01-01

This report documents modifications to the Streamflow-Routing Package (SFR2) to route streamflow through grids constructed using the multiple-refined-areas capability of shared node Local Grid Refinement (LGR) of MODFLOW-2005. MODFLOW-2005 is the U.S. Geological Survey modular, three-dimensional, finite-difference groundwater-flow model. LGR provides the capability to simulate groundwater flow by using one or more block-shaped, higher resolution local grids (child model) within a coarser grid (parent model). LGR accomplishes this by iteratively coupling separate MODFLOW-2005 models such that heads and fluxes are balanced across the shared interfacing boundaries. Compatibility with SFR2 allows for streamflow routing across grids. LGR can be used in two- and three-dimensional, steady-state and transient simulations and for simulations of confined and unconfined groundwater systems.

A data-input program (MFI2005) for the U.S. Geological Survey modular groundwater model (MODFLOW-2005) and parameter estimation program (UCODE_2005)

USGS Publications Warehouse

Harbaugh, Arien W.

2011-01-01

The MFI2005 data-input (entry) program was developed for use with the U.S. Geological Survey modular three-dimensional finite-difference groundwater model, MODFLOW-2005. MFI2005 runs on personal computers and is designed to be easy to use; data are entered interactively through a series of display screens. MFI2005 supports parameter estimation using the UCODE_2005 program for parameter estimation. Data for MODPATH, a particle-tracking program for use with MODFLOW-2005, also can be entered using MFI2005. MFI2005 can be used in conjunction with other data-input programs so that the different parts of a model dataset can be entered by using the most suitable program.

Analysis of groundwater flow in arid areas with limited hydrogeological data using the Grey Model: a case study of the Nubian Sandstone, Kharga Oasis, Egypt

NASA Astrophysics Data System (ADS)

Mahmod, Wael Elham; Watanabe, Kunio; Zahr-Eldeen, Ashraf A.

2013-08-01

Management of groundwater resources can be enhanced by using numerical models to improve development strategies. However, the lack of basic data often limits the implementation of these models. The Kharga Oasis in the western desert of Egypt is an arid area that mainly depends on groundwater from the Nubian Sandstone Aquifer System (NSAS), for which the hydrogeological data needed for groundwater simulation are lacking, thereby introducing a problem for model calibration and validation. The Grey Model (GM) was adopted to analyze groundwater flow. This model combines a finite element method (FEM) with a linear regression model to try to obtain the best-fit piezometric-level trends compared to observations. The GM simulation results clearly show that the future water table in the northeastern part of the study area will face a severe drawdown compared with that in the southwestern part and that the hydraulic head difference between these parts will reach 140 m by 2060. Given the uncertainty and limitation of available data, the GM produced more realistic results compared with those obtained from a FEM alone. The GM could be applied to other cases with similar data limitations.

HCMM energy budget data as a model input for assessing regions of high potential groundwater pollution

NASA Technical Reports Server (NTRS)

Moore, D. G. (Principal Investigator); Tunheim, J. A.; Heilman, J.

1977-01-01

The author has identified the following significant results. The finite difference model was used to calculate the differences in surface temperature between two hypothetical sites which result from a temperature difference at 50 cm due to the presence of shallow ground water at one of the sites. Although qualitative results of the model seemed consistant with experimental results, further evaluation showed a need for taking account of differences in thermal conductivity due to different moisture profiles at the two sites considered.

Gravity-driven groundwater flow and slope failure potential: 1. Elastic effective-stress model

USGS Publications Warehouse

Iverson, Richard M.; Reid, Mark E.

1992-01-01

Hilly or mountainous topography influences gravity-driven groundwater flow and the consequent distribution of effective stress in shallow subsurface environments. Effective stress, in turn, influences the potential for slope failure. To evaluate these influences, we formulate a two-dimensional, steady state, poroelastic model. The governing equations incorporate groundwater effects as body forces, and they demonstrate that spatially uniform pore pressure changes do not influence effective stresses. We implement the model using two finite element codes. As an illustrative case, we calculate the groundwater flow field, total body force field, and effective stress field in a straight, homogeneous hillslope. The total body force and effective stress fields show that groundwater flow can influence shear stresses as well as effective normal stresses. In most parts of the hillslope, groundwater flow significantly increases the Coulomb failure potential Φ, which we define as the ratio of maximum shear stress to mean effective normal stress. Groundwater flow also shifts the locus of greatest failure potential toward the slope toe. However, the effects of groundwater flow on failure potential are less pronounced than might be anticipated on the basis of a simpler, one-dimensional, limit equilibrium analysis. This is a consequence of continuity, compatibility, and boundary constraints on the two-dimensional flow and stress fields, and it points to important differences between our elastic continuum model and limit equilibrium models commonly used to assess slope stability.

Transient Conditions at the Ice/bed Interface Under a Palaeo-ice Stream Derived from Numerical Simulation of Groundwater Flow and Sedimentological Observations in a Drumlin Field, NW Poland

NASA Astrophysics Data System (ADS)

Hermanowski, P.; Piotrowski, J. A.

2017-12-01

Evacuation of glacial meltwater through the substratum is an important agent modulating the ice/bed interface processes. The amount of meltwater production, subglacial water pressure, flow patterns and fluxes all affect the strength of basal coupling and thus impact the ice-sheet dynamics. Despite much research into the subglacial processes of past ice sheets which controlled sediment transport and the formation of specific landforms, our understanding of the ice/bed interface remains fragmentary. In this study we numerically simulated, using finite difference and finite element codes, groundwater flow pattern and fluxes during an ice advance in the Stargard Drumlin Field, NW Poland to examine the potential influence of groundwater drainage on the landforming processes. The results are combined with sedimentological observations of the internal composition of the drumlins to validate the outcome of the numerical model. Our numerical experiments of groundwater flow suggest a highly time-dependent response of the subglacial hydrogeological system to the advancing ice margin. This is manifested as diversified areas of downward- and upward-oriented groundwater flows whereby the drumlin field area experienced primarily groundwater discharge towards the ice sole. The investigated drumlins are composed of (i) mainly massive till with thin stringers of meltwater sand, and (ii) sorted sediments carrying ductile deformations. The model results and sedimentological observations suggest a high subglacial pore-water pressure in the drumlin field area, which contributed to sediment deformation intervening with areas of basal decoupling and enhanced basal sliding.

Modifications of the U.S. Geological Survey modular, finite-difference, ground-water flow model to read and write geographic information system files

USGS Publications Warehouse

Orzol, Leonard L.; McGrath, Timothy S.

1992-01-01

This report documents modifications to the U.S. Geological Survey modular, three-dimensional, finite-difference, ground-water flow model, commonly called MODFLOW, so that it can read and write files used by a geographic information system (GIS). The modified model program is called MODFLOWARC. Simulation programs such as MODFLOW generally require large amounts of input data and produce large amounts of output data. Viewing data graphically, generating head contours, and creating or editing model data arrays such as hydraulic conductivity are examples of tasks that currently are performed either by the use of independent software packages or by tedious manual editing, manipulating, and transferring data. Programs such as GIS programs are commonly used to facilitate preparation of the model input data and analyze model output data; however, auxiliary programs are frequently required to translate data between programs. Data translations are required when different programs use different data formats. Thus, the user might use GIS techniques to create model input data, run a translation program to convert input data into a format compatible with the ground-water flow model, run the model, run a translation program to convert the model output into the correct format for GIS, and use GIS to display and analyze this output. MODFLOWARC, avoids the two translation steps and transfers data directly to and from the ground-water-flow model. This report documents the design and use of MODFLOWARC and includes instructions for data input/output of the Basic, Block-centered flow, River, Recharge, Well, Drain, Evapotranspiration, General-head boundary, and Streamflow-routing packages. The modification to MODFLOW and the Streamflow-Routing package was minimized. Flow charts and computer-program code describe the modifications to the original computer codes for each of these packages. Appendix A contains a discussion on the operation of MODFLOWARC using a sample problem.

Death Valley regional ground-water flow system, Nevada and California -- hydrogeologic framework and transient ground-water flow model

USGS Publications Warehouse

Belcher, Wayne R.

2004-01-01

A numerical three-dimensional (3D) transient ground-water flow model of the Death Valley region was developed by the U.S. Geological Survey for the U.S. Department of Energy programs at the Nevada Test Site and at Yucca Mountain, Nevada. Decades of study of aspects of the ground-water flow system and previous less extensive ground-water flow models were incorporated and reevaluated together with new data to provide greater detail for the complex, digital model. A 3D digital hydrogeologic framework model (HFM) was developed from digital elevation models, geologic maps, borehole information, geologic and hydrogeologic cross sections, and other 3D models to represent the geometry of the hydrogeologic units (HGUs). Structural features, such as faults and fractures, that affect ground-water flow also were added. The HFM represents Precambrian and Paleozoic crystalline and sedimentary rocks, Mesozoic sedimentary rocks, Mesozoic to Cenozoic intrusive rocks, Cenozoic volcanic tuffs and lavas, and late Cenozoic sedimentary deposits of the Death Valley Regional Ground-Water Flow System (DVRFS) region in 27 HGUs. Information from a series of investigations was compiled to conceptualize and quantify hydrologic components of the ground-water flow system within the DVRFS model domain and to provide hydraulic-property and head-observation data used in the calibration of the transient-flow model. These studies reevaluated natural ground-water discharge occurring through evapotranspiration and spring flow; the history of ground-water pumping from 1913 through 1998; ground-water recharge simulated as net infiltration; model boundary inflows and outflows based on regional hydraulic gradients and water budgets of surrounding areas; hydraulic conductivity and its relation to depth; and water levels appropriate for regional simulation of prepumped and pumped conditions within the DVRFS model domain. Simulation results appropriate for the regional extent and scale of the model were provided by acquiring additional data, by reevaluating existing data using current technology and concepts, and by refining earlier interpretations to reflect the current understanding of the regional ground-water flow system. Ground-water flow in the Death Valley region is composed of several interconnected, complex ground-water flow systems. Ground-water flow occurs in three subregions in relatively shallow and localized flow paths that are superimposed on deeper, regional flow paths. Regional ground-water flow is predominantly through a thick Paleozoic carbonate rock sequence affected by complex geologic structures from regional faulting and fracturing that can enhance or impede flow. Spring flow and evapotranspiration (ET) are the dominant natural ground-water discharge processes. Ground water also is withdrawn for agricultural, commercial, and domestic uses. Ground-water flow in the DVRFS was simulated using MODFLOW-2000, a 3D finite-difference modular ground-water flow modeling code that incorporates a nonlinear least-squares regression technique to estimate aquifer parameters. The DVRFS model has 16 layers of defined thickness, a finite-difference grid consisting of 194 rows and 160 columns, and uniform cells 1,500 m on each side. Prepumping conditions (before 1913) were used as the initial conditions for the transient-state calibration. The model uses annual stress periods with discrete recharge and discharge components. Recharge occurs mostly from infiltration of precipitation and runoff on high mountain ranges and from a small amount of underflow from adjacent basins. Discharge occurs primarily through ET and spring discharge (both simulated as drains) and water withdrawal by pumping and, to a lesser amount, by underflow to adjacent basins, also simulated by drains. All parameter values estimated by the regression are reasonable and within the range of expected values. The simulated hydraulic heads of the final calibrated transient model gener

Effect of Different Groundwater Levels on Seismic Dynamic Response and Failure Mode of Sandy Slope

PubMed Central

Huang, Shuai; Lv, Yuejun; Peng, Yanju; Zhang, Lifang; Xiu, Liwei

2015-01-01

Heavy seismic damage tends to occur in slopes when groundwater is present. The main objectives of this paper are to determine the dynamic response and failure mode of sandy slope subjected simultaneously to seismic forces and variable groundwater conditions. This paper applies the finite element method, which is a fast and efficient design tool in modern engineering analysis, to evaluate dynamic response of the slope subjected simultaneously to seismic forces and variable groundwater conditions. Shaking table test is conducted to analyze the failure mode and verify the accuracy of the finite element method results. The research results show that dynamic response values of the slope have different variation rules under near and far field earthquakes. And the damage location and pattern of the slope are different in varying groundwater conditions. The destruction starts at the top of the slope when the slope is in no groundwater, which shows that the slope appears obvious whipping effect under the earthquake. The destruction starts at the toe of the slope when the slope is in the high groundwater levels. Meanwhile, the top of the slope shows obvious seismic subsidence phenomenon after earthquake. Furthermore, the existence of the groundwater has a certain effect of damping. PMID:26560103

A finite difference model for free surface gravity drainage

DOE Office of Scientific and Technical Information (OSTI.GOV)

Couri, F.R.; Ramey, H.J. Jr.

1993-09-01

The unconfined gravity flow of liquid with a free surface into a well is a classical well test problem which has not been well understood by either hydrologists or petroleum engineers. Paradigms have led many authors to treat an incompressible flow as compressible flow to justify the delayed yield behavior of a time-drawdown test. A finite-difference model has been developed to simulate the free surface gravity flow of an unconfined single phase, infinitely large reservoir into a well. The model was verified with experimental results in sandbox models in the literature and with classical methods applied to observation wells inmore » the Groundwater literature. The simulator response was also compared with analytical Theis (1935) and Ramey et al. (1989) approaches for wellbore pressure at late producing times. The seepage face in the sandface and the delayed yield behavior were reproduced by the model considering a small liquid compressibility and incompressible porous medium. The potential buildup (recovery) simulated by the model evidenced a different- phenomenon from the drawdown, contrary to statements found in the Groundwater literature. Graphs of buildup potential vs time, buildup seepage face length vs time, and free surface head and sand bottom head radial profiles evidenced that the liquid refills the desaturating cone as a flat moving surface. The late time pseudo radial behavior was only approached after exaggerated long times.« less

Groundwater withdrawal in the Central Valley, California: implications for San Andreas Fault stressing and lithosphere rheology

NASA Astrophysics Data System (ADS)

Lundgren, P.; Liu, Z.; Ali, S. T.; Farr, T.; Faunt, C. C.

2016-12-01

Anthropogenic perturbations to crustal loading due to groundwater pumping are increasingly recognized as causing changes in nearby fault stresses. We present preliminary analysis of crustal unloading in the Central Valley (CV), California, for the period 2006-2010 to infer Coulomb stress changes on the central San Andreas Fault (CSAF), lithospheric rheology, and system memory due to more than a century of groundwater withdrawal in the southern CV. We use data-driven unloading estimates to drive three-dimensional (3-D) finite element method models and compare model vertical surface deformation rates with observed GPS uplift rates outside the CV. Groundwater level changes are observed through well water elevation changes and through the resultant surface deformation (subsidence) by interferometric synthetic aperture radar (InSAR) and through broader scale changes in gravity from the GRACE satellite time variable gravity data [Famiglietti et al., 2011] that constrain the overall water volume changes. Combining InSAR with well-water data we are able to estimate the aquifer skeletal elastic and inelastic response and through a linear inversion derive the water volume (load) changes across the Central Valley and compare them with GRACE-inferred groundwater changes. Preliminary 3-D finite element method modeling that considers elastic and viscosity structure in the lithosphere gives three interesting results: 1) elastic models poorly fit the uplift rates near the SAF; 2) viscoelastic models that simulate different unloading histories show the past history of groundwater unloading has significant residual uplift rates and fault stress changes; 3) Coulomb stress change varies from inhibited on the locked (Carrizo) section to promoted on the creeping section of the SAF north of Parkfield. Thus, 3D models that account for lithosphere rheology, loading history viscous relaxation, have significant implications for longer-term time-dependent deformation, stress perturbation, and earthquake hazard on the nearby faults. Reference: Famiglietti, J. S., M. Lo, S. L. Ho, J. Bethune, K. J. Anderson, T. H. Syed, S. C. Swenson, C. R. de Linage, and M. Rodell, 2011, Satellites measure recent rates of groundwater depletion in California's Central Valley, Geophys. Res. Lett., 38, L03403, doi:10.1029/2010GL046442.

Simulation of regional ground-water flow in the Upper Deschutes Basin, Oregon

USGS Publications Warehouse

Gannett, Marshall W.; Lite, Kenneth E.

2004-01-01

This report describes a numerical model that simulates regional ground-water flow in the upper Deschutes Basin of central Oregon. Ground water and surface water are intimately connected in the upper Deschutes Basin and most of the flow of the Deschutes River is supplied by ground water. Because of this connection, ground-water pumping and reduction of artificial recharge by lining leaking irrigation canals can reduce the amount of ground water discharging to streams and, consequently, streamflow. The model described in this report is intended to help water-management agencies and the public evaluate how the regional ground-water system and streamflow will respond to ground-water pumping, canal lining, drought, and other stresses. Ground-water flow is simulated in the model by the finite-difference method using MODFLOW and MODFLOWP. The finite-difference grid consists of 8 layers, 127 rows, and 87 columns. All major streams and most principal tributaries in the upper Deschutes Basin are included. Ground-water recharge from precipitation was estimated using a daily water-balance approach. Artificial recharge from leaking irrigation canals and on-farm losses was estimated from diversion and delivery records, seepage studies, and crop data. Ground-water pumpage for irrigation and public water supplies, and evapotranspiration are also included in the model. The model was calibrated to mean annual (1993-95) steady-state conditions using parameter-estimation techniques employing nonlinear regression. Fourteen hydraulic-conductivity parameters and two vertical conductance parameters were determined using nonlinear regression. Final parameter values are all within expected ranges. The general shape and slope of the simulated water-table surface and overall hydraulic-head distribution match the geometry determined from field measurements. The fitted standard deviation for hydraulic head is about 76 feet. The general magnitude and distribution of ground-water discharge to streams is also well simulated throughout the model. Ground-water discharge to streams in the area of the confluence of the Deschutes, Crooked, and Metolius Rivers is closely matched. The model was also calibrated to transient conditions from 1978 to 1997 using traditional trial-and-error methods. Climatic cycles during this period provided an excellent regional hydrologic signal for calibration. Climate-driven water-level fluctuations are simulated with reasonable accuracy over most of the model area. The timing and magnitude of simulated water-level fluctuations caused by annual pulses of recharge from precipitation match those observed reasonably well, given the limitations of the time discretization in the model. Water-level fluctuations caused by annual canal leakage are simulated very well over most of the area where such fluctuations occur. The transient model also simulates the volumetric distribution and temporal variations in ground-water discharge reasonably well. The match between simulated and measured volume of and variations in ground-water discharge is, however, somewhat dependent on geographic scale. The rates of and variations in ground-water discharge are matched best at regional scales. Example simulations were made to demonstrate the utility of the model for evaluating the effects of ground-water pumping or canal lining. Pumping simulations show that pumped water comes largely from aquifer storage when pumping begins, but as the water table stabilizes, the pumping increasingly diminishes the discharge to streams and, hence, streamflow. The time it takes for pumping to affect streamflow varies spatially depending, in general, on the location of pumping relative to the discharge areas. Canal-lining simulations show similar effects.

MODFLOW-2000, the U.S. Geological Survey modular ground-water model : user guide to the LMT6 package, the linkage with MT3DMS for multi-species mass transport modeling

USGS Publications Warehouse

Zheng, Chunmiao; Hill, Mary Catherine; Hsieh, Paul A.

2001-01-01

MODFLOW-2000, the newest version of MODFLOW, is a computer program that numerically solves the three-dimensional ground-water flow equation for a porous medium using a finite-difference method. MT3DMS, the successor to MT3D, is a computer program for modeling multi-species solute transport in three-dimensional ground-water systems using multiple solution techniques, including the finite-difference method, the method of characteristics (MOC), and the total-variation-diminishing (TVD) method. This report documents a new version of the Link-MT3DMS Package, which enables MODFLOW-2000 to produce the information needed by MT3DMS, and also discusses new visualization software for MT3DMS. Unlike the Link-MT3D Packages that coordinated previous versions of MODFLOW and MT3D, the new Link-MT3DMS Package requires an input file that, among other things, provides enhanced support for additional MODFLOW sink/source packages and allows list-directed (free) format for the flow model produced flow-transport link file. The report contains four parts: (a) documentation of the Link-MT3DMS Package Version 6 for MODFLOW-2000; (b) discussion of several issues related to simulation setup and input data preparation for running MT3DMS with MODFLOW-2000; (c) description of two test example problems, with comparison to results obtained using another MODFLOW-based transport program; and (d) overview of post-simulation visualization and animation using the U.S. Geological Survey?s Model Viewer.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aleman, S.E.

This report documents a finite element code designed to model subsurface flow and contaminant transport, named FACT. FACT is a transient three-dimensional, finite element code designed to simulate isothermal groundwater flow, moisture movement, and solute transport in variably saturated and fully saturated subsurface porous media.

GSFLOW - Coupled Ground-Water and Surface-Water Flow Model Based on the Integration of the Precipitation-Runoff Modeling System (PRMS) and the Modular Ground-Water Flow Model (MODFLOW-2005)

USGS Publications Warehouse

Markstrom, Steven L.; Niswonger, Richard G.; Regan, R. Steven; Prudic, David E.; Barlow, Paul M.

2008-01-01

The need to assess the effects of variability in climate, biota, geology, and human activities on water availability and flow requires the development of models that couple two or more components of the hydrologic cycle. An integrated hydrologic model called GSFLOW (Ground-water and Surface-water FLOW) was developed to simulate coupled ground-water and surface-water resources. The new model is based on the integration of the U.S. Geological Survey Precipitation-Runoff Modeling System (PRMS) and the U.S. Geological Survey Modular Ground-Water Flow Model (MODFLOW). Additional model components were developed, and existing components were modified, to facilitate integration of the models. Methods were developed to route flow among the PRMS Hydrologic Response Units (HRUs) and between the HRUs and the MODFLOW finite-difference cells. This report describes the organization, concepts, design, and mathematical formulation of all GSFLOW model components. An important aspect of the integrated model design is its ability to conserve water mass and to provide comprehensive water budgets for a location of interest. This report includes descriptions of how water budgets are calculated for the integrated model and for individual model components. GSFLOW provides a robust modeling system for simulating flow through the hydrologic cycle, while allowing for future enhancements to incorporate other simulation techniques.

Finite-element three-dimensional ground-water (FE3DGW) flow model - formulation, program listings and users' manual

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, S.K.; Cole, C.R.; Bond, F.W.

1979-12-01

The Assessment of Effectiveness of Geologic Isolation Systems (AEGIS) Program is developing and applying the methodology for assessing the far-field, long-term post-closure safety of deep geologic nuclear waste repositories. AEGIS is being performed by Pacific Northwest Laboratory (PNL) under contract with the Office of Nuclear Waste Isolation (OWNI) for the Department of Energy (DOE). One task within AEGIS is the development of methodology for analysis of the consequences (water pathway) from loss of repository containment as defined by various release scenarios. Analysis of the long-term, far-field consequences of release scenarios requires the application of numerical codes which simulate the hydrologicmore » systems, model the transport of released radionuclides through the hydrologic systems to the biosphere, and, where applicable, assess the radiological dose to humans. Hydrologic and transport models are available at several levels of complexity or sophistication. Model selection and use are determined by the quantity and quality of input data. Model development under AEGIS and related programs provides three levels of hydrologic models, two levels of transport models, and one level of dose models (with several separate models). This document consists of the description of the FE3DGW (Finite Element, Three-Dimensional Groundwater) Hydrologic model third level (high complexity) three-dimensional, finite element approach (Galerkin formulation) for saturated groundwater flow.« less

MODFLOW-2005, The U.S. Geological Survey Modular Ground-Water Model - Documentation of the Multiple-Refined-Areas Capability of Local Grid Refinement (LGR) and the Boundary Flow and Head (BFH) Package

USGS Publications Warehouse

Mehl, Steffen W.; Hill, Mary C.

2007-01-01

This report documents the addition of the multiple-refined-areas capability to shared node Local Grid Refinement (LGR) and Boundary Flow and Head (BFH) Package of MODFLOW-2005, the U.S. Geological Survey modular, three-dimensional, finite-difference ground-water flow model. LGR now provides the capability to simulate ground-water flow by using one or more block-shaped, higher resolution local grids (child model) within a coarser grid (parent model). LGR accomplishes this by iteratively coupling separate MODFLOW-2005 models such that heads and fluxes are balanced across the shared interfacing boundaries. The ability to have multiple, nonoverlapping areas of refinement is important in situations where there is more than one area of concern within a regional model. In this circumstance, LGR can be used to simulate these distinct areas with higher resolution grids. LGR can be used in two-and three-dimensional, steady-state and transient simulations and for simulations of confined and unconfined ground-water systems. The BFH Package can be used to simulate these situations by using either the parent or child models independently.

Effects of Projected Future Climate Change on Groundwater Recharge and Storage for Two Coastal Aquifers in Guanacaste Province, Costa Rica

NASA Astrophysics Data System (ADS)

Kolb, C.

2017-12-01

Climate change is expected to pose a significant threat to water resources in the future. Guanacaste Province, located in northwestern Costa Rica, has a unique climate that is influenced by the Pacific Ocean and Caribbean Sea, as well as the Central Cordillera mountain range. Although the region experiences a marked rainy season between May and November, the hot, dry summers often stress water resources. Climate change projections suggest increased temperatures and reduced precipitation for the region, which will further stress water supplies. This study focuses on the effects of climate change on groundwater resources for two coastal aquifers, Potrero and Brasilito. The UZF model package coupled with the finite difference groundwater flow model MODFLOW were used to evaluate the effect of climate change on groundwater recharge and storage. A potential evapotranspiration model was used to estimate groundwater infiltration rates used in the MODFLOW model. Climate change projections for temperature, precipitation, and sea level rise were used to develop climate scenarios, which were compared to historical data. Preliminary results indicate that climate change could reduce future recharge, especially during the dry season. Additionally, the coastal aquifers are at increased risk of reduced storage and increased salinization due to the reductions in groundwater recharge and sea level rise. Climate change could also affect groundwater quality in the region, disrupting the ecosystem and impairing a primary source of drinking water.

Development and evaluation of a local grid refinement method for block-centered finite-difference groundwater models using shared nodes

USGS Publications Warehouse

Mehl, S.; Hill, M.C.

2002-01-01

A new method of local grid refinement for two-dimensional block-centered finite-difference meshes is presented in the context of steady-state groundwater-flow modeling. The method uses an iteration-based feedback with shared nodes to couple two separate grids. The new method is evaluated by comparison with results using a uniform fine mesh, a variably spaced mesh, and a traditional method of local grid refinement without a feedback. Results indicate: (1) The new method exhibits quadratic convergence for homogeneous systems and convergence equivalent to uniform-grid refinement for heterogeneous systems. (2) Coupling the coarse grid with the refined grid in a numerically rigorous way allowed for improvement in the coarse-grid results. (3) For heterogeneous systems, commonly used linear interpolation of heads from the large model onto the boundary of the refined model produced heads that are inconsistent with the physics of the flow field. (4) The traditional method works well in situations where the better resolution of the locally refined grid has little influence on the overall flow-system dynamics, but if this is not true, lack of a feedback mechanism produced errors in head up to 3.6% and errors in cell-to-cell flows up to 25%. ?? 2002 Elsevier Science Ltd. All rights reserved.

Documentation of a numerical code for the simulation of variable density ground-water flow in three dimensions

USGS Publications Warehouse

Kuiper, L.K.

1985-01-01

A numerical code is documented for the simulation of variable density time dependent groundwater flow in three dimensions. The groundwater density, although variable with distance, is assumed to be constant in time. The Integrated Finite Difference grid elements in the code follow the geologic strata in the modeled area. If appropriate, the determination of hydraulic head in confining beds can be deleted to decrease computation time. The strongly implicit procedure (SIP), successive over-relaxation (SOR), and eight different preconditioned conjugate gradient (PCG) methods are used to solve the approximating equations. The use of the computer program that performs the calculations in the numerical code is emphasized. Detailed instructions are given for using the computer program, including input data formats. An example simulation and the Fortran listing of the program are included. (USGS)

A two-dimensional analytical model for groundwater flow in a leaky aquifer extending finite distance under the estuary

NASA Astrophysics Data System (ADS)

Chuang, Mo-Hsiung; Hung, Chi-Tung; -Yen Lin, Wen; Ma, Kuo-chen

2017-04-01

In recent years, cities and industries in the vicinity of the estuarine region have developed rapidly, resulting in a sharp increase in the population concerned. The increasing demand for human activities, agriculture irrigation, and aquaculture relies on massive pumping of water in estuarine area. Since the 1950s, numerous studies have focused on the effects of tidal fluctuations on groundwater flow in the estuarine area. Tide-induced head fluctuation in a two-dimensional estuarine aquifer system is complicated and rather important in dealing with many groundwater management or remediation problems. The conceptual model of the aquifer system considered is multi-layered with estuarine bank and the leaky aquifer extend finite distance under the estuary. The solution of the model describing the groundwater head distribution in such an estuarine aquifer system and subject to the tidal fluctuation effects from estuarine river is developed based on the method of separation of variables along with river boundary. The solutions by Sun (Sun H. A two-dimensional analytical solution of groundwater response to tidal loading in an estuary, Water Resour. Res. 1997; 33:1429-35) as well as Tang and Jiao (Tang Z. and J. J. Jiao, A two-dimensional analytical solution for groundwater flow in a leaky confined aquifer system near open tidal water, Hydrological Processes, 2001; 15: 573-585) can be shown to be special cases of the present solution. On the basis of the analytical solution, the groundwater head distribution in response to estuarine boundary is examined and the influences of leakage, hydraulic parameters, and loading effect on the groundwater head fluctuation due to tide are investigated and discussed. KEYWORDS: analytical model, estuarine river, groundwater fluctuation, leaky aquifer.

Finite-element simulation of ground-water flow in the vicinity of Yucca Mountain, Nevada-California

USGS Publications Warehouse

Czarnecki, J.B.; Waddell, R.K.

1984-01-01

A finite-element model of the groundwater flow system in the vicinity of Yucca Mountain at the Nevada Test Site was developed using parameter estimation techniques. The model simulated steady-state ground-water flow occurring in tuffaceous, volcanic , and carbonate rocks, and alluvial aquifers. Hydraulic gradients in the modeled area range from 0.00001 for carbonate aquifers to 0.19 for barriers in tuffaceous rocks. Three model parameters were used in estimating transmissivity in six zones. Simulated hydraulic-head values range from about 1,200 m near Timber Mountain to about 300 m near Furnace Creek Ranch. Model residuals for simulated versus measured hydraulic heads range from -28.6 to 21.4 m; most are less than +/-7 m, indicating an acceptable representation of the hydrologic system by the model. Sensitivity analyses of the model 's flux boundary condition variables were performed to assess the effect of varying boundary fluxes on the calculation of estimated model transmissivities. Varying the flux variables representing discharge at Franklin Lake and Furnace Creek Ranch has greater effect than varying other flux variables. (Author 's abstract)

Forward and Inverse Modeling of Self-potential. A Tomography of Groundwater Flow and Comparison Between Deterministic and Stochastic Inversion Methods

NASA Astrophysics Data System (ADS)

Quintero-Chavarria, E.; Ochoa Gutierrez, L. H.

2016-12-01

Applications of the Self-potential Method in the fields of Hydrogeology and Environmental Sciences have had significant developments during the last two decades with a strong use on groundwater flows identification. Although only few authors deal with the forward problem's solution -especially in geophysics literature- different inversion procedures are currently being developed but in most cases they are compared with unconventional groundwater velocity fields and restricted to structured meshes. This research solves the forward problem based on the finite element method using the St. Venant's Principle to transform a point dipole, which is the field generated by a single vector, into a distribution of electrical monopoles. Then, two simple aquifer models were generated with specific boundary conditions and head potentials, velocity fields and electric potentials in the medium were computed. With the model's surface electric potential, the inverse problem is solved to retrieve the source of electric potential (vector field associated to groundwater flow) using deterministic and stochastic approaches. The first approach was carried out by implementing a Tikhonov regularization with a stabilized operator adapted to the finite element mesh while for the second a hierarchical Bayesian model based on Markov chain Monte Carlo (McMC) and Markov Random Fields (MRF) was constructed. For all implemented methods, the result between the direct and inverse models was contrasted in two ways: 1) shape and distribution of the vector field, and 2) magnitude's histogram. Finally, it was concluded that inversion procedures are improved when the velocity field's behavior is considered, thus, the deterministic method is more suitable for unconfined aquifers than confined ones. McMC has restricted applications and requires a lot of information (particularly in potentials fields) while MRF has a remarkable response especially when dealing with confined aquifers.

Effects of simulated ground-water pumping and recharge on ground-water flow in Cape Cod, Martha's Vineyard, and Nantucket Island basins, Massachusetts

USGS Publications Warehouse

Masterson, John P.; Barlow, Paul M.

1997-01-01

Three-dimensional transient ground-water-flow models that simulate both freshwater and saltwater flow were developed for the flow cells of the Cape Cod Basin to determine the effects of long-term pumping and recharge, seasonal fluctuations in pumping and recharge, and prolonged reductions of natural recharge, on the position of the freshwater-saltwater interface, water-table and pond altitudes, and streamflow and discharge to coastal marshes and embayments. Two-dimensional, finite-difference change models were developed for Martha's Vineyard and Nantucket Island basins to determine anticipated drawdowns in response to projected summer season pumping rates for 180 days of no recharge.

Simulation of ground-water flow in glaciofluvial aquifers in the Grand Rapids area, Minnesota

USGS Publications Warehouse

Jones, Perry M.

2004-01-01

A calibrated steady-state, finite-difference, ground-waterflow model was constructed to simulate ground-water flow in three glaciofluvial aquifers, defined in this report as the upper, middle, and lower aquifers, in an area of about 114 mi2 surrounding the city of Grand Rapids in north-central Minnesota. The calibrated model will be used by Minnesota Department of Health and communities in the Grand Rapids area in the development of wellhead protection plans for their water supplies. The model was calibrated through comparison of simulated ground-water levels to measured static water levels in 351 wells, and comparison of simulated base-flow rates to estimated base-flow rates for reaches of the Mississippi and Prairie Rivers. Model statistics indicate that the model tends to overestimate ground-water levels. The root mean square errors ranged from +12.83 ft in wells completed in the upper aquifer to +19.10 ft in wells completed in the middle aquifer. Mean absolute differences between simulated and measured water levels ranged from +4.43 ft for wells completed in the upper aquifer to +9.25 ft for wells completed in the middle aquifer. Mean algebraic differences ranged from +9.35 ft for wells completed in the upper aquifer to +14.44 ft for wells completed in the middle aquifer, with the positive differences indicating that the simulated water levels were higher than the measured water levels. Percentage errors between simulated and estimated base-flow rates for the three monitored reaches all were less than 10 percent, indicating good agreement. Simulated ground-water levels were most sensitive to changes in general-head boundary conductance, indicating that this characteristic is the predominant model input variable controlling steady-state water-level conditions. Simulated groundwater flow to stream reaches was most sensitive to changes in horizontal hydraulic conductivity, indicating that this characteristic is the predominant model input variable controlling steady-state flow conditions.

New ghost-node method for linking different models with varied grid refinement

USGS Publications Warehouse

James, S.C.; Dickinson, J.E.; Mehl, S.W.; Hill, M.C.; Leake, S.A.; Zyvoloski, G.A.; Eddebbarh, A.-A.

2006-01-01

A flexible, robust method for linking grids of locally refined ground-water flow models constructed with different numerical methods is needed to address a variety of hydrologic problems. This work outlines and tests a new ghost-node model-linking method for a refined "child" model that is contained within a larger and coarser "parent" model that is based on the iterative method of Steffen W. Mehl and Mary C. Hill (2002, Advances in Water Res., 25, p. 497-511; 2004, Advances in Water Res., 27, p. 899-912). The method is applicable to steady-state solutions for ground-water flow. Tests are presented for a homogeneous two-dimensional system that has matching grids (parent cells border an integer number of child cells) or nonmatching grids. The coupled grids are simulated by using the finite-difference and finite-element models MODFLOW and FEHM, respectively. The simulations require no alteration of the MODFLOW or FEHM models and are executed using a batch file on Windows operating systems. Results indicate that when the grids are matched spatially so that nodes and child-cell boundaries are aligned, the new coupling technique has error nearly equal to that when coupling two MODFLOW models. When the grids are nonmatching, model accuracy is slightly increased compared to that for matching-grid cases. Overall, results indicate that the ghost-node technique is a viable means to couple distinct models because the overall head and flow errors relative to the analytical solution are less than if only the regional coarse-grid model was used to simulate flow in the child model's domain.

Development of solute transport models in YMPYRÄ framework to simulate solute migration in military shooting and training areas

NASA Astrophysics Data System (ADS)

Warsta, L.; Karvonen, T.

2017-12-01

There are currently 25 shooting and training areas in Finland managed by The Finnish Defence Forces (FDF), where military activities can cause contamination of open waters and groundwater reservoirs. In the YMPYRÄ project, a computer software framework is being developed that combines existing open environmental data and proprietary information collected by FDF with computational models to investigate current and prevent future environmental problems. A data centric philosophy is followed in the development of the system, i.e. the models are updated and extended to handle available data from different areas. The results generated by the models are summarized as easily understandable flow and risk maps that can be opened in GIS programs and used in environmental assessments by experts. Substances investigated with the system include explosives and metals such as lead, and both surface and groundwater dominated areas can be simulated. The YMPYRÄ framework is composed of a three dimensional soil and groundwater flow model, several solute transport models and an uncertainty assessment system. Solute transport models in the framework include particle based, stream tube and finite volume based approaches. The models can be used to simulate solute dissolution from source area, transport in the unsaturated layers to groundwater and finally migration in groundwater to water extraction wells and springs. The models can be used to simulate advection, dispersion, equilibrium adsorption on soil particles, solubility and dissolution from solute phase and dendritic solute decay chains. Correct numerical solutions were confirmed by comparing results to analytical 1D and 2D solutions and by comparing the numerical solutions to each other. The particle based and stream tube type solute transport models were useful as they could complement the traditional finite volume based approach which in certain circumstances produced numerical dispersion due to piecewise solution of the governing equations in computational grids and included computationally intensive and in some cases unstable iterative solutions. The YMPYRÄ framework is being developed by WaterHope, Gain Oy, and SITO Oy consulting companies and funded by FDF.

Sustainable yield of a karst aquifer system: a case study of Jinan springs in northern China

NASA Astrophysics Data System (ADS)

Kang, Fengxin; Jin, Menggui; Qin, Pinrui

2011-06-01

Based on the long-term monitoring data of rainfall, groundwater levels, groundwater abstraction, spring flow rates and groundwater quality, an assessment has been undertaken of the sustainable yield of a karst aquifer system in Shandong Province, northern China, to maintain perennial outflow of the karst springs while meeting water demands. One of the fundamental indicators for sustainable yield of groundwater is identified as maximum allowable water-level drawdown. A regional three-dimensional finite-difference numerical model has been developed to optimize the schemes associated with well fields and their locations and sustainable yields, in the Jinan spring catchment and its adjacent karst groundwater catchments, with the aim of maintaining the water level higher than the allowable lowest water level of 27.5 m above sea level. Furthermore, measures necessary to move towards sustainable use of the karst groundwater are outlined, drawing on contingency plans of water-source replacement and artificial recharge, dual water supply (based in water quality), use of the spring waters themselves, and groundwater quality protection.

User guide for MODPATH version 6 - A particle-tracking model for MODFLOW

USGS Publications Warehouse

Pollock, David W.

2012-01-01

MODPATH is a particle-tracking post-processing model that computes three-dimensional flow paths using output from groundwater flow simulations based on MODFLOW, the U.S. Geological Survey (USGS) finite-difference groundwater flow model. This report documents MODPATH version 6. Previous versions were documented in USGS Open-File Reports 89-381 and 94-464. The program uses a semianalytical particle-tracking scheme that allows an analytical expression of a particle's flow path to be obtained within each finite-difference grid cell. A particle's path is computed by tracking the particle from one cell to the next until it reaches a boundary, an internal sink/source, or satisfies another termination criterion. Data input to MODPATH consists of a combination of MODFLOW input data files, MODFLOW head and flow output files, and other input files specific to MODPATH. Output from MODPATH consists of several output files, including a number of particle coordinate output files intended to serve as input data for other programs that process, analyze, and display the results in various ways. MODPATH is written in FORTRAN and can be compiled by any FORTRAN compiler that fully supports FORTRAN-2003 or by most commercially available FORTRAN-95 compilers that support the major FORTRAN-2003 language extensions.

Simulation of the effects of ground-water withdrawals and recharge on ground-water flow in Cape Cod, Martha's Vineyard, and Nantucket Island basins, Massachusetts

USGS Publications Warehouse

Masterson, John P.; Barlow, Paul M.

1994-01-01

The effects of changing patterns of ground-water pumping and aquifer recharge on the surface-water and ground-water hydrologic systems were determined for the Cape Cod, Martha's Vineyard, and Nantucket Island Basins. Three-dimensional, transient, ground-water-flow modelS that simulate both freshwater and saltwater flow were developed for the f1ow cells of Cape Cod which currently have large-capacity public-supply wells. Only the freshwater-flow system was simulated for the Cape Cod flow cells where public-water supply demands are satisfied by small-capacity domestic wells. Two- dimensional, finite-difference, change models were developed for Martha's Vineyard and Nantucket Island to determine the projected drawdowns in response to projected in-season pumping rates for 180 days of no aquifer recharge. Results of the simulations indicate very little change in the position of the freshwater-saltwater interface from predevelopment flow conditions to projected ground-water pumping and recharge rates for Cape Cod in the year 2020. Results of change model simulations for Martha's Vineyard and Nantucket Island indicate that the greatest impact in response to projected in-season ground-water pumping occurs at the pumping centers and the magnitude of the drawdowns are minimal with respect to the total thickness of the aquifers.

Local Modelling of Groundwater Flow Using Analytic Element Method Three-dimensional Transient Unconfined Groundwater Flow With Partially Penetrating Wells and Ellipsoidal Inhomogeneites

NASA Astrophysics Data System (ADS)

Jankovic, I.; Barnes, R. J.; Soule, R.

2001-12-01

The analytic element method is used to model local three-dimensional flow in the vicinity of partially penetrating wells. The flow domain is bounded by an impermeable horizontal base, a phreatic surface with recharge and a cylindrical lateral boundary. The analytic element solution for this problem contains (1) a fictitious source technique to satisfy the head and the discharge conditions along the phreatic surface, (2) a fictitious source technique to satisfy specified head conditions along the cylindrical boundary, (3) a method of imaging to satisfy the no-flow condition across the impermeable base, (4) the classical analytic solution for a well and (5) spheroidal harmonics to account for the influence of the inhomogeneities in hydraulic conductivity. Temporal variations of the flow system due to time-dependent recharge and pumping are represented by combining the analytic element method with a finite difference method: analytic element method is used to represent spatial changes in head and discharge, while the finite difference method represents temporal variations. The solution provides a very detailed description of local groundwater flow with an arbitrary number of wells of any orientation and an arbitrary number of ellipsoidal inhomogeneities of any size and conductivity. These inhomogeneities may be used to model local hydrogeologic features (such as gravel packs and clay lenses) that significantly influence the flow in the vicinity of partially penetrating wells. Several options for specifying head values along the lateral domain boundary are available. These options allow for inclusion of the model into steady and transient regional groundwater models. The head values along the lateral domain boundary may be specified directly (as time series). The head values along the lateral boundary may also be assigned by specifying the water-table gradient and a head value at a single point (as time series). A case study is included to demonstrate the application of the model in local modeling of the groundwater flow. Transient three-dimensional capture zones are delineated for a site on Prairie Island, MN. Prairie Island is located on the Mississippi River 40 miles south of the Twin Cities metropolitan area. The case study focuses on a well that has been known to contain viral DNA. The objective of the study was to assess the potential for pathogen migration toward the well.

Modeling the role of groundwater and vegetation in the hydrological response of tropical glaciated watersheds to climate change

NASA Astrophysics Data System (ADS)

Ng, G. H. C.; Wickert, A. D.; McLaughlin, R.; La Frenierre, J.; Liess, S.; Saberi, L.

2016-12-01

Climate change projections show greater rates at higher elevations, making tropical glaciated regions some of the most vulnerable hydrological systems and the earliest windows into changing conditions in mountainous watersheds. Many of the subsistence agrarian communities below Volcán Chimborazo, Ecuador, experience water stress, heightening the urgency to understand the hydrological impacts of climate change. Previous hydrochemical and physical observations suggest that a significant fraction of glacial melt may first recharge underlying groundwater before discharging to streams at lower elevations. This has important implications for tracking hydrological response to climate change, due to differences in the spatiotemporal behavior of surface water vs. groundwater. However, differentiating meltwater-sourced and precipitation-sourced groundwater throughout the watershed poses a challenge in elucidating the influence of accelerated but finite glacial melt on streamflow. In addition to glacial melt, recently noted upslope vegetation migration on Chimborazo will likely complicate future predictions of water availability by influencing the relative amounts of groundwater sources and changing discharge through altered evapotranspiration along riparian zones. To investigate the roles of groundwater pathways and vegetation on glacial melt contributions to streamflow, we implement the coupled groundwater/rainfall-runoff model GSFLOW. We infer hydrogeological model inputs from geological maps of Chimborazo and vegetation properties from a combination of remotely sensed imagery and in-situ surveys. Dynamically downscaled meteorological state variables, checked against field data, force the model. Such a model enables the quantification of the current meltwater contribution to streamflow at critical water extraction points and allows us to probe potential meltwater and water resource changes under future climate change scenarios.

Patterns and rates of ground-water flow on Long Island, New York

USGS Publications Warehouse

Buxton, Herbert T.; Modica, Edward

1992-01-01

Increased ground-water contamination from human activities on Long Island has prompted studies to define the pattern and rate of ground-water movement. A two-dimensional, fine-mesh, finite-element model consisting of 11,969 nodes and 22,880 elements was constructed to represent ground-water flow along a north-south section through central Long Island. The model represents average hydrologic conditions within a corridor approximately 15 miles wide. The model solves discrete approximations of both the potential and stream functions. The resulting flownet depicts flow paths and defines the vertical distribution of flow within the section. Ground-water flow rates decrease with depth. Sixty-two percent of the water flows no deeper than the upper glacial (water-table) aquifer, 38 percent enters the underlying Magothy aquifer, and only 3.1 percent enters the Lloyd aquifer. The limiting streamlines for flow to the Magothy and Lloyd aquifers indicate that aquifer recharge areas are narrow east-west bands through the center of the island. The recharge area of the Magothy aquifer is only 5.4 miles wide; that of the Lloyd aquifer is less than 0.5 miles. The distribution of ground-water traveltime and a flownet are calculated from model results; both are useful in the investigation of contaminant transport or the chemical evolution of ground water within the flow system. A major discontinuity in traveltime occurs across the streamline which separates the flow subsystems of the two confined aquifers. Water that reaches the Lloyd aquifer attains traveltimes as high as 10,000 years, whereas water that has not penetrated deeper than the Magothy aquifer attains traveltimes of only 2,000 years. The finite-element approach used in this study is particularly suited to ground-water systems that have complex hydrostratigraphy and cross-sectional symmetry.

Study on the stress changes due to the regional groundwater exploitation based on a 3-D fully coupled poroelastic model: An example of the North China Plain

NASA Astrophysics Data System (ADS)

Cheng, H.; Zhang, H.; Pang, Y. J.; Shi, Y.

2017-12-01

With the quick urban development, over-exploitation of groundwater resources becomes more and more intense, which leads to not only widespread groundwater depression cones but also a series of harsh environmental and geological hazards. Among which, the most intuitive phenomenon is the ground subsidence in loose sediments. However, another direct consequence triggered by the groundwater depletion is the substantial crustal deformation and potential modulation of crustal stress underneath the groundwater over-pumping zones. In our previous 3-D viscoelastic finite element model, we found that continuous over-exploitation of groundwater resources in North China Plain during the past 60 years give rise to crustal-scale uplift reaching 4.9cm, with the Coulomb failure stress decreasing by up to 12 kPa, which may inhibit the nucleation of possible big earthquake events. Furthermore, according to the effective pressure principle and lab experiments, the pore pressure may also have changed due to the reduced water level. In order to quantitatively analyze the stress changes due to the regional groundwater exploitation in North China Plain, a three-dimensional fully coupled poroelastic finite element model is developed in this study. The high resolution topography, grounwater level fluctuation, fault parameters and etc, are taken into consideration. Further, the changes of Coulomb Failure Stress, in correspondence to elastic stress and pore pressure changes induced by fluid diffusion are calculated. Meanwhile, the elastic strain energy accumulation in region due to the regional groundwater exploitation is obtained. Finally, we try to analyze the seismic risk of major faults within North China Plain to further discuss the regional seismic activities.

Groundwater transport of strontium 90 in a glacial outwash environment

USGS Publications Warehouse

Kipp, Kenneth L.; Stollenwerk, Kenneth G.; Grove, David B.

1986-01-01

As part of the investigation of groundwater contamination at a uranium-scrap recovery plant at Wood River Junction, Rhode Island, laboratory experiments led to the development of a model for predicting the transport of strontium 90 in glacial outwash sediments based on an approximate mechanism for ion exchange. The multicomponent system was simplified to two components by regarding all exchangeable cations other than strontium 90 as a single component. The binary ion-exchange parameter was a function of the variable, total ion concentration. A one-dimensional solute transport model was formulated to evaluate the time necessary for natural groundwater flow to remove the strontium 90 contamination plume from the groundwater system to the Pawcatuck River. The finite difference transport equations were solved sequentially for total ion concentrations, then strontium 90 concentrations. Clay-free quartz and feldspar sands at the study site have little potential for strontium 90 sorption, and high calcium, magnesium, and sodium concentrations compete for the few ion exchange sites. As the total ion concentration plume moves out of the system, ion exchange of strontium 90 increases, reducing the strontium 90 concentration in the groundwater. Cleanout times predicted using the binary ion exchange mechanism were about two thirds of those predicted using a constant distribution coefficient. It is suggested that this type of model can simulate solute transport more realistically in many groundwater systems where the total ion concentration is not constant.

Delineation of areas contributing groundwater to selected receiving surface water bodies for long-term average hydrologic conditions from 1968 to 1983 for Long Island, New York

USGS Publications Warehouse

Misut, Paul E.; Monti,, Jack

2016-10-05

To assist resource managers and planners in developing informed strategies to address nitrogen loading to coastal water bodies of Long Island, New York, the U.S. Geological Survey and the New York State Department of Environmental Conservation initiated a program to delineate a comprehensive dataset of groundwater recharge areas (or areas contributing groundwater), travel times, and outflows to streams and saline embayments on Long Island. A four-layer regional three-dimensional finite-difference groundwater-flow model of hydrologic conditions from 1968 to 1983 was used to provide delineations of 48 groundwater watersheds on Long Island. Sixteen particle starting points were evenly spaced within each of the 4,000- by 4,000-foot model cells that receive water-table recharge and tracked using forward particle-tracking analysis modeling software to outflow zones. For each particle, simulated travel times were grouped by age as follows: less than or equal to 10 years, greater than 10 years and less than or equal to 100 years, greater than 100 years and less than or equal to 1,000 years, and greater than 1,000 years; and simulated ending zones were grouped into 48 receiving water bodies, based on the New York State Department of Environmental Conservation Waterbody Inventory/Priority Waterbodies List. Areal delineation of travel time zones and groundwater contributing areas were generated and a table was prepared presenting the sum of groundwater outflow for each area.

Uncertainty of climate change impact on groundwater reserves - Application to a chalk aquifer

NASA Astrophysics Data System (ADS)

Goderniaux, Pascal; Brouyère, Serge; Wildemeersch, Samuel; Therrien, René; Dassargues, Alain

2015-09-01

Recent studies have evaluated the impact of climate change on groundwater resources for different geographical and climatic contexts. However, most studies have either not estimated the uncertainty around projected impacts or have limited the analysis to the uncertainty related to climate models. In this study, the uncertainties around impact projections from several sources (climate models, natural variability of the weather, hydrological model calibration) are calculated and compared for the Geer catchment (465 km2) in Belgium. We use a surface-subsurface integrated model implemented using the finite element code HydroGeoSphere, coupled with climate change scenarios (2010-2085) and the UCODE_2005 inverse model, to assess the uncertainty related to the calibration of the hydrological model. This integrated model provides a more realistic representation of the water exchanges between surface and subsurface domains and constrains more the calibration with the use of both surface and subsurface observed data. Sensitivity and uncertainty analyses were performed on predictions. The linear uncertainty analysis is approximate for this nonlinear system, but it provides some measure of uncertainty for computationally demanding models. Results show that, for the Geer catchment, the most important uncertainty is related to calibration of the hydrological model. The total uncertainty associated with the prediction of groundwater levels remains large. By the end of the century, however, the uncertainty becomes smaller than the predicted decline in groundwater levels.

Storm Water Infiltration and Focused Groundwater Recharge in a Rain Garden: Finite Volume Model and Numerical Simulations for Different Configurations and Climates

NASA Astrophysics Data System (ADS)

Aravena, J.; Dussaillant, A. R.

2006-12-01

Source control is the fundamental principle behind sustainable management of stormwater. Rain gardens are an infiltration practice that provides volume and water quality control, recharge, and multiple landscape, ecological and economic potential benefits. The fulfillment of these objectives requires understanding their behavior during events as well as long term, and tools for their design. We have developed a model based on Richards equation coupled to a surface water balance, solved with a 2D finite volume Fortran code which allows alternating upper boundary conditions, including ponding, which is not present in available 2D models. Also, it can simulate non homogeneous water input, heterogeneous soil (layered or more complex geometries), and surface irregularities -e.g. terracing-, so as to estimate infiltration and recharge. The algorithm is conservative; being an advantage compared to available finite difference and finite element methods. We will present performance comparisons to known models, to experimental data from a bioretention cell, which receives roof water to its surface depression planted with native species in an organic-rich root zone soil layer (underlain by a high conductivity lower layer that, while providing inter-event storage, percolates water readily), as well as long term simulations for different rain garden configurations. Recharge predictions for different climates show significant increases from natural recharge, and that the optimal area ratio (raingarden vs. contributing impervious area) reduces from 20% (humid) to 5% (dry).

Recovery of injected freshwater to differentiate fracture flow in a low-permeability brackish aquifer

NASA Astrophysics Data System (ADS)

Miotliński, Konrad; Dillon, Peter J.; Pavelic, Paul; Cook, Peter G.; Page, Declan W.; Levett, Kerry

2011-10-01

SummaryA low-permeability weathered siltstone-sandstone aquifer containing brackish water was investigated to measure recoverability of injected freshwater with the aim of determining the significance of secondary porosity in contributing to groundwater flow and transport. Examination of the core, borehole geophysics, Radon-222, electromagnetic flowmeter (EMF) profiles and step-drawdown pumping tests did not identify whether fractures contribute to groundwater flow. A number of injection and recovery tests lasting from 3 days to 3 months using potable water showed a large degree of mixing with native groundwater. Withdrawal greater than 12-17% of the injected volume resulted in recovered water containing more native groundwater than injected water. A finite element solute transport model was set up to reproduce the observed salinity in recovered water. Without the inclusion of discrete fractures in the model it was not possible to get a fit between the observed and modelled salinity of recovered water within a realistic range of dispersivity values. The model was subsequently verified by using data from long-term injection and recovery trials. This evaluation of mixing conclusively demonstrated that the aquifer behaved as a fractured rock aquifer and not as an aquifer with primary porosity alone. Therefore, aquifer storage and recovery can be a very useful hydrogeological method to identify the occurrence of fracture flow in aquifers where there is a measurable concentration difference between the injected water and ambient groundwater.

Use of a three-dimensional model for the analysis of the ground-water flow system in Parker Valley, Arizona and California

USGS Publications Warehouse

Tucci, Patrick

1982-01-01

A three-dimensional, finite-difference model was used to simulate ground-water flow conditions in Parker Valley. The study evaluated present knowledge and concepts of the ground-water system and the ability of the model to represent the system. Modeling assumptions and generalized physical parameters that were used may have transfer value in the construction and calibration of models of other basins along the lower Colorado River. The aquifer was simulated in two layers to represent the three-dimensional system. Ground-water conditions were simulated for 1940-41, the mid-1960's, and 1980. Overall model results generally compared favorably with available field information. The model results showed that for 1940-41 the Colorado River was a losing stream through out Parker Valley. Infiltration of surface water from the river was the major source of recharge. The dominant mechanism of discharge was evapotranspiration by phreatophytes. Agricultural development between 1941 and the mid-1960 's resulted in significant changes to the ground-water system. Model results for conditions in the mid-1960 's showed that the Colorado River had become a gaining stream in the northern part of the valley as a result of higher water levels. The rise in water levels was caused by infiltration of applied irrigation water. Diminished water-level gradients from the river in the rest of the valley reduced the amount of infiltration of surface water from the river. Models results for conditions in 1980 showed that ground-water level rises of several feet caused further reduction in the amount of surface-water infiltration from the river. (USGS)

AQUIFEM-SALT; a finite-element model for aquifers containing a seawater interface

USGS Publications Warehouse

Voss, C.I.

1984-01-01

Described are modifications to AQUIFEM, a finite element areal ground-water flow model for aquifer evaluation. The modified model, AQUIFEM-SALT, simulates an aquifer containing a freshwater body that freely floats on seawater. Parts of the freshwater lens may be confined above and below by less permeable units. Theory, code modifications, and model verification are discussed. A modified input data list is included. This report is intended as a companion to the original AQUIFEM documentation. (USGS)

Numerical analysis of one-dimensional temperature data for groundwater/surface-water exchange with 1DTempPro

NASA Astrophysics Data System (ADS)

Voytek, E. B.; Drenkelfuss, A.; Day-Lewis, F. D.; Healy, R. W.; Lane, J. W.; Werkema, D. D.

2012-12-01

Temperature is a naturally occurring tracer, which can be exploited to infer the movement of water through the vadose and saturated zones, as well as the exchange of water between aquifers and surface-water bodies, such as estuaries, lakes, and streams. One-dimensional (1D) vertical temperature profiles commonly show thermal amplitude attenuation and increasing phase lag of diurnal or seasonal temperature variations with propagation into the subsurface. This behavior is described by the heat-transport equation (i.e., the convection-conduction-dispersion equation), which can be solved analytically in 1D under certain simplifying assumptions (e.g., sinusoidal or steady-state boundary conditions and homogeneous hydraulic and thermal properties). Analysis of 1D temperature profiles using analytical models provides estimates of vertical groundwater/surface-water exchange. The utility of these estimates can be diminished when the model assumptions are violated, as is common in field applications. Alternatively, analysis of 1D temperature profiles using numerical models allows for consideration of more complex and realistic boundary conditions. However, such analyses commonly require model calibration and the development of input files for finite-difference or finite-element codes. To address the calibration and input file requirements, a new computer program, 1DTempPro, is presented that facilitates numerical analysis of vertical 1D temperature profiles. 1DTempPro is a graphical user interface (GUI) to the USGS code VS2DH, which numerically solves the flow- and heat-transport equations. Pre- and post-processor features within 1DTempPro allow the user to calibrate VS2DH models to estimate groundwater/surface-water exchange and hydraulic conductivity in cases where hydraulic head is known. This approach improves groundwater/ surface-water exchange-rate estimates for real-world data with complexities ill-suited for examination with analytical methods. Additionally, the code allows for time-varying temperature and hydraulic boundary conditions. Here, we present the approach and include examples for several datasets from stream/aquifer systems.

SUTRA: A model for 2D or 3D saturated-unsaturated, variable-density ground-water flow with solute or energy transport

USGS Publications Warehouse

Voss, Clifford I.; Provost, A.M.

2002-01-01

SUTRA (Saturated-Unsaturated Transport) is a computer program that simulates fluid movement and the transport of either energy or dissolved substances in a subsurface environment. This upgraded version of SUTRA adds the capability for three-dimensional simulation to the former code (Voss, 1984), which allowed only two-dimensional simulation. The code employs a two- or three-dimensional finite-element and finite-difference method to approximate the governing equations that describe the two interdependent processes that are simulated: 1) fluid density-dependent saturated or unsaturated ground-water flow; and 2) either (a) transport of a solute in the ground water, in which the solute may be subject to: equilibrium adsorption on the porous matrix, and both first-order and zero-order production or decay; or (b) transport of thermal energy in the ground water and solid matrix of the aquifer. SUTRA may also be used to simulate simpler subsets of the above processes. A flow-direction-dependent dispersion process for anisotropic media is also provided by the code and is introduced in this report. As the primary calculated result, SUTRA provides fluid pressures and either solute concentrations or temperatures, as they vary with time, everywhere in the simulated subsurface system. SUTRA flow simulation may be employed for two-dimensional (2D) areal, cross sectional and three-dimensional (3D) modeling of saturated ground-water flow systems, and for cross sectional and 3D modeling of unsaturated zone flow. Solute-transport simulation using SUTRA may be employed to model natural or man-induced chemical-species transport including processes of solute sorption, production, and decay. For example, it may be applied to analyze ground-water contaminant transport problems and aquifer restoration designs. In addition, solute-transport simulation with SUTRA may be used for modeling of variable-density leachate movement, and for cross sectional modeling of saltwater intrusion in aquifers at near-well or regional scales, with either dispersed or relatively sharp transition zones between freshwater and saltwater. SUTRA energy-transport simulation may be employed to model thermal regimes in aquifers, subsurface heat conduction, aquifer thermal-energy storage systems, geothermal reservoirs, thermal pollution of aquifers, and natural hydrogeologic convection systems. Mesh construction, which is quite flexible for arbitrary geometries, employs quadrilateral finite elements in 2D Cartesian or radial-cylindrical coordinate systems, and hexahedral finite elements in 3D systems. 3D meshes are currently restricted to be logically rectangular; in other words, they are similar to deformable finite-difference-style grids. Permeabilities may be anisotropic and may vary in both direction and magnitude throughout the system, as may most other aquifer and fluid properties. Boundary conditions, sources and sinks may be time dependent. A number of input data checks are made to verify the input data set. An option is available for storing intermediate results and restarting a simulation at the intermediate time. Output options include fluid velocities, fluid mass and solute mass or energy budgets, and time-varying observations at points in the system. Both the mathematical basis for SUTRA and the program structure are highly general, and are modularized to allow for straightforward addition of new methods or processes to the simulation. The FORTRAN-90 coding stresses clarity and modularity rather than efficiency, providing easy access for later modifications.

Simulation of groundwater storage changes in the eastern Pasco Basin, Washington

USGS Publications Warehouse

Heywood, Charles E.; Kahle, Sue C.; Olsen, Theresa D.; Patterson, James D.; Burns, Erick

2016-03-29

The Miocene Columbia River Basalt Group and younger sedimentary deposits of lacustrine, fluvial, eolian, and cataclysmic-flood origins compose the aquifer system of the Pasco Basin in eastern Washington. Irrigation return flow and canal leakage from the Columbia Basin Project have caused groundwater levels to rise substantially in some areas, contributing to landslides along the Columbia River. Water resource managers are considering extraction of additional stored groundwater to supply increasing demand and possibly mitigate problems caused by the increased water levels. To help address these concerns, the transient groundwater model of the Pasco Basin documented in this report was developed to quantify the changes in groundwater flow and storage. The MODFLOW model uses a 1-kilometer finite-difference grid and is constrained by logs and water levels from 846 wells in the study area. Eight model layers represent five sedimentary hydrogeologic units and underlying basalt formations. Head‑dependent flux boundaries represent the Columbia and Snake Rivers to the west and south, respectively, underflow to and (or) from adjacent areas to the northeast, and discharge to agricultural drains, springs, and groundwater withdrawal wells. Specified flux boundaries represent recharge from infiltrated precipitation and anthropogenic sources, including irrigation return flow and leakage from water-distribution canals. The model was calibrated with the parameter‑estimation code PEST++ to groundwater levels measured from 1907 through 2013 and measured discharge to springs and estimated discharge to agricultural drains. Increased recharge since pre-development resulted in a 6.8 million acre-feet increase in storage in the 508-14 administrative area of the Pasco Basin. Four groundwater-management scenarios simulate the 7-year drawdown resulting from withdrawals in different locations. Withdrawals of 2 million gallons per day (Mgal/d) from a hypothetical well field in the upper Ringold Formation along the Columbia River could generate 30–70 feet of drawdown, which may reduce landslide susceptibility along the White Bluffs. Drawdowns resulting from a 1 Mgal/d withdrawal from wells screened in either Pasco gravels, upper Ringold Formation, or both Ringold Formation and underlying basalt are simulated in the other three scenarios, and differ because of the contrasting hydraulic conductivities within the screened intervals.

Mathematical modelling of surface water-groundwater flow and salinity interactions in the coastal zone

NASA Astrophysics Data System (ADS)

Spanoudaki, Katerina; Kampanis, Nikolaos A.

2014-05-01

Coastal areas are the most densely-populated areas in the world. Consequently water demand is high, posing great pressure on fresh water resources. Climatic change and its direct impacts on meteorological variables (e.g. precipitation) and indirect impact on sea level rise, as well as anthropogenic pressures (e.g. groundwater abstraction), are strong drivers causing groundwater salinisation and subsequently affecting coastal wetlands salinity with adverse effects on the corresponding ecosystems. Coastal zones are a difficult hydrologic environment to represent with a mathematical model due to the large number of contributing hydrologic processes and variable-density flow conditions. Simulation of sea level rise and tidal effects on aquifer salinisation and accurate prediction of interactions between coastal waters, groundwater and neighbouring wetlands requires the use of integrated surface water-groundwater models. In the past few decades several computer codes have been developed to simulate coupled surface and groundwater flow. In these numerical models surface water flow is usually described by the 1-D Saint Venant equations (e.g. Swain and Wexler, 1996) or the 2D shallow water equations (e.g. Liang et al., 2007). Further simplified equations, such as the diffusion and kinematic wave approximations to the Saint Venant equations, are also employed for the description of 2D overland flow and 1D stream flow (e.g. Gunduz and Aral, 2005). However, for coastal bays, estuaries and wetlands it is often desirable to solve the 3D shallow water equations to simulate surface water flow. This is the case e.g. for wind-driven flows or density-stratified flows. Furthermore, most integrated models are based on the assumption of constant fluid density and therefore their applicability to coastal regions is questionable. Thus, most of the existing codes are not well-suited to represent surface water-groundwater interactions in coastal areas. To this end, the 3D integrated surface water-groundwater model IRENE (Spanoudaki et al., 2009; Spanoudaki, 2010) has been modified in order to simulate surface water-groundwater flow and salinity interactions in the coastal zone. IRENE, in its original form, couples the 3D, non-steady state Navier-Stokes equations, after Reynolds averaging and with the assumption of hydrostatic pressure distribution, to the equations describing 3D saturated groundwater flow of constant density. A semi-implicit finite difference scheme is used to solve the surface water flow equations, while a fully implicit finite difference scheme is used for the groundwater equations. Pollution interactions are simulated by coupling the advection-diffusion equation describing the fate and transport of contaminants introduced in a 3D turbulent flow field to the partial differential equation describing the fate and transport of contaminants in 3D transient groundwater flow systems. The model has been further developed to include the effects of density variations on surface water and groundwater flow, while the already built-in solute transport capabilities are used to simulate salinity interactions. Initial results show that IRENE can accurately predict surface water-groundwater flow and salinity interactions in coastal areas. Important research issues that can be investigated using IRENE include: (a) sea level rise and tidal effects on aquifer salinisation and the configuration of the saltwater wedge, (b) the effects of surface water-groundwater interaction on salinity increase of coastal wetlands and (c) the estimation of the location and magnitude of groundwater discharge to coasts. Acknowledgement The work presented in this paper has been funded by the Greek State Scholarships Foundation (IKY), Fellowships of Excellence for Postdoctoral Studies (Siemens Program), 'A simulation-optimization model for assessing the best practices for the protection of surface water and groundwater in the coastal zone', (2013 - 2015). References Gunduz, O. and Aral, M.M. (2005). River networks and groundwater flow: a simultaneous solution of a coupled system. Journal of Hydrology 301 (1-4), 216-234. Liang, D., Falconer, R.A. and Lin, B. (2007). Coupling surface and subsurface flows in a depth-averaged flood wave model. Journal of Hydrology 337, 147-158. Spanoudaki, K., Stamou, A.I. and Nanou-Giannarou, A. (2009). Development and verification of a 3-D integrated surface water-groundwater model. Journal of Hydrology, 375 (3-4), 410-427. Spanoudaki, K. (2010). Integrated numerical modelling of surface water groundwater systems (in Greek). Ph.D. Thesis, National Technical University of Athens, Greece. Swain, E.D. and Wexler, E.J. (1996). A coupled surface water and groundwater flow model (Modbranch) for simulation of stream-aquifer interaction. United States Geological Survey, Techniques of Water Resources Investigations (Book 6, Chapter A6).

Improving large-scale groundwater models by considering fossil gradients

NASA Astrophysics Data System (ADS)

Schulz, Stephan; Walther, Marc; Michelsen, Nils; Rausch, Randolf; Dirks, Heiko; Al-Saud, Mohammed; Merz, Ralf; Kolditz, Olaf; Schüth, Christoph

2017-05-01

Due to limited availability of surface water, many arid to semi-arid countries rely on their groundwater resources. Despite the quasi-absence of present day replenishment, some of these groundwater bodies contain large amounts of water, which was recharged during pluvial periods of the Late Pleistocene to Early Holocene. These mostly fossil, non-renewable resources require different management schemes compared to those which are usually applied in renewable systems. Fossil groundwater is a finite resource and its withdrawal implies mining of aquifer storage reserves. Although they receive almost no recharge, some of them show notable hydraulic gradients and a flow towards their discharge areas, even without pumping. As a result, these systems have more discharge than recharge and hence are not in steady state, which makes their modelling, in particular the calibration, very challenging. In this study, we introduce a new calibration approach, composed of four steps: (i) estimating the fossil discharge component, (ii) determining the origin of fossil discharge, (iii) fitting the hydraulic conductivity with a pseudo steady-state model, and (iv) fitting the storage capacity with a transient model by reconstructing head drawdown induced by pumping activities. Finally, we test the relevance of our approach and evaluated the effect of considering or ignoring fossil gradients on aquifer parameterization for the Upper Mega Aquifer (UMA) on the Arabian Peninsula.

Unsteady solute-transport simulation in streamflow using a finite-difference model

USGS Publications Warehouse

Land, Larry F.

1978-01-01

This report documents a rather simple, general purpose, one-dimensional, one-parameter, mass-transport model for field use. The model assumes a well-mixed conservative solute that may be coming from an unsteady source and is moving in unsteady streamflow. The quantity of solute being transported is in the units of concentration. Results are reported as such. An implicit finite-difference technique is used to solve the mass transport equation. It consists of creating a tridiagonal matrix and using the Thomas algorithm to solve the matrix for the unknown concentrations at the new time step. The computer program pesented is designed to compute the concentration of a water-quality constituent at any point and at any preselected time in a one-dimensional stream. The model is driven by the inflowing concentration of solute at the upstream boundary and is influenced by the solute entering the stream from tributaries and lateral ground-water inflow and from a source or sink. (Woodard-USGS)

Modeling of ground-water flow in subsurface Austin Chalk and Taylor marl in Ellis County, Texas, near the superconducting super collider site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mace, R.E.

1993-02-01

Numerical models are useful tools for developing an understanding of ground-water flow in sparsely characterized low-permeability aquifers. Finite-difference, cross-sectional models of Cretaceous chalk and marl formations near the Superconducting Super Collider (SSC) were constructed using MODFLOW to evaluate ground-water circulation paths and travel times. Weathered and fractured zones with enhanced permeability were included to assess the effect these features had on flow paths and times. Pump tests, slug tests, packer tests, core tests, and estimates were used to define hydraulic properties for model input. The model was calibrated with water-level data from monitor wells and from wire-line piezometers near amore » test shaft excavated by the SSC project. A ratio of vertical-to-horizontal permeability of 0.0085 was estimated through model calibration. A chalk-to-marl permeability ratio of 18 was needed to reproduce artesian head in a well completed in chalk beneath marl. Hydraulic head distributions and ground-water flow paths reflected local, intermediate, and regional flow systems with recharge beneath upland surface-water divides and discharge in valleys. Most of the flow (99%) occurred in the weathered zone, with average residence times of 5 to 10 years. Residence time in unweathered chalk bedrock was substantially longer, at an average of 1.7 Ma. As expected, the model demonstrated that deep and rapid ground-water circulation might occur in fracture zones. Particle paths calculated using MODPATH showed that ground-water travel times from recharge areas to the SSC subsurface facilities might be 20 to 60 years where flow is through fracture zones.« less

Examining the contradiction in 'sustainable urban growth': an example of groundwater sustainability

USGS Publications Warehouse

Zellner, Moira L.; Reeves, Howard W.

2012-01-01

The environmental planning literature proposes a set of 'best management practices' for urban development that assumes improvement in environmental quality as a result of specific urban patterns. These best management practices, however, often do not recognise finite biophysical limits and social impacts that urban patterns alone cannot overcome. To shed light on this debate, we explore the effects of different degrees of urban clustering on groundwater levels using a coupled land-use change and groundwater-flow model. Our simulations show that specific urban forms only slow down the impact on groundwater. As population increases, the pattern in which it is accommodated ceases to matter, and widespread depletion ensues. These results are predictable, yet current planning practice tends to take growth for granted and is reluctant to envision either no-growth scenarios or the prospect of depletion. We propose to use simulations such as those presented here to aid in policy discussions that allow decision makers to question the assumption of sustainable growth and suggest alternative forms of development.

Documentation of a computer program to simulate transient leakage from confining units using the modular finite-difference, ground-water flow model

USGS Publications Warehouse

Leake, S.A.; Leahy, P.P.; Navoy, A.S.

1994-01-01

Transient leakage into or out of a compressible fine-grained confining unit results from ground- water storage changes within the unit. The computer program described in this report provides a new method of simulating transient leakage using the U.S. Geological Survey modular finite- difference ground-water flow model (MODFLOW). The new program is referred to as the Transient- Leakage Package. The Transient-Leakage Package solves integrodifferential equations that describe flow across the upper and lower boundaries of confining units. For each confining unit, vertical hydraulic conductivity, thickness, and specific storage are specified in input arrays. These properties can vary from cell to cell and the confining unit need not be present at all locations in the grid; however, the confining units must be bounded above and below by model layers in which head is calculated or specified. The package was used in an example problem to simulate drawdown around a pumping well in a system with two aquifers separated by a confining unit. For drawdown values in excess of 1 centimeter, the solution using the new package closely matched an exact analytical solution. The problem also was simulated without the new package by using a separate model layer to represent the confining unit. That simulation was refined by using two model layers to represent the confining unit. The simulation using the Transient-Leakage Package was faster and more accurate than either of the simulations using model layers to represent the confining unit.

Applications of numerical methods to simulate the movement of contaminants in groundwater.

PubMed Central

Sun, N Z

1989-01-01

This paper reviews mathematical models and numerical methods that have been extensively used to simulate the movement of contaminants through the subsurface. The major emphasis is placed on the numerical methods of advection-dominated transport problems and inverse problems. Several mathematical models that are commonly used in field problems are listed. A variety of numerical solutions for three-dimensional models are introduced, including the multiple cell balance method that can be considered a variation of the finite element method. The multiple cell balance method is easy to understand and convenient for solving field problems. When the advection transport dominates the dispersion transport, two kinds of numerical difficulties, overshoot and numerical dispersion, are always involved in solving standard, finite difference methods and finite element methods. To overcome these numerical difficulties, various numerical techniques are developed, such as upstream weighting methods and moving point methods. A complete review of these methods is given and we also mention the problems of parameter identification, reliability analysis, and optimal-experiment design that are absolutely necessary for constructing a practical model. PMID:2695327

PRECONDITIONED CONJUGATE-GRADIENT 2 (PCG2), a computer program for solving ground-water flow equations

USGS Publications Warehouse

Hill, Mary C.

1990-01-01

This report documents PCG2 : a numerical code to be used with the U.S. Geological Survey modular three-dimensional, finite-difference, ground-water flow model . PCG2 uses the preconditioned conjugate-gradient method to solve the equations produced by the model for hydraulic head. Linear or nonlinear flow conditions may be simulated. PCG2 includes two reconditioning options : modified incomplete Cholesky preconditioning, which is efficient on scalar computers; and polynomial preconditioning, which requires less computer storage and, with modifications that depend on the computer used, is most efficient on vector computers . Convergence of the solver is determined using both head-change and residual criteria. Nonlinear problems are solved using Picard iterations. This documentation provides a description of the preconditioned conjugate gradient method and the two preconditioners, detailed instructions for linking PCG2 to the modular model, sample data inputs, a brief description of PCG2, and a FORTRAN listing.

Hydrogeology, water quality, and ground-water development alternatives in the Beaver-Pasquiset ground-water reservoir, Rhode Island

USGS Publications Warehouse

Dickerman, D.C.; Ozbilgin, M.M.

1985-01-01

In a 23 sq mi study area, the Beaver-Pasquiset groundwater reservoir within the Pawcatuck River basin in southern Rhode Island, stratified drift is the only principal geologic unit capable of producing yields > 350 gal/min. Transmissivity of the aquifer ranges from 7,200 to 24,300 sq ft/day. Water table conditions prevail in the aquifer, which is in good hydraulic connection with perennial streams and ponds. A digital model of two-dimensional groundwater flow was used to simulate the interaction between surface water and groundwater, and to evaluate the impact of alternative schemes of groundwater development on groundwater levels, pond levels, and streamflow in the Beaver-Pasquiset groundwater reservoir. Transient simulations of theoretical pumpage were made for a drought period (1963-66) and a wet period (1976-78). The areas most favorable for development of high-capacity wells (350 gal/min or more) are along the Beaver River and near Pasquiset Pond. The water is soft and generally contains < 100 mg/L dissolved solids. Locally, groundwater contains elevated concentrations of iron and manganese (7.5 and 3.7 mg/L, respectively), southeast of Pasquiset Pond, and will require treatment if used for public supply. The groundwater reservoir was simulated with a two-dimensional finite-difference model using a block-centered grid consisting of 33 rows and 75 columns. Differences between measured and simulated water table altitudes for the final steady state run for 21 selected observation wells averaged +0.07 ft. Combined pumping rates for simulation of groundwater development alternatives at eight sites ranged from 3.25 to 7.00 Mgal/d. Pumping rates for individual wells ranged from 0.25 to 1.50 Mgal/d. Transient simulations suggest that the Beaver-Pasquiset groundwater reservoir is capable of sustaining a pumping rate of 4.25 Mgal/d during years of average groundwater recharge with minimal impact on groundwater levels, pond levels, and streamflow. During extreme drought periods (1965 and 1966) it would be necessary to reduce pumpage below 3.25 Mgal/d to maintain flow in both the Beaver River and Pasquiset Brook. (Author 's abstract)

Groundwater flow and its effect on salt dissolution in Gypsum Canyon watershed, Paradox Basin, southeast Utah, USA

NASA Astrophysics Data System (ADS)

Reitman, Nadine G.; Ge, Shemin; Mueller, Karl

2014-09-01

Groundwater flow is an important control on subsurface evaporite (salt) dissolution. Salt dissolution can drive faulting and associated subsidence on the land surface and increase salinity in groundwater. This study aims to understand the groundwater flow system of Gypsum Canyon watershed in the Paradox Basin, Utah, USA, and whether or not groundwater-driven dissolution affects surface deformation. The work characterizes the groundwater flow and solute transport systems of the watershed using a three-dimensional (3D) finite element flow and transport model, SUTRA. Spring samples were analyzed for stable isotopes of water and total dissolved solids. Spring water and hydraulic conductivity data provide constraints for model parameters. Model results indicate that regional groundwater flow is to the northwest towards the Colorado River, and shallow flow systems are influenced by topography. The low permeability obtained from laboratory tests is inconsistent with field observed discharges, supporting the notion that fracture permeability plays a significant role in controlling groundwater flow. Model output implies that groundwater-driven dissolution is small on average, and cannot account for volume changes in the evaporite deposits that could cause surface deformation, but it is speculated that dissolution may be highly localized and/or weaken evaporite deposits, and could lead to surface deformation over time.

An Open Source Framework for Coupled Hydro-Hydrogeo-Chemical Systems in Catchment Research

NASA Astrophysics Data System (ADS)

Delfs, J.; Sachse, A.; Gayler, S.; Grathwohl, P.; He, W.; Jang, E.; Kalbacher, T.; Klein, C.; Kolditz, O.; Maier, U.; Priesack, E.; Rink, K.; Selle, B.; Shao, H.; Singh, A. K.; Streck, T.; Sun, Y.; Wang, W.; Walther, M.

2013-12-01

This poster presents an open-source framework designed to assist water scientists in the study of catchment hydraulic functions with associated chemical processes, e.g. contaminant degradation, plant nutrient turnover. The model successfully calculates the feedbacks between surface water, subsurface water and air in standard benchmarks. In specific model applications to heterogeneous catchments, subsurface water is driven by density variations and runs through double porous media. Software codes of water science are tightly coupled by iteration, namely the Storm Water Management Model (SWMM) for urban runoff, Expert-N for simulating water fluxes and nutrient turnover in agricultural and forested soils, and OpenGeoSys (OGS) for groundwater. The coupled model calculates flow of hydrostatic shallow water over the land surface with finite volume and difference methods. The flow equations for water in the porous subsurface are discretized in space with finite elements. Chemical components are transferred through 1D, 2D or 3D watershed representations with advection-dispersion solvers or, as an alternative, random walk particle tracking. A transport solver can be in sequence with a chemical solver, e.g. PHREEQ-C, BRNS, additionally. Besides coupled partial differential equations, the concept of hydrological response units is employed in simulations at regional scale with scarce data availability. In this case, a conceptual hydrological model, specifically the Jena Adaptable Modeling System (JAMS), passes groundwater recharge through a software interface into OGS, which solves the partial differential equations of groundwater flow. Most components of the modeling framework are open source and can be modified for individual purposes. Applications range from temperate climate regions in Germany (Ammer catchment and Hessian Ried) to arid regions in the Middle East (Oman and Dead See). Some of the presented examples originate from intensively monitored research sites of the WESS research centre and the monitoring initiative TERENO. Other examples originate from the IWAS project on integrated water resources management. The model applications are primarily concerned with groundwater resources, which are endangered by overexploitation, intrusion of saltwater, and nitrate loads.

Testing density-dependent groundwater models: Two-dimensional steady state unstable convection in infinite, finite and inclined porous layers

USGS Publications Warehouse

Weatherill, D.; Simmons, C.T.; Voss, C.I.; Robinson, N.I.

2004-01-01

This study proposes the use of several problems of unstable steady state convection with variable fluid density in a porous layer of infinite horizontal extent as two-dimensional (2-D) test cases for density-dependent groundwater flow and solute transport simulators. Unlike existing density-dependent model benchmarks, these problems have well-defined stability criteria that are determined analytically. These analytical stability indicators can be compared with numerical model results to test the ability of a code to accurately simulate buoyancy driven flow and diffusion. The basic analytical solution is for a horizontally infinite fluid-filled porous layer in which fluid density decreases with depth. The proposed test problems include unstable convection in an infinite horizontal box, in a finite horizontal box, and in an infinite inclined box. A dimensionless Rayleigh number incorporating properties of the fluid and the porous media determines the stability of the layer in each case. Testing the ability of numerical codes to match both the critical Rayleigh number at which convection occurs and the wavelength of convection cells is an addition to the benchmark problems currently in use. The proposed test problems are modelled in 2-D using the SUTRA [SUTRA-A model for saturated-unsaturated variable-density ground-water flow with solute or energy transport. US Geological Survey Water-Resources Investigations Report, 02-4231, 2002. 250 p] density-dependent groundwater flow and solute transport code. For the case of an infinite horizontal box, SUTRA results show a distinct change from stable to unstable behaviour around the theoretical critical Rayleigh number of 4??2 and the simulated wavelength of unstable convection agrees with that predicted by the analytical solution. The effects of finite layer aspect ratio and inclination on stability indicators are also tested and numerical results are in excellent agreement with theoretical stability criteria and with numerical results previously reported in traditional fluid mechanics literature. ?? 2004 Elsevier Ltd. All rights reserved.

Analysis of potential water-supply management options, 2010-60, and documentation of revisions to the model of the Irwin Basin Aquifer System, Fort Irwin National Training Center, California

USGS Publications Warehouse

Voronin, Lois M.; Densmore, Jill N.; Martin, Peter

2014-01-01

The Fort Irwin National Training Center is considering several alternatives to manage their limited water-supply sources in the Irwin Basin. An existing three-dimensional, finite-difference groundwater-flow model—the U.S. Geological Survey’s MODFLOW—of the aquifer system in the basin was updated and the initial input dataset was supplemented with groundwater withdrawal data for the period 2000–10. The updated model was then used to simulate four combinations, or scenarios, of groundwater withdrawal and recharge over the next 50 years (January 2011 through December 2060). The scenarios included combinations of continuing withdrawals from currently active production wells, supplementing any increases in demand with withdrawals from an inactive production well, reducing withdrawal amounts and rates, and reducing the discharge of treated wastewater to infiltration ponds that provide a recharge source to the underlying aquifer. Results of the simulations indicated that, depending on the scenario implemented, groundwater levels would rise (over the next 50 years) from 40 feet to as much as 65 feet in the northwestern part of the Irwin Basin, and from 5 feet to 10 feet in the southeastern part.

Modeling hydrology, groundwater recharge and non-point nitrate loadings in the Himalayan Upper Yamuna basin.

PubMed

Narula, Kapil K; Gosain, A K

2013-12-01

The mountainous Himalayan watersheds are important hydrologic systems responsible for much of the water supply in the Indian sub-continent. These watersheds are increasingly facing anthropogenic and climate-related pressures that impact spatial and temporal distribution of water availability. This study evaluates temporal and spatial distribution of water availability including groundwater recharge and quality (non-point nitrate loadings) for a Himalayan watershed, namely, the Upper Yamuna watershed (part of the Ganga River basin). The watershed has an area of 11,600 km(2) with elevation ranging from 6300 to 600 m above mean sea level. Soil and Water Assessment Tool (SWAT), a physically-based, time-continuous model, has been used to simulate the land phase of the hydrological cycle, to obtain streamflows, groundwater recharge, and nitrate (NO3) load distributions in various components of runoff. The hydrological SWAT model is integrated with the MODular finite difference groundwater FLOW model (MODFLOW), and Modular 3-Dimensional Multi-Species Transport model (MT3DMS), to obtain groundwater flow and NO3 transport. Validation of various modules of this integrated model has been done for sub-basins of the Upper Yamuna watershed. Results on surface runoff and groundwater levels obtained as outputs from simulation show a good comparison with the observed streamflows and groundwater levels (Nash-Sutcliffe and R(2) correlations greater than +0.7). Nitrate loading obtained after nitrification, denitrification, and NO3 removal from unsaturated and shallow aquifer zones is combined with groundwater recharge. Results for nitrate modeling in groundwater aquifers are compared with observed NO3 concentration and are found to be in good agreement. The study further evaluates the sensitivity of water availability to climate change. Simulations have been made with the weather inputs of climate change scenarios of A2, B2, and A1B for end of the century. Water yield estimates under climate change scenarios have been made and implications on groundwater and groundwater quality have been assessed. The delicate groundwater resource balance that connects livelihoods of millions of people seems to be under tremendously increasing pressure due to the dynamic conditions of the natural environment of the region and the future climate changes. Copyright © 2013 Elsevier B.V. All rights reserved.

A modular finite-element model (MODFE) for areal and axisymmetric ground-water-flow problems, Part 2: Derivation of finite-element equations and comparisons with analytical solutions

USGS Publications Warehouse

Cooley, Richard L.

1992-01-01

MODFE, a modular finite-element model for simulating steady- or unsteady-state, area1 or axisymmetric flow of ground water in a heterogeneous anisotropic aquifer is documented in a three-part series of reports. In this report, part 2, the finite-element equations are derived by minimizing a functional of the difference between the true and approximate hydraulic head, which produces equations that are equivalent to those obtained by either classical variational or Galerkin techniques. Spatial finite elements are triangular with linear basis functions, and temporal finite elements are one dimensional with linear basis functions. Physical processes that can be represented by the model include (1) confined flow, unconfined flow (using the Dupuit approximation), or a combination of both; (2) leakage through either rigid or elastic confining units; (3) specified recharge or discharge at points, along lines, or areally; (4) flow across specified-flow, specified-head, or head-dependent boundaries; (5) decrease of aquifer thickness to zero under extreme water-table decline and increase of aquifer thickness from zero as the water table rises; and (6) head-dependent fluxes from springs, drainage wells, leakage across riverbeds or confining units combined with aquifer dewatering, and evapotranspiration. The matrix equations produced by the finite-element method are solved by the direct symmetric-Doolittle method or the iterative modified incomplete-Cholesky conjugate-gradient method. The direct method can be efficient for small- to medium-sized problems (less than about 500 nodes), and the iterative method is generally more efficient for larger-sized problems. Comparison of finite-element solutions with analytical solutions for five example problems demonstrates that the finite-element model can yield accurate solutions to ground-water flow problems.

Simulation of ground-water flow, surface-water flow, and a deep sewer tunnel system in the Menomonee Valley, Milwaukee, Wisconsin

USGS Publications Warehouse

Dunning, C.P.; Feinstein, D.T.; Hunt, R.J.; Krohelski, J.T.

2004-01-01

Numerical models were constructed for simulation of ground-water flow in the Menomonee Valley Brownfield, in Milwaukee, Wisconsin. An understanding of ground-water flow is necessary to develop an efficient program to sample ground water for contaminants. Models were constructed in a stepwise fashion, beginning with a regional, single-layer, analytic-element model (GFLOW code) that provided boundary conditions for a local, eight layer, finite-difference model (MODFLOW code) centered on the Menomonee Valley Brownfield. The primary source of ground water to the models is recharge over the model domains; primary sinks for ground water within the models are surface-water features and the Milwaukee Metropolitan Sewerage District Inline Storage System (ISS). Calibration targets were hydraulic heads, surface-water fluxes, vertical gradients, and ground-water infiltration to the ISS. Simulation of ground-water flow by use of the MODFLOW model indicates that about 73 percent of recharge within the MODFLOW domain circulates to the ISS and 27 percent discharges to gaining surface-water bodies. In addition, infiltration to the ISS comes from the following sources: 36 percent from recharge within the model domain, 45 percent from lateral flow into the domain, 15 percent from Lake Michigan, and 4 percent from other surface-water bodies. Particle tracking reveals that the median traveltime from the recharge point to surface-water features is 8 years; the median time to the ISS is 255 years. The traveltimes to the ISS are least over the northern part of the valley, where dolomite is near the land surface. The distribution of traveltimes in the MODFLOW simulation is greatly influenced by the effective porosity values assigned to the various lithologies.

A modular finite-element model (MODFE) for areal and axisymmetric ground-water-flow problems, Part 1: Model Description and User's Manual

USGS Publications Warehouse

Torak, L.J.

1993-01-01

A MODular, Finite-Element digital-computer program (MODFE) was developed to simulate steady or unsteady-state, two-dimensional or axisymmetric ground-water flow. Geometric- and hydrologic-aquifer characteristics in two spatial dimensions are represented by triangular finite elements and linear basis functions; one-dimensional finite elements and linear basis functions represent time. Finite-element matrix equations are solved by the direct symmetric-Doolittle method or the iterative modified, incomplete-Cholesky, conjugate-gradient method. Physical processes that can be represented by the model include (1) confined flow, unconfined flow (using the Dupuit approximation), or a combination of both; (2) leakage through either rigid or elastic confining beds; (3) specified recharge or discharge at points, along lines, and over areas; (4) flow across specified-flow, specified-head, or bead-dependent boundaries; (5) decrease of aquifer thickness to zero under extreme water-table decline and increase of aquifer thickness from zero as the water table rises; and (6) head-dependent fluxes from springs, drainage wells, leakage across riverbeds or confining beds combined with aquifer dewatering, and evapotranspiration. The report describes procedures for applying MODFE to ground-water-flow problems, simulation capabilities, and data preparation. Guidelines for designing the finite-element mesh and for node numbering and determining band widths are given. Tables are given that reference simulation capabilities to specific versions of MODFE. Examples of data input and model output for different versions of MODFE are provided.

A modular finite-element model (MODFE) for areal and axisymmetric ground-water-flow problems; Part 1, Model description and user's manual

USGS Publications Warehouse

Torak, Lynn J.

1992-01-01

A MODular, Finite-Element digital-computer program (MODFE) was developed to simulate steady or unsteady-state, two-dimensional or axisymmetric ground-water flow. Geometric- and hydrologic-aquifer characteristics in two spatial dimensions are represented by triangular finite elements and linear basis functions; one-dimensional finite elements and linear basis functions represent time. Finite-element matrix equations are solved by the direct symmetric-Doolittle method or the iterative modified, incomplete-Cholesky, conjugate-gradient method. Physical processes that can be represented by the model include (1) confined flow, unconfined flow (using the Dupuit approximation), or a combination of both; (2) leakage through either rigid or elastic confining beds; (3) specified recharge or discharge at points, along lines, and over areas; (4) flow across specified-flow, specified-head, or head-dependent boundaries; (5) decrease of aquifer thickness to zero under extreme water-table decline and increase of aquifer thickness from zero as the water table rises; and (6) head-dependent fluxes from springs, drainage wells, leakage across riverbeds or confining beds combined with aquifer dewatering, and evapotranspiration.The report describes procedures for applying MODFE to ground-water-flow problems, simulation capabilities, and data preparation. Guidelines for designing the finite-element mesh and for node numbering and determining band widths are given. Tables are given that reference simulation capabilities to specific versions of MODFE. Examples of data input and model output for different versions of MODFE are provided.

Hydrogeological modelling as a tool for understanding rockslides evolution

NASA Astrophysics Data System (ADS)

Crosta, Giovanni B.; De Caro, Mattia; Frattini, Paolo; Volpi, Giorgio

2015-04-01

Several case studies of large rockslides have been presented in the literature showing dependence of displacement rate on seasonal and annual changes of external factors (e.g. rainfall, snowmelt, temperature oscillations) or on human actions (e.g. impounding of landslide toe by artificial lakes, toe excavation). The study of rockslide triggering can focus on either the initial failure or the successive reactivations driven by either meteo-climatic events or other perturbations (e.g. seismic, anthropic). A correlation between groundwater level oscillations and slope movements has been observed at many different sites and in very different materials and slope settings. This seasonal dynamic behavior generally shows a delay between perturbation (e.g., groundwater recharge and increase in water table level) and system reaction (e.g., increase in displacement rate). For this reason, groundwater modeling offers the means for assessing the oscillation of groundwater level which is a major input in rockslide and deep-seated gravitational slope deformation modelling, and that could explain both the initial failure event as well the successive reactivation or the continuous slow motion. Using a finite element software (FEFLOW, WASY GmbH) we developed 2D saturated/unsaturated and steady-state/transient groundwater flow models for two case studies for which a suitable dataset is available: the Vajont rockslide (from 1960 to October 9th 1963) and the Mt. de La Saxe rockslide (2009-2012, Aosta valley; Italian Western Alps). The transient models were implemented starting from hydraulic head distributions simulated in the previous steady-state models to investigate the groundwater fluctuation within the two chosen times interval (Vajont: 1960-1963 ; La Saxe: 2009-2012). Time series of infiltration resulting from precipitation, temperature, snowmelt data (La Saxe rockslide) and reservoir level (Vajont rockslide) were applied to the models. The assumptions made during the construction of the models, in particular the partition of the slope in different sectors with different hydraulic conductivities, are coherent with the geological, structural, hydrological and hydrogeological field and laboratory data. The sensitivity analysis shows that the hydraulic conductivity of some slope sectors (e.g. morphostructures, compressed or relaxed slope-toe, basal shear band) strongly influence the water table position and evolution. In transient models, the values of specific storage coefficient play a major control on the amplitude of groundwater level fluctuations, deriving from snowmelt or induced reservoir level rise. The calibrated groundwater flow-models are consistent with groundwater levels measured in the proximity of the piezometers aligned along the sections. The two examples can be considered important for a more advanced understanding of the evolution of rockslides and suggest the required set of data and modelling approaches both for seasonal and long term slope stability analyses. The use of the results of such analyses is reported, for both the case studies, in a companion abstract in session 3.7 where elasto-visco-plastic rheologies have been adopted for the shear band materials to replicate the available displacement time-series.

Overpumping leads to California groundwater arsenic threat.

PubMed

Smith, Ryan; Knight, Rosemary; Fendorf, Scott

2018-06-05

Water resources are being challenged to meet domestic, agricultural, and industrial needs. To complement finite surface water supplies that are being stressed by changes in precipitation and increased demand, groundwater is increasingly being used. Sustaining groundwater use requires considering both water quantity and quality. A unique challenge for groundwater use, as compared with surface water, is the presence of naturally occurring contaminants within aquifer sediments, which can enter the water supply. Here we find that recent groundwater pumping, observed through land subsidence, results in an increase in aquifer arsenic concentrations in the San Joaquin Valley of California. By comparison, historic groundwater pumping shows no link to current groundwater arsenic concentrations. Our results support the premise that arsenic can reside within pore water of clay strata within aquifers and is released due to overpumping. We provide a quantitative model for using subsidence as an indicator of arsenic concentrations correlated with groundwater pumping.

Aspects of choosing appropriate concepts for modelling groundwater resources in regional integrated water resources management Examples from the Neckar (Germany) and Ouémé catchment (Benin)

NASA Astrophysics Data System (ADS)

Barthel, R.; Jagelke, J.; Götzinger, J.; Gaiser, T.; Printz, Andreas

Two regional groundwater flow models (Neckar catchment, Germany, 14,000 km 2, and Southern Ouémé Basin, Benin, 11,000 km 2) were developed within the framework of the integrated management project ‘RIVERTWIN’ ( www.rivertwin.org). Both models were evaluated with respect to the question if the chosen modelling approaches (multi-layered finite difference numerical flow modelling, steady state and transient) are appropriate in view of the existing management problems in the catchments, the data availability and the hydrogeological and hydrological conditions in the basins. It is shown that neither the model in the well-investigated, data-rich basin in Western Europe with its highly developed water related infrastructure, nor the model in the hydrogeologically less well-known and less developed basin in Western Africa provide results that are fully applicable to the main regional management tasks. In the case of the Ouémé, the groundwater related problems are foremost of local character and therefore cannot be addressed by regional models in a meaningful way. Data scarcity and complex, unfavourable geological conditions (crystalline rocks, discontinuous aquifers) support the conclusion that numerical 3D groundwater flow models are currently not helpful to manage groundwater related management problems in the Ouémé basin. A better understanding of regional hydrological surface and subsurface processes is required first. Methods for a reliable estimation of groundwater recharge and subsequently groundwater availability were identified as the most urgently needed tool for meaningful groundwater management in view of climatic, demographic and land use change. In the Neckar catchment the results of the analysis are less pronounced; here regional groundwater problems could clearly benefit from a physically based 3D model since the hydrogeological system is strictly stratified with several important aquifers in the vertical sequence. As a general conclusion it can be stated that regional scale groundwater flow modelling concepts seem to be difficult to integrate in management systems and difficult to transfer from one basin to another. This means the question of how to represent the groundwater resources appropriately has to be discussed very thoroughly for any new integrated water resources management problem. It is not possible to give a final recommendation on which modelling concept is the most appropriate one in regional integrated modelling and management. Hence, this article is only intended to provide an in depth discussion of the aspects that need to be considered in the process of choosing appropriate modelling concepts.

Modeling chloride movement in the alluvial aquifer at the Rocky Mountain Arsenal, Colorado

USGS Publications Warehouse

Konikow, Leonard F.

1977-01-01

A solute-transport model that can be used to predict the movement of dissolved chemicals in flowing ground water was applied to a problem of ground-water contamination at the Rocky Mountain Arsenal, near Denver, Colo. The model couples a finite-difference solution to the ground-water flow equation with the method-of-characteristics solution to the solute-transport equation. From 1943 to 1956 liquid industrial wastes containing high chloride concentrations were disposed into unlined ponds at the Arsenal. Wastes seeped out of the unlined disposal ponds and spread for many square miles in the underlying shallow alluvial aquifer. Since 1956 disposal has been into an asphalt-lined reservoir, which contributed to a decline in ground-water contamination by 1972. The simulation model quantitatively integrated the effects of the major factors that controlled changes in chloride concentrations and accurately reproduced the 30-year history of chloride ground-water contamination. Analysis of the simulation results indicates that the geologic framework of the area markedly restricted the transport and dispersion of dissolved chemicals in the alluvium. Dilution, from irrigation recharge and seepage from unlined canals, was an important factor in reducing the level of chloride concentrations downgradient from the Arsenal. Similarly, recharge of uncontaminated water from the unlined ponds since 1956 has helped to dilute and flush the contaminated ground water.

Ground-water hydrology and simulated effects of development in the Milford area, an arid basin in southwestern Utah

USGS Publications Warehouse

Mason, James L.

1998-01-01

A three-dimensional, finite-difference model was constructed to simulate ground-water flow in the Milford area. The purpose of the study was to evaluate present knowledge and concepts of the groundwater system, to analyze the ability of the model to represent past and current (1984) conditions, and to estimate the effects of various groundwater development alternatives. The alternative patterns of groundwater development might prove effective in capturing natural discharge from the basin-fill aquifer while limiting water-level declines. Water levels measured during this study indicate that ground water in the Milford area flows in a northwesterly direction through consolidated rocks in the northern San Francisco Mountains toward Sevier Lake. The revised potentiometric surface shows a large area for probable basin outflow, indicating that more water leaves the Milford area than the 8 acre-feet per year estimated previously.Simulations made to calibrate the model were able to approximate steady-state conditions for 1927, before ground-water development began, and transient conditions for 1950-82, during which groundwater withdrawal increased. Basin recharge from the consolidated rocks and basin outflow were calculated during the calibration process. Transient simulations using constant and variable recharge from surface water were made to test effects of large flows in the Beaver River.Simulations were made to project water-level declines over a 37- year period (1983-2020) using the present pumping distribution. Ground-water withdrawals were simulated at 1, 1.5, and 2 times the 1979-82 average rate.The concepts of "sustained" yield, ground-water mining, and the capture of natural discharge were tested using several hypothetical pumping distributions over a 600-year simulation period. Simulations using concentrated pumping centers were the least efficient at capturing natural discharge and produced the largest water-level declines. Simulations using strategically placed ground-water withdrawals in the discharge area were the most efficient at eliminating natural discharge with small water-level declines.

Effect of numerical dispersion as a source of structural noise in the calibration of a highly parameterized saltwater intrusion model

USGS Publications Warehouse

Langevin, Christian D.; Hughes, Joseph D.

2010-01-01

A model with a small amount of numerical dispersion was used to represent saltwater 7 intrusion in a homogeneous aquifer for a 10-year historical calibration period with one 8 groundwater withdrawal location followed by a 10-year prediction period with two groundwater 9 withdrawal locations. Time-varying groundwater concentrations at arbitrary locations in this low-10 dispersion model were then used as observations to calibrate a model with a greater amount of 11 numerical dispersion. The low-dispersion model was solved using a Total Variation Diminishing 12 numerical scheme; an implicit finite difference scheme with upstream weighting was used for 13 the calibration simulations. Calibration focused on estimating a three-dimensional hydraulic 14 conductivity field that was parameterized using a regular grid of pilot points in each layer and a 15 smoothness constraint. Other model parameters (dispersivity, porosity, recharge, etc.) were 16 fixed at the known values. The discrepancy between observed and simulated concentrations 17 (due solely to numerical dispersion) was reduced by adjusting hydraulic conductivity through the 18 calibration process. Within the transition zone, hydraulic conductivity tended to be lower than 19 the true value for the calibration runs tested. The calibration process introduced lower hydraulic 20 conductivity values to compensate for numerical dispersion and improve the match between 21 observed and simulated concentration breakthrough curves at monitoring locations. 22 Concentrations were underpredicted at both groundwater withdrawal locations during the 10-23 year prediction period.

A new package in MODFLOW to simulate unconfined groundwater flow in sloping aquifers.

PubMed

Wang, Quanrong; Zhan, Hongbin; Tang, Zhonghua

2014-01-01

The nonhorizontal-model-layer (NHML) grid system is more accurate than the horizontal-model-layer grid system to describe groundwater flow in an unconfined sloping aquifer on the basis of MODFLOW-2000. However, the finite-difference scheme of NHML was based on the Dupuit-Forchheimer assumption that the streamlines were horizontal, which was acceptable for slope less than 0.10. In this study, we presented a new finite-difference scheme of NHML based on the Boussinesq assumption and developed a new package SLOPE which was incorporated into MODFLOW-2000 to become the MODFLOW-SP model. The accuracy of MODFLOW-SP was tested against solution of Mac Cormack (1969). The differences between the solutions of MODFLOW-2000 and MODFLOW-SP were nearly negligible when the slope was less than 0.27, and they were noticeable during the transient flow stage and vanished in steady state when the slope increased above 0.27. We established a model considering the vertical flow using COMSOL Multiphysics to test the robustness of constrains used in MODFLOW-SP. The results showed that streamlines quickly became parallel with the aquifer base except in the narrow regions near the boundaries when the initial flow was not parallel to the aquifer base. MODFLOW-SP can be used to predict the hydraulic head of an unconfined aquifer along the profile perpendicular to the aquifer base when the slope was smaller than 0.50. The errors associated with constrains used in MODFLOW-SP were small but noticeable when the slope increased to 0.75, and became significant for the slope of 1.0. © 2013, National Ground Water Association.

ADHydro: A Large-scale High Resolution Multi-Physics Distributed Water Resources Model for Water Resource Simulations in a Parallel Computing Environment

NASA Astrophysics Data System (ADS)

lai, W.; Steinke, R. C.; Ogden, F. L.

2013-12-01

Physics-based watershed models are useful tools for hydrologic studies, water resources management and economic analyses in the contexts of climate, land-use, and water-use changes. This poster presents development of a physics-based, high-resolution, distributed water resources model suitable for simulating large watersheds in a massively parallel computing environment. Developing this model is one of the objectives of the NSF EPSCoR RII Track II CI-WATER project, which is joint between Wyoming and Utah. The model, which we call ADHydro, is aimed at simulating important processes in the Rocky Mountain west, includes: rainfall and infiltration, snowfall and snowmelt in complex terrain, vegetation and evapotranspiration, soil heat flux and freezing, overland flow, channel flow, groundwater flow and water management. The ADHydro model uses the explicit finite volume method to solve PDEs for 2D overland flow, 2D saturated groundwater flow coupled to 1D channel flow. The model has a quasi-3D formulation that couples 2D overland flow and 2D saturated groundwater flow using the 1D Talbot-Ogden finite water-content infiltration and redistribution model. This eliminates difficulties in solving the highly nonlinear 3D Richards equation, while the finite volume Talbot-Ogden infiltration solution is computationally efficient, guaranteed to conserve mass, and allows simulation of the effect of near-surface groundwater tables on runoff generation. The process-level components of the model are being individually tested and validated. The model as a whole will be tested on the Green River basin in Wyoming and ultimately applied to the entire Upper Colorado River basin. ADHydro development has necessitated development of tools for large-scale watershed modeling, including open-source workflow steps to extract hydromorphological information from GIS data, integrate hydrometeorological and water management forcing input, and post-processing and visualization of large output data sets. The ADHydro model will be coupled with relevant components of the NOAH-MP land surface scheme and the WRF mesoscale meteorological model. Model objectives include well documented Application Programming Interfaces (APIs) to facilitate modifications and additions by others. We will release the model as open-source in 2014 and begin establishing a users' community.

Analysis of Changes in Ground-Water Levels in a Sewered and an Unsewered Area of Nassau County, Long Island, New York.

PubMed

Sulam, Dennis J

1979-09-01

From the 195O's to the early 1970's expansion of sanitary sewerage in southwest Nassau County contributed to progressive declines in ground-water levels. Since the early 197O's, however, 10 years after the area was fully sewered, water levels have not declined significantly, which suggests that the water table may have reached a new equilibrium position. Double-mass-curve analyses show that during 1953-76 the average weighted ground-water levels in a 32-square-mile (83-square-kilometer) part of the sewered area declined 12.2 feet (3.73 meters) more than those in the unsewered area to the east. However, by 1973 this decline was 13.5 feet (4.1 meters). Finite-difference digital-model results indicate that 3.6 feet (1.1 meters) of the relative 1953-76 decline was due to pumping in adjacent Queens County and that most of the remaining decline was a result of sewerage. Streamflow within the sewered area decreased in response to the lowered ground-water levels, and ground-water levels in the adjacent unsewered area were also lowered because of the sewerage.

Numerical simulation of freshwater/seawater interaction in a dual-permeability karst system with conduits: the development of discrete-continuum VDFST-CFP model

NASA Astrophysics Data System (ADS)

Xu, Zexuan; Hu, Bill

2016-04-01

Dual-permeability karst aquifers of porous media and conduit networks with significant different hydrological characteristics are widely distributed in the world. Discrete-continuum numerical models, such as MODFLOW-CFP and CFPv2, have been verified as appropriate approaches to simulate groundwater flow and solute transport in numerical modeling of karst hydrogeology. On the other hand, seawater intrusion associated with fresh groundwater resources contamination has been observed and investigated in numbers of coastal aquifers, especially under conditions of sea level rise. Density-dependent numerical models including SEAWAT are able to quantitatively evaluate the seawater/freshwater interaction processes. A numerical model of variable-density flow and solute transport - conduit flow process (VDFST-CFP) is developed to provide a better description of seawater intrusion and submarine groundwater discharge in a coastal karst aquifer with conduits. The coupling discrete-continuum VDFST-CFP model applies Darcy-Weisbach equation to simulate non-laminar groundwater flow in the conduit system in which is conceptualized and discretized as pipes, while Darcy equation is still used in continuum porous media. Density-dependent groundwater flow and solute transport equations with appropriate density terms in both conduit and porous media systems are derived and numerically solved using standard finite difference method with an implicit iteration procedure. Synthetic horizontal and vertical benchmarks are created to validate the newly developed VDFST-CFP model by comparing with other numerical models such as variable density SEAWAT, couplings of constant density groundwater flow and solute transport MODFLOW/MT3DMS and discrete-continuum CFPv2/UMT3D models. VDFST-CFP model improves the simulation of density dependent seawater/freshwater mixing processes and exchanges between conduit and matrix. Continuum numerical models greatly overestimated the flow rate under turbulent flow condition but discrete-continuum models provide more accurate results. Parameters sensitivities analysis indicates that conduit diameter and friction factor, matrix hydraulic conductivity and porosity are important parameters that significantly affect variable-density flow and solute transport simulation. The pros and cons of model assumptions, conceptual simplifications and numerical techniques in VDFST-CFP are discussed. In general, the development of VDFST-CFP model is an innovation in numerical modeling methodology and could be applied to quantitatively evaluate the seawater/freshwater interaction in coastal karst aquifers. Keywords: Discrete-continuum numerical model; Variable density flow and transport; Coastal karst aquifer; Non-laminar flow

MODFLOW-NWT – Robust handling of dry cells using a Newton Formulation of MODFLOW-2005

USGS Publications Warehouse

Hunt, Randal J.; Feinstein, Daniel T.

2012-01-01

The first versions of the widely used groundwater flow model MODFLOW (McDonald and Harbaugh 1988) had a sure but inflexible way of handling unconfined finite-difference aquifer cells where the water table dropped below the bottom of the cell—these "dry cells" were turned inactive for the remainder of the simulation. Problems with this formulation were easily seen, including the potential for inadvertent loss of simulated recharge in the model (Doherty 2001; Painter et al. 2008), and rippling of dry cells through the solution that unacceptably changed the groundwater flow system (Juckem et al. 2006). Moreover, solving problems of the natural world often required the ability to reactivate dry cells when the water table rose above the cell bottom. This seemingly simple desire resulted in a two-decade attempt to include the simulation flexibility while avoiding numerical instability.

Modelling the effect of buried valleys on groundwater flow: case study in Ventspils vicinity, Latvia

NASA Astrophysics Data System (ADS)

Delina, Aija; Popovs, Konrads; Bikse, Janis; Retike, Inga; Babre, Alise; Kalvane, Gunta

2015-04-01

Buried subglacial valleys are widely distributed in glaciated regions and they can have great influence on groundwater flow and hence on groundwater resources. The aim of this study is to evaluate the effect of the buried valleys on groundwater flow in a confined aquifer (Middle Devonian Eifelian stage Arukila aquifer, D2ar) applying numerical modelling. The study area is located at vicinity of Ventspils Town, near wellfield Ogsils where number of the buried valleys with different depth and filling material are present. Area is located close to the Baltic Sea at Piejūra lowland Rinda plain and regional groundwater flow is towards sea. Territory is covered by thin layer of Quaternary sediments in thicknesses of 10 to 20 meters although Prequaternary sediments are exposed at some places. Buried valleys are characterized as narrow, elongated and deep formations that is be filled with various, mainly Pleistocene glacigene sediments - either till loam of different ages or sand and gravel or interbedding of both above mentioned. The filling material of the valleys influences groundwater flow in the confined aquifers which is intercepted by the valleys. It is supposed that glacial till loam filled valleys serves as a barrier to groundwater flow and as a recharge conduit when filled with sand and gravel deposits. Numerical model was built within MOSYS modelling system (Virbulis et al. 2012) using finite element method in order to investigate buried valley influence on groundwater flow in the study area. Several conceptual models were tested in numerical model depending on buried valley filling material: sand and gravel, till loam or mixture of them. Groundwater flow paths and travel times were studied. Results suggested that valley filled with glacial till is acting as barrier and it causes sharp drop of piezometric head and downward flow. Valley filled with sand and gravel have almost no effect on piezometric head distribution, however it this case buried valleys encourage groundwater recharge from shallower aquifers. Modelling results with and without valleys shows that buried valleys affect piezometric head in narrow zone around valley. Sand and gravel filled buried valleys recharges confined aquifer with relatively "new" water, thus creating high vulnerability zones in the study area. This research is supported by European Regional Development Fund project Nr.2013/0054/2DP/2.1.1.1.0/13/APIA/VIAA/007 and NRP project EVIDENnT project "Groundwater and climate scenarios" subproject "Groundwater Research". References: Virbulis, J., Timuhins, A., Klints, I., Seņņikovs, J., Bethers, U., Popovs, K. 2012. Script based MOSYS system for the generation of a three dimensional geological structure and the calculation of groundwater flow: case study of the Baltic Artesian Basin. In: Highlights of groundwater research in the Baltic Artesian Basin. University of Latvia, Riga, pp. 53-74.

Methods to quantify seepage beneath Levee 30, Miami-Dade County, Florida

USGS Publications Warehouse

Sonenshein, R.S.

2001-01-01

A two-dimensional, cross-sectional, finite-difference, ground-water flow model and a simple application of Darcy?s law were used to quantify ground-water flow (from a wetlands) beneath Levee 30 in Miami-Dade County, Florida. Geologic and geophysical data, vertical seepage data from the wetlands, canal discharge data, ground-water-level data, and surface-water-stage data collected during 1995 and 1996 were used as boundary conditions and calibration data for the ground-water flow model and as input for the analytical model. Vertical seepage data indicated that water from the wetlands infiltrated the subsurface, near Levee 30, at rates ranging from 0.033 to 0.266 foot per day when the gates at the control structures along Levee 30 canal were closed. During the same period, stage differences between the wetlands (Water Conservation Area 3B) and Levee 30 canal ranged from 0.11 to 1.27 feet. A layer of low-permeability limestone, located 7 to 10 feet below land surface, restricts vertical flow between the surface water in the wetlands and the ground water. Based on measured water-level data, ground-water flow appears to be generally horizontal, except in the direct vicinity of the canal. The increase in discharge rate along a 2-mile reach of the Levee 30 canal ranged from 9 to 30 cubic feet per second per mile and can be attributed primarily to ground-water inflow. Flow rates in Levee 30 canal were greatest when the gates at the control structures were open. The ground-water flow model data were compared with the measured ground-water heads and vertical seepage from the wetlands. Estimating the horizontal ground-water flow rate beneath Levee 30 was difficult owing to the uncertainty in the horizontal hydraulic conductivity of the main flow zone of the Biscayne aquifer. Measurements of ground-water flows into Levee 30 canal, a substantial component of the water budget, were also uncertain, which lessened the ability to validate the model results. Because of vertical flows near Levee 30 canal and a very low hydraulic gradient east of the canal, a simplified Darcian approach simulated with the ground-water flow model does not accurately estimate the horizontal ground-water flow rate. Horizontal ground-water flow rates simulated with the ground-water flow model (for a 60-foot-deep by 1-foot-wide section of the Biscayne aquifer) ranged from 150 to 450 cubic feet per day west of Levee 30 and from 15 to 170 cubic feet per day east of Levee 30 canal. Vertical seepage from the wetlands, within 500 feet of Levee 30, generally accounted for 10 to 15 percent of the total horizontal flow beneath the levee. Simulated horizontal ground-water flow was highest during the wet season and when the gates at the control structures were open.

Technique for predicting ground-water discharge to surface coal mines and resulting changes in head

USGS Publications Warehouse

Weiss, L.S.; Galloway, D.L.; Ishii, Audrey L.

1986-01-01

Changes in seepage flux and head (groundwater level) from groundwater drainage into a surface coal mine can be predicted by a technique that considers drainage from the unsaturated zone. The user applies site-specific data to precalculated head and seepage-flux profiles. Groundwater flow through hypothetical aquifer cross sections was simulated using the U.S. Geological Survey finite-difference model, VS2D, which considers variably saturated two-dimensional flow. Conceptual models considered were (1) drainage to a first cut, and (2) drainage to multiple cuts, which includes drainage effects of an area surface mine. Dimensionless head and seepage flux profiles from 246 simulations are presented. Step-by-step instructions and examples are presented. Users are required to know aquifer characteristics and to estimate size and timing of the mine operation at a proposed site. Calculated groundwater drainage to the mine is from one excavated face only. First cut considers confined and unconfined aquifers of a wide range of permeabilities; multiple cuts considers unconfined aquifers of higher permeabilities only. The technique, developed for Illinois coal-mining regions that use area surface mining and evaluated with an actual field example, will be useful in assessing potential hydrologic impacts of mining. Application is limited to hydrogeologic settings and mine operations similar to those considered. Fracture flow, recharge, and leakage are nor considered. (USGS)

Numerical study on the responses of groundwater and strata to pumping and recharge in a deep confined aquifer

NASA Astrophysics Data System (ADS)

Zhang, Yang-Qing; Wang, Jian-Hua; Chen, Jin-Jian; Li, Ming-Guang

2017-05-01

Groundwater drawdown and strata settlements induced by dewatering in confined aquifers can be relieved by artificial recharge. In this study, numerical simulations of a field multi-well pumping-recharge test in a deep confined aquifer are conducted to analyze the responses of groundwater and strata to pumping and recharge. A three-dimensional numerical model is developed in a finite-difference software, which considers the fluid-mechanical interaction using the Biot consolidation theory. The predicted groundwater drawdown and ground settlements are compared to the measured data to confirm the validation of the numerical analysis of the pumping and recharge. Both numerical results and measured data indicate that the effect of recharge on controlling the groundwater drawdown and strata settlements correlates with the injection rate and well arrangements. Since the groundwater drawdown induced by pumping can be controlled by artificial recharge, soil compression can be relieved by reducing the changes of effective stress of the soils. Consequently, strata settlement induced by pumping can be relieved by artificial recharge and ground settlements can be eliminated if an appropriate injection rate and well arrangement are being determined. Moreover, the changes of the pore pressure and seepage force induced by pumping and recharge will also result in significant horizontal deformations in the strata near the recharge wells.

A Graphical-User Interface for the U. S. Geological Survey's SUTRA Code using Argus ONE (for simulation of variable-density saturated-unsaturated ground-water flow with solute or energy transport)

USGS Publications Warehouse

Voss, Clifford I.; Boldt, David; Shapiro, Allen M.

1997-01-01

This report describes a Graphical-User Interface (GUI) for SUTRA, the U.S. Geological Survey (USGS) model for saturated-unsaturated variable-fluid-density ground-water flow with solute or energy transport,which combines a USGS-developed code that interfaces SUTRA with Argus ONE, a commercial software product developed by Argus Interware. This product, known as Argus Open Numerical Environments (Argus ONETM), is a programmable system with geographic-information-system-like (GIS-like) functionality that includes automated gridding and meshing capabilities for linking geospatial information with finite-difference and finite-element numerical model discretizations. The GUI for SUTRA is based on a public-domain Plug-In Extension (PIE) to Argus ONE that automates the use of ArgusONE to: automatically create the appropriate geospatial information coverages (information layers) for SUTRA, provide menus and dialogs for inputting geospatial information and simulation control parameters for SUTRA, and allow visualization of SUTRA simulation results. Following simulation control data and geospatial data input bythe user through the GUI, ArgusONE creates text files in a format required for normal input to SUTRA,and SUTRA can be executed within the Argus ONE environment. Then, hydraulic head, pressure, solute concentration, temperature, saturation and velocity results from the SUTRA simulation may be visualized. Although the GUI for SUTRA discussed in this report provides all of the graphical pre- and post-processor functions required for running SUTRA, it is also possible for advanced users to apply programmable features within Argus ONE to modify the GUI to meet the unique demands of particular ground-water modeling projects.

Simulated water-level and water-quality changes in the bolson-fill aquifer, Post Headquarters area, White Sands Missile Range, New Mexico

USGS Publications Warehouse

Risser, D.W.

1988-01-01

The quantity of freshwater available in the Post Headquarters well field, White Sand Missile Range, New Mexico, is limited and its quality is threatened by saltwater enroachment. A three-dimensional, finite-difference, groundwater flow model and a cross-sectional, density-dependent solute-transport model were constructed to simulate possible future water level declines and water quality changes in the Post Headquarters well field. A six-layer flow model was constructed using hydraulic-conductivity values in the upper 600 ft of saturated aquifer ranging from 0.1 to 10 ft/day, specific yield of 0.15, and average recharge of about 1,590 acre-ft/yr. Water levels simulated by the model closely matched measured water levels for 1948-82. Possible future water level changes for 1983-2017 were simulated using rates of groundwater withdrawal of 1,033 and 2 ,066 acre-ft/year and wastewater return flow of 0 or 30% of the groundwater withdrawal rate. The cross-sectional solute-transport model indicated that the freshwater zone is about 1,500 to 2,000 ft thick beneath the well field. Transient simulations show that solutes probably will move laterally toward the well field rather than from beneath the well field. (USGS)

Water resources of Borrego Valley and vicinity, San Diego County, California; Phase 2, Development of a ground-water flow model

USGS Publications Warehouse

Mitten, H.T.; Lines, G.C.; Berenbrock, Charles; Durbin, T.J.

1988-01-01

Because of the imbalance between recharge and pumpage, groundwater levels declined as much as 100 ft in some areas of Borrego Valley, California during drinking 1945-80. As an aid to analyzing the effects of pumping on the groundwater system, a three-dimensional finite-element groundwater flow model was developed. The model was calibrated for both steady-state (1945) and transient-state (1946-79) conditions. For the steady-state calibration, hydraulic conductivities of the three aquifers were varied within reasonable limits to obtain an acceptable match between measured and computed hydraulic heads. Recharge from streamflow infiltration (4,800 acre-ft/yr) was balanced by computed evapotranspiration (3,900 acre-ft/yr) and computed subsurface outflow from the model area (930 acre-ft/yr). For the transient state calibration, the volumes and distribution of net groundwater pumpage were estimated from land-use data and estimates of consumptive use for irrigated crops. The pumpage was assigned to the appropriate nodes in the model for each of seventeen 2-year time steps representing the period 1946-79. The specific yields of the three aquifers were varied within reasonable limits to obtain an acceptable match between measured and computed hydraulic heads. Groundwater pumpage input to the model was compensated by declines in both the computed evapotranspiration and the amount of groundwater in storage. (USGS)

Utilizing Temperature and Resistivity Data as a Way to Characterize Water and Solute Movement and Groundwater-Surface Water Interaction in Variably Saturated Porous Media

NASA Astrophysics Data System (ADS)

Scotch, C.; Murgulet, D.; Hay, R.

2012-12-01

This study utilizes a multidisciplinary approach to better analyze the extent to which groundwater and surface water interact in the Oso Creek water shed of South Texas using temperature data, electrical resistivity and numerical modeling methods. The three primary objectives of this study are to: (1) identify primary areas of streambed groundwater-surface water interaction using temperature time series and resistivity soundings; (2) improve understanding of solute flow and groundwater, surface water, and sediment interaction in a semiarid, urban coastal area; (3) improve our understanding of groundwater contribution to contaminant transport and discharge to the bays and estuaries and ultimately the Gulf of Mexico. Temperature data was acquired over a one year period, using temperature loggers, from June 11, 2009 to May 18, 2010 at 15-minute intervals from 17 monitoring sites along Oso Creek and its tributaries. Each monitoring site consisted of 4 temperature loggers equally vertically spaced from the stream surface down to a depth of one meter. Furthermore, groundwater temperatures and water levels were collected from wells adjacent to the temperature monitoring sites. In order to fulfill the objectives of this study, existing hydrogeologic, stratigraphic, and other ancillary data are being integrated into a finite difference model developed using the USGS VS2DT software for the Oso Creek Watershed. The model will be calibrated using existing temperature and water level data and a resistivity component will also be added to assure accuracy of the model and temperature data by helping to identify varying lithologies and water conductivities. Compiling a time-series of temperature data and incorporating available hydrostratigraphic, geomorphologic and water level data will enable the development of a comprehensive database. This database is necessary to develop the detailed flow model that will enable an understanding of the extent of groundwater surface water interaction and their associated flow regimes.

Description and application of capture zone delineation for a wellfield at Hilton Head Island, South Carolina

USGS Publications Warehouse

Landmeyer, J.E.

1994-01-01

Ground-water capture zone boundaries for individual pumped wells in a confined aquffer were delineated by using groundwater models. Both analytical and numerical (semi-analytical) models that more accurately represent the $round-water-flow system were used. All models delineated 2-dimensional boundaries (capture zones) that represent the areal extent of groundwater contribution to a pumped well. The resultant capture zones were evaluated on the basis of the ability of each model to realistically rapresent the part of the ground-water-flow system that contributed water to the pumped wells. Analytical models used were based on a fixed radius approach, and induded; an arbitrary radius model, a calculated fixed radius model based on the volumetric-flow equation with a time-of-travel criterion, and a calculated fixed radius model derived from modification of the Theis model with a drawdown criterion. Numerical models used induded the 2-dimensional, finite-difference models RESSQC and MWCAP. The arbitrary radius and Theis analytical models delineated capture zone boundaries that compared least favorably with capture zones delineated using the volumetric-flow analytical model and both numerical models. The numerical models produced more hydrologically reasonable capture zones (that were oriented parallel to the regional flow direction) than the volumetric-flow equation. The RESSQC numerical model computed more hydrologically realistic capture zones than the MWCAP numerical model by accounting for changes in the shape of capture zones caused by multiple-well interference. The capture zone boundaries generated by using both analytical and numerical models indicated that the curnmtly used 100-foot radius of protection around a wellhead in South Carolina is an underestimate of the extent of ground-water capture for pumped wetis in this particular wellfield in the Upper Floridan aquifer. The arbitrary fixed radius of 100 feet was shown to underestimate the upgradient contribution of ground-water flow to a pumped well.

SUTRA (Saturated-Unsaturated Transport). A Finite-Element Simulation Model for Saturated-Unsaturated, Fluid-Density-Dependent Ground-Water Flow with Energy Transport or Chemically-Reactive Single-Species Solute Transport.

DTIC Science & Technology

1984-12-30

as three dimensional, when the assumption is made that all SUTRA parameters and coefficients have a constant value in the third space direction. A...finite element. The type of element employed by SUTRA for two-dimensional simulation is a quadrilateral which has a finite thickness in the third ... space dimension. This type of a quad- rilateral element and a typical two-dimensional mesh is shown in Figure 3.1. - All twelve edges of the two

Constant-concentration boundary condition: Lessons from the HYDROCOIN variable-density groundwater benchmark problem

USGS Publications Warehouse

Konikow, Leonard F.; Sanford, W.E.; Campbell, P.J.

1997-01-01

In a solute-transport model, if a constant-concentration boundary condition is applied at a node in an active flow field, a solute flux can occur by both advective and dispersive processes. The potential for advective release is demonstrated by reexamining the Hydrologic Code Intercomparison (HYDROCOIN) project case 5 problem, which represents a salt dome overlain by a shallow groundwater system. The resulting flow field includes significant salinity and fluid density variations. Several independent teams simulated this problem using finite difference or finite element numerical models. We applied a method-of-characteristics model (MOCDENSE). The previous numerical implementations by HYDROCOIN teams of a constant-concentration boundary to represent salt release by lateral dispersion only (as stipulated in the original problem definition) was flawed because this boundary condition allows the release of salt into the flow field by both dispersion and advection. When the constant-concentration boundary is modified to allow salt release by dispersion only, significantly less salt is released into the flow field. The calculated brine distribution for case 5 depends very little on which numerical model is used, as long as the selected model is solving the proper equations. Instead, the accuracy of the solution depends strongly on the proper conceptualization of the problem, including the detailed design of the constant-concentration boundary condition. The importance and sensitivity to the manner of specification of this boundary does not appear to have been recognized previously in the analysis of this problem.

An open-loop ground-water heat pump system: transient numerical modeling and site experimental results

NASA Astrophysics Data System (ADS)

Lo Russo, S.; Taddia, G.; Gnavi, L.

2012-04-01

KEY WORDS: Open-loop ground water heat pump; Feflow; Low-enthalpy; Thermal Affected Zone; Turin; Italy The increasing diffusion of low-enthalpy geothermal open-loop Groundwater Heat Pumps (GWHP) providing buildings air conditioning requires a careful assessment of the overall effects on groundwater system, especially in the urban areas where several plants can be close together and interfere. One of the fundamental aspects in the realization of an open loop low-enthalpy geothermal system is therefore the capacity to forecast the effects of thermal alteration produced in the ground, induced by the geothermal system itself. The impact on the groundwater temperature in the surrounding area of the re-injection well (Thermal Affected Zone - TAZ) is directly linked to the aquifer properties. The transient dynamic of groundwater discharge and temperature variations should be also considered to assess the subsurface environmental effects of the plant. The experimental groundwater heat pump system used in this study is installed at the "Politecnico di Torino" (NW Italy, Piedmont Region). This plant provides summer cooling needs for the university buildings. This system is composed by a pumping well, a downgradient injection well and a control piezometer. The system is constantly monitored by multiparameter probes measuring the dynamic of groundwater temperature. A finite element subsurface flow and transport simulator (FEFLOW) was used to investigate the thermal aquifer alteration. Simulations were continuously performed during May-October 2010 (cooling period). The numerical simulation of the heat transport in the aquifer was solved with transient conditions. The simulation was performed by considering only the heat transfer within the saturated aquifer, without any heat dispersion above or below the saturated zone due to the lack of detailed information regarding the unsaturated zone. Model results were compared with experimental temperature data derived from groundwater monitoring in the surrounding area of the injection well. Such analysis showed that the measured values differ slightly from the simulated values. That small difference is probably due to the simplification assumptions in the modelling. This hypothesis is still under investigation.

Death Valley regional groundwater flow system, Nevada and California-Hydrogeologic framework and transient groundwater flow model

USGS Publications Warehouse

Belcher, Wayne R.; Sweetkind, Donald S.

2010-01-01

A numerical three-dimensional (3D) transient groundwater flow model of the Death Valley region was developed by the U.S. Geological Survey for the U.S. Department of Energy programs at the Nevada Test Site and at Yucca Mountain, Nevada. Decades of study of aspects of the groundwater flow system and previous less extensive groundwater flow models were incorporated and reevaluated together with new data to provide greater detail for the complex, digital model. A 3D digital hydrogeologic framework model (HFM) was developed from digital elevation models, geologic maps, borehole information, geologic and hydrogeologic cross sections, and other 3D models to represent the geometry of the hydrogeologic units (HGUs). Structural features, such as faults and fractures, that affect groundwater flow also were added. The HFM represents Precambrian and Paleozoic crystalline and sedimentary rocks, Mesozoic sedimentary rocks, Mesozoic to Cenozoic intrusive rocks, Cenozoic volcanic tuffs and lavas, and late Cenozoic sedimentary deposits of the Death Valley regional groundwater flow system (DVRFS) region in 27 HGUs. Information from a series of investigations was compiled to conceptualize and quantify hydrologic components of the groundwater flow system within the DVRFS model domain and to provide hydraulic-property and head-observation data used in the calibration of the transient-flow model. These studies reevaluated natural groundwater discharge occurring through evapotranspiration (ET) and spring flow; the history of groundwater pumping from 1913 through 1998; groundwater recharge simulated as net infiltration; model boundary inflows and outflows based on regional hydraulic gradients and water budgets of surrounding areas; hydraulic conductivity and its relation to depth; and water levels appropriate for regional simulation of prepumped and pumped conditions within the DVRFS model domain. Simulation results appropriate for the regional extent and scale of the model were provided by acquiring additional data, by reevaluating existing data using current technology and concepts, and by refining earlier interpretations to reflect the current understanding of the regional groundwater flow system. Groundwater flow in the Death Valley region is composed of several interconnected, complex groundwater flow systems. Groundwater flow occurs in three subregions in relatively shallow and localized flow paths that are superimposed on deeper, regional flow paths. Regional groundwater flow is predominantly through a thick Paleozoic carbonate rock sequence affected by complex geologic structures from regional faulting and fracturing that can enhance or impede flow. Spring flow and ET are the dominant natural groundwater discharge processes. Groundwater also is withdrawn for agricultural, commercial, and domestic uses. Groundwater flow in the DVRFS was simulated using MODFLOW-2000, the U.S. Geological Survey 3D finitedifference modular groundwater flow modeling code that incorporates a nonlinear least-squares regression technique to estimate aquifer parameters. The DVRFS model has 16 layers of defined thickness, a finite-difference grid consisting of 194 rows and 160 columns, and uniform cells 1,500 meters (m) on each side. Prepumping conditions (before 1913) were used as the initial conditions for the transient-state calibration. The model uses annual stress periods with discrete recharge and discharge components. Recharge occurs mostly from infiltration of precipitation and runoff on high mountain ranges and from a small amount of underflow from adjacent basins. Discharge occurs primarily through ET and spring discharge (both simulated as drains) and water withdrawal by pumping and, to a lesser amount, by underflow to adjacent basins simulated by constant-head boundaries. All parameter values estimated by the regression are reasonable and within the range of expected values. The simulated hydraulic heads of the final calibrated transient mode

Modeling the impact of the nitrate contamination on groundwater at the groundwater body scale : The Geer basin case study (Invited)

NASA Astrophysics Data System (ADS)

Brouyere, S.; Orban, P.; Hérivaux, C.

2009-12-01

In the next decades, groundwater managers will have to face regional degradation of the quantity and quality of groundwater under pressure of land-use and socio-economic changes. In this context, the objectives of the European Water Framework Directive require that groundwater be managed at the scale of the groundwater body, taking into account not only all components of the water cycle but also the socio-economic impact of these changes. One of the main challenges remains to develop robust and efficient numerical modeling applications at such a scale and to couple them with economic models, as a support for decision support in groundwater management. An integrated approach between hydrogeologists and economists has been developed by coupling the hydrogeological model SUFT3D and a cost-benefit economic analysis to study the impact of agricultural practices on groundwater quality and to design cost-effective mitigation measures to decrease nitrate pressure on groundwater so as to ensure the highest benefit to the society. A new modeling technique, the ‘Hybrid Finite Element Mixing Cell’ approach has been developed for large scale modeling purposes. The principle of this method is to fully couple different mathematical and numerical approaches to solve groundwater flow and solute transport problems. The mathematical and numerical approaches proposed allows an adaptation to the level of local hydrogeological knowledge and the amount of available data. In combination with long time series of nitrate concentrations and tritium data, the regional scale modelling approach has been used to develop a 3D spatially distributed groundwater flow and solute transport model for the Geer basin (Belgium) of about 480 km2. The model is able to reproduce the spatial patterns of nitrate concentrations together nitrate trends with time. The model has then been used to predict the future evolution of nitrate trends for two types of scenarios: (i) a “business as usual scenario” where current polluting pressures remain the same and (ii) two contrasted scenarios that simulate the implementation of programs of measures aiming at reaching good chemical status. The results of the hydrogeological model under the “business as usual scenario” have been used to assess the cost for the society of the continuous degradation of the groundwater quality. The results of the hydrogeological model under the two contrasted scenarios have been used to assess the economical benefit as avoided damage resulting from the decrease in the nitrate load. A cost-benefit analysis has been thus performed to assess the programme of mitigation measures which provides the largest benefits at the lowest cost.

Ground-water flow and the possible effects of remedial actions at J-Field, Aberdeen Proving Ground, Maryland

USGS Publications Warehouse

Hughes, W.B.

1995-01-01

J-Field, located in the Edgewood Area of Aberdeen Proving Ground, Md, has been used since World War II to test and dispose of explosives, chemical warfare agents, and industrial chemicals resulting in ground-water, surface-water, and soil contami- nation. The U.S. Geological Survey finite-difference model was used to better understand ground-water flow at the site and to simulate the effects of remedial actions. A surficial aquifer and a confined aquifer were simulated with the model. A confining unit separates these units and is represented by leakance between the layers. The area modeled is 3.65 mi2; the model was constructed with a variably spaced 40 X 38 grid. The horizontal and lower boundaries of the model are all no-flow boundaries. Steady-state conditions were used. Ground water at the areas under investigation flows from disposal pit areas toward discharge areas in adjacent estuaries or wetlands. Simulations indicate that capping disposal areas with an impermeable cover effectively slows advective ground water flow by 0.7 to 0.5 times. Barriers to lateral ground-water flow were simulated and effectively prevented the movement of ground water toward discharge areas. Extraction wells were simulated as a way to contain ground-water contamination and to extract ground water for treatment. Two wells pumping 5 gallons per minute each at the toxic-materials disposal area and a single well pumping 2.5 gallons per minute at the riot-control-agent disposal area effectively contained contamination at these sites. A combi- nation of barriers to horizontal flow east and south of the toxic-materials disposal area, and a single extraction well pumping at 5 gallons per minute can extract contaminated ground water and prevent pumpage of marsh water.

Determining the turnover time of groundwater systems with the aid of environmental tracers. 1. Models and their applicability

NASA Astrophysics Data System (ADS)

Małoszewski, P.; Zuber, A.

1982-06-01

Three new lumped-parameter models have been developed for the interpretation of environmental radioisotope data in groundwater systems. Two of these models combine other simpler models, i.e. the piston flow model is combined either with the exponential model (exponential distribution of transit times) or with the linear model (linear distribution of transit times). The third model is based on a new solution to the dispersion equation which more adequately represents the real systems than the conventional solution generally applied so far. The applicability of models was tested by the reinterpretation of several known case studies (Modry Dul, Cheju Island, Rasche Spring and Grafendorf). It has been shown that two of these models, i.e. the exponential-piston flow model and the dispersive model give better fitting than other simpler models. Thus, the obtained values of turnover times are more reliable, whereas the additional fitting parameter gives some information about the structure of the system. In the examples considered, in spite of a lower number of fitting parameters, the new models gave practically the same fitting as the multiparameter finite state mixing-cell models. It has been shown that in the case of a constant tracer input a prior physical knowledge of the groundwater system is indispensable for determining the turnover time. The piston flow model commonly used for age determinations by the 14C method is an approximation applicable only in the cases of low dispersion. In some cases the stable-isotope method aids in the interpretation of systems containing mixed waters of different ages. However, when 14C method is used for mixed-water systems a serious mistake may arise by neglecting the different bicarbonate contents in particular water components.

Interactions between deep bedrock aquifers and surface water in function of recharge and topography: a numerical study

NASA Astrophysics Data System (ADS)

Goderniaux, P.; Davy, P.; Le Borgne, T.; Bresciani, E.; Jimenez-Martinez, J.

2011-12-01

In crystalline rock regions, such as Brittany (France), important reserves of groundwater into deep fractured aquifers are increasingly used and provide high quality water compared to shallow aquifers which can be subject to agricultural contamination. However, recharge processes of these deep aquifers and interactions with surface water are not yet fully understood. In some areas, intensive pumping is carried out without guarantee of the resource quantity and quality. Understanding these processes is crucial for sustainable management of the resource. In this study, we study how deep groundwater fluxes, pathways, ages, and river-aquifer interactions vary according to recharge. We assume that water flowing from the ground surface is distributed between shallow more permeable layers and deep layers. This repartition mostly depends on recharge rates. With high recharge, groundwater levels are high and subsurface streamlines are relatively short between recharge areas and existing draining rivers, which constitutes a very dense network. Therefore, most of the groundwater fluxes occur through the more permeable shallow layers. With low recharge, groundwater levels are lower, and river and shallow permeable levels are partly disconnected from each other. This induces a general increase of the groundwater streamlines length from the recharge areas to more sporadic discharge areas, and more fluxes occur through the deep layers. Recharge conditions and river-aquifer interactions have changed over the last thousands of years, due to change in precipitation, temperatures, existence of permafrost, etc. They have strongly influenced deep groundwater fluxes and can explain current groundwater age and flux distribution. To study these interactions, a regional-scale finite difference flow model was implemented. The model covers an area of 1400 km 2 , a depth of 1 km, and the topography is characteristic of Brittany. As rivers are mainly fed by groundwater drainage, seepages faces are used on the whole modelled area, so that the river network is not prescribed but dependent on simulated groundwater conditions. Different recharge conditions were tested (from 20 to 500 mm/yr). Results show that streamline lengths and groundwater ages have exponential distributions with characteristic lengths increasing with decreasing recharge. The total area of discharge zones decreases with recharge. Groundwater age is quite variable and increases with depth, but the variability is much more important in discharge areas than recharge areas. The proportion of groundwater discharge into the sea (compared to total recharge) increases when total recharge decreases. The model was also used to test the influence of heterogeneity or hydraulic conductivity contrast between shallow and deep layers on deep groundwater fluxes. In a completely homogeneous model, deep fluxes are correlated with recharge fluxes. Correlation decreases while contrast increases. If the permeability of the shallow weather zone is now 3 orders of magnitude larger than of deep aquifer, we observed that simulated deep groundwater fluxes increase locally, despite total recharge at the level of the ground surface decreases.

Simulations of potential future conditions in the cache critical groundwater area, Arkansas

USGS Publications Warehouse

Rashid, Haveen M.; Clark, Brian R.; Mahdi, Hanan H.; Rifai, Hanadi S.; Al-Shukri, Haydar J.

2015-01-01

A three-dimensional finite-difference model for part of the Mississippi River Valley alluvial aquifer in the Cache Critical Groundwater Area of eastern Arkansas was constructed to simulate potential future conditions of groundwater flow. The objectives of this study were to test different pilot point distributions to find reasonable estimates of aquifer properties for the alluvial aquifer, to simulate flux from rivers, and to demonstrate how changes in pumping rates for different scenarios affect areas of long-term water-level declines over time. The model was calibrated using the parameter estimation code. Additional calibration was achieved using pilot points with regularization and singular value decomposition. Pilot point parameter values were estimated at a number of discrete locations in the study area to obtain reasonable estimates of aquifer properties. Nine pumping scenarios for the years 2011 to 2020 were tested and compared to the simulated water-level heads from 2010. Hydraulic conductivity values from pilot point calibration ranged between 42 and 173 m/d. Specific yield values ranged between 0.19 and 0.337. Recharge rates ranged between 0.00009 and 0.0006 m/d. The model was calibrated using 2,322 hydraulic head measurements for the years 2000 to 2010 from 150 observation wells located in the study area. For all scenarios, the volume of water depleted ranged between 5.7 and 23.3 percent, except in Scenario 2 (minimum pumping rates), in which the volume increased by 2.5 percent.

Finite-difference model to simulate the areal flow of saltwater and fresh water separated by an interface

USGS Publications Warehouse

Mercer, James W.; Larson, S.P.; Faust, Charles R.

1980-01-01

Model documentation is presented for a two-dimensional (areal) model capable of simulating ground-water flow of salt water and fresh water separated by an interface. The partial differential equations are integrated over the thicknesses of fresh water and salt water resulting in two equations describing the flow characteristics in the areal domain. These equations are approximated using finite-difference techniques and the resulting algebraic equations are solved for the dependent variables, fresh water head and salt water head. An iterative solution method was found to be most appropriate. The program is designed to simulate time-dependent problems such as those associated with the development of coastal aquifers, and can treat water-table conditions or confined conditions with steady-state leakage of fresh water. The program will generally be most applicable to the analysis of regional aquifer problems in which the zone between salt water and fresh water can be considered a surface (sharp interface). Example problems and a listing of the computer code are included. (USGS).

Analytical Modeling of Groundwater Seepages to St. Lucie Estuary

NASA Astrophysics Data System (ADS)

Lee, J.; Yeh, G.; Hu, G.

2008-12-01

In this paper, six analytical models describing hydraulic interaction of stream-aquifer systems were applied to St Lucie Estuary (SLE) River Estuaries. These are analytical solutions for: (1) flow from a finite aquifer to a canal, (2) flow from an infinite aquifer to a canal, (3) the linearized Laplace system in a seepage surface, (4) wave propagation in the aquifer, (5) potential flow through stratified unconfined aquifers, and (6) flow through stratified confined aquifers. Input data for analytical solutions were obtained from monitoring wells and river stages at seepage-meter sites. Four transects in the study area are available: Club Med, Harbour Ridge, Lutz/MacMillan, and Pendarvis Cove located in the St. Lucie River. The analytical models were first calibrated with seepage meter measurements and then used to estimate of groundwater discharges into St. Lucie River. From this process, analytical relationships between the seepage rate and river stages and/or groundwater tables were established to predict the seasonal and monthly variation in groundwater seepage into SLE. It was found the seepage rate estimations by analytical models agreed well with measured data for some cases but only fair for some other cases. This is not unexpected because analytical solutions have some inherently simplified assumptions, which may be more valid for some cases than the others. From analytical calculations, it is possible to predict approximate seepage rates in the study domain when the assumptions underlying these analytical models are valid. The finite and infinite aquifer models and the linearized Laplace method are good for sites Pendarvis Cove and Lutz/MacMillian, but fair for the other two sites. The wave propagation model gave very good agreement in phase but only fairly agreement in magnitude for all four sites. The stratified unconfined and confined aquifer models gave similarly good agreements with measurements at three sites but poorly at the Club Med site. None of the analytical models presented here can fit the data at this site. To give better estimates at all sites numerical modeling that couple river hydraulics and groundwater flow involving less simplifications of and assumptions for the system may have to be adapted.

Large-Scale Water Resources Management within the Framework of GLOWA-Danube - Part A: The Groundwater Model

NASA Astrophysics Data System (ADS)

Barthel, R.; Rojanschi, V.; Wolf, J.; Braun, J.

2003-04-01

The interdisciplinary research co-operation Glowa-Danube aims at the development of innovative techniques, scenarios and strategies to investigate the impacts of Global Change on the hydrological cycle within the catchment area of the Upper Danube Basin (Gauge Passau). Both the influence of natural changes in the ecosystem, such as climate change, and changes in human behavior, such as changes in land use or water consumption, are considered. A globally applicable decision support tool "DANUBIA" that comprises 15 individual disciplinary models will be developed. The models are connected with each other via customized interfaces that facilitate network-based parallel calculations. The strictly object-oriented DANUBIA architecture was developed using the graphical notation tool UML (Unified Modeling Language) and has been implemented in Java code. The Institute of Hydraulic Engineering of the Universitaet Stuttgart contributes two models to DANUBIA: A groundwater flow and transport model and a water supply model. The latter is dealt with in a second contribution to this conference. This paper focuses on the groundwater model. The catchment basin of the Upper Danube covers an area of approximately 77.000 km2. The elevation difference from the highest peaks of the Alps to the lowest flatlands in the Danube valley is more than 3.000 m. In addition to the Alps, several lower mountain ranges such as the Black Forest, the Swabian and Franconian Alb and the Bavarian Forest are located respectively in the Northeast, North and Northwest of the basin. The climatic conditions, geomorphology, geology and land use show a wide range of different characteristics. The size and heterogeneity of the area make it extremely difficult to represent the natural conditions in a numerical model. Both data availability and accessibility add to the difficulties that one encounters in the approach to simulate groundwater flow and contaminant transport in this area. The groundwater flow model of the catchment developed by the research group uses a finite difference approach (MODFLOW). A transport model (nitrogen) will be added in a second stage (MT3D). A three-dimensional conceptual hydrogeological model consisting of four layers was developed. Only aquifers with basin-wide occurrence are considered. Aquifers on the local scale cannot be included in the model due to insufficient data availability, the model grid resolution (1km2) used and various limitations arising from the MODFLOW-approach. The cell size of 1 km is compulsory for all models in DANUBIA in order to facilitate 1:1 parameter exchange. The concept of DANUBIA is based on the parallel execution of strictly independent disciplinary models. At each time step, the required parameters are exchanged. On the "physical side" the groundwater model has interfaces to a soil water and a surface water model which provide important parameters that are used as model boundary conditions. The soil water model calculates the groundwater recharge as the infiltration through a layered soil zone. The surface water model calculates the heads in the rivers, which are used to determine flow from the aquifers to the rivers and vice versa. The main aim of the groundwater model is to assess and forecast quantity and quality of the groundwater resources together with the other physically based models under conditions of global change. On the "socio-economic side", the groundwater model exchanges data with the so-called "Actors" component, a group of models concerned with the human impact on the water cycle. The amount of groundwater extraction for drinking water purposes is a boundary condition of the groundwater model calculated by the Actors models. The feedback between demand and supply invokes the need for complex optimization algorithms.

Steady-state simulation of ground-water flow in the Blaine Aquifer, southwestern Oklahoma and northwestern Texas

USGS Publications Warehouse

Runkle, Donna L.; McLean, J.S.

1995-01-01

A generalized finite-difference model was prepared for the Blaine aquifer in southwestern Oklahoma and northwestern Texas. This report releases the model for use and modification. A grid of 1-square-mile nodes was established over the area, with 1,030 of the nodes actively simulated in the model. The steady-state model simulation used a uniform recharge rate of 2.2 inches per year and three values of hydraulic conductivity: 80, 19, and 4.7 feet per day. About 44 percent of the recharge is discharged as pumpage from wells, and the remainder is discharged to rivers and creeks within and adjacent to the study area.

Quasi 3D modeling of water flow and solute transport in vadose zone and groundwater

NASA Astrophysics Data System (ADS)

Yakirevich, A.; Kuznetsov, M.; Weisbrod, N.; Pachepsky, Y. A.

2013-12-01

The complexity of subsurface flow systems calls for a variety of concepts leading to the multiplicity of simplified flow models. One commonly used simplification is based on the assumption that lateral flow and transport in unsaturated zone is insignificant unless the capillary fringe is involved. In such cases the flow and transport in the unsaturated zone above groundwater level can be simulated as a 1D phenomenon, whereas through groundwater they are viewed as 2D or 3D phenomena. A new approach for a numerical scheme for 3D variably saturated flow and transport is presented. A Quasi-3D approach allows representing flow in the 'vadose zone - aquifer' system by a series of 1D Richards' equations solved in variably-saturated zone and by 3D-saturated flow equation in groundwater (modified MODFLOW code). The 1D and 3D equations are coupled at the phreatic surface in a way that aquifer replenishment is calculated using the Richards' equation, and solving for the moving water table does not require definition of the specific yield parameter. The 3D advection-dispersion equation is solved in the entire domain by the MT3D code. Using implicit finite differences approximation to couple processes in the vadose zone and groundwater provides mass conservation and increase of computational efficiency. The above model was applied to simulate the impact of irrigation on groundwater salinity in the Alto Piura aquifer (Northern Peru). Studies on changing groundwater quality in arid and semi-arid lands show that irrigation return flow is one of the major factors contributing to aquifer salinization. Existing mathematical models do not account explicitly for the solute recycling during irrigation on a daily scale. Recycling occurs throughout the unsaturated and saturated zones, as function of the solute mass extracted from pumping wells. Salt concentration in irrigation water is calculated at each time step as a function of concentration of both surface water and groundwater extracted at specific locations. Three scenarios were considered: (i) use of furrow irrigation and groundwater extraction (the present situation); (ii) increase of groundwater pumping by 50% compared to the first scenario; and (iii) transition from furrow irrigation to drip irrigation, thus decreasing irrigation volume by around 60% compared to the first scenario. Results indicate that in different irrigation areas, the simulated increase rates of total dissolved solids in groundwater vary from 3 to17 mg/L/ year, depending on hydrogeological and hydrochemical conditions, volumes of water extracted, and proportion between surface water and groundwater applied. The transition from furrow irrigation to drip irrigation can decrease the negative impact of return flow on groundwater quality; however drip irrigation causes faster simulated soil salinization compared to furrow irrigation. The quasi 3D modeling appeared to be efficient in elucidating solute recycling effects on soil and groundwater salinity.

Use of finite-difference arrays of observation wells to estimate evapotranspiration from ground water in the Arkansas River Valley, Colorado

USGS Publications Warehouse

Weeks, Edwin P.; Sorey, M.L.

1973-01-01

A method to determine evapotranspiration from ground water was tested at four sites in the flood plain of the Arkansas River in Colorado. Approximate ground-water budgets were obtained by analyzing water-level data from observation wells installed in five-point arrays. The analyses were based on finite difference approximations of the differential equation describing ground-water flow. Data from the sites were divided into two groups by season. It was assumed that water levels during the dormant season were unaffected by evapotranspiration of ground water or by recharge, collectively termed 'accretion.' Regression analyses of these data were made to provide an equation for separating the effects of changes in aquifer storage and of aquifer heterogeneity from those due to accretion during the growing season. The data collected during the growing season were thus analyzed to determine accretion.

MODFLOW-2005, the U.S. Geological Survey modular ground-water model - documentation of shared node local grid refinement (LGR) and the boundary flow and head (BFH) package

USGS Publications Warehouse

Mehl, Steffen W.; Hill, Mary C.

2006-01-01

This report documents the addition of shared node Local Grid Refinement (LGR) to MODFLOW-2005, the U.S. Geological Survey modular, transient, three-dimensional, finite-difference ground-water flow model. LGR provides the capability to simulate ground-water flow using one block-shaped higher-resolution local grid (a child model) within a coarser-grid parent model. LGR accomplishes this by iteratively coupling two separate MODFLOW-2005 models such that heads and fluxes are balanced across the shared interfacing boundary. LGR can be used in two-and three-dimensional, steady-state and transient simulations and for simulations of confined and unconfined ground-water systems. Traditional one-way coupled telescopic mesh refinement (TMR) methods can have large, often undetected, inconsistencies in heads and fluxes across the interface between two model grids. The iteratively coupled shared-node method of LGR provides a more rigorous coupling in which the solution accuracy is controlled by convergence criteria defined by the user. In realistic problems, this can result in substantially more accurate solutions and require an increase in computer processing time. The rigorous coupling enables sensitivity analysis, parameter estimation, and uncertainty analysis that reflects conditions in both model grids. This report describes the method used by LGR, evaluates LGR accuracy and performance for two- and three-dimensional test cases, provides input instructions, and lists selected input and output files for an example problem. It also presents the Boundary Flow and Head (BFH) Package, which allows the child and parent models to be simulated independently using the boundary conditions obtained through the iterative process of LGR.

Locally refined block-centred finite-difference groundwater models: Evaluation of parameter sensitivity and the consequences for inverse modelling

USGS Publications Warehouse

Mehl, S.; Hill, M.C.

2002-01-01

Models with local grid refinement, as often required in groundwater models, pose special problems for model calibration. This work investigates the calculation of sensitivities and the performance of regression methods using two existing and one new method of grid refinement. The existing local grid refinement methods considered are: (a) a variably spaced grid in which the grid spacing becomes smaller near the area of interest and larger where such detail is not needed, and (b) telescopic mesh refinement (TMR), which uses the hydraulic heads or fluxes of a regional model to provide the boundary conditions for a locally refined model. The new method has a feedback between the regional and local grids using shared nodes, and thereby, unlike the TMR methods, balances heads and fluxes at the interfacing boundary. Results for sensitivities are compared for the three methods and the effect of the accuracy of sensitivity calculations are evaluated by comparing inverse modelling results. For the cases tested, results indicate that the inaccuracies of the sensitivities calculated using the TMR approach can cause the inverse model to converge to an incorrect solution.

Locally refined block-centered finite-difference groundwater models: Evaluation of parameter sensitivity and the consequences for inverse modelling and predictions

USGS Publications Warehouse

Mehl, S.; Hill, M.C.

2002-01-01

Models with local grid refinement, as often required in groundwater models, pose special problems for model calibration. This work investigates the calculation of sensitivities and performance of regression methods using two existing and one new method of grid refinement. The existing local grid refinement methods considered are (1) a variably spaced grid in which the grid spacing becomes smaller near the area of interest and larger where such detail is not needed and (2) telescopic mesh refinement (TMR), which uses the hydraulic heads or fluxes of a regional model to provide the boundary conditions for a locally refined model. The new method has a feedback between the regional and local grids using shared nodes, and thereby, unlike the TMR methods, balances heads and fluxes at the interfacing boundary. Results for sensitivities are compared for the three methods and the effect of the accuracy of sensitivity calculations are evaluated by comparing inverse modelling results. For the cases tested, results indicate that the inaccuracies of the sensitivities calculated using the TMR approach can cause the inverse model to converge to an incorrect solution.

Groundwater-flow model of the northern High Plains aquifer in Colorado, Kansas, Nebraska, South Dakota, and Wyoming

USGS Publications Warehouse

Peterson, Steven M.; Flynn, Amanda T.; Traylor, Jonathan P.

2016-12-13

The High Plains aquifer is a nationally important water resource underlying about 175,000 square miles in parts of eight states: Colorado, Kansas, Oklahoma, Nebraska, New Mexico, South Dakota, Texas, and Wyoming. Droughts across much of the Northern High Plains from 2001 to 2007 have combined with recent (2004) legislative mandates to elevate concerns regarding future availability of groundwater and the need for additional information to support science-based water-resource management. To address these needs, the U.S. Geological Survey began the High Plains Groundwater Availability Study to provide a tool for water-resource managers and other stakeholders to assess the status and availability of groundwater resources.A transient groundwater-flow model was constructed using the U.S. Geological Survey modular three-dimensional finite-difference groundwater-flow model with Newton-Rhapson solver (MODFLOW–NWT). The model uses an orthogonal grid of 565 rows and 795 columns, and each grid cell measures 3,281 feet per side, with one variably thick vertical layer, simulated as unconfined. Groundwater flow was simulated for two distinct periods: (1) the period before substantial groundwater withdrawals, or before about 1940, and (2) the period of increasing groundwater withdrawals from May 1940 through April 2009. A soil-water-balance model was used to estimate recharge from precipitation and groundwater withdrawals for irrigation. The soil-water-balance model uses spatially distributed soil and landscape properties with daily weather data and estimated historical land-cover maps to calculate spatial and temporal variations in potential recharge. Mean annual recharge estimated for 1940–49, early in the history of groundwater development, and 2000–2009, late in the history of groundwater development, was 3.3 and 3.5 inches per year, respectively.Primary model calibration was completed using statistical techniques through parameter estimation using the parameter estimation suite of software with Tikhonov regularization. Calibration targets for the groundwater model included 343,067 groundwater levels measured in wells and 10,820 estimated monthly stream base flows at streamgages. A total of 1,312 parameters were adjusted during calibration to improve the match between calibration targets and simulated equivalents. Comparison of calibration targets to simulated equivalents indicated that, at the regional scale, the model correctly reproduced groundwater levels and stream base flows for 1940–2009. This comparison indicates that the model can be used to examine the likely response of the aquifer system to potential future stresses.Mean calibrated recharge for 1940–49 and 2000–2009 was smaller than that estimated with the soil-water-balance model. This indicated that although the general spatial patterns of recharge estimated with the soil-water-balance model were approximately correct at the regional scale of the Northern High Plains aquifer, the soil-water-balance model had overestimated recharge, and adjustments were needed to decrease recharge to improve the match of the groundwater model to calibration targets. The largest components of the simulated groundwater budgets were recharge from precipitation, recharge from canal seepage, outflows to evapotranspiration, and outflows to stream base flow. Simulated outflows to irrigation wells increased from 7 percent of total outflows in 1940–49 to 38 percent of 1970–79 total outflows and 49 percent of 2000–2009 total outflows.

Groundwater transport of crater-lake brine at Poas Volcano, Costa Rica

USGS Publications Warehouse

Sanford, W.E.; Konikow, Leonard F.; Rowe, G.L.; Brantley, S.L.

1995-01-01

This study analyzes the regional groundwater system at Poas and demonstrates the likelihood that the water discharging from the acidic springs in the Rio Agrio watershed originates at the acidic crater lake. Both heat and solute transport are analyzed on a regional scale through numerical simulations using the HST3D finite-difference model, which solves the coupled equations for fluid flow, heat transport, and solute transport. The code allows fluid viscosity and density to be functions of both temperature and solute concentration. The simulations use estimates for recharge to the mountain and a range of values and various distributions of permeability and porosity. Several sensitivity analyses are performed to test how the uncertainty in many of the model parameters affects the simulation results. These uncertainties yield an estimated range of travel times from the crater lake to the Rio Agrio springs of 1-30 yr, which is in close agreement with the results of tritium analyses of the springs. Calculated groundwater fluxes into and out of the crater lake are both about several hundred kg/s. These fluxes must be accounted for in water budgets of the crater lake. -from Authors

Ground-Water Contributions to Reservoir Storage and the Effect on Estimates of Firm Yield for Reservoirs in Massachusetts

USGS Publications Warehouse

Archfield, Stacey A.; Carlson, Carl S.

2006-01-01

Potential ground-water contributions to reservoir storage were determined for nine reservoirs in Massachusetts that had shorelines in contact with sand and gravel aquifers. The effect of ground water on firm yield was not only substantial, but furthermore, the firm yield of a reservoir in contact with a sand and gravel aquifer was always greater when the ground-water contribution was included in the water balance. Increases in firm yield ranged from 2 to 113 percent, with a median increase in firm yield of 10 percent. Additionally, the increase in firm yield in two reservoirs was greater than 85 percent. This study identified a set of equations that are based on an analytical solution to the ground-water-flow equation for the case of one-dimensional flow in a finite-width aquifer bounded by a linear surface-water feature such as a stream. These equations, which require only five input variables, were incorporated into an existing firm-yield-estimator (FYE) model, and the potential effect of ground water on firm yield was evaluated. To apply the FYE model to a reservoir in Massachusetts, the model requires that the drainage area to the reservoir be clearly defined and that some surface water flows into the reservoir. For surface-water-body shapes having a more realistic representation of a reservoir shoreline than a stream, a comparison of ground-water-flow rates simulated by the ground-water equations with flow rates simulated by a two-dimensional, finite-difference ground-water-flow model indicate that the agreement between the simulated flow rates is within ?10 percent when the ratio of the distance from the reservoir shoreline to the aquifer boundary to the length of shoreline in contact with the aquifer is between values of 0.5 and 3.5. Idealized reservoir-aquifer systems were assumed to verify that the ground-water-flow equations were implemented correctly into the existing FYE model; however, the modified FYE model has not been validated through a comparison of simulated and observed data. A comparison of simulated and observed reservoir water levels would further define limitations to the applicability of the ground-water-flow equations to reservoirs in Massachusetts whose shorelines are in contact with a sand and gravel aquifer.

Fast analysis of radionuclide decay chain migration

NASA Astrophysics Data System (ADS)

Chen, J. S.; Liang, C. P.; Liu, C. W.; Li, L.

2014-12-01

A novel tool for rapidly predicting the long-term plume behavior of an arbitrary length radionuclide decay chain is presented in this study. This fast tool is achieved based on generalized analytical solutions in compact format derived for a set of two-dimensional advection-dispersion equations coupled with sequential first-order decay reactions in groundwater system. The performance of the developed tool is evaluated by a numerical model using a Laplace transform finite difference scheme. The results of performance evaluation indicate that the developed model is robust and accurate. The developed model is then used to fast understand the transport behavior of a four-member radionuclide decay chain. Results show that the plume extents and concentration levels of any target radionuclide are very sensitive to longitudinal, transverse dispersion, decay rate constant and retardation factor. The developed model are useful tools for rapidly assessing the ecological and environmental impact of the accidental radionuclide releases such as the Fukushima nuclear disaster where multiple radionuclides leaked through the reactor, subsequently contaminating the local groundwater and ocean seawater in the vicinity of the nuclear plant.

Verification of the karst flow model under laboratory controlled conditions

NASA Astrophysics Data System (ADS)

Gotovac, Hrvoje; Andric, Ivo; Malenica, Luka; Srzic, Veljko

2016-04-01

Karst aquifers are very important groundwater resources around the world as well as in coastal part of Croatia. They consist of extremely complex structure defining by slow and laminar porous medium and small fissures and usually fast turbulent conduits/karst channels. Except simple lumped hydrological models that ignore high karst heterogeneity, full hydraulic (distributive) models have been developed exclusively by conventional finite element and finite volume elements considering complete karst heterogeneity structure that improves our understanding of complex processes in karst. Groundwater flow modeling in complex karst aquifers are faced by many difficulties such as a lack of heterogeneity knowledge (especially conduits), resolution of different spatial/temporal scales, connectivity between matrix and conduits, setting of appropriate boundary conditions and many others. Particular problem of karst flow modeling is verification of distributive models under real aquifer conditions due to lack of above-mentioned information. Therefore, we will show here possibility to verify karst flow models under the laboratory controlled conditions. Special 3-D karst flow model (5.6*2.6*2 m) consists of concrete construction, rainfall platform, 74 piezometers, 2 reservoirs and other supply equipment. Model is filled by fine sand (3-D porous matrix) and drainage plastic pipes (1-D conduits). This model enables knowledge of full heterogeneity structure including position of different sand layers as well as conduits location and geometry. Moreover, we know geometry of conduits perforation that enable analysis of interaction between matrix and conduits. In addition, pressure and precipitation distribution and discharge flow rates from both phases can be measured very accurately. These possibilities are not present in real sites what this model makes much more useful for karst flow modeling. Many experiments were performed under different controlled conditions such as different levels in left and right end of reservoirs (boundary conditions), different flow regimes in conduits, flow with and without precipitation, free and pressurized discharge from conduits or influence of epikarst (top layer) on recession period. Experimental results are verified by conventional karst flow model (such as MODFLOW-CFP) showing that hydraulic (distributive) models can describe complex behavior of karst flow processes if substantial amount of input data are known from site investigations and monitoring. These results enable us to develop more advanced karst flow models that will improve understanding and analysis of complex flow processes in the real karst aquifers.

Modelling of spatial contaminant probabilities of occurrence of chlorinated hydrocarbons in an urban aquifer.

PubMed

Greis, Tillman; Helmholz, Kathrin; Schöniger, Hans Matthias; Haarstrick, Andreas

2012-06-01

In this study, a 3D urban groundwater model is presented which serves for calculation of multispecies contaminant transport in the subsurface on the regional scale. The total model consists of two submodels, the groundwater flow and reactive transport model, and is validated against field data. The model equations are solved applying finite element method. A sensitivity analysis is carried out to perform parameter identification of flow, transport and reaction processes. Coming from the latter, stochastic variation of flow, transport, and reaction input parameters and Monte Carlo simulation are used in calculating probabilities of pollutant occurrence in the domain. These probabilities could be part of determining future spots of contamination and their measure of damages. Application and validation is exemplarily shown for a contaminated site in Braunschweig (Germany), where a vast plume of chlorinated ethenes pollutes the groundwater. With respect to field application, the methods used for modelling reveal feasible and helpful tools to assess natural attenuation (MNA) and the risk that might be reduced by remediation actions.

A coupled surface-water and ground-water flow model (MODBRANCH) for simulation of stream-aquifer interaction

USGS Publications Warehouse

Swain, Eric D.; Wexler, Eliezer J.

1996-01-01

Ground-water and surface-water flow models traditionally have been developed separately, with interaction between subsurface flow and streamflow either not simulated at all or accounted for by simple formulations. In areas with dynamic and hydraulically well-connected ground-water and surface-water systems, stream-aquifer interaction should be simulated using deterministic responses of both systems coupled at the stream-aquifer interface. Accordingly, a new coupled ground-water and surface-water model was developed by combining the U.S. Geological Survey models MODFLOW and BRANCH; the interfacing code is referred to as MODBRANCH. MODFLOW is the widely used modular three-dimensional, finite-difference ground-water model, and BRANCH is a one-dimensional numerical model commonly used to simulate unsteady flow in open- channel networks. MODFLOW was originally written with the River package, which calculates leakage between the aquifer and stream, assuming that the stream's stage remains constant during one model stress period. A simple streamflow routing model has been added to MODFLOW, but is limited to steady flow in rectangular, prismatic channels. To overcome these limitations, the BRANCH model, which simulates unsteady, nonuniform flow by solving the St. Venant equations, was restructured and incorporated into MODFLOW. Terms that describe leakage between stream and aquifer as a function of streambed conductance and differences in aquifer and stream stage were added to the continuity equation in BRANCH. Thus, leakage between the aquifer and stream can be calculated separately in each model, or leakages calculated in BRANCH can be used in MODFLOW. Total mass in the coupled models is accounted for and conserved. The BRANCH model calculates new stream stages for each time interval in a transient simulation based on upstream boundary conditions, stream properties, and initial estimates of aquifer heads. Next, aquifer heads are calculated in MODFLOW based on stream stages calculated by BRANCH, aquifer properties, and stresses. This process is repeated until convergence criteria are met for head and stage. Because time steps used in ground-water modeling can be much longer than time intervals used in surface- water simulations, provision has been made for handling multiple BRANCH time intervals within one MODFLOW time step. An option was also added to BRANCH to allow the simulation of channel drying and rewetting. Testing of the coupled model was verified by using data from previous studies; by comparing results with output from a simpler, four-point implicit, open-channel flow model linked with MODFLOW; and by comparison to field studies of L-31N canal in southern Florida.

Implementation and use of direct-flow connections in a coupled ground-water and surface-water model

USGS Publications Warehouse

Swain, Eric D.

1994-01-01

The U.S. Geological Survey's MODFLOW finite-difference ground-water flow model has been coupled with three surface-water packages - the MODBRANCH, River, and Stream packages - to simulate surface water and its interaction with ground water. Prior to the development of the coupling packages, the only interaction between these modeling packages was that leakage values could be passed between MODFLOW and the three surface-water packages. To facilitate wider and more flexible uses of the models, a computer program was developed and added to MODFLOW to allow direct flows or stages to be passed between any of the packages and MODFLOW. The flows or stages calculated in one package can be set as boundary discharges or stages to be used in another package. Several modeling packages can be used in the same simulation depending upon the level of sophistication needed in the various reaches being modeled. This computer program is especially useful when any of the River, Stream, or MODBRANCH packages are used to model a river flowing directly into or out of wetlands in direct connection with the aquifer and represented in the model as an aquifer block. A field case study is shown to illustrate an application.

The effect of bedrock originated groundwater on the triggering mechanism of different landslides in Switzerland

NASA Astrophysics Data System (ADS)

Broennimann, Cornelia; Tacher, Laurent; Jaboyedoff, Michel; Jongmans, Denis; Springman, Sarah; Askarinejad, Amin

2010-05-01

It is well known that the most important triggering mechanism for rapid landslides is the infiltration of precipitation water at the surface of slopes which decreases the soils shear strength. However, the present study put focus on the exfiltration of groundwater from the substratum and its effect on the triggering of overlying landslides. Which is the origin of this groundwater? Which role does the hydrogeology play on the triggering mechanism of landslides? Is the bedrock locally feeding (springs) or draining (fractures) the overlying soil material in slopes? Due to the invisibility of the underground, these questions are difficult to answer. The aims of this research are 1) combining suitable field methods in order to create geological and hydrogeological conceptual models for different landslides located in representative geological settings in Switzerland, 2) to compare the different models and 3) to complement them with numerical flow modelling. For this purpose, three different case studies were chosen: • Landslide triggerd by artificial rainfall on a natural slope: This experiment was carried out in the Northern Swiss Molasse Basin where horizontally layered porous and fractured sandstone intersects with marlstone and is overlied by silty colluvium and sandy eluvium. The role of the joints and the groundwater in the porous sandstone is studied. • Reactivated fast moving landslide: This landslide affects moraine material and weathered bedrock which overlies black schist, flysch and rauhwacke in a tectonically affected zone in the Western Swiss Prealps. The origin of the groundwater in the landslide area and the influence of a spring at the base of the landslide are of special interest. • Slope prone to landslides: This slope is located in the Swiss Subalpine Molasse where inclined and heavily fractured conglomerate is interbedded with sandstone and marlstone and covered with silty and clayey eluvium. The destabilizing effect of springs on the slope, their origin from the fractured conglomerate and their response to rainfall is investigated. In a first project step, the geology and geometry of the landslides are investigated by the combination of geophysical methods (active seismic and electric resistivity), LIDAR, borehole drilling and geological mapping. In a second step, the hydrological/hydrogeological regime is investigated by measuring the hydraulic conductivity with the use of infiltration tests, measuring of precipitation and spring flux, monitoring the groundwater level in boreholes and analyzing hydrogeochemical parameters. Based on these investigations, hydrogeological conceptual models are created. In a next step, different water flow scenarios will be simulated using finite element hydrological flow models. The first results give evidence that for the understanding of the triggering mechanism of the different landslide types it is important to take into account the groundwater regime of the substratum: either it acts as a drain or it is feeding the overlying unstable mass and therefore either disadvantages the triggering or brings it forward. In a further step, the described conceptual models will be compared and verified with related landslides in similar geological settings.

Ground-water flow in the shallow aquifer system at the Naval Weapons Station Yorktown, Virginia

USGS Publications Warehouse

Smith, Barry S.

2001-01-01

The Environmental Directorate of the Naval Weapons Station Yorktown, Virginia, is concerned about possible contamination of ground water at the Station. Ground water at the Station flows through a shallow system of layered aquifers and leaky confining units. The units of the shallow aquifer system are the Columbia aquifer, the Cornwallis Cave confining unit, the Cornwallis Cave aquifer, the Yorktown confining unit, and the Yorktown-Eastover aquifer. The Eastover-Calvert confining unit separates the shallow aquifer system from deeper confined aquifers beneath the Station. A three-dimensional, finite-difference, ground-water flow model was used to simulate steady-state ground-water flow of the shallow aquifer system in and around the Station. The model simulated ground-water flow from the peninsular drainage divide that runs across the Lackey Plain near the southern end of the Station north to King Creek and the York River and south to Skiffes Creek and the James River. The model was calibrated by minimizing the root mean square error between 4 7 measured and corresponding simulated water levels. The calibrated model was used to determine the ground-water budget and general directions of ground-water flow. A particle-tracking routine was used with the calibrated model to estimate groundwater flow paths, flow rates, and traveltimes from selected sites at the Station. Simulated ground-water flow velocities of the Station-area model were small beneath the interstream areas of the Lackey Plain and Croaker Flat, but increased outward toward the streams and rivers where the hydraulic gradients are larger. If contaminants from the land surface entered the water table at or near the interstream areas of the Station, where hydraulic gradients are smaller, they would migrate more slowly than if they entered closer to the streams or the shores of the rivers where gradients commonly are larger. The ground-water flow simulations indicate that some ground water leaks downward from the water table to the Yorktown confining unit and, where the confining unit is absent, to the Yorktown-Eastover aquifer. The velocities of advective-driven contaminants would decrease considerably when entering the Yorktown confining unit because the hydraulic conductivity of the confining unit is small compared to that of the aquifers. Any contaminants that moved with advective ground-water flow near the groundwater divide of the Lackey Plain would move relatively slowly because the hydraulic gradients are small there. The direction in which the contaminants would move, however, would be determined by precisely where the contaminants entered the water table. The model was not designed to accurately simulate ground-water flow paths through local karst features. Beneath Croaker Flat, ground water flows downward through the Columbia aquifer and the Yorktown confining unit into the Yorktown-Eastover aquifer. Analyses of the movement of simulated particles from two adjacent sites at Croaker Flat indicated that ground-water flow paths were similar at first but diverged and discharged to different tributaries of Indian Field Creek or to the York River. These simulations indicate that complex and possibly divergent flow paths and traveltimes are possible at the Station. Although the Station-area model is not detailed enough to simulate ground-water flow at the scales commonly used to track and remediate contaminants at specific sites, general concepts about possible contaminant migration at the Station can be inferred from the simulations.

Effects of warming on groundwater flow in mountainous snowmelt-dominated catchments

NASA Astrophysics Data System (ADS)

Evans, S. G.; Ge, S.; Molotch, N. P.

2015-12-01

In mountainous regions, warmer air temperatures have led to an earlier onset of spring snowmelt and lower snowmelt rates; i.e. because snowmelt has shifted earlier when energy availability is lower. These changes to snowmelt will likely affect the partitioning of snowmelt water between surface runoff and groundwater flow, and therefore, the lag time between snowmelt and streamflow. While the connection between snowmelt and surface runoff has been well-studied, the impact of snowmelt variability on groundwater flow processes has received limited attention, especially in mountainous catchments. We construct a two-dimensional, finite element, coupled flow and heat transport hydrogeologic model to evaluate how changes in snowmelt onset and rate may alter groundwater discharge to streams in mountainous catchments. The coupled hydrogeologic model simulates seasonally frozen ground by incorporating permeability variation as a function of temperature and allows for modeling of pore water freeze and thaw. We apply the model to the Green Lakes Valley (GLV) watershed in the Rocky Mountains of Colorado, a representative snowmelt-dominated catchment. Snowmelt for the GLV catchment is reconstructed from a 12 year (1996-2007) dataset of hydrometeorological records and satellite-derived snow covered area. Modeling results suggest that on a yearly cycle, groundwater infiltration and discharge is limited by the seasonally frozen subsurface. Under average conditions from 1996 to 2007, maximum groundwater discharge to the surface lags maximum snowmelt by approximately two months. Ongoing modeling is exploring how increasing air temperatures affect lag times between snowmelt and groundwater discharge to streams. This study has implications for water resource availability and its temporal variability in a warming global climate.

Modeling climate change impacts on groundwater resources using transient stochastic climatic scenarios

NASA Astrophysics Data System (ADS)

Goderniaux, Pascal; BrouyèRe, Serge; Blenkinsop, Stephen; Burton, Aidan; Fowler, Hayley J.; Orban, Philippe; Dassargues, Alain

2011-12-01

Several studies have highlighted the potential negative impact of climate change on groundwater reserves, but additional work is required to help water managers plan for future changes. In particular, existing studies provide projections for a stationary climate representative of the end of the century, although information is demanded for the near future. Such time-slice experiments fail to account for the transient nature of climatic changes over the century. Moreover, uncertainty linked to natural climate variability is not explicitly considered in previous studies. In this study we substantially improve upon the state-of-the-art by using a sophisticated transient weather generator in combination with an integrated surface-subsurface hydrological model (Geer basin, Belgium) developed with the finite element modeling software "HydroGeoSphere." This version of the weather generator enables the stochastic generation of large numbers of equiprobable climatic time series, representing transient climate change, and used to assess impacts in a probabilistic way. For the Geer basin, 30 equiprobable climate change scenarios from 2010 to 2085 have been generated for each of six different regional climate models (RCMs). Results show that although the 95% confidence intervals calculated around projected groundwater levels remain large, the climate change signal becomes stronger than that of natural climate variability by 2085. Additionally, the weather generator's ability to simulate transient climate change enabled the assessment of the likely time scale and associated uncertainty of a specific impact, providing managers with additional information when planning further investment. This methodology constitutes a real improvement in the field of groundwater projections under climate change conditions.

Effects of recharge, Upper Floridan aquifer heads, and time scale on simulated ground-water exchange with Lake Starr, a seepage lake in central Florida

USGS Publications Warehouse

Swancar, Amy; Lee, Terrie Mackin

2003-01-01

Lake Starr and other lakes in the mantled karst terrain of Florida's Central Lake District are surrounded by a conductive surficial aquifer system that receives highly variable recharge from rainfall. In addition, downward leakage from these lakes varies as heads in the underlying Upper Floridan aquifer change seasonally and with pumpage. A saturated three-dimensional finite-difference ground-water flow model was used to simulate the effects of recharge, Upper Floridan aquifer heads, and model time scale on ground-water exchange with Lake Starr. The lake was simulated as an active part of the model using high hydraulic conductivity cells. Simulated ground-water flow was compared to net ground-water flow estimated from a rigorously derived water budget for the 2-year period August 1996-July 1998. Calibrating saturated ground-water flow models with monthly stress periods to a monthly lake water budget will result in underpredicting gross inflow to, and leakage from, ridge lakes in Florida. Underprediction of ground-water inflow occurs because recharge stresses and ground-water flow responses during rainy periods are averaged over too long a time period using monthly stress periods. When inflow is underestimated during calibration, leakage also is underestimated because inflow and leakage are correlated if lake stage is maintained over the long term. Underpredicted leakage reduces the implied effect of ground-water withdrawals from the Upper Floridan aquifer on the lake. Calibrating the weekly simulation required accounting for transient responses in the water table near the lake that generated the greater range of net ground-water flow values seen in the weekly water budget. Calibrating to the weekly lake water budget also required increasing the value of annual recharge in the nearshore region well above the initial estimate of 35 percent of the rainfall, and increasing the hydraulic conductivity of the deposits around and beneath the lake. To simulate the total ground-water inflow to lakes, saturated-flow models of lake basins need to account for the potential effects of rapid and efficient recharge in the surficial aquifer system closest to the lake. In this part of the basin, the ability to accurately estimate recharge is crucial because the water table is shallowest and the response time between rainfall and recharge is shortest. Use of the one-dimensional LEACHM model to simulate the effects of the unsaturated zone on the timing and magnitude of recharge in the nearshore improved the simulation of peak values of ground-water inflow to Lake Starr. Results of weekly simulations suggest that weekly recharge can approach the majority of weekly rainfall on the nearshore part of the lake basin. However, even though a weekly simulation with higher recharge in the nearshore was able to reproduce the extremes of ground-water exchange with the lake more accurately, it was not consistently better at predicting net ground-water flow within the water budget error than a simulation with lower recharge. The more subtle effects of rainfall and recharge on ground-water inflow to the lake were more difficult to simulate. The use of variably saturated flow modeling, with time scales that are shorter than weekly and finer spatial discretization, is probably necessary to understand these processes. The basin-wide model of Lake Starr had difficulty simulating the full spectrum of ground-water inflows observed in the water budget because of insufficient information about recharge to ground water, and because of practical limits on spatial and temporal discretization in a model at this scale. In contrast, the saturated flow model appeared to successfully simulate the effects of heads in the Upper Floridan aquifer on water levels and ground-water exchange with the lake at both weekly and monthly stress periods. Most of the variability in lake leakage can be explained by the average vertical head difference between the lake and a re

Analysis of water control in an underground mine under strong karst media influence (Vazante mine, Brazil)

NASA Astrophysics Data System (ADS)

Ninanya, Hugo; Guiguer, Nilson; Vargas, Eurípedes A.; Nascimento, Gustavo; Araujo, Edmar; Cazarin, Caroline L.

2018-05-01

This work presents analysis of groundwater flow conditions and groundwater control measures for Vazante underground mine located in the state of Minas Gerais, Brazil. According to field observations, groundwater flow processes in this mine are highly influenced by the presence of karst features located in the near-surface terrain next to Santa Catarina River. The karstic features, such as caves, sinkholes, dolines and conduits, have direct contact with the aquifer and tend to increase water flow into the mine. These effects are more acute in areas under the influence of groundwater-level drawdown by pumping. Numerical analyses of this condition were carried out using the computer program FEFLOW. This program represents karstic features as one-dimensional discrete flow conduits inside a three-dimensional finite element structure representing the geologic medium following a combined discrete-continuum approach for representing the karst system. These features create preferential flow paths between the river and mine; their incorporation into the model is able to more realistically represent the hydrogeological environment of the mine surroundings. In order to mitigate the water-inflow problems, impermeabilization of the river through construction of a reinforced concrete channel was incorporated in the developed hydrogeological model. Different scenarios for channelization lengths for the most critical zones along the river were studied. Obtained results were able to compare effectiveness of different river channelization scenarios. It was also possible to determine whether the use of these impermeabilization measures would be able to reduce, in large part, the elevated costs of pumping inside the mine.

Groundwater protection of minimal water supply systems integrating simple hydrogeological information

NASA Astrophysics Data System (ADS)

Rodrigo-Ilarri, Javier; Rodrigo-Clavero, María Elena

2016-04-01

According to the current EU environmental legislation, groundwater protection is one of the key issues to be addressed when new industrial activities have to be authorised. This work shows a simple methodology that could be used by local and environmental authorities in order to analyse the potential risk caused by an industrial spill on a natural environment. The methodology leads to the determination of the protection area around an extraction well system using the information given by: i) a set of local piezometers, ii) the chemical nature of the industrial spill and iii) the hydrogeological parameters of the local aquifer. The exact location of the contaminant source is not needed for the analysis. The flow equation is afterwards solved using a finite-difference approximation scheme under stationary conditions. Finally, the capture zones for different times are computed by a simple upstream advective transport model. Results on the determination of the perimeter protection area definition of a water supply system in the municipality of L'Alcora (Castellón) in Spain are shown.

Water use, ground-water recharge and availability, and quality of water in the Greenwich area, Fairfield County, Connecticut and Westchester County, New York, 2000-2002

USGS Publications Warehouse

Mullaney, John R.

2004-01-01

Ground-water budgets were developed for 32 small basin-based zones in the Greenwich area of southwestern Connecticut, where crystalline-bedrock aquifers supply private wells, to determine the status of residential ground-water consumption relative to rates of ground-water recharge and discharge. Estimated residential ground-water withdrawals for small basins (averaging 1.7 square miles (mi2)) ranged from 0 to 0.16 million gallons per day per square mile (Mgal/d/mi2). To develop these budgets, residential ground-water withdrawals were estimated using multiple-linear regression models that relate water use from public water supply to data on residential property characteristics. Average daily water use of households with public water supply ranged from 219 to 1,082 gallons per day (gal/d). A steady-state finite-difference ground-water- flow model was developed to track water budgets, and to estimate optimal values for hydraulic conductivity of the bedrock (0.05 feet per day) and recharge to the overlying till deposits (6.9 inches) using nonlinear regression. Estimated recharge rates to the small basins ranged from 3.6 to 7.5 inches per year (in/yr) and relate to the percentage of the basin underlain by coarse- grained glacial stratified deposits. Recharge was not applied to impervious areas to account for the effects of urbanization. Net residential ground-water consumption was estimated as ground-water withdrawals increased during the growing season, and ranged from 0 to 0.9 in/yr. Long-term average stream base flows simulated by the ground-water-flow model were compared to calculated values of average base flow and low flow to determine if base flow was substantially reduced in any of the basins studied. Three of the 32 basins studied had simulated base flows less than 3 in/yr, as a result of either ground-water withdrawals or reduced recharge due to urbanization. A water-availability criteria of the difference between the 30-day 2-year low flow and the recharge rate for each basin was explored as a method to rate the status of water consumption in each basin. Water consumption ranged from 0 to 14.3 percent of available water based on this criteria for the 32 basins studied. Base-flow water quality was related to the amount of urbanized area in each basin sampled. Concentrations of total nitrogen and phosphorus, chloride, indicator bacteria, and the number of pesticide detections increased with basin urbanization, which ranged from 18 to 63 percent of basin area.

Comparing Budget-based and Tracer-based Residence Times in Butte Basin, California

NASA Astrophysics Data System (ADS)

Moran, J. E.; Visser, A.; Esser, B.; Buck, C.

2017-12-01

The California Sustainable Groundwater Management Act of 2014 (SGMA) calls for basin-scale Groundwater Sustainability Plans (GSPs) that include a water budget covering a 50 year planning horizon. A nine layer, Integrated Water Flow Model (IWFM) developed for Butte Basin, California, allows examination of water budgets within 36 sub-regions having varying land and water use, to inform SGMA efforts. Detailed land use, soil type, groundwater pumping, and surface water delivery data were applied in the finite element IWFM calibration. In a sustainable system, the volume of storage does not change over a defined time period, and the residence time can be calculated from the water storage volume divided by the flux (recharge or discharge rate). Groundwater ages based on environmental tracer data reflect the mean residence time of groundwater, or its inverse, the turnover rate. Comparisons between budget-based residence times determined from storage and flux, and residence times determined from isotopic tracers of groundwater age, can provide insight into data quality, model reliability, and system sustainability. Budget-based groundwater residence times were calculated from IWFM model output by assuming constant storage and dividing by either averaged annual net recharge or discharge. Calculated residence times range between approximately 100 and 1000 years, with shorter times in subregions where pumping dominates discharge. Independently, 174 wells within the model boundaries were analyzed for tritium-helium groundwater age as part of the California Groundwater Ambient Monitoring and Assessment program. Age distributions from isotopic tracers were compared to model-derived groundwater residence times from groundwater budgets within the subregions of Butte Basin. Mean, apparent, tracer-based residence times are mostly between 20 and 40 years, but 25% of the long-screened wells that were sampled do not have detectable tritium, indicating residence times of more than about 60 years and broad age distributions. A key factor in making meaningful comparisons is to examine budget-based and tracer-based results over transmissive vertical sections, where pumping increases turnover time.

Developing a high resolution groundwater model for Indonesia

NASA Astrophysics Data System (ADS)

Sutanudjaja, E.; de Graaf, I. E.; Alberti, K.; Van Beek, L. P.; Bierkens, M. F.

2013-12-01

Groundwater is important in many parts of Indonesia. It serves as a primary source of drinking water and industrial activities. During times of drought, it sustains water flows in streams, rivers, lakes and wetlands, and thus support ecosystem habitat and biodiversity, as well as preventing hazardous forest fire. Besides its importance, groundwater is known as a vulnerable resource as unsustainable groundwater exploitation and management occurs in many areas of the country. Therefore, in order to ensure sustainable management of groundwater resources, monitoring and predicting groundwater changes in Indonesia are imperative. However, large-extent groundwater models to assess these changes on a regional scale are almost non-existent and are hampered by the strong topographical and lithological transitions that characterize Indonesia. In this study, we built an 1 km resolution of steady-state groundwater model for the entire Indonesian archipelago (total inland area: about 2 million km2). Here we adopted the approach of Sutanudjaja et al. (2011) in order to make a MODFLOW (McDonald and Harbaugh, 1988) groundwater model by using only global datasets. Aquifer schematization and properties of the groundwater model were developed from available global lithological map (e.g. Dürr et al., 2005; Gleeson et al., 2010; Hartmann and Moorsdorf, 2012). We forced the groundwater model with the output from the global hydrological model PCR-GLOBWB (van Beek et al., 2011), specifically the long term net groundwater recharge and average surface water levels derived from routed channel discharge. Results are promising. The MODFLOW model can converge with realistic aquifer properties (i.e. transmissivities) and produce reasonable groundwater head spatial distribution that reflects the positions of major groundwater bodies and surface water bodies in the country. For this session, we aim to demonstrate and discuss the results and the prospects of this modeling study. References: Dürr, H. H., Meybeck, M., & Dürr, S. H.: Lithologic composition of the Earth's continental surfaces derived from a new digital map emphasizing riverine material transfer, Global Biogeochem. Cycles, 19, GB4S10, http://dx.doi.org/10.1029/2005GB002515, 2005. Gleeson, T., Smith, L., Moosdorf, N., Hartmann, J., Dürr, H. H., Manning, A. H., van Beek, L. P. H., & Jellinek, A. M.: Mapping permeability over the surface of the earth. Geophys. Res. Lett. 38 (2), L02401, http://dx.doi.org/10.1029/2010GL045565, 2011. Hartmann, J., & Moosdorf, N.: The new global lithological map database GLiM: A representation of rock properties at the Earth surface, Geochem. Geophys. Geosyst., 13, Q12004, http://dx.doi.org/10.1029/2012GC004370, 2012. McDonald, M. & Harbaugh, A.: A modular three-dimensional finite-difference ground-water flow model, US Geological Survey, http://pubs.water.usgs.gov/twri6a1, 1988. Sutanudjaja, E. H., van Beek, L. P. H., de Jong, S. M., van Geer, F. C., & Bierkens, M. F. P.: Large-scale groundwater modeling using global datasets: a test case for the Rhine-Meuse basin, Hydrol. Earth Syst. Sci., 15, 2913-2935, http://dx.doi.org/10.5194/hess-15-2913-2011, 2011. van Beek, L. P. H., Wada, Y., & Bierkens, M. F. P.: Global monthly water stress: 1. Water balance and water availability. Water Resources Research 47 (7), W07517, http://dx.doi.org/10.1029/2010WR009791, 2011

Appraising options to reduce shallow groundwater tables and enhance flow conditions over regional scales in an irrigated alluvial aquifer system

USGS Publications Warehouse

Morway, Eric D.; Gates, Timothy K.; Niswonger, Richard G.

2013-01-01

Some of the world’s key agricultural production systems face big challenges to both water quantity and quality due to shallow groundwater that results from long-term intensive irrigation, namely waterlogging and salinity, water losses, and environmental problems. This paper focuses on water quantity issues, presenting finite-difference groundwater models developed to describe shallow water table levels, non-beneficial groundwater consumptive use, and return flows to streams across two regions within an irrigated alluvial river valley in southeastern Colorado, USA. The models are calibrated and applied to simulate current baseline conditions in the alluvial aquifer system and to examine actions for potentially improving these conditions. The models provide a detailed description of regional-scale subsurface unsaturated and saturated flow processes, thereby enabling detailed spatiotemporal description of groundwater levels, recharge to infiltration ratios, partitioning of ET originating from the unsaturated and saturated zones, and groundwater flows, among other variables. Hybrid automated and manual calibration of the models is achieved using extensive observations of groundwater hydraulic head, groundwater return flow to streams, aquifer stratigraphy, canal seepage, total evapotranspiration, the portion of evapotranspiration supplied by upflux from the shallow water table, and irrigation flows. Baseline results from the two regional-scale models are compared to model predictions under variations of four alternative management schemes: (1) reduced seepage from earthen canals, (2) reduced irrigation applications, (3) rotational lease fallowing (irrigation water leased to municipalities, resulting in temporary dry-up of fields), and (4) combinations of these. The potential for increasing the average water table depth by up to 1.1 and 0.7 m in the two respective modeled regions, thereby reducing the threat of waterlogging and lowering non-beneficial consumptive use from adjacent fallow and naturally-vegetated lands, is demonstrated for the alternative management intervention scenarios considered. Net annual average savings of up to about 9.9 million m3 (8000 ac ft) and 2.3 million m3 (1900 ac ft) of non-beneficial groundwater consumptive use is demonstrated for the study periods in each of the two respective study regions. Alternative water management interventions achieve varying degrees of benefits in each of the two regions, suggesting a need to adopt region-specific interventions and avoid a ‘one-size-fits-all’ approach. Impacts of the considered interventions on return flows to the river were predicted to be significant, highlighting the need for flow augmentation to comply with an interstate river compact and portending beneficial impacts on solute loading.

Groundwater simulation and management models for the upper Klamath Basin, Oregon and California

USGS Publications Warehouse

Gannett, Marshall W.; Wagner, Brian J.; Lite, Kenneth E.

2012-01-01

The upper Klamath Basin encompasses about 8,000 square miles, extending from the Cascade Range east to the Basin and Range geologic province in south-central Oregon and northern California. The geography of the basin is dominated by forested volcanic uplands separated by broad interior basins. Most of the interior basins once held broad shallow lakes and extensive wetlands, but most of these areas have been drained or otherwise modified and are now cultivated. Major parts of the interior basins are managed as wildlife refuges, primarily for migratory waterfowl. The permeable volcanic bedrock of the upper Klamath Basin hosts a substantial regional groundwater system that provides much of the flow to major streams and lakes that, in turn, provide water for wildlife habitat and are the principal source of irrigation water for the basin's agricultural economy. Increased allocation of surface water for endangered species in the past decade has resulted in increased groundwater pumping and growing interest in the use of groundwater for irrigation. The potential effects of increased groundwater pumping on groundwater levels and discharge to springs and streams has caused concern among groundwater users, wildlife and Tribal interests, and State and Federal resource managers. To provide information on the potential impacts of increased groundwater development and to aid in the development of a groundwater management strategy, the U.S. Geological Survey, in collaboration with the Oregon Water Resources Department and the Bureau of Reclamation, has developed a groundwater model that can simulate the response of the hydrologic system to these new stresses. The groundwater model was developed using the U.S. Geological Survey MODFLOW finite-difference modeling code and calibrated using inverse methods to transient conditions from 1989 through 2004 with quarterly stress periods. Groundwater recharge and agricultural and municipal pumping are specified for each stress period. All major streams and most major tributaries for which a substantial part of the flow comes from groundwater discharge are included in the model. Groundwater discharge to agricultural drains, evapotranspiration from aquifers in areas of shallow groundwater, and groundwater flow to and from adjacent basins also are simulated in key areas. The model has the capability to calculate the effects of pumping and other external stresses on groundwater levels, discharge to streams, and other boundary fluxes, such as discharge to drains. Historical data indicate that the groundwater system in the upper Klamath Basin fluctuates in response to decadal climate cycles, with groundwater levels and spring flows rising and declining in response to wet and dry periods. Data also show that groundwater levels fluctuate seasonally and interannually in response to groundwater pumping. The most prominent response is to the marked increase in groundwater pumping starting in 2001. The calibrated model is able to simulate observed decadal-scale climate-driven fluctuations in the groundwater system as well as observed shorter-term pumping-related fluctuations. Example model simulations show that the timing and location of the effects of groundwater pumping vary markedly depending on the pumping location. Pumping from wells close (within a few miles) to groundwater discharge features, such as springs, drains, and certain streams, can affect those features within weeks or months of the onset of pumping, and the impacts can be essentially fully manifested in several years. Simulations indicate that seasonal variations in pumping rates are buffered by the groundwater system, and peak impacts are closer to mean annual pumping rates than to instantaneous rates. Thus, pumping effects are, to a large degree, spread out over the entire year. When pumping locations are distant (more than several miles) from discharge features, the effects take many years or decades to fully impact those features, and much of the pumped water comes from groundwater storage over a broad geographic area even after two decades. Moreover, because the effects are spread out over a broad area, the impacts to individual features are much smaller than in the case of nearby pumping. Simulations show that the discharge features most affected by pumping in the area of the Bureau of Reclamation's Klamath Irrigation Project are agricultural drains, and impacts to other surface-water features are small in comparison. A groundwater management model was developed that uses techniques of constrained optimization along with the groundwater flow model to identify the optimal strategy to meet water user needs while not violating defined constraints on impacts to groundwater levels and streamflows. The coupled groundwater simulation-optimization models were formulated to help identify strategies to meet water demand in the upper Klamath Basin. The models maximize groundwater pumping while simultaneously keeping the detrimental impacts of pumping on groundwater levels and groundwater discharge within prescribed limits. Total groundwater withdrawals were calculated under alternative constraints for drawdown, reductions in groundwater discharge to surface water, and water demand to understand the potential benefits and limitations for groundwater development in the upper Klamath Basin. The simulation-optimization model for the upper Klamath Basin provides an improved understanding of how the groundwater and surface-water system responds to sustained groundwater pumping within the Bureau of Reclamation's Klamath Project. Optimization model results demonstrate that a certain amount of supplemental groundwater pumping can occur without exceeding defined limits on drawdown and stream capture. The results of the different applications of the model demonstrate the importance of identifying constraint limits in order to better define the amount and distribution of groundwater withdrawal that is sustainable.

Simulation of groundwater flow and the interaction of groundwater and surface water in the Willamette Basin and Central Willamette subbasin, Oregon

USGS Publications Warehouse

Herrera, Nora B.; Burns, Erick R.; Conlon, Terrence D.

2014-01-01

Full appropriation of tributary streamflow during summer, a growing population, and agricultural needs are increasing the demand for groundwater in the Willamette Basin. Greater groundwater use could diminish streamflow and create seasonal and long-term declines in groundwater levels. The U.S. Geological Survey (USGS) and the Oregon Water Resources Department (OWRD) cooperated in a study to develop a conceptual and quantitative understanding of the groundwater-flow system of the Willamette Basin with an emphasis on the Central Willamette subbasin. This final report from the cooperative study describes numerical models of the regional and local groundwater-flow systems and evaluates the effects of pumping on groundwater and surface‑water resources. The models described in this report can be used to evaluate spatial and temporal effects of pumping on groundwater, base flow, and stream capture. The regional model covers about 6,700 square miles of the 12,000-square mile Willamette and Sandy River drainage basins in northwestern Oregon—referred to as the Willamette Basin in this report. The Willamette Basin is a topographic and structural trough that lies between the Coast Range and the Cascade Range and is divided into five sedimentary subbasins underlain and separated by basalts of the Columbia River Basalt Group (Columbia River basalt) that crop out as local uplands. From north to south, these five subbasins are the Portland subbasin, the Tualatin subbasin, the Central Willamette subbasin, the Stayton subbasin, and the Southern Willamette subbasin. Recharge in the Willamette Basin is primarily from precipitation in the uplands of the Cascade Range, Coast Range, and western Cascades areas. Groundwater moves downward and laterally through sedimentary or basalt units until it discharges locally to wells, evapotranspiration, or streams. Mean annual groundwater withdrawal for water years 1995 and 1996 was about 400 cubic feet per second; irrigation withdrawals accounted for about 80 percent of that total. The upper 180 feet of productive aquifers in the Central Willamette and Southern Willamette subbasins produced about 70 percent of the total pumped volume. In this study, the USGS constructed a three-dimensional numerical finite-difference groundwater-flow model of the Willamette Basin representing the six hydrogeologic units, defined in previous investigations, as six model layers. From youngest to oldest, and [generally] uppermost to lowermost they are the: upper sedimentary unit, Willamette silt unit, middle sedimentary unit, lower sedimentary unit, Columbia River basalt unit, and basement confining unit. The high Cascade unit is not included in the groundwater-flow model because it is not present within the model boundaries. Geographic boundaries are simulated as no-flow (no water flowing in or out of the model), except where the Columbia River is simulated as a constant hydraulic head boundary. Streams are designated as head-dependent-flux boundaries, in which the flux depends on the elevation of the stream surface. Groundwater recharge from precipitation was estimated using the Precipitation-Runoff Modeling System (PRMS), a watershed model that accounts for evapotranspiration from the unsaturated zone. Evapotranspiration from the saturated zone was not considered an important component of groundwater discharge. Well pumping was simulated as specified flux and included public supply, irrigation, and industrial pumping. Hydraulic conductivity values were estimated from previous studies through aquifer slug and permeameter tests, specific capacity data, core analysis, and modeling. Upper, middle and lower sedimentary unit horizontal hydraulic conductivity values were differentiated between the Portland subbasin and the Tualatin, Central Willamette, and Southern Willamette subbasins based on preliminary model results.

Assessing the groundwater recharge under various irrigation schemes in Central Taiwan

NASA Astrophysics Data System (ADS)

Chen, Shih-Kai; Jang, Cheng-Shin; Lin, Zih-Ciao; Tsai, Cheng-Bin

2014-05-01

The flooded paddy fields can be considered as a major source of groundwater recharge in Central Taiwan. The risk of rice production has increased notably due to climate change in this area. To respond to agricultural water shortage caused by climate change without affecting rice yield in the future, the application of water-saving irrigation is the substantial resolution. The System of Rice Intensification (SRI) was developed as a set of insights and practices used in growing irrigated rice. Based on the water-saving irrigation practice of SRI, impacts of the new methodology on the reducing of groundwater recharge were assessed in central Taiwan. The three-dimensional finite element groundwater model (FEMWATER) with the variable boundary condition analog functions, was applied in simulating groundwater recharge under different irrigation schemes. According to local climatic and environmental characteristics associated with SRI methodology, the change of infiltration rate was evaluated and compared with the traditional irrigation schemes, including continuous irrigation and rotational irrigation scheme. The simulation results showed that the average infiltration rate in the rice growing season decreased when applying the SRI methodology, and the total groundwater recharge amount of SRI with a 5-day irrigation interval reduced 12% and 9% compared with continuous irrigation (6cm constant ponding water depth) and rotational scheme (5-day irrigation interval with 6 cm initial ponding water depth), respectively. The results could be used as basis for planning long-term adaptive water resource management strategies to climate change in Central Taiwan. Keywords: SRI, Irrigation schemes, Groundwater recharge, Infiltration

A Block Iterative Finite Element Model for Nonlinear Leaky Aquifer Systems

NASA Astrophysics Data System (ADS)

Gambolati, Giuseppe; Teatini, Pietro

1996-01-01

A new quasi three-dimensional finite element model of groundwater flow is developed for highly compressible multiaquifer systems where aquitard permeability and elastic storage are dependent on hydraulic drawdown. The model is solved by a block iterative strategy, which is naturally suggested by the geological structure of the porous medium and can be shown to be mathematically equivalent to a block Gauss-Seidel procedure. As such it can be generalized into a block overrelaxation procedure and greatly accelerated by the use of the optimum overrelaxation factor. Results for both linear and nonlinear multiaquifer systems emphasize the excellent computational performance of the model and indicate that convergence in leaky systems can be improved up to as much as one order of magnitude.

Large-scale water resources management within the framework of GLOWA-Danube. Part A: The groundwater model

NASA Astrophysics Data System (ADS)

Barthel, Roland; Rojanschi, Vlad; Wolf, Jens; Braun, Juergen

The research project GLOWA-Danube, financed by the German Federal Government, is investigating long-term changes in the water cycle of the upper Danube river basin (77,000 km 2) in light of global climatic change. Its aim is to build a fully integrated decision-support tool “DANUBIA” that combines the competence of 11 different research institutes in domains covering all major aspects governing the water cycle-from the formation of clouds, to groundwater flow patterns, to the behaviour of the water consumer. Both the influence of natural changes in the ecosystem, such as climate change, and changes in human behaviour, such as changes in land use or water consumption, are considered. DANUBIA is comprised of 15 individual disciplinary models that are connected via customized interfaces that facilitate network-based parallel calculations. The strictly object-oriented DANUBIA architecture was developed using the graphical notation tool UML (Unified Modeling Language) and has been implemented in Java code. All models use the same spatial discretisation for the exchange of data (1 × 1 km grid cells) but are using different time steps. The representation of a vast number of relevant physical and social processes that occur at different spatial and temporal scales is a very demanding task. Newly developed up- and downscaling procedures [Rojanschi, V., 2001. Effects of upscaling for a finite-difference flow model. Master’s Thesis, Institut für Wasserbau, Universität Stuttgart, Stuttgart, Germany] and a sophisticated time controller developed by the computer sciences group [Hennicker, R., Barth, M., Kraus, A., Ludwig, M., 2002. DANUBIA: A Web-based modelling and decision support system for integrative global change research in the upper Danube basin. In: GSF (Ed.), GLOWA, German Program on Global Change in the Hydrological Cycle Status Report 2002. GSF, Munich, pp. 35-38; Kraus, A., Ludwig, M., 2003. GLOWA-Danube Papers Technical Release No. 002 (Danubia Framework), Software-Release No.: 0.9.2, Documentation Version: 0.10, Release Date: 27 March 2003] are required to solve the emerging problems. After a first successful public demonstration of the DANUBIA package (nine models) in May 2002 [Mauser, W., Stolz, R., Colgan, A., 2002. GLOWA-Danube: integrative techniques, scenarios and strategies regarding global change of the water cycle. In: GSF (Ed.), GLOWA, German Program on Global Change in the Hydrological Cycle (Phase I, 2000-2003) Status Report 2002. GSF, Munich, pp. 31-34], the research consortium is now preparing a first validation run of DANUBIA for the period 1995-1999 with all 15 models. After successful completion of the validation, a scenario run based on IPCC climate scenarios [IPCC, 2001. Climate Change 2001: Synthesis Report. In: Watson, R.T., Core Writing Team (Eds.), A Contribution of Working Groups I, II, and III to the Third Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press, Cambridge, UK and New York, NY, USA, 398pp] for a five year period between 2025 and 2040 will follow at the end of 2003. The research group “Groundwater and Water Resources Management” at the Institute of Hydraulic Engineering, Universität Stuttgart, is contributing both a three-dimensional groundwater flow model of the catchment and an agent-based model for simulating water supply and distribution. This paper gives a general overview of the GLOWA-Danube project and describes the groundwater modeling segment. Nickel et al. deal with the water supply model in a second contribution to this special issue. A three-dimensional numerical groundwater flow model consisting of four main layers has been developed and is in a continual state of refinement (MODFLOW, [McDonald, M.G., Harbaugh, A.W., 1988. A modular three-dimensional finite-difference ground-water flow model: US Geological Survey Techniques of Water-Resources Investigations, Washington, USA (book 6, Chapter A1)]). One main research focus has been on the investigation of upscaling techniques to meet the requirement of a fixed 1 × 1 km cell size. This cell size is compulsory for all models in DANUBIA in order to facilitate a one to one parameter exchange. In a second stage, a transport model (nitrogen) will be added (MT3D: [Zheng, C., Hathaway, D.-L., 1991. MT3D: a new modular three-dimensional transport model and its application in predicting the persistence and transport of dissolved compounds from a gasoline spill, with implications for remediation. Association of Ground Water Scientists and Engineers Annual Meeting on Innovative Ground Water Technologies for the ’90s, National Ground Water Association, Westerville, Ohio, USA. Ground Water 29 (5)].

Integrated surface and groundwater modelling in the Thames Basin, UK using the Open Modelling Interface

NASA Astrophysics Data System (ADS)

Mackay, Jonathan; Abesser, Corinna; Hughes, Andrew; Jackson, Chris; Kingdon, Andrew; Mansour, Majdi; Pachocka, Magdalena; Wang, Lei; Williams, Ann

2013-04-01

The River Thames catchment is situated in the south-east of England. It covers approximately 16,000 km2 and is the most heavily populated river basin in the UK. It is also one of the driest and has experienced severe drought events in the recent past. With the onset of climate change and human exploitation of our environment, there are now serious concerns over the sustainability of water resources in this basin with 6 million m3 consumed every day for public water supply alone. Groundwater in the Thames basin is extremely important, providing 40% of water for public supply. The principal aquifer is the Chalk, a dual permeability limestone, which has been extensively studied to understand its hydraulic properties. The fractured Jurassic limestone in the upper catchment also forms an important aquifer, supporting baseflow downstream during periods of drought. These aquifers are unconnected other than through the River Thames and its tributaries, which provide two-thirds of London's drinking water. Therefore, to manage these water resources sustainably and to make robust projections into the future, surface and groundwater processes must be considered in combination. This necessitates the simulation of the feedbacks and complex interactions between different parts of the water cycle, and the development of integrated environmental models. The Open Modelling Interface (OpenMI) standard provides a method through which environmental models of varying complexity and structure can be linked, allowing them to run simultaneously and exchange data at each timestep. This architecture has allowed us to represent the surface and subsurface flow processes within the Thames basin at an appropriate level of complexity based on our understanding of particular hydrological processes and features. We have developed a hydrological model in OpenMI which integrates a process-driven, gridded finite difference groundwater model of the Chalk with a more simplistic, semi-distributed conceptual model of the Jurassic limestone. A distributed river routing model of the Thames has also been integrated to connect the surface and subsurface hydrological processes. This application demonstrates the potential benefits and issues associated with implementing this approach.

Documentation of a computer program to simulate aquifer-system compaction using the modular finite-difference ground-water flow model

USGS Publications Warehouse

Leake, S.A.; Prudic, David E.

1991-01-01

Removal of ground water by pumping from aquifers may result in compaction of compressible fine-grained beds that are within or adjacent to the aquifers. Compaction of the sediments and resulting land subsidence may be permanent if the head declines result in vertical stresses beyond the previous maximum stress. The process of permanent compaction is not routinely included in simulations of ground-water flow. To simulate storage changes from both elastic and inelastic compaction, a computer program was written for use with the U.S. Geological Survey modular finite-difference ground- water flow model. The new program, the Interbed-Storage Package, is designed to be incorporated into this model. In the Interbed-Storage Package, elastic compaction or expansion is assumed to be proportional to change in head. The constant of proportionality is the product of the skeletal component of elastic specific storage and the thickness of the sediments. Similarly, inelastic compaction is assumed to be proportional to decline in head. The constant of proportionality is the product of the skeletal component of inelastic specific storage and the thickness of the sediments. Storage changes are incorporated into the ground-water flow model by adding an additional term to the right-hand side of the flow equation. Within a model time step, the package appropriately apportions storage changes between elastic and inelastic components on the basis of the relation of simulated head to the previous minimum (preconsolidation) head. Two tests were performed to verify that the package works correctly. The first test compared model-calculated storage and compaction changes to hand-calculated values for a three-dimensional simulation. Model and hand-calculated values were essentially equal. The second test was performed to compare the results of the Interbed-Storage Package with results of the one-dimensional Helm compaction model. This test problem simulated compaction in doubly draining confining beds stressed by head changes in adjacent aquifers. The Interbed-Storage Package and the Helm model computed essentially equal values of compaction. Documentation of the Interbed-Storage Package includes data input instructions, flow charts, narratives, and listings for each of the five modules included in the package. The documentation also includes an appendix describing input instructions and a listing of a computer program for time-variant specified-head boundaries. That package was developed to reduce the amount of data input and output associated with one of the Interbed-Storage Package test problems.

SutraPrep, a pre-processor for SUTRA, a model for ground-water flow with solute or energy transport

USGS Publications Warehouse

Provost, Alden M.

2002-01-01

SutraPrep facilitates the creation of three-dimensional (3D) input datasets for the USGS ground-water flow and transport model SUTRA Version 2D3D.1. It is most useful for applications in which the geometry of the 3D model domain and the spatial distribution of physical properties and boundary conditions is relatively simple. SutraPrep can be used to create a SUTRA main input (?.inp?) file, an initial conditions (?.ics?) file, and a 3D plot of the finite-element mesh in Virtual Reality Modeling Language (VRML) format. Input and output are text-based. The code can be run on any platform that has a standard FORTRAN-90 compiler. Executable code is available for Microsoft Windows.

Groundwater availability in the Crouch Branch and McQueen Branch aquifers, Chesterfield County, South Carolina, 1900-2012

USGS Publications Warehouse

Campbell, Bruce G.; Landmeyer, James E.

2014-01-01

Chesterfield County is located in the northeastern part of South Carolina along the southern border of North Carolina and is primarily underlain by unconsolidated sediments of Late Cretaceous age and younger of the Atlantic Coastal Plain. Approximately 20 percent of Chesterfield County is in the Piedmont Physiographic Province, and this area of the county is not included in this study. These Atlantic Coastal Plain sediments compose two productive aquifers: the Crouch Branch aquifer that is present at land surface across most of the county and the deeper, semi-confined McQueen Branch aquifer. Most of the potable water supplied to residents of Chesterfield County is produced from the Crouch Branch and McQueen Branch aquifers by a well field located near McBee, South Carolina, in the southwestern part of the county. Overall, groundwater availability is good to very good in most of Chesterfield County, especially the area around and to the south of McBee, South Carolina. The eastern part of Chesterfield County does not have as abundant groundwater resources but resources are generally adequate for domestic purposes. The primary purpose of this study was to determine groundwater-flow rates, flow directions, and changes in water budgets over time for the Crouch Branch and McQueen Branch aquifers in the Chesterfield County area. This goal was accomplished by using the U.S. Geological Survey finite-difference MODFLOW groundwater-flow code to construct and calibrate a groundwater-flow model of the Atlantic Coastal Plain of Chesterfield County. The model was created with a uniform grid size of 300 by 300 feet to facilitate a more accurate simulation of groundwater-surface-water interactions. The model consists of 617 rows from north to south extending about 35 miles and 884 columns from west to east extending about 50 miles, yielding a total area of about 1,750 square miles. However, the active part of the modeled area, or the part where groundwater flow is simulated, totaled about 1,117 square miles. Major types of data used as input to the model included groundwater levels, groundwater-use data, and hydrostratigraphic data, along with estimates and measurements of stream base flows made specifically for this study. The groundwater-flow model was calibrated to groundwater-level and stream base-flow conditions from 1900 to 2012 using 39 stress periods. The model was calibrated with an automated parameter-estimation approach using the computer program PEST, and the model used regularized inversion and pilot points. The groundwater-flow model was calibrated using field data that included groundwater levels that had been collected between 1940 and 2012 from 239 wells and base-flow measurements from 44 locations distributed within the study area. To better understand recharge and inter-aquifer interactions, seven wells were equipped with continuous groundwater-level recording equipment during the course of the study, between 2008 and 2012. These water levels were included in the model calibration process. The observed groundwater levels were compared to the simulated ones, and acceptable calibration fits were achieved. Root mean square error for the simulated groundwater levels compared to all observed groundwater levels was 9.3 feet for the Crouch Branch aquifer and 8.6 feet for the McQueen Branch aquifer. The calibrated groundwater-flow model was then used to calculate groundwater budgets for the entire study area and for two sub-areas. The sub-areas are the Alligator Rural Water and Sewer Company well field near McBee, South Carolina, and the Carolina Sandhills National Wildlife Refuge acquisition boundary area. For the overall model area, recharge rates vary from 56 to 1,679 million gallons per day (Mgal/d) with a mean of 737 Mgal/d over the simulation period (1900–2012). The simulated water budget for the streams and rivers varies from 653 to 1,127 Mgal/d with a mean of 944 Mgal/d. The simulated “storage-in term” ranges from 0 to 565 Mgal/d with a mean of 276 Mgal/d. The simulated “storage-out term” has a range of 0 to 552 Mgal/d with a mean of 77 Mgal/d. Groundwater budgets for the McBee, South Carolina, area and the Carolina Sandhills National Wildlife Refuge acquisition area had similar results. An analysis of the effects of past and current groundwater withdrawals on base flows in the McBee area indicated a negligible effect of pumping from the Alligator Rural Water and Sewer well field on local stream base flows. Simulate base flows for 2012 for selected streams in and around the McBee area were similar with and without simulated groundwater withdrawals from the well field. Removing all pumping from the model for the entire simulation period (1900–2012) produces a negligible difference in increased base flow for the selected streams. The 2012 flow for Lower Alligator Creek was 5.04 Mgal/d with the wells pumping and 5.08 Mgal/d without the wells pumping; this represents the largest difference in simulated flows for the six streams.

One-dimensional analytical solution for hydraulic head and numerical solution for solute transport through a horizontal fracture for submarine groundwater discharge.

PubMed

He, Cairong; Wang, Tongke; Zhao, Zhixue; Hao, Yonghong; Yeh, Tian-Chyi J; Zhan, Hongbin

2017-11-01

Submarine groundwater discharge (SGD) has been recognized as a major pathway of groundwater flow to coastal oceanic environments. It could affect water quality and marine ecosystems due to pollutants and trace elements transported through groundwater. Relations between different characteristics of aquifers and SGD have been investigated extensively before, but the role of fractures in SGD still remains unknown. In order to better understand the mechanism of groundwater flow and solute transport through fractures in SGD, one-dimensional analytical solutions of groundwater hydraulic head and velocity through a synthetic horizontal fracture with periodic boundary conditions were derived using a Laplace transform technique. Then, numerical solutions of solute transport associated with the given groundwater velocity were developed using a finite-difference method. The results indicated that SGD associated with groundwater flow and solute transport was mainly controlled by sea level periodic fluctuations, which altered the hydraulic head and the hydraulic head gradient in the fracture. As a result, the velocity of groundwater flow associated with SGD also fluctuated periodically. We found that the pollutant concentration associated with SGD oscillated around a constant value, and could not reach a steady state. This was particularly true at locations close to the seashore. This finding of the role of fracture in SGD will assist pollution remediation and marine conservation in coastal regions. Copyright © 2017 Elsevier B.V. All rights reserved.

One-dimensional analytical solution for hydraulic head and numerical solution for solute transport through a horizontal fracture for submarine groundwater discharge

NASA Astrophysics Data System (ADS)

He, Cairong; Wang, Tongke; Zhao, Zhixue; Hao, Yonghong; Yeh, Tian-Chyi J.; Zhan, Hongbin

2017-11-01

Submarine groundwater discharge (SGD) has been recognized as a major pathway of groundwater flow to coastal oceanic environments. It could affect water quality and marine ecosystems due to pollutants and trace elements transported through groundwater. Relations between different characteristics of aquifers and SGD have been investigated extensively before, but the role of fractures in SGD still remains unknown. In order to better understand the mechanism of groundwater flow and solute transport through fractures in SGD, one-dimensional analytical solutions of groundwater hydraulic head and velocity through a synthetic horizontal fracture with periodic boundary conditions were derived using a Laplace transform technique. Then, numerical solutions of solute transport associated with the given groundwater velocity were developed using a finite-difference method. The results indicated that SGD associated with groundwater flow and solute transport was mainly controlled by sea level periodic fluctuations, which altered the hydraulic head and the hydraulic head gradient in the fracture. As a result, the velocity of groundwater flow associated with SGD also fluctuated periodically. We found that the pollutant concentration associated with SGD oscillated around a constant value, and could not reach a steady state. This was particularly true at locations close to the seashore. This finding of the role of fracture in SGD will assist pollution remediation and marine conservation in coastal regions.

The U.S. Geological Survey Modular Ground-Water Model - PCGN: A Preconditioned Conjugate Gradient Solver with Improved Nonlinear Control

USGS Publications Warehouse

Naff, Richard L.; Banta, Edward R.

2008-01-01

The preconditioned conjugate gradient with improved nonlinear control (PCGN) package provides addi-tional means by which the solution of nonlinear ground-water flow problems can be controlled as compared to existing solver packages for MODFLOW. Picard iteration is used to solve nonlinear ground-water flow equations by iteratively solving a linear approximation of the nonlinear equations. The linear solution is provided by means of the preconditioned conjugate gradient algorithm where preconditioning is provided by the modi-fied incomplete Cholesky algorithm. The incomplete Cholesky scheme incorporates two levels of fill, 0 and 1, in which the pivots can be modified so that the row sums of the preconditioning matrix and the original matrix are approximately equal. A relaxation factor is used to implement the modified pivots, which determines the degree of modification allowed. The effects of fill level and degree of pivot modification are briefly explored by means of a synthetic, heterogeneous finite-difference matrix; results are reported in the final section of this report. The preconditioned conjugate gradient method is coupled with Picard iteration so as to efficiently solve the nonlinear equations associated with many ground-water flow problems. The description of this coupling of the linear solver with Picard iteration is a primary concern of this document.

Simulation analysis of the ground-water system in Mesozoic rocks in the Four Corners area, Utah, Colorado, Arizona, and New Mexico

USGS Publications Warehouse

Thomas, B.E.

1989-01-01

The steady-state groundwater system in Mesozoic rocks in the Four Corners area, Utah, Colorado, Arizona, and New Mexico, was simulated with a finite-difference digital-computer model to improve the understanding of the system. The simulated area is 4 ,100 sq mi, and it includes three aquifers. The Entrada-Navajo aquifer includes the Wingate, Navajo, and Entrada Sandstones. The Morrison aquifer includes the sandstone units of the Morrison Formation. The Dakota aquifer includes the Burro Canyon Formation and Dakota Sandstone. The simulation of the groundwater system had a mean error (error is absolute value of residual) of 70 ft for the Entrada-Navajo aquifer, 67 ft for the Morrison aquifer and 79 ft for the Dakota aquifer. The hydraulic conductivity used in the simulation ranged from 0.38 to 0.47 ft/day. Simulated inflow to the groundwater system was 30,000 acre-ft/yr. 48% of the inflow is from infiltration of precipitation within the simulated area, and 42% is from infiltration in 145 sq mi of mountain areas adjacent to the simulated area. Simulations indicated that some vertical inflow of water is needed between the Entrada-Navajo and Morrison aquifers to develop a reasonable representation of the system. (USGS)

Estimating the uncertainty of the impact of climate change on alluvial aquifers. Case study in central Italy

NASA Astrophysics Data System (ADS)

Romano, Emanuele; Camici, Stefania; Brocca, Luca; Moramarco, Tommaso; Pica, Federico; Preziosi, Elisabetta

2014-05-01

There is evidence that the precipitation pattern in Europe is trending towards more humid conditions in the northern region and drier conditions in the southern and central-eastern regions. However, a great deal of uncertainty concerns how the changes in precipitations will have an impact on water resources, particularly on groundwater, and this uncertainty should be evaluated on the basis of that coming from 1) future climate scenarios of Global Circulation Models (GCMs) and 2) modeling chains including the downscaling technique, the infiltration model and the calibration/validation procedure used to develop the groundwater flow model. With the aim of quantifying the uncertainty of these components, the Valle Umbra porous aquifer (Central Italy) has been considered as a case study. This aquifer, that is exploited for human consumption and irrigation, is mainly fed by the effective infiltration from the ground surface and partly by the inflow from the carbonate aquifers bordering the valley. A numerical groundwater flow model has been developed through the finite difference MODFLOW2005 code and it has been calibrated and validated considering the recharge regime computed through a Thornthwaite-Mather infiltration model under the climate conditions observed in the period 1956-2012. Future scenarios (2010-2070) of temperature and precipitation have been obtained from three different GMCs: ECHAM-5 (Max Planck Institute, Germany), PCM (National Centre Atmospheric Research) and CCSM3 (National Centre Atmospheric Research). Each scenario has been downscaled (DSC) to the data of temperature and precipitation collected in the baseline period 1960-1990 at the stations located in the study area through two different statistical techniques (linear rescaling and quantile mapping). Then, stochastic rainfall and temperature time series are generated through the Neyman-Scott Rectangular Pulses model (NSRP) for precipitation and the Fractionally Differenced ARIMA model (FARIMA) for temperature. Such a procedure has allowed to estimate, through the Thornthwaite-Mather model, the uncertainty related to the future scenarios of recharge to the aquifer. Finally, all the scenarios of recharge have been used as input to the groundwater flow model and the results have been evaluated in terms of the uncertainty on the computed aquifer heads and total budget. The main results have indicated that most of the uncertainty on the impact to the aquifer arise from the uncertainty on the first part of the processing chain GCM-DSC.

A compositional multiphase model for groundwater contamination by petroleum products: 2. Numerical solution

USGS Publications Warehouse

Baehr, Arthur L.; Corapcioglu, M. Yavuz

1987-01-01

In this paper we develop a numerical solution to equations developed in part 1 (M. Y. Corapcioglu and A. L. Baehr, this issue) to predict the fate of an immiscible organic contaminant such as gasoline in the unsaturated zone subsequent to plume establishment. This solution, obtained by using a finite difference scheme and a method of forward projection to evaluate nonlinear coefficients, provides estimates of the flux of solubilized hydrocarbon constituents to groundwater from the portion of a spill which remains trapped in a soil after routine remedial efforts to recover the product have ceased. The procedure was used to solve the one-dimensional (vertical) form of the system of nonlinear partial differential equations defining the transport for each constituent of the product. Additionally, a homogeneous, isothermal soil with constant water content was assumed. An equilibrium assumption partitions the constituents between air, water, adsorbed, and immiscible phases. Free oxygen transport in the soil was also simulated to provide an upper bound estimate of aerobic biodgradation rates. Results are presented for a hypothetical gasoline consisting of eight groups of hydrocarbon constituents. Rates at which hydrocarbon mass is removed from the soil, entering either the atmosphere or groundwater, or is biodegraded are presented. A significant sensitivity to model parameters, particularly the parameters characterizing diffusive vapor transport, was discovered. We conclude that hydrocarbon solute composition in groundwater beneath a gasoline contaminated soil would be heavily weighted toward aromatic constituents like benzene, toluene, and xylene.

First status report on regional ground-water flow modeling for the Paradox Basin, Utah

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andrews, R.W.

1984-05-01

Regional ground-water flow within the principal hydrogeologic units of the Paradox Basin is evaluated by developing a conceptual model of the flow regime in the shallow aquifers and the deep-basin brine aquifers and testing these models using a three-dimensional, finite-difference flow code. Semiquantitative sensitivity analysis (a limited parametric study) is conducted to define the system response to changes in hydrologic properties or boundary conditions. A direct method for sensitivity analysis using an adjoint form of the flow equation is applied to the conceptualized flow regime in the Leadville limestone aquifer. All steps leading to the final results and conclusions aremore » incorporated in this report. The available data utilized in this study is summarized. The specific conceptual models, defining the areal and vertical averaging of litho-logic units, aquifer properties, fluid properties, and hydrologic boundary conditions, are described in detail. Two models were evaluated in this study: a regional model encompassing the hydrogeologic units above and below the Paradox Formation/Hermosa Group and a refined scale model which incorporated only the post Paradox strata. The results are delineated by the simulated potentiometric surfaces and tables summarizing areal and vertical boundary fluxes, Darcy velocities at specific points, and ground-water travel paths. Results from the adjoint sensitivity analysis include importance functions and sensitivity coefficients, using heads or the average Darcy velocities to represent system response. The reported work is the first stage of an ongoing evaluation of the Gibson Dome area within the Paradox Basin as a potential repository for high-level radioactive wastes.« less

Potential depletion of surface water in the Colorado River and agricultural drains by groundwater pumping in the Parker-Palo Verde-Cibola area, Arizona and California

USGS Publications Warehouse

Leake, Stanley A.; Owen-Joyce, Sandra J.; Heilman, Julian A.

2013-01-01

Water use along the lower Colorado River is allocated as “consumptive use,” which is defined to be the amount of water diverted from the river minus the amount that returns to the river. Diversions of water from the river include surface water in canals and water removed from the river by pumping wells in the aquifer connected to the river. A complication in accounting for water pumped by wells occurs if the pumping depletes water in drains and reduces measured return flow in those drains. In that case, consumptive use of water pumped by the wells is accounted for in the reduction of measured return flow. A method is needed to understand where groundwater pumping will deplete water in the river and where it will deplete water in drains. To provide a basis for future accounting for pumped groundwater in the Parker-Palo Verde-Cibola area, a superposition model was constructed. The model consists of three layers of finite-difference cells that cover most of the aquifer in the study area. The model was run repeatedly with each run having a pumping well in a different model cell. The source of pumped water that is depletion of the river, expressed as a fraction of the pumping rate, was computed for all active cells in model layer 1, and maps were constructed to understand where groundwater pumping depletes the river and where it depletes drains. The model results indicate that if one or more drains exist between a pumping well location and the river, nearly all of the depletion will be from drains, and little or no depletion will come from the Colorado River. Results also show that if a well pumps on a side of the river with no drains in the immediate area, depletion will come from the Colorado River. Finally, if a well pumps between the river and drains that parallel the river, a fraction of the pumping will come from the river and the rest will come from the drains. Model results presented in this report may be considered in development or refinement of strategies for accounting for groundwater pumping in the river aquifer connected to the Colorado River in the study area.

Ground-Water Flow Model for the Spokane Valley-Rathdrum Prairie Aquifer, Spokane County, Washington, and Bonner and Kootenai Counties, Idaho

USGS Publications Warehouse

Hsieh, Paul A.; Barber, Michael E.; Contor, Bryce A.; Hossain, Md. Akram; Johnson, Gary S.; Jones, Joseph L.; Wylie, Allan H.

2007-01-01

This report presents a computer model of ground-water flow in the Spokane Valley-Rathdrum Prairie (SVRP) aquifer in Spokane County, Washington, and Bonner and Kootenai Counties, Idaho. The aquifer is the sole source of drinking water for more than 500,000 residents in the area. In response to the concerns about the impacts of increased ground-water withdrawals resulting from recent and projected urban growth, a comprehensive study was initiated by the Idaho Department of Water Resources, the Washington Department of Ecology, and the U.S. Geological Survey to improve the understanding of ground-water flow in the aquifer and of the interaction between ground water and surface water. The ground-water flow model presented in this report is one component of this comprehensive study. The primary purpose of the model is to serve as a tool for analyzing aquifer inflows and outflows, simulating the effects of future changes in ground-water withdrawals from the aquifer, and evaluating aquifer management strategies. The scale of the model and the level of detail are intended for analysis of aquifer-wide water-supply issues. The SVRP aquifer model was developed by the Modeling Team formed within the comprehensive study. The Modeling Team consisted of staff and personnel working under contract with the Idaho Department of Water Resources, personnel working under contract with the Washington Department of Ecology, and staff of the U.S. Geological Survey. To arrive at a final model that has the endorsement of all team members, decisions on modeling approach, methodology, assumptions, and interpretations were reached by consensus. The ground-water flow model MODFLOW-2000 was used to simulate ground-water flow in the SVPR aquifer. The finite-difference model grid consists of 172 rows, 256 columns, and 3 layers. Ground-water flow was simulated from September 1990 through September 2005 using 181 stress periods of 1 month each. The areal extent of the model encompasses an area of approximately 326 square miles. For the most part, the model extent coincides with the 2005 revised extent of the Spokane Valley-Rathdrum Prairie aquifer as defined in a previous report. However, the model excludes Spirit and Hoodoo Valleys because of uncertainties about the ground-water flow directions in those valleys and the degree of hydraulic connection between the valleys and northern Rathdrum Prairie. The SVRP aquifer is considered to be a single hydrogeologic unit except in Hillyard Trough and the Little Spokane River Arm. In those areas, a continuous clay layer divides the aquifer into an upper, unconfined unit and a lower, confined unit. The model includes all known components of inflows to and outflows from the aquifer. Inflows to the SVRP aquifer include (1) recharge from precipitation, (2) inflows from tributary basins and adjacent uplands, (3) subsurface seepage and surface overflows from lakes that border the aquifer, (4) flow from losing segments of the Spokane River to the aquifer, (5) return percolation from irrigation, and (6) effluent from septic systems. Outflows from the SVRP aquifer include (1) ground-water withdrawals from wells, (2) flow from the aquifer to gaining segments of the Spokane River, (3) aquifer discharge to the Little Spokane River, and (4) subsurface outflow from the lower unit at the western limit of the model area near Long Lake. These inflow and outflow components are represented in the model by using MODFLOW-2000 packages. The parameter-estimation program PEST was used to calibrate the SVRP aquifer model. PEST implements a nonlinear least-squares regression method to estimate model parameters so that the differences between measured and simulated quantities are minimized with respect to an optimal criterion. Calibration data include 1,573 measurements of water levels and 313 measurements of streamflow gains and losses along segments of the Spokane and Little Spokane Rivers. Model parameters estimated during calib

Nachlassender Nitratabbau im Grundwasser und deren Folgen - abgestufte modellgestützte Bewertungsansätze

NASA Astrophysics Data System (ADS)

Wilde, Siegfried; Hansen, Carsten; Bergmann, Axel

2017-11-01

In many water catchment areas, denitrification processes in aquifers ensure lower nitrate contamination in groundwater. The denitrification capacity of aquifers mainly depends on organic carbon and iron disulfide which, being finite resources, are susceptible to depletion. This will generally result in increasing nitrate concentrations in groundwater. Within the scope of a DVGW-supported research project, consequences of a decreasing denitrification capacity in aquifers have been investigated and evaluated in 38 water catchment areas. A scaled four-stage evaluation procedure enables adapting to specific regional settings and assessment requirements. Based on measured and predicted nitrate concentrations in raw water, the "sustainability" of groundwater resources management has been assessed. Hydrogeochemical models and methods of varying complexity were applied. Thus, consequences and risks of nitrate pollution in raw water can be identified and assessed, and effects of groundwater protection measures can be shown.

Numerical modeling of coupled nitrification-denitrification in sediment perfusion cores from the hyporheic zone of the Shingobee River, MN

USGS Publications Warehouse

Sheibley, R.W.; Jackman, A.P.; Duff, J.H.; Triska, F.J.

2003-01-01

Nitrification and denitrification kinetics in sediment perfusion cores were numerically modeled and compared to experiments on cores from the Shingobee River MN, USA. The experimental design incorporated mixing groundwater discharge with stream water penetration into the cores, which provided a well-defined, one-dimensional simulation of in situ hydrologic conditions. Ammonium (NH+4) and nitrate (NO-3) concentration gradients suggested the upper region of the cores supported coupled nitrification-denitrification, where groundwater-derived NH+4 was first oxidized to NO-3 then subsequently reduced via denitrification to N2. Nitrification and denitrification were modeled using a Crank-Nicolson finite difference approximation to a one-dimensional advection-dispersion equation. Both processes were modeled using first-order reaction kinetics because substrate concentrations (NH+4 and NO-3) were much smaller than published Michaelis constants. Rate coefficients for nitrification and denitrification ranged from 0.2 to 15.8 h-1 and 0.02 to 8.0 h-1, respectively. The rate constants followed an Arrhenius relationship between 7.5 and 22 ??C. Activation energies for nitrification and denitrification were 162 and 97.3 kJ/mol, respectively. Seasonal NH+4 concentration patterns in the Shingobee River were accurately simulated from the relationship between perfusion core temperature and NH+4 flux to the overlying water. The simulations suggest that NH+4 in groundwater discharge is controlled by sediment nitrification that, consistent with its activation energy, is strongly temperature dependent. ?? 2003 Elsevier Ltd. All rights reserved.

Documentation of a graphical display program for the saturated- unsaturated transport (SUTRA) finite-element simulation model

USGS Publications Warehouse

Souza, W.R.

1987-01-01

This report documents a graphical display program for the U. S. Geological Survey finite-element groundwater flow and solute transport model. Graphic features of the program, SUTRA-PLOT (SUTRA-PLOT = saturated/unsaturated transport), include: (1) plots of the finite-element mesh, (2) velocity vector plots, (3) contour plots of pressure, solute concentration, temperature, or saturation, and (4) a finite-element interpolator for gridding data prior to contouring. SUTRA-PLOT is written in FORTRAN 77 on a PRIME 750 computer system, and requires Version 9.0 or higher of the DISSPLA graphics library. The program requires two input files: the SUTRA input data list and the SUTRA simulation output listing. The program is menu driven and specifications for individual types of plots are entered and may be edited interactively. Installation instruction, a source code listing, and a description of the computer code are given. Six examples of plotting applications are used to demonstrate various features of the plotting program. (Author 's abstract)

Modelling water uptake efficiency of root systems

NASA Astrophysics Data System (ADS)

Leitner, Daniel; Tron, Stefania; Schröder, Natalie; Bodner, Gernot; Javaux, Mathieu; Vanderborght, Jan; Vereecken, Harry; Schnepf, Andrea

2016-04-01

Water uptake is crucial for plant productivity. Trait based breeding for more water efficient crops will enable a sustainable agricultural management under specific pedoclimatic conditions, and can increase drought resistance of plants. Mathematical modelling can be used to find suitable root system traits for better water uptake efficiency defined as amount of water taken up per unit of root biomass. This approach requires large simulation times and large number of simulation runs, since we test different root systems under different pedoclimatic conditions. In this work, we model water movement by the 1-dimensional Richards equation with the soil hydraulic properties described according to the van Genuchten model. Climatic conditions serve as the upper boundary condition. The root system grows during the simulation period and water uptake is calculated via a sink term (after Tron et al. 2015). The goal of this work is to compare different free software tools based on different numerical schemes to solve the model. We compare implementations using DUMUX (based on finite volumes), Hydrus 1D (based on finite elements), and a Matlab implementation of Van Dam, J. C., & Feddes 2000 (based on finite differences). We analyse the methods for accuracy, speed and flexibility. Using this model case study, we can clearly show the impact of various root system traits on water uptake efficiency. Furthermore, we can quantify frequent simplifications that are introduced in the modelling step like considering a static root system instead of a growing one, or considering a sink term based on root density instead of considering the full root hydraulic model (Javaux et al. 2008). References Tron, S., Bodner, G., Laio, F., Ridolfi, L., & Leitner, D. (2015). Can diversity in root architecture explain plant water use efficiency? A modeling study. Ecological modelling, 312, 200-210. Van Dam, J. C., & Feddes, R. A. (2000). Numerical simulation of infiltration, evaporation and shallow groundwater levels with the Richards equation. Journal of Hydrology, 233(1), 72-85. Javaux, M., Schröder, T., Vanderborght, J., & Vereecken, H. (2008). Use of a three-dimensional detailed modeling approach for predicting root water uptake. Vadose Zone Journal, 7(3), 1079-1088.

Regional transport modelling for nitrate trend assessment and forecasting in a chalk aquifer.

PubMed

Orban, Philippe; Brouyère, Serge; Batlle-Aguilar, Jordi; Couturier, Julie; Goderniaux, Pascal; Leroy, Mathieu; Maloszewski, Piotr; Dassargues, Alain

2010-10-21

Regional degradation of groundwater resources by nitrate has become one of the main challenges for water managers worldwide. Regulations have been defined to reverse observed nitrate trends in groundwater bodies, such as the Water Framework Directive and the Groundwater Daughter Directive in the European Union. In such a context, one of the main challenges remains to develop efficient approaches for groundwater quality assessment at regional scale, including quantitative numerical modelling, as a decision support for groundwater management. A new approach combining the use of environmental tracers and the innovative 'Hybrid Finite Element Mixing Cell' (HFEMC) modelling technique is developed to study and forecast the groundwater quality at the regional scale, with an application to a regional chalk aquifer in the Geer basin in Belgium. Tritium data and nitrate time series are used to produce a conceptual model for regional groundwater flow and contaminant transport in the combined unsaturated and saturated zones of the chalk aquifer. This shows that the spatial distribution of the contamination in the Geer basin is essentially linked to the hydrodynamic conditions prevailing in the basin, more precisely to groundwater age and mixing and not to the spatial patterns of land use or local hydrodispersive processes. A three-dimensional regional scale groundwater flow and solute transport model is developed. It is able to reproduce the spatial patterns of tritium and nitrate and the observed nitrate trends in the chalk aquifer and it is used to predict the evolution of nitrate concentrations in the basin. The modelling application shows that the global inertia of groundwater quality is strong in the basin and trend reversal is not expected to occur before the 2015 deadline fixed by the European Water Framework Directive. The expected time required for trend reversal ranges between 5 and more than 50 years, depending on the location in the basin and the expected reduction in nitrate application. To reach a good chemical status, nitrate concentrations in the infiltrating water should be reduced as soon as possible below 50mg/l; however, even in that case, more than 50 years is needed to fully reverse upward trends. Copyright © 2010 Elsevier B.V. All rights reserved.

Computer model of two-dimensional solute transport and dispersion in ground water

USGS Publications Warehouse

Konikow, Leonard F.; Bredehoeft, J.D.

1978-01-01

This report presents a model that simulates solute transport in flowing ground water. The model is both general and flexible in that it can be applied to a wide range of problem types. It is applicable to one- or two-dimensional problems involving steady-state or transient flow. The model computes changes in concentration over time caused by the processes of convective transport, hydrodynamic dispersion, and mixing (or dilution) from fluid sources. The model assumes that the solute is non-reactive and that gradients of fluid density, viscosity, and temperature do not affect the velocity distribution. However, the aquifer may be heterogeneous and (or) anisotropic. The model couples the ground-water flow equation with the solute-transport equation. The digital computer program uses an alternating-direction implicit procedure to solve a finite-difference approximation to the ground-water flow equation, and it uses the method of characteristics to solve the solute-transport equation. The latter uses a particle- tracking procedure to represent convective transport and a two-step explicit procedure to solve a finite-difference equation that describes the effects of hydrodynamic dispersion, fluid sources and sinks, and divergence of velocity. This explicit procedure has several stability criteria, but the consequent time-step limitations are automatically determined by the program. The report includes a listing of the computer program, which is written in FORTRAN IV and contains about 2,000 lines. The model is based on a rectangular, block-centered, finite difference grid. It allows the specification of any number of injection or withdrawal wells and of spatially varying diffuse recharge or discharge, saturated thickness, transmissivity, boundary conditions, and initial heads and concentrations. The program also permits the designation of up to five nodes as observation points, for which a summary table of head and concentration versus time is printed at the end of the calculations. The data input formats for the model require three data cards and from seven to nine data sets to describe the aquifer properties, boundaries, and stresses. The accuracy of the model was evaluated for two idealized problems for which analytical solutions could be obtained. In the case of one-dimensional flow the agreement was nearly exact, but in the case of plane radial flow a small amount of numerical dispersion occurred. An analysis of several test problems indicates that the error in the mass balance will be generally less than 10 percent. The test problems demonstrated that the accuracy and precision of the numerical solution is sensitive to the initial number of particles placed in each cell and to the size of the time increment, as determined by the stability criteria. Mass balance errors are commonly the greatest during the first several time increments, but tend to decrease and stabilize with time.

Effects of groundwater pumping in the lower Apalachicola-Chattahoochee-Flint River basin

USGS Publications Warehouse

Jones, L. Elliott

2012-01-01

USGS developed a groundwater-flow model of the Upper Floridan aquifer in lower Apalachicola-Chattahoochee-Flint River basin in southwest Georgia and adjacent parts of Alabama and Florida to determine the effect of agricultural groundwater pumping on aquifer/stream flow within the basin. Aquifer/stream flow is the sum of groundwater outflow to and inflow from streams, and is an important consideration for water managers in the development of water-allocation and operating plans. Specifically, the model was used to evaluate how agricultural pumping relates to 7Q10 low streamflow, a statistical low flow indicative of drought conditions that would occur during seven consecutive days, on average, once every 10 years. Argus ONETM, a software package that combines a geographic information system (GIS) and numerical modeling in an Open Numerical Environment, facilitated the design of a detailed finite-element mesh to represent the complex geometry of the stream system in the lower basin as a groundwater-model boundary. To determine the effects on aquifer/stream flow of pumping at different locations within the model area, a pumping rate equivalent to a typical center-pivot irrigation system (50,000 ft3/d) was applied individually at each of the 18,951 model nodes in repeated steady-state simulations that were compared to a base case representing drought conditions during October 1999. Effects of nodal pumping on aquifer/stream flow and other boundary flows, as compared with the base-case simulation, were computed and stored in a response matrix. Queries to the response matrix were designed to determine the sensitivity of targeted stream reaches to agricultural pumping. Argus ONE enabled creation of contour plots of query results to illustrate the spatial variation across the model area of simulated aquifer/streamflow reductions, expressed as a percentage of the long-term 7Q10 low streamflow at key USGS gaging stations in the basin. These results would enable water managers to assess the relative impact of agricultural pumping and drought conditions on streamflow throughout the basin, and to develop mitigation strategies to conserve water resources and preserve aquatic habitat.

Full Coupling Between the Atmosphere, Surface, and Subsurface for Integrated Hydrologic Simulation

NASA Astrophysics Data System (ADS)

Davison, Jason Hamilton; Hwang, Hyoun-Tae; Sudicky, Edward A.; Mallia, Derek V.; Lin, John C.

2018-01-01

An ever increasing community of earth system modelers is incorporating new physical processes into numerical models. This trend is facilitated by advancements in computational resources, improvements in simulation skill, and the desire to build numerical simulators that represent the water cycle with greater fidelity. In this quest to develop a state-of-the-art water cycle model, we coupled HydroGeoSphere (HGS), a 3-D control-volume finite element surface and variably saturated subsurface flow model that includes evapotranspiration processes, to the Weather Research and Forecasting (WRF) Model, a 3-D finite difference nonhydrostatic mesoscale atmospheric model. The two-way coupled model, referred to as HGS-WRF, exchanges the actual evapotranspiration fluxes and soil saturations calculated by HGS to WRF; conversely, the potential evapotranspiration and precipitation fluxes from WRF are passed to HGS. The flexible HGS-WRF coupling method allows for unique meshes used by each model, while maintaining mass and energy conservation between the domains. Furthermore, the HGS-WRF coupling implements a subtime stepping algorithm to minimize computational expense. As a demonstration of HGS-WRF's capabilities, we applied it to the California Basin and found a strong connection between the depth to the groundwater table and the latent heat fluxes across the land surface.

Simulation of ground-water flow near the nuclear-fuel reprocessing facility at the Western New York Nuclear Service Center, Cattaraugus County, New York

USGS Publications Warehouse

Yager, R.M.

1987-01-01

A two-dimensional finite-difference model was developed to simulate groundwater flow in a surficial sand and gravel deposit underlying the nuclear fuel reprocessing facility at Western New York Nuclear Service Center near West Valley, N.Y. The sand and gravel deposit overlies a till plateau that abuts an upland area of siltstone and shale on its west side, and is bounded on the other three sides by deeply incised stream channels that drain to Buttermilk Creek, a tributary to Cattaraugus Creek. Radioactive materials are stored within the reprocessing plant and are also buried within a till deposit at the facility. Tritiated water is stored in a lagoon system near the plant and released under permit to Franks Creek, a tributary to Buttermilk Creek. Groundwater levels predicted by steady-state simulations closely matched those measured in 23 observation wells, with an average error of 0.5 meter. Simulated groundwater discharges to two stream channels and a subsurface drain were within 5% of recorded values. Steady-state simulations used an average annual recharge rate of 46 cm/yr; predicted evapotranspiration loss from the ground was 20 cm/yr. The lateral range in hydraulic conductivity obtained through model calibration was 0.6 to 10 m/day. Model simulations indicated that 33% of the groundwater discharged from the sand and gravel unit (2.6 L/sec) is lost by evapotranspiration, 3% (3.0 L/sec) flows to seepage faces at the periphery of the plateau, 20% (1.6 L/sec) discharges to stream channels that drain a large wetland area near the center of the plateau, and the remaining 8% (0.6 L/sec) discharges to a subsurface french drain and to a wastewater treatment system. Groundwater levels computed by a transient-state simulation of an annual climatic cycle, including seasonal variation in recharge and evapotranspiration, closely matched water levels measured in eight observation wells. The model predicted that the subsurface drain and the stream channel that drains the wetland would intercept most of the recharge originating near the reprocessing plant. (Lantz-PTT)

Coupled modelling of groundwater flow-heat transport for assessing river-aquifer interactions

NASA Astrophysics Data System (ADS)

Engeler, I.; Hendricks Franssen, H. J.; Müller, R.; Stauffer, F.

2010-05-01

A three-dimensional finite element model for coupled variably saturated groundwater flow and heat transport was developed for the aquifer below the city of Zurich. The piezometric heads in the aquifer are strongly influenced by the river Limmat. In the model region, the river Limmat looses water to the aquifer. The river-aquifer interaction was modelled with the standard linear leakage concept. Coupling was implemented by considering temperature dependence of the hydraulic conductivity and of the leakage coefficient (via water viscosity) and density dependent transport. Calibration was performed for isothermal conditions by inverse modelling using the pilot point method. Independent model testing was carried out with help of the available dense monitoring network for piezometric heads and groundwater temperature. The model was tested by residuals analysis with the help of measurements for both groundwater temperature and head. The comparison of model results and measurements showed high accuracy for temperature except for the Southern part of the model area, where important geological heterogeneity is expected, which could not be reproduced by the model. The comparison of simulated and measured head showed that especially in the vicinity of river Limmat model results were improved by a temperature dependent leakage coefficient. Residuals were reduced up to 30% compared to isothermal leakage coefficients. This holds particularly for regions, where the river stage is considerably above the groundwater level. Furthermore additional analysis confirmed prior findings, that seepage rates during flood events cannot be reproduced with the implemented linear leakage-concept. Infiltration during flood events is larger than expected, which can be potentially attributed to additional infiltration areas. It is concluded that the temperature dependent leakage concept improves the model results for this study area significantly, and that we expect that this is also for other areas the case.

Climate change impacts on the temperature and magnitude of groundwater discharge from shallow, unconfined aquifers

USGS Publications Warehouse

Kurylyk, Barret L.; MacQuarrie, Kerry T.B; Voss, Clifford I.

2014-01-01

Cold groundwater discharge to streams and rivers can provide critical thermal refuge for threatened salmonids and other aquatic species during warm summer periods. Climate change may influence groundwater temperature and flow rates, which may in turn impact riverine ecosystems. This study evaluates the potential impact of climate change on the timing, magnitude, and temperature of groundwater discharge from small, unconfined aquifers that undergo seasonal freezing and thawing. Seven downscaled climate scenarios for 2046–2065 were utilized to drive surficial water and energy balance models (HELP3 and ForHyM2) to obtain future projections for daily ground surface temperature and groundwater recharge. These future surface conditions were then applied as boundary conditions to drive subsurface simulations of variably saturated groundwater flow and energy transport. The subsurface simulations were performed with the U.S. Geological Survey finite element model SUTRA that was recently modified to include the dynamic freeze-thaw process. The SUTRA simulations indicate a potential rise in the magnitude (up to 34%) and temperature (up to 3.6°C) of groundwater discharge to the adjacent river during the summer months due to projected increases in air temperature and precipitation. The thermal response of groundwater to climate change is shown to be strongly dependent on the aquifer dimensions. Thus, the simulations demonstrate that the thermal sensitivity of aquifers and baseflow-dominated streams to decadal climate change may be more complex than previously thought. Furthermore, the results indicate that the probability of exceeding critical temperature thresholds within groundwater-sourced thermal refugia may significantly increase under the most extreme climate scenarios.

Documentation of programs used to determine a wetlands hydroperiod from model-simulated water-surface elevations

USGS Publications Warehouse

Sonenshein, R.S.

1996-01-01

A technique has been developed to determine a wetlands hydroperiod by comparing simulated water levels from a ground-water flow model and land- surface elevation data through a geographic information system. The simulated water levels are compared with the land-surface elevation data to determine the height of the water surface above or below land surface for the area of interest. Finally, the hydroperiod is determined for established time periods using criteria specified by the user. The program application requires the use of geographic information system software (ARC/INFO), including the TIN and GRID subsystems of the software. The application consists of an ANSI compatible C program to translate ground- water data output from the U.S. Geological Survey modular three-dimensional, finite-difference, ground-water flow model (MODFLOW) into a format that can be used as input for the geographic information system programs (AML's). The application uses ARC/INFO AML programs and ARC/INFO menu interface programs to create digital spatial data layers of the land surface and water surface and to determine the hydroperiod. The technique can be used to evaluate and manage wetlands hydrology.

Simulation of interaction between ground water in an alluvial aquifer and surface water in a large braided river

USGS Publications Warehouse

Leake, S.A.; Lilly, M.R.

1995-01-01

The Fairbanks, Alaska, area has many contaminated sites in a shallow alluvial aquifer. A ground-water flow model is being developed using the MODFLOW finite-difference ground-water flow model program with the River Package. The modeled area is discretized in the horizontal dimensions into 118 rows and 158 columns of approximately 150-meter square cells. The fine grid spacing has the advantage of providing needed detail at the contaminated sites and surface-water features that bound the aquifer. However, the fine spacing of cells adds difficulty to simulating interaction between the aquifer and the large, braided Tanana River. In particular, the assignment of a river head is difficult if cells are much smaller than the river width. This was solved by developing a procedure for interpolating and extrapolating river head using a river distance function. Another problem is that future transient simulations would require excessive numbers of input records using the current version of the River Package. The proposed solution to this problem is to modify the River Package to linearly interpolate river head for time steps within each stress period, thereby reducing the number of stress periods required.

MODFLOW-CDSS, a version of MODFLOW-2005 with modifications for Colorado Decision Support Systems

USGS Publications Warehouse

Banta, Edward R.

2011-01-01

MODFLOW-CDSS is a three-dimensional, finite-difference groundwater-flow model based on MODFLOW-2005, with two modifications. The first modification is the introduction of a Partition Stress Boundaries capability, which enables the user to partition a selected subset of MODFLOW's stress-boundary packages, with each partition defined by a separate input file. Volumetric water-budget components of each partition are tracked and listed separately in the volumetric water-budget tables. The second modification enables the user to specify that execution of a simulation should continue despite failure of the solver to satisfy convergence criteria. This modification is particularly intended to be used in conjunction with automated model-analysis software; its use is not recommended for other purposes.

A Regional-Scale Groundwater Model Supporting Management of the Sian Ka'an Biosphere Reserve and its Catchment, Quintana Roo, Mexico

NASA Astrophysics Data System (ADS)

Neuman, B. R.; Merediz Alonso, G.; Rebolledo Vieyra, M.; Marin, L.; Supper, R.; Bauer-Gottwein, P.

2007-05-01

The Caribbean Coast of the Yucatan Peninsula is a rapidly developing area featuring a booming tourism industry. The number of hotel rooms in the Riviera Maya has increased from 2600 in 1996 to 26,000 in 2005, while the total population in the Mexican federal state of Quintana Roo has grown from 500,000 in 1990 to 1,115,000 in 2005. This explosive growth threatens the region's water resources, which primarily consist of a less than 50m thick freshwater lens residing in the regional karst aquifer underlying the entire Yucatan Peninsula. The Sian Ka'an Biosphere Reserve, a 6400 km2 combined marine/terrestrial nature protection area is situated south of Tulum (approx. 87.3° - 88° W, 19° - 20° N). The site is listed as a UNESCO world heritage site and is protected under the Ramsar Convention. It includes extensive freshwater wetlands, saline/brackish mangrove swamps, tropical rainforests and parts of the world's second largest coral reef. The freshwater supply to the system occurs primarily via subsurface inflow. Large freshwater springs emerge through vertical sinkholes (cenotes) in the lagoons of Sian Ka'an. Management of this unique ecosystem in view of the rapid development and urbanization of the surrounding areas requires detailed knowledge on the groundwater flow paths in and around the reserve. Moreover, mapping and delineation of its groundwater catchment zone and groundwater traveling time zones is essential. To this end, a regional-scale steady-state groundwater flow model of the Sian Ka'an Biosphere reserve and its catchment was developed. The model is implemented in MIKE SHE with a finite-difference cell size of 1 km2 and is driven with temporally averaged climate forcings. The karst aquifer is treated as an equivalent porous medium. Darcy's law is assumed to be valid over regional scales and the main structural elements of the karst aquifer are included in the model as zones of varying hydraulic conductivity. High conductivity zones in the Sian Ka'an catchment area were identified from existing geological maps and remote sensing data. Selected high conductivity zones were surveyed using geophysical techniques (EM-34, multi-electrode profiling) to confirm their existence on the ground. Modeled groundwater catchment zones and groundwater traveling times to Sian Ka'an were shown to sensitively depend on the location and parameterization of the high conductivity zones. In order to target groundwater and wetland protection efforts, regional-scale mapping of the aquifer structure using airborne geophysical techniques is recommended.

Noble Gas Thermometry and Hydrologic Ages: Evidence for Late Holocene Warming in Southwest Texas

NASA Astrophysics Data System (ADS)

Castro, M.; Goblet, P.

2003-12-01

Paleoclimatic reconstruction through the use of noble gases dissolved in groundwater has been the object of numerous studies in recent years. Unlike many other continental temperature proxies, noble gases have the advantage of providing direct information on atmospheric temperatures at the time rainwater penetrated the ground and joined a particular groundwater reservoir. In recent years, new methods for determination of noble gas temperatures have been developed, which provide a high level of accuracy on such temperature estimations. The issue of paleoclimatic reconstruction through noble gases however, is not only one of accurate temperature determination, but also one of accurate water age estimation so that a correct correspondence between noble gas temperatures and groundwater age can be established and proper paleoclimatic reconstruction attempted. The typical approach to estimate groundwater ages has been based on computing water travel times along streamlines from the recharge to the observation point taking into account only advection. This approach is limited because, like any other tracer, the movement of water in porous media is also affected by cinematic dispersion and molecular diffusion. We have therefore undertaken the formulation of hydrologic models that yield significantly better constraints on groundwater ages in the Carrizo aquifer and surrounding formations of south Texas, where noble gas temperatures have already been determined. To account for groundwater mixing we treat age as one would treat a solute concentration. In order to simulate groundwater ages we used a finite element model of groundwater flow that has been validated by 4He and 3He. The finite model spans a 120.6 Km cross-section between altitudes of +220m and -2210 m, and comprises 58,968 elements and 31,949 nodes. Combination of these newly calculated water ages and previously reported noble gas temperatures reveals new aspects of late Pleistocene and Holocene climate in southwestern Texas, in particular, an abrupt late Holocene temperature increase previously unidentified through 14C dating. Temperature increased by up to 3.4° C in the first half of the last millennium and by 1.5° C between ˜5.6 and 3.7 kyrs BP. More important than the resolution of individual paleoclimate episodes is the identification of a slow cooling trend between ˜1,200 kyrs and ˜200 kyrs, a trend that accelerates during the late Pleistocene and early Holocene. This cooling trend gives way to an extremely rapid increase in temperature in the late Holocene. Such abrupt warming seems to have accelerated in the last millennium and seems to continue at present. This temperature increase is the most striking feature arising from the determination of new groundwater ages.

General well function for soil vapor extraction

NASA Astrophysics Data System (ADS)

Perina, Tomas

2014-04-01

This paper develops a well function applicable to extraction of groundwater or soil vapor from a well under the most common field test conditions. The general well function (Perina and Lee, 2006) [12] is adapted to soil vapor extraction and constant head boundary at the top. For groundwater flow, the general well function now applies to an extraction well of finite diameter with uniform drawdown along the screen, finite-thickness skin, and partially penetrating an unconfined, confined, and leaky aquifer, or an aquifer underneath a reservoir. With a change of arguments, the model applies to soil vapor extraction from a vadose zone with no cover or with leaky cover at the ground surface. The extraction well can operate in specified drawdown (pressure for soil vapor) or specified flowrate mode. Frictional well loss is computed as flow-only dependent component of the drawdown inside the extraction well. In general case, the calculated flow distribution is not proportional to screen length for a multiscreen well.

Multi-scale approach for 3D hydrostratigraphic and groundwater flow modelling of Milan (Northern Italy) urban aquifers.

NASA Astrophysics Data System (ADS)

De Caro, Mattia; Crosta, Giovanni; Frattini, Paolo; Perico, Roberta

2017-04-01

During the last century, urban groundwater was heavily exploited for public and industrial supply. As the water demands of industry have fallen, many cities are now experiencing rising groundwater levels with consequent concerns about localized flooding of basements, reduction of soil bearing capacities under foundations, soil internal erosion and the mobilization of contaminants. The city of Milan (Northern Italy) draws water for domestic and industrial purposes from aquifers beneath the urban area. The rate of abstraction has been varying during the last century, depending upon the number of inhabitants and the development of industrial activities. The groundwater abstraction raised to a maximum of about 350x106 m3/yr in the middle 1970s and has successively decreased to a value of about 230x106 m3/yr at present days. This caused a water table raise at an average rate of about 1 m/yr inducing infiltrations and flooding of deep constructions (e.g. building foundations and basements, underground subway excavations). Starting from a large hydrostratigraphic database (8628 borehole logs), a multi-scale approach for the reconstruction of the aquifers geometry (unconfined and semi-confined) at regional-scale has been used. First, a three-level hierarchical classification of the lithologies (lithofacies, hydrofacies, aquifer groups) has been adopted. Then, the interpretation of several 2D cross-sections was attained with Target for ArcGIS exploration software. The interpretation of cross-sections was based on the characteristics of depositional environments of the analysed aquifers (from meandering plain to proximal outwash deposits), on the position of quaternary deposits, and on the distribution of geochemical parameters (i.e. indicator contaminants and major ions). Finally, the aquifer boundary surfaces were interpolated with standard algorithms. The hydraulic properties of analysed aquifers were estimated through the analyses of available step-drawdown tests (Theis with the superimposition solution) and use of empirical relationships from grain-size distribution data, respectively for semi-confined and unconfined aquifers. Finally, 3D Finite Element groundwater flow models have been developed both at regional and local "metropolitan" scale. The regional model covers an area of 3,135.15 km2, while the local model comprises the Milan metropolitan area with an extension of 457 km2. Both models were discretized into a triangular finite element mesh with local refinement in proximity of pumping wells. The element size ranges from 350 to 30 meters and from 200 to 2 meters, respectively for regional and local model. The calibration was done by the comparison with the available water level data for different years (from 1994 to 2016). The calibrated permeability values are consistent with the estimated ones and the sensitivity analysis on hydraulic parameters suggests a minor influence of the aquiclude layer separating the two aquifers. The challenge is to provide the basis for new types of applied outputs so that they may better inform strategic planning options, ground investigation, and abstraction strategies.

Transport of volatile organic compounds across the capillary fringe

USGS Publications Warehouse

McCarthy, Kathleen A.; Johnson, Richard L.

1993-01-01

Physical experiments were conducted to investigate the transport of a dissolved volatile organic compound (trichloroethylene, TCE) from shallow groundwater to the unsaturated zone under a variety of conditions including changes in the soil moisture profile and water table position. Experimental data indicated that at moderate groundwater velocities (0.1 m/d), vertical mechanical dispersion was negligible and molecular diffusion was the dominant vertical transport mechanism. Under these conditions, TCE concentrations decreased nearly 3 orders of magnitude across the capillary fringe and soil gas concentrations remained low relative to those of underlying groundwater. Data collected during a water table drop showed a short-term increase in concentrations throughout most of the unsaturated zone, but these concentrations quickly declined and approached initial values after the water table was returned to its original level. In the deep part of the unsaturated zone, the water table drop resulted in a long-term decrease in concentrations, illustrating the effects of hysteresis in the soil moisture profile. A two-dimensional random walk advection-diffusion model was developed to simulate the experimental conditions, and numerical simulations agreed well with experimental data. A simpler, one-dimensional finite-difference diffusion-dispersion model was also developed. One-dimensional simulations based on molecular diffusion also agreed well with experimental data. Simulations which incorporated mechanical dispersion tended to overestimate flux across the capillary fringe. Good agreement between the one- and two-dimensional models suggested that a simple, one-dimensional approximation of vertical transport across the capillary fringe can be useful when conditions are appropriate.

Simulation analysis of water-level changes in the Navajo sandstone due to changes in the altitude of Lake Powell near Wahweap Bay, Utah and Arizona

USGS Publications Warehouse

Thomas, B.E.

1986-01-01

A two-dimensional, finite difference, digital computer model was used to simulate various concepts of groundwater flow near Wahweap Bay, Lake Powell. The filling of Lake Powell started in March 1963; and by 1983 the lake had risen almost 550 ft. This resulted in a maximum observed water level rise of 395 ft in a well in the Navajo Sandstone 1 mi from the lake. A steady-state model was prepared with subsurface recharge rates of 5,720 acre-ft/yr, 10,440 acre-ft/yr, and 14,820 acre-ft/yr, resulting in a range of hydraulic conductivity of 0.25 to 3.38 ft/da. Comparing measured and simulated water level changes resulted in a range of specific yield of 0.02 to 0.15. Using larger values for hydraulic conductivity in the model area corresponding to the axis of the Wahweap syncline and the Echo monocline was instrumental in attaining a reasonable match for the water level distribution. This supports previous concepts that areas where rocks are structurally deformed more readily transmit groundwater because of the higher degree of fracturing. Using the most likely simulation of the flow system, groundwater storage in the Navajo increased by about 25,000 acre ft/mi of shoreline form 1963-83, but the flow system will require about 400 yr to reach a state of equilibrium. (Author 's abstract)

Hydrogeology and ground-water flow in the carbonate rocks of the Little Lehigh Creek basin, Lehigh County, Pennsylvania

USGS Publications Warehouse

Sloto, R.A.; Cecil, L.D.; Senior, L.A.

1991-01-01

The Little Lehigh Creek basin is underlain mainly by a complex assemblage of highly-deformed Cambrian and Ordovician carbonate rocks. The Leithsville Formation, Allentown Dolomite, Beekmantown Group, and Jacksonburg Limestone act as a single hydrologic unit. Ground water moves through fractures and other secondary openings and generally is under water-table conditions. Median annual ground-water discharge (base flow) to Little Lehigh Creek near Allentown (station 01451500) during 1946-86 was 12.97 inches or 82 percent of streamflow. Average annual recharge for 1975-83 was 21.75 inches. Groundwater and surface-water divides do not coincide in the basin. Ground-water underflow from the Little Lehigh Creek basin to the Cedar Creek basin in 1987 was 4 inches per year. A double-mass curve analysis of the relation of cumulative precipitation at Allentown to the flow of Schantz Spring for 1956-84 showed that cessation of quarry pumping and development of ground water for public supply in the Schantz Spring basin did not affect the flow of Schantz Spring. Ground-water flow in the Little Lehigh Creek basin was simulated using a finite-difference, two-dimensional computer model. The geologic units in the modeled area were simulated as a single water-table aquifer. The 134-squaremile area of carbonate rocks between the Lehigh River and Sacony Creek was modeled to include the natural hydrologic boundaries of the ground-water-flow system. The ground-water-flow model was calibrated under steady-state conditions using 1975-83 average recharge, evapotranspiration, and pumping rates. Each geologic unit was assigned a different hydraulic conductivity. Initial aquifer hydraulic conductivity was estimated from specific-capacity data. The average (1975-83) water budget for the Little Lehigh Creek basin was simulated. The simulated base flow from the carbonate rocks of the Little Lehigh Creek basin above gaging station 01451500 is 11.85 inches per year. The simulated ground-water underflow from the Little Lehigh Creek basin to the Cedar Creek basin is 4.04 inches per year. For steady-state calibration, the root-mean-squared difference between observed and simulated heads was 21.19 feet. The effects of increased ground-water development on base flow and underflow out of the Little Lehigh Creek basin for average and drought conditions were simulated by locating a hypothetical well field in different parts of the basin. Steady-state simulations were used to represent equilibrium conditions, which would be the maximum expected long-term effect. Increased ground-water development was simulated as hypothetical well fields pumping at the rate of 15, 25, and 45 million gallons per day in addition to existing ground-water withdrawals. Four hypothetical well fields were located near and away from Little Lehigh Creek in upstream and downstream areas. The effects of pumping a well field in different parts of the Little Lehigh Creek basin were compared. Pumping a well field located near the headwaters of Little Lehigh Creek and away from the stream would have greatest effect on inducing underflow from the Sacony Greek basin and the least effect on reducing base flow and underflow to the Ceda^r Creek basin. Pumping a well field located near the headwaters of Little Leh|igh Creek near the stream would have less impact on inducing underflow from|the Sacony Creek basin and a greater impact on reducing the base flow of Little Lehigh Creek because more of the pumpage would come from diverted base flow. Pumping a well field located in the downstream area of the Little Lehigh Creek basin away from the stream would have the greatest effect on the underflow to the Cedar Creek basin. Pumping a well field located in the downstream area of the Little Lehigh Creek basin near the stream would have the greatest effect on reducing the base flow of Little Lehigh Cteek. Model simulations show that groundwater withdrawals do not cause a proportional reduction in base flow. Under average conditions, ground-water withdrawals are equal to 48 to 70 percent of simulated base-flow reductions; under drought conditions, ground-water withdrawals are equal to 35 to 73 percent of simulated base-flow reductions. The hydraulic effects of pumping largely depend on well location. In the Little Lehigh basin, surface-water and ground-water divides do not coincide, and ground-water development, especially near surface-water divides, can cause ground-water divides to shift and induce ground-water underflow from adjacent basins. Large-scale ground-water pumping in a basin may not produce expected reductions of base flow in that basin because of shifts in the ground-water divide; however, such shifts can reduce base flow in adjacent surface-water basins. 

Improving a complex finite-difference ground water flow model through the use of an analytic element screening model

USGS Publications Warehouse

Hunt, R.J.; Anderson, M.P.; Kelson, V.A.

1998-01-01

This paper demonstrates that analytic element models have potential as powerful screening tools that can facilitate or improve calibration of more complicated finite-difference and finite-element models. We demonstrate how a two-dimensional analytic element model was used to identify errors in a complex three-dimensional finite-difference model caused by incorrect specification of boundary conditions. An improved finite-difference model was developed using boundary conditions developed from a far-field analytic element model. Calibration of a revised finite-difference model was achieved using fewer zones of hydraulic conductivity and lake bed conductance than the original finite-difference model. Calibration statistics were also improved in that simulated base-flows were much closer to measured values. The improved calibration is due mainly to improved specification of the boundary conditions made possible by first solving the far-field problem with an analytic element model.This paper demonstrates that analytic element models have potential as powerful screening tools that can facilitate or improve calibration of more complicated finite-difference and finite-element models. We demonstrate how a two-dimensional analytic element model was used to identify errors in a complex three-dimensional finite-difference model caused by incorrect specification of boundary conditions. An improved finite-difference model was developed using boundary conditions developed from a far-field analytic element model. Calibration of a revised finite-difference model was achieved using fewer zones of hydraulic conductivity and lake bed conductance than the original finite-difference model. Calibration statistics were also improved in that simulated base-flows were much closer to measured values. The improved calibration is due mainly to improved specification of the boundary conditions made possible by first solving the far-field problem with an analytic element model.

Simulation of saltwater movement in the Upper Floridan aquifer in the Savannah, Georgia-Hilton Head Island, South Carolina, area, predevelopment-2004, and projected movement for 2000 pumping conditions

USGS Publications Warehouse

Provost, Alden M.; Payne, Dorothy F.; Voss, Clifford I.

2006-01-01

A digital model was developed to simulate ground-water flow and solute transport for the Upper Floridan aquifer in the Savannah, Georgia-Hilton Head Island, South Carolina, area. The model was used to (1) simulate trends of saltwater intrusion from predevelopment to the present day (1885-2004), (2) project these trends from the present day into the future, and (3) evaluate the relative influence of different assumptions regarding initial and boundary conditions and physical properties. The model is based on a regional, single-density ground-water flow model of coastal Georgia and adjacent parts of South Carolina and Florida. Variable-density ground-water flow and solute transport were simulated using the U.S. Geological Survey finite-element, variable-density solute-transport simulator SUTRA, 1885-2004. The model comprises seven layers: the surficial aquifer system, the Brunswick aquifer system, the Upper Floridan aquifer, the Lower Floridan aquifer, and the intervening confining units. The model was calibrated to September 1998 water levels, for single-density freshwater conditions, then refined using variable density and chloride concentration to give a reasonable match to the trend in the chloride distribution in the Upper Floridan aquifer inferred from field measurements of specific conductance made during 2000, 2002, 2003, and 2004. The model was modified to simulate solute transport by allowing saltwater to enter the system through localized areas near the northern end of Hilton Head Island, at Pinckney Island, and near the Colleton River, and was calibrated to match chloride concentrations inferred from field measurements of specific conductance. This simulation is called the 'Base Case.'

MODFLOW–LGR—Documentation of ghost node local grid refinement (LGR2) for multiple areas and the boundary flow and head (BFH2) package

USGS Publications Warehouse

Mehl, Steffen W.; Hill, Mary C.

2013-01-01

This report documents the addition of ghost node Local Grid Refinement (LGR2) to MODFLOW-2005, the U.S. Geological Survey modular, transient, three-dimensional, finite-difference groundwater flow model. LGR2 provides the capability to simulate groundwater flow using multiple block-shaped higher-resolution local grids (a child model) within a coarser-grid parent model. LGR2 accomplishes this by iteratively coupling separate MODFLOW-2005 models such that heads and fluxes are balanced across the grid-refinement interface boundary. LGR2 can be used in two-and three-dimensional, steady-state and transient simulations and for simulations of confined and unconfined groundwater systems. Traditional one-way coupled telescopic mesh refinement methods can have large, often undetected, inconsistencies in heads and fluxes across the interface between two model grids. The iteratively coupled ghost-node method of LGR2 provides a more rigorous coupling in which the solution accuracy is controlled by convergence criteria defined by the user. In realistic problems, this can result in substantially more accurate solutions and require an increase in computer processing time. The rigorous coupling enables sensitivity analysis, parameter estimation, and uncertainty analysis that reflects conditions in both model grids. This report describes the method used by LGR2, evaluates accuracy and performance for two-and three-dimensional test cases, provides input instructions, and lists selected input and output files for an example problem. It also presents the Boundary Flow and Head (BFH2) Package, which allows the child and parent models to be simulated independently using the boundary conditions obtained through the iterative process of LGR2.

Numerical simulation of the groundwater-flow system of the Kitsap Peninsula, west-central Washington

USGS Publications Warehouse

Frans, Lonna M.; Olsen, Theresa D.

2016-05-05

A groundwater-flow model was developed to improve understanding of water resources on the Kitsap Peninsula. The Kitsap Peninsula is in the Puget Sound lowland of west-central Washington, is bounded by Puget Sound on the east and by Hood Canal on the west, and covers an area of about 575 square miles. The peninsula encompasses all of Kitsap County, Mason County north of Hood Canal, and part of Pierce County west of Puget Sound. The peninsula is surrounded by saltwater, and the hydrologic setting is similar to that of an island. The study area is underlain by a thick sequence of unconsolidated glacial and interglacial deposits that overlie sedimentary and volcanic bedrock units that crop out in the central part of the study area. Twelve hydrogeologic units consisting of aquifers, confining units, and an underlying bedrock unit form the basis of the groundwater-flow model.Groundwater flow on the Kitsap Peninsula was simulated using the groundwater-flow model, MODFLOW‑NWT. The finite difference model grid comprises 536 rows, 362 columns, and 14 layers. Each model cell has a horizontal dimension of 500 by 500 feet, and the model contains a total of 1,227,772 active cells. Groundwater flow was simulated for transient conditions. Transient conditions were simulated for January 1985–December 2012 using annual stress periods for 1985–2004 and monthly stress periods for 2005–2012. During model calibration, variables were adjusted within probable ranges to minimize differences between measured and simulated groundwater levels and stream baseflows. As calibrated to transient conditions, the model has a standard deviation for heads and flows of 47.04 feet and 2.46 cubic feet per second, respectively.Simulated inflow to the model area for the 2005–2012 period from precipitation and secondary recharge was 585,323 acre-feet per year (acre-ft/yr) (93 percent of total simulated inflow ignoring changes in storage), and simulated inflow from stream and lake leakage was 43,905 acre-ft/yr (7 percent of total simulated inflow). Simulated outflow from the model primarily was through discharge to streams, lakes, springs, seeps, and Puget Sound (594,595 acre-ft/yr; 95 percent of total simulated outflow excluding changes in storage) and through withdrawals from wells (30,761 acre-ft/yr; 5 percent of total simulated outflow excluding changes in storage).Six scenarios were formulated with input from project stakeholders and were simulated using the calibrated model to provide representative examples of how the model could be used to evaluate the effects on water levels and stream baseflows of potential changes in groundwater withdrawals, in consumptive use, and in recharge. These included simulations of a steady-state system, no-pumping and return flows, 15-percent increase in current withdrawals in all wells, 80-percent decrease in outdoor water to simulate effects of conservation efforts, 15-percent decrease in recharge from precipitation to simulate a drought, and particle tracking to determine flow paths.Changes in water-level altitudes and baseflow amounts vary depending on the stress applied to the system in these various scenarios. Reducing recharge by 15 percent between 2005 and 2012 had the largest effect, with water-level altitudes declining throughout the model domain and baseflow amounts decreasing by as much as 18 percent compared to baseline conditions. Changes in pumping volumes had a smaller effect on the model. Removing all pumping and resulting return flows caused increased water-level altitudes in many areas and increased baseflow amounts of between 1 and 3 percent.

Do Groundwater Management Plans Work? A statistical evaluation of the effectiveness of groundwater management plans towards achieving water supply and environmental objectives under a changing climate.

NASA Astrophysics Data System (ADS)

White, E.; Peterson, T. J.; Costelloe, J. F.; Western, A. W.; Carrara, E.

2017-12-01

Regulation of groundwater through the use of management plans is becoming increasingly prevalent as global groundwater levels decline. But plans are seldom systematically and quantitatively assessed for effectiveness. Instead, the state of an aquifer is commonly considered a proxy for plan effectiveness despite a lack of casaulity. Groundwater managers face myraid challenges such as finite resources, conflicting uses and the uncertainty inherent in any groundwater investigation. Groundwater models have been used to provide insights into what may happen to the aquifer under various levels of stress. Generally, these models simulate the impact of predefined stresses for a certain time-span. However, this is not how management occurs in reality. Managers only see a fraction of the aquifer and use this limited knowledgeto make aquifer-wide decisions. Also, management changes over time in response to aquifer state, and groundwater management plans commonly contain trigger levels in monitoring wells that prompt management intervention. In this way there is a feedback between the aquifer state and management that is rarely captured by groundwater management models. To capture this management/aquifer feedback, groundwater management was structured as a systems control problem, and using this framework, a testability assessment rubric developed. The rubric was applied to 15 Australian groundwater management plans and 47% of plans were found to be testable. To numerically quantify the effectiveness of groundwater managment, the impact of extraction restrictions was probabilistically assessed by simulating "the act of management" of a simple unconfined groundwater system using MODFLOW and Flopy. Water managers were privy only to head levels in a varying number of grid cells assigned as monitoring wells, and used that limited information to make allocation decisions at each time step. Extraction rates for each simulated management period were determined based upon the observed heads from the previous management period and adjusted depending upon triggers outlined in the management plan. The effectiveness of water restrictions as a management technique for the purpose of maintaining supply reliability under various decision making frequencies, aquifer response times and climate scenarios was explored.

Slope instability caused by small variations in hydraulic conductivity

USGS Publications Warehouse

Reid, M.E.

1997-01-01

Variations in hydraulic conductivity can greatly modify hillslope ground-water flow fields, effective-stress fields, and slope stability. In materials with uniform texture, hydraulic conductivities can vary over one to two orders of magnitude, yet small variations can be difficult to determine. The destabilizing effects caused by small (one order of magnitude or less) hydraulic conductivity variations using ground-water flow modeling, finite-element deformation analysis, and limit-equilibrium analysis are examined here. Low hydraulic conductivity materials that impede downslope ground-water flow can create unstable areas with locally elevated pore-water pressures. The destabilizing effects of small hydraulic heterogeneities can be as great as those induced by typical variations in the frictional strength (approximately 4??-8??) of texturally similar materials. Common "worst-case" assumptions about ground-water flow, such as a completely saturated "hydrostatic" pore-pressure distribution, do not account for locally elevated pore-water pressures and may not provide a conservative slope stability analysis. In site characterization, special attention should be paid to any materials that might impede downslope ground-water flow and create unstable regions.

Near-field transport of {sup 129}I from a point source in an in-room disposal vault

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kolar, M.; Leneveu, D.M.; Johnson, L.H.

1995-12-31

A very small number of disposal containers of heat generating nuclear waste may have initial manufacturing defects that would lead to pin-hole type failures at the time of or shortly after emplacement. For sufficiently long-lived containers, only the initial defects need to be considered in modeling of release rates from the disposal vault. Two approaches to modeling of near-field mass transport from a single point source within a disposal room have been compared: the finite-element code MOTIF (A Model Of Transport In Fractured/porous media) and a boundary integral method (BIM). These two approaches were found to give identical results formore » a simplified model of the disposal room without groundwater flow. MOTIF has then been used to study the effects of groundwater flow on the mass transport out of the emplacement room.« less

Hydrology of the Little Androscoggin River Valley aquifer, Oxford County, Maine

USGS Publications Warehouse

Morrissey, D.J.

1983-01-01

The Little Androscoggin River valley aquifer, a 15-square-mile sand and gravel valley-fill aquifer in southwestern Maine, is the source of water for the towns of Norway, Oxford, and South Paris. Estimated inflows to the aquifer during the 1981 water year were 16.4 cubic feet per second from precipitation directly on the aquifer, 11.2 cubic feet per second from till covered uplands adjacent to the aquifer, and 1.4 cubic feet per second from surface-water leakage. Outflows from the aquifer were 26.7 cubic feet per second to surface water and 2.3 cubic feet per second to wells. A finite-difference ground-water flow model was used to simulate conditions observed in the aquifer during 1981. Model conditions observed in the aquifer during 1981. Model simulations indicate that a 50 percent reduction of average 1981 recharge to the aquifer would cause water level declines of up to 20 feet in some areas. Model simulations of increased pumping at a high yield well in the northern part of the aquifer indicate that resulting changes in the water table will not be sufficient to intercept groundwater contaminated by a sludge disposal site. Water in the aquifer is low in dissolved solids (average for 38 samples was 67 mg/L), slightly acidic and soft. Ground-water contamination has occurred near a sludge-disposal site and in the vicinity of a sanitary landfill. Dissolved solids in ground water near the sludge disposal site were as much as ten times greater than average background values for the aquifer. (USGS)

Efficient discretization in finite difference method

NASA Astrophysics Data System (ADS)

Rozos, Evangelos; Koussis, Antonis; Koutsoyiannis, Demetris

2015-04-01

Finite difference method (FDM) is a plausible and simple method for solving partial differential equations. The standard practice is to use an orthogonal discretization to form algebraic approximate formulations of the derivatives of the unknown function and a grid, much like raster maps, to represent the properties of the function domain. For example, for the solution of the groundwater flow equation, a raster map is required for the characterization of the discretization cells (flow cell, no-flow cell, boundary cell, etc.), and two raster maps are required for the hydraulic conductivity and the storage coefficient. Unfortunately, this simple approach to describe the topology comes along with the known disadvantages of the FDM (rough representation of the geometry of the boundaries, wasted computational resources in the unavoidable expansion of the grid refinement in all cells of the same column and row, etc.). To overcome these disadvantages, Hunt has suggested an alternative approach to describe the topology, the use of an array of neighbours. This limits the need for discretization nodes only for the representation of the boundary conditions and the flow domain. Furthermore, the geometry of the boundaries is described more accurately using a vector representation. Most importantly, graded meshes can be employed, which are capable of restricting grid refinement only in the areas of interest (e.g. regions where hydraulic head varies rapidly, locations of pumping wells, etc.). In this study, we test the Hunt approach against MODFLOW, a well established finite difference model, and the Finite Volume Method with Simplified Integration (FVMSI). The results of this comparison are examined and critically discussed.

Use of RORA for Complex Ground-Water Flow Conditions

USGS Publications Warehouse

Rutledge, A.T.

2004-01-01

The RORA computer program for estimating recharge is based on a condition in which ground water flows perpendicular to the nearest stream that receives ground-water discharge. The method, therefore, does not explicitly account for the ground-water-flow component that is parallel to the stream. Hypothetical finite-difference simulations are used to demonstrate effects of complex flow conditions that consist of two components: one that is perpendicular to the stream and one that is parallel to the stream. Results of the simulations indicate that the RORA program can be used if certain constraints are applied in the estimation of the recession index, an input variable to the program. These constraints apply to a mathematical formulation based on aquifer properties, recession of ground-water levels, and recession of streamflow.

A computer program (MODFLOWP) for estimating parameters of a transient, three-dimensional ground-water flow model using nonlinear regression

USGS Publications Warehouse

Hill, Mary Catherine

1992-01-01

This report documents a new version of the U.S. Geological Survey modular, three-dimensional, finite-difference, ground-water flow model (MODFLOW) which, with the new Parameter-Estimation Package that also is documented in this report, can be used to estimate parameters by nonlinear regression. The new version of MODFLOW is called MODFLOWP (pronounced MOD-FLOW*P), and functions nearly identically to MODFLOW when the ParameterEstimation Package is not used. Parameters are estimated by minimizing a weighted least-squares objective function by the modified Gauss-Newton method or by a conjugate-direction method. Parameters used to calculate the following MODFLOW model inputs can be estimated: Transmissivity and storage coefficient of confined layers; hydraulic conductivity and specific yield of unconfined layers; vertical leakance; vertical anisotropy (used to calculate vertical leakance); horizontal anisotropy; hydraulic conductance of the River, Streamflow-Routing, General-Head Boundary, and Drain Packages; areal recharge rates; maximum evapotranspiration; pumpage rates; and the hydraulic head at constant-head boundaries. Any spatial variation in parameters can be defined by the user. Data used to estimate parameters can include existing independent estimates of parameter values, observed hydraulic heads or temporal changes in hydraulic heads, and observed gains and losses along head-dependent boundaries (such as streams). Model output includes statistics for analyzing the parameter estimates and the model; these statistics can be used to quantify the reliability of the resulting model, to suggest changes in model construction, and to compare results of models constructed in different ways.

Finite difference model for aquifer simulation in two dimensions with results of numerical experiments

USGS Publications Warehouse

Trescott, Peter C.; Pinder, George Francis; Larson, S.P.

1976-01-01

The model will simulate ground-water flow in an artesian aquifer, a water-table aquifer, or a combined artesian and water-table aquifer. The aquifer may be heterogeneous and anisotropic and have irregular boundaries. The source term in the flow equation may include well discharge, constant recharge, leakage from confining beds in which the effects of storage are considered, and evapotranspiration as a linear function of depth to water. The theoretical development includes presentation of the appropriate flow equations and derivation of the finite-difference approximations (written for a variable grid). The documentation emphasizes the numerical techniques that can be used for solving the simultaneous equations and describes the results of numerical experiments using these techniques. Of the three numerical techniques available in the model, the strongly implicit procedure, in general, requires less computer time and has fewer numerical difficulties than do the iterative alternating direction implicit procedure and line successive overrelaxation (which includes a two-dimensional correction procedure to accelerate convergence). The documentation includes a flow chart, program listing, an example simulation, and sections on designing an aquifer model and requirements for data input. It illustrates how model results can be presented on the line printer and pen plotters with a program that utilizes the graphical display software available from the Geological Survey Computer Center Division. In addition the model includes options for reading input data from a disk and writing intermediate results on a disk.

Numerical modelling of climate change impacts on freshwater lenses on the North Sea Island of Borkum

NASA Astrophysics Data System (ADS)

Sulzbacher, H.; Wiederhold, H.; Siemon, B.; Grinat, M.; Igel, J.; Burschil, T.; Günther, T.; Hinsby, K.

2012-03-01

A numerical variable-density groundwater model is set up for the North Sea Island of Borkum to estimate climate change impacts on coastal aquifers and especially the situation of barrier islands in the Wadden Sea. The database includes information from boreholes, a seismic survey, a helicopter-borne electromagnetic survey (HEM), monitoring of the freshwater-saltwater boundary by vertical electrode chains in two boreholes, measurements of groundwater table, pumping and slug tests, as well as water samples. Based on a statistical analysis of borehole columns, seismic sections and HEM, a hydrogeological model is set up. The groundwater model is developed using the finite-element programme FEFLOW. The variable-density groundwater model is calibrated on the basis of hydraulic, hydrological and geophysical data, in particular spatial HEM and local monitoring data. Verification runs with the calibrated model show good agreement between measured and computed hydraulic heads. A good agreement is also obtained between measured and computed density or total dissolved solids data for both the entire freshwater lens on a large scale and in the area of the well fields on a small scale. For simulating future changes in this coastal groundwater system until the end of the current century we use the climate scenario A2, specified by the Intergovernmental Panel on Climate Change and in particular the data for the German North Sea coast. Simulation runs show proceeding salinization with time beneath the well fields of the two waterworks Waterdelle and Ostland. The modelling study shows that spreading of well fields is an appropriate protection measure against excessive salinization of the water supply until the end of the current century.

Numerical modelling of climate change impacts on freshwater lenses on the North Sea Island of Borkum using hydrological and geophysical methods

NASA Astrophysics Data System (ADS)

Sulzbacher, H.; Wiederhold, H.; Siemon, B.; Grinat, M.; Igel, J.; Burschil, T.; Günther, T.; Hinsby, K.

2012-10-01

A numerical, density dependent groundwater model is set up for the North Sea Island of Borkum to estimate climate change impacts on coastal aquifers and especially the situation of barrier islands in the Wadden Sea. The database includes information from boreholes, a seismic survey, a helicopter-borne electromagnetic (HEM) survey, monitoring of the freshwater-saltwater boundary by vertical electrode chains in two boreholes, measurements of groundwater table, pumping and slug tests, as well as water samples. Based on a statistical analysis of borehole columns, seismic sections and HEM, a hydrogeological model is set up. The groundwater model is developed using the finite-element programme FEFLOW. The density dependent groundwater model is calibrated on the basis of hydraulic, hydrological and geophysical data, in particular spatial HEM and local monitoring data. Verification runs with the calibrated model show good agreement between measured and computed hydraulic heads. A good agreement is also obtained between measured and computed density or total dissolved solids data for both the entire freshwater lens on a large scale and in the area of the well fields on a small scale. For simulating future changes in this coastal groundwater system until the end of the current century, we use the climate scenario A2, specified by the Intergovernmental Panel on Climate Change and, in particular, the data for the German North Sea coast. Simulation runs show proceeding salinisation with time beneath the well fields of the two waterworks Waterdelle and Ostland. The modelling study shows that the spreading of well fields is an appropriate protection measure against excessive salinisation of the water supply until the end of the current century.

Coupled basin-scale water resource models for arid and semiarid regions

NASA Astrophysics Data System (ADS)

Winter, C.; Springer, E.; Costigan, K.; Fasel, P.; Mniewski, S.; Zyvoloski, G.

2003-04-01

Managers of semi-arid and arid water resources must allocate increasingly variable surface sources and limited groundwater resources to growing demands. This challenge is leading to a new generation of detailed computational models that link multiple interacting sources and demands. We will discuss a new computational model of arid region hydrology that we are parameterizing for the upper Rio Grande Basin of the United States. The model consists of linked components for the atmosphere (the Regional Atmospheric Modeling System, RAMS), surface hydrology (the Los Alamos Distributed Hydrologic System, LADHS), and groundwater (the Finite Element Heat and Mass code, FEHM), and the couplings between them. The model runs under the Parallel Application WorkSpace software developed at Los Alamos for applications running on large distributed memory computers. RAMS simulates regional meteorology coupled to global climate data on the one hand and land surface hydrology on the other. LADHS generates runoff by infiltration or saturation excess mechanisms, as well as interception, evapotranspiration, and snow accumulation and melt. FEHM simulates variably saturated flow and heat transport in three dimensions. A key issue is to increase the components’ spatial and temporal resolution to account for changes in topography and other rapidly changing variables that affect results such as soil moisture distribution or groundwater recharge. Thus, RAMS’ smallest grid is 5 km on a side, LADHS uses 100 m spacing, while FEHM concentrates processing on key volumes by means of an unstructured grid. Couplings within our model are based on new scaling methods that link groundwater-groundwater systems and streams to aquifers and we are developing evapotranspiration methods based on detailed calculations of latent heat and vegetative cover. Simulations of precipitation and soil moisture for the 1992-93 El Nino year will be used to demonstrate the approach and suggest further needs.

Groundwater Impact Assessment of Tailings Storage Facility, Western Turkey

NASA Astrophysics Data System (ADS)

Peksezer-Sayit, A.; Yazicigil, H.

2015-12-01

A tailings storage facility (TSF) is a fundamental part of the mining process and should be carefully designed and managed to prevent any adverse environmental effects. TSF is site-specific and its design criteria are determined by regulations. The new mine waste regulation for the deposition of hazardous waste in a tailings storage facility in Turkey enforces, from bottom to top, 0.5 m thick compacted clay layer with K less than or equal to 1X10-9 m/s , 2 mm thick HDPE geomembrane, and a protective natural material or geotextile. Although these criteria seem to be enough to prevent leakage from the base, in practice, manufacturing and application errors may cause leakage and subsequent contamination of groundwater. The purpose of this study is to assess potential impacts of leakage from the base of TSF on groundwater quality both in operational and post-closure period of a mine site in western Turkey. For this purpose, analytical and 2-D and 3-D numerical models are used together. The potential leakage rate of sulphate-bearing solution from the base of TSF is determined from analytical model. 2-D finite element models (SEEP/W and CTRAN/W) are used to simulate unsaturated flow conditions and advective-dispersive contaminant transport below the TSF under steady-state and transient conditions for the operating period. The long-term impacts of leakage from the base of TSF on groundwater resources are evaluated by 3-D numerical groundwater flow (MODFLOW) and contaminant transport models (MT3DMS). The model results suggest that sulphate-bearing solution leaking from the base of TSF can reach water table in about 290 years. Hence, during the operational period (i.e. 21 years), no interaction is expected between the solution and groundwater. Moreover, long-term simulation results show that about 500 years later, the sulphate concentration in groundwater will be below the maximum allowable limits (i.e. 250 mg/L).

Construction and calibration of a groundwater-flow model to assess groundwater availability in the uppermost principal aquifer systems of the Williston Basin, United States and Canada

USGS Publications Warehouse

Davis, Kyle W.; Long, Andrew J.

2018-05-31

The U.S. Geological Survey developed a groundwater-flow model for the uppermost principal aquifer systems in the Williston Basin in parts of Montana, North Dakota, and South Dakota in the United States and parts of Manitoba and Saskatchewan in Canada as part of a detailed assessment of the groundwater availability in the area. The assessment was done because of the potential for increased demands and stresses on groundwater associated with large-scale energy development in the area. As part of this assessment, a three-dimensional groundwater-flow model was developed as a tool that can be used to simulate how the groundwater-flow system responds to changes in hydrologic stresses at a regional scale.The three-dimensional groundwater-flow model was developed using the U.S. Geological Survey’s numerical finite-difference groundwater model with the Newton-Rhapson solver, MODFLOW–NWT, to represent the glacial, lower Tertiary, and Upper Cretaceous aquifer systems for steady-state (mean) hydrological conditions for 1981‒2005 and for transient (temporally varying) conditions using a combination of a steady-state period for pre-1960 and transient periods for 1961‒2005. The numerical model framework was constructed based on existing and interpreted hydrogeologic and geospatial data and consisted of eight layers. Two layers were used to represent the glacial aquifer system in the model; layer 1 represented the upper one-half and layer 2 represented the lower one-half of the glacial aquifer system. Three layers were used to represent the lower Tertiary aquifer system in the model; layer 3 represented the upper Fort Union aquifer, layer 4 represented the middle Fort Union hydrogeologic unit, and layer 5 represented the lower Fort Union aquifer. Three layers were used to represent the Upper Cretaceous aquifer system in the model; layer 6 represented the upper Hell Creek hydrogeologic unit, layer 7 represented the lower Hell Creek aquifer, and layer 8 represented the Fox Hills aquifer. The numerical model was constructed using a uniform grid with square cells that are about 1 mile (1,600 meters) on each side with a total of about 657,000 active cells.Model calibration was completed by linking Parameter ESTimation (PEST) software with MODFLOW–NWT. The PEST software uses statistical parameter estimation techniques to identify an optimum set of input parameters by adjusting individual model input parameters and assessing the differences, or residuals, between observed (measured or estimated) data and simulated values. Steady-state model calibration consisted of attempting to match mean simulated values to measured or estimated values of (1) hydraulic head, (2) hydraulic head differences between model layers, (3) stream infiltration, and (4) discharge to streams. Calibration of the transient model consisted of attempting to match simulated and measured temporally distributed values of hydraulic head changes, stream base flow, and groundwater discharge to artesian flowing wells. Hydraulic properties estimated through model calibration included hydraulic conductivity, vertical hydraulic conductivity, aquifer storage, and riverbed hydraulic conductivity in addition to groundwater recharge and well skin.The ability of the numerical model to accurately simulate groundwater flow in the Williston Basin was assessed primarily by its ability to match calibration targets for hydraulic head, stream base flow, and flowing well discharge. The steady-state model also was used to assess the simulated potentiometric surfaces in the upper Fort Union aquifer, the lower Fort Union aquifer, and the Fox Hills aquifer. Additionally, a previously estimated regional groundwater-flow budget was compared with the simulated steady-state groundwater-flow budget for the Williston Basin. The simulated potentiometric surfaces typically compared well with the estimated potentiometric surfaces based on measured hydraulic head data and indicated localized groundwater-flow gradients that were topographically controlled in outcrop areas and more generalized regional gradients where the aquifers were confined. The differences between the measured and simulated (residuals) hydraulic head values for 11,109 wells were assessed, which indicated that the steady-state model generally underestimated hydraulic head in the model area. This underestimation is indicated by a positive mean residual of 11.2 feet for all model layers. Layer 7, which represents the lower Hell Creek aquifer, is the only layer for which the steady-state model overestimated hydraulic head. Simulated groundwater-level changes for the transient model matched within plus or minus 2.5 feet of the measured values for more than 60 percent of all measurements and to within plus or minus 17.5 feet for 95 percent of all measurements; however, the transient model underestimated groundwater-level changes for all model layers. A comparison between simulated and estimated base flows for the steady-state and transient models indicated that both models overestimated base flow in streams and underestimated annual fluctuations in base flow.The estimated and simulated groundwater budgets indicate the model area received a substantial amount of recharge from precipitation and stream infiltration. The steady-state model indicated that reservoir seepage was a larger component of recharge in the Williston Basin than was previously estimated. Irrigation recharge and groundwater inflow from outside the Williston Basin accounted for a relatively small part of total groundwater recharge when compared with recharge from precipitation, stream infiltration, and reservoir seepage. Most of the estimated and simulated groundwater discharge in the Williston Basin was to streams and reservoirs. Simulated groundwater withdrawal, discharge to reservoirs, and groundwater outflow in the Williston Basin accounted for a smaller part of total groundwater discharge.The transient model was used to simulate discharge to 571 flowing artesian wells within the model area. Of the 571 established flowing artesian wells simulated by the model, 271 wells did not flow at any time during the simulation because hydraulic head was always below the land-surface altitude. As hydraulic head declined throughout the simulation, 68 of these wells responded by ceasing to flow by the end of 2005. Total mean simulated discharge for the 571 flowing artesian wells was 55.1 cubic feet per second (ft3/s), and the mean simulated flowing well discharge for individual wells was 0.118 ft3/s. Simulated discharge to individual flowing artesian wells increased from 0.039 to 0.177 ft3/s between 1961 and 1975 and decreased to 0.102 ft3/s by 2005. The mean residual for 34 flowing wells with measured discharge was 0.014 ft3/s, which indicates the transient model overestimated discharge to flowing artesian wells in the model area.Model limitations arise from aspects of the conceptual model and from simplifications inherent in the construction and calibration of a regional-scale numerical groundwater-flow model. Simplifying assumptions in defining hydraulic parameters in space and hydrologic stresses and time-varying observational data in time can limit the capabilities of this tool to simulate how the groundwater-flow system responds to changes in hydrologic stresses, particularly at the local scale; nevertheless, the steady-state model adequately simulated flow in the uppermost principal aquifer systems in the Williston Basin based on the comparison between the simulated and estimated groundwater-flow budget, the comparison between simulated and estimated potentiometric surfaces, and the results of the calibration process.

Joint three-dimensional inversion of coupled groundwater flow and heat transfer based on automatic differentiation: sensitivity calculation, verification, and synthetic examples

NASA Astrophysics Data System (ADS)

Rath, V.; Wolf, A.; Bücker, H. M.

2006-10-01

Inverse methods are useful tools not only for deriving estimates of unknown parameters of the subsurface, but also for appraisal of the thus obtained models. While not being neither the most general nor the most efficient methods, Bayesian inversion based on the calculation of the Jacobian of a given forward model can be used to evaluate many quantities useful in this process. The calculation of the Jacobian, however, is computationally expensive and, if done by divided differences, prone to truncation error. Here, automatic differentiation can be used to produce derivative code by source transformation of an existing forward model. We describe this process for a coupled fluid flow and heat transport finite difference code, which is used in a Bayesian inverse scheme to estimate thermal and hydraulic properties and boundary conditions form measured hydraulic potentials and temperatures. The resulting derivative code was validated by comparison to simple analytical solutions and divided differences. Synthetic examples from different flow regimes demonstrate the use of the inverse scheme, and its behaviour in different configurations.

User guide for MODPATH Version 7—A particle-tracking model for MODFLOW

USGS Publications Warehouse

Pollock, David W.

2016-09-26

MODPATH is a particle-tracking post-processing program designed to work with MODFLOW, the U.S. Geological Survey (USGS) finite-difference groundwater flow model. MODPATH version 7 is the fourth major release since its original publication. Previous versions were documented in USGS Open-File Reports 89–381 and 94–464 and in USGS Techniques and Methods 6–A41.MODPATH version 7 works with MODFLOW-2005 and MODFLOW–USG. Support for unstructured grids in MODFLOW–USG is limited to smoothed, rectangular-based quadtree and quadpatch grids.A software distribution package containing the computer program and supporting documentation, such as input instructions, output file descriptions, and example problems, is available from the USGS over the Internet (http://water.usgs.gov/ogw/modpath/).

Documentation of the Surface-Water Routing (SWR1) Process for modeling surface-water flow with the U.S. Geological Survey Modular Ground-Water Model (MODFLOW-2005)

USGS Publications Warehouse

Hughes, Joseph D.; Langevin, Christian D.; Chartier, Kevin L.; White, Jeremy T.

2012-01-01

A flexible Surface-Water Routing (SWR1) Process that solves the continuity equation for one-dimensional and two-dimensional surface-water flow routing has been developed for the U.S. Geological Survey three-dimensional groundwater model, MODFLOW-2005. Simple level- and tilted-pool reservoir routing and a diffusive-wave approximation of the Saint-Venant equations have been implemented. Both methods can be implemented in the same model and the solution method can be simplified to represent constant-stage elements that are functionally equivalent to the standard MODFLOW River or Drain Package boundary conditions. A generic approach has been used to represent surface-water features (reaches) and allows implementation of a variety of geometric forms. One-dimensional geometric forms include rectangular, trapezoidal, and irregular cross section reaches to simulate one-dimensional surface-water features, such as canals and streams. Two-dimensional geometric forms include reaches defined using specified stage-volume-area-perimeter (SVAP) tables and reaches covering entire finite-difference grid cells to simulate two-dimensional surface-water features, such as wetlands and lakes. Specified SVAP tables can be used to represent reaches that are smaller than the finite-difference grid cell (for example, isolated lakes), or reaches that cannot be represented accurately using the defined top of the model. Specified lateral flows (which can represent point and distributed flows) and stage-dependent rainfall and evaporation can be applied to each reach. The SWR1 Process can be used with the MODFLOW Unsaturated Zone Flow (UZF1) Package to permit dynamic simulation of runoff from the land surface to specified reaches. Surface-water/groundwater interactions in the SWR1 Process are mathematically defined to be a function of the difference between simulated stages and groundwater levels, and the specific form of the reach conductance equation used in each reach. Conductance can be specified directly or calculated as a function of the simulated wetted perimeter and defined reach bed hydraulic properties, or as a weighted combination of both reach bed hydraulic properties and horizontal hydraulic conductivity. Each reach can be explicitly coupled to a single specific groundwater-model layer or coupled to multiple groundwater-model layers based on the reach geometry and groundwater-model layer elevations in the row and column containing the reach. Surface-water flow between reservoirs is simulated using control structures. Surface-water flow between reaches, simulated by the diffusive-wave approximation, can also be simulated using control structures. A variety of control structures have been included in the SWR1 Process and include (1) excess-volume structures, (2) uncontrolled-discharge structures, (3) pumps, (4) defined stage-discharge relations, (5) culverts, (6) fixed- or movable-crest weirs, and (7) fixed or operable gated spillways. Multiple control structures can be implemented in individual reaches and are treated as composite flow structures. Solution of the continuity equation at the reach-group scale (a single reach or a user-defined collection of individual reaches) is achieved using exact Newton methods with direct solution methods or exact and inexact Newton methods with Krylov sub-space methods. Newton methods have been used in the SWR1 Process because of their ability to solve nonlinear problems. Multiple SWR1 time steps can be simulated for each MODFLOW time step, and a simple adaptive time-step algorithm, based on user-specified rainfall, stage, flow, or convergence constraints, has been implemented to better resolve surface-water response. A simple linear- or sigmoid-depth scaling approach also has been implemented to account for increased bed roughness at small surface-water depths and to increase numerical stability. A line-search algorithm also has been included to improve the quality of the Newton-step upgrade vector, if possible. The SWR1 Process has been benchmarked against one- and two-dimensional numerical solutions from existing one- and two-dimensional numerical codes that solve the dynamic-wave approximation of the Saint-Venant equations. Two-dimensional solutions test the ability of the SWR1 Process to simulate the response of a surface-water system to (1) steady flow conditions for an inclined surface (solution of Manning's equation), and (2) transient inflow and rainfall for an inclined surface. The one-dimensional solution tests the ability of the SWR1 Process to simulate a looped network with multiple upstream inflows and several control structures. The SWR1 Process also has been compared to a level-pool reservoir solution. A synthetic test problem was developed to evaluate a number of different SWR1 solution options and simulate surface-water/groundwater interaction. The solution approach used in the SWR1 Process may not be applicable for all surface-water/groundwater problems. The SWR1 Process is best suited for modeling long-term changes (days to years) in surface-water and groundwater flow. Use of the SWR1 Process is not recommended for modeling the transient exchange of water between streams and aquifers when local and convective acceleration and other secondary effects (for example, wind and Coriolis forces) are substantial. Dam break evaluations and two-dimensional evaluations of spatially extensive domains are examples where acceleration terms and secondary effects would be significant, respectively.

Combination of poroelasticity theory and constant strain rate test in modelling land subsidence due to groundwater extraction

NASA Astrophysics Data System (ADS)

Pham, Tien Hung; Rühaak, Wolfram; Sass, Ingo

2017-04-01

Extensive groundwater extraction leads to a drawdown of the ground water table. Consequently, soil effective stress increases and can cause land subsidence. Analysis of land subsidence generally requires a numerical model based on poroelasticity theory, which was first proposed by Biot (1941). In the review of regional land subsidence accompanying groundwater extraction, Galloway and Burbey (2011) stated that more research and application is needed in coupling of stress-dependent land subsidence process. In geotechnical field, the constant rate of strain tests (CRS) was first introduced in 1969 (Smith and Wahls 1969) and was standardized in 1982 through the designation D4186-82 by American Society for Testing and Materials. From the reading values of CRS tests, the stress-dependent parameters of poroelasticity model can be calculated. So far, there is no research to link poroelasticity theory with CRS tests in modelling land subsidence due to groundwater extraction. One dimensional CRS tests using conventional compression cell and three dimension CRS tests using Rowe cell were performed. The tests were also modelled by using finite element method with mixed elements. Back analysis technique is used to find the suitable values of hydraulic conductivity and bulk modulus that depend on the stress or void ratio. Finally, the obtained results are used in land subsidence models. Biot, M. A. (1941). "General theory of three-dimensional consolidation." Journal of applied physics 12(2): 155-164. Galloway, D. L. and T. J. Burbey (2011). "Review: Regional land subsidence accompanying groundwater extraction." Hydrogeology Journal 19(8): 1459-1486. Smith, R. E. and H. E. Wahls (1969). "Consolidation under constant rates of strain." Journal of Soil Mechanics & Foundations Div.

SutraPlot, a graphical post-processor for SUTRA, a model for ground-water flow with solute or energy transport

USGS Publications Warehouse

Souza, W.R.

1999-01-01

This report documents a graphical display post-processor (SutraPlot) for the U.S. Geological Survey Saturated-Unsaturated flow and solute or energy TRAnsport simulation model SUTRA, Version 2D3D.1. This version of SutraPlot is an upgrade to SutraPlot for the 2D-only SUTRA model (Souza, 1987). It has been modified to add 3D functionality, a graphical user interface (GUI), and enhanced graphic output options. Graphical options for 2D SUTRA (2-dimension) simulations include: drawing the 2D finite-element mesh, mesh boundary, and velocity vectors; plots of contours for pressure, saturation, concentration, and temperature within the model region; 2D finite-element based gridding and interpolation; and 2D gridded data export files. Graphical options for 3D SUTRA (3-dimension) simulations include: drawing the 3D finite-element mesh; plots of contours for pressure, saturation, concentration, and temperature in 2D sections of the 3D model region; 3D finite-element based gridding and interpolation; drawing selected regions of velocity vectors (projected on principal coordinate planes); and 3D gridded data export files. Installation instructions and a description of all graphic options are presented. A sample SUTRA problem is described and three step-by-step SutraPlot applications are provided. In addition, the methodology and numerical algorithms for the 2D and 3D finite-element based gridding and interpolation, developed for SutraPlot, are described. 1

Nonlinear-regression groundwater flow modeling of a deep regional aquifer system

USGS Publications Warehouse

Cooley, Richard L.; Konikow, Leonard F.; Naff, Richard L.

1986-01-01

A nonlinear regression groundwater flow model, based on a Galerkin finite-element discretization, was used to analyze steady state two-dimensional groundwater flow in the areally extensive Madison aquifer in a 75,000 mi2 area of the Northern Great Plains. Regression parameters estimated include intrinsic permeabilities of the main aquifer and separate lineament zones, discharges from eight major springs surrounding the Black Hills, and specified heads on the model boundaries. Aquifer thickness and temperature variations were included as specified functions. The regression model was applied using sequential F testing so that the fewest number and simplest zonation of intrinsic permeabilities, combined with the simplest overall model, were evaluated initially; additional complexities (such as subdivisions of zones and variations in temperature and thickness) were added in stages to evaluate the subsequent degree of improvement in the model results. It was found that only the eight major springs, a single main aquifer intrinsic permeability, two separate lineament intrinsic permeabilities of much smaller values, and temperature variations are warranted by the observed data (hydraulic heads and prior information on some parameters) for inclusion in a model that attempts to explain significant controls on groundwater flow. Addition of thickness variations did not significantly improve model results; however, thickness variations were included in the final model because they are fairly well defined. Effects on the observed head distribution from other features, such as vertical leakage and regional variations in intrinsic permeability, apparently were overshadowed by measurement errors in the observed heads. Estimates of the parameters correspond well to estimates obtained from other independent sources.

Nonlinear-Regression Groundwater Flow Modeling of a Deep Regional Aquifer System

NASA Astrophysics Data System (ADS)

Cooley, Richard L.; Konikow, Leonard F.; Naff, Richard L.

1986-12-01

A nonlinear regression groundwater flow model, based on a Galerkin finite-element discretization, was used to analyze steady state two-dimensional groundwater flow in the areally extensive Madison aquifer in a 75,000 mi2 area of the Northern Great Plains. Regression parameters estimated include intrinsic permeabilities of the main aquifer and separate lineament zones, discharges from eight major springs surrounding the Black Hills, and specified heads on the model boundaries. Aquifer thickness and temperature variations were included as specified functions. The regression model was applied using sequential F testing so that the fewest number and simplest zonation of intrinsic permeabilities, combined with the simplest overall model, were evaluated initially; additional complexities (such as subdivisions of zones and variations in temperature and thickness) were added in stages to evaluate the subsequent degree of improvement in the model results. It was found that only the eight major springs, a single main aquifer intrinsic permeability, two separate lineament intrinsic permeabilities of much smaller values, and temperature variations are warranted by the observed data (hydraulic heads and prior information on some parameters) for inclusion in a model that attempts to explain significant controls on groundwater flow. Addition of thickness variations did not significantly improve model results; however, thickness variations were included in the final model because they are fairly well defined. Effects on the observed head distribution from other features, such as vertical leakage and regional variations in intrinsic permeability, apparently were overshadowed by measurement errors in the observed heads. Estimates of the parameters correspond well to estimates obtained from other independent sources.

Simulation of ground-water flow in the Potomac-Raritan-Magothy aquifer system near the Defense Supply Center Philadelphia, and the Point Breeze Refinery, southern Philadelphia County, Pennsylvania

USGS Publications Warehouse

Schreffler, Curtis L.

2001-01-01

Ground-water flow in the Potomac-Raritan- Magothy aquifer system (PRM) in south Philadelphia and adjacent southwestern New Jersey was simulated by use of a three-dimensional, seven-layer finite-difference numerical flow model. The simulation was run from 1900, which was prior to groundwater development, through 1995 with 21 stress periods. The focus of the modeling was on a smaller area of concern in south Philadelphia in the vicinity of the Defense Supply Center Philadelphia (DSCP) and the Point Breeze Refinery (PBR). In order to adequately simulate the ground-water flow system in the area of concern, a much larger area was modeled that included parts of New Jersey where significant ground-water withdrawals, which affect water levels in southern Philadelphia, had occurred in the past. At issue in the area of concern is a hydrocarbon plume of unknown origin and time of release.The ground-water-flow system was simulated to estimate past water-level altitudes in and near the area of concern and to determine the effect of the Packer Avenue sewer, which lies south of the DSCP, on the ground-water-flow system. Simulated water-level altitudes for the lower sand unit of the PRM on the DSCP prior to 1945 ranged from pre-development, unstressed altitudes to 3 feet below sea level. Simulated water-level altitudes for the lower sand unit ranged from 3 to 7 feet below sea level from 1946 to 1954, from 6 to 10 feet below sea level from 1955 to 1968, and from 9 to 11 feet below sea level from 1969 to 1978. The lowest simulated water-level altitude on the DSCP was 10.69 feet below sea level near the end of 1974. Model simulations indicate ground water was infiltrating the Packer Avenue sewer prior to approximately 1947 or 1948. Subsequent to that time, simulated ground-water-level altitudes were lower than the bottom of the sewer.

Optimal groundwater remediation design of pump and treat systems via a simulation-optimization approach and firefly algorithm

NASA Astrophysics Data System (ADS)

Javad Kazemzadeh-Parsi, Mohammad; Daneshmand, Farhang; Ahmadfard, Mohammad Amin; Adamowski, Jan; Martel, Richard

2015-01-01

In the present study, an optimization approach based on the firefly algorithm (FA) is combined with a finite element simulation method (FEM) to determine the optimum design of pump and treat remediation systems. Three multi-objective functions in which pumping rate and clean-up time are design variables are considered and the proposed FA-FEM model is used to minimize operating costs, total pumping volumes and total pumping rates in three scenarios while meeting water quality requirements. The groundwater lift and contaminant concentration are also minimized through the optimization process. The obtained results show the applicability of the FA in conjunction with the FEM for the optimal design of groundwater remediation systems. The performance of the FA is also compared with the genetic algorithm (GA) and the FA is found to have a better convergence rate than the GA.

A multilayered sharp interface model of coupled freshwater and saltwater flow in coastal systems: Model development and application

USGS Publications Warehouse

Essaid, Hedeff I.

1990-01-01

A quasi three-dimensional, finite difference model, that simulates freshwater and saltwater flow separated by a sharp interface, has been developed to study layered coastal aquifer systems. The model allows for regional simulation of coastal groundwater conditions, including the effects of saltwater dynamics on the freshwater system. Vertically integrated freshwater and saltwater flow equations incorporating the interface boundary condition are solved within each aquifer. Leakage through confining layers is calculated by Darcy's law, accounting for density differences across the layer. The locations of the interface tip and toe, within grid blocks, are tracked by linearly extrapolating the position of the interface. The model has been verified using available analytical solutions and experimental results. Application of the model to the Soquel-Aptos basin, Santa Cruz County, California, illustrates the use of the quasi three-dimensional, sharp interface approach for the examination of freshwater-saltwater dynamics in regional systems. Simulation suggests that the interface, today, is still responding to long-term Pleistocene sea level fluctuations and has not achieved equilibrium with present day sea level conditions.

Mathematical Simulation of the Subsidence of Ravenna

NASA Astrophysics Data System (ADS)

Gambolati, Giuseppe; Ricceri, Giuseppe; Bertoni, Werter; Brighenti, Giovanni; Vuillermin, Enzo

1991-11-01

Land subsidence at Ravenna is the result of aquitard and reservoir compaction caused, respectively, by extensive groundwater withdrawals from the unconsolidated Quaternary basin and gas production from a number of pre-Quaternary pools scattered over the area. Water pumpage paralleled the postwar industrial development of Ravenna until the middle seventies when consumption was drastically curtailed owing to the economic crisis and the activation of a new aqueduct. Gas production started in 1952. The exploitation of several reservoirs is currently under way and the search for new fields is still in progress. Geodetic records indicate that the maximum cumulative subsidence over the period 1950-1986, including a natural geologic settlement of perhaps 2 mm/yr, has been 1.30 m in the industrial zone of Ravenna. In 1980 the municipality promoted a reconnaissance study with the primary aim of providing the information base needed to reconstruct the actual occurrence, understand correctly the physical behavior and produce the essential input data to a mathematical model which realistically relates the subsidence of the city to groundwater withdrawal and gas removal with an emphasis on their respective influences. The results from the three-dimensional numerical simulations, performed with the aid of mixed finite element, finite difference and integral models, show that the primary responsibility for the regional land sinking should be placed on the subsurface water overdraft which occurred until the middle 1970s. Gas withdrawal plays a role restricted to the area overlying each reservoir with a magnitude depending on the depth of burial, thickness of mineralized rocks and overall volumetric production. A major environmental impact may be expected where the gas subsidence bowl is intersected by the Adriatic coastline.

User guide for the farm process (FMP1) for the U.S. Geological Survey's modular three-dimensional finite-difference ground-water flow model, MODFLOW-2000

USGS Publications Warehouse

Schmid, Wolfgang; Hanson, R.T.; Maddock, Thomas; Leake, S.A.

2006-01-01

There is a need to estimate dynamically integrated supply-and-demand components of irrigated agriculture as part of the simulation of surface-water and ground-water flow. To meet this need, a computer program called the Farm Process (FMP1) was developed for the U.S. Geological Survey three-dimensional finite-difference modular ground-water flow model, MODFLOW- 2000 (MF2K). The FMP1 allows MF2K users to simulate conjunctive use of surface- and ground water for irrigated agriculture for historical and future simulations, water-rights issues and operational decisions, nondrought and drought scenarios. By dynamically integrating farm delivery requirement, surface- and ground-water delivery, as well as irrigation-return flow, the FMP1 allows for the estimation of supplemental well pumpage. While farm delivery requirement and irrigation return flow are simulated by the FMP1, the surface-water delivery to the farm can be simulated optionally by coupling the FMP1 with the Streamflow Routing Package (SFR1) and the farm well pumping can be simulated optionally by coupling the FMP1 to the Multi-Node Well (MNW) Package. In addition, semi-routed deliveries can be specified that are associated with points of diversion in the SFR1 stream network. Nonrouted surface-water deliveries can be specified independently of any stream network. The FMP1 maintains a dual mass balance of a farm budget and as part of the ground-water budget. Irrigation demand, supply, and return flow are in part subject to head-dependent sources and sinks such as evapotranspiration from ground water and leakage between the conveyance system and the aquifer. Farm well discharge and farm net recharge are source/sink terms in the FMP1, which depend on transpiration uptake from ground water and other head dependent consumptive use components. For heads rising above the bottom of the root zone, the actual transpiration is taken to vary proportionally with the depth of the active root zone, which can be restricted by anoxia or wilting. Depths corresponding to anoxia- or wilting-related pressure heads within the root zone are found using analytical solutions of a vertical pseudo steady-state pressure- head distribution over the depth of the total root zone (Consumptive Use Concept 1). Alternatively, a simpler, conceptual model is available, which defines how consumptive use (CU) components vary with changing head (CU Concept 2). Subtracting the ground water and precipitation transpiration components from the total transpiration yields a transpiratory irrigation requirement for each cell. The total farm delivery requirement (TFDR) then is determined as cumulative transpiratory and evaporative irrigation requirements of all farm cells and increased sufficiently to compensate for inefficient use from irrigation with respect to plant consumption. The TFDR subsequently is satisfied with surface- and ground-water delivery, respectively constrained by allotments, water rights, or maximum capacities. Five economic and noneconomic drought response policies can be applied optionally, if the potential supply of surface water and ground water is insufficient to meet the crop demand: acreage-optimization with or without a water conservation pool, deficit irrigation with or without water-stacking, and zero policy.

Use of 3H/3He Ages to evaluate and improve groundwater flow models in a complex buried-valley aquifer

USGS Publications Warehouse

Sheets, Rodney A.; Bair, E. Scott; Rowe, Gary L.

1998-01-01

Combined use of the tritium/helium 3 (3H/3He) dating technique and particle-tracking analysis can improve flow-model calibration. As shown at two sites in the Great Miami buried-valley aquifer in southwestern Ohio, the combined use of 3H/3He age dating and particle tracking led to a lower mean absolute error between measured heads and simulated heads than in the original calibrated models and/or between simulated travel times and 3H/3He ages. Apparent groundwater ages were obtained for water samples collected from 44 wells at two locations where previously constructed finite difference models of groundwater flow were available (Mound Plant and Wright-Patterson Air Force Base (WPAFB)). The two-layer Mound Plant model covers 11 km2 within the buried-valley aquifer. The WPAFB model has three layers and covers 262 km2 within the buried-valley aquifer and adjacent bedrock uplands. Sampled wells were chosen along flow paths determined from potentiometric maps or particle-tracking analyses. Water samples were collected at various depths within the aquifer. In the Mound Plant area, samples used for comparison of 3H/3He ages with simulated travel times were from wells completed in the uppermost model layer. Simulated travel times agreed well with 3H/3He ages. The mean absolute error (MAE) was 3.5 years. Agreement in ages at WPAFB decreased with increasing depth in the system. The MAEs were 1.63, 17.2, and 255 years for model layers 1, 2, and 3, respectively. Discrepancies between the simulated travel times and 3H/3He ages were assumed to be due to improper conceptualization or incorrect parameterization of the flow models. Selected conceptual and parameter modifications to the models resulted in improved agreement between 3H/3He ages and simulated travel times and between measured and simulated heads and flows.

Steady-state numerical groundwater flow model of the Great Basin carbonate and alluvial aquifer system

USGS Publications Warehouse

Brooks, Lynette E.; Masbruch, Melissa D.; Sweetkind, Donald S.; Buto, Susan G.

2014-01-01

Examples of potential use of the model to investigate the groundwater system include (1) the effects of different recharge, (2) different interpretations of the extent or offset of long faults or fault zones, and (3) different conceptual models of the spatial variation of hydraulic properties. The model can also be used to examine the ultimate effects of groundwater withdrawals on a regional scale, to provide boundary conditions for local-scale models, and to guide data collection.

Evaluation of the ground-water resources of parts of Lancaster and Berks Counties, Pennsylvania

USGS Publications Warehouse

Gerhart, J.M.; Lazorchick, G.J.

1984-01-01

Secondary openings in bedrock are the avenues for virtually all ground-water flow in a 626-sqare-mile area in Lancaster and Berks Counties, Pennsylvania. The number, size, and interconnection of secondary openings are functions of lithology, depth, and topography. Ground water actively circulates to depths of 150 to 300 feet below land surface. Total average annual ground-water recharge for the area is 388 million gallons per day, most of which discharges to streams from local, unconfined flow systems. A digital ground-water flow model was developed to simulate unconfined flow under several different recharge and withdrawal scenarios. On the basis of lithologic and hydrologic differences, the modeled area was sub-divided into 22 hydrogeologic units. A finite-difference grid with rectangular blocks, each 2,015 by 2,332 feet, was used. The model was calibrated under steady-state and transient conditions. The steady-state calibration was used to determine hydraulic conductivities and stream leakage coefficients and the transient calibration was used to determine specific yields. The 22 hydrogeologic units fall into four general lithologies: Carbonate rocks, metamorphic rocks, Paleozoic sedimentary rocks, and Triassic sedimentary rocks. Average hydraulic conductivity ranges from about 8.8 feet per day in carbonate units to about .5 feet per day in metamorphic units. The Stonehenge Formation (limestone) has the greatest average hydraulic conductivity--85.2 feet per day in carbonate units to about 0.11 feet per day in the greatest gaining-strem leakage coefficient--16.81 feet per day. Specific yield ranges from 0.06 to 0.09 in carbonate units, and is 0.02 to 0.015, and 0.012 in metamorphic, Paleozoic sedimentary, and Triassic sedimentary units, respectively. Transient simulations were made to determine the effects of four different combinations of natural and artificial stresses. Natural aquifer conditions (no ground-water withdrawals) and actual aquifer conditions (current ground-water withdrawals) were simulated for two years under normal seasonal and hypothetical drought (60-percent reduction in winter-spring recharge) conditions. In October, 6 months after the hypothetical drought, simulated declines in water-table altitude due to the drought occurred everywhere and ranged from a median of 3.6 feet in carbonate units to 8.7 feet in carbonate units. Simulated base flows for five major streams were reduced by 33 to 51 percent during the hypothetical drought. Also in October, maximum simulated declines in water-table altitude due to ground-water withdrawls ranged from 33 feet in carbonate units to 79 feet in Triassic sedimentary units. Simulated base flows for five major streams were reduced by the amount of ground water withdrawn. Finally, again in October, maximum simulated declines in water-table altitude due to the combination of hypothetical drought and ground-water withdrawls ranged from 38 feet in carbonate units to 109 feet in Triassic sedimentary units. Due to aquifer dewatering, simulated declines were as much as 24 feet greater than the sum of the separate simulated declines that were caused by hypothetical drought and ground-water withdrawals. Some of the greatest simulated declines were in well fields, operated by three municipalities that experienced water-supply problems during the 1980-81 drought.

Audiomagnetotelluric investigation of Snake Valley, eastern Nevada and western Utah

USGS Publications Warehouse

McPhee, Darcy K.; Pari, Keith; Baird, Frank

2009-01-01

As support for an exploratory well-drilling and hydraulic-testing program, AMT data were collected using a Geometrics Stratagem EH4 system along four profiles that extend roughly east-west from the southern Snake Range into Snake Valley. The profiles range from 3 to 5 kilometers in length, and station spacing was 200 to 400 meters. Two-dimensional inverse models were computed using the data from the transverse-electric (TE), transverse-magnetic (TM), and combined (TE+TM) mode using a conjugate gradient, finite-difference method. Interpretation of the 2-D AMT models defines several faults, some of which may influence ground-water flow in the basins, as well as identify underlying Paleozoic carbonate and clastic rocks and the thickness of basin-fill sediments. These AMT data and models, coupled with the geologic mapping and other surface geophysical methods, form the basis for identifying potential well sites and defining the subsurface structures and stratigraphy within Snake Valley.

Hydrogeology and simulation of ground-water flow in the thick regolith-fractured crystalline rock aquifer system of Indian Creek basin, North Carolina

USGS Publications Warehouse

Daniel, Charles C.; Smith, Douglas G.; Eimers, Jo Leslie

1997-01-01

The Indian Creek Basin in the southwestern Piedmont of North Carolina is one of five type areas studied as part of the Appalachian Valleys-Piedmont Regional Aquifer-System analysis. Detailed studies of selected type areas were used to quantify ground-water flow characteristics in various conceptual hydrogeologic terranes. The conceptual hydrogeologic terranes are considered representative of ground-water conditions beneath large areas of the three physiographic provinces--Valley and Ridge, Blue Ridge, and Piedmont--that compose the Appalachian Valleys-Piedmont Regional Aquifer-System Analysis area. The Appalachian Valleys-Piedmont Regional Aquifer-System Analysis study area extends over approximately 142,000 square miles in 11 states and the District of Columbia in the Appalachian highlands of the Eastern United States. The Indian Creek type area is typical of ground-water conditions in a single hydrogeologic terrane that underlies perhaps as much as 40 percent of the Piedmont physiographic province. The hydrogeologic terrane of the Indian Creek model area is one of massive and foliated crystalline rocks mantled by thick regolith. The area lies almost entirely within the Inner Piedmont geologic belt. Five hydrogeologic units occupy major portions of the model area, but statistical tests on well yields, specific capacities, and other hydrologic characteristics show that the five hydrogeologic units can be treated as one unit for purposes of modeling ground-water flow. The 146-square-mile Indian Creek model area includes the Indian Creek Basin, which has a surface drainage area of about 69 square miles. The Indian Creek Basin lies in parts of Catawba, Lincoln, and Gaston Counties, North Carolina. The larger model area is based on boundary conditions established for digital simulation of ground-water flow within the smaller Indian Creek Basin. The ground-water flow model of the Indian Creek Basin is based on the U.S. Geological Survey?s modular finite-difference ground-water flow model. The model area is divided into a uniformly spaced grid having 196 rows and 140 columns. The grid spacing is 500 feet. The model grid is oriented to coincide with fabric elements such that rows are oriented parallel to fractures (N. 72? E.) and columns are oriented parallel to foliation (N. 18? W.). The model is discretized vertically into 11 layers; the top layer represents the soil and saprolite of the regolith, and the lower 10 layers represent bedrock. The base of the model is 850 feet below land surface. The top bedrock layer, which is only 25 feet thick, represents the transition zone between saprolite and unweathered bedrock. The assignment of different values of transmissivity to the bedrock according to the topographic setting of model cells and depth results in inherent lateral and vertical anisotropy in the model with zones of high transmissivity in bedrock coinciding with valleys and draws, and zones of low transmissivity in bedrock coinciding with hills and ridges. Lateral anisotropy tends to be most pronounced in the north-northwest to south-southeast direction. Transmissivities decrease nonlineraly with depth. At 850 feet, depending on topographic setting, transmissivities have decreased to about 1 to 4 percent of the value of transmissivity immediately below the regolith-bedrock interface. The model boundaries are, for the most part, specified-flux boundaries that coincide with streams that surround the Indian Creek Basin. The area of active model nodes within the boundaries is about 146 square miles and has about 17,400 active cells. The numerical model is designed not as a predictive tool, but as an interpretive one. The model is designed to help gain insight into flow-system dynamics. Predictive capabilities of the numerical model are limited by the constraints placed on the flow system by specified fluxes and recharge distribution. Results of steady-state analyses that simulate long-term, average annual conditi

Numerical simulation of earth fissures caused by overly aquifer exploitation at Guangming Village, China

NASA Astrophysics Data System (ADS)

Ye, S.; Franceschini, A.; Zhang, Y.; Janna, C.; Gong, X.; Yu, J.; Teatini, P.

2017-12-01

Earth fissures accompanying anthropogenic land subsidence due to overly aquifer exploitation create significant geohazards in China. In the framework of an efficient and safe management of groundwater, numerical models represent a unique scientific approach to predict the generation and development of earth fissures. However, the common geomechanical simulators fail to reproduce fissure development because, due to compatibility conditions, they cannot be effectively applied in discontinuous mechanics. We present an innovative modelling approach for the simulation of fissure development. Firstly, a regional 3D groundwater model is calibrated on available piezometric records; secondly, the regional outcome is used to define the boundary conditions of a local 3D groundwater model developed at the fissure scale and implementing a refined discretization of the local hydrogeologic setting; finally, the pressure change are used as forcing factor in a local 3D geomechanical model, which combines Finite Elements and Interface Elements to simulate the deformation of the continuous aquifer system and the generation and sliding/opening of earth fissures The approach has been applied to simulate the earth fissure at Guangming Village in Wuxi, China with land subsidence of more than 1 m caused by the overexploitation of the second confined aquifer. The first earth fissure was observed in 1998. It developed fast from 1998 to 2007. The domain addressed by the local simulations is 2 km wide and 5 km long. The thickness of the aquifer system ranges from 0 m, in the proximity of a mountain ridge southward, to 210 m northward and includes a phreatic aquifer, the first and second confined aquifers, and four aquitards. The simulations spanned the period from 1980, i.e. before the inception of large groundwater withdrawals, to 2015. The modelling results highlight that the earth fissures at Guangming Village have been caused by tension and shear, which developed from the land surface downward. The main factors contributing to fissure generation include the shallow bedrock with a sharp ridge, the asymmetric shape of ridge, the uneven thickness of the sedimentary deposits at the west and east side of the buried ridge together with a different pressure change that have been responsible for differential land subsidence.

User's guide to the Variably Saturated Flow (VSF) process to MODFLOW

USGS Publications Warehouse

Thoms, R. Brad; Johnson, Richard L.; Healy, Richard W.

2006-01-01

A new process for simulating three-dimensional (3-D) variably saturated flow (VSF) using Richards' equation has been added to the 3-D modular finite-difference ground-water model MODFLOW. Five new packages are presented here as part of the VSF Process--the Richards' Equation Flow (REF1) Package, the Seepage Face (SPF1) Package, the Surface Ponding (PND1) Package, the Surface Evaporation (SEV1) Package, and the Root Zone Evapotranspiration (RZE1) Package. Additionally, a new Adaptive Time-Stepping (ATS1) Package is presented for use by both the Ground-Water Flow (GWF) Process and VSF. The VSF Process allows simulation of flow in unsaturated media above the ground-water zone and facilitates modeling of ground-water/surface-water interactions. Model performance is evaluated by comparison to an analytical solution for one-dimensional (1-D) constant-head infiltration (Dirichlet boundary condition), field experimental data for a 1-D constant-head infiltration, laboratory experimental data for two-dimensional (2-D) constant-flux infiltration (Neumann boundary condition), laboratory experimental data for 2-D transient drainage through a seepage face, and numerical model results (VS2DT) of a 2-D flow-path simulation using realistic surface boundary conditions. A hypothetical 3-D example case also is presented to demonstrate the new capability using periodic boundary conditions (for example, daily precipitation) and varied surface topography over a larger spatial scale (0.133 square kilometer). The new model capabilities retain the modular structure of the MODFLOW code and preserve MODFLOW's existing capabilities as well as compatibility with commercial pre-/post-processors. The overall success of the VSF Process in simulating mixed boundary conditions and variable soil types demonstrates its utility for future hydrologic investigations. This report presents a new flow package implementing the governing equations for variably saturated ground-water flow, four new boundary condition packages unique to unsaturated flow, the Adaptive Time-Stepping Package for use with both the GWF Process and the new VSF Process, detailed descriptions of the input and output files for each package, and six simulation examples verifying model performance.

Adaptive multiresolution modeling of groundwater flow in heterogeneous porous media

NASA Astrophysics Data System (ADS)

Malenica, Luka; Gotovac, Hrvoje; Srzic, Veljko; Andric, Ivo

2016-04-01

Proposed methodology was originally developed by our scientific team in Split who designed multiresolution approach for analyzing flow and transport processes in highly heterogeneous porous media. The main properties of the adaptive Fup multi-resolution approach are: 1) computational capabilities of Fup basis functions with compact support capable to resolve all spatial and temporal scales, 2) multi-resolution presentation of heterogeneity as well as all other input and output variables, 3) accurate, adaptive and efficient strategy and 4) semi-analytical properties which increase our understanding of usually complex flow and transport processes in porous media. The main computational idea behind this approach is to separately find the minimum number of basis functions and resolution levels necessary to describe each flow and transport variable with the desired accuracy on a particular adaptive grid. Therefore, each variable is separately analyzed, and the adaptive and multi-scale nature of the methodology enables not only computational efficiency and accuracy, but it also describes subsurface processes closely related to their understood physical interpretation. The methodology inherently supports a mesh-free procedure, avoiding the classical numerical integration, and yields continuous velocity and flux fields, which is vitally important for flow and transport simulations. In this paper, we will show recent improvements within the proposed methodology. Since "state of the art" multiresolution approach usually uses method of lines and only spatial adaptive procedure, temporal approximation was rarely considered as a multiscale. Therefore, novel adaptive implicit Fup integration scheme is developed, resolving all time scales within each global time step. It means that algorithm uses smaller time steps only in lines where solution changes are intensive. Application of Fup basis functions enables continuous time approximation, simple interpolation calculations across different temporal lines and local time stepping control. Critical aspect of time integration accuracy is construction of spatial stencil due to accurate calculation of spatial derivatives. Since common approach applied for wavelets and splines uses a finite difference operator, we developed here collocation one including solution values and differential operator. In this way, new improved algorithm is adaptive in space and time enabling accurate solution for groundwater flow problems, especially in highly heterogeneous porous media with large lnK variances and different correlation length scales. In addition, differences between collocation and finite volume approaches are discussed. Finally, results show application of methodology to the groundwater flow problems in highly heterogeneous confined and unconfined aquifers.

Ground-water flow and the potential effects of remediation at Graces Quarters, Aberdeen Proving Ground, Maryland

USGS Publications Warehouse

Tenbus, F.J.; Fleck, W.B.

1996-01-01

Ground water in the east-central part of Graces Quarters, a former open-air chemical-agent test facility at Aberdeen Proving Ground, Maryland, is contaminated with chlorinated volatile organic compounds. The U.S. Geological Survey's finite- difference model was used to help understand ground-water flow and simulate the effects of alternative remedial actions to clean up the ground water. Scenarios to simulate unstressed conditions and three extraction well con- figurations were used to compare alternative remedial actions on the contaminant plume. The scenarios indicate that contaminants could migrate from their present location to wetland areas within 10 years under unstressed conditions. Pumping 7 gal/min (gallons per minute) from one well upgradient of the plume will not result in containment or removal of the highest contaminant concentrations. Pumping 7 gal/min from three wells along the central axis of the plume should result in containment and removal of dissolved contami- nants, as should pumping 7 gal/min from three wells at the leading edge of the plume while injecting 7 gal/min back into an upgradient well.

Three-dimensional digital-computer model of the Ferron sandstone aquifer near Emery, Utah

USGS Publications Warehouse

Morrissey, Daniel J.; Lines, Gregory C.; Bartholoma, Scott D.

1980-01-01

A three-dimensional finite-difference computer model of the Ferron sandstone aquifer was used to simulate groundwater flow in the Emery coal field in east-central Utah. The model also was used to predict the effects of proposed surface mining and the resulting mine dewatering on potentiometric surfaces of the aquifer. The model was calibrated in a steady-state simulation using water levels and manmade discharges from the aquifer that were observed during 1979. Too few data were available to verify the calibrated model in a transient-state simulation with historical aquifer response to manmade discharges. Predictions made with the model are considered to be semiquantitative. Discharge from the proposed surface mine was predicted to average 0.3 cubic foot per second through 15 years of operation. Drawdowns of 5 feet in the potentiometric surface of the aquifer were predicted to extend as much as 3 miles from the proposed mine after 15 years of operation. (USGS)

Simulation of groundwater flow, effects of artificial recharge, and storage volume changes in the Equus Beds aquifer near the city of Wichita, Kansas well field, 1935–2008

USGS Publications Warehouse

Kelly, Brian P.; Pickett, Linda L.; Hansen, Cristi V.; Ziegler, Andrew C.

2013-01-01

The Equus Beds aquifer is a primary water-supply source for Wichita, Kansas and the surrounding area because of shallow depth to water, large saturated thickness, and generally good water quality. Substantial water-level declines in the Equus Beds aquifer have resulted from pumping groundwater for agricultural and municipal needs, as well as periodic drought conditions. In March 2006, the city of Wichita began construction of the Equus Beds Aquifer Storage and Recovery project to store and later recover groundwater, and to form a hydraulic barrier to the known chloride-brine plume near Burrton, Kansas. In October 2009, the U.S. Geological Survey, in cooperation with the city of Wichita, began a study to determine groundwater flow in the area of the Wichita well field, and chloride transport from the Arkansas River and Burrton oilfield to the Wichita well field. Groundwater flow was simulated for the Equus Beds aquifer using the three-dimensional finite-difference groundwater-flow model MODFLOW-2000. The model simulates steady-state and transient conditions. The groundwater-flow model was calibrated by adjusting model input data and model geometry until model results matched field observations within an acceptable level of accuracy. The root mean square (RMS) error for water-level observations for the steady-state calibration simulation is 9.82 feet. The ratio of the RMS error to the total head loss in the model area is 0.049 and the mean error for water-level observations is 3.86 feet. The difference between flow into the model and flow out of the model across all model boundaries is -0.08 percent of total flow for the steady-state calibration. The RMS error for water-level observations for the transient calibration simulation is 2.48 feet, the ratio of the RMS error to the total head loss in the model area is 0.0124, and the mean error for water-level observations is 0.03 feet. The RMS error calculated for observed and simulated base flow gains or losses for the Arkansas River for the transient simulation is 7,916,564 cubic feet per day (91.6 cubic feet per second) and the RMS error divided by (/) the total range in streamflow (7,916,564/37,461,669 cubic feet per day) is 22 percent. The RMS error calculated for observed and simulated streamflow gains or losses for the Little Arkansas River for the transient simulation is 5,610,089 cubic feet per day(64.9 cubic feet per second) and the RMS error divided by the total range in streamflow (5,612,918/41,791,091 cubic feet per day) is 13 percent. The mean error between observed and simulated base flow gains or losses was 29,999 cubic feet per day (0.34 cubic feet per second) for the Arkansas River and -1,369,250 cubic feet per day (-15.8 cubic feet per second) for the Little Arkansas River. Cumulative streamflow gain and loss observations are similar to the cumulative simulated equivalents. Average percent mass balance difference for individual stress periods ranged from -0.46 to 0.51 percent. The cumulative mass balance for the transient calibration was 0.01 percent. Composite scaled sensitivities indicate the simulations are most sensitive to parameters with a large areal distribution. For the steady-state calibration, these parameters include recharge, hydraulic conductivity, and vertical conductance. For the transient simulation, these parameters include evapotranspiration, recharge, and hydraulic conductivity. The ability of the calibrated model to account for the additional groundwater recharged to the Equus Beds aquifer as part of the Aquifer Storage and Recovery project was assessed by using the U.S. Geological Survey subregional water budget program ZONEBUDGET and comparing those results to metered recharge for 2007 and 2008 and previous estimates of artificial recharge. The change in storage between simulations is the volume of water that estimates the recharge credit for the aquifer storage and recovery system. The estimated increase in storage of 1,607 acre-ft in the basin storage area compared to metered recharge of 1,796 acre-ft indicates some loss of metered recharge. Increased storage outside of the basin storage area of 183 acre-ft accounts for all but 6 acre-ft or 0.33 percent of the total. Previously estimated recharge credits for 2007 and 2008 are 1,018 and 600 acre-ft, respectively, and a total estimated recharge credit of 1,618 acre-ft. Storage changes calculated for this study are 4.42 percent less for 2007 and 5.67 percent more for 2008 than previous estimates. Total storage change for 2007 and 2008 is 0.68 percent less than previous estimates. The small difference between the increase in storage from artificial recharge estimated with the groundwater-flow model and metered recharge indicates the groundwater model correctly accounts for the additional water recharged to the Equus Beds aquifer as part of the Aquifer Storage and Recovery project. Small percent differences between inflows and outflows for all stress periods and all index cells in the basin storage area, improved calibration compared to the previous model, and a reasonable match between simulated and measured long-term base flow indicates the groundwater model accurately simulates groundwater flow in the study area. The change in groundwater level through recent years compared to the August 1940 groundwater level map has been documented and used to assess the change of storage volume of the Equus Beds aquifer in and near the Wichita well field for three different areas. Two methods were used to estimate changes in storage from simulation results using simulated change in groundwater levels in layer 1 between stress periods, and using ZONEBUDGET to calculate the change in storage in the same way the effects of artificial recharge were estimated within the basin storage area. The three methods indicate similar trends although the magnitude of storage changes differ. Information about the change in storage in response to hydrologic stresses is important for managing groundwater resources in the study area. The comparison between the three methods indicates similar storage change trends are estimated and each could be used to determine relative increases or decreases in storage. Use of groundwater level changes that do not include storage changes that occur in confined or semi-confined parts of the aquifer will slightly underestimate storage changes; however, use of specific yield and groundwater level changes to estimate storage change in confined or semi-confined parts of the aquifer will overestimate storage changes. Using only changes in shallow groundwater levels would provide more accurate storage change estimates for the measured groundwater levels method. The value used for specific yield is also an important consideration when estimating storage. For the Equus Beds aquifer the reported specific yield ranges between 0.08 and 0.35 and the storage coefficient (for confined conditions) ranges between 0.0004 and 0.16. Considering the importance of the value of specific yield and storage coefficient to estimates of storage change over time, and the wide range and substantial overlap for the reported values for specific yield and storage coefficient in the study area, further information on the distribution of specific yield and storage coefficient within the Equus Beds aquifer in the study area would greatly enhance the accuracy of estimated storage changes using both simulated groundwater level, simulated groundwater budget, or measured groundwater level methods.

Uncertainty of simulated groundwater levels arising from stochastic transient climate change scenarios

NASA Astrophysics Data System (ADS)

Goderniaux, Pascal; Brouyère, Serge; Blenkinsop, Stephen; Burton, Aidan; Fowler, Hayley; Dassargues, Alain

2010-05-01

The evaluation of climate change impact on groundwater reserves represents a difficult task because both hydrological and climatic processes are complex and difficult to model. In this study, we present an innovative methodology that combines the use of integrated surface - subsurface hydrological models with advanced stochastic transient climate change scenarios. This methodology is applied to the Geer basin (480 km²) in Belgium, which is intensively exploited to supply the city of Liège (Belgium) with drinking water. The physically-based, spatially-distributed, surface-subsurface flow model has been developed with the finite element model HydroGeoSphere . The simultaneous solution of surface and subsurface flow equations in HydroGeoSphere, as well as the internal calculation of the actual evapotranspiration as a function of the soil moisture at each node of the evaporative zone, enables a better representation of interconnected processes in all domains of the catchment (fully saturated zone, partially saturated zone, surface). Additionally, the use of both surface and subsurface observed data to calibrate the model better constrains the calibration of the different water balance terms. Crucially, in the context of climate change impacts on groundwater resources, the evaluation of groundwater recharge is improved. . This surface-subsurface flow model is combined with advanced climate change scenarios for the Geer basin. Climate change simulations were obtained from six regional climate model (RCM) scenarios assuming the SRES A2 greenhouse gases emission (medium-high) scenario. These RCM scenarios were statistically downscaled using a transient stochastic weather generator technique, combining 'RainSim' and the 'CRU weather generator' for temperature and evapotranspiration time series. This downscaling technique exhibits three advantages compared with the 'delta change' method usually used in groundwater impact studies. (1) Corrections to climate model output are applied not only to the mean of climatic variables, but also across the statistical distributions of these variables. This is important as these distributions are expected to change in the future, with more extreme rainfall events, separated by longer dry periods. (2) The novel approach used in this study can simulate transient climate change from 2010 to 2085, rather than time series representative of a stationary climate for the period 2071-2100. (3) The weather generator is used to generate a large number of equiprobable climate change scenarios for each RCM, representative of the natural variability of the weather. All of these scenarios are applied as input to the Geer basin model to assess the projected impact of climate change on groundwater levels, the uncertainty arising for different RCM projections and the uncertainty linked to natural climatic variability. Using the output results from all scenarios, 95% confidence intervals are calculated for each year and month between 2010 and 2085. The climate change scenarios for the Geer basin model predict hotter and drier summers and warmer and wetter winters. Considering the results of this study, it is very likely that groundwater levels and surface flow rates in the Geer basin will decrease by the end of the century. This is of concern because it also means that groundwater quantities available for abstraction will also decrease. However, this study also shows that the uncertainty of these projections is relatively large compared to the projected changes so that it remains difficult to confidently determine the magnitude of the decrease. The use and combination of an integrated surface - subsurface model and stochastic climate change scenarios has never been used in previous climate change impact studies on groundwater resources. It constitutes an innovation and is an important tool for helping water managers to take decisions.

Comparing stream-specific to generalized temperature models to guide salmonid management in a changing climate

USGS Publications Warehouse

Andrew K. Carlson,; William W. Taylor,; Hartikainen, Kelsey M.; Dana M. Infante,; Beard, Douglas; Lynch, Abigail

2017-01-01

Global climate change is predicted to increase air and stream temperatures and alter thermal habitat suitability for growth and survival of coldwater fishes, including brook charr (Salvelinus fontinalis), brown trout (Salmo trutta), and rainbow trout (Oncorhynchus mykiss). In a changing climate, accurate stream temperature modeling is increasingly important for sustainable salmonid management throughout the world. However, finite resource availability (e.g. funding, personnel) drives a tradeoff between thermal model accuracy and efficiency (i.e. cost-effective applicability at management-relevant spatial extents). Using different projected climate change scenarios, we compared the accuracy and efficiency of stream-specific and generalized (i.e. region-specific) temperature models for coldwater salmonids within and outside the State of Michigan, USA, a region with long-term stream temperature data and productive coldwater fisheries. Projected stream temperature warming between 2016 and 2056 ranged from 0.1 to 3.8 °C in groundwater-dominated streams and 0.2–6.8 °C in surface-runoff dominated systems in the State of Michigan. Despite their generally lower accuracy in predicting exact stream temperatures, generalized models accurately projected salmonid thermal habitat suitability in 82% of groundwater-dominated streams, including those with brook charr (80% accuracy), brown trout (89% accuracy), and rainbow trout (75% accuracy). In contrast, generalized models predicted thermal habitat suitability in runoff-dominated streams with much lower accuracy (54%). These results suggest that, amidst climate change and constraints in resource availability, generalized models are appropriate to forecast thermal conditions in groundwater-dominated streams within and outside Michigan and inform regional-level salmonid management strategies that are practical for coldwater fisheries managers, policy makers, and the public. We recommend fisheries professionals reserve resource-intensive stream-specific models for runoff-dominated systems containing high-priority fisheries resources (e.g. trophy individuals, endangered species) that will be directly impacted by projected stream warming.

Hydrogeologic Setting and Ground-Water Flow in the Leetown Area, West Virginia

USGS Publications Warehouse

Kozar, Mark D.; Weary, David J.; Paybins, Katherine S.; Pierce, Herbert A.

2007-01-01

The Leetown Science Center is a research facility operated by the U.S. Geological Survey that occupies approximately 455-acres near Kearneysville, Jefferson County, West Virginia. Aquatic and fish research conducted at the Center requires adequate supplies of high-quality, cold ground water. Three large springs and three production wells currently (in 2006) supply water to the Center. The recent construction of a second research facility (National Center for Cool and Cold Water Aquaculture) operated by the U.S. Department of Agriculture and co-located on Center property has placed additional demands on available water resources in the area. A three-dimensional steady-state finite-difference ground-water flow model was developed to simulate ground-water flow in the Leetown area and was used to assess the availability of ground water to sustain current and anticipated future demands. The model also was developed to test a conceptual model of ground-water flow in the complex karst aquifer system in the Leetown area. Due to the complexity of the karst aquifer system, a multidisciplinary research study was required to define the hydrogeologic setting. Geologic mapping, surface- and borehole-geophysical surveys, stream base-flow surveys, and aquifer tests were conducted to provide the hydrogeologic data necessary to develop and calibrate the model. It would not have been possible to develop a numerical model of the study area without the intensive data collection and methods developments components of the larger, more comprehensive hydrogeologic investigation. Results of geologic mapping and surface-geophysical surveys verified the presence of several prominent thrust faults and identified additional faults and other complex geologic structures (including overturned anticlines and synclines) in the area. These geologic structures are known to control ground-water flow in the region. Results of this study indicate that cross-strike faults and fracture zones are major avenues of ground-water flow. Prior to this investigation, the conceptual model of ground-water flow for the region focused primarily on bedding planes and strike-parallel faults and joints as controls on ground-water flow but did not recognize the importance of cross-strike faults and fracture zones that allow ground water to flow downgradient across or through less permeable geologic formations. Results of the ground-water flow simulation indicate that current operations at the Center do not substantially affect either streamflow (less than a 5-percent reduction in annual streamflow) or ground-water levels in the Leetown area under normal climatic conditions but potentially could have greater effects on streamflow during long-term drought (reduction in streamflow of approximately 14 percent). On the basis of simulation results, ground-water withdrawals based on the anticipated need for an additional 150 to 200 gal/min (gallons per minute) of water at the Center also would not seriously affect streamflow (less than 8 to 9 percent reduction in streamflow) or ground-water levels in the area during normal climatic conditions. During drought conditions, however, the effects of current ground-water withdrawals and anticipated additional withdrawals of 150 to 200 gal/min to augment existing supplies result in moderate to substantial declines in water levels of 0.5-1.2 feet (ft) in the vicinity of the Center's springs and production wells. Streamflow was predicted to be reduced locally by approximately 21 percent. Such withdrawals during a drought or prolonged period of below normal ground-water levels would result in substantial declines in the flow of the Center's springs and likely would not be sustainable for more than a few months. The drought simulated in this model was roughly equivalent to the more than 1-year drought that affected the region from November 1998 through February 2000. The potential reduction in streamflow is a result of capture of ground water tha

Multi-objective analysis of the conjunctive use of surface water and groundwater in a multisource water supply system

NASA Astrophysics Data System (ADS)

Vieira, João; da Conceição Cunha, Maria

2017-04-01

A multi-objective decision model has been developed to identify the Pareto-optimal set of management alternatives for the conjunctive use of surface water and groundwater of a multisource urban water supply system. A multi-objective evolutionary algorithm, Borg MOEA, is used to solve the multi-objective decision model. The multiple solutions can be shown to stakeholders allowing them to choose their own solutions depending on their preferences. The multisource urban water supply system studied here is dependent on surface water and groundwater and located in the Algarve region, southernmost province of Portugal, with a typical warm Mediterranean climate. The rainfall is low, intermittent and concentrated in a short winter, followed by a long and dry period. A base population of 450 000 inhabitants and visits by more than 13 million tourists per year, mostly in summertime, turns water management critical and challenging. Previous studies on single objective optimization after aggregating multiple objectives together have already concluded that only an integrated and interannual water resources management perspective can be efficient for water resource allocation in this drought prone region. A simulation model of the multisource urban water supply system using mathematical functions to represent the water balance in the surface reservoirs, the groundwater flow in the aquifers, and the water transport in the distribution network with explicit representation of water quality is coupled with Borg MOEA. The multi-objective problem formulation includes five objectives. Two objective evaluate separately the water quantity and the water quality supplied for the urban use in a finite time horizon, one objective calculates the operating costs, and two objectives appraise the state of the two water sources - the storage in the surface reservoir and the piezometric levels in aquifer - at the end of the time horizon. The decision variables are the volume of withdrawals from each water source in each time step (i.e., reservoir diversion and groundwater pumping). The results provide valuable information for analysing the impacts of the conjunctive use of surface water and groundwater. For example, considering a drought scenario, the results show how the same level of total water supplied can be achieved by different management alternatives with different impact on the water quality, costs, and the state of the water sources at the end of the time horizon. The results allow also the clear understanding of the potential benefits from the conjunctive use of surface water and groundwater thorough the mitigation of the variation in the availability of surface water, improving the water quantity and/or water quality delivered to the users, or the better adaptation of such systems to a changing world.

A Semi-Analytical Solution to Time Dependent Groundwater Flow Equation Incorporating Stream-Wetland-Aquifer Interactions

NASA Astrophysics Data System (ADS)

Boyraz, Uǧur; Melek Kazezyılmaz-Alhan, Cevza

2017-04-01

Groundwater is a vital element of hydrologic cycle and the analytical & numerical solutions of different forms of groundwater flow equations play an important role in understanding the hydrological behavior of subsurface water. The interaction between groundwater and surface water bodies can be determined using these solutions. In this study, new hypothetical approaches are implemented to groundwater flow system in order to contribute to the studies on surface water/groundwater interactions. A time dependent problem is considered in a 2-dimensional stream-wetland-aquifer system. The sloped stream boundary is used to represent the interaction between stream and aquifer. The rest of the aquifer boundaries are assumed as no-flux boundary. In addition, a wetland is considered as a surface water body which lies over the whole aquifer. The effect of the interaction between the wetland and the aquifer is taken into account with a source/sink term in the groundwater flow equation and the interaction flow is calculated by using Darcy's approach. A semi-analytical solution is developed for the 2-dimensional groundwater flow equation in 5 steps. First, Laplace and Fourier cosine transforms are employed to obtain the general solution in Fourier and Laplace domain. Then, the initial and boundary conditions are applied to obtain the particular solution. Finally, inverse Fourier transform is carried out analytically and inverse Laplace transform is carried out numerically to obtain the final solution in space and time domain, respectively. In order to verify the semi-analytical solution, an explicit finite difference algorithm is developed and analytical and numerical solutions are compared for synthetic examples. The comparison of the analytical and numerical solutions shows that the analytical solution gives accurate results.

Hybrid Multiscale Finite Volume method for multiresolution simulations of flow and reactive transport in porous media

NASA Astrophysics Data System (ADS)

Barajas-Solano, D. A.; Tartakovsky, A. M.

2017-12-01

We present a multiresolution method for the numerical simulation of flow and reactive transport in porous, heterogeneous media, based on the hybrid Multiscale Finite Volume (h-MsFV) algorithm. The h-MsFV algorithm allows us to couple high-resolution (fine scale) flow and transport models with lower resolution (coarse) models to locally refine both spatial resolution and transport models. The fine scale problem is decomposed into various "local'' problems solved independently in parallel and coordinated via a "global'' problem. This global problem is then coupled with the coarse model to strictly ensure domain-wide coarse-scale mass conservation. The proposed method provides an alternative to adaptive mesh refinement (AMR), due to its capacity to rapidly refine spatial resolution beyond what's possible with state-of-the-art AMR techniques, and the capability to locally swap transport models. We illustrate our method by applying it to groundwater flow and reactive transport of multiple species.

Evaluation of ground-water flow and solute transport in the Lompoc area, Santa Barbara County, California

USGS Publications Warehouse

Bright, Daniel J.; Nash, David B.; Martin, Peter

1997-01-01

Ground-water quality in the Lompoc area, especially in the Lompoc plain, is only marginally acceptable for most uses. Demand for ground water has increased for municipal use since the late 1950's and has continued to be high for irrigation on the Lompoc plain, the principal agricultural area in the Santa Ynez River basin. As use has increased, the quality of ground water has deteriorated in some areas of the Lompoc plain. The dissolved-solids concentration in the main zone of the upper aquifer beneath most of the central and western plains has increased from less than 1,000 milligrams per liter in the 1940's to greater than 2,000 milligrams per liter in the 1960's. Dissolved- solids concentration have remained relatively constant since the 1960's. A three-dimensional finite-difference model was used to simulate ground-water flow in the Lompoc area and a two-dimensional finite-element model was used to simulate solute transport to gain a better understanding of the ground-water system and to evaluate the effects of proposed management plans for the ground-water basin. The aquifer system was simulated in the flow model as four horizontal layers. In the area of the Lompoc plain, the layers represent the shallow, middle, and main zones of the upper aquifer, and the lower aquifer. For the Lompoc upland and Lompoc terrace, the four layers represent the lower aquifer. The solute transport model was used to simulate dissolved-solids transport in the main zone of the upper aquifer beneath the Lompoc plain. The flow and solute-transport models were calibrated to transient conditions for 1941-88. A steady-state simulation was made to provide initial conditions for the transient-state simulation by using long-term average (1941-88) recharge rates. Model- simulated hydraulic heads generally were within 5 feet of measured heads in the main zone for transient conditions. Model-simulated dissolved- solids concentrations for the main zone generally differed less than 200milligrams per liter from concentrations in 1988. During 1941-88 about 1,096,000 acre-feet of water was pumped from the aquifer system. Average pumpage for this period (22,830 acre-feet per year) exceeded pumpage for the steady-state simulation by 16,590 acre-feet per year. The results of the transient simulation indicate that about 60 percent of this increase in pumpage was contributed by increased recharge, 28 percent by decreased natural discharge from the system (primarily discharge to the Santa Ynez River and transpiration), and 13 percent was withdrawn from storage. Total simulated downward leakage from the middle zone to the main zone in the central plain and upward leakage from the consolidated rocks to the main zone significantly increased in response to increased pumpage, which increased from about 6,240 to 30,870 acre-feet per year from 1941 to 1988. Average dissolved-solid concentration in the middle zone in 1987-88 ranged from 2,000 to 3,000 milligrams per liter beneath the northeastern plain and the dissolved-solids concentration of two samples from the consolidated rocks beneath the western plain averaged 4,300 milligrams per liter. Because the dissolved-solids concentration for the middle zone and the consolidated rocks is higher than the simulated steady-state dissolved-solids concentration of the main zone, the increase in the leakage from these two sources resulted in increased dissolved-solids concentration in the main zone during the transient period. The model results indicate that the main source of increased dissolved- solids concentration in the northeastern and central plains was downward leakage from the middle zone; whereas, upward leakage from the consolidated rocks was the main source of the increased dissolved-solids concentrations in the northwestern and western plains. The models were used to estimate changes in hydraulic head and in dissolved-solids concentration resulting from three proposed management alternatives: (1) average recharge

Modelling nitrate pollution pressure using a multivariate statistical approach: the case of Kinshasa groundwater body, Democratic Republic of Congo

NASA Astrophysics Data System (ADS)

Mfumu Kihumba, Antoine; Ndembo Longo, Jean; Vanclooster, Marnik

2016-03-01

A multivariate statistical modelling approach was applied to explain the anthropogenic pressure of nitrate pollution on the Kinshasa groundwater body (Democratic Republic of Congo). Multiple regression and regression tree models were compared and used to identify major environmental factors that control the groundwater nitrate concentration in this region. The analyses were made in terms of physical attributes related to the topography, land use, geology and hydrogeology in the capture zone of different groundwater sampling stations. For the nitrate data, groundwater datasets from two different surveys were used. The statistical models identified the topography, the residential area, the service land (cemetery), and the surface-water land-use classes as major factors explaining nitrate occurrence in the groundwater. Also, groundwater nitrate pollution depends not on one single factor but on the combined influence of factors representing nitrogen loading sources and aquifer susceptibility characteristics. The groundwater nitrate pressure was better predicted with the regression tree model than with the multiple regression model. Furthermore, the results elucidated the sensitivity of the model performance towards the method of delineation of the capture zones. For pollution modelling at the monitoring points, therefore, it is better to identify capture-zone shapes based on a conceptual hydrogeological model rather than to adopt arbitrary circular capture zones.

Numerical Simulation of Ground-Water Flow and Assessment of the Effects of Artificial Recharge in the Rialto-Colton Basin, San Bernardino County, California

USGS Publications Warehouse

Woolfenden, Linda R.; Koczot, Kathryn M.

2001-01-01

The Rialto?Colton Basin, in western San Bernardino County, California, was chosen for storage of imported water because of the good quality of native ground water, the known storage capacity for additional ground-water storage in the basin, and the availability of imported water. To supplement native ground-water resources and offset overdraft conditions in the basin during dry periods, artificial-recharge operations during wet periods in the Rialto?Colton Basin were begun in 1982 to store surplus imported water. Local water purveyors recognized that determining the movement and ultimate disposition of the artificially recharged imported water would require a better understanding of the ground-water flow system. In this study, a finite-difference model was used to simulate ground-water flow in the Rialto?Colton Basin to gain a better understanding of the ground-water flow system and to evaluate the hydraulic effects of artificial recharge of imported water. The ground-water basin was simulated as four horizontal layers representing the river- channel deposits and the upper, middle, and lower water-bearing units. Several flow barriers bordering and internal to the Rialto?Colton Basin influence the direction of ground-water flow. Ground water may flow relatively unrestricted in the shallow parts of the flow system; however, the faults generally become more restrictive at depth. A particle-tracking model was used to simulate advective transport of imported water within the ground-water flow system and to evaluate three artificial-recharge alternatives. The ground-water flow model was calibrated to transient conditions for 1945?96. Initial conditions for the transient-state simulation were established by using 1945 recharge and discharge rates, and assuming no change in storage in the basin. Average hydrologic conditions for 1945?96 were used for the predictive simulations (1997?2027). Ground-water-level measurements made during 1945 were used for comparison with the initial-conditions simulation to determine if there was a reasonable match, and thus reasonable starting heads, for the transient simulation. The comparison between simulated head and measured water levels indicates that, overall, the simulated heads match measured water levels well; the goodness-of-fit value is 0.99. The largest differences between simulated head and measured water level occurred between Barrier H and the Rialto?Colton Fault. Simulated heads near the Santa Ana River and Warm Creek, and simulated heads northwest of Barrier J, generally are within 30 feet of measured water levels and five are within 20 feet. Model-simulated heads were compared with measured long-term changes in hydrographs of composite water levels in selected wells, and with measured short-term changes in hydrographs of water levels in multiple-depth observation wells installed for this project. Simulated hydraulic heads generally matched measured water levels in wells northwest of Barrier J (in the northwestern part of the basin) and in the central part of the basin during 1945?96. In addition, the model adequately simulated water levels in the southeastern part of the basin near the Santa Ana River and Warm Creek and east of an unnamed fault that subparallels the San Jacinto Fault. Simulated heads and measured water levels in the central part of the basin generally are within 10 feet until about 1982?85 when differences become greater. In the northwestern part of the basin southeast of Barrier J, simulated heads were as much as 50 feet higher than measured water levels during 1945?82 but matched measured water levels well after 1982. In the compartment between Barrier H and the Rialto?Colton Fault, simulated heads match well during 1945?82 but are comparatively low during 1982?96. Near the Santa Ana River and Warm Creek, simulated heads generally rose above measured water levels except during 1965?72 when simulated heads compared well with measured water levels. Average

Reliable groundwater levels: failures and lessons learned from modeling and monitoring studies

NASA Astrophysics Data System (ADS)

Van Lanen, Henny A. J.

2017-04-01

Adequate management of groundwater resources requires an a priori assessment of impacts of intended groundwater abstractions. Usually, groundwater flow modeling is used to simulate the influence of the planned abstraction on groundwater levels. Model performance is tested by using observed groundwater levels. Where a multi-aquifer system occurs, groundwater levels in the different aquifers have to be monitored through observation wells with filters at different depths, i.e. above the impermeable clay layer (phreatic water level) and beneath (artesian aquifer level). A reliable artesian level can only be measured if the space between the outer wall of the borehole (vertical narrow shaft) and the observation well is refilled with impermeable material at the correct depth (post-drilling phase) to prevent a vertical hydraulic connection between the artesian and phreatic aquifer. We were involved in improper refilling, which led to impossibility to monitor reliable artesian aquifer levels. At the location of the artesian observation well, a freely overflowing spring was seen, which implied water leakage from the artesian aquifer affected the artesian groundwater level. Careful checking of the monitoring sites in a study area is a prerequisite to use observations for model performance assessment. After model testing the groundwater model is forced with proposed groundwater abstractions (sites, extraction rates). The abstracted groundwater volume is compensated by a reduction of groundwater flow to the drainage network and the model simulates associated groundwater tables. The drawdown of groundwater level is calculated by comparing the simulated groundwater level with and without groundwater abstraction. In lowland areas, such as vast areas of the Netherlands, the groundwater model has to consider a variable drainage network, which means that small streams only carry water during the wet winter season, and run dry during the summer. The main streams drain groundwater throughout the whole year. We simulated groundwater levels with a steady-state groundwater flow model with and without groundwater abstraction for the wet and dry season, i.e. considering a high (all streams included) and low drainage density (only major streams), respectively. Groundwater drawdown maps for the wet and dry season were compiled. Stakeholders (farmers, ecologists) were very concerned about the large drawdowns. After a while and discussions with the Water Supply Company and stakeholders, we realised that we had calculated unrealistic large drawdowns of the phreatic groundwater level for the dry season. We learnt that by applying a steady-state model we did not take into account the large volume of groundwater, which is released from the groundwater storage. The transient groundwater model that we developed then, showed that the volume of groundwater released from the storage per unit of time is significant and that the drawdown of the phreatic groundwater level by the end of the dry period is substantially smaller than the one simulated by the steady-state model. The results of the transient groundwater flow model agreed rather well with the pumping test that lasted the whole dry season.

Application of the finite element groundwater model FEWA to the engineered test facility

DOE Office of Scientific and Technical Information (OSTI.GOV)

Craig, P.M.; Davis, E.C.

1985-09-01

A finite element model for water transport through porous media (FEWA) has been applied to the unconfined aquifer at the Oak Ridge National Laboratory Solid Waste Storage Area 6 Engineered Test Facility (ETF). The model was developed in 1983 as part of the Shallow Land Burial Technology - Humid Task (ONL-WL14) and was previously verified using several general hydrologic problems for which an analytic solution exists. Model application and calibration, as described in this report, consisted of modeling the ETF water table for three specialized cases: a one-dimensional steady-state simulation, a one-dimensional transient simulation, and a two-dimensional transient simulation. Inmore » the one-dimensional steady-state simulation, the FEWA output accurately predicted the water table during a long period in which there were no man-induced or natural perturbations to the system. The input parameters of most importance for this case were hydraulic conductivity and aquifer bottom elevation. In the two transient cases, the FEWA output has matched observed water table responses to a single rainfall event occurring in February 1983, yielding a calibrated finite element model that is useful for further study of additional precipitation events as well as contaminant transport at the experimental site.« less

Hydrology and simulation of ground-water flow in Juab Valley, Juab County, Utah.

USGS Publications Warehouse

Thiros, Susan A.; Stolp, Bernard J.; Hadley, Heidi K.; Steiger, Judy I.

1996-01-01

Plans to import water to Juab Valley, Utah, primarily for irrigation, are part of the Central Utah Project. A better understanding of the hydrology of the valley is needed to help manage the water resources and to develop conjunctive-use plans.The saturated unconsolidated basin-fill deposits form the ground-water system in Juab Valley. Recharge is by seepage from streams, unconsumed irrigation water, and distribution systems; infiltration of precipitation; and subsurface inflow from consolidated rocks that surround the valley. Discharge is by wells, springs, seeps, evapotranspiration, and subsurface outflow to consolidated rocks. Ground-water pumpage is used to supplement surface water for irrigation in most of the valley and has altered the direction of groundwater flow from that of pre-ground-water development time in areas near and in Nephi and Levan.Greater-than-average precipitation during 1980-87 corresponds with a rise in water levels measured in most wells in the valley and the highest water level measured in some wells. Less-than average precipitation during 1988-91 corresponds with a decline in water levels measured during 1988-93 in most wells. Geochemical analyses indicate that the sources of dissolved ions in water sampled from the southern part of the valley are the Arapien Shale, evaporite deposits that occur in the unconsolidated basin-fill deposits, and possibly residual sea water that has undergone evaporation in unconsolidated basin-fill deposits in selected areas. Water discharging from a spring at Burriston Ponds is a mixture of about 70 percent ground water from a hypothesized flow path that extends downgradient from where Salt Creek enters Juab Valley and 30 percent from a hypothesized flow path from the base of the southern Wasatch Range.The ground-water system of Juab Valley was simulated by using the U.S. Geological Survey modular, three-dimensional, finite-difference, ground-water flow model. The numerical model was calibrated to simulate the steady-state conditions of 1949, multi-year transient-state conditions during 1949-92, and seasonal transient-state conditions during 1992-94. Calibration parameters were adjusted until model-computed water levels reasonably matched measured water levels. Parameters important to the calibration process include horizontal hydraulic conductivity, transmissivity, and the spatial distribution and amount of recharge from subsurface inflow and seepage from ephemeral streams to the east side of Juab Valley.

Recalibration of a ground-water flow model of the Mississippi River Valley alluvial aquifer in Southeastern Arkansas, 1918, with simulations of hydraulic heads caused by projected ground-water withdrawals through 2049

USGS Publications Warehouse

Stanton, Gregory P.; Clark, Brian R.

2003-01-01

The Mississippi River Valley alluvial aquifer, encompassing parts of Arkansas, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee supplies an average of 5 billion gallons of water per day. However, withdrawals from the aquifer in recent years have caused considerable drawdown in the hydraulic heads in southeastern Arkansas and other areas. The effects of current ground-water withdrawals and potential future withdrawals on water availability are major concerns of water managers and users as well as the general public. A full understanding of the behavior of the aquifer under various water-use scenarios is critical for the development of viable water-management and alternative source plans. To address these concerns, the U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, Vicksburg District, and the Arkansas Soil and Water Conservation Commission developed and calibrated a ground-water flow model for the Mississippi River valley alluvial aquifer in southeastern Arkansas to simulate hydraulic heads caused by projected ground-water withdrawals. A previously published ground-water flow model for the alluvial aquifer in southeastern Arkansas was updated and recalibrated to reflect more current pumping stresses with additional stress periods added to bring the model forward from 1982 to 1998. The updated model was developed and calibrated with MODFLOW-2000 finite difference numerical modeling and parameter estimation software. The model was calibrated using hydraulic-head data collected during 1972 and 1982 and hydraulic-head measurements made during spring (February to April) of 1992 and 1998. The residuals for 1992 and 1998 have a mean absolute value of 4.74 and 5.45 feet, respectively, and a root mean square error of 5.9 and 6.72 feet, respectively. The effects of projected ground-water withdrawals were simulated through 2049 in three predictive scenarios by adding five additional stress periods of 10 years each. In the three scenarios, pumpage was defined by either continuing 1997 pumpage into the future (scenario 1) or by continuing water-use trends into the future (scenario 2), and increasing water-use trends with a 10 percent reduction in pumpage in selected areas (scenario 3). Scenario 1 indicates a cone of depression centered in Desha County and extensive dewatering with areas of simulated hydraulic heads dropping below 50 percent saturated thickness. Scenario 2 indicates a larger area of simulated hydraulic heads dropping below 50 percent saturated thickness and additional dewatering with model cells going dry and smaller cones of depression appearing in Ashley and Chicot Counties. Scenario 3 indicates overall reduction in depth and extent of the cones of depression of those in scenario 2, and the number of dry cells are only about two-thirds that of dry cells in scenario 2.

Numerical simulation of in-situ chemical oxidation (ISCO) and biodegradation of petroleum hydrocarbons using a coupled model for bio-geochemical reactive transport

NASA Astrophysics Data System (ADS)

Marin, I. S.; Molson, J. W.

2013-05-01

Petroleum hydrocarbons (PHCs) are a major source of groundwater contamination, being a worldwide and well-known problem. Formed by a complex mixture of hundreds of organic compounds (including BTEX - benzene, toluene, ethylbenzene and xylenes), many of which are toxic and persistent in the subsurface and are capable of creating a serious risk to human health. Several remediation technologies can be used to clean-up PHC contamination. In-situ chemical oxidation (ISCO) and intrinsic bioremediation (IBR) are two promising techniques that can be applied in this case. However, the interaction of these processes with the background aquifer geochemistry and the design of an efficient treatment presents a challenge. Here we show the development and application of BIONAPL/Phreeqc, a modeling tool capable of simulating groundwater flow, contaminant transport with coupled biological and geochemical processes in porous or fractured porous media. BIONAPL/Phreeqc is based on the well-tested BIONAPL/3D model, using a powerful finite element simulation engine, capable of simulating non-aqueous phase liquid (NAPL) dissolution, density-dependent advective-dispersive transport, and solving the geochemical and kinetic processes with the library Phreeqc. To validate the model, we compared BIONAPL/Phreeqc with results from the literature for different biodegradation processes and different geometries, with good agreement. We then used the model to simulate the behavior of sodium persulfate (NaS2O8) as an oxidant for BTEX degradation, coupled with sequential biodegradation in a 2D case and to evaluate the effect of inorganic geochemistry reactions. The results show the advantages of a treatment train remediation scheme based on ISCO and IBR. The numerical performance and stability of the integrated BIONAPL/Phreeqc model was also verified.

Geohydrology and simulated ground-water flow, Plymouth-Carver Aquifer, southeastern Massachusetts

USGS Publications Warehouse

Hansen, Bruce P.; Lapham, Wayne W.

1992-01-01

The Plymouth-Carver aquifer underlies an area of 140 square miles and is the second largest aquifer in areal extent in Massachusetts. It is composed primarily of saturated glacial sand and gravel. The water-table and bedrock surface were mapped and used to determine saturated thickness of the aquifer, which ranged from less than 20 feet to greater than 200 feet. Ground water is present mainly under unconfined conditions, except in a few local areas such as beneath Plymouth Harbor. Recharge to the aquifer is derived almost entirely from precipitation and averages about 1.15 million gallons per day per square mile. Water discharges from the aquifer by pumping, evapotranspiration, direct evaporation from the water table, and seepage to streams, ponds, wetlands, bogs, and the ocean. In 1985, water use was about 59.6 million gallons per day, of which 82 percent was used for cranberry production. The Plymouth-Carver aquifer was simulated by a three-dimensional, finite difference ground-water-flow model. Most model boundaries represent the natural hydrologic boundaries of the aquifer. The model simulates aquifer recharge, withdrawals by pumped wells, leakage through streambeds, and discharge to the ocean. The model was calibrated for steady-state and transient conditions. Model results were compared with measured values of hydraulic head and ground-water discharge. Results of simulations indicate that the modeled ground-water system closely simulates actual aquifer conditions. Four hypothetical ground-water development alternatives were simulated to demonstrate the use of the model and to examine the effects on the ground-water system. Simulation of a 2-year period of no recharge and average pumping rates that occurred from 1980-85 resulted in water-level declines exceeding 5 feet throughout most of the aquifer and a decrease of 54 percent in average ground-water discharge to streams. In a second simulation, four wells in the northern part of the area were pumped at 10.4 million gallons per day in excess of rates simulated in the steady-state model for the four wells. This resulted in water-level declines of 2 feet or more in an area of 25 square miles and a decline in average ground-water discharge to streams of 6 percent. When this pumpage was simulated as recharge to the aquifer, water levels beneath the recharge area rose more than 40 feet, and ground-water discharge remained equal to average discharge in the calibrated steady-state model. In a third simulation, all 21 existing production wells were pumped at nearly the design capacity of 17.8 million gallons per day; this pumping rate produced water-level declines of less than 2 feet throughout most of the aquifer. When simulated pumpage was increased to 32.8 million gallons per day from existing wells and from 15 additional wells, the area where water-level declines exceeded 2 feet significantly increased. In another set of simulations, a well field close to a stream was pumped at rates of 2, 4, and 6 million gallons per day. At a pumping rate of 6 million gallons per day, ground-water discharge to the stream decreased 34 percent during periods of normal precipitation and 56 percent during drought conditions.

Nonlinear effects of locally heterogeneous hydraulic conductivity fields on regional stream-aquifer exchanges

NASA Astrophysics Data System (ADS)

Zhu, J.; Winter, C. L.; Wang, Z.

2015-11-01

Computational experiments are performed to evaluate the effects of locally heterogeneous conductivity fields on regional exchanges of water between stream and aquifer systems in the Middle Heihe River basin (MHRB) of northwestern China. The effects are found to be nonlinear in the sense that simulated discharges from aquifers to streams are systematically lower than discharges produced by a base model parameterized with relatively coarse effective conductivity. A similar, but weaker, effect is observed for stream leakage. The study is organized around three hypotheses: (H1) small-scale spatial variations of conductivity significantly affect regional exchanges of water between streams and aquifers in river basins, (H2) aggregating small-scale heterogeneities into regional effective parameters systematically biases estimates of stream-aquifer exchanges, and (H3) the biases result from slow paths in groundwater flow that emerge due to small-scale heterogeneities. The hypotheses are evaluated by comparing stream-aquifer fluxes produced by the base model to fluxes simulated using realizations of the MHRB characterized by local (grid-scale) heterogeneity. Levels of local heterogeneity are manipulated as control variables by adjusting coefficients of variation. All models are implemented using the MODFLOW (Modular Three-dimensional Finite-difference Groundwater Flow Model) simulation environment, and the PEST (parameter estimation) tool is used to calibrate effective conductivities defined over 16 zones within the MHRB. The effective parameters are also used as expected values to develop lognormally distributed conductivity (K) fields on local grid scales. Stream-aquifer exchanges are simulated with K fields at both scales and then compared. Results show that the effects of small-scale heterogeneities significantly influence exchanges with simulations based on local-scale heterogeneities always producing discharges that are less than those produced by the base model. Although aquifer heterogeneities are uncorrelated at local scales, they appear to induce coherent slow paths in groundwater fluxes that in turn reduce aquifer-stream exchanges. Since surface water-groundwater exchanges are critical hydrologic processes in basin-scale water budgets, these results also have implications for water resources management.

Effects of linking a soil-water-balance model with a groundwater-flow model

USGS Publications Warehouse

Stanton, Jennifer S.; Ryter, Derek W.; Peterson, Steven M.

2013-01-01

A previously published regional groundwater-flow model in north-central Nebraska was sequentially linked with the recently developed soil-water-balance (SWB) model to analyze effects to groundwater-flow model parameters and calibration results. The linked models provided a more detailed spatial and temporal distribution of simulated recharge based on hydrologic processes, improvement of simulated groundwater-level changes and base flows at specific sites in agricultural areas, and a physically based assessment of the relative magnitude of recharge for grassland, nonirrigated cropland, and irrigated cropland areas. Root-mean-squared (RMS) differences between the simulated and estimated or measured target values for the previously published model and linked models were relatively similar and did not improve for all types of calibration targets. However, without any adjustment to the SWB-generated recharge, the RMS difference between simulated and estimated base-flow target values for the groundwater-flow model was slightly smaller than for the previously published model, possibly indicating that the volume of recharge simulated by the SWB code was closer to actual hydrogeologic conditions than the previously published model provided. Groundwater-level and base-flow hydrographs showed that temporal patterns of simulated groundwater levels and base flows were more accurate for the linked models than for the previously published model at several sites, particularly in agricultural areas.

The 2016 groundwater flow model for Dane County, Wisconsin

USGS Publications Warehouse

Parsen, Michael J.; Bradbury, Kenneth R.; Hunt, Randall J.; Feinstein, Daniel T.

2016-01-01

A new groundwater flow model for Dane County, Wisconsin, replaces an earlier model developed in the 1990s by the Wisconsin Geological and Natural History Survey (WGNHS) and the U.S. Geological Survey (USGS). This modeling study was conducted cooperatively by the WGNHS and the USGS with funding from the Capital Area Regional Planning Commission (CARPC). Although the overall conceptual model of the groundwater system remains largely unchanged, the incorporation of newly acquired high-quality datasets, recent research findings, and improved modeling and calibration techniques have led to the development of a more detailed and sophisticated model representation of the groundwater system. The new model is three-dimensional and transient, and conceptualizes the county’s hydrogeology as a 12-layer system including all major unlithified and bedrock hydrostratigraphic units and two high-conductivity horizontal fracture zones. Beginning from the surface down, the model represents the unlithified deposits as two distinct model layers (1 and 2). A single layer (3) simulates the Ordovician sandstone and dolomite of the Sinnipee, Ancell, and Prairie du Chien Groups. Sandstone of the Jordan Formation (layer 4) and silty dolostone of the St. Lawrence Formation (layer 5) each comprise separate model layers. The underlying glauconitic sandstone of the Tunnel City Group makes up three distinct layers: an upper aquifer (layer 6), a fracture feature (layer 7), and a lower aquifer (layer 8). The fracture layer represents a network of horizontal bedding-plane fractures that serve as a preferential pathway for groundwater flow. The model simulates the sandstone of the Wonewoc Formation as an upper aquifer (layer 9) with a bedding-plane fracture feature (layer 10) at its base. The Eau Claire aquitard (layer 11) includes shale beds within the upper portion of the Eau Claire Formation. This layer, along with overlying bedrock units, is mostly absent in the preglacially eroded valleys along the Yahara River valley and in northeastern Dane County. Layer 12 represents the Mount Simon sandstone as the lowermost model layer. It directly overlies the Precambrian crystalline basement rock, whose top surface forms the lower boundary of the model. The model uses the USGS MODFLOW-NWT finite-difference code, a standalone version of MODFLOW-2005 that incorporates the Newton (NWT) solver. MODFLOW-NWT improves the handling of unconfined conditions by smoothing the transition from wet to dry cells. The model explicitly simulates groundwater–surface-water interaction with streamflow routing and lake-level fluctuation. Model input included published and unpublished hydrogeologic data from recent estimates of aquifer hydraulic conductivities. A spatial groundwater recharge distribution was obtained from a recent GIS-based, soil-water-balance model for Dane County. Groundwater withdrawals from pumping were simulated for 572 wells across the entire model domain, which includes Dane County and portions of seven neighboring counties—Columbia, Dodge, Green, Iowa, Jefferson, Lafayette, and Rock. These wells withdrew an average of 60 million gallons per day (mgd) over the 5-year period from 2006 through 2010. Within Dane County, 385 wells were simulated with an average withdrawal rate of 52 mgd.Model calibration used the parameter estimation code PEST, and calibration targets included heads, stream and spring flows, lake levels, and borehole flows. Steady-state calibration focused on the period 2006 through 2010; the transient calibration focused on the 7-week drought period from late May through July 2012. This model represents a significant step forward from previous work because of its finer grid resolution, improved hydrostratigraphic discretization, transient capabilities, and more sophisticated representation of surface-water features and multi-aquifer wells.Potential applications of the model include evaluation of potential sites for and impacts of new high-capacity wells, development of wellhead protection plans, evaluating the effects of changing land use and climate on groundwater, and quantifying the relationships between groundwater and surface water.

Assessing the changes of groundwater recharge / irrigation water use between SRI and traditional irrigation schemes in Central Taiwan

NASA Astrophysics Data System (ADS)

Chen, Shih-Kai; Jang, Cheng-Shin; Tsai, Cheng-Bin

2015-04-01

To respond to agricultural water shortage impacted by climate change without affecting rice yield in the future, the application of water-saving irrigation, such as SRI methodology, is considered to be adopted in rice-cultivation in Taiwan. However, the flooded paddy fields could be considered as an important source of groundwater recharge in Central Taiwan. The water-saving benefit of this new methodology and its impact on the reducing of groundwater recharge should be integrally assessed in this area. The objective of this study was to evaluate the changes of groundwater recharge/ irrigation water use between the SRI and traditional irrigation schemes (continuous irrigation, rotational irrigation). An experimental paddy field located in the proximal area of the Choushui River alluvial fan (the largest groundwater pumping region in Taiwan) was chosen as the study area. The 3-D finite element groundwater model (FEMWATER) with the variable boundary condition analog functions, was applied in simulating groundwater recharge process and amount under traditional irrigation schemes and SRI methodology. The use of effective rainfall was taken into account or not in different simulation scenarios for each irrigation scheme. The simulation results showed that there were no significant variations of infiltration rate in the use of effective rainfall or not, but the low soil moisture setting in deep soil layers resulted in higher infiltration rate. Taking the use of effective rainfall into account, the average infiltration rate for continuous irrigation, rotational irrigation, and SRI methodology in the first crop season of 2013 were 4.04 mm/day, 4.00 mm/day and 3.92 mm/day, respectively. The groundwater recharge amount of SRI methodology was slightly lower than those of traditional irrigation schemes, reducing 4% and 2% compared with continuous irrigation and rotational irrigation, respectively. The field irrigation requirement amount of SRI methodology was significantly lower than those of traditional irrigation schemes, saving 35% and 9% compared with continuous irrigation and rotational irrigation, respectively. The SRI methodology significantly improved water-saving benefit compared with the disadvantage of reducing groundwater recharge. The results could be used as a basis for the relevant government agency to formulate the integral water resource management strategies in this area. Keywords: SRI, Paddy field, Infiltration, Groundwater recharge

Prediction and uncertainty analysis of surface and groundwater exchange in a Rhine floodplain in south-west Germany

NASA Astrophysics Data System (ADS)

Maier, Nadine; Breuer, Lutz; Kraft, Philipp

2017-04-01

Inundations and the resulting exchange between surface water and groundwater are of importance for all floodplain ecosystems. Because of the high groundwater level in floodplains and the groundwater dependence of floodplain vegetation habitat models of floodplains should include detailed information of groundwater and surface water dynamics. Such models can, for example, serve as a basis for restoration measures, focusing on the re-establishment of rare species. To capture these groundwater and surface water dynamics we use a distributed model approach to simulate the groundwater levels in a floodplain stream section of the Rhine in Hesse, Germany (14.8 km2). This area is part of the large nature reserve "Kühkopf-Knoblochsaue" and hosts rare and endangered flora and fauna. We developed a physical-deterministic model of a floodplain to simulate the groundwater situation and the flooding events in the floodplain. The model is built with the Catchment Modeling Framework (CMF) and includes the interaction of groundwater and surface water flow. To reduce the computation time of the model, we used a simple flood distribution scheme instead of solving the St. Venant equation for surface water fluxes. The floodplain is split into two sub-regions, according to the two nature reserve regions with the same model setup. Each model divides the study area laterally into irregular polygonal cells (270 - 400) with different sizes (114 - 480'000 m2), based on similar elevation and land use. For each sub-region the water level of the Rhine and the groundwater levels of three monitoring wells at the boundary of the model area are used as driving factors. As predictor variables we use observation data from four to six different groundwater monitoring wells in the sub-regions. For each model we run 5,000 simulations following a Latin Hypercube sampling procedure to investigate parameter uncertainty and derive behavioral model runs. We received RMSEs between 0.18 and 0.28 m for the different groundwater wells for the calibration period of 2.5 years and RMSEs between 0.16 and 0.23 m for the validation period of 9.5 years. Finally, we derived hydrological predictors (e.g. longest flooding period, amount of flooding days during the vegetation period, etc) from the model runs for following habitat models.

Computer program for simulation of variable recharge with the U. S. Geological Survey modular finite-difference ground-water flow model (MODFLOW)

USGS Publications Warehouse

Kontis, A.L.

2001-01-01

The Variable-Recharge Package is a computerized method designed for use with the U.S. Geological Survey three-dimensional finitedifference ground-water flow model (MODFLOW-88) to simulate areal recharge to an aquifer. It is suitable for simulations of aquifers in which the relation between ground-water levels and land surface can affect the amount and distribution of recharge. The method is based on the premise that recharge to an aquifer cannot occur where the water level is at or above land surface. Consequently, recharge will vary spatially in simulations in which the Variable- Recharge Package is applied, if the water levels are sufficiently high. The input data required by the program for each model cell that can potentially receive recharge includes the average land-surface elevation and a quantity termed ?water available for recharge,? which is equal to precipitation minus evapotranspiration. The Variable-Recharge Package also can be used to simulate recharge to a valley-fill aquifer in which the valley fill and the adjoining uplands are explicitly simulated. Valley-fill aquifers, which are the most common type of aquifer in the glaciated northeastern United States, receive much of their recharge from upland sources as channeled and(or) unchanneled surface runoff and as lateral ground-water flow. Surface runoff in the uplands is generated in the model when the applied water available for recharge is rejected because simulated water levels are at or above land surface. The surface runoff can be distributed to other parts of the model by (1) applying the amount of the surface runoff that flows to upland streams (channeled runoff) to explicitly simulated streams that flow onto the valley floor, and(or) (2) applying the amount that flows downslope toward the valley- fill aquifer (unchanneled runoff) to specified model cells, typically those near the valley wall. An example model of an idealized valley- fill aquifer is presented to demonstrate application of the method and the type of information that can be derived from its use. Documentation of the Variable-Recharge Package is provided in the appendixes and includes listings of model code and of program variables. Comment statements in the program listings provide a narrative of the code. Input-data instructions and printed model output for the package are included.

Grundwasserfließgeschehen Mecklenburg-Vorpommerns - Geohydraulische Modellierung mit Detrended Kriging

NASA Astrophysics Data System (ADS)

Hilgert, Toralf; Hennig, Heiko

2017-03-01

Groundwater heads were mapped for the entire State of Mecklenburg-Western Pomerania by applying a Detrended Kriging method based on a numerical geohydraulic model. The general groundwater flow system (trend surface) was represented by a two-dimensional horizontal flow model. Thus deviations of observed groundwater heads from simulated groundwater heads are no longer subject to a regional trend and can be interpolated by means of Ordinary Kriging. Subsequently, the groundwater heads were obtained from the sum of the simulated trend surface and interpolated residuals. Furthermore, the described procedure allowed a plausibility check of observed groundwater heads by comparing them to results of the hydraulic model. If significant deviations were seen, the observation wells could be allocated to different aquifers. The final results are two hydraulically established groundwater head distributions - one for the regional main aquifer and one for the upper aquifer which may differ locally from the main aquifer.

Simulation and particle-tracking analysis of ground-water flow near the Savannah River site, Georgia and South Carolina, 2002, and for selected ground-water management scenarios, 2002 and 2020

USGS Publications Warehouse

Cherry, Gregory S.

2006-01-01

Ground-water flow under 2002 hydrologic conditions was evaluated in an eight-county area in Georgia and South Carolina near the Savannah River Site (SRS), by updating boundary conditions and pumping rates in an existing U.S. Geological Survey (USGS) ground-water model. The original ground-water model, developed to simulate hydrologic conditions during 1987-92, used the quasi-three-dimensional approach by dividing the Floridan, Dublin, and Midville aquifer systems into seven aquifers. The hydrogeologic system was modeled using six active layers (A2-A7) that were separated by confining units with an overlying source-sink layer to simulate the unconfined Upper Three Runs aquifer (layer A1). Potentiometric- surface maps depicting September 2002 for major aquifers were used to update, evaluate, and modify boundary conditions used by the earlier ground-water flow model. The model was updated using the USGS finite-difference code MODFLOW-2000 for mean-annual conditions during 1987-92 and 2002. The specified heads in the source-sink layer A1 were lowered to reflect observed water-level declines during the 1998-2002 drought. These declines resulted in a decrease of 12.1 million gallons per day (Mgal/d) in simulated recharge or vertical inflow to the uppermost confined aquifer (Gordon, layer A2). Although ground-water pumpage in the study area has increased by 32 Mgal/d since 1995, most of this increase (17.5 Mgal/d) was from the unconfined Upper Three Runs aquifer (source-sink layer A1) with the remaining 14.5 Mgal/d assigned to the active layers within the model (A2-A7). The simulated water budget for 2002 shows a decrease from the 1987-92 model from 1,040 Mgal/d to 1,035 Mgal/d. The decreased ground-water inflows and increased ground-water withdrawal rates reduced the simulated ground-water outflow to river cells in the active layers of the model by 43 Mgal/d. The calibration statistics for all layers of the 2002 simulation resulted in a decrease in the root mean square (RMS) of the residuals from 10.6 to 8.0 feet (ft). The residuals indicate 83.3 percent of the values for the 2002 simulation met the calibration error criteria established in the original model, whereas 88.8 percent was within the specified range for the 1987-92 simulation. Simulated ground-water outflow to the Savannah River and its tributaries during water year 2002 was 560 cubic feet per second (ft3/s), or 86 percent of the observed gain in mean-annual streamflow between streamflow gaging stations at the Millhaven, Ga., and Augusta, Ga. At Upper Three Runs Creek, simulated ground-water discharge during 2002 was 110 ft3/s, or 83 percent of the observed streamflow at two streamflow gaging stations near the SRS. These results indicate that the constructed model calibrated to 1987-92 conditions and modified for 2002 dry conditions is still representative of the hydrologic system. The USGS particle-tracking code MODPATH was used to generate advective water-particle pathlines and their associated time-of-travel based on MODFLOW simulations for 1987-92, 2002, and each of four hypothetical ground-water management scenarios. The four hypothetical ground-water management scenarios represent hydrologic conditions for (1) reported pumping for 2002 and boundary conditions for an average year; (2) reported pumping for 2002 with SRS pumping discontinued and boundary conditions for an average year; (3) projected 2020 pumping and boundary conditions for an average year; and (4) projected 2020 pumping and boundary conditions for a dry year. The MODPATH code was used in forward-tracking mode to evaluate flowpaths from areas on the SRS and in backtracking mode to evaluate further areas of previously documented trans-river flow on the Georgia side of the Savannah River. Trans-river flow is a condition in which the local head gradients might allow migration of contaminants from the SRS into the underlying aquifers and beneath the Savannah River into Georgia. More...

THM large spatial-temporal model to simulate the past 2 Ma hydrogeological evolution of Paris Basin including natural tracer transport as part of site characterization for radwaste repository project Cigéo - France

NASA Astrophysics Data System (ADS)

Benabderrahmane, A., Sr.

2017-12-01

Hydrogeological site characterization for deep geological high level and intermediate level long lived radioactive waste repository cover a large time scale needed for safety analysis and calculation. Hydrogeological performance of a site relies also on the effects of geodynamic evolution as tectonic uplift, erosion/sedimentation and climate including glaciation on the groundwater flow and solute and heat transfer. Thermo-Hydro-Mechanical model of multilayered aquifer system of Paris Basin is developed to reproduce the present time flow and the natural tracer (Helium) concentration profiles based on the last 2 Ma of geodynamic evolution. Present time geological conceptual model consist of 27 layers at Paris Basin (Triassic-Tertiary) with refinement at project site scale (29 layers from Triassic to Portlandian). Target layers are the clay host formation of Callovo-Oxfrodian age (160 Ma) and the surrounding aquifer layers of Oxfordian and Dogger. Modelled processes are: groundwater flow, heat and solutes (natural tracers) transport, freezing and thawing of groundwater (expansion and retreat of permafrost), deformation of the multilayered aquifer system induced by differential tectonic uplift and the hydro-mechanical stress effect as caused by erosion of the outcropping layers. Numerical simulation considers a period from 2 Ma BP and up to the present. Transient boundary conditions are governed by geodynamic processes: (i) modification of the geometry of the basin and (ii) temperatures along the topography will change according to a series of 15 identical climate cycles with multiple permafrost (glaciation) periods. Numerical model contains 71 layers and 18 million cells. The solution procedure solves three coupled systems of equations, head, temperature and concentrations, by the use of a finite difference method, and by applying extensive parallel processing. The major modelling results related to the processes of importance for site characterization as hydraulic head distribution, flow velocity, heat and natural tracer transport impacted by geodynamic past evolution are discussed.

Groundwater management under uncertainty using a stochastic multi-cell model

NASA Astrophysics Data System (ADS)

Joodavi, Ata; Zare, Mohammad; Ziaei, Ali Naghi; Ferré, Ty P. A.

2017-08-01

The optimization of spatially complex groundwater management models over long time horizons requires the use of computationally efficient groundwater flow models. This paper presents a new stochastic multi-cell lumped-parameter aquifer model that explicitly considers uncertainty in groundwater recharge. To achieve this, the multi-cell model is combined with the constrained-state formulation method. In this method, the lower and upper bounds of groundwater heads are incorporated into the mass balance equation using indicator functions. This provides expressions for the means, variances and covariances of the groundwater heads, which can be included in the constraint set in an optimization model. This method was used to formulate two separate stochastic models: (i) groundwater flow in a two-cell aquifer model with normal and non-normal distributions of groundwater recharge; and (ii) groundwater management in a multiple cell aquifer in which the differences between groundwater abstractions and water demands are minimized. The comparison between the results obtained from the proposed modeling technique with those from Monte Carlo simulation demonstrates the capability of the proposed models to approximate the means, variances and covariances. Significantly, considering covariances between the heads of adjacent cells allows a more accurate estimate of the variances of the groundwater heads. Moreover, this modeling technique requires no discretization of state variables, thus offering an efficient alternative to computationally demanding methods.

A staggered-grid finite-difference scheme optimized in the time–space domain for modeling scalar-wave propagation in geophysical problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tan, Sirui, E-mail: siruitan@hotmail.com; Huang, Lianjie, E-mail: ljh@lanl.gov

For modeling scalar-wave propagation in geophysical problems using finite-difference schemes, optimizing the coefficients of the finite-difference operators can reduce numerical dispersion. Most optimized finite-difference schemes for modeling seismic-wave propagation suppress only spatial but not temporal dispersion errors. We develop a novel optimized finite-difference scheme for numerical scalar-wave modeling to control dispersion errors not only in space but also in time. Our optimized scheme is based on a new stencil that contains a few more grid points than the standard stencil. We design an objective function for minimizing relative errors of phase velocities of waves propagating in all directions within amore » given range of wavenumbers. Dispersion analysis and numerical examples demonstrate that our optimized finite-difference scheme is computationally up to 2.5 times faster than the optimized schemes using the standard stencil to achieve the similar modeling accuracy for a given 2D or 3D problem. Compared with the high-order finite-difference scheme using the same new stencil, our optimized scheme reduces 50 percent of the computational cost to achieve the similar modeling accuracy. This new optimized finite-difference scheme is particularly useful for large-scale 3D scalar-wave modeling and inversion.« less

Three-dimensional numerical model of ground-water flow in northern Utah Valley, Utah County, Utah

USGS Publications Warehouse

Gardner, Philip M.

2009-01-01

A three-dimensional, finite-difference, numerical model was developed to simulate ground-water flow in northern Utah Valley, Utah. The model includes expanded areal boundaries as compared to a previous ground-water flow model of the valley and incorporates more than 20 years of additional hydrologic data. The model boundary was generally expanded to include the bedrock in the surrounding mountain block as far as the surface-water divide. New wells have been drilled in basin-fill deposits near the consolidated-rock boundary. Simulating the hydrologic conditions within the bedrock allows for improved simulation of the effect of withdrawal from these wells. The inclusion of bedrock also allowed for the use of a recharge model that provided an alternative method for spatially distributing areal recharge over the mountains.The model was calibrated to steady- and transient-state conditions. The steady-state simulation was developed and calibrated by using hydrologic data that represented average conditions for 1947. The transient-state simulation was developed and calibrated by using hydrologic data collected from 1947 to 2004. Areally, the model grid is 79 rows by 70 columns, with variable cell size. Cells throughout most of the model domain represent 0.3 mile on each side. The largest cells are rectangular with dimensions of about 0.3 by 0.6 mile. The largest cells represent the mountain block on the eastern edge of the model domain where the least hydrologic data are available. Vertically, the aquifer system is divided into 4 layers which incorporate 11 hydrogeologic units. The model simulates recharge to the ground-water flow system as (1) infiltration of precipitation over the mountain block, (2) infiltration of precipitation over the valley floor, (3) infiltration of unconsumed irrigation water from fields, lawns, and gardens, (4) seepage from streams and canals, and (5) subsurface inflow from Cedar Valley. Discharge of ground water is simulated by the model to (1) flowing and pumping wells, (2) drains and springs, (3) evapotranspiration, (4) Utah Lake, (5) the Jordan River and mountain streams, and (6) Salt Lake Valley by subsurface outflow through the Jordan Narrows.During steady-state calibration, variables were adjusted within probable ranges to minimize differences between model-computed and measured water levels as well as between model-computed and independently estimated flows that include: recharge by seepage from individual streams and canals, discharge by seepage to individual streams and the Jordan River, discharge to Utah Lake, discharge to drains and springs, discharge by evapotranspiration, and subsurface flows into and out of northern Utah Valley from Cedar Valley and to Salt Lake Valley, respectively. The transient-state simulation was calibrated to measured water levels and water-level changes with consideration given to annual changes in the flows listed above.

Coupled hydromechanical paleoclimate analyses of density-dependant groundwater flow in discretely fractured crystalline rock settings

NASA Astrophysics Data System (ADS)

Normani, S. D.; Sykes, J. F.; Jensen, M. R.

2009-04-01

A high resolution sub-regional scale (84 km2) density-dependent, fracture zone network groundwater flow model with hydromechanical coupling and pseudo-permafrost, was developed from a larger 5734 km2 regional scale groundwater flow model of a Canadian Shield setting in fractured crystalline rock. The objective of the work is to illustrate aspects of regional and sub-regional groundwater flow that are relevant to the long-term performance of a hypothetical nuclear fuel repository. The discrete fracture dual continuum numerical model FRAC3DVS-OPG was used for all simulations. A discrete fracture zone network model delineated from surface features was superimposed onto an 789887 element flow domain mesh. Orthogonal fracture faces (between adjacent finite element grid blocks) were used to best represent the irregular discrete fracture zone network. The crystalline rock between these structural discontinuities was assigned properties characteristic of those reported for the Canadian Shield at the Underground Research Laboratory at Pinawa, Manitoba. Interconnectivity of permeable fracture features is an important pathway for the possibly relatively rapid migration of average water particles and subsequent reduction in residence times. The multiple 121000 year North American continental scale paleoclimate simulations are provided by W.R. Peltier using the University of Toronto Glacial Systems Model (UofT GSM). Values of ice sheet normal stress, and proglacial lake depth from the UofT GSM are applied to the sub-regional model as surface boundary conditions, using a freshwater head equivalent to the normal stress imposed by the ice sheet at its base. Permafrost depth is applied as a permeability reduction to both three-dimensional grid blocks and fractures that lie within the time varying permafrost zone. Two different paleoclimate simulations are applied to the sub-regional model to investigate the effect on the depth of glacial meltwater migration into the subsurface. In addition, different conceptualizations of fracture permeability with depth, and various hydromechanical loading efficiencies are used to investigate glacial meltwater penetration. The importance of density dependent flow, due to pore waters deep in the Canadian Shield with densities of up to 1200 kg/m3 and total dissolved solids concentrations in excess of 300 g/L, is also illustrated. Performance measures used in the assessment include depth of glacial meltwater penetration using a tracer, and mean life expectancy. Consistent with the findings from isotope and geochemical assessments, the analyses support the conclusion that for the discrete fracture zone and matrix properties simulated in this study, glacial meltwaters would not likely impact a deep geologic repository in a crystalline rock setting.

Accounting for aquifer heterogeneity from geological data to management tools.

PubMed

Blouin, Martin; Martel, Richard; Gloaguen, Erwan

2013-01-01

A nested workflow of multiple-point geostatistics (MPG) and sequential Gaussian simulation (SGS) was tested on a study area of 6 km(2) located about 20 km northwest of Quebec City, Canada. In order to assess its geological and hydrogeological parameter heterogeneity and to provide tools to evaluate uncertainties in aquifer management, direct and indirect field measurements are used as inputs in the geostatistical simulations to reproduce large and small-scale heterogeneities. To do so, the lithological information is first associated to equivalent hydrogeological facies (hydrofacies) according to hydraulic properties measured at several wells. Then, heterogeneous hydrofacies (HF) realizations are generated using a prior geological model as training image (TI) with the MPG algorithm. The hydraulic conductivity (K) heterogeneity modeling within each HF is finally computed using SGS algorithm. Different K models are integrated in a finite-element hydrogeological model to calculate multiple transport simulations. Different scenarios exhibit variations in mass transport path and dispersion associated with the large- and small-scale heterogeneity respectively. Three-dimensional maps showing the probability of overpassing different thresholds are presented as examples of management tools. © 2012, The Author(s). Groundwater © 2012, National Ground Water Association.

Sustainable Hydro Assessment and Groundwater Recharge Projects (SHARP) in Germany - Water Balance Models

NASA Astrophysics Data System (ADS)

Niemand, C.; Kuhn, K.; Schwarze, R.

2010-12-01

SHARP is a European INTERREG IVc Program. It focuses on the exchange of innovative technologies to protect groundwater resources for future generations by considering the climate change and the different geological and geographical conditions. Regions involved are Austria, United Kingdom, Poland, Italy, Macedonia, Malta, Greece and Germany. They will exchange practical know-how and also determine know-how demands concerning SHARP’s key contents: general groundwater management tools, artificial groundwater recharge technologies, groundwater monitoring systems, strategic use of groundwater resources for drinking water, irrigation and industry, techniques to save water quality and quantity, drinking water safety plans, risk management tools and water balance models. SHARP Outputs & results will influence the regional policy in the frame of sustainable groundwater management to save and improve the quality and quantity of groundwater reservoirs for future generations. The main focus of the Saxon State Office for Environment, Agriculture and Landscape in this project is the enhancement and purposive use of water balance models. Already since 1992 scientists compare different existing water balance models on different scales and coupled with groundwater models. For example in the KLIWEP (Assessment of Impacts of Climate Change Projections on Water and Matter Balance for the Catchment of River Parthe in Saxony) project the coupled model WaSiM-ETH - PCGEOFIM® has been used to study the impact of climate change on water balance and water supplies. The project KliWES (Assessment of the Impacts of Climate Change Projections on Water and Matter Balance for Catchment Areas in Saxony) still running, comprises studies of fundamental effects of climate change on catchments in Saxony. Project objective is to assess Saxon catchments according to the vulnerability of their water resources towards climate change projections in order to derive region-specific recommendations for management actions. The model comparisons within reference areas showed significant differences in outcome. The values of water balance components calculated with different models partially fluctuate by a multiple of their value. The SHARP project was prepared in several previous projects that were testing suitable water balance models and is now able to assist the knowledge transfer.

Non-Fickian dispersion of groundwater age

PubMed Central

Engdahl, Nicholas B.; Ginn, Timothy R.; Fogg, Graham E.

2014-01-01

We expand the governing equation of groundwater age to account for non-Fickian dispersive fluxes using continuous random walks. Groundwater age is included as an additional (fifth) dimension on which the volumetric mass density of water is distributed and we follow the classical random walk derivation now in five dimensions. The general solution of the random walk recovers the previous conventional model of age when the low order moments of the transition density functions remain finite at their limits and describes non-Fickian age distributions when the transition densities diverge. Previously published transition densities are then used to show how the added dimension in age affects the governing differential equations. Depending on which transition densities diverge, the resulting models may be nonlocal in time, space, or age and can describe asymptotic or pre-asymptotic dispersion. A joint distribution function of time and age transitions is developed as a conditional probability and a natural result of this is that time and age must always have identical transition rate functions. This implies that a transition density defined for age can substitute for a density in time and this has implications for transport model parameter estimation. We present examples of simulated age distributions from a geologically based, heterogeneous domain that exhibit non-Fickian behavior and show that the non-Fickian model provides better descriptions of the distributions than the Fickian model. PMID:24976651

Digital-model simulation of the glacial-outwash aquifer, Otter Creek-Dry Creek basin, Cortland County, New York

USGS Publications Warehouse

Cosner, O.J.; Harsh, J.F.

1978-01-01

The city of Cortland, New York, and surrounding areas obtain water from the highly productive glacial-outwash aquifer underlying the Otter Creek-Dry Creek basin. Pumpage from the aquifer in 1976 was approximately 6.3 million gallons per day and is expected to increase as a result of population growth and urbanization. A digital ground-water model that uses a finite-difference approximation technique to solve partial differential equations of flow through a porous medium was used to simulate the movement of water within the aquifer. The model was calibrated to equilibrium conditions by comparing water levels measured in the aquifer in March 1976 with those computed by the model. Then, from the simulated water-level surface for March, a transient-condition run was made to simulate the surface as measured in September 1976. Computed water levels presented as contours are generally in close agreement with potentiometric-surface maps prepared from field measurements of March and September 1976. (Woodard-USGS)

Ground-water flow near two radioactive-waste-disposal areas at the Western New York Nuclear Service Center, Cattaraugus County, New York; results of flow simulation

USGS Publications Warehouse

Bergeron, M.P.; Bugliosi, E.F.

1988-01-01

Two adjacent burial areas were excavated in a clay-rich till at a radioactive waste disposal site near West Valley in Cattaraugus County, N.Y.: (1) which contains mainly low-level radioactive wastes generated onsite by a nuclear fuel reprocessing plant, has been in operation since 1966; and (2) which contains commercial low-level radioactive wastes, was operated during 1963-75. Groundwater below the upper 3 meters of till generally moves downward through a 20- to 30-meter thick sequence of tills underlain by lacustrine and kame-delta deposits of fine sand and silt. Groundwater in the weathered, upper 3 meters of till can move laterally for several meters before either moving downward into the kame-delta deposits or discharging to the land surface. A two-dimensional finite-element model that simulates two vertical sections was used to evaluate hydrologic factors that control groundwater flow in the till. Conditions observed during March 1983 were reproduced accurately in steady-state simulations that used four isotropic units of differing hydraulic conductivity to represent two fractured and weathered till units near land surfaces, an intermediate group of isolated till zones that contain significant amounts of fine sand and silt, and a sequence of till units at depths that have been consolidated by overburden pressure. Recharge rates used in the best-fit simulation ranged from 1.4 cm/yr along smooth, sloping or compacted surfaces to 3.8 cm/yr near swampy areas. Values of hydraulic conductivity and infiltration used in the calibrated best-fit model were nearly identical to values used in a previous model analysis of the nearby commercial-waste burial area. Results of the model simulations of a burial pit assumed to be filled with water indicate that water near the bottom of the burial pit would migrate laterally in the shallow, weathered till for 5 to 6 meters before moving downward into the unweathered till, and water near the top of the pit would move laterally less than 20 meters before moving downward into the unweathered till. These results indicate that subsurface migration of radionuclides in groundwater to points of discharge to land surface is unlikely as long as the water level does not rise into the reworked cover material. (Author 's abstract)

Characterization and simulation of ground-water flow in the Kansas River Valley at Fort Riley, Kansas, 1990-98

USGS Publications Warehouse

Myers, Nathan C.

2000-01-01

Hydrologic data and a ground-water flow model were used to characterize ground-water flow in the Kansas River alluvial aquifer at Fort Riley in northeast Kansas. The ground-water flow model was developed as a tool to project ground-water flow and potential contaminant-transport paths in the alluvial aquifer on the basis of past hydrologic conditions. The model also was used to estimate historical and hypothetical ground-water flow paths with respect to a private- and several public-supply wells. The ground-water flow model area extends from the Smoky Hill and Republican Rivers downstream to about 2.5 miles downstream from the city of Ogden. The Kansas River Valley has low relief and, except for the area within the Fort Riley Military Reservation, is used primarily for crop production. Sedimentary deposits in the Kansas River Valley, formed after the ancestral Kansas River eroded into bedrock, primarily are alluvial sediment deposited by the river during Quaternary time. The alluvial sediment consists of as much as about 75 feet of poorly sorted, coarse-to-fine sand, silt, and clay, 55 feet of which can be saturated with ground water. The alluvial aquifer is unconfined and is bounded on the sides and bottom by Permian-age shale and limestone bedrock. Hydrologic data indicate that ground water in the Kansas River Valley generally flows in a downstream direction, but flow direction can be quite variable near the Kansas River due to changes in river stage. Ground-water-level changes caused by infiltration of precipitation are difficult to detect because they are masked by larger changes caused by fluctuation in Kansas River stage. Ratios of strontium isotopes Sr87 and Sr86 in water collected from wells in the Camp Funston Area indicate that the ground water along the northern valley wall originates, in part, from upland areas north of the river valley. Water from Threemile Creek, which flows out of the uplands north of the river valley, had Sr87:Sr86 ratios similar to those in ground water from wells in the northern Camp Funston Area. In addition, comparison of observed water levels from wells CF90-06, CF97-101, and CF97-401 in the Camp Funston Area and ground-water levels simulated for these wells using floodwave-response analysis indicates that ground-water inflow from bedrock is a hydraulic stress that, in addition to the changing stage in the Kansas River, acts on the aquifer. This hydraulic stress seems to be located near the northern valley wall because the effect of this stress is greater for well CF97-101, which is the well closest to the valley wall. Ground-water flow was simulated using a modular, three-dimensional, finite-difference ground-water flow model (MODFLOW). Particle tracking, used to visualize ground-water flow paths in the alluvial aquifer, was accomplished using MODPATH. Forward-in-time particle tracking indicated that, in general, particles released near the Kansas River followed much more variable paths than particles released near the valley wall. Although particle tracking does not simulate solute transport, this increased path variability indicates that, near the river, ground-water contaminants could follow many possible paths towards the river, whereas more distant from the river, ground-water contaminants likely would follow a narrower corridor. Particle tracks in the Camp Funston Area indicate that, for the 1990-98 simulation period, contaminants from the ground-water study sites in the Camp Funston Area would be unlikely to move into the vicinity of Ogden's supply wells. Backward-in-time particle tracking indicated that the flow-path and recharge areas for model cells corresponding to Ogden's supply wells lie near the northern valley wall and extend into the northern Camp Funston Area. The flow-path and recharge areas for model cells corresponding to Morris County Rural Water District wells lie within Clarks Creek Valley and probably extend outside the model area. Three hypothetical simulations, i

A dual-porosity model for simulating solute transport in oil shale

USGS Publications Warehouse

Glover, K.C.

1987-01-01

A model is described for simulating three-dimensional groundwater flow and solute transport in oil shale and associated geohydrologic units. The model treats oil shale as a dual-porosity medium by simulating flow and transport within fractures using the finite-element method. Diffusion of solute between fractures and the essentially static water of the shale matrix is simulated by including an analytical solution that acts as a source-sink term to the differential equation of solute transport. While knowledge of fracture orientation and spacing is needed to effectively use the model, it is not necessary to map the locations of individual fractures. The computer program listed in the report incorporates many of the features of previous dual-porosity models while retaining a practical approach to solving field problems. As a result the theory of solute transport is not extended in any appreciable way. The emphasis is on bringing together various aspects of solute transport theory in a manner that is particularly suited to the unusual groundwater flow and solute transport characteristics of oil shale systems. (Author 's abstract)

Unsaturated flow dynamics during irrigation with wastewater: field and modelling study

NASA Astrophysics Data System (ADS)

Martinez-Hernandez, V.; de Miguel, A.; Meffe, R.; Leal, M.; González-Naranjo, V.; de Bustamante, I.

2012-04-01

To deal with water scarcity combined with a growing water demand, the reuse of wastewater effluents of wastewater treatment plants (WWTP) for industrial and agricultural purposes is considered as a technically and economically feasible solution. In agriculture, irrigation with wastewater emerges as a sustainable practice that should be considered in such scenarios. Water infiltration, soil moisture storage and evapotranspiration occurring in the unsaturated zone are fundamental processes that play an important role in soil water balance. An accurate estimation of unsaturated flow dynamics (during and after irrigation) is essential to improve wastewater management (i.e. estimating groundwater recharge or maximizing irrigation efficiency) and to avoid possible soil and groundwater affections (i.e. predicting contaminant transport). The study site is located in the Experimental Plant of Carrión de los Céspedes (Seville, Spain). Here, treated wastewater is irrigated over the soil to enhance plants growth. To obtain physical characteristics of the soil (granulometry, bulk density and water retention curve), soil samples were collected at different depths. A drain gauge passive capillary lysimeter was installed to determine the volume of water draining from the vadose zone. Volumetric water content of the soil was monitored by measuring the dielectric constant using capacitance/frequency domain technology. Three soil moisture probes were located at different depths (20, 50 and 70 cm below the ground surface) to control the variation of the volumetric water content during infiltration. The main aim of this study is to understand water flow dynamics through the unsaturated zone during irrigation by using the finite element model Hydrus-1D. The experimental conditions were simulated by a 90 cm long, one dimensional solution domain. Specific climatic conditions, wastewater irrigation rates and physical properties of the soil were introduced in the model as input parameters. Data from the lysimeter and soil moisture probes were used to calibrate the model. The overall simulation time period included the dry (irrigation as main source of water) and the wet season (precipitation as main source of water). Future investigation concerning groundwater affections and contaminant transport at the field site will be based on the results obtained through the flow model developed in this study.

Optimizing Wastewater Reuse in Agricultural Fields via Merging of Embedded Network Sensor Data and Flow and Transport Models Using Data Assimilation

NASA Astrophysics Data System (ADS)

Wu, C.; Margulis, S. A.

2007-12-01

Wastewater re-use via crop irrigation has the potential to be an effective means of wastewater disposal. However, nitrate in wastewater may contaminate groundwater if it does not decay before reaching the groundwater table. In order to dispose of wastewater while preventing long-term groundwater pollution, irrigation rates need to be optimized based on the current and predicted states of the soil, such as soil moisture content and/or nitrate concentration. A real-time soil states estimation system using the Ensemble Kalman Filter (EnKF) has been developed for application to a test bed for wastewater re-use in Palmdale, CA. This test bed, covered with alfalfa, is a 30-acre irrigation plot with a 200-meter long rotating pivot arm that irrigates the area with reclaimed wastewater. A sensor network is deployed in the soil near the surface. The data assimilation system has shown the ability to characterize soil states and fluxes from sparse measurements. The real-time estimation system will then be used to explore the potential feedback for optimizing the sprinkler operation (i.e. maximizing the magnitude of wastewater release while minimizing the ultimate groundwater pollution). In optimization models, soil states and fluxes can be regarded as functions of irrigation rate. Through optimization, the irrigation rate in a finite horizon can be maximized while still satisfying all criteria in soil states and fluxes to ensure the safety of groundwater. Since the data assimilation system provides reliable estimation of soil states and fluxes, it is expected to define the optimal irrigation rate with higher confidence compared to using models or sensors only.

Determination of timescales of nitrate contamination by groundwater age models in a complex aquifer system

NASA Astrophysics Data System (ADS)

Koh, E. H.; Lee, E.; Kaown, D.; Lee, K. K.; Green, C. T.

2017-12-01

Timing and magnitudes of nitrate contamination are determined by various factors like contaminant loading, recharge characteristics and geologic system. Information of an elapsed time since recharged water traveling to a certain outlet location, which is defined as groundwater age, can provide indirect interpretation related to the hydrologic characteristics of the aquifer system. There are three major methods (apparent ages, lumped parameter model, and numerical model) to date groundwater ages, which differently characterize groundwater mixing resulted by various groundwater flow pathways in a heterogeneous aquifer system. Therefore, in this study, we compared the three age models in a complex aquifer system by using observed age tracer data and reconstructed history of nitrate contamination by long-term source loading. The 3H-3He and CFC-12 apparent ages, which did not consider the groundwater mixing, estimated the most delayed response time and a highest period of the nitrate loading had not reached yet. However, the lumped parameter model could generate more recent loading response than the apparent ages and the peak loading period influenced the water quality. The numerical model could delineate various groundwater mixing components and its different impacts on nitrate dynamics in the complex aquifer system. The different age estimation methods lead to variations in the estimated contaminant loading history, in which the discrepancy in the age estimation was dominantly observed in the complex aquifer system.

Hydrogeology and water chemistry of Montezuma Well in Montezuma Castle National Monument and surrounding area, Arizona

USGS Publications Warehouse

Konieczki, Alice D.; Leake, Stanley A.

1997-01-01

Increasing population and associated residential and commercial development have greatly increased water use and consumption in the Verde Valley near Montezuma Well, a unit of Montezuma Castle National Monument in central Arizona. Flow from Montezuma Well and water levels in eight wells that are measured annually do not indicate that the ground-water system has been affected by development. Additional data are needed to develop an adequate ground-water monitoring program so that future effects of development can be detected. Monitoring the ground-water system would detect changes in discharge from the Montezuma Well or changes in the ground-water system that might indicate a potential change of flow to the well. Water samples were collected, and field measurements of specific conductance, pH, temperature, and dissolved oxygen were made throughout the pond at Montezuma Well during an exploration in May 1991. The exploration included two fissures in the bottom of the pond that were filled with sand. The sand in the fissures was kept in suspension by water entering the pond. Water chemistry indicates that the ground water from the area is a mixed combination of calcium, magnesium, sodium, and bicarbonate type water. The analyses for 18O/16O and 2H/1H show that the water from the wells and springs in the area, including Montezuma Well, has been exposed to similar environmental conditions and could have had similar flow paths. The MODFLOW finite-difference ground-water model was used to develop an uncalibrated interpretive model to study possible mechanisms for discharge of water at Montezuma Well. The study presents the hypothesis that ground water in the Supai Formation is the source of discharge to Montezuma Well because of the differences between the surface elevation of the pond at Montezuma Well and the stage in the adjacent Wet Beaver Creek. A series of simulations shows that upward flow from the Supai Formation is a possible mechanism for discharge to Montezuma Well, and that a geologic structure in the Supai Formation could play a role in the upward movement of water to Montezuma Well. The mechanism for inflow from the Verde Formation is not understood; however, this study concludes that the Verde Formation, Supai Formation, and other underlying rock units are probably the sources of water to Montezuma Well.

A total variation diminishing finite difference algorithm for sonic boom propagation models

NASA Technical Reports Server (NTRS)

Sparrow, Victor W.

1993-01-01

It is difficult to accurately model the rise phases of sonic boom waveforms with traditional finite difference algorithms because of finite difference phase dispersion. This paper introduces the concept of a total variation diminishing (TVD) finite difference method as a tool for accurately modeling the rise phases of sonic booms. A standard second order finite difference algorithm and its TVD modified counterpart are both applied to the one-way propagation of a square pulse. The TVD method clearly outperforms the non-TVD method, showing great potential as a new computational tool in the analysis of sonic boom propagation.

Application of a Density-Dependent Numerical Model (MODHMS) to Assess Salinity Intrusion in the Biscayne Aquifer, North Miami-Dade County, Florida

NASA Astrophysics Data System (ADS)

Guha, H.; Panday, S.

2005-05-01

Miami-Dade County is located at the Southeastern part of the State of Florida adjoining the Atlantic coast. The sole drinking water source is the Biscayne Aquifer, which is an unconfined freshwater aquifer, composed of marine limestone with intermediate sand lenses. The aquifer is highly conductive with hydraulic conductivity values ranging from 1,000 ft/day to over 100,000 ft/day in some areas. Saltwater intrusion from the coast is an immediate threat to the freshwater resources of the County. Therefore, a multilayer density-dependent transient groundwater model was developed to evaluate the saltwater intrusion characteristics of the system. The model was developed using MODHMS, a finite difference, fully coupled groundwater and surface water flow and transport model. The buoyancy term is included in the equation for unconfined flow and the flow and transport equations are coupled using an iterative scheme. The transport equation was solved using an adaptive implicit total variation diminishing (TVD) scheme and anisotropy of dispersivity was included for longitudinal, transverse, vertical transverse, and vertical longitudinal directions. The model eastern boundaries extended approximately 3.5 miles into the Atlantic Ocean while the western boundary extended approximately 27 miles inland from the coast. The northern and southern boundaries extend 6 miles into Broward County and up to the C-100 canal in Miami-Dade County respectively. Close to 2 million active nodes were simulated, with horizontal discretization of 500 feet. A total of nine different statistical analyses were conducted with observed and simulated hydraulic heads. The analysis indicates that the model simulated hydraulic heads matched closely with the observed heads across the model domain. In general, the model reasonably simulated the inland extent of saltwater intrusion within the aquifer, and matched relatively well with limited observed chloride data from monitoring wells along the coast. Saltwater intrusion in the Biscayne aquifer is the result of a combination of natural variations in recharge, evapotranspiration, ground-water withdrawals from the aquifer, and relative canal stages in comparison to tidal stages in the Biscayne Bay. Pre- and post wellfield pumpage scenarios were conducted to determine the effect of wellfield pumpage on saltwater intrusion. The model is being used for future water supply management scenarios and for evaluating the best placement of saltwater intrusion monitoring wells along the coast.

Application of MODFLOW’s farm process to California’s Central Valley

USGS Publications Warehouse

Faunt, Claudia; Hanson, Randall T.; Schmid, Wolfgang; Belitz, Kenneth

2008-01-01

landscape processes. The FMP provides coupled simulation of the ground-water and surface-water components of the hydrologic cycle for irrigated and non-irrigated areas. A dynamic allocation of ground-water recharge and ground-water pumping is simulated on the basis of residual crop-water demand after surface-water deliveries and root uptake from shallow ground water. The FMP links with the Streamflow Routing Package SFR1) to facilitate the simulated conveyance of surface-water deliveries. Ground-water Pumpage through both single-aquifer and multi-node wells, irrigation return flow, and variable irrigation efficiencies also are simulated by the FMP. The simulated deliveries and ground-water pumpage in the updated model reflect climatic differences, differences among defined water-balance regions, and changes in the waterdelivery system, during the 1961–2003 simulation period. The model is designed to accept forecasts from Global Climate Models (GCMs) to simulate the potential effects on surface-water delivery, ground-water pumpage, and ground-water storage in response to climate change. The model provides a detailed transient analysis of changes in ground-water availability in relation to climatic variability, urbanization, and changes in irrigated agriculture.

Palaeo-modeling of coastal salt water intrusion during the Holocene: an application to the Netherlands

NASA Astrophysics Data System (ADS)

Delsman, J. R.; Hu-a-ng, K. R. M.; Vos, P. C.; de Louw, P. G. B.; Oude Essink, G. H. P.; Stuyfzand, P. J.; Bierkens, M. F. P.

2013-11-01

Management of coastal fresh groundwater reserves requires a thorough understanding of the present-day groundwater salinity distribution and its possible future development. However, coastal groundwater often still reflects a complex history of marine transgressions and regressions, and is only rarely in equilibrium with current boundary conditions. In addition, the distribution of groundwater salinity is virtually impossible to characterize satisfactorily, complicating efforts to model and predict coastal groundwater flow. A way forward may be to account for the historical development of groundwater salinity when modeling present-day coastal groundwater flow. In this paper, we construct a palaeo-hydrogeological model to simulate the evolution of groundwater salinity in the coastal area of the Netherlands throughout the Holocene. While intended as a perceptual tool, confidence in our model results is warranted by a good correspondence with a hydrochemical characterization of groundwater origin. Model results attest to the impact of groundwater density differences on coastal groundwater flow on millennial timescales and highlight their importance in shaping today's groundwater salinity distribution. Not once reaching steady-state throughout the Holocene, our results demonstrate the long-term dynamics of salinity in coastal aquifers. This stresses the importance of accounting for the historical evolution of coastal groundwater salinity when modeling present-day coastal groundwater flow, or when predicting impacts of e.g. sea level rise on coastal aquifers. Of more local importance, our findings suggest a more significant role of pre-Holocene groundwater in the present-day groundwater salinity distribution in the Netherlands than previously recognized. The implications of our results extend beyond understanding the present-day distribution of salinity, as the proven complex history of coastal groundwater also holds important clues for understanding and predicting the distribution of other societally relevant groundwater constituents.

Assessing the influence of climate change and inter-basin water diversion on Haihe River basin, eastern China: a coupled model approach

NASA Astrophysics Data System (ADS)

Xia, Jun; Wang, Qiang; Zhang, Xiang; Wang, Rui; She, Dunxian

2018-04-01

The modeling of changes in surface water and groundwater in the areas of inter-basin water diversion projects is quite difficult because surface water and groundwater models are run separately most of the time and the lack of sufficient data limits the application of complex surface-water/groundwater coupling models based on physical laws, especially for developing countries. In this study, a distributed surface-water and groundwater coupling model, named the distributed time variant gain model-groundwater model (DTVGM-GWM), was used to assess the influence of climate change and inter-basin water diversion on a watershed hydrological cycle. The DTVGM-GWM model can reflect the interaction processes of surface water and groundwater at basin scale. The model was applied to the Haihe River Basin (HRB) in eastern China. The possible influences of climate change and the South-to-North Water Diversion Project (SNWDP) on surface water and groundwater in the HRB were analyzed under various scenarios. The results showed that the newly constructed model DTVGM-GWM can reasonably simulate the surface and river runoff, and describe the spatiotemporal distribution characteristics of groundwater level, groundwater storage and phreatic recharge. The prediction results under different scenarios showed a decline in annual groundwater exploitation and also runoff in the HRB, while an increase of groundwater storage and groundwater level after the SNWDP's operation. Additionally, as the project also addresses future scenarios, a slight increase is predicted in the actual evapotranspiration, soil water content and phreatic recharge. This study provides valuable insights for developing sustainable groundwater management options for the HRB.

Real-time management of an urban groundwater well field threatened by pollution.

PubMed

Bauser, Gero; Franssen, Harrie-Jan Hendricks; Kaiser, Hans-Peter; Kuhlmann, Ulrich; Stauffer, Fritz; Kinzelbach, Wolfgang

2010-09-01

We present an optimal real-time control approach for the management of drinking water well fields. The methodology is applied to the Hardhof field in the city of Zurich, Switzerland, which is threatened by diffuse pollution. The risk of attracting pollutants is higher if the pumping rate is increased and can be reduced by increasing artificial recharge (AR) or by adaptive allocation of the AR. The method was first tested in offline simulations with a three-dimensional finite element variably saturated subsurface flow model for the period January 2004-August 2005. The simulations revealed that (1) optimal control results were more effective than the historical control results and (2) the spatial distribution of AR should be different from the historical one. Next, the methodology was extended to a real-time control method based on the Ensemble Kalman Filter method, using 87 online groundwater head measurements, and tested at the site. The real-time control of the well field resulted in a decrease of the electrical conductivity of the water at critical measurement points which indicates a reduced inflow of water originating from contaminated sites. It can be concluded that the simulation and the application confirm the feasibility of the real-time control concept.

Documentation and verification of VST2D; a model for simulating transient, Variably Saturated, coupled water-heat-solute Transport in heterogeneous, anisotropic 2-Dimensional, ground-water systems with variable fluid density

USGS Publications Warehouse

Friedel, Michael J.

2001-01-01

This report describes a model for simulating transient, Variably Saturated, coupled water-heatsolute Transport in heterogeneous, anisotropic, 2-Dimensional, ground-water systems with variable fluid density (VST2D). VST2D was developed to help understand the effects of natural and anthropogenic factors on quantity and quality of variably saturated ground-water systems. The model solves simultaneously for one or more dependent variables (pressure, temperature, and concentration) at nodes in a horizontal or vertical mesh using a quasi-linearized general minimum residual method. This approach enhances computational speed beyond the speed of a sequential approach. Heterogeneous and anisotropic conditions are implemented locally using individual element property descriptions. This implementation allows local principal directions to differ among elements and from the global solution domain coordinates. Boundary conditions can include time-varying pressure head (or moisture content), heat, and/or concentration; fluxes distributed along domain boundaries and/or at internal node points; and/or convective moisture, heat, and solute fluxes along the domain boundaries; and/or unit hydraulic gradient along domain boundaries. Other model features include temperature and concentration dependent density (liquid and vapor) and viscosity, sorption and/or decay of a solute, and capability to determine moisture content beyond residual to zero. These features are described in the documentation together with development of the governing equations, application of the finite-element formulation (using the Galerkin approach), solution procedure, mass and energy balance considerations, input requirements, and output options. The VST2D model was verified, and results included solutions for problems of water transport under isohaline and isothermal conditions, heat transport under isobaric and isohaline conditions, solute transport under isobaric and isothermal conditions, and coupled water-heat-solute transport. The first three problems considered in model verification were compared to either analytical or numerical solutions, whereas the coupled problem was compared to measured laboratory results for which no known analytic solutions or numerical models are available. The test results indicate the model is accurate and applicable for a wide range of conditions, including when water (liquid and vapor), heat (sensible and latent), and solute are coupled in ground-water systems. The cumulative residual errors for the coupled problem tested was less than 10-8 cubic centimeter per cubic centimeter, 10-5 moles per kilogram, and 102 calories per cubic meter for liquid water content, solute concentration and heat content, respectively. This model should be useful to hydrologists, engineers, and researchers interested in studying coupled processes associated with variably saturated transport in ground-water systems.

Hydrologic conditions in urban Miami-Dade County, Florida, and the effect of groundwater pumpage and increased sea level on canal leakage and regional groundwater flow

USGS Publications Warehouse

Hughes, Joseph D.; White, Jeremy T.

2014-01-01

The model was designed specifically to evaluate the effect of groundwater pumpage on canal leakage at the surface-water-basin scale and thus may not be appropriate for (1) predictions that are dependent on data not included in the calibration process (for example, subdaily simulation of high-intensity events and travel times) and (or) (2) hydrologic conditions that are substantially different from those during the calibration and verification periods. The reliability of the model is limited by the conceptual model of the surface-water and groundwater system, the spatial distribution of physical properties, the scale and discretization of the system, and specified boundary conditions. Some of the model limitations are manifested in model errors. Despite these limitations, however, the model represents the complexities of the interconnected surface-water and groundwater systems that affect how the systems respond to groundwater pumpage, sea-level rise, and other hydrologic stresses. The model also quantifies the relative effects of groundwater pumpage and sea-level rise on the surface-water and groundwater systems.

Digital simulation of ground-water flow in the Warwick Aquifer, Fort Totten Indian Reservation, North Dakota

USGS Publications Warehouse

Reed, Thomas B.

1997-01-01

The demand for water from the Warwick aquifer, which underlies the Fort Totten Indian Reservation in northeastern North Dakota, has been increasing during recent years. Therefore, the Spirit Lake Sioux Nation is interested in resolving questions about the quantity and quality of water in the aquifer and in developing a water-management plan for future water use. A study was conducted to evaluate the surface-water and ground-water resources of the Fort Totten Indian Reservation and, in particular, the ground-water resources in the area of the Warwick aquifer. A major component of the study, addressed by this report, was to define the ground-water flow system of the aquifer. The Warwick aquifer consists of outwash deposits of the Warwick outwash plain that are as much as 30 feet thick and buried-valley deposits beneath the outwash plain that are as much as 200 feet thick. The aquifer is bounded on the north and west by end-moraine deposits and Devils Lake, on the south by the Sheyenne River Valley, and on the east by outwash deposits and ravines. The aquifer is underlain by Pierre Shale or by glacial till, clay, or silt. Ground-water gradients generally are small and rarely are more than 3 or 4 feet per mile. From 1982 to 1993, withdrawals from the Devils Lake well field averaged 1.5 cubic feet per second, and withdrawals from irrigation wells averaged 1.29 cubic feet per second. The combined discharge from springs may be about 3 cubic feet per second. During the early 1990s, the Warwick aquifer probably was in a steady-state condition with regard to storage change in the aquifer. A finite-difference, three-dimensional, ground-water flow model provided a reasonable simulation of ground-water flow in the Warwick aquifer. The aquifer was divided vertically into two layers and horizontally into a grid of 83 by 109 cells, each measuring 656 feet (200 meters) per side. The steady-state simulation was conducted using 1992 pumpage rates and October 1992 water levels. The mean absolute difference between simulated and derived water-level altitudes during final calibration of the model was 1.52 feet. The two transient simulations were conducted for 20 time intervals of 1 year each using both the small and large storage estimates, doubled 1992 pumpage from the Devils Lake well field, 1992 irrigation pumpage, and initial water-level altitudes simulated by the October 1992 steady-state simulation. In the simulation using the small storage estimate and doubled pumpage, model cells in the area of the well field went dry after 13 years.Assumptions made in the design of the model generally are supported by the digital simulation. Except in the area of Warwick Springs and smaller springs, lateral and basal boundaries of the aquifer are impermeable. The flow system is dominated by recharge and evapotranspiration. Recharge rates obtained during the calibration process were lower in topographically high areas than in topographically low areas. Hydraulic conductivity in the area of the Devils Lake well field was larger than that in the rest of the aquifer.

Development and application of a comprehensive simulation model to evaluate impacts of watershed structures and irrigation water use on streamflow and groundwater: The case of Wet Walnut Creek Watershed, Kansas, USA

USGS Publications Warehouse

Ramireddygari, S.R.; Sophocleous, M.A.; Koelliker, J.K.; Perkins, S.P.; Govindaraju, R.S.

2000-01-01

This paper presents the results of a comprehensive modeling study of surface and groundwater systems, including stream-aquifer interactions, for the Wet Walnut Creek Watershed in west-central Kansas. The main objective of this study was to assess the impacts of watershed structures and irrigation water use on streamflow and groundwater levels, which in turn affect availability of water for the Cheyenne Bottoms Wildlife Refuge Management area. The surface-water flow model, POTYLDR, and the groundwater flow model, MODFLOW, were combined into an integrated, watershed-scale, continuous simulation model. Major revisions and enhancements were made to the POTYLDR and MODFLOW models for simulating the detailed hydrologic budget for the Wet Walnut Creek Watershed. The computer simulation model was calibrated and verified using historical streamflow records (at Albert and Nekoma gaging stations), reported irrigation water use, observed water-level elevations in watershed structure pools, and groundwater levels in the alluvial aquifer system. To assess the impact of watershed structures and irrigation water use on streamflow and groundwater levels, a number of hypothetical management scenarios were simulated under various operational criteria for watershed structures and different annual limits on water use for irrigation. A standard 'base case' was defined to allow comparative analysis of the results of different scenarios. The simulated streamflows showed that watershed structures decrease both streamflows and groundwater levels in the watershed. The amount of water used for irrigation has a substantial effect on the total simulated streamflow and groundwater levels, indicating that irrigation is a major budget item for managing water resources in the watershed. (C) 2000 Elsevier Science B.V.This paper presents the results of a comprehensive modeling study of surface and groundwater systems, including stream-aquifer interactions, for the Wet Walnut Creek Watershed in west-central Kansas. The main objective of this study was to assess the impacts of watershed structures and irrigation water use on streamflow and groundwater levels, which in turn affect availability of water for the Cheyenne Bottoms Wildlife Refuge Management area. The surface-water flow model, POTYLDR, and the groundwater flow model, MODFLOW, were combined into an integrated, watershed-scale, continuous simulation model. Major revisions and enhancements were made to the POTYLDR and MODFLOW models for simulating the detailed hydrologic budget for the Wet Walnut Creek Watershed. The computer simulation model was calibrated and verified using historical streamflow records (at Albert and Nekoma gaging stations), reported irrigation water use, observed water-level elevations in watershed structure pools, and groundwater levels in the alluvial aquifer system. To assess the impact of watershed structures and irrigation water use on streamflow and groundwater levels, a number of hypothetical management scenarios were simulated under various operational criteria for watershed structures and different annual limits on water use for irrigation. A standard `base case' was defined to allow comparative analysis of the results of different scenarios. The simulated streamflows showed that watershed structures decrease both streamflows and groundwater levels in the watershed. The amount of water used for irrigation has a substantial effect on the total simulated streamflow and groundwater levels, indicating that irrigation is a major budget item for managing water resources in the watershed.A comprehensive simulation model that combines the surface water flow model POTYLDR and the groundwater flow model MODFLOW was used to study the impacts of watershed structures (e.g., dams) and irrigation water use (including stream-aquifer interactions) on streamflow and groundwater. The model was revised, enhanced, calibrated, and verified, then applied to evaluate the hydrologic budget for Wet Wal

A Kirchhoff Approach to Seismic Modeling and Prestack Depth Migration

DTIC Science & Technology

1993-05-01

continuation of sources and geophones by finite difference (S-G finite - difference migration ), are relatively slow and dip-limited. Compared to S-G... finite - difference migration , the Kirchhoff integral implements prestack migration relatively efficiently and has no dip limitation. Liu .Mlodeling and...for modeling and migration . In this paper, a finite - difference algorithm is used to calculate traveltimes and amplitudes. With the help of

Simulation of future groundwater recharge using a climate model ensemble and SAR-image based soil parameter distributions - A case study in an intensively-used Mediterranean catchment.

PubMed

Herrmann, Frank; Baghdadi, Nicolas; Blaschek, Michael; Deidda, Roberto; Duttmann, Rainer; La Jeunesse, Isabelle; Sellami, Haykel; Vereecken, Harry; Wendland, Frank

2016-02-01

We used observed climate data, an ensemble of four GCM-RCM combinations (global and regional climate models) and the water balance model mGROWA to estimate present and future groundwater recharge for the intensively-used Thau lagoon catchment in southern France. In addition to a highly resolved soil map, soil moisture distributions obtained from SAR-images (Synthetic Aperture Radar) were used to derive the spatial distribution of soil parameters covering the full simulation domain. Doing so helped us to assess the impact of different soil parameter sources on the modelled groundwater recharge levels. Groundwater recharge was simulated in monthly time steps using the ensemble approach and analysed in its spatial and temporal variability. The soil parameters originating from both sources led to very similar groundwater recharge rates, proving that soil parameters derived from SAR images may replace traditionally used soil maps in regions where soil maps are sparse or missing. Additionally, we showed that the variance in different GCM-RCMs influences the projected magnitude of future groundwater recharge change significantly more than the variance in the soil parameter distributions derived from the two different sources. For the period between 1950 and 2100, climate change impacts based on the climate model ensemble indicated that overall groundwater recharge will possibly show a low to moderate decrease in the Thau catchment. However, as no clear trend resulted from the ensemble simulations, reliable recommendations for adapting the regional groundwater management to changed available groundwater volumes could not be derived. Copyright © 2015 Elsevier B.V. All rights reserved.

Simulation of groundwater and surface-water resources and evaluation of water-management alternatives for the Chamokane Creek basin, Stevens County, Washington

USGS Publications Warehouse

Ely, D. Matthew; Kahle, Sue C.

2012-01-01

A three-dimensional, transient numerical model of groundwater and surface-water flow was constructed for Chamokane Creek basin to better understand the groundwater-flow system and its relation to surface-water resources. The model described in this report can be used as a tool by water-management agencies and other stakeholders to quantitatively evaluate the effects of potential increases in groundwater pumping on groundwater and surface-water resources in the basin. The Chamokane Creek model was constructed using the U.S. Geological Survey (USGS) integrated model, GSFLOW. GSFLOW was developed to simulate coupled groundwater and surface-water resources. The model uses 1,000-foot grid cells that subdivide the model domain by 102 rows and 106 columns. Six hydrogeologic units in the model are represented using eight model layers. Daily precipitation and temperature were spatially distributed and subsequent groundwater recharge was computed within GSFLOW. Streamflows in Chamokane Creek and its major tributaries are simulated in the model by routing streamflow within a stream network that is coupled to the groundwater-flow system. Groundwater pumpage and surface-water diversions and returns specified in the model were derived from monthly and annual pumpage values previously estimated from another component of this study and new data reported by study partners. The model simulation period is water years 1980-2010 (October 1, 1979, to September 30, 2010), but the model was calibrated to the transient conditions for water years 1999-2010 (October 1, 1998, to September 30, 2010). Calibration was completed by using traditional trial-and-error methods and automated parameter-estimation techniques. The model adequately reproduces the measured time-series groundwater levels and daily streamflows. At well observation points, the mean difference between simulated and measured hydraulic heads is 7 feet with a root-mean-square error divided by the total difference in water levels of 4.7 percent. Simulated streamflow was compared to measured streamflow at the USGS streamflow-gaging station-Chamokane Creek below Falls, near Long Lake (12433200). Annual differences between measured and simulated streamflow for the site ranged from -63 to 22 percent. Calibrated model output includes a 31-year estimate of monthly water budget components for the hydrologic system. Five model applications (scenarios) were completed to obtain a better understanding of the relation between groundwater pumping and surface-water resources. The calibrated transient model was used to evaluate: (1) the connection between the upper- and middle-basin groundwater systems, (2) the effect of surface-water and groundwater uses in the middle basin, (3) the cumulative impacts of claims registry use and permit-exempt wells on Chamokane Creek streamflow, (4) the frequency of regulation due to impacted streamflow, and (5) the levels of domestic and stockwater use that can be regulated. The simulation results indicated that streamflow is affected by existing groundwater pumping in the upper and middle basins. Simulated water-management scenarios show streamflow increased relative to historical conditions as groundwater and surface-water withdrawals decreased.

Gradient-based model calibration with proxy-model assistance

NASA Astrophysics Data System (ADS)

Burrows, Wesley; Doherty, John

2016-02-01

Use of a proxy model in gradient-based calibration and uncertainty analysis of a complex groundwater model with large run times and problematic numerical behaviour is described. The methodology is general, and can be used with models of all types. The proxy model is based on a series of analytical functions that link all model outputs used in the calibration process to all parameters requiring estimation. In enforcing history-matching constraints during the calibration and post-calibration uncertainty analysis processes, the proxy model is run for the purposes of populating the Jacobian matrix, while the original model is run when testing parameter upgrades; the latter process is readily parallelized. Use of a proxy model in this fashion dramatically reduces the computational burden of complex model calibration and uncertainty analysis. At the same time, the effect of model numerical misbehaviour on calculation of local gradients is mitigated, this allowing access to the benefits of gradient-based analysis where lack of integrity in finite-difference derivatives calculation would otherwise have impeded such access. Construction of a proxy model, and its subsequent use in calibration of a complex model, and in analysing the uncertainties of predictions made by that model, is implemented in the PEST suite.

Estimating Natural Recharge in a Desert Environment Facing Increasing Ground-Water Demands

NASA Astrophysics Data System (ADS)

Nishikawa, T.; Izbicki, J. A.; Hevesi, J. A.; Martin, P.

2004-12-01

Ground water historically has been the sole source of water supply for the community of Joshua Tree in the Joshua Tree ground-water subbasin of the Morongo ground-water basin in the southern Mojave Desert. Joshua Basin Water District (JBWD) supplies water to the community from the underlying Joshua Tree ground-water subbasin, and ground-water withdrawals averaging about 960 acre-ft/yr have resulted in as much as 35 ft of drawdown. As growth continues in the desert, ground-water resources may need to be supplemented using imported water. To help meet future demands, JBWD plans to construct production wells in the adjacent Copper Mountain ground-water subbasin. To manage the ground-water resources and to identify future mitigating measures, a thorough understanding of the ground-water system is needed. To this end, field and numerical techniques were applied to determine the distribution and quantity of natural recharge. Field techniques included the installation of instrumented boreholes in selected washes and at a nearby control site. Numerical techniques included the use of a distributed-parameter watershed model and a ground-water flow model. The results from the field techniques indicated that as much as 70 acre-ft/yr of water infiltrated downward through the two principal washes during the study period (2001-3). The results from the watershed model indicated that the average annual recharge in the ground-water subbasins is about 160 acre-ft/yr. The results from the calibrated ground-water flow model indicated that the average annual recharge for the same area is about 125 acre-ft/yr. Although the field and numerical techniques were applied to different scales (local vs. large), all indicate that natural recharge in the Joshua Tree area is very limited; therefore, careful management of the limited ground-water resources is needed. Moreover, the calibrated model can now be used to estimate the effects of different water-management strategies on the ground-water subbasins.

Evapotranspiration Within the Groundwater Model Domain of the Tuba City, Arizona, Disposal Site Interim Report

DOE Office of Scientific and Technical Information (OSTI.GOV)

None, None

The revised groundwater model includes estimates of evapotranspiration (ET). The types of vegetation and the influences of ET on groundwater hydrology vary within the model domain. Some plant species within the model domain, classified as phreatophytes, survive by extracting groundwater. ET within these plant communities can result in a net discharge of groundwater if ET exceeds precipitation. Other upland desert plants within the model domain survive on meteoric water, potentially limiting groundwater recharge if ET is equivalent to precipitation. For all plant communities within the model domain, excessive livestock grazing or other disturbances can tip the balance to a netmore » groundwater recharge. This task characterized and mapped vegetation within the groundwater model domain at the Tuba City, Arizona, Site, and then applied a remote sensing algorithm to estimate ET for each vegetation type. The task was designed to address five objectives: 1. Characterize and delineate different vegetation or ET zones within the groundwater model domain, focusing on the separation of plant communities with phreatophytes that survive by tapping groundwater and upland plant communities that are dependent on precipitation. 2. Refine a remote sensing method, developed to estimate ET at the Monument Valley site, for application at the Tuba City site. 3. Estimate recent seasonal and annual ET for all vegetation zones, separating phreatophytic and upland plant communities within the Tuba City groundwater model domain. 4. For selected vegetation zones, estimate ET that might be achieved given a scenario of limited livestock grazing. 5. Analyze uncertainty of ET estimates for each vegetation zone and for the entire groundwater model domain.« less

Evaluation of bias associated with capture maps derived from nonlinear groundwater flow models

USGS Publications Warehouse

Nadler, Cara; Allander, Kip K.; Pohll, Greg; Morway, Eric D.; Naranjo, Ramon C.; Huntington, Justin

2018-01-01

The impact of groundwater withdrawal on surface water is a concern of water users and water managers, particularly in the arid western United States. Capture maps are useful tools to spatially assess the impact of groundwater pumping on water sources (e.g., streamflow depletion) and are being used more frequently for conjunctive management of surface water and groundwater. Capture maps have been derived using linear groundwater flow models and rely on the principle of superposition to demonstrate the effects of pumping in various locations on resources of interest. However, nonlinear models are often necessary to simulate head-dependent boundary conditions and unconfined aquifers. Capture maps developed using nonlinear models with the principle of superposition may over- or underestimate capture magnitude and spatial extent. This paper presents new methods for generating capture difference maps, which assess spatial effects of model nonlinearity on capture fraction sensitivity to pumping rate, and for calculating the bias associated with capture maps. The sensitivity of capture map bias to selected parameters related to model design and conceptualization for the arid western United States is explored. This study finds that the simulation of stream continuity, pumping rates, stream incision, well proximity to capture sources, aquifer hydraulic conductivity, and groundwater evapotranspiration extinction depth substantially affect capture map bias. Capture difference maps demonstrate that regions with large capture fraction differences are indicative of greater potential capture map bias. Understanding both spatial and temporal bias in capture maps derived from nonlinear groundwater flow models improves their utility and defensibility as conjunctive-use management tools.

Model-based evaluation of subsurface monitoring networks for improved efficiency and predictive certainty of regional groundwater models

NASA Astrophysics Data System (ADS)

Gosses, M. J.; Wöhling, Th.; Moore, C. R.; Dann, R.; Scott, D. M.; Close, M.

2012-04-01

Groundwater resources worldwide are increasingly under pressure. Demands from different local stakeholders add to the challenge of managing this resource. In response, groundwater models have become popular to make predictions about the impact of different management strategies and to estimate possible impacts of changes in climatic conditions. These models can assist to find optimal management strategies that comply with the various stakeholder needs. Observations of the states of the groundwater system are essential for the calibration and evaluation of groundwater flow models, particularly when they are used to guide the decision making process. On the other hand, installation and maintenance of observation networks are costly. Therefore it is important to design monitoring networks carefully and cost-efficiently. In this study, we analyse the Central Plains groundwater aquifer (~ 4000 km2) between the Rakaia and Waimakariri rivers on the Eastern side of the Southern Alps in New Zealand. The large sedimentary groundwater aquifer is fed by the two alpine rivers and by recharge from the land surface. The area is mainly under agricultural land use and large areas of the land are irrigated. The other major water use is the drinking water supply for the city of Christchurch. The local authority in the region, Environment Canterbury, maintains an extensive groundwater quantity and quality monitoring programme to monitor the effects of land use and discharges on groundwater quality, and the suitability of the groundwater for various uses, especially drinking-water supply. Current and projected irrigation water demand has raised concerns about possible impacts on groundwater-dependent lowland streams. We use predictive uncertainty analysis and the Central Plains steady-state groundwater flow model to evaluate the worth of pressure head observations in the existing groundwater well monitoring network. The data worth of particular observations is dependent on the problem-specific prediction target under consideration. Therefore, the worth of individual observation locations may differ for different prediction targets. Our evaluation is based on predictions of lowland stream discharge resulting from changes in land use and irrigation in the upper Central Plains catchment. In our analysis, we adopt the model predictive uncertainty analysis method by Moore and Doherty (2005) which accounts for contributions from both measurement errors and uncertain structural heterogeneity. The method is robust and efficient due to a linearity assumption in the governing equations and readily implemented for application in the model-independent parameter estimation and uncertainty analysis toolkit PEST (Doherty, 2010). The proposed methods can be applied not only for the evaluation of monitoring networks, but also for the optimization of networks, to compare alternative monitoring strategies, as well as to identify best cost-benefit monitoring design even prior to any data acquisition.

Simulation of groundwater conditions and streamflow depletion to evaluate water availability in a Freeport, Maine, watershed

USGS Publications Warehouse

Nielsen, Martha G.; Locke, Daniel B.

2012-01-01

In order to evaluate water availability in the State of Maine, the U.S. Geological Survey (USGS) and the Maine Geological Survey began a cooperative investigation to provide the first rigorous evaluation of watersheds deemed "at risk" because of the combination of instream flow requirements and proportionally large water withdrawals. The study area for this investigation includes the Harvey and Merrill Brook watersheds and the Freeport aquifer in the towns of Freeport, Pownal, and Yarmouth, Maine. A numerical groundwater- flow model was used to evaluate groundwater withdrawals, groundwater-surface-water interactions, and the effect of water-management practices on streamflow. The water budget illustrates the effect that groundwater withdrawals have on streamflow and the movement of water within the system. Streamflow measurements were made following standard USGS techniques, from May through September 2009 at one site in the Merrill Brook watershed and four sites in the Harvey Brook watershed. A record-extension technique was applied to estimate long-term monthly streamflows at each of the five sites. The conceptual model of the groundwater system consists of a deep, confined aquifer (the Freeport aquifer) in a buried valley that trends through the middle of the study area, covered by a discontinuous confining unit, and topped by a thin upper saturated zone that is a mixture of sandy units, till, and weathered clay. Harvey and Merrill Brooks flow southward through the study area, and receive groundwater discharge from the upper saturated zone and from the deep aquifer through previously unknown discontinuities in the confining unit. The Freeport aquifer gets most of its recharge from local seepage around the edges of the confining unit, the remainder is received as inflow from the north within the buried valley. Groundwater withdrawals from the Freeport aquifer in the study area were obtained from the local water utility and estimated for other categories. Overall, the public-supply withdrawals (105.5 million gallons per year (Mgal/yr)) were much greater than those for any other category, being almost 7 times greater than all domestic well withdrawals (15.3 Mgal/yr). Industrial withdrawals in the study area (2.0 Mgal/yr) are mostly by a company that withdraws from an aquifer at the edge of the Merrill Brook watershed. Commercial withdrawals are very small (1.0 Mgal/yr), and no irrigation or other agricultural withdrawals were identified in this study area. A three-dimensional, steady-state groundwater-flow model was developed to evaluate stream-aquifer interactions and streamflow depletion from pumping, to help refine the conceptual model, and to predict changes in streamflow resulting from changes in pumping and recharge. Groundwater levels and flow in the Freeport aquifer study area were simulated with the three-dimensional, finite-difference groundwater-flow modeling code, MODFLOW-2005. Study area hydrology was simulated with a 3-layer model, under steady-state conditions. The groundwater model was used to evaluate changes that could occur in the water budgets of three parts of the local hydrologic system (the Harvey Brook watershed, the Merrill Brook watershed, and the buried aquifer from which pumping occurs) under several different climatic and pumping scenarios. The scenarios were (1) no pumping well withdrawals; (2) current (2009) pumping, but simulated drought conditions (20-percent reduction in recharge); (3) current (2009) recharge, but a 50-percent increase in pumping well withdrawals for public supply; and (4) drought conditions and increased pumping combined. In simulated drought situations, the overall recharge to the buried valley is about 15 percent less and the total amount of streamflow in the model area is reduced by about 19 percent. Without pumping, infiltration to the buried valley aquifer around the confining unit decreased by a small amount (0.05 million gallons per day (Mgal/d)), and discharge to the streams increased by about 8 percent (0.3 Mgal/d). A 50-percent increase in pumping resulted in a simulated decrease in streamflow discharge of about 4 percent (0.14 Mgal/d). Streamflow depletion in Harvey Brook was evaluated by use of the numerical groundwater-flow model and an analytical model. The analytical model estimated negligible depletion from Harvey Brook under current (2009) pumping conditions, whereas the numerical model estimated that flow to Harvey Brook decreased 0.38 cubic feet per second (ft3/s) because of the pumping well withdrawals. A sensitivity analysis of the analytical model method showed that conducting a cursory evaluation using an analytical model of streamflow depletion using available information may result in a very wide range in results, depending on how well the hydraulic conductivity variables and aquifer geometry of the system are known, and how well the aquifer fits the assumptions of the model. Using the analytical model to evaluate the streamflow depletion with an incomplete understanding of the hydrologic system gave results that seem unlikely to reflect actual streamflow depletion in the Freeport aquifer study area. In contrast, the groundwater-flow model was a more robust method of evaluating the amount of streamflow depletion that results from withdrawals in the Freeport aquifer, and could be used to evaluate streamflow depletion in both streams. Simulations of streamflow without pumping for each measurement site were compared to the calibratedmodel streamflow (with pumping), the difference in the total being streamflow depletion. Simulations without pumping resulted in a simulated increase in the steady-state flow rate of 0.38 ft3/s in Harvey Brook and 0.01 ft3/s in Merrill Brook. This translates into a streamflow-depletion amount equal to about 8.5 percent of the steady-state base flow in Harvey Brook, and an unmeasurable amount of depletion in Merrill Brook. If pumping was increased by 50 percent and recharge reduced by 20 percent, the amount of streamflow depletion in Harvey Brook could reach 1.41 ft3/s.

Simulated effects of increased recharge on the ground-water flow system of Yucca Mountain and vicinity, Nevada-California

USGS Publications Warehouse

Czarnecki, J.B.

1984-01-01

A study was performed to assess the potential effects of changes in future climatic conditions on the groundwater system in the vicinity of Yucca Mountain, the site of a potential mined geologic repository for high-level nuclear wastes. These changes probably would result in greater rates of precipitation and, consequently, greater rates of recharge. The study was performed by simulating the groundwater system, using a two-dimensional, finite-element, groundwater flow model. The simulated position of the water table rose as much as 130 meters near the U.S. Department of Energy 's preferred repository area at Yucca Mountain for a simulation involving a 100-percent increase in precipitation compared to modern-day conditions. Despite the water table rise, no flooding of the potential repository would occur at its current proposed location. According to the simulation, springs would discharge south and west of Timber Mountain, along Fortymile Canyon, in the Amargosa Desert near Lathrop Wells and Franklin Lake playa, and near Furnace Creek Ranch in Death Valley, where they presently discharge. Simulated directions of groundwater flow paths near the potential repository area generally would be the same for the baseline (modern-day climate) and the increased-recharge simulations, but the magnitude of flow would increase by 2 to 4 times that of the baseline-simulation flow. (USGS)

Coupled Heat and Moisture Transport Simulation on the Re-saturation of Engineered Clay Barrier

NASA Astrophysics Data System (ADS)

Huang, W. H.; Chuang, Y. F.

2014-12-01

Engineered clay barrier plays a major role for the isolation of radioactive wastes in a underground repository. This paper investigates the resaturation processes of clay barrier, with emphasis on the coupling effects of heat and moisture during the intrusion of groundwater to the repository. A reference bentonite and a locally available clay were adopted in the laboratory program. Soil suction of clay specimens was measured by psychrometers embedded in clay specimens and by vapor equilibrium technique conducted at varying temperatures so as to determine the soil water characteristic curves of the two clays at different temperatures. And water uptake tests were conducted on clay specimens compacted at various densities to simulate the intrusion of groundwater into the clay barrier. Using the soil water characteristic curve, an integration scheme was introduced to estimate the hydraulic conductivity of unsaturated clay. It was found that soil suction decreases as temperature increases, resulting in a reduction in water retention capability. The finite element method was then employed to carry out the numerical simulation of the saturation process in the near field of a repository. Results of the numerical simulation were validated using the degree of saturation profile obtained from the water uptake tests on the clays. The numerical scheme was then extended to establish a model simulating the resaturation process after the closure of a repository. Finally, the model was then used to evaluate the effect of clay barrier thickness on the time required for groundwater to penetrate the clay barrier and approach saturation. Due to the variation in clay suction and thermal conductivity with temperature of clay barrier material, the calculated temperature field shows a reduction as a result of incorporating the hydro-properties in the calculations.

Groundwater transport of crater-lake brine at Poa´s Volcano, Costa Rica

USGS Publications Warehouse

Sanford, Ward E.; Konikow, Leonard F.; Rowe, Gary L.; Brantley, Susan L.

1995-01-01

Poa´s Volcano is an active stratovolcano in Costa Rica that has a lake in its active crater. The crater lake has high temperatures (50–90 °C), high acidity (pH ≈ 0.0), and a high dissolved-solids content (100 g/kg). The volcano has numerous freshwater springs on its flanks, but a few on the northwestern flank are highly acidic (pH = 1.6–2.5) and have high dissolved-solids concentrations (2–22 g/kg). This study analyzes the regional groundwater system at Poa´s and demonstrates the likelihood that the water discharging from the acidic springs in the Rio Agrio watershed originates at the acidic crater lake. Both heat and solute transport are analyzed on a regional scale through numerical simulations using the HST3D finite-difference model, which solves the coupled equations for fluid flow, heat transport, and solute transport. The code allows fluid viscosity and density to be functions of both temperature and solute concentration. The simulations use estimates for recharge to the mountain and a range of values and various distributions of permeability and porosity. Several sensitivity analyses are performed to test how the uncertainty in many of the model parameters affects the simulation results. These uncertainties yield an estimated range of travel times from the crater lake to the Rio Agrio springs of 1–30 years, which is in close agreement with the results of tritium analyses of the springs. Calculated groundwater fluxes into and out of the crater lake are both about several hundred kg/s. These fluxes must be accounted for in water budgets of the crater lake.

The Use of Hydrograph Analysis and Impulse Response Functions to Improve Understanding of Groundwater Flooding: A Case Study from the Chalk Aquifer, United Kingdom.

NASA Astrophysics Data System (ADS)

Ascott, M.; Bloomfield, J.; Macdonald, D.; Marchant, B.; McKenzie, A.

2017-12-01

The Cretaceous Chalk, the most important aquifer in the United Kingdom (UK) for public water supply, underlies many large cities in southern and eastern England including parts of London, however, it is prone to groundwater flooding. We have developed a new approach to analyse the spatio-temporal extent of groundwater flooding using statistical analysis of groundwater level hydrographs and impulse response functions (IRFs) applied to a major Chalk groundwater flooding event in the UK during winter 2013/14. Using monthly groundwater levels for 26 boreholes in the Chalk and a new standardised index for groundwater flooding, we have: estimated standardised series; grouped them using k-means cluster analysis; and, cross-correlated the cluster centroids with the Standardised Precipitation Index accumulated over time intervals between 1 and 60 months. This analysis reveals two spatially coherent groups of standardised hydrographs which respond to precipitation over different timescales. We estimate IRF models of the groundwater level response to effective precipitation for three boreholes in each group. The IRF models support the SPI analysis showing different response functions between the two groups. If we apply identical effective precipitation inputs to each of the IRF models we see differences between the hydrographs from each group. It is proposed that these differences are due to the intrinsic, hydrogeological properties of the Chalk and of overlying relatively low permeability superficial deposits. Consequently, it is concluded that the overarching controls on groundwater flood response are a complex combination of antecedent conditions, rainfall and catchment hydrogeological properties. These controls should be taken into consideration when anticipating and managing future groundwater flood events.

Improved Uncertainty Quantification in Groundwater Flux Estimation Using GRACE

NASA Astrophysics Data System (ADS)

Reager, J. T., II; Rao, P.; Famiglietti, J. S.; Turmon, M.

2015-12-01

Groundwater change is difficult to monitor over large scales. One of the most successful approaches is in the remote sensing of time-variable gravity using NASA Gravity Recovery and Climate Experiment (GRACE) mission data, and successful case studies have created the opportunity to move towards a global groundwater monitoring framework for the world's largest aquifers. To achieve these estimates, several approximations are applied, including those in GRACE processing corrections, the formulation of the formal GRACE errors, destriping and signal recovery, and the numerical model estimation of snow water, surface water and soil moisture storage states used to isolate a groundwater component. A major weakness in these approaches is inconsistency: different studies have used different sources of primary and ancillary data, and may achieve different results based on alternative choices in these approximations. In this study, we present two cases of groundwater change estimation in California and the Colorado River basin, selected for their good data availability and varied climates. We achieve a robust numerical estimate of post-processing uncertainties resulting from land-surface model structural shortcomings and model resolution errors. Groundwater variations should demonstrate less variability than the overlying soil moisture state does, as groundwater has a longer memory of past events due to buffering by infiltration and drainage rate limits. We apply a model ensemble approach in a Bayesian framework constrained by the assumption of decreasing signal variability with depth in the soil column. We also discuss time variable errors vs. time constant errors, across-scale errors v. across-model errors, and error spectral content (across scales and across model). More robust uncertainty quantification for GRACE-based groundwater estimates would take all of these issues into account, allowing for more fair use in management applications and for better integration of GRACE-based measurements with observations from other sources.

Aquifer Reclamation Design: The Use of Contaminant Transport Simulation Combined With Nonlinear Programing

NASA Astrophysics Data System (ADS)

Gorelick, Steven M.; Voss, Clifford I.; Gill, Philip E.; Murray, Walter; Saunders, Michael A.; Wright, Margaret H.

1984-04-01

A simulation-management methodology is demonstrated for the rehabilitation of aquifers that have been subjected to chemical contamination. Finite element groundwater flow and contaminant transport simulation are combined with nonlinear optimization. The model is capable of determining well locations plus pumping and injection rates for groundwater quality control. Examples demonstrate linear or nonlinear objective functions subject to linear and nonlinear simulation and water management constraints. Restrictions can be placed on hydraulic heads, stresses, and gradients, in addition to contaminant concentrations and fluxes. These restrictions can be distributed over space and time. Three design strategies are demonstrated for an aquifer that is polluted by a constant contaminant source: they are pumping for contaminant removal, water injection for in-ground dilution, and a pumping, treatment, and injection cycle. A transient model designs either contaminant plume interception or in-ground dilution so that water quality standards are met. The method is not limited to these cases. It is generally applicable to the optimization of many types of distributed parameter systems.

Soil moisture data as a constraint for groundwater recharge estimation

NASA Astrophysics Data System (ADS)

Mathias, Simon A.; Sorensen, James P. R.; Butler, Adrian P.

2017-09-01

Estimating groundwater recharge rates is important for water resource management studies. Modeling approaches to forecast groundwater recharge typically require observed historic data to assist calibration. It is generally not possible to observe groundwater recharge rates directly. Therefore, in the past, much effort has been invested to record soil moisture content (SMC) data, which can be used in a water balance calculation to estimate groundwater recharge. In this context, SMC data is measured at different depths and then typically integrated with respect to depth to obtain a single set of aggregated SMC values, which are used as an estimate of the total water stored within a given soil profile. This article seeks to investigate the value of such aggregated SMC data for conditioning groundwater recharge models in this respect. A simple modeling approach is adopted, which utilizes an emulation of Richards' equation in conjunction with a soil texture pedotransfer function. The only unknown parameters are soil texture. Monte Carlo simulation is performed for four different SMC monitoring sites. The model is used to estimate both aggregated SMC and groundwater recharge. The impact of conditioning the model to the aggregated SMC data is then explored in terms of its ability to reduce the uncertainty associated with recharge estimation. Whilst uncertainty in soil texture can lead to significant uncertainty in groundwater recharge estimation, it is found that aggregated SMC is virtually insensitive to soil texture.

Finite-difference interblock transmissivity for unconfined aquifers and for aquifers having smoothly varying transmissivity

USGS Publications Warehouse

Goode, D.J.; Appel, C.A.

1992-01-01

More accurate alternatives to the widely used harmonic mean interblock transmissivity are proposed for block-centered finite-difference models of ground-water flow in unconfined aquifers and in aquifers having smoothly varying transmissivity. The harmonic mean is the exact interblock transmissivity for steady-state one-dimensional flow with no recharge if the transmissivity is assumed to be spatially uniform over each finite-difference block, changing abruptly at the block interface. However, the harmonic mean may be inferior to other means if transmissivity varies in a continuous or smooth manner between nodes. Alternative interblock transmissivity functions are analytically derived for the case of steady-state one-dimensional flow with no recharge. The second author has previously derived the exact interblock transmissivity, the logarithmic mean, for one-dimensional flow when transmissivity is a linear function of distance in the direction of flow. We show that the logarithmic mean transmissivity is also exact for uniform flow parallel to the direction of changing transmissivity in a two- or three-dimensional model, regardless of grid orientation relative to the flow vector. For the case of horizontal flow in a homogeneous unconfined or water-table aquifer with a horizontal bottom and with areally distributed recharge, the exact interblock transmissivity is the unweighted arithmetic mean of transmissivity at the nodes. This mean also exhibits no grid-orientation effect for unidirectional flow in a two-dimensional model. For horizontal flow in an unconfined aquifer with no recharge where hydraulic conductivity is a linear function of distance in the direction of flow the exact interblock transmissivity is the product of the arithmetic mean saturated thickness and the logarithmic mean hydraulic conductivity. For several hypothetical two- and three-dimensional cases with smoothly varying transmissivity or hydraulic conductivity, the harmonic mean is shown to yield the least accurate solution to the flow equation of the alternatives considered. Application of the alternative interblock transmissivities to a regional aquifer system model indicates that the changes in computed heads and fluxes are typically small, relative to model calibration error. For this example, the use of alternative interblock transmissivities resulted in an increase in computational effort of less than 3 percent. Numerical algorithms to compute alternative interblock transmissivity functions in a modular three-dimensional flow model are presented and documented.

A new method of fully three dimensional analysis of stress field in the soil layer of a soil-mantled hillslope

NASA Astrophysics Data System (ADS)

Wu, Y. H.; Nakakita, E.

2017-12-01

Hillslope stability is highly related to stress equilibrium near the top surface of soil-mantled hillslopes. Stress field in a hillslope can also be significantly altered by variable groundwater motion under the rainfall influence as well as by different vegetation above and below the slope. The topographic irregularity, biological effects from vegetation and variable rainfall patterns couple with others to make the prediction of shallow landslide complicated and difficult. In an increasing tendency of extreme rainfall, the mountainous area in Japan has suffered more and more shallow landslides. To better assess shallow landslide hazards, we would like to develop a new mechanically-based method to estimate the fully three-dimensional stress field in hillslopes. The surface soil-layer of hillslope is modelled as a poroelastic medium, and the tree surcharge on the slope surface is considered as a boundary input of stress forcing. The modelling of groundwater motion is involved to alter effective stress state in the soil layer, and the tree root-reinforcement estimated by allometric equations is taken into account for influencing the soil strength. The Mohr-Coulomb failure theory is then used for locating possible yielding surfaces, or says for identifying failure zones. This model is implemented by using the finite element method. Finally, we performed a case study of the real event of massive shallow landslides occurred in Hiroshima in August, 2014. The result shows good agreement with the field condition.

Geohydrology of alluvium and terrace deposits of the Cimarron River from freedom to Guthrie, Oklahoma

USGS Publications Warehouse

Adams, G.P.; Bergman, D.L.

1996-01-01

Ground water in 1,305 square miles of Quaternary alluvium and terrace deposits along the Cimarron River from Freedom to Guthrie, Oklahoma, is used for irrigation, municipal, stock, and domestic supplies. As much as 120 feet of clay, silt, sand, and gravel form an unconfined aquifer with an average saturated thickness of 28 feet. The 1985-86 water in storage, assuming a specific yield of 0.20, was 4.47 million acre-feet. The aquifer is bounded laterally and underlain by relatively impermeable Permian geologic units. Regional ground-water flow is generally southeast to southwest toward the Cimarron River, except where the flow direction is affected by perennial tributaries. Estimated average recharge to the aquifer is 207 cubic feet per second. Estimated average discharge from the aquifer by seepage and evapotranspiration is 173 cubic feet per second. Estimated 1985 discharge by withdrawals from wells was 24.43 cubic feet per second. Most water in the terrace deposits varied from a calcium bicarbonate to mixed bicarbonate type, with median dissolved-solids concentration of 538 milligrams per liter. Cimarron River water is a sodium chloride type with up to 16,600 milligrams per liter dissolved solids. A finite-difference ground-water flow model was developed and calibrated to test the conceptual model of the aquifer under steady-state conditions. The model was calibrated to match 1985-86 aquifer heads and discharge to the Cimarron River between Waynoka and Dover.

Groundwater flow pattern and related environmental phenomena in complex geologic setting based on integrated model construction

NASA Astrophysics Data System (ADS)

Tóth, Ádám; Havril, Tímea; Simon, Szilvia; Galsa, Attila; Monteiro Santos, Fernando A.; Müller, Imre; Mádl-Szőnyi, Judit

2016-08-01

Groundwater flow, driven, controlled and determined by topography, geology and climate, is responsible for several natural surface manifestations and affected by anthropogenic processes. Therefore, flowing groundwater can be regarded as an environmental agent. Numerical simulation of groundwater flow could reveal the flow pattern and explain the observed features. In complex geologic framework, where the geologic-hydrogeologic knowledge is limited, the groundwater flow model could not be constructed based solely on borehole data, but geophysical information could aid the model building. The integrated model construction was presented via the case study of the Tihany Peninsula, Hungary, with the aims of understanding the background and occurrence of groundwater-related environmental phenomena, such as wetlands, surface water-groundwater interaction, slope instability, and revealing the potential effect of anthropogenic activity and climate change. The hydrogeologic model was prepared on the basis of the compiled archive geophysical database and the results of recently performed geophysical measurements complemented with geologic-hydrogeologic data. Derivation of different electrostratigraphic units, revealing fracturing and detecting tectonic elements was achieved by systematically combined electromagnetic geophysical methods. The deduced information can be used as model input for groundwater flow simulation concerning hydrostratigraphy, geometry and boundary conditions. The results of numerical modelling were interpreted on the basis of gravity-driven regional groundwater flow concept and validated by field mapping of groundwater-related phenomena. The 3D model clarified the hydraulic behaviour of the formations, revealed the subsurface hydraulic connection between groundwater and wetlands and displayed the groundwater discharge pattern, as well. The position of wetlands, their vegetation type, discharge features and induced landslides were explained as environmental imprints of groundwater. The highly vulnerable wetlands and groundwater-dependent ecosystems have to be in the focus of water management and natural conservation policy.

3D modeling of groundwater heat transport in the shallow Westliches Leibnitzer Feld aquifer, Austria

NASA Astrophysics Data System (ADS)

Rock, Gerhard; Kupfersberger, Hans

2018-02-01

For the shallow Westliches Leibnitzer feld aquifer (45 km2) we applied the recently developed methodology by Kupfersberger et al. (2017a) to derive the thermal upper boundary for a 3D heat transport model from observed air temperatures. We distinguished between land uses of grass and agriculture, sealed surfaces, forest and water bodies. To represent the heat flux from heated buildings and the mixture between different land surfaces in urban areas we ran the 1D vertical heat conduction module SoilTemp which is coupled to the heat transport model (using FEFLOW) on a time step basis. Over a simulation period of 23 years the comparison between measured and observed groundwater temperatures yielded NSE values ranging from 0.41 to 0.92 including readings at different depths. The model results showed that the thermal input signals lead to distinctly different vertical groundwater temperature distributions. To overcome the influence of specific warm or cold years we introduced the computation of an annual averaged groundwater temperature profile. With respect to the use of groundwater cooling or heating facilities we evaluated the application of vertically averaged statistical groundwater temperature distributions compared to the use of temperature distributions at selected dates. We concluded that the heat transport model serves well as an aquifer scale management tool to optimize the use of the shallow subsurface for thermal purposes and to analyze the impacts of corresponding measures on groundwater temperatures.

Simulation of Ground-Water Flow in the Shenandoah Valley, Virginia and West Virginia, Using Variable-Direction Anisotropy in Hydraulic Conductivity to Represent Bedrock Structure

USGS Publications Warehouse

Yager, Richard M.; Southworth, Scott C.; Voss, Clifford I.

2008-01-01

Ground-water flow was simulated using variable-direction anisotropy in hydraulic conductivity to represent the folded, fractured sedimentary rocks that underlie the Shenandoah Valley in Virginia and West Virginia. The anisotropy is a consequence of the orientations of fractures that provide preferential flow paths through the rock, such that the direction of maximum hydraulic conductivity is oriented within bedding planes, which generally strike N30 deg E; the direction of minimum hydraulic conductivity is perpendicular to the bedding. The finite-element model SUTRA was used to specify variable directions of the hydraulic-conductivity tensor in order to represent changes in the strike and dip of the bedding throughout the valley. The folded rocks in the valley are collectively referred to as the Massanutten synclinorium, which contains about a 5-km thick section of clastic and carbonate rocks. For the model, the bedrock was divided into four units: a 300-m thick top unit with 10 equally spaced layers through which most ground water is assumed to flow, and three lower units each containing 5 layers of increasing thickness that correspond to the three major rock units in the valley: clastic, carbonate and metamorphic rocks. A separate zone in the carbonate rocks that is overlain by colluvial gravel - called the western-toe carbonate unit - was also distinguished. Hydraulic-conductivity values were estimated through model calibration for each of the four rock units, using data from 354 wells and 23 streamflow-gaging stations. Conductivity tensors for metamorphic and western-toe carbonate rocks were assumed to be isotropic, while conductivity tensors for carbonate and clastic rocks were assumed to be anisotropic. The directions of the conductivity tensor for carbonate and clastic rocks were interpolated for each mesh element from a stack of 'form surfaces' that provided a three-dimensional representation of bedrock structure. Model simulations were run with (1) variable strike and dip, in which conductivity tensors were aligned with the strike and dip of the bedding, and (2) uniform strike in which conductivity tensors were assumed to be horizontally isotropic with the maximum conductivity direction parallel to the N30 deg E axis of the valley and the minimum conductivity direction perpendicular to the horizontal plane. Simulated flow penetrated deeper into the aquifer system with the uniform-strike tensor than with the variable-strike-and-dip tensor. Sensitivity analyses suggest that additional information on recharge rates would increase confidence in the estimated parameter values. Two applications of the model were conducted - the first, to determine depth of recent ground-water flow by simulating the distribution of ground-water ages, showed that most shallow ground water is less than 10 years old. Ground-water age distributions computed by variable-strike-and-dip and uniform-strike models were similar, but differed beneath Massanutten Mountain in the center of the valley. The variable-strike-and-dip model simulated flow from west to east parallel to the bedding of the carbonate rocks beneath Massanutten Mountain, while the uniform-strike model, in which flow was largely controlled by topography, simulated this same area as an east-west ground-water divide. The second application, which delineated capture zones for selected well fields in the valley, showed that capture zones delineated with both models were similar in plan view, but differed in vertical extent. Capture zones simulated by the variable-strike-and-dip model extended downdip with the bedding of carbonate rock and were relatively shallow, while those simulated by the uniform-strike model extended to the bottom of the flow system, which is unrealistic. These results suggest that simulations of ground-water flow through folded fractured rock can be constructed using SUTRA to represent variable orientations of the hydraulic-conductivity tensor and produce a

HST3D; a computer code for simulation of heat and solute transport in three-dimensional ground-water flow systems

USGS Publications Warehouse

Kipp, K.L.

1987-01-01

The Heat- and Soil-Transport Program (HST3D) simulates groundwater flow and associated heat and solute transport in three dimensions. The three governing equations are coupled through the interstitial pore velocity, the dependence of the fluid density on pressure, temperature, the solute-mass fraction , and the dependence of the fluid viscosity on temperature and solute-mass fraction. The solute transport equation is for only a single, solute species with possible linear equilibrium sorption and linear decay. Finite difference techniques are used to discretize the governing equations using a point-distributed grid. The flow-, heat- and solute-transport equations are solved , in turn, after a particle Gauss-reduction scheme is used to modify them. The modified equations are more tightly coupled and have better stability for the numerical solutions. The basic source-sink term represents wells. A complex well flow model may be used to simulate specified flow rate and pressure conditions at the land surface or within the aquifer, with or without pressure and flow rate constraints. Boundary condition types offered include specified value, specified flux, leakage, heat conduction, and approximate free surface, and two types of aquifer influence functions. All boundary conditions can be functions of time. Two techniques are available for solution of the finite difference matrix equations. One technique is a direct-elimination solver, using equations reordered by alternating diagonal planes. The other technique is an iterative solver, using two-line successive over-relaxation. A restart option is available for storing intermediate results and restarting the simulation at an intermediate time with modified boundary conditions. This feature also can be used as protection against computer system failure. Data input and output may be in metric (SI) units or inch-pound units. Output may include tables of dependent variables and parameters, zoned-contour maps, and plots of the dependent variables versus time. (Lantz-PTT)

Hydrogeology of, and Simulation of Ground-Water Flow In, the Pohatcong Valley, Warren County, New Jersey

USGS Publications Warehouse

Carleton, Glen B.; Gordon, Alison D.

2007-01-01

A numerical ground-water-flow model was constructed to simulate ground-water flow in the Pohatcong Valley, including the area within the U.S. Environmental Protection Agency Pohatcong Valley Ground Water Contamination Site. The area is underlain by glacial till, alluvial sediments, and weathered and competent carbonate bedrock. The northwestern and southeastern valley boundaries are regional-scale thrust faults and ridges underlain by crystalline rocks. The unconsolidated sediments and weathered bedrock form a minor surficial aquifer and the carbonate rocks form a highly transmissive fractured-rock aquifer. Ground-water flow in the carbonate rocks is primarily downvalley towards the Delaware River, but the water discharges through the surficial aquifer to Pohatcong Creek under typical conditions. The hydraulic characteristics of the carbonate-rock aquifer are highly heterogeneous. Horizontal hydraulic conductivities span nearly five orders of magnitude, from 0.5 feet per day (ft/d) to 1,800 ft/d. The maximum transmissivity calculated is 37,000 feet squared per day. The horizontal hydraulic conductivities calculated from aquifer tests using public supply wells open to the Leithsville Formation and Allentown Dolomite are 34 ft/d (effective hydraulic conductivity) and 85 to 190 ft/d (minimum and maximum hydraulic conductivity, respectively, yielding a horizontal anisotropy ratio of 0.46). Stream base-flow data were used to estimate the net gain (or loss) for selected reaches on Brass Castle Creek, Shabbecong Creek, three smaller tributaries to Pohatcong Creek, and for five reaches on Pohatcong Creek. Estimated mean annual base flows for Brass Castle Creek, Pohatcong Creek at New Village, and Pohatcong Creek at Carpentersville (from correlations of partial- and continuous-record stations) are 2.4, 25, and 45 cubic feet per second (ft3/s) (10, 10, and 11 inches per year (in/yr)), respectively. Ground-water ages estimated using sulfur hexafluoride (SF6), chlorofluorocarbon (CFC), and tritium-helium age-dating techniques range from 0 to 27 years, with a median age of 6 years. Land-surface and ground-water water budgets were calculated, yielding an estimated rate of direct recharge tothe surficial aquifer of about 23 in/yr, and an estimated net recharge to the ground-water system within the area underlain by carbonate rock (11.4 mi2) of 29 in/yr (10 in/yr over the entire 33.3 mi2 basin). A finite-difference, numerical model was developed to simulate ground-water flow in the Pohatcong Valley. The four-layer model encompasses the entire carbonate-rock part of the valley. The carbonate-rock aquifer was modeled as horizontally anisotropic, with the direction of maximum transmissivity aligned with the longitudinal axis of the valley. All lateral boundaries are no-flow boundaries. Recharge was applied uniformly to the topmost active layer with additional recharge added near the lateral boundaries to represent infiltration of runoff from adjacent crystalline-rock areas. The model was calibrated to June 2001 water levels in wells completed in the carbonate-rock aquifer, August 2000 stream base-flow measurements, and the approximate ground-water age. The ground-water-flow model was constructed in part to test possible site contamination remediation alternatives. Four previously determined ground-water remediation alternatives (GW1, GW2, GW3, and GW4) were simulated. For GW1, the no-action alternative, simulated pathlines originating in the tetrachloroethene (PCE) and trichloroethene (TCE) source areas within the Ground-Water Contamination Site end at Pohatcong Creek near the confluence with Shabbecong Creek, although some particles went deeper in the aquifer system and ultimately discharge to Pohatcong Creek about 10 miles downvalley in Pohatcong Township. Remediation alternatives GW2, GW3, and GW4 include ground-water withdrawal, treatment, and reinjection. The design for GW2 includes wells in the TCE and PCE source areas that wit

Simulation of ground-water flow in the Coastal Plain aquifer system of North Carolina

USGS Publications Warehouse

Giese, G.I.; Eimers, J.L.; Coble, R.W.

1997-01-01

A three-dimensional finite-difference digital model was used to simulate ground-water flow in the 25,000-square-mile aquifer system of the North Carolina Coastal Plain. The model was developed from a hydrogeologic framework that is based on an alternating sequence of 10 aquifers and 9 confining units, which make up a seaward-thickening wedge of sediments that form the Coastal Plain aquifer system in the State of North Carolina. The model was calibrated by comparing observed and simulated water levels. The model calibration was achieved by adjusting model parameters, primarily leakance of confining units and transmissivity of aquifers, until differences between observed and simulated water levels were within acceptable limits, generally within 15 feet. The maximum transmissivity of an individual aquifer in the calibrated model is 200,000 feet squared per day in a part of the Castle Hayne aquifer, which consists predominantly of limestone. The maximum value for simulated vertical hydraulic conductivity in a confining unit was 2.5 feet per day, in a part of the confining unit overlying the upper Cape Fear aquifer. The minimum value was 4.1x10-6 feet per day, in part of the confining unit overlying the lower Cape Fear aquifer. Analysis indicated the model is highly sensitive to changes in transmissivity and leakance near pumping centers; away from pumping centers, the model is only slightly sensitive to changes in transmissivity but is moderately sensitive to changes in leakance. Recharge from precipitation to the surficial aquifer ranges from about 12 inches per year in areas having clay at the surface to about 20 inches per year in areas having sand at the surface. Most of this recharge moves laterally to streams, and only about 1 inch per year moves downward to the confined parts of the aquifer system. Under predevelopment conditions, the confined aquifers were generally recharged in updip interstream areas and discharged through streambeds and in downdip coastward areas. Hydrologic analysis of the flow system using the calibrated model indicated that, because of ground-water withdrawals, areas of ground-water recharge have expanded and encroached upon some major stream valleys and into coastal area. Simulations of pumping conditions indicate that by 1980 large parts of the former coastal discharge areas had become areas of potential or actual recharge. Declines of ground-water level, which are the result of water taken from storage, are extensive in some areas and minimal in others. Hydraulic head declines of more than 135 feet have occurred in the northern Coastal Plain since 1940 primarily due to withdrawals in the Franklin area in Virginia. Declines of ground-water levels greater than 110 feet have occurred in aquifers in the central Coastal Plain due to combined effects of pumpage for public and industrial water supplies. Water-level declines exceeding 100 feet have occurred in the Beaufort County area because of withdrawals for a mining operation and water supplies for a chemical plant. Head declines have been less than 10 feet in the shallow surficial and Yorktown aquifers and in the updip parts of the major confined aquifers distant from areas of major withdrawals. In 1980, contribution from aquifer storage was 14 cubic feet per second, which is about 4.8 percent of pumpage and about 0.05 percent of ground-water recharge. A water-budget analysis using the model simulations indicates that much of the water removed from the ground-water system by pumping ultimately is made up by a reduction in water leaving the aquifer system, which discharges to streams as base flow. The reduction in stream base flow was 294 cubic feet per second in 1980 and represents about 1.1 percent of the ground-water recharge. The net reduction to streamflow is not large, however, because most pumped ground water is eventually discharged to streams. In places, such as at rock quarries in Onslow and Craven Counties, water is lost from st

Implementation of a 3d numerical model of a folded multilayer carbonate aquifer

NASA Astrophysics Data System (ADS)

Di Salvo, Cristina; Guyennon, Nicolas; Romano, Emanuele; Bruna Petrangeli, Anna; Preziosi, Elisabetta

2016-04-01

The main objective of this research is to present a case study of the numerical model implementation of a complex carbonate, structurally folded aquifer, with a finite difference, porous equivalent model. The case study aquifer (which extends over 235 km2 in the Apennine chain, Central Italy) provides a long term average of 3.5 m3/s of good quality groundwater to the surface river network, sustaining the minimum vital flow, and it is planned to be exploited in the next years for public water supply. In the downstream part of the river in the study area, a "Site of Community Importance" include the Nera River for its valuable aquatic fauna. However, the possible negative effects of the foreseen exploitation on groundwater dependent ecosystems are a great concern and model grounded scenarios are needed. This multilayer aquifer was conceptualized as five hydrostratigraphic units: three main aquifers (the uppermost unconfined, the central and the deepest partly confined), are separated by two locally discontinuous aquitards. The Nera river cuts through the two upper aquifers and acts as the main natural sink for groundwater. An equivalent porous medium approach was chosen. The complex tectonic structure of the aquifer requires several steps in defining the conceptual model; the presence of strongly dipping layers with very heterogeneous hydraulic conductivity, results in different thicknesses of saturated portions. Aquifers can have both unconfined or confined zones; drying and rewetting must be allowed when considering recharge/discharge cycles. All these characteristics can be included in the conceptual and numerical model; however, being the number of flow and head target scarce, the over-parametrization of the model must be avoided. Following the principle of parsimony, three steady state numerical models were developed, starting from a simple model, and then adding complexity: 2D (single layer), QUASI -3D (with leackage term simulating flow through aquitards) and fully-3D (with aquitards simulated explicitly and transient flow represented by 3D governing equations). At first, steady state simulation were run under average seasonal recharge. To overcome dry-cell problems in the FULL-3D model, the Newton-Raphson formulation for MODFLOW-2005 was invoked. Steady state calibration was achieved mainly using annual average flow along four streambed's Nera River springs and average water level data available only in two observation wells. Results show that a FULL-3D zoned model was required to match the observed distribution of river base flow. The FULL-3D model was then run in transient conditions (1990-2013) by using monthly spatially distributed recharge estimated using the Thornthwaite-Mather method based on 60 years of climate data. The monitored flow of one spring, used for public water supply, was used as proxy data for reconstruct Nera River hydrogram; proxy-based hydrogram was used for calibration of storage coefficients and further model's parameters adjustment. Once calibrated, the model was run under different aquifer management scenario (i.e., pumping wells planned to be active for water supply); the related risk of depletion of spring discharge and groundwater-surface water interaction was evaluated.

Index-based groundwater vulnerability mapping models using hydrogeological settings: A critical evaluation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Prashant, E-mail: prashantkumar@csio.res.in; Academy of Scientific and Innovative Research—CSIO, Chandigarh 160030; Bansod, Baban K.S.

2015-02-15

Groundwater vulnerability maps are useful for decision making in land use planning and water resource management. This paper reviews the various groundwater vulnerability assessment models developed across the world. Each model has been evaluated in terms of its pros and cons and the environmental conditions of its application. The paper further discusses the validation techniques used for the generated vulnerability maps by various models. Implicit challenges associated with the development of the groundwater vulnerability assessment models have also been identified with scientific considerations to the parameter relations and their selections. - Highlights: • Various index-based groundwater vulnerability assessment models havemore » been discussed. • A comparative analysis of the models and its applicability in different hydrogeological settings has been discussed. • Research problems of underlying vulnerability assessment models are also reported in this review paper.« less

Rapid reconnaissance hydrogeologic modeling on public lands using analytic element solutions coupled with MODFLOW - application to the Eagle Creek watershed, New Mexico

NASA Astrophysics Data System (ADS)

Congdon, R. D.

2012-12-01

There is frequently a need in land management agencies for a quick and easy method for estimating hydrogeologic conditions in a watershed for which there is very little subsurface information. Setting up a finite difference or finite element model takes valuable time that often is not available when decisions need to be made quickly. An analytic element model (AEM), GFLOW in this case, may enable the investigator to produce a preliminary steady-state model for a watershed, and to easily evaluate variants of the conceptual model. Use of preexisting data, such as stream gage data or USGS reports makes the job much easier. Solutions to analytic element models are obtained within seconds. The Eagle Creek watershed in central New Mexico is a site of local water supply issues in an area of volcanic and plutonic rocks. Parameters estimated by groundwater consultants and the USGS, and discharge data from three USGS stream gages were used to set up the steady-state analytical model (GFLOW). Matching gage records with line-sink fluxes facilitated conceptualization of local groundwater flow and quick analysis of the effects of steady water supply pumping on Eagle Creek. Because of steep topgraphy and limited access, a water supply well is located within the stream channel within 20 meters of the creek, and it would be useful to evaluate the effects of the well on stream flow. A USGS report (SIR 2010-5205) revealed a section of Eagle Creek with a high vertical conductivity which results in flow loss of up to 34 l/s (including flow to the water table and flow into alluvium) when the well was pumped and the water table was lowered below the channel bottom. The water supply well was simulated with a steady-state well pumping at the average and maximum rates of 12 l/s and 31 l/s. The initial simulation shows that pumping at these rates results in stream flow loss of 19% and 51%, respectively. The simulation was conducted with average flow conditions, and this information will be important in planning for management during periods of drought, as well as times of more normal precipitation; as water uses must be balanced with the needs of the existing ecosystem. Alternatives, such as low conductivity blocks between stream channels and different volumetric and geographic pumping scenarios may also be readily explored in an AEM. Exporting these scenarios into MODFLOW simulations will enable us to evaluate transient and cyclical pumping effects on the surface waters for each AEM conceptualization, as well as being able to simulate seasonal recharge. However, in many cases the use of MODFLOW may not be necessary, if the AEM proves sufficient to answer the relevant questions. Symbiotic use of GFLOW and MODFLOW will be an invaluable aid in evaluating groundwater and its uses in National Forest watersheds, especially in cases when time is a critical factor in informed decision-making.

Novel patch modelling method for efficient simulation and prediction uncertainty analysis of multi-scale groundwater flow and transport processes

NASA Astrophysics Data System (ADS)

Sreekanth, J.; Moore, Catherine

2018-04-01

The application of global sensitivity and uncertainty analysis techniques to groundwater models of deep sedimentary basins are typically challenged by large computational burdens combined with associated numerical stability issues. The highly parameterized approaches required for exploring the predictive uncertainty associated with the heterogeneous hydraulic characteristics of multiple aquifers and aquitards in these sedimentary basins exacerbate these issues. A novel Patch Modelling Methodology is proposed for improving the computational feasibility of stochastic modelling analysis of large-scale and complex groundwater models. The method incorporates a nested groundwater modelling framework that enables efficient simulation of groundwater flow and transport across multiple spatial and temporal scales. The method also allows different processes to be simulated within different model scales. Existing nested model methodologies are extended by employing 'joining predictions' for extrapolating prediction-salient information from one model scale to the next. This establishes a feedback mechanism supporting the transfer of information from child models to parent models as well as parent models to child models in a computationally efficient manner. This feedback mechanism is simple and flexible and ensures that while the salient small scale features influencing larger scale prediction are transferred back to the larger scale, this does not require the live coupling of models. This method allows the modelling of multiple groundwater flow and transport processes using separate groundwater models that are built for the appropriate spatial and temporal scales, within a stochastic framework, while also removing the computational burden associated with live model coupling. The utility of the method is demonstrated by application to an actual large scale aquifer injection scheme in Australia.

A Novel Approach to Model Earth Fissure Caused by Extensive Aquifer Exploitation and its Application to the Wuxi Case, China

NASA Astrophysics Data System (ADS)

Ye, Shujun; Franceschini, Andrea; Zhang, Yan; Janna, Carlo; Gong, Xulong; Yu, Jun; Teatini, Pietro

2018-03-01

Initially observed in the semiarid basins of southwestern USA, earth fissures due to aquifer over-exploitation are presently threatening a large number of subsiding basins in various countries worldwide. Different mechanics have been proposed to explain this process, such as differential compaction, horizontal movements, and fault reactivation. Numerical modeling and prediction of this major geohazard caused by overuse of groundwater resources are challenging because of two main requirements: shifting from the classical continuous to discontinuous geomechanics and incorporating two-dimensional features (the earth fissures) into large three-dimensional (3-D) modeling domain (the subsiding basin). In this work, we proposed a novel modeling approach to simulate earth fissure generation and propagation in 3-D complex geological settings. A nested two-scale approach associated with an original nonlinear elastoplastic finite element/interface element simulator allows modeling the mechanics of earth discontinuities, in terms of both sliding and opening. The model is applied on a case study in Wuxi, China, where groundwater pumping between 1985 and 2004 has caused land subsidence larger than 2 m. The model outcomes highlight that the presence of a shallow (˜80 m deep) bedrock ridge crossing the Yangtze River delta is the key factor triggering the earth fissure development in this area. Bending of the alluvial deposits around the ridge tip and shear stress due to the uneven piezometric change and asymmetrical shape of the bedrock have caused the earth fissure to onset at the land surface and propagate downward to a maximum depth of about 20-30 m. Maximum sliding and opening are computed in the range of 10-40 cm, in agreement with the order of magnitude estimated in the field.

Ground-water models for water resources planning

USGS Publications Warehouse

Moore, John E.

1980-01-01

In the past decade hydrologists have emphasized the development of computer-based mathematical models to aid in the understanding of flow, the transport of solutes, transport of heat, and deformation in the groundwater system. These models have been used to provide information and predictions for water managers. Too frequently, groundwater was neglected in water-resource planning because managers believed that it could not be adequately evaluated in terms of availability, quality, and effect of development on surface water supplies. Now, however, with newly developed digital groundwater models, effects of development can be predicted. Such models have been used to predict hydrologic and quality changes under different stresses. These models have grown in complexity over the last 10 years from simple one-layer flow models to three-dimensional simulations of groundwater flow which may include solute transport, heat transport, effects of land subsidence, and encroachment of salt water. This paper illustrates, through case histories, how predictive groundwater models have provided the information needed for the sound planning and management of water resources in the United States. (USGS)

USGS Regional Groundwater Availability Studies: Quantifying Aquifer Response

NASA Astrophysics Data System (ADS)

Reeves, H. W.

2017-12-01

The U.S. Geological Survey (USGS) identified six challenges in determining groundwater availability: 1) limited direct measurement, 2) varying response times for different systems, 3) varying spatial scales for different availability questions and aquifer systems, 4) varying tolerance to changes in water levels or outflows, 5) redistribution of stresses and potential return-flow of water pumped from the system, and 6) varying chemical quality of groundwater and the role of quality in determining suitability for different uses. USGS Regional groundwater availability studies are designed to address these challenges. USGS regional groundwater availability studies focus on quantifying the groundwater budget for principal aquifers and determining how this budget has changed in response to pumping or variations in climate. This focus requires relating limited measurements to a quantitative understanding of the temporal and spatial response of regional aquifers. For most principal aquifer studies, aquifer response is quantified using regional groundwater flow models, and USGS regional groundwater availability studies have provided test cases for the development and application of advanced modeling techniques and methods. Results from regional studies from the Lake Michigan Basin and Northern Atlantic Coastal Plain illustrate how different parts of these systems respond differently to pumping with some areas showing large drawdowns and others having much less drawdown but greater capture of discharge. The Central Valley and Mississippi Embayment studies show how extensive pumping and transfer of water have resulted in much more groundwater moving through the aquifer system under current conditions compared to pre-development. These and other results from regional studies will be explored to illustrate how regional groundwater availability and related studies address the six challenges to determining groundwater availability.

Groundwater response to leakage of surface water through a thick vadose zone in the middle reaches area of Heihe River Basin, in China

NASA Astrophysics Data System (ADS)

Wang, X.-S.; Ma, M.-G.; Li, X.; Zhao, J.; Dong, P.; Zhou, J.

2010-04-01

The behavior of groundwater response to leakage of surface water in the middle reaches area of Heihe River Basin is significantly influenced by a thick vadose zone. The groundwater regime is a result of two recharge events due to leakage of Heihe River and irrigation water with different delay time. A nonlinear leakage model is developed to calculate the monthly leakage of Heihe River in considering changes of streamflow, river stage and agricultural water utilization. Numerical modeling of variable saturated flow is carried out to investigate the general behaviors of leakage-recharge conversion through a thick vadose zone. It is found that the recharge pattern can be approximated by simple reservoir models of leakages under a river and under an irrigation district with different delay-time and recession coefficient. A triple-reservoir model of relationship between surface water, vadose zone and groundwater is developed. It reproduces the groundwater regime during 1989-2006 with variable streamflow of Heihe River and agricultural water utilization. The model is applied to interpret changes of groundwater level during 2007-2008 that observed in the Watershed Airborne Telemetry Experimental Research (WATER).

A three-dimensional method-of-characteristics solute-transport model (MOC3D)

USGS Publications Warehouse

Konikow, Leonard F.; Goode, D.J.; Hornberger, G.Z.

1996-01-01

This report presents a model, MOC3D, that simulates three-dimensional solute transport in flowing ground water. The model computes changes in concentration of a single dissolved chemical constituent over time that are caused by advective transport, hydrodynamic dispersion (including both mechanical dispersion and diffusion), mixing (or dilution) from fluid sources, and mathematically simple chemical reactions (including linear sorption, which is represented by a retardation factor, and decay). The transport model is integrated with MODFLOW, a three-dimensional ground-water flow model that uses implicit finite-difference methods to solve the transient flow equation. MOC3D uses the method of characteristics to solve the transport equation on the basis of the hydraulic gradients computed with MODFLOW for a given time step. This implementation of the method of characteristics uses particle tracking to represent advective transport and explicit finite-difference methods to calculate the effects of other processes. However, the explicit procedure has several stability criteria that may limit the size of time increments for solving the transport equation; these are automatically determined by the program. For improved efficiency, the user can apply MOC3D to a subgrid of the primary MODFLOW grid that is used to solve the flow equation. However, the transport subgrid must have uniform grid spacing along rows and columns. The report includes a description of the theoretical basis of the model, a detailed description of input requirements and output options, and the results of model testing and evaluation. The model was evaluated for several problems for which exact analytical solutions are available and by benchmarking against other numerical codes for selected complex problems for which no exact solutions are available. These test results indicate that the model is very accurate for a wide range of conditions and yields minimal numerical dispersion for advection-dominated problems. Mass-balance errors are generally less than 10 percent, and tend to decrease and stabilize with time.

The impact of groundwater velocity fields on streamlines in an aquifer system with a discontinuous aquitard (Inner Mongolia, China)

NASA Astrophysics Data System (ADS)

Wu, Qiang; Zhao, Yingwang; Xu, Hua

2018-04-01

Many numerical methods that simulate groundwater flow, particularly the continuous Galerkin finite element method, do not produce velocity information directly. Many algorithms have been proposed to improve the accuracy of velocity fields computed from hydraulic potentials. The differences in the streamlines generated from velocity fields obtained using different algorithms are presented in this report. The superconvergence method employed by FEFLOW, a popular commercial code, and some dual-mesh methods proposed in recent years are selected for comparison. The applications to depict hydrogeologic conditions using streamlines are used, and errors in streamlines are shown to lead to notable errors in boundary conditions, the locations of material interfaces, fluxes and conductivities. Furthermore, the effects of the procedures used in these two types of methods, including velocity integration and local conservation, are analyzed. The method of interpolating velocities across edges using fluxes is shown to be able to eliminate errors associated with refraction points that are not located along material interfaces and streamline ends at no-flow boundaries. Local conservation is shown to be a crucial property of velocity fields and can result in more accurate streamline densities. A case study involving both three-dimensional and two-dimensional cross-sectional models of a coal mine in Inner Mongolia, China, are used to support the conclusions presented.

Modeling the spatial distribution of landslide-prone colluvium and shallow groundwater on hillslopes of Seattle, WA

USGS Publications Warehouse

Schulz, W.H.; Lidke, D.J.; Godt, J.W.

2008-01-01

Landslides in partially saturated colluvium on Seattle, WA, hillslopes have resulted in property damage and human casualties. We developed statistical models of colluvium and shallow-groundwater distributions to aid landslide hazard assessments. The models were developed using a geographic information system, digital geologic maps, digital topography, subsurface exploration results, the groundwater flow modeling software VS2DI and regression analyses. Input to the colluvium model includes slope, distance to a hillslope-crest escarpment, and escarpment slope and height. We developed different statistical relations for thickness of colluvium on four landforms. Groundwater model input includes colluvium basal slope and distance from the Fraser aquifer. This distance was used to estimate hydraulic conductivity based on the assumption that addition of finer-grained material from down-section would result in lower conductivity. Colluvial groundwater is perched so we estimated its saturated thickness. We used VS2DI to establish relations between saturated thickness and the hydraulic conductivity and basal slope of the colluvium. We developed different statistical relations for three groundwater flow regimes. All model results were validated using observational data that were excluded from calibration. Eighty percent of colluvium thickness predictions were within 25% of observed values and 88% of saturated thickness predictions were within 20% of observed values. The models are based on conditions common to many areas, so our method can provide accurate results for similar regions; relations in our statistical models require calibration for new regions. Our results suggest that Seattle landslides occur in native deposits and colluvium, ultimately in response to surface-water erosion of hillstope toes. Regional groundwater conditions do not appear to strongly affect the general distribution of Seattle landslides; historical landslides were equally dispersed within and outside of the area potentially affected by regional groundwater conditions.

A 2D forward and inverse code for streaming potential problems

NASA Astrophysics Data System (ADS)

Soueid Ahmed, A.; Jardani, A.; Revil, A.

2013-12-01

The self-potential method corresponds to the passive measurement of the electrical field in response to the occurrence of natural sources of current in the ground. One of these sources corresponds to the streaming current associated with the flow of the groundwater. We can therefore apply the self- potential method to recover non-intrusively some information regarding the groundwater flow. We first solve the forward problem starting with the solution of the groundwater flow problem, then computing the source current density, and finally solving a Poisson equation for the electrical potential. We use the finite-element method to solve the relevant partial differential equations. In order to reduce the number of (petrophysical) model parameters required to solve the forward problem, we introduced an effective charge density tensor of the pore water, which can be determined directly from the permeability tensor for neutral pore waters. The second aspect of our work concerns the inversion of the self-potential data using Tikhonov regularization with smoothness and weighting depth constraints. This approach accounts for the distribution of the electrical resistivity, which can be independently and approximately determined from electrical resistivity tomography. A numerical code, SP2DINV, has been implemented in Matlab to perform both the forward and inverse modeling. Three synthetic case studies are discussed.

Geohydrology and Numerical Simulation of the Ground-Water Flow System of Kona, Island of Hawaii

USGS Publications Warehouse

Oki, Delwyn S.

1999-01-01

Prior to the early 1990's, ground-water in the Kona area, which is in the western part of the island of Hawaii, was withdrawn from wells located within about 3 mi from the coast where water levels were less than 10 feet above sea level. In 1990, exploratory drilling in the uplands east of the existing coastal wells first revealed the presence of high water levels (greater than 40 feet above sea level) in the Kona area. Measured water levels from 16 wells indicate that high water levels exist in a zone parallel to and inland of the Kona coast, between Kalaoa and Honaunau. Available hydrologic and geophysical evidence is generally consistent with the concept that the high ground-water levels are associated with a buried dike complex. A two-dimensional (areal), steady-state, freshwater-saltwater, sharp-interface ground-water flow model was developed for the Kona area of the island of Hawaii, to enhance the understanding of (1) the distribution of aquifer hydraulic properties, (2) the conceptual framework of the ground-water flow system, and (3) the regional effects of ground-water withdrawals on water levels and coastal discharge. The model uses the finite-difference code SHARP. To estimate the hydraulic characteristics, average recharge, withdrawals, and water-level conditions for the period 1991-93 were simulated. The following horizontal hydraulic-conductivity values were estimated: (1) 7,500 feet per day for the dike-free volcanic rocks of Hualalai and Mauna Loa, (2) 0.1 feet per day for the buried dike complex of Hualalai, (3) 10 feet per day for the northern marginal dike zone (north of Kalaoa), and (4) 0.5 feet per day for the southern marginal dike zone between Palani Junction and Holualoa. The coastal leakance was estimated to be 0.05 feet per day per foot. Measured water levels indicate that ground water generally flows from inland areas to the coast. Model results are in general agreement with the limited set of measured water levels in the Kona area. Model results indicate, however, that water levels do not strictly increase in an inland direction and that a ground-water divide exists within the buried dike complex. Data are not available, however, to verify model results in the area near and inland of the model-calculated ground-water divide. Three simulations to determine the effects of proposed withdrawals from the high water-level area on coastal discharge and water levels, relative to model-calculated, steady-state coastal discharge and water levels for 1997 withdrawal rates, show that the effects are widespread. During 1997, the total withdrawal of ground water from the high water-level area between Palani Junction and Holualoa was about 1 million gallons per day. Model results indicate that it may not be possible to withdraw 25.6 million gallons per day of freshwater from this area between Palani Junction and Holualoa, but that it may be possible to withdraw between 5 to 8 million gallons per day from the same area. For a proposed withdrawal rate of 5.0 million gallons per day uniformly distributed to 12 sites between Palani Junction and Holualoa, the model-calculated drawdown of 0.01 foot or more extends about 9 miles north-northwest and about 7 miles south of the proposed well sites. In all scenarios, freshwater coastal discharge is reduced by an amount equal to the additional freshwater withdrawal. Additional data needed to improve the understanding of the ground-water flow system in the Kona area include: (1) a wider spatial distribution and longer temporal distribution of water levels, (2) improved information about the subsurface geology, (3) independent estimates of hydraulic conductivity, (4) improved recharge estimates, and (5) information about the vertical distribution of salinity in ground water.

Identifying the groundwater basin boundaries, using environmental isotopes: a case study

NASA Astrophysics Data System (ADS)

Demiroğlu, Muhterem

2017-06-01

Groundwater, which is renewable under current climatic conditions separately from other natural sources, in fact is a finite resource in terms of quality and fossil groundwater. Researchers have long emphasized the necessity of exploiting, operating, conserving and managing groundwater in an efficient and sustainable manner with an integrated water management approach. The management of groundwater needs reliable information about changes on groundwater quantity and quality. Environmental isotopes are the most important tools to provide this support. No matter which method we use to calculate the groundwater budget and flow equations, we need to determine boundary conditions or the physical boundaries of the domain. The Groundwater divide line or basin boundaries that separate the two adjacent basin recharge areas from each other must be drawn correctly to be successful in defining complex groundwater basin boundary conditions. Environmental isotope data, as well as other methods provide support for determining recharge areas of the aquifers, especially for karst aquifers, residence time and interconnections between aquifer systems. This study demonstrates the use of environmental isotope data to interpret and correct groundwater basin boundaries giving as an example the Yeniçıkrı basin within the main Sakarya basin.

Comparison of Estimated Areas Contributing Recharge to Selected Springs in North-Central Florida by Using Multiple Ground-Water Flow Models

USGS Publications Warehouse

Shoemaker, W. Barclay; O'Reilly, Andrew M.; Sepúlveda, Nicasio; Williams, Stanley A.; Motz, Louis H.; Sun, Qing

2004-01-01

Areas contributing recharge to springs are defined in this report as the land-surface area wherein water entering the ground-water system at the water table eventually discharges to a spring. These areas were delineated for Blue Spring, Silver Springs, Alexander Springs, and Silver Glen Springs in north-central Florida using four regional ground-water flow models and particle tracking. As expected, different models predicted different areas contributing recharge. In general, the differences were due to different hydrologic stresses, subsurface permeability properties, and boundary conditions that were used to calibrate each model, all of which are considered to be equally feasible because each model matched its respective calibration data reasonably well. To evaluate the agreement of the models and to summarize results, areas contributing recharge to springs from each model were combined into composite areas. During 1993-98, the composite areas contributing recharge to Blue Spring, Silver Springs, Alexander Springs, and Silver Glen Springs were about 130, 730, 110, and 120 square miles, respectively. The composite areas for all springs remained about the same when using projected 2020 ground-water withdrawals.

Numerical simulation of the groundwater-flow system in Chimacum Creek Basin and vicinity, Jefferson County, Washington

USGS Publications Warehouse

Jones, Joseph L.; Johnson, Kenneth H.; Frans, Lonna M.

2013-01-01

A groundwater-flow model was developed to evaluate potential future effects of growth and of water-management strategies on water resources in the Chimacum Creek Basin. The model covers an area of about 64 square miles (mi2) on the Olympic Peninsula in northeastern Jefferson County, Washington. The Chimacum Creek Basin drains an area of about 53 mi2 and consists of Chimacum Creek and its tributary East Fork Chimacum Creek, which converge near the town of Chimacum and discharge to Port Townsend Bay near the town of Irondale. The topography of the model area consists of north-south oriented, narrow, regularly spaced parallel ridges and valleys that are characteristic of fluted glaciated surfaces. Thick accumulations of peat occur along the axis of East Fork Chimacum Creek and provide rich soils for agricultural use. The study area is underlain by a north-thickening sequence of unconsolidated glacial (till and outwash) and interglacial (fluvial and lacustrine) deposits, and sedimentary and igneous bedrock units that crop out along the margins and the western interior of the model area. Six hydrogeologic units in the model area form the basis of the groundwater-flow model. They are represented by model layers UC (upper confining), UA (upper aquifer), MC (middle confining), LA (lower aquifer), LC (lower confining), and OE (bedrock). Groundwater flow in the Chimacum Creek Basin and vicinity was simulated using the groundwater-flow model, MODFLOW-2005. The finite-difference model grid comprises 245 columns, 313 rows, and 6 layers. Each model cell has a horizontal dimension of 200 × 200 feet (ft). The thickness of model layers varies throughout the model area and ranges from 5 ft in the non-bedrock units to more than 2,400 ft in the bedrock. Groundwater flow was simulated for steady-state conditions, which were simulated for calibration of the model using average recharge, discharge, and water levels for the 180-month period October 1994–September 2009. The model as calibrated has a mean residual of 4.5 ft and a standard error on the mean of 2.1 ft for heads, and 0.64±0.42 cubic feet per second for streamflows. After the model was calibrated, a Current Conditions simulation was developed to reflect current (October 2008–September 2009) hydrologic conditions, with representative pumping, return flows, and “normal” recharge (based on National Weather Service average precipitation for 1981 to 2010). The Current Conditions simulation was used to estimate current flow quantities, and as a basis to compare other simulations.Simulated steady-state inflow to the model area from precipitation and secondary recharge, or “return flow,” was 16,347 acre-feet per year (acre-ft/yr); groundwater inflow from other basins to the north of the model boundary was 1,518 acre-ft/yr (net, 3,114 acre-ft/yr in and 1,596 acre-ft/yr out) and simulated inflow from lake leakage was 613 acre-ft/yr (net, 684 acre-ft/yr in and 71 acre-ft/yr out). Simulated outflow from the model primarily was through discharge to Puget Sound (10,022 acre-ft/yr), streams (5,424 acre-ft/yr ), springs and seeps (1,521 acre-ft/yr), and through withdrawals from wells (1,506 acre-ft/yr). Four simulations were formulated using the calibrated model—one to represent current conditions (2009, the end of the period used for calibration) and three to provide representative examples of how the model can be used to evaluate the relative effects of potential changes in groundwater withdrawals and consumptive use on groundwater levels and stream base flows: Probable Future Use, based on population projections; Full Beneficial Use, based on Jefferson County Public Utility District #1 water rights; Sanitary Sewer, based on eliminating septic return flows in the Urban Growth Area. Particle tracking was used to assess flowpaths from sources and to sinks, and the effects of the presence of irrigation wells and their depths was assessed.

Subsidence Modeling of the Over-exploited Granular Aquifer System in Aguascalientes, Mexico

NASA Astrophysics Data System (ADS)

Solano Rojas, D. E.; Wdowinski, S.; Minderhoud, P. P. S.; Pacheco, J.; Cabral, E.

2016-12-01

The valley of Aguascalientes in central Mexico experiences subsidence rates of up to 100 [mm/yr] due to overexploitation of its aquifer system, as revealed from satellite-based geodetic observations. The spatial pattern of the subsidence over the valley is inhomogeneous and affected by shallow faulting. The understanding of the subsoil mechanics is still limited. A better understanding of the subsidence process in Aguascalientes is needed to provide insights for future subsidence in the valley. We present here a displacement-constrained finite-element subsidence model using Deltares iMOD (interactive MODeling), based on the USGS MODFLOW software. The construction of our model relies on 3 main inputs: (1) groundwater level time series obtained from extraction wells' hydrographs, (2) subsurface lithostratigraphy interpreted from well drilling logs, and (3) hydrogeological parameters obtained from field pumping tests. The groundwater level measurements were converted to pore pressure in our model's layers, and used in Terzaghi's equation for calculating effective stress. We then used the effective stresse along with the displacement obtained from geodetic observations to constrain and optimize five geo-mechanical parameters: compression ratio, reloading ratio, secondary compression index, over consolidation ratio, and consolidation coefficient. Finally, we use the NEN-Bjerrum linear stress model formulation for settlements to determine elastic and visco-plastic strain, accounting for the aquifer system units' aging effect. Preliminary results show higher compaction response in clay-saturated intervals (i.e. aquitards) of the aquifer system, as reflected in the spatial pattern of the surface deformation. The forecasted subsidence for our proposed scenarios show a much more pronounced deformation when we consider higher groundwater extraction regimes.

The Effect of modeled recharge distribution on simulated groundwater availability and capture

USGS Publications Warehouse

Tillman, Fred D.; Pool, Donald R.; Leake, Stanley A.

2015-01-01

Simulating groundwater flow in basin-fill aquifers of the semiarid southwestern United States commonly requires decisions about how to distribute aquifer recharge. Precipitation can recharge basin-fill aquifers by direct infiltration and transport through faults and fractures in the high-elevation areas, by flowing overland through high-elevation areas to infiltrate at basin-fill margins along mountain fronts, by flowing overland to infiltrate along ephemeral channels that often traverse basins in the area, or by some combination of these processes. The importance of accurately simulating recharge distributions is a current topic of discussion among hydrologists and water managers in the region, but no comparative study has been performed to analyze the effects of different recharge distributions on groundwater simulations. This study investigates the importance of the distribution of aquifer recharge in simulating regional groundwater flow in basin-fill aquifers by calibrating a groundwater-flow model to four different recharge distributions, all with the same total amount of recharge. Similarities are seen in results from steady-state models for optimized hydraulic conductivity values, fit of simulated to observed hydraulic heads, and composite scaled sensitivities of conductivity parameter zones. Transient simulations with hypothetical storage properties and pumping rates produce similar capture rates and storage change results, but differences are noted in the rate of drawdown at some well locations owing to the differences in optimized hydraulic conductivity. Depending on whether the purpose of the groundwater model is to simulate changes in groundwater levels or changes in storage and capture, the distribution of aquifer recharge may or may not be of primary importance.

Toward developing more realistic groundwater models using big data

NASA Astrophysics Data System (ADS)

Vahdat Aboueshagh, H.; Tsai, F. T. C.; Bhatta, D.; Paudel, K.

2017-12-01

Rich geological data is the backbone of developing realistic groundwater models for groundwater resources management. However, constructing realistic groundwater models can be challenging due to inconsistency between different sources of geological, hydrogeological and geophysical data and difficulty in processing big data to characterize the subsurface environment. This study develops a framework to utilize a big geological dataset to create a groundwater model for the Chicot Aquifer in the southwestern Louisiana, which borders on the Gulf of Mexico at south. The Chicot Aquifer is the principal source of fresh water in southwest Louisiana, underlying an area of about 9,000 square miles. Agriculture is the largest groundwater consumer in this region and overpumping has caused significant groundwater head decline and saltwater intrusion from the Gulf and deep formations. A hydrostratigraphy model was constructed using around 29,000 electrical logs and drillers' logs as well as screen lengths of pumping wells through a natural neighbor interpolation method. These sources of information have different weights in terms of accuracy and trustworthy. A data prioritization procedure was developed to filter untrustworthy log information, eliminate redundant data, and establish consensus of various lithological information. The constructed hydrostratigraphy model shows 40% sand facies, which is consistent with the well log data. The hydrostratigraphy model confirms outcrop areas of the Chicot Aquifer in the north of the study region. The aquifer sand formation is thinning eastward to merge into Atchafalaya River alluvial aquifer and coalesces to the underlying Evangeline aquifer. A grid generator was used to convert the hydrostratigraphy model into a MODFLOW grid with 57 layers. A Chicot groundwater model was constructed using the available hydrologic and hydrogeological data for 2004-2015. Pumping rates for irrigation wells were estimated using the crop type and acreage data from the USDACropScape. Groundwater level data obtained from the USGS were used to determine the model boundary and initial conditions. Recharge rates were approximated based on surficial lithology and rainfall data. The Chicot aquifer model will be used to understand groundwater availability in southwest Louisiana.

A Finite Difference Numerical Model for the Propagation of Finite Amplitude Acoustical Blast Waves Outdoors Over Hard and Porous Surfaces

DTIC Science & Technology

1991-09-01

Difference Numerical Model for the Propagation of Finite Amplitude Acoustical Blast Waves Outdoors Over Hard and Porous Surfaces by Victor W. Sparrow...The nonlinear acoustic propagation effects require a numerical solution in the time domain. To model a porous ground surface, which in the frequency...incident on the hard and porous surfaces were produced. The model predicted that near grazing finite amplitude acoustic blast waves decay with distance

Impacts of hydrogeological characteristics on groundwater-level changes induced by earthquakes

NASA Astrophysics Data System (ADS)

Liu, Ching-Yi; Chia, Yeeping; Chuang, Po-Yu; Chiu, Yung-Chia; Tseng, Tai-Lin

2018-03-01

Changes in groundwater level during earthquakes have been reported worldwide. In this study, field observations of co-seismic groundwater-level changes in wells under different aquifer conditions and sampling intervals due to near-field earthquake events in Taiwan are presented. Sustained changes, usually observed immediately after earthquakes, are found in the confined aquifer. Oscillatory changes due to the dynamic strain triggered by passing earthquake waves can only be recorded by a high-frequency data logger. While co-seismic changes recover rapidly in an unconfined aquifer, they can sustain for months or longer in a confined aquifer. Three monitoring wells with long-term groundwater-level data were examined to understand the association of co-seismic changes with local hydrogeological conditions. The finite element software ABAQUS is used to simulate the pore-pressure changes induced by the displacements due to fault rupture. The calculated co-seismic change in pore pressure is related to the compressibility of the formation. The recovery rate of the change is rapid in the unconfined aquifer due to the hydrostatic condition at the water table, but slow in the confined aquifer due to the less permeable confining layer. Fracturing of the confining layer during earthquakes may enhance the dissipation of pore pressure and induce the discharge of the confined aquifer. The study results indicated that aquifer characteristics play an important role in determining groundwater-level changes during and after earthquakes.

Groundwater Pumping and Streamflow in the Yuba Basin, Sacramento Valley, California

NASA Astrophysics Data System (ADS)

Moss, D. R.; Fogg, G. E.; Wallender, W. W.

2011-12-01

Water transfers during drought in California's Sacramento Valley can lead to increased groundwater pumping, and as yet unknown effects on stream baseflow. Two existing groundwater models of the greater Sacramento Valley together with localized, monitoring of groundwater level fluctuations adjacent to the Bear, Feather, and Yuba Rivers, indicate cause and effect relations between the pumping and streamflow. The models are the Central Valley Hydrologic Model (CVHM) developed by the U.S. Geological Survey and C2VSIM developed by Department of Water Resources. Using two models which have similar complexity and data but differing approaches to the agricultural water boundary condition illuminates both the water budget and its uncertainty. Water budget and flux data for localized areas can be obtained from the models allowing for parameters such as precipitation, irrigation recharge, and streamflow to be compared to pumping on different temporal scales. Continuous groundwater level measurements at nested, near-stream piezometers show seasonal variations in streamflow and groundwater levels as well as the timing and magnitude of recharge and pumping. Preliminary results indicate that during years with relatively wet conditions 65 - 70% of the surface recharge for the groundwater system comes from irrigation and precipitation and 30 - 35% comes from streamflow losses. The models further indicate that during years with relatively dry conditions, 55 - 60% of the surface recharge for the groundwater system comes from irrigation and precipitation while 40 - 45% comes from streamflow losses. The models irrigation water demand, surface-water and groundwater supply, and deep percolation are integrated producing values for irrigation pumping. Groundwater extractions during the growing season, approximately between April and October, increase by almost 200%. The effects of increased pumping seasonally are not readily evident in stream stage measurements. However, during dry time periods net streamflow gains are about half of the gains seen during wet period.

Global scale groundwater flow model

NASA Astrophysics Data System (ADS)

Sutanudjaja, Edwin; de Graaf, Inge; van Beek, Ludovicus; Bierkens, Marc

2013-04-01

As the world's largest accessible source of freshwater, groundwater plays vital role in satisfying the basic needs of human society. It serves as a primary source of drinking water and supplies water for agricultural and industrial activities. During times of drought, groundwater sustains water flows in streams, rivers, lakes and wetlands, and thus supports ecosystem habitat and biodiversity, while its large natural storage provides a buffer against water shortages. Yet, the current generation of global scale hydrological models does not include a groundwater flow component that is a crucial part of the hydrological cycle and allows the simulation of groundwater head dynamics. In this study we present a steady-state MODFLOW (McDonald and Harbaugh, 1988) groundwater model on the global scale at 5 arc-minutes resolution. Aquifer schematization and properties of this groundwater model were developed from available global lithological model (e.g. Dürr et al., 2005; Gleeson et al., 2010; Hartmann and Moorsdorff, in press). We force the groundwtaer model with the output from the large-scale hydrological model PCR-GLOBWB (van Beek et al., 2011), specifically the long term net groundwater recharge and average surface water levels derived from routed channel discharge. We validated calculated groundwater heads and depths with available head observations, from different regions, including the North and South America and Western Europe. Our results show that it is feasible to build a relatively simple global scale groundwater model using existing information, and estimate water table depths within acceptable accuracy in many parts of the world.

Modeling vulnerability of groundwater to pollution under future scenarios of climate change and biofuels-related land use change: a case study in North Dakota, USA.

PubMed

Li, Ruopu; Merchant, James W

2013-03-01

Modeling groundwater vulnerability to pollution is critical for implementing programs to protect groundwater quality. Most groundwater vulnerability modeling has been based on current hydrogeology and land use conditions. However, groundwater vulnerability is strongly dependent on factors such as depth-to-water, recharge and land use conditions that may change in response to future changes in climate and/or socio-economic conditions. In this research, a modeling framework, which employs three sets of models linked within a geographic information system (GIS) environment, was used to evaluate groundwater pollution risks under future climate and land use changes in North Dakota. The results showed that areas with high vulnerability will expand northward and/or northwestward in Eastern North Dakota under different scenarios. GIS-based models that account for future changes in climate and land use can help decision-makers identify potential future threats to groundwater quality and take early steps to protect this critical resource. Copyright © 2013 Elsevier B.V. All rights reserved.

Watershed Scale Analysis of Groundwater Surface Water Interactions and Its Application to Conjunctive Management under Climatic and Anthropogenic Stresses over the US Sunbelt

NASA Astrophysics Data System (ADS)

Seo, Seung Beom

Although water is one of the most essential natural resources, human activities have been exerting pressure on water resources. In order to reduce these stresses on water resources, two key issues threatening water resources sustainability - interaction between surface water and groundwater resources and groundwater withdrawal impacts of streamflow depletion - were investigated in this study. First, a systematic decomposition procedure was proposed for quantifying the errors arising from various sources in the model chain in projecting the changes in hydrologic attributes using near-term climate change projections. Apart from the unexplained changes by GCMs, the process of customizing GCM projections to watershed scale through a model chain - spatial downscaling, temporal disaggregation and hydrologic model - also introduces errors, thereby limiting the ability to explain the observed changes in hydrologic variability. Towards this, we first propose metrics for quantifying the errors arising from different steps in the model chain in explaining the observed changes in hydrologic variables (streamflow, groundwater). The proposed metrics are then evaluated using a detailed retrospective analyses in projecting the changes in streamflow and groundwater attributes in four target basins that span across a diverse hydroclimatic regimes over the US Sunbelt. Our analyses focused on quantifying the dominant sources of errors in projecting the changes in eight hydrologic variables - mean and variability of seasonal streamflow, mean and variability of 3-day peak seasonal streamflow, mean and variability of 7-day low seasonal streamflow and mean and standard deviation of groundwater depth - over four target basins using an Penn state Integrated Hydrologic Model (PIHM) between the period 1956-1980 and 1981-2005. Retrospective analyses show that small/humid (large/arid) basins show increased (reduced) uncertainty in projecting the changes in hydrologic attributes. Further, changes in error due to GCMs primarily account for the unexplained changes in mean and variability of seasonal streamflow. On the other hand, the changes in error due to temporal disaggregation and hydrologic model account for the inability to explain the observed changes in mean and variability of seasonal extremes. Thus, the proposed metrics provide insights on how the error in explaining the observed changes being propagated through the model under different hydroclimatic regimes. To understand interaction between surface water and groundwater resources, transient pumping impacts on streamflow and groundwater level were analyzed by imposing shortterm pumping scenarios under historic drought conditions. Since surface water and groundwater systems are fully coupled and integrated systems, increased groundwater withdrawal during drought may reduce baseflow into the stream and prolong both systems' recovery from drought. Towards this, we proposed an uncertainty framework to understand the resiliency of groundwater and surface water systems using a fully-coupled hydrologic model under transient pumping. Using this framework, we quantified the restoration time of surface water and groundwater systems and also estimated the changes in the state variables after pumping. Groundwater pumping impacts over the watershed were also analyzed under different pumping volumes and different potential climate scenarios. Our analyses show that groundwater restoration time is more sensitive to changes in pumping volumes as opposed to changes in climate. After the cessation of pumping, streamflow recovers quickly in comparison to groundwater. Pumping impacts on other state variables are also discussed. Given that surface water and groundwater are inter-connected, optimal management of the both resources should be considered to improve the watershed resiliency under drought. Subsequently, conjunctive use of surface water and groundwater has been considered as an effective approach to mitigate water shortage problems that are primarily caused by a drought. It is found that appropriate use of groundwater withdrawal was able to reduce water scarcity in surface water resources in drought condition. Besides, recovery time constraint was embedded in the management model so that trade-off between minimizing water scarcity and maximizing sustainability on groundwater was successfully addressed.

Current and future groundwater recharge in West Africa as estimated from a range of coupled climate model outputs

NASA Astrophysics Data System (ADS)

Verhoef, Anne; Cook, Peter; Black, Emily; Macdonald, David; Sorensen, James

2017-04-01

This research addresses the terrestrial water balance for West Africa. Emphasis is on the prediction of groundwater recharge and how this may change in the future, which has relevance to the management of surface and groundwater resources. The study was conducted as part of the BRAVE research project, "Building understanding of climate variability into planning of groundwater supplies from low storage aquifers in Africa - Second Phase", funded under the NERC/DFID/ESRC Programme, Unlocking the Potential of Groundwater for the Poor (UPGro). We used model output data of water balance components (precipitation, surface and subsurface run-off, evapotranspiration and soil moisture content) from ERA-Interim/ERA-LAND reanalysis, CMIP5, and high resolution model runs with HadGEM3 (UPSCALE; Mizielinski et al., 2014), for current and future time-periods. Water balance components varied widely between the different models; variation was particularly large for sub-surface runoff (defined as drainage from the bottom-most soil layer of each model). In-situ data for groundwater recharge obtained from the peer-reviewed literature were compared with the model outputs. Separate off-line model sensitivity studies with key land surface models were performed to gain understanding of the reasons behind the model differences. These analyses were centered on vegetation, and soil hydraulic parameters. The modelled current and future recharge time series that had the greatest degree of confidence were used to examine the spatiotemporal variability in groundwater storage. Finally, the implications for water supply planning were assessed. Mizielinski, M.S. et al., 2014. High-resolution global climate modelling: the UPSCALE project, a large-simulation campaign. Geoscientific Model Development, 7(4), pp.1629-1640.

Improved regional-scale groundwater representation by the coupling of the mesoscale Hydrologic Model (mHM v5.7) to the groundwater model OpenGeoSys (OGS)

NASA Astrophysics Data System (ADS)

Jing, Miao; Heße, Falk; Kumar, Rohini; Wang, Wenqing; Fischer, Thomas; Walther, Marc; Zink, Matthias; Zech, Alraune; Samaniego, Luis; Kolditz, Olaf; Attinger, Sabine

2018-06-01

Most large-scale hydrologic models fall short in reproducing groundwater head dynamics and simulating transport process due to their oversimplified representation of groundwater flow. In this study, we aim to extend the applicability of the mesoscale Hydrologic Model (mHM v5.7) to subsurface hydrology by coupling it with the porous media simulator OpenGeoSys (OGS). The two models are one-way coupled through model interfaces GIS2FEM and RIV2FEM, by which the grid-based fluxes of groundwater recharge and the river-groundwater exchange generated by mHM are converted to fixed-flux boundary conditions of the groundwater model OGS. Specifically, the grid-based vertical reservoirs in mHM are completely preserved for the estimation of land-surface fluxes, while OGS acts as a plug-in to the original mHM modeling framework for groundwater flow and transport modeling. The applicability of the coupled model (mHM-OGS v1.0) is evaluated by a case study in the central European mesoscale river basin - Nägelstedt. Different time steps, i.e., daily in mHM and monthly in OGS, are used to account for fast surface flow and slow groundwater flow. Model calibration is conducted following a two-step procedure using discharge for mHM and long-term mean of groundwater head measurements for OGS. Based on the model summary statistics, namely the Nash-Sutcliffe model efficiency (NSE), the mean absolute error (MAE), and the interquartile range error (QRE), the coupled model is able to satisfactorily represent the dynamics of discharge and groundwater heads at several locations across the study basin. Our exemplary calculations show that the one-way coupled model can take advantage of the spatially explicit modeling capabilities of surface and groundwater hydrologic models and provide an adequate representation of the spatiotemporal behaviors of groundwater storage and heads, thus making it a valuable tool for addressing water resources and management problems.

Use of machine learning methods to reduce predictive error of groundwater models.

PubMed

Xu, Tianfang; Valocchi, Albert J; Choi, Jaesik; Amir, Eyal

2014-01-01

Quantitative analyses of groundwater flow and transport typically rely on a physically-based model, which is inherently subject to error. Errors in model structure, parameter and data lead to both random and systematic error even in the output of a calibrated model. We develop complementary data-driven models (DDMs) to reduce the predictive error of physically-based groundwater models. Two machine learning techniques, the instance-based weighting and support vector regression, are used to build the DDMs. This approach is illustrated using two real-world case studies of the Republican River Compact Administration model and the Spokane Valley-Rathdrum Prairie model. The two groundwater models have different hydrogeologic settings, parameterization, and calibration methods. In the first case study, cluster analysis is introduced for data preprocessing to make the DDMs more robust and computationally efficient. The DDMs reduce the root-mean-square error (RMSE) of the temporal, spatial, and spatiotemporal prediction of piezometric head of the groundwater model by 82%, 60%, and 48%, respectively. In the second case study, the DDMs reduce the RMSE of the temporal prediction of piezometric head of the groundwater model by 77%. It is further demonstrated that the effectiveness of the DDMs depends on the existence and extent of the structure in the error of the physically-based model. © 2013, National GroundWater Association.

Coupling Agent-Based and Groundwater Modeling to Explore Demand Management Strategies for Shared Resources

NASA Astrophysics Data System (ADS)

Al-Amin, S.

2015-12-01

Municipal water demands in growing population centers in the arid southwest US are typically met through increased groundwater withdrawals. Hydro-climatic uncertainties attributed to climate change and land use conversions may also alter demands and impact the replenishment of groundwater supply. Groundwater aquifers are not necessarily confined within municipal and management boundaries, and multiple diverse agencies may manage a shared resource in a decentralized approach, based on individual concerns and resources. The interactions among water managers, consumers, and the environment influence the performance of local management strategies and regional groundwater resources. This research couples an agent-based modeling (ABM) framework and a groundwater model to analyze the effects of different management approaches on shared groundwater resources. The ABM captures the dynamic interactions between household-level consumers and policy makers to simulate water demands under climate change and population growth uncertainties. The groundwater model is used to analyze the relative effects of management approaches on reducing demands and replenishing groundwater resources. The framework is applied for municipalities located in the Verde River Basin, Arizona that withdraw groundwater from the Verde Formation-Basin Fill-Carbonate aquifer system. Insights gained through this simulation study can be used to guide groundwater policy-making under changing hydro-climatic scenarios for a long-term planning horizon.

Combination of the discontinuous Galerkin method with finite differences for simulation of seismic wave propagation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lisitsa, Vadim, E-mail: lisitsavv@ipgg.sbras.ru; Novosibirsk State University, Novosibirsk; Tcheverda, Vladimir

We present an algorithm for the numerical simulation of seismic wave propagation in models with a complex near surface part and free surface topography. The approach is based on the combination of finite differences with the discontinuous Galerkin method. The discontinuous Galerkin method can be used on polyhedral meshes; thus, it is easy to handle the complex surfaces in the models. However, this approach is computationally intense in comparison with finite differences. Finite differences are computationally efficient, but in general, they require rectangular grids, leading to the stair-step approximation of the interfaces, which causes strong diffraction of the wavefield. Inmore » this research we present a hybrid algorithm where the discontinuous Galerkin method is used in a relatively small upper part of the model and finite differences are applied to the main part of the model.« less

The Importance of Capturing Topographic Features for Modeling Groundwater Flow and Transport in Mountainous Watersheds

NASA Astrophysics Data System (ADS)

Wang, C.; Gomez-Velez, J. D.; Wilson, J. L.

2017-12-01

Groundwater plays a key role in runoff generation and stream water chemistry from reach to watershed scales. The spatial distribution of ridges and streams can influence the spatial patterns of groundwater recharge and drainage, specially in mountainous terrains where these features are more prominent. However, typical modeling efforts simplify or ignore some of these features due to computational limitations without a systematic investigation of the implications for flow and transport within the watershed. In this study, we investigate the effect of capturing key topographic features on modeled groundwater flow and transport characteristics in a mountainous watershed. We build model scenarios of different topographic complexity levels (TCLs) to capture different levels of representation of streams and ridges in the model. Modeled baseflow and groundwater mean residence time (MRT) are used to quantify the differences among TCLs. Our results show that capturing the streams and ridges has a significant influence on simulated groundwater flow and transport patterns. Topographic complexity controls the proportion of baseflow generated from local, intermediate, and regional flow paths, thus influencing the amount and MRT of basefow flowing into streams of different Horton-Strahler orders. We further simulate the concentration of solute exported into streams from subsurface chemical weathering. The concentration of chemical weathering products in streams is less sensitive to model TCL due to the thermodynamic constraint on the equilibrium concentration of the chemical weathering. We also tested the influence of geology on the effect of TCL. The effect of TCL is consistent under different geological conditions; however, it is enhanced in models with low hydraulic conductivity because more of the flow is forced into shallow and local flow paths. All of these changes can affect our ability to interpret environmental tracer data and predict bio- and geo-chemical evolution of stream water in mountainous watersheds.

VS2DI: Model use, calibration, and validation

USGS Publications Warehouse

Healy, Richard W.; Essaid, Hedeff I.

2012-01-01

VS2DI is a software package for simulating water, solute, and heat transport through soils or other porous media under conditions of variable saturation. The package contains a graphical preprocessor for constructing simulations, a postprocessor for displaying simulation results, and numerical models that solve for flow and solute transport (VS2DT) and flow and heat transport (VS2DH). Flow is described by the Richards equation, and solute and heat transport are described by advection-dispersion equations; the finite-difference method is used to solve these equations. Problems can be simulated in one, two, or three (assuming radial symmetry) dimensions. This article provides an overview of calibration techniques that have been used with VS2DI; included is a detailed description of calibration procedures used in simulating the interaction between groundwater and a stream fed by drainage from agricultural fields in central Indiana. Brief descriptions of VS2DI and the various types of problems that have been addressed with the software package are also presented.

Evaluation of Groundwater Leakage into a Drainage Tunnel in Jinping-I Arch Dam Foundation in Southwestern China: A Case Study

NASA Astrophysics Data System (ADS)

Chen, Yi-Feng; Hong, Jia-Min; Zheng, Hua-Kang; Li, Yi; Hu, Ran; Zhou, Chuang-Bing

2016-03-01

The Jinping-I double-curvature arch dam, located in the middle reach of Yalong River and with a maximum height of 305 m, is the world's highest dam of this type that has been completed. Since the second stage of reservoir impounding, after which the reservoir water level was gradually raised by about 232 m, a significant amount of leakage was observed from the drainage holes drilled in the lowest drainage tunnel at the left bank abutment at an elevation of 1595 m a.s.l. (above sea level), with an observed maximum pressure of about 0.3 MPa. A number of investigations, including water quality analysis, digital borehole imaging, tunnel geological mapping, and in situ groundwater monitoring, were performed to examine the source of leaking, the groundwater flow paths, and the performance of the grouting curtains. By defining two objective functions using the in situ time series measurements of flow rate and hydraulic head, respectively, a multiobjective inverse modeling procedure was proposed to evaluate the permeability of the foundation rocks that was underestimated in the design stage. This procedure takes advantage of the orthogonal design, finite element forward modeling of the transient groundwater flow, artificial neural network, and non-dominated sorting genetic algorithm, hence significantly reducing the computational cost and improving the reliability of the inversed results. The geological structures that lead to the leakage were identified and the seepage flow behaviors in the dam foundation and the left bank abutment were assessed. Based on the field measurements and the inverse modeling results, the effects of the engineering treatments of the leakage event on the dam safety were analyzed. It has been demonstrated that the seepage control system is effective in lowering the groundwater level and limiting the amount of seepage in the dam foundation, and the leakage event does not pose a threat to the safety of the dam.

Modeling the Impact of Soil and Water Conservation on Surface and Ground Water Based on the SCS and Visual Modflow

PubMed Central

Wang, Hong; Gao, Jian-en; Zhang, Shao-long; Zhang, Meng-jie; Li, Xing-hua

2013-01-01

Soil and water conservation measures can impact hydrological cycle, but quantitative analysis of this impact is still difficult in a watershed scale. To assess the effect quantitatively, a three-dimensional finite-difference groundwater flow model (MODFLOW) with a surface runoff model–the Soil Conservation Service (SCS) were calibrated and applied based on the artificial rainfall experiments. Then, three soil and water conservation scenarios were simulated on the sand-box model to assess the effect of bare slope changing to grass land and straw mulching on water volume, hydraulic head, runoff process of groundwater and surface water. Under the 120 mm rainfall, 60 mm/h rainfall intensity, 5 m2 area, 3° slope conditions, the comparative results indicated that the trend was decrease in surface runoff and increase in subsurface runoff coincided with the land-use converted from bare slope to grass land and straw mulching. The simulated mean surface runoff modulus was 3.64×10−2 m3/m2/h in the bare slope scenario, while the observed values were 1.54×10−2 m3/m2/h and 0.12×10−2 m3/m2/h in the lawn and straw mulching scenarios respectively. Compared to the bare slope, the benefits of surface water reduction were 57.8% and 92.4% correspondingly. At the end of simulation period (T = 396 min), the simulated mean groundwater runoff modulus was 2.82×10−2 m3/m2/h in the bare slope scenario, while the observed volumes were 3.46×10−2 m3/m2/h and 4.91×10−2 m3/m2/h in the lawn and straw mulching scenarios respectively. So the benefits of groundwater increase were 22.7% and 60.4% correspondingly. It was concluded that the soil and water conservation played an important role in weakening the surface runoff and strengthening the underground runoff. Meanwhile the quantitative analysis using a modeling approach could provide a thought for the study in a watershed scale to help decision-makers manage water resources. PMID:24244427

Thermal Imagery of Groundwater Seeps: Possibilities and Limitations.

PubMed

Mundy, Erin; Gleeson, Tom; Roberts, Mark; Baraer, Michel; McKenzie, Jeffrey M

2017-03-01

Quantifying groundwater flow at seepage faces is crucial because seepage faces influence the hydroecology and water budgets of watersheds, lakes, rivers and oceans, and because measuring groundwater fluxes directly in aquifers is extremely difficult. Seepage faces provide a direct and measurable groundwater flux but there is no existing method to quantitatively image groundwater processes at this boundary. Our objective is to determine the possibilities and limitations of thermal imagery in quantifying groundwater discharge from discrete seeps. We developed a conceptual model of temperature below discrete seeps, observed 20 seeps spectacularly exposed in three dimensions at an unused limestone quarry and conducted field experiments to examine the role of diurnal changes and rock face heterogeneity on thermal imagery. The conceptual model suggests that convective air-water heat exchange driven by temperature differences is the dominant heat transfer mechanism. Thermal imagery is effective at locating and characterizing the flux of groundwater seeps. Areas of active groundwater flow and ice growth can be identified from thermal images in the winter, and seepage rates can be differentiated in the summer. However, the application of thermal imagery is limited by diverse factors including technical issues of image acquisition, diurnal changes in radiation and temperature, and rock face heterogeneity. Groundwater discharge rates could not be directly quantified from thermal imagery using our observations but our conceptual model and experiments suggest that thermal imagery could quantify groundwater discharge when there are large temperature differences, simple cliff faces, non-freezing conditions, and no solar radiation. © 2016, National Ground Water Association.

Reliability of groundwater supply from a coastal aquifer in the context of climate and socio-economic changes

NASA Astrophysics Data System (ADS)

Eley, Malte; Schöniger, Hans Matthias; Gelleszun, Marlene; Wolf, Jens; Schneider, Anke; Wiederhold, Helga; Meon, Günter

2017-04-01

Especially coastal areas are vulnerable in case of sea level rise and changing climate conditions. Therefore, the NAWAK study (design of sustainable adaptation strategies for infrastructures in water management under the conditions of climatic and demographic change) started in 2013. It is designed to assess impairments of groundwater availability for a coastal lowland aquifer system in North-West Germany (> 1.000 km2) in the context of climate and socio-economic changes. The research results are focused on the quantification of the groundwater availability for past and future scenarios. Impacts from both climatic and socio-economic changes on the water availability and water balance are assessed by means of hydrologic, hydrogeological and geophysical models and methods, which where developed and adapted by project partners. For the model area there are three fields of work to create the conditions for a density dependent calculation of changings in salt-freshwater budget with the numerical model d3f++ (distributed density-driven Flow). The first is the description of initial conditions in three dimensions, especially for the salt-freshwater boundary. That description is based on airborne electromagnetic data of the underground and a complex processing to identify the differences between salt and freshwater, without anthropogenic and geologic influences. A validation is possible by comparison with groundwater measurements and an online monitoring of specific conductivity. The second is the calculation and measurement of flow conditions to derive the boundary conditions and the groundwater recharge. The groundwater recharge was calculated by using the hydrologic model PANTA RHEI. It is a conceptual model with partly physic-based modules, especially for the soil water processes. The model was calibrated and validated by discharge measurements and groundwater levels. The third step is a detailed information about the spatial discretization and the reconstruction of the geologic body. The interpolation of point information's from boreholes and geologic sections was calculated with the geologic modelling software SubsurfaceViewerMX. For implementation in the groundwater model, the layers were combined to hydrogeological similar units. With this sophisticated models it is possible to model the density-dependent complex groundwater systems at large spatial scales as well as contaminant transport. The modeling analysis is focused on water-budget components (groundwater recharge, submarine groundwater discharge, surface-groundwater interaction and water supply), salt- water intrusion and sea level rise under different climate and water-use scenarios. With our models we offer the capability to evaluate possible coastal aquifer management strategies of real-world applications.

Process-based modelling to evaluate simulated groundwater levels and frequencies in a Chalk catchment in south-western England

NASA Astrophysics Data System (ADS)

Brenner, Simon; Coxon, Gemma; Howden, Nicholas J. K.; Freer, Jim; Hartmann, Andreas

2018-02-01

Chalk aquifers are an important source of drinking water in the UK. Due to their properties, they are particularly vulnerable to groundwater-related hazards like floods and droughts. Understanding and predicting groundwater levels is therefore important for effective and safe water management. Chalk is known for its high porosity and, due to its dissolvability, exposed to karstification and strong subsurface heterogeneity. To cope with the karstic heterogeneity and limited data availability, specialised modelling approaches are required that balance model complexity and data availability. In this study, we present a novel approach to evaluate simulated groundwater level frequencies derived from a semi-distributed karst model that represents subsurface heterogeneity by distribution functions. Simulated groundwater storages are transferred into groundwater levels using evidence from different observations wells. Using a percentile approach we can assess the number of days exceeding or falling below selected groundwater level percentiles. Firstly, we evaluate the performance of the model when simulating groundwater level time series using a spilt sample test and parameter identifiability analysis. Secondly, we apply a split sample test to the simulated groundwater level percentiles to explore the performance in predicting groundwater level exceedances. We show that the model provides robust simulations of discharge and groundwater levels at three observation wells at a test site in a chalk-dominated catchment in south-western England. The second split sample test also indicates that the percentile approach is able to reliably predict groundwater level exceedances across all considered timescales up to their 75th percentile. However, when looking at the 90th percentile, it only provides acceptable predictions for long time periods and it fails when the 95th percentile of groundwater exceedance levels is considered. By modifying the historic forcings of our model according to expected future climate changes, we create simple climate scenarios and we show that the projected climate changes may lead to generally lower groundwater levels and a reduction of exceedances of high groundwater level percentiles.

Ground-water models for water resource planning

USGS Publications Warehouse

Moore, J.E.

1983-01-01

In the past decade hydrogeologists have emphasized the development of computer-based mathematical models to aid in the understanding of flow, the transport of solutes, transport of heat, and deformation in the ground-water system. These models have been used to provide information and predictions for water managers. Too frequently, ground-water was neglected in water resource planning because managers believed that it could not be adequately evaluated in terms of availability, quality, and effect of development on surface-water supplies. Now, however, with newly developed digital ground-water models, effects of development can be predicted. Such models have been used to predict hydrologic and quality changes under different stresses. These models have grown in complexity over the last ten years from simple one-layer models to three-dimensional simulations of ground-water flow, which may include solute transport, heat transport, effects of land subsidence, and encroachment of saltwater. Case histories illustrate how predictive ground-water models have provided the information needed for the sound planning and management of water resources in the USA. ?? 1983 D. Reidel Publishing Company.

Subsidence Modeling of the Over-exploited Granular Aquifer System in Aguascalientes, Mexico

NASA Astrophysics Data System (ADS)

Solano Rojas, D. E.; Pacheco, J.; Wdowinski, S.; Minderhoud, P. S. J.; Cabral-Cano, E.; Albino, F.

2017-12-01

The valley of Aguascalientes in central Mexico experiences subsidence rates of up to 100 [mm/yr] due to overexploitation of its aquifer system, as revealed from satellite-based geodetic observations. The spatial pattern of the subsidence over the valley is inhomogeneous and affected by shallow faulting. The understanding of the subsoil mechanics is still limited. A better understanding of the subsidence process in Aguascalientes is needed to provide insights for future subsidence in the valley. We present here a displacement-constrained finite-element subsidence model, based on the USGS MODFLOW software. The construction of our model relies on 3 main inputs: (1) groundwater level time series obtained from extraction wells' hydrographs, (2) subsurface lithostratigraphy interpreted from well drilling logs, and (3) hydrogeological parameters obtained from field pumping tests. The groundwater level measurements were converted to pore pressure in our model's layers, and used in Terzaghi's equation for calculating effective stress. We then used the effective stress along with the displacement obtained from geodetic observations to constrain and optimize five geo-mechanical parameters: compression ratio, reloading ratio, secondary compression index, over consolidation ratio, and consolidation coefficient. Finally, we use the NEN-Bjerrum linear stress model formulation for settlements to determine elastic and visco-plastic strain, accounting for the aquifer system units' aging effect. Preliminary results show higher compaction response in clay-saturated intervals (i.e. aquitards) of the aquifer system, as reflected in the spatial pattern of the surface deformation. The forecasted subsidence for our proposed scenarios show a much more pronounced deformation when we consider higher groundwater extraction regimes.

Understanding heterogeneity and data assimilation in karst groundwater surface water interactions: The role of geophysics and hydrologic models in a semi-confined aquifer

NASA Astrophysics Data System (ADS)

Meyerhoff, Steven B.

Groundwater and surface water historically have been treated as different entities. Due to this, planning and development of groundwater and surface water resources, both quantity and quality are often also treated separately. Recently, there has been work to characterize groundwater and surface water as a single system. Karstic systems are widely influenced by these interactions due to varying permeability, fracture geometry and porosity. Here, three different approaches are used to characterize groundwater surface water interactions in karstic environments. 1) A hydrologic model, ParFlow, is conditioned with known subsurface data to determine whether a reduction in subsurface uncertainty will enhance the prediction of surface water variables. A reduction in subsurface uncertainty resulted in substantial reductions in uncertainty in Hortonian runoff and less reductions in Dunne runoff. 2) Geophysical data is collected at a field site in O'leno State Park, Florida to visualize groundwater and surface water interactions in karstic environments. Significant changes in resistivity are seen through time at two locations. It is hypothesized that these changes are related to changing fluid source waters (e.g groundwater or surface water). 3). To confirm these observations an ensemble of synthetic forward models are simulated, inverted and compared directly with field observations and End-Member-Mixing-Analysis (EMMA). Field observations and synthetic models have comparable resistivity anomalies patterns and mixing fractions. This allows us to characterize and quantify subsurface mixing of groundwater and surface in karst environments. These three approaches (hydrologic models, field data and forward model experiments), (1) show the complexity and dynamics of groundwater and surface mixing in karstic environments in varying flow conditions, (2) showcase a novel geophysical technique to visualize groundwater and surface water interactions and (3) confirm hypothesis of flow and mixing in subsurface karst environments.

Modeling flow in wetlands and underlying aquifers using a discharge potential formulation

NASA Astrophysics Data System (ADS)

Gusyev, M. A.; Haitjema, H. M.

2011-09-01

SummaryAn accurate assessment of water and nutrient balances in large scale wetland systems such as the Florida Everglades requires conjunctive modeling of surface water flow in wetlands and groundwater flow in underlying aquifers. Earlier work was based on the finite difference code MODFLOW with a special "wetlands package." This model treats the wetland flow as laminar with a very high transmissivity that is proportional to the wetland water depth cubed. However, these MODFLOW solutions appear sensitive to this highly non-linear wetland transmissivity, particularly under conditions of low vegetation density when the model may fail to converge. We propose to formulate the governing differential equation in terms of a discharge potential instead of potentiometric heads as done in MODFLOW, but otherwise using the same assumptions as in its wetlands package. We tested our approach on a few cases of one- and two-dimensional flow, both with a constant and a varying wetland bottom elevation. For the latter the discharge potential represents an irrotational part of the flow field which is combined with a component of the flow field that contains the curl. We found that both the robustness and the accuracy of the solution in terms of potentials was superior to the solution in terms of heads. In some cases the latter solution failed altogether, even for simple one-dimensional flow. We applied our method to model the effects of wetland hydrology on the nutrient redistribution in and near tree islands. We found that the subtle velocity distributions near these tree islands, as resulted from our conjunctive wetlands and groundwater flow solution, could help explain the increased nutrient depositions at these islands, particularly at the head of the islands, where, consequently, most of the vegetation occurs.

The effect of modeled recharge distribution on simulated groundwater availability and capture.

PubMed

Tillman, F D; Pool, D R; Leake, S A

2015-01-01

Simulating groundwater flow in basin-fill aquifers of the semiarid southwestern United States commonly requires decisions about how to distribute aquifer recharge. Precipitation can recharge basin-fill aquifers by direct infiltration and transport through faults and fractures in the high-elevation areas, by flowing overland through high-elevation areas to infiltrate at basin-fill margins along mountain fronts, by flowing overland to infiltrate along ephemeral channels that often traverse basins in the area, or by some combination of these processes. The importance of accurately simulating recharge distributions is a current topic of discussion among hydrologists and water managers in the region, but no comparative study has been performed to analyze the effects of different recharge distributions on groundwater simulations. This study investigates the importance of the distribution of aquifer recharge in simulating regional groundwater flow in basin-fill aquifers by calibrating a groundwater-flow model to four different recharge distributions, all with the same total amount of recharge. Similarities are seen in results from steady-state models for optimized hydraulic conductivity values, fit of simulated to observed hydraulic heads, and composite scaled sensitivities of conductivity parameter zones. Transient simulations with hypothetical storage properties and pumping rates produce similar capture rates and storage change results, but differences are noted in the rate of drawdown at some well locations owing to the differences in optimized hydraulic conductivity. Depending on whether the purpose of the groundwater model is to simulate changes in groundwater levels or changes in storage and capture, the distribution of aquifer recharge may or may not be of primary importance. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Calibration of a transient transport model to tritium data in streams and simulation of groundwater ages in the western Lake Taupo catchment, New Zealand

NASA Astrophysics Data System (ADS)

Gusyev, M. A.; Toews, M.; Morgenstern, U.; Stewart, M.; White, P.; Daughney, C.; Hadfield, J.

2013-03-01

Here we present a general approach of calibrating transient transport models to tritium concentrations in river waters developed for the MT3DMS/MODFLOW model of the western Lake Taupo catchment, New Zealand. Tritium has a known pulse-shaped input to groundwater systems due to the bomb tritium in the early 1960s and, with its radioactive half-life of 12.32 yr, allows for the determination of the groundwater age. In the transport model, the tritium input (measured in rainfall) passes through the groundwater system, and the simulated tritium concentrations are matched to the measured tritium concentrations in the river and stream outlets for the Waihaha, Whanganui, Whareroa, Kuratau and Omori catchments from 2000-2007. For the Kuratau River, tritium was also measured between 1960 and 1970, which allowed us to fine-tune the transport model for the simulated bomb-peak tritium concentrations. In order to incorporate small surface water features in detail, an 80 m uniform grid cell size was selected in the steady-state MODFLOW model for the model area of 1072 km2. The groundwater flow model was first calibrated to groundwater levels and stream baseflow observations. Then, the transient tritium transport MT3DMS model was matched to the measured tritium concentrations in streams and rivers, which are the natural discharge of the groundwater system. The tritium concentrations in the rivers and streams correspond to the residence time of the water in the groundwater system (groundwater age) and mixing of water with different age. The transport model output showed a good agreement with the measured tritium values. Finally, the tritium-calibrated MT3DMS model is applied to simulate groundwater ages, which are used to obtain groundwater age distributions with mean residence times (MRTs) in streams and rivers for the five catchments. The effect of regional and local hydrogeology on the simulated groundwater ages is investigated by demonstrating groundwater ages at five model cross-sections to better understand MRTs simulated with tritium-calibrated MT3DMS and lumped parameter models.

Simulation of ground-water flow in the Potomac-Raritan-Magothy aquifer system, Pennsauken Township and vicinity, New Jersey

USGS Publications Warehouse

Pope, Daryll A.; Watt, Martha K.

2004-01-01

The Potomac-Raritan-Magothy aquifer system is one of the primary sources of potable water in the Coastal Plain of New Jersey, particularly in heavily developed areas along the Delaware River. In Pennsauken Township, Camden County, local drinking-water supplies from this aquifer system have been contaminated by hexavalent chromium at concentrations that exceed the New Jersey maximum contaminant level. In particular, ground water at the Puchack well field has been adversely affected to the point where, since 1984, water is no longer withdrawn from this well field for public supply. The area that contains the Puchack well field was added to the National Priorities List in 1998 as a Superfund site. The U.S. Geological Survey (USGS) conducted a reconnaissance study from 1996 to 1998 during which hydrogeologic and water-quality data were collected and a ground-water-flow model was developed to describe the conditions in the aquifer system in the Pennsauken Township area. The current investigation by the USGS, in cooperation with the U.S. Environmental Protection Agency (USEPA), is an extension of the previous study. Results of the current study can be applied to a Remedial Investigation and Feasibility Study conducted at the Puchack well field Superfund site. The USGS study collected additional data on the hydrogeology and water-quality in the area. These data were incorporated into a refined model of the ground-water-flow system in the Potomac-Raritan-Magothy aquifer system. A finite-difference model was developed to simulate ground-water flow and the advective transport of chromium-contaminated ground water in the aquifers of the Potomac-Raritan-Magothy aquifer system in the Pennsauken Township area. An 11-layer model was used to represent the complex hydrogeologic framework. The model was calibrated using steady-state water-level data from March 1998, April 1998, and April 2001. Water-level recovery during the shutdown of Puchack 1 during March to April 1998 was simulated to evaluate model performance in relation to changing stresses. The Delaware River contributes appreciable-flow to the ground-water system from areas where the Middle and Lower aquifers crop out beneath the river. A transient simulation of an aquifer test near the Delaware River was run to help characterize the hydraulic conductivity of the riverbed sediments represented in the model. Vertical flow across confining units between the aquifers is highly variable and is important in the movement of water and associated contaminants through the flow system. The model was imbedded within a regional model of the Potomac-Raritan-Magothy aquifer system in Camden County. In general, a simulation of baseline conditions, which can provide a representation on which simulations of various alternatives can be based for the feasibility study, incorporated average conditions from 1998 to 2000. Ground-water withdrawals within the model area during this period averaged about 14 Mgal/d. Regional ground-water flow is from recharge areas and from the Delaware River to downgradient pumped wells located just east of the model area in central Camden County. Simulation results show an important connection between the Intermediate sand and the Lower aquifer of the Potomac-Raritan-Magothy aquifer system in the vicinity of the chromium-contaminated area. The Delaware River contributes nearly 10 Mgal/d to the flow system, whereas recharge contributes about 6 Mgal/d. Ground-water withdrawals within the model area account for nearly 14 Mgal/d (mostly from the Lower aquifer of the Potomac-Raritan-Magothy aquifer system).

Simulation of ground-water flow in coastal Georgia and adjacent parts of South Carolina and Florida-predevelopment, 1980, and 2000

USGS Publications Warehouse

Payne, Dorothy F.; Rumman, Malek Abu; Clarke, John S.

2005-01-01

A digital model was developed to simulate steady-state ground-water flow in a 42,155-square-mile area of coastal Georgia and adjacent parts of South Carolina and Florida. The model was developed to (1) understand and refine the conceptual model of regional ground-water flow, (2) serve as a framework for the development of digital subregional ground-water flow and solute-transport models, and (3) serve as a tool for future evaluations of hypothetical pumping scenarios used to facilitate water management in the coastal area. Single-density ground-water flow was simulated using the U.S. Geological Survey finite-difference code MODFLOW-2000 for mean-annual conditions during predevelopment (pre?1900) and the years 1980 and 2000. The model comprises seven layers: the surficial aquifer system, the Brunswick aquifer system, the Upper Floridan aquifer, the Lower Floridan aquifer, and the intervening confining units. A combination of boundary conditions was applied, including a general-head boundary condition on the top active cells of the model and a time-variable fixed-head boundary condition along part of the southern lateral boundary. Simulated heads for 1980 and 2000 conditions indicate a good match to observed values, based on a plus-or-minus 10-foot (ft) calibration target and calibration statistics. The root-mean square of residual water levels for the Upper Floridan aquifer was 13.0 ft for the 1980 calibration and 9.94 ft for the 2000 calibration. Some spatial patterns of residuals were indicated for the 1980 and 2000 simulations, and are likely a result of model-grid cell size and insufficiently detailed hydraulic-property and pumpage data in some areas. Simulated potentiometric surfaces for predevelopment, 1980, and 2000 conditions all show major flow system features that are indicated by estimated peotentiometric maps. During 1980?2000, simulated water levels at the centers of pumping at Savannah and Brunswick rose more than 20 ft and 8 ft, respectively, in response to decreased pumping. Simulated drawdown exceeded 10 ft in the Upper Floridan aquifer across much of the western half of the model area, with drawdown exceeding 20 ft along parts of the western, northern, and southern boundaries where irrigation pumping increased during this period. From predevelopment to 2000 conditions, the simulated water budget showed an increase in inflow from, and decrease in outflow to, the general-head boundaries, and a reversal from net seaward flow to net landward flow across the coastline. Simulated changes in recharge and discharge distribution from predevelopment to 2000 conditions showed an increase in extent and magnitude of net recharge cells in the northern part of the model area, and a decrease in discharge or change to recharge in cells containing major streams and beneath major pumping centers. The model is relatively sensitive to pumping and the controlling head at the fixed-head boundary and less sensitive to the distribution of aquifer properties in general. Model limitations include: (1) its spatial scale and discretization, (2) the extent to which data are available to physically define the flow system, (3) the type of boundary conditions and controlling parameters used, (4) uncertainty in the distribution of pumping, and (5) uncertainty in field-scale hydraulic properties. The model could be improved with more accurate estimates of ground-water pumpage and better characterization of recharge and discharge.

Optimization of finite difference forward modeling for elastic waves based on optimum combined window functions

NASA Astrophysics Data System (ADS)

Jian, Wang; Xiaohong, Meng; Hong, Liu; Wanqiu, Zheng; Yaning, Liu; Sheng, Gui; Zhiyang, Wang

2017-03-01

Full waveform inversion and reverse time migration are active research areas for seismic exploration. Forward modeling in the time domain determines the precision of the results, and numerical solutions of finite difference have been widely adopted as an important mathematical tool for forward modeling. In this article, the optimum combined of window functions was designed based on the finite difference operator using a truncated approximation of the spatial convolution series in pseudo-spectrum space, to normalize the outcomes of existing window functions for different orders. The proposed combined window functions not only inherit the characteristics of the various window functions, to provide better truncation results, but also control the truncation error of the finite difference operator manually and visually by adjusting the combinations and analyzing the characteristics of the main and side lobes of the amplitude response. Error level and elastic forward modeling under the proposed combined system were compared with outcomes from conventional window functions and modified binomial windows. Numerical dispersion is significantly suppressed, which is compared with modified binomial window function finite-difference and conventional finite-difference. Numerical simulation verifies the reliability of the proposed method.

Ground-water flow in the surficial aquifer system and potential movement of contaminants from selected waste-disposal sites at Naval Station Mayport, Florida

USGS Publications Warehouse

Halford, K.J.

1998-01-01

Ground-water flow through the surficial aquifer system at Naval Station Mayport near Jacksonville, Florida, was simulated with a two-layer finite-difference model as part of an investigation conducted by the U.S. Geological Survey. The model was calibrated to 229 water-level measurements from 181 wells during three synoptic surveys (July 17, 1995; July 31, 1996; and October 24, 1996). A quantifiable understanding of ground-water flow through the surficial aquifer was needed to evaluate remedial-action alternatives under consideration by the Naval Station Mayport to control the possible movement of contaminants from sites on the station. Multi-well aquifer tests, single-well tests, and slug tests were conducted to estimate the hydraulic properties of the surficial aquifer system, which was divided into three geohydrologic units?an S-zone and an I-zone separated by a marsh-muck confining unit. The recharge rate was estimated to range from 4 to 15 inches per year (95 percent confidence limits), based on a chloride-ratio method. Most of the simulations following model calibration were based on a recharge rate of 8 inches per year to unirrigated pervious areas. The advective displacement of saline pore water during the last 200 years was simulated using a particle-tracking routine, MODPATH, applied to calibrated steady-state and transient models of the Mayport peninsula. The surficial aquifer system at Naval Station Mayport has been modified greatly by natural and anthropogenic forces so that the freshwater flow system is expanding and saltwater is being flushed from the system. A new MODFLOW package (VAR1) was written to simulate the temporal variation of hydraulic properties caused by construction activities at Naval Station Mayport. The transiently simulated saltwater distribution after 200 years of displacement described the chloride distribution in the I-zone (determined from measurements made during 1993 and 1996) better than the steady-state simulation. The advective movement of contaminants from selected sites within the solid waste management units to discharge points was simulated using MODPATH. Most of the particles were discharged to the nearest surface-water feature after traveling less than 1,000 feet in the ground-water system. Most areas within 1,000 feet of a surface-water feature or storm sewer had traveltimes of less than 50 years, based on an effective porosity of 40 percent. Contributing areas, traveltimes, and pathlines were identified for 224 wells at Naval Station Mayport under steady-state and transient conditions by back-tracking a particle from the midpoint of the wetted screen of each well. Traveltimes to contributing areas that ranged between 15 and 50 years, estimated by the steady-state model, differed most from the transient traveltime estimates. Estimates of traveltimes and pathlines based on steady-state model results typically were 10 to 20 years more and about twice as long as corresponding estimates from the transient model. The models differed because the steady-state model simulated 1996 conditions when Naval Station Mayport had more impervious surfaces than at any earlier time. The expansion of the impervious surfaces increased the average distance between contributing areas and observation wells.

Field estimates of groundwater circulation depths in two mountainous watersheds in the western U.S. and the effect of deep circulation on solute concentrations in streamflow

NASA Astrophysics Data System (ADS)

Frisbee, Marty D.; Tolley, Douglas G.; Wilson, John L.

2017-04-01

Estimates of groundwater circulation depths based on field data are lacking. These data are critical to inform and refine hydrogeologic models of mountainous watersheds, and to quantify depth and time dependencies of weathering processes in watersheds. Here we test two competing hypotheses on the role of geology and geologic setting in deep groundwater circulation and the role of deep groundwater in the geochemical evolution of streams and springs. We test these hypotheses in two mountainous watersheds that have distinctly different geologic settings (one crystalline, metamorphic bedrock and the other volcanic bedrock). Estimated circulation depths for springs in both watersheds range from 0.6 to 1.6 km and may be as great as 2.5 km. These estimated groundwater circulation depths are much deeper than commonly modeled depths suggesting that we may be forcing groundwater flow paths too shallow in models. In addition, the spatial relationships of groundwater circulation depths are different between the two watersheds. Groundwater circulation depths in the crystalline bedrock watershed increase with decreasing elevation indicative of topography-driven groundwater flow. This relationship is not present in the volcanic bedrock watershed suggesting that both the source of fracturing (tectonic versus volcanic) and increased primary porosity in the volcanic bedrock play a role in deep groundwater circulation. The results from the crystalline bedrock watershed also indicate that relatively deep groundwater circulation can occur at local scales in headwater drainages less than 9.0 km2 and at larger fractions than commonly perceived. Deep groundwater is a primary control on streamflow processes and solute concentrations in both watersheds.

A Hydrostratigraphic System for Modeling Groundwater Flow and Radionuclide Migration at the Corrective Action Unit Scale, Nevada Test Site and Surrounding Areas, Clark, Lincoln, and Nye Counties, Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prothro, Lance; Drellack Jr., Sigmund; Mercadante, Jennifer

2009-01-31

Underground Test Area (UGTA) corrective action unit (CAU) groundwater flow and contaminant transport models of the Nevada Test Site (NTS) and vicinity are built upon hydrostratigraphic framework models (HFMs) that utilize the hydrostratigraphic unit (HSU) as the fundamental modeling component. The delineation and three-dimensional (3-D) modeling of HSUs within the highly complex geologic terrain that is the NTS requires a hydrostratigraphic system that is internally consistent, yet flexible enough to account for overlapping model areas, varied geologic terrain, and the development of multiple alternative HFMs. The UGTA CAU-scale hydrostratigraphic system builds on more than 50 years of geologic and hydrologicmore » work in the NTS region. It includes 76 HSUs developed from nearly 300 stratigraphic units that span more than 570 million years of geologic time, and includes rock units as diverse as marine carbonate and siliciclastic rocks, granitic intrusives, rhyolitic lavas and ash-flow tuffs, and alluvial valley-fill deposits. The UGTA CAU-scale hydrostratigraphic system uses a geology-based approach and two-level classification scheme. The first, or lowest, level of the hydrostratigraphic system is the hydrogeologic unit (HGU). Rocks in a model area are first classified as one of ten HGUs based on the rock’s ability to transmit groundwater (i.e., nature of their porosity and permeability), which at the NTS is mainly a function of the rock’s primary lithology, type and degree of postdepositional alteration, and propensity to fracture. The second, or highest, level within the UGTA CAU-scale hydrostratigraphic system is the HSU, which is the fundamental mapping/modeling unit within UGTA CAU-scale HFMs. HSUs are 3-D bodies that are represented in the finite element mesh for the UGTA groundwater modeling process. HSUs are defined systematically by stratigraphically organizing HGUs of similar character into larger HSUs designations. The careful integration of stratigraphic information in the development of HSUs is important to assure individual HSUs are internally consistent, correlatable, and mappable throughout all the model areas.« less

Model averaging techniques for quantifying conceptual model uncertainty.

PubMed

Singh, Abhishek; Mishra, Srikanta; Ruskauff, Greg

2010-01-01

In recent years a growing understanding has emerged regarding the need to expand the modeling paradigm to include conceptual model uncertainty for groundwater models. Conceptual model uncertainty is typically addressed by formulating alternative model conceptualizations and assessing their relative likelihoods using statistical model averaging approaches. Several model averaging techniques and likelihood measures have been proposed in the recent literature for this purpose with two broad categories--Monte Carlo-based techniques such as Generalized Likelihood Uncertainty Estimation or GLUE (Beven and Binley 1992) and criterion-based techniques that use metrics such as the Bayesian and Kashyap Information Criteria (e.g., the Maximum Likelihood Bayesian Model Averaging or MLBMA approach proposed by Neuman 2003) and Akaike Information Criterion-based model averaging (AICMA) (Poeter and Anderson 2005). These different techniques can often lead to significantly different relative model weights and ranks because of differences in the underlying statistical assumptions about the nature of model uncertainty. This paper provides a comparative assessment of the four model averaging techniques (GLUE, MLBMA with KIC, MLBMA with BIC, and AIC-based model averaging) mentioned above for the purpose of quantifying the impacts of model uncertainty on groundwater model predictions. Pros and cons of each model averaging technique are examined from a practitioner's perspective using two groundwater modeling case studies. Recommendations are provided regarding the use of these techniques in groundwater modeling practice.

Emulation of recharge and evapotranspiration processes in shallow groundwater systems

NASA Astrophysics Data System (ADS)

Doble, Rebecca C.; Pickett, Trevor; Crosbie, Russell S.; Morgan, Leanne K.; Turnadge, Chris; Davies, Phil J.

2017-12-01

In shallow groundwater systems, recharge and evapotranspiration are highly sensitive to changes in the depth to water table. To effectively model these fluxes, complex functions that include soil and vegetation properties are often required. Model emulation (surrogate modelling or meta-modelling) can provide a means of incorporating detailed conceptualisation of recharge and evapotranspiration processes, while maintaining the numerical tractability and computational performance required for regional scale groundwater models and uncertainty analysis. A method for emulating recharge and evapotranspiration processes in groundwater flow models was developed, and applied to the South East region of South Australia and western Victoria, which is characterised by shallow groundwater, wetlands and coastal lakes. The soil-vegetation-atmosphere transfer (SVAT) model WAVES was used to generate relationships between net recharge (diffuse recharge minus evapotranspiration from groundwater) and depth to water table for different combinations of climate, soil and land cover types. These relationships, which mimicked previously described soil, vegetation and groundwater behaviour, were combined into a net recharge lookup table. The segmented evapotranspiration package in MODFLOW was adapted to select values of net recharge from the lookup table depending on groundwater depth, and the climate, soil and land use characteristics of each cell. The model was found to be numerically robust in steady state testing, had no major increase in run time, and would be more efficient than tightly-coupled modelling approaches. It made reasonable predictions of net recharge and groundwater head compared with remotely sensed estimates of net recharge and a standard MODFLOW comparison model. In particular, the method was better able to predict net recharge and groundwater head in areas with steep hydraulic gradients.

Adaptability of Irrigation to a Changing Monsoon in India: How far can we go?

NASA Astrophysics Data System (ADS)

Zaveri, E.; Grogan, D. S.; Fisher-Vanden, K.; Frolking, S. E.; Wrenn, D. H.; Nicholas, R.

2014-12-01

Agriculture and the monsoon are inextricably linked in India. A large part of the steady rise in agricultural production since the onset of the Green Revolution in the 1960's has been attributed to irrigation. Irrigation is used to supplement and buffer crops against precipitation shocks, but water availability for such use is itself sensitive to the erratic, seasonal and spatially heterogeneous nature of the monsoon. We provide new evidence on the relationship between monsoon changes, irrigation variability and water availability by linking a process based hydrology model with an econometric model for one of the world's most water stressed countries. India uses more groundwater for irrigation than any other country, and there is substantial evidence that this has led to depletion of groundwater aquifers. First, we build an econometric model of historical irrigation decisions using detailed agriculture and weather data spanning 35 years. Multivariate regression models reveal that for crops grown in the wet season, irrigation is sensitive to distribution and total monsoon rainfall but not to ground or surface water availability. For crops grown in the dry season, total monsoon rainfall matters most, and its effect is sensitive to groundwater availability. The historical estimates from the econometric model are used to calculate future irrigated areas under three different climate model predictions of monsoon climate for the years 2010 - 2050. These projections are then used as input to a physical hydrology model, which quantifies supply of irrigation water from sustainable sources such as rechargeable shallow groundwater, rivers and reservoirs, to unsustainable sources such as non- rechargeable groundwater. We find that the significant variation in monsoon projections lead to very different results. Crops grown in the dry season show particularly divergent trends between model projections, leading to very different groundwater resource requirements.

A multicomponent coupled model of glacier hydrology 1. Theory and synthetic examples

NASA Astrophysics Data System (ADS)

Flowers, Gwenn E.; Clarke, Garry K. C.

2002-11-01

Basal hydrology is acknowledged as a fundamental control on glacier dynamics, especially in cases where surface meltwater reaches the bed. For many glaciers at midlatitudes, basal drainage is influenced by subaerial, englacial, and subsurface water flow. One of the major shortcomings of existing basal hydrology models is the treatment of the glacier bed as an isolated system. We present theoretical and computational models that couple glacier surface runoff, englacial water storage and transport, subglacial drainage, and subsurface groundwater flow. Each of the four model components is represented as a two-dimensional, vertically integrated layer that communicates with its neighbors through water exchange. Governing equations are derived from the law of mass conservation and are expressed as a balance between the internal distribution of water and external sources. The numerical exposition of this theory is a time-dependent finite difference model that can be used to simulate glacier drainage. In this paper we outline the theory and conduct simple tests using an idealized glacier geometry. In the companion paper, the model is tailored to Trapridge Glacier, Yukon Territory, Canada, where results are compared with measurements of subglacial water pressure.

Accuracy of finite-difference modeling of seismic waves : Simulation versus laboratory measurements

NASA Astrophysics Data System (ADS)

Arntsen, B.

2017-12-01

The finite-difference technique for numerical modeling of seismic waves is still important and for some areas extensively used.For exploration purposes is finite-difference simulation at the core of both traditional imaging techniques such as reverse-time migration and more elaborate Full-Waveform Inversion techniques.The accuracy and fidelity of finite-difference simulation of seismic waves are hard to quantify and meaningfully error analysis is really onlyeasily available for simplistic media. A possible alternative to theoretical error analysis is provided by comparing finite-difference simulated data with laboratory data created using a scale model. The advantage of this approach is the accurate knowledge of the model, within measurement precision, and the location of sources and receivers.We use a model made of PVC immersed in water and containing horizontal and tilted interfaces together with several spherical objects to generateultrasonic pressure reflection measurements. The physical dimensions of the model is of the order of a meter, which after scaling represents a model with dimensions of the order of 10 kilometer and frequencies in the range of one to thirty hertz.We find that for plane horizontal interfaces the laboratory data can be reproduced by the finite-difference scheme with relatively small error, but for steeply tilted interfaces the error increases. For spherical interfaces the discrepancy between laboratory data and simulated data is sometimes much more severe, to the extent that it is not possible to simulate reflections from parts of highly curved bodies. The results are important in view of the fact that finite-difference modeling is often at the core of imaging and inversion algorithms tackling complicatedgeological areas with highly curved interfaces.

Groundwater-abstraction induced land subsidence and groundwater regulation in the North China Plain

NASA Astrophysics Data System (ADS)

Guo, H.; Wang, L.; Cheng, G.; Zhang, Z.

2015-11-01

Land subsidence can be induced when various factors such as geological, and hydrogeological conditions and intensive groundwater abstraction combine. The development and utilization of groundwater in the North China Plain (NCP) bring great benefits, and at the same time have led to a series of environmental and geological problems accompanying groundwater-level declines and land subsidence. Subsidence occurs commonly in the NCP and analyses show that multi-layer aquifer systems with deep confined aquifers and thick compressible clay layers are the key geological and hydrogeological conditions responsible for its development in this region. Groundwater overdraft results in aquifer-system compaction, resulting in subsidence. A calibrated, transient groundwater-flow numerical model of the Beijing plain portion of the NCP was developed using MODFLOW. According to available water supply and demand in Beijing plain, several groundwater regulation scenarios were designed. These different regulation scenarios were simulated with the groundwater model, and assessed using a multi-criteria fuzzy pattern recognition model. This approach is proven to be very useful for scientific analysis of sustainable development and utilization of groundwater resources. The evaluation results show that sustainable development of groundwater resources may be achieved in Beijing plain when various measures such as control of groundwater abstraction and increase of artificial recharge combine favourably.

Modelling surface water-groundwater interaction with a conceptual approach: model development and application in New Zealand

NASA Astrophysics Data System (ADS)

Yang, J.; Zammit, C.; McMillan, H. K.

2016-12-01

As in most countries worldwide, water management in lowland areas is a big concern for New Zealand due to its economic importance for water related human activities. As a result, the estimation of available water resources in these areas (e.g., for irrigation and water supply purpose) is crucial and often requires an understanding of complex hydrological processes, which are often characterized by strong interactions between surface water and groundwater (usually expressed as losing and gaining rivers). These processes are often represented and simulated using integrated physically based hydrological models. However models with physically based groundwater modules typically require large amount of non-readily available geologic and aquifer information and are computationally intensive. Instead, this paper presents a conceptual groundwater model that is fully integrated into New Zealand's national hydrological model TopNet based on TopModel concepts (Beven, 1992). Within this conceptual framework, the integrated model can simulate not only surface processes, but also groundwater processes and surface water-groundwater interaction processes (including groundwater flow, river-groundwater interaction, and groundwater interaction with external watersheds). The developed model was applied to two New Zealand catchments with different hydro-geological and climate characteristics (Pareora catchment in the Canterbury Plains and Grey catchment on the West Coast). Previous studies have documented strong interactions between the river and groundwater, based on the analysis of a large number of concurrent flow measurements and associated information along the river main stem. Application of the integrated hydrological model indicates flow simulation (compared to the original hydrological model conceptualisation) during low flow conditions are significantly improved and further insights on local river dynamics are gained. Due to its conceptual characteristics and low level of data requirement, the integrated model could be used at local and national scales to improve the simulation of hydrological processes in non-topographically driven areas (where groundwater processes are important), and to assess impact of climate change on the integrated hydrological cycle in these areas.

Inter-aquifer Dynamics in and Near a Confining Unit Window in Shelby County, Tennessee, USA

NASA Astrophysics Data System (ADS)

Gentry, R. W.; McKay, L. D.; Larsen, D.; Carmichael, J. K.; Solomon, D. K.; Thonnard, N.; Anderson, J. L.

2003-12-01

An interdisplinary research team is investigating the interaction between the surficial alluvial aquifer and the deeper confined Memphis aquifer in the Memphis area, Shelby County, Tennessee. Previous research has identified a window in the clay-rich, upper Claiborne confining unit that separates the two aquifers near a closed municipal landfill in east-central Shelby County, an area undergoing rapid urbanization. For this investigation, a combination of environmental tracers (tritium/helium-3), major and trace ion geochemistry, hydraulic response testing, measurement of hydraulic gradients, and groundwater flow modeling is being used to quantify recharge of young water from the alluvial aquifer through the window to the Memphis aquifer. The research will provide results to better understand how windows were formed and how they influence recharge and water quality in otherwise confined parts of the Memphis aquifer downdip of its outcrop/subcrop area. Examination of continuous core samples and geophysical logs from wells installed for the study using Rotasonic drilling methods confirmed the existence of a sand-dominated window that may be as much as 1 km in diameter in the upper Claiborne confining unit. The upper Claiborne confining unit is 15 to 20 m thick in most of the study area and is overlain by a 10 to 12 m thick alluvial aquifer. The window is interpreted to have formed as a result of depositional and incisional processes in an Eocene-age deltaic system. Hydraulic gradients of several feet exist vertically between the alluvial and Memphis aquifers within the window, indicating downward flow. Groundwater age-dates from tritium/helium-3 analyses indicate that groundwater in the window at the depth of the base of the surrounding confining unit (approximately 30 m) has an apparent age of 19.8 years, which confirms the occurrence of downward flow. Young groundwater age dates (less than 32 years) also were obtained from wells in the Memphis aquifer at confined sites downgradient of the window, suggesting that a plume of young water is spreading outwards from the window and mixing with the older Memphis aquifer water. Preliminary inverse modeling of the site using a genetic algorithm coupled with a central finite difference flow model indicates a probable steady-state downward flux of about 12,000 m3/d through the window. Collection and analysis of additional groundwater samples are planned to examine geochemical conditions in the confining unit and in the Memphis aquifer upgradient of the window. These analyses will aid in developing a final conceptual model and in subsequent numerical modeling of mixing of the young recharge water with the older Memphis aquifer water.

Urban groundwater quality in sub-Saharan Africa: current status and implications for water security and public health

NASA Astrophysics Data System (ADS)

Lapworth, D. J.; Nkhuwa, D. C. W.; Okotto-Okotto, J.; Pedley, S.; Stuart, M. E.; Tijani, M. N.; Wright, J.

2017-06-01

Groundwater resources are important sources of drinking water in Africa, and they are hugely important in sustaining urban livelihoods and supporting a diverse range of commercial and agricultural activities. Groundwater has an important role in improving health in sub-Saharan Africa (SSA). An estimated 250 million people (40% of the total) live in urban centres across SSA. SSA has experienced a rapid expansion in urban populations since the 1950s, with increased population densities as well as expanding geographical coverage. Estimates suggest that the urban population in SSA will double between 2000 and 2030. The quality status of shallow urban groundwater resources is often very poor due to inadequate waste management and source protection, and poses a significant health risk to users, while deeper borehole sources often provide an important source of good quality drinking water. Given the growth in future demand from this finite resource, as well as potential changes in future climate in this region, a detailed understanding of both water quantity and quality is required to use this resource sustainably. This paper provides a comprehensive assessment of the water quality status, both microbial and chemical, of urban groundwater in SSA across a range of hydrogeological terrains and different groundwater point types. Lower storage basement terrains, which underlie a significant proportion of urban centres in SSA, are particularly vulnerable to contamination. The relationship between mean nitrate concentration and intrinsic aquifer pollution risk is assessed for urban centres across SSA. Current knowledge gaps are identified and future research needs highlighted.

Inverse modeling and uncertainty analysis of potential groundwater recharge to the confined semi-fossil Ohangwena II Aquifer, Namibia

NASA Astrophysics Data System (ADS)

Wallner, Markus; Houben, Georg; Lohe, Christoph; Quinger, Martin; Himmelsbach, Thomas

2017-12-01

The identification of potential recharge areas and estimation of recharge rates to the confined semi-fossil Ohangwena II Aquifer (KOH-2) is crucial for its future sustainable use. The KOH-2 is located within the endorheic transboundary Cuvelai-Etosha-Basin (CEB), shared by Angola and Namibia. The main objective was the development of a strategy to tackle the problem of data scarcity, which is a well-known problem in semi-arid regions. In a first step, conceptual geological cross sections were created to illustrate the possible geological setting of the system. Furthermore, groundwater travel times were estimated by simple hydraulic calculations. A two-dimensional numerical groundwater model was set up to analyze flow patterns and potential recharge zones. The model was optimized against local observations of hydraulic heads and groundwater age. The sensitivity of the model against different boundary conditions and internal structures was tested. Parameter uncertainty and recharge rates were estimated. Results indicate that groundwater recharge to the KOH-2 mainly occurs from the Angolan Highlands in the northeastern part of the CEB. The sensitivity of the groundwater model to different internal structures is relatively small in comparison to changing boundary conditions in the form of influent or effluent streams. Uncertainty analysis underlined previous results, indicating groundwater recharge originating from the Angolan Highlands. The estimated recharge rates are less than 1% of mean yearly precipitation, which are reasonable for semi-arid regions.

Three-dimensional hydrogeological modelling application to the Alverà mudslide (Cortina d'Ampezzo, Italy)

NASA Astrophysics Data System (ADS)

Bonomi, Tullia; Cavallin, Angelo

1999-10-01

Within the framework of Geographic Information System (GIS), the distributed three-dimensional groundwater model MODFLOW has been applied to evaluate the groundwater processes of the hydrogeological system in the Alverà mudslide (Cortina d'Ampezzo, Italy; test site in the TESLEC Project of the European Union). The application of this model has permitted an analysis of the spatial distribution of the structure (DTM and landslide bottom) and the mass transfer elements of the hydrogeological system. The field survey suggested zoning the area on the basis of the recharge, groundwater fluctuation and drainage system. For each zone, a hydraulic conductivity value to simulate the different recharge and the drainage responses has been assigned. The effect of rainfall infiltration into the ground and its effect on the groundwater table, with different intensity related to different time periods, have been simulated to reproduce the real condition of the area. The applied model can simulate the positive fluctuations of the water table on the whole landslide, with a different response of the hydrogeological system in each zone. The spatial simulated water level distribution is in accordance with the real one, with very small difference between them. The application of distributed three-dimensional models, within the framework of GIS, is an approach which permits data to be continually updated, standardised and integrated.

A groundwater data assimilation application study in the Heihe mid-reach

NASA Astrophysics Data System (ADS)

Ragettli, S.; Marti, B. S.; Wolfgang, K.; Li, N.

2017-12-01

The present work focuses on modelling of the groundwater flow in the mid-reach of the endorheic river Heihe in the Zhangye oasis (Gansu province) in arid north-west China. In order to optimise the water resources management in the oasis, reliable forecasts of groundwater level development under different management options and environmental boundary conditions have to be produced. For this means, groundwater flow is modelled with Modflow and coupled to an Ensemble Kalman Filter programmed in Matlab. The model is updated with monthly time steps, featuring perturbed boundary conditions to account for uncertainty in model forcing. Constant biases between model and observations have been corrected prior to updating and compared to model runs without bias correction. Different options for data assimilation (states and/or parameters), updating frequency, and measures against filter inbreeding (damping factor, covariance inflation, spatial localization) have been tested against each other. Results show a high dependency of the Ensemble Kalman filter performance on the selection of observations for data assimilation. For the present regional model, bias correction is necessary for a good filter performance. A combination of spatial localization and covariance inflation is further advisable to reduce filter inbreeding problems. Best performance is achieved if parameter updates are not large, an indication for good prior model calibration. Asynchronous updating of parameter values once every five years (with data of the past five years) and synchronous updating of the groundwater levels is better suited for this groundwater system with not or slow changing parameter values than synchronous updating of both groundwater levels and parameters at every time step applying a damping factor. The filter is not able to correct time lags of signals.

Integrated surface-subsurface model to investigate the role of groundwater in headwater catchment runoff generation: A minimalist approach to parameterisation

NASA Astrophysics Data System (ADS)

Ala-aho, Pertti; Soulsby, Chris; Wang, Hailong; Tetzlaff, Doerthe

2017-04-01

Understanding the role of groundwater for runoff generation in headwater catchments is a challenge in hydrology, particularly so in data-scarce areas. Fully-integrated surface-subsurface modelling has shown potential in increasing process understanding for runoff generation, but high data requirements and difficulties in model calibration are typically assumed to preclude their use in catchment-scale studies. We used a fully integrated surface-subsurface hydrological simulator to enhance groundwater-related process understanding in a headwater catchment with a rich background in empirical data. To set up the model we used minimal data that could be reasonably expected to exist for any experimental catchment. A novel aspect of our approach was in using simplified model parameterisation and including parameters from all model domains (surface, subsurface, evapotranspiration) in automated model calibration. Calibration aimed not only to improve model fit, but also to test the information content of the observations (streamflow, remotely sensed evapotranspiration, median groundwater level) used in calibration objective functions. We identified sensitive parameters in all model domains (subsurface, surface, evapotranspiration), demonstrating that model calibration should be inclusive of parameters from these different model domains. Incorporating groundwater data in calibration objectives improved the model fit for groundwater levels, but simulations did not reproduce well the remotely sensed evapotranspiration time series even after calibration. Spatially explicit model output improved our understanding of how groundwater functions in maintaining streamflow generation primarily via saturation excess overland flow. Steady groundwater inputs created saturated conditions in the valley bottom riparian peatlands, leading to overland flow even during dry periods. Groundwater on the hillslopes was more dynamic in its response to rainfall, acting to expand the saturated area extent and thereby promoting saturation excess overland flow during rainstorms. Our work shows the potential of using integrated surface-subsurface modelling alongside with rigorous model calibration to better understand and visualise the role of groundwater in runoff generation even with limited datasets.

Shallow groundwater in the Matanuska-Susitna Valley, Alaska—Conceptualization and simulation of flow

USGS Publications Warehouse

Kikuchi, Colin P.

2013-01-01

The Matanuska-Susitna Valley is in the Upper Cook Inlet Basin and is currently undergoing rapid population growth outside of municipal water and sewer service areas. In response to concerns about the effects of increasing water use on future groundwater availability, a study was initiated between the Alaska Department of Natural Resources and the U.S. Geological Survey. The goals of the study were (1) to compile existing data and collect new data to support hydrogeologic conceptualization of the study area, and (2) to develop a groundwater flow model to simulate flow dynamics important at the regional scale. The purpose of the groundwater flow model is to provide a scientific framework for analysis of regional-scale groundwater availability. To address the first study goal, subsurface lithologic data were compiled into a database and were used to construct a regional hydrogeologic framework model describing the extent and thickness of hydrogeologic units in the Matanuska-Susitna Valley. The hydrogeologic framework model synthesizes existing maps of surficial geology and conceptual geochronologies developed in the study area with the distribution of lithologies encountered in hundreds of boreholes. The geologic modeling package Geological Surveying and Investigation in Three Dimensions (GSI3D) was used to construct the hydrogeologic framework model. In addition to characterizing the hydrogeologic framework, major groundwater-budget components were quantified using several different techniques. A land-surface model known as the Deep Percolation Model was used to estimate in-place groundwater recharge across the study area. This model incorporates data on topography, soils, vegetation, and climate. Model-simulated surface runoff was consistent with observed streamflow at U.S. Geological Survey streamgages. Groundwater withdrawals were estimated on the basis of records from major water suppliers during 2004-2010. Fluxes between groundwater and surface water were estimated during field investigations on several small streams. Regional groundwater flow patterns were characterized by synthesizing previous water-table maps with a synoptic water-level measurement conducted during 2009. Time-series water-level data were collected at groundwater and lake monitoring stations over the study period (2009–present). Comparison of historical groundwater-level records with time-series groundwater-level data collected during this study showed similar patterns in groundwater-level fluctuation in response to precipitation. Groundwater-age data collected during previous studies show that water moves quickly through the groundwater system, suggesting that the system responds quickly to changes in climate forcing. Similarly, the groundwater system quickly returns to long-term average conditions following variability due to seasonal or interannual changes in precipitation. These analyses indicate that the groundwater system is in a state of dynamic equilibrium, characterized by water-level fluctuation about a constant average state, with no long-term trends in aquifer-system storage. To address the second study goal, a steady-state groundwater flow model was developed to simulate regional groundwater flow patterns. The groundwater flow model was bounded by physically meaningful hydrologic features, and appropriate internal model boundaries were specified on the basis of conceptualization of the groundwater system resulting in a three-layer model. Calibration data included 173 water‑level measurements and 18 measurements of streamflow gains and losses along small streams. Comparison of simulated and observed heads and flows showed that the model accurately simulates important regional characteristics of the groundwater flow system. This model is therefore appropriate for studying regional-scale groundwater availability. Mismatch between model-simulated and observed hydrologic quantities is likely because of the coarse grid size of the model and seasonal transient effects. Next steps towards model refinement include the development of a transient groundwater flow model that is suitable for analysis of seasonal variability in hydraulic heads and flows. In addition, several important groundwater budget components remain poorly quantified—including groundwater outflow to the Matanuska River, Little Susitna River, and Knik Arm.

Groundwater Profession in Transition: Discovery toAdaptation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Narasimhan, T.N.

2005-04-04

Over the past century and half, groundwater has played an important role in the economic prosperity of the United States. The groundwater profession which has contributed to this prosperity has grown through the contributions of the U.S. and State Geological Surveys,academia, and industry. A century ago, the energies of the profession were channeled towards discovering new sources of groundwater in a largely unexplored land, and exploiting the resources for maximum economic benefit. Experience has since revealed that groundwater systems are finite, and are intimately linked to surface water bodies and the biosphere. A consequence is that aggressive exploitation of groundwatermore » can lead to unacceptable environmental degradation and social cost. At present, the groundwater profession is in a state of transition from one of discovery and exploitation, to one of balancing resource development with avoiding unacceptable damage to the environment. This paper outlines the history of the groundwater profession in the United States since the late nineteenth century, and speculates on what may lie ahead in the near future, as the profession makes the transition from discovering new sources of groundwater to one of better understanding and adapting to nature's constraints.« less

Groundwater Profession in Transition: Discovery toAdaptation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Narasimhan, T.N.

Over the past century and half, groundwater has played an important role in the economic prosperity of the United States. The groundwater profession which has contributed to this prosperity has grown through the contributions of the U.S. and State Geological Surveys,academia, and industry. A century ago, the energies of the profession were channeled towards discovering new sources of groundwater in a largely unexplored land, and exploiting the resources for maximum economic benefit. Experience has since revealed that groundwater systems are finite, and are intimately linked to surface water bodies and the biosphere. A consequence is that aggressive exploitation of groundwatermore » can lead to unacceptable environmental degradation and social cost. At present, the groundwater profession is in a state of transition from one of discovery and exploitation, to one of balancing resource development with avoiding unacceptable damage to the environment. This paper outlines the history of the groundwater profession in the United States since the late nineteenth century, and speculates on what may lie ahead in the near future, as the profession makes the transition from discovering new sources of groundwater to one of better understanding and adapting to nature's constraints.« less

Ground-water flow in the surficial aquifer system and potential movement of contaminants from selected waste-disposal sites at Cecil Field Naval Air Station, Jacksonville, Florida

USGS Publications Warehouse

Halford, K.J.

1998-01-01

As part of the Installation Restoration Program, Cecil Field Naval Air Station, Jacksonville, Florida, is considering remedialaction alternatives to control the possible movement of contaminants from sites that may discharge to the surface. This requires a quantifiable understanding of ground-water flow through the surficial aquifer system and how the system will respond to any future stresses. The geologic units of interest in the study area consist of sediments of Holocene to Miocene age that extend from land surface to the base of the Hawthorn Group. The hydrogeology within the study area was determined from gamma-ray and geologists? logs. Ground-water flow through the surficial aquifer system was simulated with a seven-layer, finite-difference model that extended vertically from the water table to the top of the Upper Floridan aquifer. Results from the calibrated model were based on a long-term recharge rate of 6 inches per year, which fell in the range of 4 to 10 inches per year, estimated using stream hydrograph separation methods. More than 80 percent of ground-water flow circulates within the surficial-sand aquifer, which indicates that most contaminant movement also can be expected to move through the surficial-sand aquifer alone. The surficial-sand aquifer is the uppermost unit of the surficial aquifer system. Particle-tracking results showed that the distances of most flow paths were 1,500 feet or less from a given site to its discharge point. For an assumed effective porosity of 20 percent, typical traveltimes are 40 years or less. At all of the sites investigated, particles released 10 feet below the water table had shorter traveltimes than those released 40 feet below the water table. Traveltimes from contaminated sites to their point of discharge ranged from 2 to 300 years. The contributing areas of the domestic supply wells are not very extensive. The shortest traveltimes for particles to reach the domestic supply wells from their respective contributing areas ranged from 70 to 200 years.

Groundwater response to leakage of surface water through a thick vadose zone in the middle reaches area of Heihe River Basin, in China

NASA Astrophysics Data System (ADS)

Wang, X.-S.; Ma, M.-G.; Li, X.; Zhao, J.; Dong, P.; Zhou, J.

2009-12-01

The behavior of groundwater response to leakage of surface water in the middle reaches area of Heihe River Basin is significantly influenced by a thick vadose zone. The variation of groundwater level is a result of two recharge events corresponding to leakage of Heihe River and irrigation water with different delay time. A nonlinear leakage model is developed to calculate the monthly leakage of Heihe River in considering changes of streamflow, river stage and agricultural water utilization. Numerical modeling of variable saturated flow is carried out to investigate the general behaviors of leakage-recharge conversion through a thick vadose zone. It is found that the variable recharge can be approximated by simple reservoir models for both leakage under a river and leakage under an irrigation district but with different delay-time and recession coefficient. A triple-reservoir model of relationship between surface water, vadose zone and groundwater is developed. It reproduces the in situ water table movement during 1989-2006 with variable streamflow of Heihe River and agricultural water utilization. The model is applied to interpret groundwater dynamics during 2007-2008 that observed in the Watershed Airborne Telemetry Experimental Research (WATER).

Geohydrology and Numerical Simulation of the Ground-Water Flow System of Molokai, Hawaii

USGS Publications Warehouse

Oki, Delwyn S.

1997-01-01

A two-dimensional, steady-state, areal ground-water flow model was developed for the island of Molokai, Hawaii, to enhance the understanding of (1) the conceptual framework of the ground-water flow system, (2) the distribution of aquifer hydraulic properties, and (3) the regional effects of ground-water withdrawals on water levels and coastal discharge. The model uses the finite-element code AQUIFEM-SALT, which simulates flow of fresh ground water in systems that may have a freshwater lens floating on denser underlying saltwater. Model results are in agreement with the general conceptual model of the flow system on Molokai, where ground water flows from the interior, high-recharge areas to the coast. The model-calculated ground-water divide separating flow to the northern and southern coasts lies to either the north or the south of the topographic divide but is generally not coincident with the topographic divide. On the basis of model results, the following horizontal hydraulic conductivities were estimated: (1) 1,000 feet per day for the dike-free volcanic rocks of East and West Molokai, (2) 100 feet per day for the marginal dike zone of the East Molokai Volcano, (3) 2 feet per day for the West Molokai dike complex, (4) 0.02 feet per day for the East Molokai dike complex, and (5) 500 feet per day for the Kalaupapa Volcanics. Three simulations to determine the effects of proposed ground-water withdrawals on water levels and coastal discharge, relative to model-calculated water levels and coastal discharge for 1992-96 withdrawal rates, show that the effects are widespread. For a withdrawal rate of 0.337 million gallons per day from a proposed well about 4 miles southeast of Kualapuu and 3 miles north of Kamiloloa, the model-calculated drawdown of 0.01 foot or more extends 4 miles southeast and 6 miles northwest from the well. For a withdrawal rate of 1.326 million gallons per day from the same well, the model-calculated drawdown of 0.01 foot or more extends 6 miles southeast and 9 miles northwest from the well. In a third scenario, the withdrawal rate from an existing well near Kualapuu was increased by 0.826 million gallons per day. The model-calculated drawdown of 0.01 foot or more extends 6 miles southeast and 8 miles northwest from the well. In all scenarios, coastal discharge is reduced by an amount equal to the additional withdrawal. Additional data needed to improve the understanding of the ground-water flow system on Molokai include: (1) a wider spatial distribution and longer temporal distribution of water-levels, (2) independent estimates of hydraulic conductivity, (3) improved recharge estimates, (4) information about the vertical distribution of salinity in ground water, (5) streamflow data at additional sites, and (6) improved information about the subsurface geology.

Applying downscaled global climate model data to a hydrodynamic surface-water and groundwater model

USGS Publications Warehouse

Swain, Eric; Stefanova, Lydia; Smith, Thomas

2014-01-01

Precipitation data from Global Climate Models have been downscaled to smaller regions. Adapting this downscaled precipitation data to a coupled hydrodynamic surface-water/groundwater model of southern Florida allows an examination of future conditions and their effect on groundwater levels, inundation patterns, surface-water stage and flows, and salinity. The downscaled rainfall data include the 1996-2001 time series from the European Center for Medium-Range Weather Forecasting ERA-40 simulation and both the 1996-1999 and 2038-2057 time series from two global climate models: the Community Climate System Model (CCSM) and the Geophysical Fluid Dynamic Laboratory (GFDL). Synthesized surface-water inflow datasets were developed for the 2038-2057 simulations. The resulting hydrologic simulations, with and without a 30-cm sea-level rise, were compared with each other and field data to analyze a range of projected conditions. Simulations predicted generally higher future stage and groundwater levels and surface-water flows, with sea-level rise inducing higher coastal salinities. A coincident rise in sea level, precipitation and surface-water flows resulted in a narrower inland saline/fresh transition zone. The inland areas were affected more by the rainfall difference than the sea-level rise, and the rainfall differences make little difference in coastal inundation, but a larger difference in coastal salinities.

Voxel inversion of airborne electromagnetic data for improved groundwater model construction and prediction accuracy

NASA Astrophysics Data System (ADS)

Kruse Christensen, Nikolaj; Ferre, Ty Paul A.; Fiandaca, Gianluca; Christensen, Steen

2017-03-01

We present a workflow for efficient construction and calibration of large-scale groundwater models that includes the integration of airborne electromagnetic (AEM) data and hydrological data. In the first step, the AEM data are inverted to form a 3-D geophysical model. In the second step, the 3-D geophysical model is translated, using a spatially dependent petrophysical relationship, to form a 3-D hydraulic conductivity distribution. The geophysical models and the hydrological data are used to estimate spatially distributed petrophysical shape factors. The shape factors primarily work as translators between resistivity and hydraulic conductivity, but they can also compensate for structural defects in the geophysical model. The method is demonstrated for a synthetic case study with sharp transitions among various types of deposits. Besides demonstrating the methodology, we demonstrate the importance of using geophysical regularization constraints that conform well to the depositional environment. This is done by inverting the AEM data using either smoothness (smooth) constraints or minimum gradient support (sharp) constraints, where the use of sharp constraints conforms best to the environment. The dependency on AEM data quality is also tested by inverting the geophysical model using data corrupted with four different levels of background noise. Subsequently, the geophysical models are used to construct competing groundwater models for which the shape factors are calibrated. The performance of each groundwater model is tested with respect to four types of prediction that are beyond the calibration base: a pumping well's recharge area and groundwater age, respectively, are predicted by applying the same stress as for the hydrologic model calibration; and head and stream discharge are predicted for a different stress situation. As expected, in this case the predictive capability of a groundwater model is better when it is based on a sharp geophysical model instead of a smoothness constraint. This is true for predictions of recharge area, head change, and stream discharge, while we find no improvement for prediction of groundwater age. Furthermore, we show that the model prediction accuracy improves with AEM data quality for predictions of recharge area, head change, and stream discharge, while there appears to be no accuracy improvement for the prediction of groundwater age.

Modelling long term rockslide displacements with non-linear time-dependent relationships

NASA Astrophysics Data System (ADS)

De Caro, Mattia; Volpi, Giorgio; Castellanza, Riccardo; Crosta, Giovanni; Agliardi, Federico

2015-04-01

Rockslides undergoing rapid changes in behaviour pose major risks in alpine areas, and require careful characterization and monitoring both for civil protection and mitigation activities. In particular, these instabilities can undergo very slow movement with occasional and intermittent acceleration/deceleration stages of motion potentially leading to collapse. Therefore, the analysis of such instabilities remains a challenging issue. Rockslide displacements are strongly conditioned by hydrologic factors as suggested by correlations with groundwater fluctuations, snowmelt, with a frequently observed delay between perturbation and system reaction. The aim of this work is the simulation of the complex time-dependent behaviour of two case studies for which also a 2D transient hydrogeological simulation has been performed: Vajont rockslide (1960 to 1963) and the recent Mt. de La Saxe rockslide (2009 to 2012). Non-linear time-dependent constitutive relationships have been used to describe long-term creep deformation. Analyses have been performed using a "rheological-mechanical" approach that fits idealized models (e.g. viscoelastic, viscoplastic, elasto-viscoplastic, Burgers, nonlinear visco-plastic) to the experimental behaviour of specific materials by means of numerical constants. Bidimensional simulations were carried out using the finite difference code FLAC. Displacements time-series, available for the two landslides, show two superimposed deformation mechanisms: a creep process, leading to movements under "steady state" conditions (e.g. constant groundwater level), and a "dynamic" process, leading to an increase in displacement rate due to changes of external loads (e.g. groundwater level). For both cases sliding mass is considered as an elasto-plastic body subject to its self-weight, inertial and seepage forces varying with time according to water table fluctuation (due to snowmelt or changing in reservoir level) and derived from the previous hydrogeological analysis (see EGU2015-14374). All non-linearities are lumped into a thin layer representing the main rockslide basal shear zone. Due to the great number of parameters characterizing viscous rheological models we separated the modelling into different stages. Firstly, starting from available geotechnical data, we carried out shear strength reduction analysis for solving elasto-plastic critical parameters of the basal shear band. Then, according to the chosen approach, we applied different viscous rheological models in order to simulate steady and dynamic creep. We identified the Burgers-creep viscoplastic model (Mohr-Coulomb failure criterion coupled with general Burgers-creep time-dependent nucleus) as the most appropriate one for simulating the behavior of the two case studies and more generally of large rockslides that exhibit similar movements. Due to the adopted continuum numerical approach, the models reproduce only portions of displacements curves associated with first and secondary creep phenomena. The models have been calibrated and subsequently validated on long temporal series of monitoring data, and reliably simulate the in situ data.

Comparison of predicted pesticide concentrations in groundwater from SCI-GROW and PRZM-GW models with historical monitoring data.

PubMed

Estes, Tammara L; Pai, Naresh; Winchell, Michael F

2016-06-01

A key factor in the human health risk assessment process for the registration of pesticides by the US Environmental Protection Agency (EPA) is an estimate of pesticide concentrations in groundwater used for drinking water. From 1997 to 2011, these estimates were obtained from the EPA empirical model SCI-GROW. Since 2012, these estimates have been obtained from the EPA deterministic model PRZM-GW, which has resulted in a significant increase in estimated groundwater concentrations for many pesticides. Historical groundwater monitoring data from the National Ambient Water Quality Assessment (NAWQA) Program (1991-2014) were compared with predicted groundwater concentrations from both SCI-GROW (v.2.3) and PRZM-GW (v.1.07) for 66 different pesticides of varying environmental fate properties. The pesticide environmental fate parameters associated with over- and underprediction of groundwater concentrations by the two models were evaluated. In general, SCI-GROW2.3 predicted groundwater concentrations were close to maximum historically observed groundwater concentrations. However, for pesticides with soil organic carbon content values below 1000 L kg(-1) and no simulated hydrolysis, PRZM-GW overpredicted, often by greater than 100 ppb. © 2015 Society of Chemical Industry. © 2015 Society of Chemical Industry.

Experimental validation of finite element modelling of a modular metal-on-polyethylene total hip replacement.

PubMed

Hua, Xijin; Wang, Ling; Al-Hajjar, Mazen; Jin, Zhongmin; Wilcox, Ruth K; Fisher, John

2014-07-01

Finite element models are becoming increasingly useful tools to conduct parametric analysis, design optimisation and pre-clinical testing for hip joint replacements. However, the verification of the finite element model is critically important. The purposes of this study were to develop a three-dimensional anatomic finite element model for a modular metal-on-polyethylene total hip replacement for predicting its contact mechanics and to conduct experimental validation for a simple finite element model which was simplified from the anatomic finite element model. An anatomic modular metal-on-polyethylene total hip replacement model (anatomic model) was first developed and then simplified with reasonable accuracy to a simple modular total hip replacement model (simplified model) for validation. The contact areas on the articulating surface of three polyethylene liners of modular metal-on-polyethylene total hip replacement bearings with different clearances were measured experimentally in the Leeds ProSim hip joint simulator under a series of loading conditions and different cup inclination angles. The contact areas predicted from the simplified model were then compared with that measured experimentally under the same conditions. The results showed that the simplification made for the anatomic model did not change the predictions of contact mechanics of the modular metal-on-polyethylene total hip replacement substantially (less than 12% for contact stresses and contact areas). Good agreements of contact areas between the finite element predictions from the simplified model and experimental measurements were obtained, with maximum difference of 14% across all conditions considered. This indicated that the simplification and assumptions made in the anatomic model were reasonable and the finite element predictions from the simplified model were valid. © IMechE 2014.

Brittle structures and their role in controlling porosity and permeability in a complex Precambrian crystalline-rock aquifer system in the Colorado Rocky Mountain front range

USGS Publications Warehouse

Caine, Jonathan S.; Tomusiak, S.R.A.

2003-01-01

Expansion of the Denver metropolitan area has resulted in substantial residential development in the foothills of the Rocky Mountain Front Range. This type of sub-urban growth, characteristic of much of the semiarid intermountain west, often relies on groundwater from individual domestic wells and is exemplified in the Turkey Creek watershed. The watershed is underlain by complexly deformed and fractured crystalline bedrock in which groundwater resources are poorly understood, and concerns regarding groundwater mining and degradation have arisen. As part of a pilot project to establish quantitative bounds on the groundwater resource, an outcrop-based geologic characterization and numerical modeling study of the brittle structures and their controls on the flow system was initiated. Existing data suggest that ground-water storage, flow, and contaminant transport are primarily controlled by a heterogeneous array of fracture networks. Inspections of well-permit data and field observations led to a conceptual model in which three dominant lithologic groups underlying sparse surface deposits form the aquifer system-metamorphic rocks, a complex array of granitic intrusive rocks, and major brittle fault zones. Pervasive but variable jointing of each lithologic group forms the "background" permeability structure and is an important component of the bulk storage capacity. This "background" is cut by brittle fault zones of varying structural styles and by pegmatite dikes, both with much higher fracture intensities relative to "background" that likely make them spatially complex conduits. Probabilistic, discrete-fracture-network and finite-element modeling was used to estimate porosity and permeability at the outcrop scale using fracture network data collected in the field. The models were conditioned to limited aquifer test and borehole geophysical data and give insight into the relative hydraulic properties between locations and geologic controls on storage and flow. Results from this study reveal a complex aquifer system in which the upper limits on estimated hydraulic properties suggest limited storage capacity and permeability as compared with many sedimentary-rock and surficial-deposit aquifers.

An integrated hydrological modeling approach for detection and attribution of climatic and human impacts on coastal water resources

NASA Astrophysics Data System (ADS)

Feng, Dapeng; Zheng, Yi; Mao, Yixin; Zhang, Aijing; Wu, Bin; Li, Jinguo; Tian, Yong; Wu, Xin

2018-02-01

Water resources in coastal areas can be profoundly influenced by both climate change and human activities. These climatic and human impacts are usually intertwined and difficult to isolate. This study developed an integrated model-based approach for detection and attribution of climatic and human impacts and applied this approach to the Luanhe Plain, a typical coastal area in northern China. An integrated surface water-groundwater model was developed for the study area using GSFLOW (coupled groundwater and surface-water flow). Model calibration and validation were performed for background years between 1975 and 2000. The variation in water resources between the 1980s and 1990s was then quantitatively attributed to climate variability, groundwater pumping and changes in upstream inflow. Climate scenarios for future years (2075-2100) were also developed by downscaling the projections in CMIP5. Potential water resource responses to climate change, as well as their uncertainty, were then investigated through integrated modeling. The study results demonstrated the feasibility and value of the integrated modeling-based analysis for water resource management in areas with complex surface water-groundwater interaction. Specific findings for the Luanhe Plain included the following: (1) During the historical period, upstream inflow had the most significant impact on river outflow to the sea, followed by climate variability, whereas groundwater pumping was the least influential. (2) The increase in groundwater pumping had a dominant influence on the decline in groundwater change, followed by climate variability. (3) Synergetic and counteractive effects among different impacting factors, while identified, were not significant, which implied that the interaction among different factors was not very strong in this case. (4) It is highly probable that future climate change will accelerate groundwater depletion in the study area, implying that strict regulations for groundwater pumping are imperative for adaptation.

Field Scale Groundwater Nitrate Loading Model for the Central Valley, California, 1945-Current

NASA Astrophysics Data System (ADS)

Harter, T.; Dzurella, K.; Bell, A.; Kourakos, G.

2015-12-01

Anthropogenic groundwater nitrate contamination in the Central Valley aquifer system, California, is widespread, with over 40% of domestic wells in some counties exceeding drinking water standards. Sources of groundwater nitrate include leaky municipal wastewater systems, municipal wastewater recharge, onsite wastewater treatment (septic) systems, atmospheric nitrogen deposition, animal farming, application of organic waste materials (sludge, biosolids, animal manure) to agricultural lands, and synthetic fertilizer. At the site or field scale, nitrogen inputs to the landscape are balanced by plant nitrogen uptake and harvest, atmospheric nitrogen losses, surface runoff of nitrogen, soil nitrogen storage changes, and leaching to groundwater. Irrigated agriculture is a dominant player in the Central Valley nitrogen cycle: The largest nitrogen fluxes are synthetic fertilizer and animal manure applications to cropland, crop nitrogen uptake, and groundwater nitrogen losses. We construct a historic field/parcel scale groundwater nitrogen loading model distinguishing urban and residential areas, individual animal farming areas, leaky wastewater lagoons, and approximately 50 different categories of agricultural crops. For non-agricultural landuses, groundwater nitrate loading is based on reported leaching values, animal population, and human population. For cropland, groundwater nitrate loading is computed from mass balance, taking into account diverse and historically changing management practices between different crops. Groundwater nitrate loading is estimated for 1945 to current. Significant increases in groundwater nitrate loading are associated with the expansion of synthetic fertilizer use in the 1950s to 1970s. Nitrate loading from synthetic fertilizer use has stagnated over the past 20 years due to improvements in nutrient use efficiency. However, an unbroken 60 year exponential increase in dairy production until the late 2000s has significantly impacted the nitrogen imbalance and is a significant threat to future groundwater quality in the Central Valley system. The model provides the basis for evaluating future planning scenarios to develop and assess long-term solutions for sustainable groundwater quality management.Anthropogenic groundwater nitrate contamination in the Central Valley aquifer system, California, is widespread, with over 40% of domestic wells in some counties exceeding drinking water standards. Sources of groundwater nitrate include leaky municipal wastewater systems, municipal wastewater recharge, onsite wastewater treatment (septic) systems, atmospheric nitrogen deposition, animal farming, application of organic waste materials (sludge, biosolids, animal manure) to agricultural lands, and synthetic fertilizer. At the site or field scale, nitrogen inputs to the landscape are balanced by plant nitrogen uptake and harvest, atmospheric nitrogen losses, surface runoff of nitrogen, soil nitrogen storage changes, and leaching to groundwater. Irrigated agriculture is a dominant player in the Central Valley nitrogen cycle: The largest nitrogen fluxes are synthetic fertilizer and animal manure applications to cropland, crop nitrogen uptake, and groundwater nitrogen losses. We construct a historic field/parcel scale groundwater nitrogen loading model distringuishing urban and residential areas, individual animal farming areas, leaky wastewater lagoons, and approximately 50 different categories of agricultural crops. For non-agricultural landuses, groundwater nitrate loading is based on reported leaching values, animal population, and human population. For cropland, groundwater nitrate loading is computed from mass balance, taking into account diverse and historically changing management practices between different crops. Groundwater nitrate loading is estimated for 1945 to current. Significant increases in groundwater nitrate loading are associated with the expansion of synthetic fertilizer use in the 1950s to 1970s. Nitrate loading from synthetic fertilizer use has stagnated over the past 20 years due to improvements in nutrient use efficiency. However, an unbroken 60 year exponential increase in dairy production until the late 2000s has significantly impacted the nitrogen imbalance and is a significant threat to future groundwater quality in the Central Valley system. The model provides the basis for evaluating future planning scenarios to develop and assess long-term solutions for sustainable groundwater quality management.

Using FOSM-Based Data Worth Analyses to Design Geophysical Surveys to Reduce Uncertainty in a Regional Groundwater Model Update

NASA Astrophysics Data System (ADS)

Smith, B. D.; White, J.; Kress, W. H.; Clark, B. R.; Barlow, J.

2016-12-01

Hydrogeophysical surveys have become an integral part of understanding hydrogeological frameworks used in groundwater models. Regional models cover a large area where water well data is, at best, scattered and irregular. Since budgets are finite, priorities must be assigned to select optimal areas for geophysical surveys. For airborne electromagnetic (AEM) geophysical surveys, optimization of mapping depth and line spacing needs to take in account the objectives of the groundwater models. The approach discussed here uses a first-order, second-moment (FOSM) uncertainty analyses which assumes an approximate linear relation between model parameters and observations. This assumption allows FOSM analyses to be applied to estimate the value of increased parameter knowledge to reduce forecast uncertainty. FOSM is used to facilitate optimization of yet-to-be-completed geophysical surveying to reduce model forecast uncertainty. The main objective of geophysical surveying is assumed to estimate values and spatial variation in hydrologic parameters (i.e. hydraulic conductivity) as well as map lower permeability layers that influence the spatial distribution of recharge flux. The proposed data worth analysis was applied to Mississippi Embayment Regional Aquifer Study (MERAS) which is being updated. The objective of MERAS is to assess the ground-water availability (status and trends) of the Mississippi embayment aquifer system. The study area covers portions of eight states including Alabama, Arkansas, Illinois, Kentucky, Louisiana, Mississippi, Missouri, and Tennessee. The active model grid covers approximately 70,000 square miles, and incorporates some 6,000 miles of major rivers and over 100,000 water wells. In the FOSM analysis, a dense network of pilot points was used to capture uncertainty in hydraulic conductivity and recharge. To simulate the effect of AEM flight lines, the prior uncertainty for hydraulic conductivity and recharge pilots along potential flight lines was reduced. The FOSM forecast uncertainty estimates were then recalculated and compared to the base forecast uncertainty estimates. The resulting reduction in forecast uncertainty is a measure of the effect on the model from the AEM survey. Iterations through this process, results in optimization of flight line location.

Sustainable groundwater management in California

USGS Publications Warehouse

Phillips, Steven P.; Rogers, Laurel Lynn; Faunt, Claudia

2015-12-01

The U.S. Geological Survey (USGS) uses data collection, modeling tools, and scientific analysis to help water managers plan for, and assess, hydrologic issues that can cause “undesirable results” associated with groundwater use. This information helps managers understand trends and investigate and predict effects of different groundwater-management strategies.

Forecasting the probability of future groundwater levels declining below specified low thresholds in the conterminous U.S.

USGS Publications Warehouse

Dudley, Robert W.; Hodgkins, Glenn A.; Dickinson, Jesse

2017-01-01

We present a logistic regression approach for forecasting the probability of future groundwater levels declining or maintaining below specific groundwater-level thresholds. We tested our approach on 102 groundwater wells in different climatic regions and aquifers of the United States that are part of the U.S. Geological Survey Groundwater Climate Response Network. We evaluated the importance of current groundwater levels, precipitation, streamflow, seasonal variability, Palmer Drought Severity Index, and atmosphere/ocean indices for developing the logistic regression equations. Several diagnostics of model fit were used to evaluate the regression equations, including testing of autocorrelation of residuals, goodness-of-fit metrics, and bootstrap validation testing. The probabilistic predictions were most successful at wells with high persistence (low month-to-month variability) in their groundwater records and at wells where the groundwater level remained below the defined low threshold for sustained periods (generally three months or longer). The model fit was weakest at wells with strong seasonal variability in levels and with shorter duration low-threshold events. We identified challenges in deriving probabilistic-forecasting models and possible approaches for addressing those challenges.

Effects of different boundary conditions on the simulation of groundwater flow in a multi-layered coastal aquifer system (Taranto Gulf, southern Italy)

NASA Astrophysics Data System (ADS)

De Filippis, Giovanna; Foglia, Laura; Giudici, Mauro; Mehl, Steffen; Margiotta, Stefano; Negri, Sergio L.

2017-11-01

The evaluation of the accuracy or reasonableness of numerical models of groundwater flow is a complex task, due to the uncertainties in hydrodynamic properties and boundary conditions and the scarcity of good-quality field data. To assess model reliability, different calibration techniques are joined to evaluate the effects of different kinds of boundary conditions on the groundwater flow in a coastal multi-layered aquifer in southern Italy. In particular, both direct and indirect approaches for inverse modeling were joined through the calibration of one of the most uncertain parameters, namely the hydraulic conductivity of the karst deep hydrostratigraphic unit. The methodology proposed here, and applied to a real case study, confirmed that the selection of boundary conditions is among the most critical and difficult aspects of the characterization of a groundwater system for conceptual analysis or numerical simulation. The practical tests conducted in this study show that incorrect specification of boundary conditions prevents an acceptable match between the model response to the hydraulic stresses and the behavior of the natural system. Such effects have a negative impact on the applicability of numerical modeling to simulate groundwater dynamics in complex hydrogeological situations. This is particularly important for management of the aquifer system investigated in this work, which represents the only available freshwater resource of the study area, and is threatened by overexploitation and saltwater intrusion.

Using MODFLOW drains to simulate groundwater flow in a karst environment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Quinn, J.; Tomasko, D.; Glennon, M.A.

1998-07-01

Modeling groundwater flow in a karst environment is both numerically challenging and highly uncertain because of potentially complex flowpaths and a lack of site-specific information. This study presents the results of MODFLOW numerical modeling in which drain cells in a finite-difference model are used as analogs for preferential flowpaths or conduits in karst environments. In this study, conduits in mixed-flow systems are simulated by assigning connected pathways of drain cells from the locations of tracer releases, sinkholes, or other karst features to outlet springs along inferred flowpaths. These paths are determined by the locations of losing stream segments, ephemeral streammore » beds, geophysical surveys, fracture lineaments, or other surficial characteristics, combined with the results of dye traces. The elevations of the drains at the discharge ends of the inferred flowpaths are estimated from field data and are adjusted when necessary during model calibration. To simulate flow in a free-flowing conduit, a high conductance is assigned to each drain to eliminate the need for drain-specific information that would be very difficult to obtain. Calculations were performed for a site near Hohenfels, Germany. The potentiometric surface produced by the simulations agreed well with field data. The head contours in the vicinity of the karst features behaved in a manner consistent with a flow system having both diffuse and conduit components, and the sum of the volumetric flow out of the drain cells agreed closely with spring discharges and stream flows. Because of the success of this approach, it is recommended for regional studies in which little site-specific information (e.g., location, number, size, and conductivity of fractures and conduits) is available, and general flow characteristics are desired.« less

Estimate of aquifer properties by numerically simulating ground-water/surface-water interactions, Fort Wainwright, Alaska

USGS Publications Warehouse

Nakanishi, Allen S.; Lilly, Michael R.

1998-01-01

MODFLOW, a finite-difference model of ground-water flow, was used to simulate the flow of water between the aquifer and the Chena River at Fort Wainwright, Alaska. The model was calibrated by comparing simulated ground-water hydrographs to those recorded in wells during periods of fluctuating river levels. The best fit between simulated and observed hydrographs occurred for the following: 20 feet per day for vertical hydraulic conductivity, 400 feet per day for horizontal hydraulic conductivity, 1:20 for anisotropy (vertical to horizontal hydraulic conductivity), and 350 per feet for riverbed conductance. These values include a 30 percent adjustment for geometry effects. The estimated values for hydraulic conductivities of the alluvium are based on assumed values of 0.25 for specific yield and 0.000001 per foot for specific storage of the alluvium; the values assumed for bedrock are 0.1 foot per day horizontal hydraulic conductivity, 0.005 foot per day vertical hydraulic conductivity, and 0.0000001 per foot for specific storage. The resulting diffusivity for the alluvial aquifer is 1,600 feet per day. The estimated values of these hydraulic properties are nearly proportional to the assumed value of specific yield. These values were not found to be sensitive to the assumed values for bedrock. The hydrologic parameters estimated using the cross-sectional model are only valid when taken in context with the other values (both estimated and assumed) used in this study. The model simulates horizontal and vertical flow directions near the river during periods of varying river stage. This information is useful for interpreting bank-storage effects, including the flow of contaminants in the aquifer near the river.

Hydrogeology and preliminary assessment of regional flow in the upper Cretaceous and adjacent aquifers in the northern Mississippi embayment

USGS Publications Warehouse

Brahana, J.V.; Mesko, T.O.

1988-01-01

On a regional scale, the groundwater system of the northern Mississippi embayment is composed of a series of nonindurated clastic sediments that overlie a thick sequence of Paleozoic carbonate, sandstones, and shales. The units that comprise the geohydrologic framework of this study are the alluvium-lower Wilcox Aquifer the Midway confining unit, the Upper Cretaceous aquifer, the Cretaceous-Paleozoic confining unit, and the Ozark-St. Francois aquifer. The Upper Cretaceous aquifer of Late Cretaceous age is the primary focus of this investigation; the study is part of the Gulf Coast Regional Aquifer-System Analysis. A four layer finite-difference groundwater flow model enabled testing of alternative boundary concepts and provide a refined definition of the hydrologic budget of the deep aquifers. The alluvium-lower Wilcox aquifer, the Upper Cretaceous aquifer, and the Ozark-St. Francois aquifer form layers 2 through 4, respectively. Layer 1 is an inactive layer of constant heads representing shallow water levels, which are a major control on recharge to and discharge from the regional system. A matrix of leakance values simulates each confining unit, allowing vertical interchange of water between different aquifers. The model was calibrated to 1980 conditions by using the assumption that 1980 was near steady-state conditions; it was calibrated to simulate observed heads were found to be most sensitive to pumping, and least sensitive to the leakance. By using all available water quality and water level data, alternative boundary conditions were tested by comparing model simulated heads to observed heads. The results of the early modeling effort also contribute to a better understanding of the regional hydrologic budget, indicating that: upward leakage from the Ozark-St. Francois aquifer to the Upper Cretaceous aquifer is about 43 cu ft/sec; upward recharge of about 68 cu ft/sec occurs to the lower Wilcox-alluvium aquifer from the Upper Cretaceous aquifer; and the Midway is an effective regional confining unit. (Author 's abstract)

A Hybrid MPI/OpenMP Approach for Parallel Groundwater Model Calibration on Multicore Computers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, Guoping; D'Azevedo, Ed F; Zhang, Fan

2010-01-01

Groundwater model calibration is becoming increasingly computationally time intensive. We describe a hybrid MPI/OpenMP approach to exploit two levels of parallelism in software and hardware to reduce calibration time on multicore computers with minimal parallelization effort. At first, HydroGeoChem 5.0 (HGC5) is parallelized using OpenMP for a uranium transport model with over a hundred species involving nearly a hundred reactions, and a field scale coupled flow and transport model. In the first application, a single parallelizable loop is identified to consume over 97% of the total computational time. With a few lines of OpenMP compiler directives inserted into the code,more » the computational time reduces about ten times on a compute node with 16 cores. The performance is further improved by selectively parallelizing a few more loops. For the field scale application, parallelizable loops in 15 of the 174 subroutines in HGC5 are identified to take more than 99% of the execution time. By adding the preconditioned conjugate gradient solver and BICGSTAB, and using a coloring scheme to separate the elements, nodes, and boundary sides, the subroutines for finite element assembly, soil property update, and boundary condition application are parallelized, resulting in a speedup of about 10 on a 16-core compute node. The Levenberg-Marquardt (LM) algorithm is added into HGC5 with the Jacobian calculation and lambda search parallelized using MPI. With this hybrid approach, compute nodes at the number of adjustable parameters (when the forward difference is used for Jacobian approximation), or twice that number (if the center difference is used), are used to reduce the calibration time from days and weeks to a few hours for the two applications. This approach can be extended to global optimization scheme and Monte Carol analysis where thousands of compute nodes can be efficiently utilized.« less

From local hydrological process analysis to regional hydrological model application in Benin: Concept, results and perspectives

NASA Astrophysics Data System (ADS)

Bormann, H.; Faß, T.; Giertz, S.; Junge, B.; Diekkrüger, B.; Reichert, B.; Skowronek, A.

This paper presents the concept, first results and perspectives of the hydrological sub-project of the IMPETUS-Benin project which is part of the GLOWA program funded by the German ministry of education and research. In addition to the research concept, first results on field hydrology, pedology, hydrogeology and hydrological modelling are presented, focusing on the understanding of the actual hydrological processes. For analysing the processes a 30 km 2 catchment acting as a super test site was chosen which is assumed to be representative for the entire catchment of about 15,000 km 2. First results of the field investigations show that infiltration, runoff generation and soil erosion strongly depend on land cover and land use which again influence the soil properties significantly. A conceptual hydrogeological model has been developed summarising the process knowledge on runoff generation and subsurface hydrological processes. This concept model shows a dominance of fast runoff components (surface runoff and interflow), a groundwater recharge along preferential flow paths, temporary interaction between surface and groundwater and separate groundwater systems on different scales (shallow, temporary groundwater on local scale and permanent, deep groundwater on regional scale). The findings of intensive measurement campaigns on soil hydrology, groundwater dynamics and soil erosion have been integrated into different, scale-dependent hydrological modelling concepts applied at different scales in the target region (upper Ouémé catchment in Benin, about 15,000 km 2). The models have been applied and successfully validated. They will be used for integrated scenario analyses in the forthcoming project phase to assess the impacts of global change on the regional water cycle and on typical problem complexes such as food security in West African countries.

Comparative study of irrigation water use and groundwater recharge under various irrigation schemes in an agricultural region, central Taiwan

NASA Astrophysics Data System (ADS)

Chen, Shih-Kai; Jang, Cheng-Shin; Tsai, Cheng-Bin

2016-04-01

The risk of rice production has increased notably due to climate change in Taiwan. To respond to growing agricultural water shortage without affecting normal food production in the future, the application of water-saving irrigation will be a substantial resolution. However, the adoption of water-saving irrigation may result in the reducing of groundwater recharge because continuous flooding in the paddy fields could be regarded as an important source for groundwater recharge. The aim of this study was to evaluate the irrigation water-saving benefit and groundwater recharge deficit when adopting the System of Rice Intensification, known as SRI methodology, in the Choushui River alluvial fan (the largest groundwater pumping and the most important rice-cropping region in central Taiwan). The three-dimensional finite element groundwater model, FEMWATER, was applied to simulate the infiltration process and groundwater recharge under SRI methodology and traditional irrigation schemes including continuous irrigation, and rotational irrigation in two rice-crop periods with hydro-climatic data of 2013. The irrigation water use was then calculated by water balance. The results showed that groundwater recharge amount of SRI methodology was slightly lower than those of traditional irrigation schemes, reduced 3.6% and 1.6% in the first crop period, and reduced 3.2% and 1.6% in the second crop period, compared with continuous irrigation and rotational irrigation, respectively. However, the SRI methodology achieved notably water-saving benefit compared to the disadvantage of reducing the groundwater recharge amount. The field irrigation requirement amount of SRI methodology was significantly lower than those of traditional irrigation schemes, saving 37% and 20% of irrigation water in the first crop period, and saving 53% and 35% in the second crop period, compared with continuous irrigation and rotational irrigation, respectively. Therefore, the amount of groundwater pumping for irrigation water use can be reduced when adopting the SRI methodology in the future. The reducing of groundwater recharge could be supplemented by using 1,500 hectares of fallow paddy fields, located at proximal-fan region, as recharge pools in the wet season. The adoption of water-saving irrigation would be helpful for the relevant government agency to formulate the integral water resource management strategies in this region. Keywords:Groundwater recharge, SRI, FEMWATER, Field irrigation requirement

Nonuniform grid implicit spatial finite difference method for acoustic wave modeling in tilted transversely isotropic media

NASA Astrophysics Data System (ADS)

Chu, Chunlei; Stoffa, Paul L.

2012-01-01

Discrete earth models are commonly represented by uniform structured grids. In order to ensure accurate numerical description of all wave components propagating through these uniform grids, the grid size must be determined by the slowest velocity of the entire model. Consequently, high velocity areas are always oversampled, which inevitably increases the computational cost. A practical solution to this problem is to use nonuniform grids. We propose a nonuniform grid implicit spatial finite difference method which utilizes nonuniform grids to obtain high efficiency and relies on implicit operators to achieve high accuracy. We present a simple way of deriving implicit finite difference operators of arbitrary stencil widths on general nonuniform grids for the first and second derivatives and, as a demonstration example, apply these operators to the pseudo-acoustic wave equation in tilted transversely isotropic (TTI) media. We propose an efficient gridding algorithm that can be used to convert uniformly sampled models onto vertically nonuniform grids. We use a 2D TTI salt model to demonstrate its effectiveness and show that the nonuniform grid implicit spatial finite difference method can produce highly accurate seismic modeling results with enhanced efficiency, compared to uniform grid explicit finite difference implementations.

Poroelastic Response to the 2012 Costa Rica Earthquake and the Effects on Geodetic Surface Deformation and Groundwater Fluxes

NASA Astrophysics Data System (ADS)

McCormack, K. A.; Hesse, M.

2016-12-01

Remote sensing and geodetic measurements are providing a new wealth of spatially distributed, time-series data that have the ability to improve our understanding of co-seismic rupture and post-seismic processes in subduction zones. Following a large earthquake, large-scale deformation is influenced by a myriad of post-seismic processes occurring on different spatial and temporal scales. These include continued slip on the fault plane (after-slip), a poroelastic response due to the movement of over-pressurized groundwater and viscoelastic relaxation of the underlying mantle. Often, the only means of observing these phenomena are through surface deformation measurements - either GPS or InSAR. Such tools measure the combined result of all these processes, which makes studying the effects of any single process difficult. For the 2012 Mw 7.6 Costa Rica Earthquake, we formulate a Bayesian inverse problem to infer the slip distribution on the plate interface using an elastic finite element model and GPS surface deformation measurements. From this study we identify a horseshoe-shaped rupture area surrounding a locked patch that is likely to release stress in the future. The results of our inversion are then used as an initial condition in a coupled poroelastic forward model to investigate the role of poroelastic effects on post-seismic deformation and stress transfer. We model the co-seismic pore pressure change as well as the pressure evolution and resulting deformation in the months after the earthquake. The surface permeability field is constrained by pump-test data from 526 groundwater wells throughout the study area. The results of the forward model indicate that earthquake-induced pore pressure changes dissipate quickly in most areas near the surface, resulting in relaxation of the surface in the seven to twenty days following the earthquake. Near the subducting slab interface, pore pressure changes can be an order of magnitude larger and may persist for many months after the earthquake. Dissipation of earthquake-induced pore pressure in deeper, low permeability areas manifests as surface deformation over a much longer timescale - on the order of months - which may influence the interpretation of longer timescale post-seismic deformation as purely viscoelastic relaxation.

MODFLOW-2000 Ground-Water Model?User Guide to the Subsidence and Aquifer-System Compaction (SUB) Package

USGS Publications Warehouse

Hoffmann, Jörn; Leake, S.A.; Galloway, D.L.; Wilson, Alicia M.

2003-01-01

This report documents a computer program, the Subsidence and Aquifer-System Compaction (SUB) Package, to simulate aquifer-system compaction and land subsidence using the U.S. Geological Survey modular finite-difference ground-water flow model, MODFLOW-2000. The SUB Package simulates elastic (recoverable) compaction and expansion, and inelastic (permanent) compaction of compressible fine-grained beds (interbeds) within the aquifers. The deformation of the interbeds is caused by head or pore-pressure changes, and thus by changes in effective stress, within the interbeds. If the stress is less than the preconsolidation stress of the sediments, the deformation is elastic; if the stress is greater than the preconsolidation stress, the deformation is inelastic. The propagation of head changes within the interbeds is defined by a transient, one-dimensional (vertical) diffusion equation. This equation accounts for delayed release of water from storage or uptake of water into storage in the interbeds. Properties that control the timing of the storage changes are vertical hydraulic diffusivity and interbed thickness. The SUB Package supersedes the Interbed Storage Package (IBS1) for MODFLOW, which assumes that water is released from or taken into storage with changes in head in the aquifer within a single model time step and, therefore, can be reasonably used to simulate only thin interbeds. The SUB Package relaxes this assumption and can be used to simulate time-dependent drainage and compaction of thick interbeds and confining units. The time-dependent drainage can be turned off, in which case the SUB Package gives results identical to those from IBS1. Three sample problems illustrate the usefulness of the SUB Package. One sample problem verifies that the package works correctly. This sample problem simulates the drainage of a thick interbed in response to a step change in head in the adjacent aquifer and closely matches the analytical solution. A second sample problem illustrates the effects of seasonally varying discharge and recharge to an aquifer system with a thick interbed. A third sample problem simulates a multilayered regional ground-water basin. Model input files for the third sample problem are included in the appendix.

A review of visual MODFLOW applications in groundwater modelling

NASA Astrophysics Data System (ADS)

Hariharan, V.; Shankar, M. Uma

2017-11-01

Visual MODLOW is a Graphical User Interface for the USGS MODFLOW. It is a commercial software that is popular among the hydrogeologists for its user-friendly features. The software is mainly used for Groundwater flow and contaminant transport models under different conditions. This article is intended to review the versatility of its applications in groundwater modelling for the last 22 years. Agriculture, airfields, constructed wetlands, climate change, drought studies, Environmental Impact Assessment (EIA), landfills, mining operations, river and flood plain monitoring, salt water intrusion, soil profile surveys, watershed analyses, etc., are the areas where the software has been reportedly used till the current date. The review will provide a clarity on the scope of the software in groundwater modelling and research.

3D groundwater modeling of the Upper Mega Aquifer System (Arabian Peninsula) using OpenGeoSys

NASA Astrophysics Data System (ADS)

Schulz, Stephan; Rausch, Randolf; Siebert, Christian; Michelsen, Nils; Kolditz, Olaf; Al-Saud, Mohammed I.; Schüth, Christoph

2013-04-01

Groundwater is the only relevant freshwater resource for most countries on the Arabian Peninsula. Due to almost no recharge in most of the areas a sustainable management of this resource is not possible. Nevertheless, a smart and intelligent mining of groundwater can extend its lifetime. For this purpose groundwater models can be applied as powerful management tools. In this work a 3D groundwater model for the most relevant aquifer complex on the Arabian Peninsula, the Upper Mega Aquifer System, will be setup by using OpenGeoSys. The aquifer system has an extent of approximately 1.7 Mio. km2 and comprises 12 hydrogeological units from the Lower Cretaceous to the Neogene. The model serves the purpose to understand the system better and makes it possible to calculate scenarios of different abstraction rates and places. It could also help to quantify complex water balance components like the discharge into the Arabian Gulf. In order to setup the model further research as the estimation of important sink and source terms like groundwater recharge and Sabkha evaporation will be implemented.

An evaluation of effects of groundwater exchange on nearshore habitats and water quality of western Lake Erie

USGS Publications Warehouse

Haack, Sheridan K.; Neff, Brian P.; Rosenberry, Donald O.; Savino, Jacqueline F.; Lundstrom, Scott C.

2005-01-01

Historically, the high potentiometric surface of groundwater in the Silurian/Devonian carbonate aquifer in Monroe County, MI resulted in discharge of highly mineralized, SO4-rich groundwater to the Lake Erie shoreline near both Erie State Game Area (ESGA) and Pointe Mouillee State Game Area (PMSGA). Recently, regional groundwater levels near PMSGA have been drawn down as much as 45 m below lake level in apparent response to quarry dewatering. From August to November of 2003, we conducted preliminary studies of groundwater flow dynamics and chemistry, shallow lake water chemistry, and fish and invertebrate communities at both sites. Consistent with regional observations, groundwater flow direction in the nearshore at ESGA was upward, or toward Lake Erie, and shallow nearshore groundwater chemistry was influenced by regional groundwater chemistry. In contrast, at PMSGA, the groundwater flow potential was downward and lake water, influenced by quarry discharge seeping downward into nearshore sediments, produced a different lake and shallow groundwater chemistry than at ESGA. Although the invertebrate and young fish community was similar at the two sites, taxonomic groups tolerant of degraded water quality were more prevalent at PMSGA. Sensitive taxa were more prevalent at ESGA. We propose a conceptual model, based on well-described models of groundwater/seawater interaction along coastal margins, to describe the interconnection among geologic, hydrologic, chemical, and biological processes in the different nearshore habitats of Lake Erie, and we identify processes that warrant further detailed study in the Great Lakes.

Modelling the long-term vertical dynamics of salt marshes

NASA Astrophysics Data System (ADS)

Zoccarato, Claudia; Teatini, Pietro

2017-04-01

Salt marshes are vulnerable environments hosting complex interactions between physical and biological processes with a strong influence on the dynamics of the marsh evolution. The estimation and prediction of the elevation of a salt-marsh platform is crucial to forecast the marsh growth or regression under different scenarios considering, for example, the potential climate changes. The long-term vertical dynamics of a salt marsh is predicted with the aid of an original finite-element (FE) numerical model accounting for the marsh accretion and compaction and for the variation rates of the relative sea level rise, i.e., land subsidence of the marsh basement and eustatic rise of the sea level. The accretion term considers the vertical sedimentation of organic and inorganic material over the marsh surface, whereas the compaction reflects the progressive consolidation of the porous medium under the increasing load of the overlying younger deposits. The modelling approach is based on a 2D groundwater flow simulator, which provides the pressure evolution within a compacting/accreting vertical cross-section of the marsh assuming that the groundwater flow obeys the relative Darcy's law, coupled to a 1D vertical geomechanical module following Terzaghi's principle of effective intergranular stress. Soil porosity, permeability, and compressibility may vary with the effective intergranular stress according to empirically based relationships. The model also takes into account the geometric non-linearity arising from the consideration of large solid grain movements by using a Lagrangian approach with an adaptive FE mesh. The element geometry changes in time to follow the deposit consolidation and the element number increases in time to follow the sedimentation of new material. The numerical model is tested on different realistic configurations considering the influence of (i) the spatial distribution of the sedimentation rate in relation to the distance from the marsh margin, (ii) the material heterogeneity (mineral vs organic), and (iii) different sequences and times of deposition. Additional experiments are performed to investigate the effect of a stochastic distribution of the material properties to account for the typical high variability of such ecosystems. The characteristic time spanned by the simulations is thousands of years, roughly corresponding to the Holocene.

Testing mixing models of old and young groundwater in a tropical lowland rain forest with environmental tracers

NASA Astrophysics Data System (ADS)

Solomon, D. Kip; Genereux, David P.; Plummer, L. Niel; Busenberg, Eurybiades

2010-04-01

We tested three models of mixing between old interbasin groundwater flow (IGF) and young, locally derived groundwater in a lowland rain forest in Costa Rica using a large suite of environmental tracers. We focus on the young fraction of water using the transient tracers CFC-11, CFC-12, CFC-113, SF6, 3H, and bomb 14C. We measured 3He, but 3H/3He dating is generally problematic due to the presence of mantle 3He. Because of their unique concentration histories in the atmosphere, combinations of transient tracers are sensitive not only to subsurface travel times but also to mixing between waters having different travel times. Samples fall into three distinct categories: (1) young waters that plot along a piston flow line, (2) old samples that have near-zero concentrations of the transient tracers, and (3) mixtures of 1 and 2. We have modeled the concentrations of the transient tracers using (1) a binary mixing model (BMM) of old and young water with the young fraction transported via piston flow, (2) an exponential mixing model (EMM) with a distribution of groundwater travel times characterized by a mean value, and (3) an exponential mixing model for the young fraction followed by binary mixing with an old fraction (EMM/BMM). In spite of the mathematical differences in the mixing models, they all lead to a similar conceptual model of young (0 to 10 year) groundwater that is locally derived mixing with old (>1000 years) groundwater that is recharged beyond the surface water boundary of the system.

Stream simulation in an analog model of the ground-water system on Long Island, New York

USGS Publications Warehouse

Harbaugh, Arlen W.; Getzen, Rufus T.

1977-01-01

The stream circuits of an electric analog model of the ground-water system of Long Island were modified to more accurately represent the relationahip between streamflow and ground-water levels. Assumptions for use of the revised circuits are (1) that streams are strictly gaining, and (2) that ground-water seepage into the streams is proportional to the difference between streambed elevation and the average water-table elevation near the stream. No seepage into streams occurs when ground-water levels drop below the streambed elevation. Regional simulation of the 1962-68 drought on Long Island was significantly improved by use of the revised stream circuits.

Simulation of ground-water flow and movement of the freshwater-saltwater interface in the New Jersey coastal plain

USGS Publications Warehouse

Pope, Daryll A.; Gordon, Alison D.

1999-01-01

The confined aquifers of the New Jersey Coastal Plain are sands that range in thickness from 50 to 600 feet and are separated by confining units. The confining units are composed of silts and clays that range in thickness from 500 to 1,000 feet. The aquifers are recharged by precipitation on their outcrop areas. This water then flows laterally downdip and vertically to the deeper confined aquifers. The confined aquifers ultimately discharge to the Raritan and Delaware Bays and to the Atlantic Ocean. In 1988, ground-water withdrawals from confined and unconfined New Jersey Coastal Plain aquifers were approximately 345 million gallons per day, more than 75 percent of which was pumped from the confined aquifers. These withdrawals have created large cones of depression in several Coastal Plain aquifers near populated areas, particularly in Camden and Monmouth Counties. The continued decline of water levels in confined aquifers can cause saltwater intrusion, reduce stream discharge near the outcrop areas, and threaten the quality of the ground-water supply. SHARP, a quasi-three-dimensional finite-difference computer model that can simulate freshwater and saltwater flow, was used to simulate the ground-water flow system in the New Jersey Coastal Plain, including the location and movement of the freshwater-saltwater interface in nine aquifers and eight intervening confining units. The freshwater-saltwater interface is defined as the hypothetical line seaward of which the chloride concentration is equal to or greater than 10,000 milligrams per liter. Model simulations were used to estimate the location and movement of the freshwater-saltwater interface resulting from (1) eustatic sea-level changes over the past 84,000 years, (2) ground-water withdrawals from 1896 through 1988, (3) and future ground-water withdrawals from 1988 to 2040 from Coastal Plain aquifers. Simultion results showed that the location and movement of the freshwater-saltwater interface are more dependent on the historical sea level than on the stresses imposed on the flow system by ground-water withdrawals from the Coastal Plain aquifers from 1896 to 1988. Results of a predictive simulation in which pumpage from existing wells was increased by 30 percent indicate that additional withdrawals from each of the eight confined aquifers in the Coastal Plain would broaden and deepen the existing cones of depression and result in significant drawdowns from the 1988 potentiometric surfaces. Drawdowns of 30 feet were simulated at the center of the cone of depression in the Upper, Middle, and Lower Potomac-Raritan-Magothy aquifers in Camden and Ocean Counties. Simulated drawdowns exceeded 80 feet at the center of the cone of depression in the Wenonah-Mount Laurel and Englishtown aquifers in Monmouth County. Drawdowns of 30 feet were simulated in the lower Kirkwood-Cohansey and confined Kirkwood aquifers in Cape May County. Simulation results showed that the increase in ground-water withdrawals would result in only minimal movement of the freshwater-saltwater interface by 2040, despite large drawdowns.

Benchmark model correction of monitoring system based on Dynamic Load Test of Bridge

NASA Astrophysics Data System (ADS)

Shi, Jing-xian; Fan, Jiang

2018-03-01

Structural health monitoring (SHM) is a field of research in the area, and it’s designed to achieve bridge safety and reliability assessment, which needs to be carried out on the basis of the accurate simulation of the finite element model. Bridge finite element model is simplified of the structural section form, support conditions, material properties and boundary condition, which is based on the design and construction drawings, and it gets the calculation models and the results.But according to the design and specification requirements established finite element model due to its cannot fully reflect the true state of the bridge, so need to modify the finite element model to obtain the more accurate finite element model. Based on Da-guan river crossing of Ma - Zhao highway in Yunnan province as the background to do the dynamic load test test, we find that the impact coefficient of the theoretical model of the bridge is very different from the coefficient of the actual test, and the change is different; according to the actual situation, the calculation model is adjusted to get the correct frequency of the bridge, the revised impact coefficient found that the modified finite element model is closer to the real state, and provides the basis for the correction of the finite model.

Transient deformation of karst aquifers observed by GPS: improved knowledge from Central Apennines (Italy)

NASA Astrophysics Data System (ADS)

Silverii, F.; D'Agostino, N.; Borsa, A. A.

2017-12-01

The redistribution of water masses due to temporal variations of hydrological conditions can produce observable deformation of the shallow crust. Space geodesy, e.g., GPS and InSAR, has provided a considerable improvement in terms of data accuracy and spatial and temporal resolution for the detection and investigation of this kind of deformation. In particular, in the areas where snow and water accumulate for long periods, such as aquifers, relatively high deformation (up to several millimeters) has been observed. Karst aquifers are able to store huge amounts of water and a clear deformation related to the groundwater storage variations has been observed in some regions. In a recent study we showed that the karst aquifers of Southern Apennines deform in response of seasonal and interannual variations of groundwater content, producing a visible transient signal in the time series of the surrounding GPS sites. In this work, we analyze the GPS time series and hydrological data of Central Italy, an interesting and complex area which hosts huge karst aquifers and is characterized by high seismic activity. We show that a noticeable transient signal with features similar to those of Southern Apennines affects also the time series of Central Apennines, suggesting that the large karst aquifers of this region experience a process analogue to the ones in Southern Italy. Thanks to the availability of a dense GPS network and different kinds of hydrological data (rainfall, spring discharge, groundwater level) we focus on the process causing the observed deformation. In particular, we model the observed deformation by inverting the GPS data using Green's functions for finite strain cuboid sources (Barbot et al. 2017). An enhanced understanding of the causes and implications of the highlighted deformation of karst aquifers is of primary interest for an improved management of this important water resource and for a better understanding of the possible interactions between groundwater variations, variations of pore pressure in the crust and seismicity.

Simulation of ground-water flow in the St. Peter aquifer in an area contaminated by coal-tar derivatives, St. Louis Park, Minnesota. Water Resources Investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lorenz, D.L.; Stark, J.R.

1990-01-01

A model constructed to simulate ground-water flow in part of the Prairie du Chien-Jordan and St. Peter aquifers, St. Louis Park, Minnesota, was used to test hypotheses about the movement of ground water contaminated with coal-tar derivatives and to simulate alternatives for reducing the downgradient movement of contamination in the St. Peter aquifer. The model, constructed for a previous study, was applied to simulate the effects of current ground-water withdrawals on the potentiometric surface of the St. Peter aquifer. Model simulations predict that the multiaquifer wells have the potential to limit downgradient migration of contaminants in the St. Peter aquifermore » caused by cones of depression created around the multiaquifer wells. Differences in vertical leakage to the St. Peter aquifer may exist in areas of bedrock valleys. Model simulations indicate that these differences are not likely to affect significantly the general patterns of ground-water flow.« less

3D Gaussian Beam Modeling

DTIC Science & Technology

2011-09-01

optimized building blocks such as a parallelized tri-diagonal linear solver (used in the “implicit finite differences ” and split-step Pade PE models...and Ding Lee. “A finite - difference treatment of interface conditions for the parabolic wave equation: The horizontal interface.” The Journal of the...Acoustical Society of America, 71(4):855, 1982. 3. Ding Lee and Suzanne T. McDaniel. “A finite - difference treatment of interface conditions for

Vulnerability Assessment of Groundwater Resources by Nutrient Source Apportionment to Individual Groundwater Wells: A Case Study in North Carolina

NASA Astrophysics Data System (ADS)

Ayub, R.; Obenour, D. R.; Keyworth, A. J.; Genereux, D. P.; Mahinthakumar, K.

2016-12-01

Groundwater contamination by nutrients (nitrogen and phosphorus) is a major concern in water table aquifers that underlie agricultural areas in the mid-Atlantic Coastal Plain of the United States. High nutrient concentrations leaching into shallow groundwater can lead to human health problems and eutrophication of receiving surface waters. Liquid manure from concentrated animal feeding operations (CAFOs) stored in open-air lagoons and applied to spray fields can be a significant source of nutrients to groundwater, along with septic waste. In this study, we developed a model-based methodology for source apportionment and vulnerability assessment using sparse groundwater quality sampling measurements for Duplin County, North Carolina (NC), obtained by the NC Department of Environmental Quality (NC DEQ). This model provides information relevant to management by estimating the nutrient transport through the aquifer from different sources and addressing the uncertainty of nutrient contaminant propagation. First, the zones of influence (dependent on nutrient pathways) for individual groundwater monitoring wells were identified using a two-dimensional vertically averaged groundwater flow and transport model incorporating geologic uncertainty for the surficial aquifer system. A multiple linear regression approach is then applied to estimate the contribution weights for different nutrient source types using the nutrient measurements from monitoring wells and the potential sources within each zone of influence. Using the source contribution weights and their uncertainty, a probabilistic vulnerability assessment of the study area due to nutrient contamination is performed. Knowledge of the contribution of different nutrient sources to contamination at receptor locations (e.g., private wells, municipal wells, stream beds etc.) will be helpful in planning and implementation of appropriate mitigation measures.

Methods for exploring uncertainty in groundwater management predictions

USGS Publications Warehouse

Guillaume, Joseph H. A.; Hunt, Randall J.; Comunian, Alessandro; Fu, Baihua; Blakers, Rachel S; Jakeman, Anthony J.; Barreteau, Olivier; Hunt, Randall J.; Rinaudo, Jean-Daniel; Ross, Andrew

2016-01-01

Models of groundwater systems help to integrate knowledge about the natural and human system covering different spatial and temporal scales, often from multiple disciplines, in order to address a range of issues of concern to various stakeholders. A model is simply a tool to express what we think we know. Uncertainty, due to lack of knowledge or natural variability, means that there are always alternative models that may need to be considered. This chapter provides an overview of uncertainty in models and in the definition of a problem to model, highlights approaches to communicating and using predictions of uncertain outcomes and summarises commonly used methods to explore uncertainty in groundwater management predictions. It is intended to raise awareness of how alternative models and hence uncertainty can be explored in order to facilitate the integration of these techniques with groundwater management.

Uncertainty in global groundwater storage estimates in a Total Groundwater Stress framework

PubMed Central

Richey, Alexandra S.; Thomas, Brian F.; Lo, Min‐Hui; Swenson, Sean; Rodell, Matthew

2015-01-01

Abstract Groundwater is a finite resource under continuous external pressures. Current unsustainable groundwater use threatens the resilience of aquifer systems and their ability to provide a long‐term water source. Groundwater storage is considered to be a factor of groundwater resilience, although the extent to which resilience can be maintained has yet to be explored in depth. In this study, we assess the limit of groundwater resilience in the world's largest groundwater systems with remote sensing observations. The Total Groundwater Stress (TGS) ratio, defined as the ratio of total storage to the groundwater depletion rate, is used to explore the timescales to depletion in the world's largest aquifer systems and associated groundwater buffer capacity. We find that the current state of knowledge of large‐scale groundwater storage has uncertainty ranges across orders of magnitude that severely limit the characterization of resilience in the study aquifers. Additionally, we show that groundwater availability, traditionally defined as recharge and redefined in this study as total storage, can alter the systems that are considered to be stressed versus unstressed. We find that remote sensing observations from NASA's Gravity Recovery and Climate Experiment can assist in providing such information at the scale of a whole aquifer. For example, we demonstrate that a groundwater depletion rate in the Northwest Sahara Aquifer System of 2.69 ± 0.8 km3/yr would result in the aquifer being depleted to 90% of its total storage in as few as 50 years given an initial storage estimate of 70 km3. PMID:26900184

A comparison study of two different control criteria for the real-time management of urban groundwater works.

PubMed

Bauser, G; Hendricks Franssen, Harrie-Jan; Stauffer, Fritz; Kaiser, Hans-Peter; Kuhlmann, U; Kinzelbach, W

2012-08-30

We present the comparison of two control criteria for the real-time management of a water well field. The criteria were used to simulate the operation of the Hardhof well field in the city of Zurich, Switzerland. This well field is threatened by diffuse pollution in the subsurface of the surrounding city area. The risk of attracting pollutants is higher if the pumping rates in four horizontal wells are increased, and can be reduced by increasing artificial recharge in several recharge basins and infiltration wells or by modifying the artificial recharge distribution. A three-dimensional finite elements flow model was built for the Hardhof site. The first control criterion used hydraulic head differences (Δh-criterion) to control the management of the well field and the second criterion used a path line method (%s-criterion) to control the percentage of inflowing water from the city area. Both control methods adapt the allocation of artificial recharge (AR) for given pumping rates in time. The simulation results show that (1) historical management decisions were less effective compared to the optimal control according to the two different criteria and (2) the distribution of artificial recharge calculated with the two control criteria also differ from each other with the %s-criterion giving better results compared to the Δh-criterion. The recharge management with the %s-criterion requires a smaller amount of water to be recharged. The ratio between average artificial recharge and average abstraction is 1.7 for the Δh-criterion and 1.5 for the %s-criterion. Both criteria were tested online. The methodologies were extended to a real-time control method using the Ensemble Kalman Filter method for assimilating 87 online available groundwater head measurements to update the model in real-time. The results of the operational implementation are also satisfying in regard of a reduced risk of well contamination. Copyright © 2012 Elsevier Ltd. All rights reserved.

Comparison of hybrid spectral-decomposition artificial neural network models for understanding climatic forcing of groundwater levels

NASA Astrophysics Data System (ADS)

Abrokwah, K.; O'Reilly, A. M.

2017-12-01

Groundwater is an important resource that is extracted every day because of its invaluable use for domestic, industrial and agricultural purposes. The need for sustaining groundwater resources is clearly indicated by declining water levels and has led to modeling and forecasting accurate groundwater levels. In this study, spectral decomposition of climatic forcing time series was used to develop hybrid wavelet analysis (WA) and moving window average (MWA) artificial neural network (ANN) models. These techniques are explored by modeling historical groundwater levels in order to provide understanding of potential causes of the observed groundwater-level fluctuations. Selection of the appropriate decomposition level for WA and window size for MWA helps in understanding the important time scales of climatic forcing, such as rainfall, that influence water levels. Discrete wavelet transform (DWT) is used to decompose the input time-series data into various levels of approximate and details wavelet coefficients, whilst MWA acts as a low-pass signal-filtering technique for removing high-frequency signals from the input data. The variables used to develop and validate the models were daily average rainfall measurements from five National Atmospheric and Oceanic Administration (NOAA) weather stations and daily water-level measurements from two wells recorded from 1978 to 2008 in central Florida, USA. Using different decomposition levels and different window sizes, several WA-ANN and MWA-ANN models for simulating the water levels were created and their relative performances compared against each other. The WA-ANN models performed better than the corresponding MWA-ANN models; also higher decomposition levels of the input signal by the DWT gave the best results. The results obtained show the applicability and feasibility of hybrid WA-ANN and MWA-ANN models for simulating daily water levels using only climatic forcing time series as model inputs.

Groundwater depth prediction in a shallow aquifer in north China by a quantile regression model

NASA Astrophysics Data System (ADS)

Li, Fawen; Wei, Wan; Zhao, Yong; Qiao, Jiale

2017-01-01

There is a close relationship between groundwater level in a shallow aquifer and the surface ecological environment; hence, it is important to accurately simulate and predict the groundwater level in eco-environmental construction projects. The multiple linear regression (MLR) model is one of the most useful methods to predict groundwater level (depth); however, the predicted values by this model only reflect the mean distribution of the observations and cannot effectively fit the extreme distribution data (outliers). The study reported here builds a prediction model of groundwater-depth dynamics in a shallow aquifer using the quantile regression (QR) method on the basis of the observed data of groundwater depth and related factors. The proposed approach was applied to five sites in Tianjin city, north China, and the groundwater depth was calculated in different quantiles, from which the optimal quantile was screened out according to the box plot method and compared to the values predicted by the MLR model. The results showed that the related factors in the five sites did not follow the standard normal distribution and that there were outliers in the precipitation and last-month (initial state) groundwater-depth factors because the basic assumptions of the MLR model could not be achieved, thereby causing errors. Nevertheless, these conditions had no effect on the QR model, as it could more effectively describe the distribution of original data and had a higher precision in fitting the outliers.

Simulation of ground-water flow in the Albuquerque Basin, central New Mexico, 1901-1994, with projections to 2020

USGS Publications Warehouse

Kernodle, J.M.; McAda, D.P.; Thorn, C.R.

1995-01-01

This report describes a three-dimensional finite-difference ground-water-flow model of the Santa Fe Group aquifer system in the Albuquerque Basin, which comprises the Santa Fe Group (late Oligocene to middle Pleistocene age) and overlying valley and basin-fill deposits (Pleistocene to Holocene age). The model is designed to be flexible and adaptive to new geologic and hydrologic information as it becomes available by using a geographic information system as a data-base manager to interface with the model. The aquifer system was defined and quantified in the model consistent with the current (July 1994) understanding of the structural and geohydrologic framework of the basin. Rather than putting the model through a rigorous calibration process, dis- crepancies between simulated and measured responses in hydraulic head were taken to indicate that the understanding of a local part of the aquifer system was incomplete or incorrect. The model simulates ground-water flow over an area of about 2,400 square miles to a depth of 1,730 to about 2,020 feet below the water table with 244 rows, 178 columns, and 11 layers. Of the 477,752 cells in the model, 310,376 are active. The top four model layers approximate the 80-foot thickness of alluvium in the incised and refilled valley of the Rio Grande to provide detail of the effect of ground-water withdrawals on the surface- water system. Away from the valley these four layers represent the interval within the Santa Fe Group aquifer system between the com- puted predevelopment water table and a level 80 feet below the grade of the Rio Grande. The simulations include initial condi- tions (steady-state), the 1901-1994 historical period, and four possible ground-water withdrawal scenarios from 1994 to 2020. The model indicates that for the year ending in March 1994, net surface-water loss in the basin resulting from the City of Albuquerque's ground-water withdrawal totaled about 53,000 acre- feet. The balance of the about 123,000 acre-feet of withdrawal came from aquifer storage depletion (about 67,800 acre-feet) and captured or salvaged evapotranspiration (about 2,500 acre-feet). In the four scenarios projected from 1994 to 2020, City of Albuquerque annual withdrawals ranged from about 98,700 to about 177,000 acre-feet by the year 2020. The range of resulting sur- face-water loss was from about 62,000 to about 77,000 acre-feet. The range of aquifer storage depletion was from about 33,400 to about 95,900 acre-feet. Captured evapotranspiration and drain- return flow remained nearly constant for all scenarios. From 1994 to 2020, maximum projected declines in hydraulic head in the pri- mary water-production zone of the aquifer (model layer 9) for the four scenarios ranged from 55 to 164 feet east of the Rio Grande, and from 91 to 258 feet west of the river. Average declines in a 383.7-square-mile area around Albuquerque ranged from 28 to 65 feet in the production zone for the same period.

Finite-difference modeling with variable grid-size and adaptive time-step in porous media

NASA Astrophysics Data System (ADS)

Liu, Xinxin; Yin, Xingyao; Wu, Guochen

2014-04-01

Forward modeling of elastic wave propagation in porous media has great importance for understanding and interpreting the influences of rock properties on characteristics of seismic wavefield. However, the finite-difference forward-modeling method is usually implemented with global spatial grid-size and time-step; it consumes large amounts of computational cost when small-scaled oil/gas-bearing structures or large velocity-contrast exist underground. To overcome this handicap, combined with variable grid-size and time-step, this paper developed a staggered-grid finite-difference scheme for elastic wave modeling in porous media. Variable finite-difference coefficients and wavefield interpolation were used to realize the transition of wave propagation between regions of different grid-size. The accuracy and efficiency of the algorithm were shown by numerical examples. The proposed method is advanced with low computational cost in elastic wave simulation for heterogeneous oil/gas reservoirs.

Groundwater economics: An object-oriented foundation for integrated studies of irrigated agricultural systems

NASA Astrophysics Data System (ADS)

Steward, David R.; Peterson, Jeffrey M.; Yang, Xiaoying; Bulatewicz, Tom; Herrera-Rodriguez, Mauricio; Mao, Dazhi; Hendricks, Nathan

2009-05-01

An integrated foundation is presented to study the impacts of external forcings on irrigated agricultural systems. Individually, models are presented that simulate groundwater hydrogeology and econometric farm level crop choices and irrigated water use. The natural association between groundwater wells and agricultural parcels is employed to couple these models using geographic information science technology and open modeling interface protocols. This approach is used to study the collective action problem of the common pool. Three different policies (existing, regulation, and incentive based) are studied in the semiarid grasslands overlying the Ogallala Aquifer in the central United States. Results show that while regulation using the prior appropriation doctrine and incentives using a water buy-back program may each achieve the same level of water savings across the study region, each policy has a different impact on spatial patterns of groundwater declines and farm level economic activity. This represents the first time that groundwater and econometric models of irrigated agriculture have been integrated at the well-parcel level and provides methods for scientific investigation of this coupled natural-human system. Results are useful for science to inform decision making and public policy debate.

Stochastic modeling of wetland-groundwater systems

NASA Astrophysics Data System (ADS)

Bertassello, Leonardo Enrico; Rao, P. Suresh C.; Park, Jeryang; Jawitz, James W.; Botter, Gianluca

2018-02-01

Modeling and data analyses were used in this study to examine the temporal hydrological variability in geographically isolated wetlands (GIWs), as influenced by hydrologic connectivity to shallow groundwater, wetland bathymetry, and subject to stochastic hydro-climatic forcing. We examined the general case of GIWs coupled to shallow groundwater through exfiltration or infiltration across wetland bottom. We also examined limiting case with the wetland stage as the local expression of the shallow groundwater. We derive analytical expressions for the steady-state probability density functions (pdfs) for wetland water storage and stage using few, scaled, physically-based parameters. In addition, we analyze the hydrologic crossing time properties of wetland stage, and the dependence of the mean hydroperiod on climatic and wetland morphologic attributes. Our analyses show that it is crucial to account for shallow groundwater connectivity to fully understand the hydrologic dynamics in wetlands. The application of the model to two different case studies in Florida, jointly with a detailed sensitivity analysis, allowed us to identify the main drivers of hydrologic dynamics in GIWs under different climate and morphologic conditions.

A progress report on estuary modeling by the finite-element method

USGS Publications Warehouse

Gray, William G.

1978-01-01

Various schemes are investigated for finite-element modeling of two-dimensional surface-water flows. The first schemes investigated combine finite-element spatial discretization with split-step time stepping schemes that have been found useful in finite-difference computations. Because of the large number of numerical integrations performed in space and the large sparse matrices solved, these finite-element schemes were found to be economically uncompetitive with finite-difference schemes. A very promising leapfrog scheme is proposed which, when combined with a novel very fast spatial integration procedure, eliminates the need to solve any matrices at all. Additional problems attacked included proper propagation of waves and proper specification of the normal flow-boundary condition. This report indicates work in progress and does not come to a definitive conclusion as to the best approach for finite-element modeling of surface-water problems. The results presented represent findings obtained between September 1973 and July 1976. (Woodard-USGS)

Effects of spatially distributed sectoral water management on the redistribution of water resources in an integrated water model: SECTORAL WATER MANAGEMENT IN IA-ESM

DOE Office of Scientific and Technical Information (OSTI.GOV)

Voisin, Nathalie; Hejazi, Mohamad I.; Leung, L. Ruby

To advance understanding of the interactions between human activities and the water cycle, an integrated terrestrial water cycle component has been developed for Earth system models. This includes a land surface model fully coupled to a river routing model and a generic water management model to simulate natural and regulated flows. A global integrated assessment model and its regionalized version for the U.S. are used to simulate water demand consistent with the energy technology and socio-economics scenarios. Human influence on the hydrologic cycle includes regulation and storage from reservoirs, consumptive use and withdrawal from multiple sectors ( irrigation and non-irrigation)more » and overall redistribution of water resources in space and time. As groundwater provides an important source of water supply for irrigation and other uses, the integrated modeling framework has been extended with a simplified representation of groundwater as an additional supply source, and return flow generated from differences between withdrawals and consumptive uses from both groundwater and surface water systems. The groundwater supply and return flow modules are evaluated by analyzing the simulated regulated flow, reservoir storage and supply deficit for irrigation and non-irrigation sectors over major hydrologic regions of the conterminous U.S. The modeling framework is then used to provide insights on the reliability of water resources by isolating the reliability due to return flow and/or groundwater sources of water. Our results show that high sectoral ratio of withdrawals over consumptive demand adds significant stress on the water resources management that can be alleviated by reservoir storage capacity. The return flow representation therefore exhibits a clear east-west contrast in its hydrologic signature, as well as in its ability to help meet water demand. Groundwater use has a limited hydrologic signature but the most pronounced signature is in terms of decreasing water supply deficit. The combined return flow and groundwater use signature conserves the east-west constrast with overall uncertainties due to the groundwater-return flow representation, varying ratios combined with different hydroclimate conditions, storage infrastructures, sectoral water uses and dependence on groundwater. The redistribution of surface and groundwater by human activities, and the uncertainties in their representation have important implications to the water and energy balances in the Earth system and land-atmosphere interactions.« less

Integrated Water Flow Model (IWFM), A Tool For Numerically Simulating Linked Groundwater, Surface Water And Land-Surface Hydrologic Processes

NASA Astrophysics Data System (ADS)

Dogrul, E. C.; Brush, C. F.; Kadir, T. N.

2006-12-01

The Integrated Water Flow Model (IWFM) is a comprehensive input-driven application for simulating groundwater flow, surface water flow and land-surface hydrologic processes, and interactions between these processes, developed by the California Department of Water Resources (DWR). IWFM couples a 3-D finite element groundwater flow process and 1-D land surface, lake, stream flow and vertical unsaturated-zone flow processes which are solved simultaneously at each time step. The groundwater flow system is simulated as a multilayer aquifer system with a mixture of confined and unconfined aquifers separated by semiconfining layers. The groundwater flow process can simulate changing aquifer conditions (confined to unconfined and vice versa), subsidence, tile drains, injection wells and pumping wells. The land surface process calculates elemental water budgets for agricultural, urban, riparian and native vegetation classes. Crop water demands are dynamically calculated using distributed soil properties, land use and crop data, and precipitation and evapotranspiration rates. The crop mix can also be automatically modified as a function of pumping lift using logit functions. Surface water diversions and groundwater pumping can each be specified, or can be automatically adjusted at run time to balance water supply with water demand. The land-surface process also routes runoff to streams and deep percolation to the unsaturated zone. Surface water networks are specified as a series of stream nodes (coincident with groundwater nodes) with specified bed elevation, conductance and stage-flow relationships. Stream nodes are linked to form stream reaches. Stream inflows at the model boundary, surface water diversion locations, and one or more surface water deliveries per location are specified. IWFM routes stream flows through the network, calculating groundwater-surface water interactions, accumulating inflows from runoff, and allocating available stream flows to meet specified or calculated deliveries. IWFM utilizes a very straight-forward input file structure, allowing rapid development of complex simulations. A key feature of IWFM is a new algorithm for computation of groundwater flow across element faces. Enhancements to version 3.0 include automatic time-tracking of input and output data sets, linkage with the HEC-DSS database, and dynamic crop allocation using logit functions. Utilities linking IWFM to the PEST automated calibration suite are also available. All source code, executables and documentation are available for download from the DWR web site. IWFM is currently being used to develop hydrologic simulations of California's Central Valley (C2VSIM); the west side of California's San Joaquin Valley (WESTSIM); Butte County, CA; Solano County, CA; Merced County, CA; and the Oregon side of the Walla Walla River Basin.

Modelling the removal of p-TSA (para-toluenesulfonamide) during rapid sand filtration used for drinking water treatment.

PubMed

Meffe, Raffaella; Kohfahl, Claus; Holzbecher, Ekkehard; Massmann, Gudrun; Richter, Doreen; Dünnbier, Uwe; Pekdeger, Asaf

2010-01-01

A finite element model was set-up to determine degradation rate constants for p-TSA during rapid sand filtration (RSF). Data used for the model originated from a column experiment carried out in the filter hall of a drinking water treatment plant in Berlin (Germany). Aerated abstracted groundwater was passed through a 1.6m long column-shaped experimental sand filter applying infiltration rates from 2 to 6mh(-1). Model results were fitted to measured profiles and breakthrough curves of p-TSA for different infiltration rates using both first-order reaction kinetics and Michaelis-Menten kinetics. Both approaches showed that degradation rates varied both in space and time. Higher degradation rates were observed in the upper part of the column, probably related to higher microbial activity in this zone. Measured and simulated breakthrough curves revealed an adaption phase with lower degradation rates after infiltration rates were changed, followed by an adapted phase with more elevated degradation rates. Irrespective of the mathematical approach and the infiltration rate, degradation rates were very high, probably owing to the fact that filter sands have been in operation for decades, receiving high p-TSA concentrations with the raw water.

Development of an Assessment Procedure for Seawater Intrusion Mitigation

NASA Astrophysics Data System (ADS)

Hsi Ting, F.; Yih Chi, T.

2017-12-01

The Pingtung Plain is one of the areas with extremely plentiful groundwater resources in Taiwan. Due to that the application of the water resource is restricted by significant variation of precipitation between wet and dry seasons, groundwater must be used as a recharge source to implement the insufficient surface water resource during dry seasons. In recent years, the coastal aquaculture rises, and the over withdrawn of groundwater by private well results in fast drop of groundwater level. Then it causes imbalance of groundwater supply and leads to serious seawater intrusion in the coastal areas. The purpose of this study is to develop an integrated numerical model of groundwater resources and seawater intrusion. Soil and Water Assessment Tool (SWAT), MODFLOW and MT3D models were applied to analyze the variation of the groundwater levels and salinity concentration to investigate the correlation of parameters, which are used to the model applications in order to disposal saltwater intrusion. The data of groundwater levels, pumping capacity and hydrogeological data to were collected to build an integrated numerical model. Firstly, we will collect the information of layered aquifer and the data of hydrological parameters to build the groundwater numerical model at Pingtung Plain, and identify the amount of the groundwater which flow into the sea. In order to deal with the future climate change conditions or extreme weather conditions, we will consider the recharge with groundwater model to improve the seawater intrusion problem. The integrated numerical model which describes that seawater intrusion to deep confined aquifers and shallow unsaturated aquifers. Secondly, we will use the above model to investigate the weights influenced by different factors to the amount area of seawater intrusion, and predict the salinity concentration distribution of evaluation at coastal area of Pingtung Plain. Finally, we will simulate groundwater recharge/ injection at the coastal areas in Pington Plain by above model to investigate the analysis of salinity concentration in deep aquifers and the improvement of salinity concentration in shallow aquifers. In addition, a complete plan for managing both the flooding and water resources will be instituted by scheming non-engineering adaptation strategies for homeland planning.

Optimization of ground-water withdrawal at the old O-Field area, Aberdeen Proving Ground, Maryland

USGS Publications Warehouse

Banks, William S.L.; Dillow, Jonathan J.A.

2001-01-01

The U.S. Army disposed of chemical agents, laboratory materials, and unexploded ordnance at the Old O-Field landfill at Aberdeen Proving Ground, Maryland, beginning prior to World War II and continuing until at least the 1950?s. Soil, ground water, surface water, and wetland sediments in the Old O-Field area were contaminated by the disposal of these materials. The site is in the Atlantic Coastal Plain, and is characterized by a complex series of Pleistocene and Holocene sediments formed in various fluvial, estuarine, and marine-marginal hydrogeologic environments. A previously constructed transient finite-difference ground-water-flow model was used to simulate ground-water flow and the effects of a pump-and-treat remediation system designed to prevent contaminated ground water from flowing into Watson Creek (a tidal estuary and a tributary to the Gunpowder River). The remediation system consists of 14 extraction wells located between the Old O-Field landfill and Watson Creek.Linear programming techniques were applied to the results of the flow-model simulations to identify optimal pumping strategies for the remediation system. The optimal management objective is to minimize total withdrawal from the water-table aquifer, while adhering to the following constraints: (1) ground-water flow from the landfill should be prevented from reaching Watson Creek, (2) no extraction pump should be operated at a rate that exceeds its capacity, and (3) no extraction pump should be operated at a rate below its minimum capacity, the minimum rate at which an Old O-Field pump can function. Water withdrawal is minimized by varying the rate and frequency of pumping at each of the 14 extraction wells over time. This minimizes the costs of both pumping and water treatment, thus providing the least-cost remediation alternative while simultaneously meeting all operating constraints.The optimal strategy identified using this objective and constraint set involved operating 13 of the 14 extraction wells at rates ranging from 0.4 to 4.9 gallons per minute.

Conjunctive-use optimization model and sustainable-yield estimation for the Sparta aquifer of southeastern Arkansas and north-central Louisiana

USGS Publications Warehouse

McKee, Paul W.; Clark, Brian R.; Czarnecki, John B.

2004-01-01

Conjunctive-use optimization modeling was done to assist water managers and planners by estimating the maximum amount of ground water that hypothetically could be withdrawn from wells within the Sparta aquifer indefinitely without violating hydraulic-head or stream-discharge constraints. The Sparta aquifer is largely a confined aquifer of regional importance that comprises a sequence of unconsolidated sand units that are contained within the Sparta Sand. In 2000, more than 35.4 million cubic feet per day (Mft3/d) of water were withdrawn from the aquifer by more than 900 wells, primarily for industry, municipal supply, and crop irrigation in Arkansas. Continued, heavy withdrawals from the aquifer have caused several large cones of depression, lowering hydraulic heads below the top of the Sparta Sand in parts of Union and Columbia Counties and several areas in north-central Louisiana. Problems related to overdraft in the Sparta aquifer can result in increased drilling and pumping costs, reduced well yields, and degraded water quality in areas of large drawdown. A finite-difference ground-water flow model was developed for the Sparta aquifer using MODFLOW, primarily in eastern and southeastern Arkansas and north-central Louisiana. Observed aquifer conditions in 1997 supported by numerical simulations of ground-water flow show that continued pumping at withdrawal rates representative of 1990 - 1997 rates cannot be sustained indefinitely without causing hydraulic heads to drop substantially below the top of the Sparta Sand in southern Arkansas and north-central Louisiana. Areas of ground-water levels below the top of the Sparta Sand have been designated as Critical Ground-Water Areas by the State of Arkansas. A steady-state conjunctive-use optimization model was developed to simulate optimized surface-water and ground-water withdrawals while maintaining hydraulic-head and streamflow constraints, thus determining the 'sustainable yield' for the aquifer. Initial attempts to estimate sustainable yield using simulated 1997 hydraulic heads as initial heads in Scenario 1 and 100 percent of the baseline 1990-1997 withdrawal rate as the lower specified limit in Scenario 2 led to infeasible results. Sustainable yield was estimated successfully for scenario 3 with three variations on the upper limit of withdrawal rates. Additionally, ground-water withdrawals in Union County were fixed at 35.6 percent of the baseline 1990-1997 withdrawal rate in Scenario 3. These fixed withdrawals are recognized by the Arkansas Soil and Water Conservation Commission to be sustainable as determined in a previous study. The optimized solutions maintained hydraulic heads at or above the top of the Sparta Sand (except in the outcrop areas where unconfined conditions occur) and streamflow within the outcrop areas was maintained at or above minimum levels. Scenario 3 used limits of 100, 150, and 200 percent of baseline 1990-1997 withdrawal rates for the upper specified limit on 1,119 withdrawal decision variables (managed wells) resulting in estimated sustainable yields ranging from 11.6 to 13.2 Mft3/d in Arkansas and 0.3 to 0.5 Mft3/d in Louisiana. Assuming the total 2 Conjunctive-Use Optimization Model and Sustainable-Yield Estimation for the Sparta Aquifer of Southeastern Arkansas and North-Central Louisiana water demand is equal to the baseline 1990-1997 withdrawal rates, the sustainable yields estimated from the three scenarios only provide 52 to 59 percent of the total ground-water demand for Arkansas; the remainder is defined as unmet demand that could be obtained from large, sustainable surface-water withdrawals.

Simulated effects of Lower Floridan aquifer pumping on the Upper Floridan aquifer at Pooler, Chatham County, Georgia

USGS Publications Warehouse

Cherry, Gregory S.; Clarke, John S.

2013-01-01

A revised regional groundwater-flow model was used to assess the potential effects on the Upper Floridan aquifer (UFA) of pumping the Lower Floridan aquifer (LFA) from a new well (35Q069) located at the City of Pooler in coastal Georgia near Savannah. The spatial resolution of the original regional, steady-state, groundwater-flow model was increased to incorporate detailed hydrogeologic information resulting from field investigations at Pooler and existing wells in the area. Simulation results using the U.S. Geological Survey finite-difference code MODFLOW indicated that long-term pumping at a rate of 780 gallons per minute (gal/min) from the LFA well 35Q069 would cause a maximum drawdown of about 2.52 feet (ft) in the UFA (scenario A). This maximum drawdown in the UFA was greater than the observed draw-down of 0.9 ft in the 72-hour aquifer test, but this is expected because the steady-state simulated drawdown represents long-term pumping conditions. Model results for scenario A indicate that drawdown in the UFA exceeded 1 ft over a 163-square-mile (mi2) area. Induced vertical leakage from the UFA provided about 98 percent of the water to the LFA; the area within 1 mile of the pumped well contributed about 81 percent of the water pumped. Simulated pumping changed regional water-budget components slightly and redistributed flow among model layers, namely increasing downward leakage in all layers, decreasing upward leakage in all layers above the LFA, increasing inflow to and decreasing outflow from lateral specified-head boundaries in the UA and LFA, and increasing the volume of induced recharge from the general head boundary to outcrop units. An additional two groundwater-pumping scenarios were run to establish that a linear relation exists between pumping rates of the LFA well 35Q069 (varied from 390 to 1,042 gal/min) and amount of drawdown in the UFA and LFA. Three groundwater-pumping scenarios were run to evaluate the amount of UFA pumping (128 to 340 gal/min) that would produce maximum drawdown in the UFA equivalent to that induced by pumping the LFA well 35Q069 at rates specified in scenarios A, B, and C (390 to 1,042 gal/min). Scenarios in which the LFA well 35Q069 was pumped produced a larger drawdown area in the UFA than scenarios in which the UFA well was pumped to offset the maximum UFA drawdown simulated by scenarios A, B, and C. Three additional groundwater-pumping scenarios were run to evaluate the combination of pumping reductions at existing Pooler UFA public-supply wells with the addition of pumping from the new LFA well. For each scenario, LFA well 35Q069 was pumped at different rates, and pumping at existing Pooler supply wells, located about 3.7 miles northward, was reduced according to UFA drawdown offsets (128 to 340 gal/min) established by scenarios D, E, and F. Decreases in the magnitude and areal extent of drawdown in the UFA in response to pumping the LFA well were realized for scenarios that simulated drawdown offsets (reductions) for the existing UFA wells at Pooler when compared with the magnitude and extent of drawdown resulting from scenarios that did not simulate drawdown offsets for the existing UFA wells at Pooler (scenarios A, B, and C). The revised model was evaluated for sensitivity by altering horizontal and vertical hydraulic conductivity in layers 5 through 7 (Floridan aquifer system) for newly established hydraulic-property zones by factors of 0.1, 0.5, 2.0, and 10.0. Results of the sensitivity analysis indicate that horizontal and vertical hydraulic conductivity of the UFA and LFA are the most important parameters in model simulations. The least sensitive parameters were the horizontal and vertical hydraulic conductivity of the Lower Floridan confining unit; changes to these parameters had little effect on simulated leakage and groundwater levels. The revised model reasonably depicts changes in groundwater levels resulting from pumping the LFA at Pooler at a rate of 780 gal/min. However, results are limited by the same model assumptions and design as the original model and placement of boundaries and type of boundary used exert the greatest control on overall groundwater flow and interaquifer leakage in the system. Simulation results have improved regional characterization of the Floridan aquifer system, which could be used by State officials in evaluating requests for groundwater withdrawal from the LFA.

Feedbacks Between Shallow Groundwater Dynamics and Surface Topography on Runoff Generation in Flat Fields

NASA Astrophysics Data System (ADS)

Appels, Willemijn M.; Bogaart, Patrick W.; van der Zee, Sjoerd E. A. T. M.

2017-12-01

In winter, saturation excess (SE) ponding is observed regularly in temperate lowland regions. Surface runoff dynamics are controlled by small topographical features that are unaccounted for in hydrological models. To better understand storage and routing effects of small-scale topography and their interaction with shallow groundwater under SE conditions, we developed a model of reduced complexity to investigate SE runoff generation, emphasizing feedbacks between shallow groundwater dynamics and mesotopography. The dynamic specific yield affected unsaturated zone water storage, causing rapid switches between negative and positive head and a flatter groundwater mound than predicted by analytical agrohydrological models. Accordingly, saturated areas were larger and local groundwater fluxes smaller than predicted, leading to surface runoff generation. Mesotopographic features routed water over larger distances, providing a feedback mechanism that amplified changes to the shape of the groundwater mound. This in turn enhanced runoff generation, but whether it also resulted in runoff events depended on the geometry and location of the depressions. Whereas conditions favorable to runoff generation may abound during winter, these feedbacks profoundly reduce the predictability of SE runoff: statistically identical rainfall series may result in completely different runoff generation. The model results indicate that waterlogged areas in any given rainfall event are larger than those predicted by current analytical groundwater models used for drainage design. This change in the groundwater mound extent has implications for crop growth and damage assessments.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Friedrichs, D.R.; Cole, C.R.; Arnett, R.C.

The Hanford Pathline Calculational Program (HPCP) is a numerical model developed to predict the movement of fluid particles from one location to another within the Hanford or similar groundwater systems. As such it can be considered a simple transport model wherein only advective changes are considered. Application of the numerical HPCP to test cases for which semianalytical results are obtainable showed that with reasonable time steps and the grid spacing requirements HPCP give good agreement with the semianalytical solution. The accuracy of the HPCP results is most sensitive in areas near steep or rapidly changing potential gradients and may requiremore » finer grid spacing in those areas than for the groundwater system as a whole. Initial applications of HPCP to the Hanford groundwater flow regime show that significant differences (improvements) in the predictions of fluid particle movement are obtainable with the pathline approach (changing groundwater potential or water table surface) as opposed to the streamline approach (unchanging potential or water table surface) used in past Hanford groundwater analyses. This report documents capability developed for estimating groundwater travel times from the Hanford high-level waste areas to the Columbia River at different water table levels.« less

Application of finite element approach to transonic flow problems

NASA Technical Reports Server (NTRS)

Hafez, M. M.; Murman, E. M.; Wellford, L. C., Jr.

1976-01-01

A variational finite element model for transonic small disturbance calculations is described. Different strategy is adopted in subsonic and supersonic regions, and blending elements are introduced between different regions. In the supersonic region, no upstream effect is allowed. If rectangular elements with linear shape functions are used, the model is similar to Murman's finite difference operators. Higher order shape functions, nonrectangular elements, and discontinuous approximation of shock waves are also discussed.

Modeling Effects of Groundwater Basin Closure, and Reversal of Closure, on Groundwater Quality

NASA Astrophysics Data System (ADS)

Pauloo, R.; Guo, Z.; Fogg, G. E.

2017-12-01

Population growth, the expansion of agriculture, and climate uncertainties have accelerated groundwater pumping and overdraft in aquifers worldwide. In many agricultural basins, a water budget may be stable or not in overdraft, yet disconnected ground and surface water bodies can contribute to the formation of a "closed" basin, where water principally exits the basin as evapotranspiration. Although decreasing water quality associated with increases in Total Dissolved Solids (TDS) have been documented in aquifers across the United States in the past half century, connections between water quality declines and significant changes in hydrologic budgets leading to closed basin formation remain poorly understood. Preliminary results from an analysis with a regional-scale mixing model of the Tulare Lake Basin in California indicate that groundwater salinization resulting from open to closed basin conversion can operate on a decades-to-century long time scale. The only way to reverse groundwater salinization caused by basin closure is to refill the basin and change the hydrologic budget sufficiently for natural groundwater discharge to resume. 3D flow and transport modeling, including the effects of heterogeneity based on a hydrostratigraphic facies model, is used to explore rates and time scales of groundwater salinization and its reversal under different water and land management scenarios. The modeling is also used to ascertain the extent to which local and regional heterogeneity need to be included in order to appropriately upscale the advection-dispersion equation in a basin scale groundwater quality management model. Results imply that persistent managed aquifer recharge may slow groundwater salinization, and complete reversal may be possible at sufficiently high water tables.

The effectiveness of element downsizing on a three-dimensional finite element model of bone trabeculae in implant biomechanics.

PubMed

Sato, Y; Wadamoto, M; Tsuga, K; Teixeira, E R

1999-04-01

More validity of finite element analysis in implant biomechanics requires element downsizing. However, excess downsizing needs computer memory and calculation time. To investigate the effectiveness of element downsizing on the construction of a three-dimensional finite element bone trabeculae model, with different element sizes (600, 300, 150 and 75 microm) models were constructed and stress induced by vertical 10 N loading was analysed. The difference in von Mises stress values between the models with 600 and 300 microm element sizes was larger than that between 300 and 150 microm. On the other hand, no clear difference of stress values was detected among the models with 300, 150 and 75 microm element sizes. Downsizing of elements from 600 to 300 microm is suggested to be effective in the construction of a three-dimensional finite element bone trabeculae model for possible saving of computer memory and calculation time in the laboratory.

Estimation of groundwater use for a groundwater-flow model of the Lake Michigan Basin and adjacent areas, 1864-2005

USGS Publications Warehouse

Buchwald, Cheryl A.; Luukkonen, Carol L.; Rachol, Cynthia M.

2010-01-01

The U.S. Geological Survey, at the request of Congress, is assessing the availability and use of the Nation's water resources to help characterize how much water is available now, how water availability is changing, and how much water can be expected to be available in the future. The Great Lakes Basin Pilot project of the U.S. Geological Survey national assessment of water availability and use focused on the Great Lakes Basin and included detailed studies of the processes governing water availability in the Great Lakes Basin. One of these studies included the development of a groundwater-flow model of the Lake Michigan Basin. This report describes the compilation and estimation of the groundwater withdrawals in those areas in Wisconsin, Michigan, Indiana, and Illinois that were needed for the Lake Michigan Basin study groundwater-flow model. These data were aggregated for 12 model time intervals spanning 1864 to 2005 and were summarized by model area, model subregion, category of water use, aquifer system, aquifer type, and hydrogeologic unit model layer. The types and availability of information on groundwater withdrawals vary considerably among states because water-use programs often differ in the types of data collected and in the methods and frequency of data collection. As a consequence, the methods used to estimate and verify the data also vary. Additionally, because of the different sources of data and different terminologies applied for the purposes of this report, the water-use data published in this report may differ from water-use data presented in other reports. These data represent only a partial estimate of groundwater use in each state because estimates were compiled only for areas in Wisconsin, Michigan, Indiana, and Illinois within the Lake Michigan Basin model area. Groundwater-withdrawal data were compiled for both nearfield and farfield model areas in Wisconsin and Illinois, whereas these data were compiled primarily for the nearfield model area in Michigan and Indiana. Overall water use for the selected areas in Wisconsin, Michigan, Indiana, and Illinois was less during early time intervals than during more recent intervals, with large increases beginning around the 1960s. Total estimated groundwater withdrawals for model input range from 18.01 million gallons per day (Mgal/d) for interval 1 (1864-1900) to 1,280.25 Mgal/d for interval 12 (2001-5). Withdrawals for the public-supply category make up the majority of the withdrawals in each of the four states. In Wisconsin and Michigan, the second largest withdrawals are for the irrigation category; in Indiana and Illinois, industrial withdrawals account for the second largest withdrawal amounts. The smallest withdrawals are for miscellaneous uses in Wisconsin and irrigation uses in Indiana and Illinois. Estimated groundwater withdrawals in the Southern Lower Peninsula of Michigan, Northeastern Illinois, and the farfield model area are generally larger than in the other model subregions. Withdrawals in Michigan and Indiana are predominantly from the Quaternary aquifer system, whereas withdrawals in Illinois are predominantly from the Cambrian-Ordovician aquifer systems. Withdrawals in Wisconsin are about equal from the Quaternary and Cambrian-Ordovician aquifer systems. Estimated groundwater withdrawals in Michigan and Indiana are predominantly from the unconfined unconsolidated aquifer type. Withdrawals in Illinois are largely from the deep confined bedrock aquifer type, although they decreased considerably in more recent time intervals. Wisconsin withdrawals are about equal from unconfined unconsolidated and deep confined bedrock aquifer types. Groundwater-withdrawal estimates in Wisconsin were compiled for the 47 easternmost counties within the boundary of the Lake Michigan Basin model, of which 32 counties, though not entirely contained, are at least partly within the Lake Michigan Basin. Overall, 6,457 withdrawal locations were estima

Estimating ground-water inflow to lakes in central Florida using the isotope mass-balance approach

USGS Publications Warehouse

Sacks, Laura A.

2002-01-01

The isotope mass-balance approach was used to estimate ground-water inflow to 81 lakes in the central highlands and coastal lowlands of central Florida. The study area is characterized by a subtropical climate and numerous lakes in a mantled karst terrain. Ground-water inflow was computed using both steady-state and transient formulations of the isotope mass-balance equation. More detailed data were collected from two study lakes, including climatic, hydrologic, and isotopic (hydrogen and oxygen isotope ratio) data. For one of these lakes (Lake Starr), ground-water inflow was independently computed from a water-budget study. Climatic and isotopic data collected from the two lakes were similar even though they were in different physiographic settings about 60 miles apart. Isotopic data from all of the study lakes plotted on an evaporation trend line, which had a very similar slope to the theoretical slope computed for Lake Starr. These similarities suggest that data collected from the detailed study lakes can be extrapolated to the rest of the study area. Ground-water inflow computed using the isotope mass-balance approach ranged from 0 to more than 260 inches per year (or 0 to more than 80 percent of total inflows). Steady-state and transient estimates of ground-water inflow were very similar. Computed ground-water inflow was most sensitive to uncertainty in variables used to calculate the isotopic composition of lake evaporate (isotopic compositions of lake water and atmospheric moisture and climatic variables). Transient results were particularly sensitive to changes in the isotopic composition of lake water. Uncertainty in ground-water inflow results is considerably less for lakes with higher ground-water inflow than for lakes with lower ground-water inflow. Because of these uncertainties, the isotope mass-balance approach is better used to distinguish whether ground-water inflow quantities fall within certain ranges of values, rather than for precise quantification. The lakes fit into three categories based on their range of ground-water inflow: low (less than 25 percent of total inflows), medium (25-50 percent of inflows), and high (greater than 50 percent of inflows). The majority of lakes in the coastal lowlands had low ground-water inflow, whereas the majority of lakes in the central highlands had medium to high ground-water inflow. Multiple linear regression models were used to predict ground-water inflow to lakes. These models help identify basin characteristics that are important in controlling ground-water inflow to Florida lakes. Significant explanatory variables include: ratio of basin area to lake surface area, depth to the Upper Floridan aquifer, maximum lake depth, and fraction of wetlands in the basin. Models were improved when lake water-quality data (nitrate, sodium, and iron concentrations) were included, illustrating the link between ground-water geochemistry and lake chemistry. Regression models that considered lakes within specific geographic areas were generally poorer than models for the entire study area. Regression results illustrate how more simplified models based on basin and lake characteristics can be used to estimate ground-water inflow. Although the uncertainty in the amount of ground-water inflow to individual lakes is high, the isotope mass-balance approach was useful in comparing the range of ground-water inflow for numerous Florida lakes. Results were also helpful in understanding differences in the geographic distribution of ground-water inflow between the coastal lowlands and central highlands. In order to use the isotope mass-balance approach to estimate inflow for multiple lakes, it is essential that all the lakes are sampled during the same time period and that detailed isotopic, hydrologic, and climatic data are collected over this same period of time. Isotopic data for Florida lakes can change over time, both seasonally and interannually, primarily because of differ

Application of a fully integrated surface-subsurface physically based flow model for evaluating groundwater recharge from a flash flood event

NASA Astrophysics Data System (ADS)

Pino, Cristian; Herrera, Paulo; Therrien, René

2017-04-01

In many arid regions around the world groundwater recharge occurs during flash floods. This transient spatially and temporally concentrated flood-recharge process takes place through the variably saturated zone between surface and usually the deep groundwater table. These flood events are characterized by rapid and extreme changes in surface flow depth and velocity and soil moisture conditions. Infiltration rates change over time controlled by the hydraulic gradients and the unsaturated hydraulic conductivity at the surface-subsurface interface. Today is a challenge to assess the spatial and temporal distribution of groundwater recharge from flash flood events under real field conditions at different scales in arid areas. We apply an integrated surface-subsurface variably saturated physically-based flow model at the watershed scale to assess the recharge process during and after a flash flood event registered in an arid fluvial valley in Northern Chile. We are able to reproduce reasonably well observed groundwater levels and surface flow discharges during and after the flood with a calibrated model. We also investigate the magnitude and spatio-temporal distribution of recharge and the response of the system to variations of different surface and subsurface parameters, initial soil moisture content and groundwater table depths and surface flow conditions. We demonstrate how an integrated physically based model allows the exploration of different spatial and temporal system states, and that the analysis of the results of the simulations help us to improve our understanding of the recharge processes in similar type of systems that are common to many arid areas around the world.

A model-averaging method for assessing groundwater conceptual model uncertainty.

PubMed

Ye, Ming; Pohlmann, Karl F; Chapman, Jenny B; Pohll, Greg M; Reeves, Donald M

2010-01-01

This study evaluates alternative groundwater models with different recharge and geologic components at the northern Yucca Flat area of the Death Valley Regional Flow System (DVRFS), USA. Recharge over the DVRFS has been estimated using five methods, and five geological interpretations are available at the northern Yucca Flat area. Combining the recharge and geological components together with additional modeling components that represent other hydrogeological conditions yields a total of 25 groundwater flow models. As all the models are plausible given available data and information, evaluating model uncertainty becomes inevitable. On the other hand, hydraulic parameters (e.g., hydraulic conductivity) are uncertain in each model, giving rise to parametric uncertainty. Propagation of the uncertainty in the models and model parameters through groundwater modeling causes predictive uncertainty in model predictions (e.g., hydraulic head and flow). Parametric uncertainty within each model is assessed using Monte Carlo simulation, and model uncertainty is evaluated using the model averaging method. Two model-averaging techniques (on the basis of information criteria and GLUE) are discussed. This study shows that contribution of model uncertainty to predictive uncertainty is significantly larger than that of parametric uncertainty. For the recharge and geological components, uncertainty in the geological interpretations has more significant effect on model predictions than uncertainty in the recharge estimates. In addition, weighted residuals vary more for the different geological models than for different recharge models. Most of the calibrated observations are not important for discriminating between the alternative models, because their weighted residuals vary only slightly from one model to another.

Comparison of the results of different scale hydrogeological models on a terraced slope of Valtellina (Northern Italy)

NASA Astrophysics Data System (ADS)

Camera, C.; Apuani, T.; Masetti, M.; Mele, M.

2012-04-01

The aim of this work was to understand and reproduce the hydrological dynamics of a slope that is terraced by dry-stone retaining walls. At first, the processes of interest were analyzed with a classical 2D unsaturated-saturated finite elements analysis, reproducing the geometry of a single terrace. In a second moment, a raster analysis at the slope scale was performed. The studied slope is located in Valtellina (Northern Italy), near the village of Tresenda, and in the last 30 years it experienced several soil slip/debris flow events that in 1983 caused 18 victims. Direct observation of the events of 1983 permitted to recognize the principal triggering cause of these events in the formation of an overpressure at the base of a dry-stone wall, that caused its failure. Using field tests and monitoring activity as input and calibration data respectively, the 2D model is able to explain the mechanisms of rainfall infiltration that can lead to the formation and evolution of a perched groundwater table at the contact between the bedrock and the walls backfill soil. Once calibrated and validated the model has been used to investigate the influence of different parameters on the studied processes, such as walls height, bedrock slope angle, and changes of both isotropic and anisotropic saturated hydraulic conductivity of soil and wall. From this sensitivity analysis, one of the most interesting results is the ability of the model to well differentiate the behaviour of a well maintained wall with an higher hydraulic conductivity than soil, from a poorly maintained wall that has lost part of its drainage capacity. In fact, only in this latter circumstance significant pore-water pressures can form at the base of the retaining structure. Moving the problem to the slope scale, although the used raster-model takes into account both the unsaturated and saturated components of flux as the 2D model, it is less precise in the description of the processes involved in the formation of the perched groundwater table. Nevertheless, the raster model is able to identify preferential infiltration zones. Moreover, it is rather precise in the prediction of the maximum groundwater levels, furnishing a valid input for a successive distributed stability analysis, that can be useful for civil protection purposes. The two models are complementary. The distributed model alone does not permit to well understand the role of all the parameters involved in the processes analyzed, while for a profitable predictive use of the acquired knowledge the 2D model needs to be assisted by the raster one.

Explicit modeling of groundwater-surface water interactions using a simple bucket-type model

NASA Astrophysics Data System (ADS)

Staudinger, Maria; Carlier, Claire; Brunner, Philip; Seibert, Jan

2017-04-01

Longer dry spells can become critical for water supply and groundwater dependent ecosystems. During these dry spells groundwater is often the most relevant source for streams. Hence, the hydrological behavior of a catchment is often dominated by groundwater surface water interactions, which can vary considerably in space and time. While classical hydrological approaches hardly consider this spatial dependence, quantitative, hydrogeological modeling approaches can couple surface runoff processes and groundwater processes. Hydrogeological modeling can help to gain an improved understanding of catchment processes during low flow. However, due to their complex parametrization and large computational requirements, such hydrogeological models are difficult to employ at catchment scale, particularly for a larger set of catchments. Then bucket-type hydrological models remain a practical alternative. In this study we combine the strengths of both the hydrogeological and bucket-type hydrological models to better understand low flow processes and ultimately to use this knowledge for low flow projections. Bucket-type hydrological models have traditionally not been developed with focus on the simulation of low flow. One consequence is that interactions between surface and groundwater are not explicitly considered. Water fluxes in bucket-type hydrological models are commonly simulated only in one direction, namely from the groundwater to the stream but not from the stream to the groundwater. This latter flux, however, can become more important during low flow situations. We therefore further developed the bucket-type hydrological model HBV to simulate low flow situations by allowing for exchange in both directions i.e. also from the stream to the groundwater. The additional HBV exchange box is developed by using a variety of synthetic hydrogeological models as training set that were generated using a fully coupled, physically based hydrogeological model. In this way processes that occur in different spatial settings within the catchment are translated to functional relationships and effective parameter values for the conceptual exchange box can be extracted. Here, we show the development and evaluation of the HBV exchange box. We further show a first application in real catchments and evaluate the model performance by comparing the simulations to benchmark models that do not consider groundwater surface water interaction.

Improving catchment discharge predictions by inferring flow route contributions from a nested-scale monitoring and model setup

NASA Astrophysics Data System (ADS)

van der Velde, Y.; Rozemeijer, J. C.; de Rooij, G. H.; van Geer, F. C.; Torfs, P. J. J. F.; de Louw, P. G. B.

2011-03-01

Identifying effective measures to reduce nutrient loads of headwaters in lowland catchments requires a thorough understanding of flow routes of water and nutrients. In this paper we assess the value of nested-scale discharge and groundwater level measurements for the estimation of flow route volumes and for predictions of catchment discharge. In order to relate field-site measurements to the catchment-scale an upscaling approach is introduced that assumes that scale differences in flow route fluxes originate from differences in the relationship between groundwater storage and the spatial structure of the groundwater table. This relationship is characterized by the Groundwater Depth Distribution (GDD) curve that relates spatial variation in groundwater depths to the average groundwater depth. The GDD-curve was measured for a single field site (0.009 km2) and simple process descriptions were applied to relate groundwater levels to flow route discharges. This parsimonious model could accurately describe observed storage, tube drain discharge, overland flow and groundwater flow simultaneously with Nash-Sutcliff coefficients exceeding 0.8. A probabilistic Monte Carlo approach was applied to upscale field-site measurements to catchment scales by inferring scale-specific GDD-curves from the hydrographs of two nested catchments (0.4 and 6.5 km2). The estimated contribution of tube drain effluent (a dominant source for nitrates) decreased with increasing scale from 76-79% at the field-site to 34-61% and 25-50% for both catchment scales. These results were validated by demonstrating that a model conditioned on nested-scale measurements improves simulations of nitrate loads and predictions of extreme discharges during validation periods compared to a model that was conditioned on catchment discharge only.

Particle swarm optimization based artificial neural network model for forecasting groundwater level in Udupi district

NASA Astrophysics Data System (ADS)

Balavalikar, Supreetha; Nayak, Prabhakar; Shenoy, Narayan; Nayak, Krishnamurthy

2018-04-01

The decline in groundwater is a global problem due to increase in population, industries, and environmental aspects such as increase in temperature, decrease in overall rainfall, loss of forests etc. In Udupi district, India, the water source fully depends on the River Swarna for drinking and agriculture purposes. Since the water storage in Bajae dam is declining day-by-day and the people of Udupi district are under immense pressure due to scarcity of drinking water, alternatively depend on ground water. As the groundwater is being heavily used for drinking and agricultural purposes, there is a decline in its water table. Therefore, the groundwater resources must be identified and preserved for human survival. This research proposes a data driven approach for forecasting the groundwater level. The monthly variations in groundwater level and rainfall data in three observation wells located in Brahmavar, Kundapur and Hebri were investigated and the scenarios were examined for 2000-2013. The focus of this research work is to develop an ANN based groundwater level forecasting model and compare with hybrid ANN-PSO forecasting model. The model parameters are tested using different combinations of the data. The results reveal that PSO-ANN based hybrid model gives a better prediction accuracy, than ANN alone.

A stochastic optimization model under modeling uncertainty and parameter certainty for groundwater remediation design--part I. Model development.

PubMed

He, L; Huang, G H; Lu, H W

2010-04-15

Solving groundwater remediation optimization problems based on proxy simulators can usually yield optimal solutions differing from the "true" ones of the problem. This study presents a new stochastic optimization model under modeling uncertainty and parameter certainty (SOMUM) and the associated solution method for simultaneously addressing modeling uncertainty associated with simulator residuals and optimizing groundwater remediation processes. This is a new attempt different from the previous modeling efforts. The previous ones focused on addressing uncertainty in physical parameters (i.e. soil porosity) while this one aims to deal with uncertainty in mathematical simulator (arising from model residuals). Compared to the existing modeling approaches (i.e. only parameter uncertainty is considered), the model has the advantages of providing mean-variance analysis for contaminant concentrations, mitigating the effects of modeling uncertainties on optimal remediation strategies, offering confidence level of optimal remediation strategies to system designers, and reducing computational cost in optimization processes. 2009 Elsevier B.V. All rights reserved.

A comparison of data-driven groundwater vulnerability assessment methods

USGS Publications Warehouse

Sorichetta, Alessandro; Ballabio, Cristiano; Masetti, Marco; Robinson, Gilpin R.; Sterlacchini, Simone

2013-01-01

Increasing availability of geo-environmental data has promoted the use of statistical methods to assess groundwater vulnerability. Nitrate is a widespread anthropogenic contaminant in groundwater and its occurrence can be used to identify aquifer settings vulnerable to contamination. In this study, multivariate Weights of Evidence (WofE) and Logistic Regression (LR) methods, where the response variable is binary, were used to evaluate the role and importance of a number of explanatory variables associated with nitrate sources and occurrence in groundwater in the Milan District (central part of the Po Plain, Italy). The results of these models have been used to map the spatial variation of groundwater vulnerability to nitrate in the region, and we compare the similarities and differences of their spatial patterns and associated explanatory variables. We modify the standard WofE method used in previous groundwater vulnerability studies to a form analogous to that used in LR; this provides a framework to compare the results of both models and reduces the effect of sampling bias on the results of the standard WofE model. In addition, a nonlinear Generalized Additive Model has been used to extend the LR analysis. Both approaches improved discrimination of the standard WofE and LR models, as measured by the c-statistic. Groundwater vulnerability probability outputs, based on rank-order classification of the respective model results, were similar in spatial patterns and identified similar strong explanatory variables associated with nitrate source (population density as a proxy for sewage systems and septic sources) and nitrate occurrence (groundwater depth).

The Heterogeneous Impacts of Groundwater Management Policies in the Republican River Basin of Colorado

NASA Astrophysics Data System (ADS)

Hrozencik, R. A.; Manning, D. T.; Suter, J. F.; Goemans, C.; Bailey, R. T.

2017-12-01

Groundwater is a critical input to agricultural production across the globe. Current groundwater pumping rates frequently exceed recharge, often by a substantial amount, leading to groundwater depletion and potential declines in agricultural profits over time. As a result, many regions reliant on irrigated agriculture have proposed policies to manage groundwater use. Even when gains from aquifer management exist, there is little information about how policies affect individual producers sharing the resource. In this paper, we investigate the variability of groundwater management policy impacts across heterogeneous agricultural producers. To measure these impacts, we develop a hydroeconomic model that captures the important role of well capacity, productivity of water, and weather uncertainty. We use the model to simulate the impacts of groundwater management policies on producers in the High Plains aquifer of eastern Colorado and compare outcomes to a no-policy baseline. The management policies considered include a pumping fee, a quantity restriction, and an irrigated acreage fee. We find that well capacity and soil type affect policy impacts but in ways that can qualitatively differ across policy type. Model results have important implications for the distributional impacts and political acceptability of groundwater management policies.

Finite-Difference Lattice Boltzmann Scheme for High-Speed Compressible Flow: Two-Dimensional Case

NASA Astrophysics Data System (ADS)

Gan, Yan-Biao; Xu, Ai-Guo; Zhang, Guang-Cai; Zhang, Ping; Zhang, Lei; Li, Ying-Jun

2008-07-01

Lattice Boltzmann (LB) modeling of high-speed compressible flows has long been attempted by various authors. One common weakness of most of previous models is the instability problem when the Mach number of the flow is large. In this paper we present a finite-difference LB model, which works for flows with flexible ratios of specific heats and a wide range of Mach number, from 0 to 30 or higher. Besides the discrete-velocity-model by Watari [Physica A 382 (2007) 502], a modified Lax Wendroff finite difference scheme and an artificial viscosity are introduced. The combination of the finite-difference scheme and the adding of artificial viscosity must find a balance of numerical stability versus accuracy. The proposed model is validated by recovering results of some well-known benchmark tests: shock tubes and shock reflections. The new model may be used to track shock waves and/or to study the non-equilibrium procedure in the transition between the regular and Mach reflections of shock waves, etc.

Landform features and seasonal precipitation predict shallow groundwater influence on temperature in headwater streams

NASA Astrophysics Data System (ADS)

Johnson, Zachary C.; Snyder, Craig D.; Hitt, Nathaniel P.

2017-07-01

Headwater stream responses to climate change will depend in part on groundwater-surface water exchanges. We used linear modeling techniques to partition likely effects of shallow groundwater seepage and air temperature on stream temperatures for 79 sites in nine focal watersheds using hourly air and water temperature measurements collected during summer months from 2012 to 2015 in Shenandoah National Park, Virginia, USA. Shallow groundwater effects exhibited more variation within watersheds than between them, indicating the importance of reach-scale assessments and the limited capacity to extrapolate upstream groundwater influences from downstream measurements. Boosted regression tree (BRT) models revealed intricate interactions among geomorphological landform features (stream slope, elevation, network length, contributing area, and channel confinement) and seasonal precipitation patterns (winter, spring, and summer months) that together were robust predictors of spatial and temporal variation in groundwater influence on stream temperatures. The final BRT model performed well for training data and cross-validated samples (correlation = 0.984 and 0.760, respectively). Geomorphological and precipitation predictors of groundwater influence varied in their importance between watersheds, suggesting differences in spatial and temporal controls of recharge dynamics and the depth of the groundwater source. We demonstrate an application of the final BRT model to predict groundwater effects from landform and precipitation covariates at 1075 new sites distributed at 100 m increments within focal watersheds. Our study provides a framework to estimate effects of groundwater seepage on stream temperature in unsampled locations. We discuss applications for climate change research to account for groundwater-surface water interactions when projecting future thermal thresholds for stream biota.

Increasing the utility of regional water table maps: a new method for estimating groundwater recharge

NASA Astrophysics Data System (ADS)

Gilmore, T. E.; Zlotnik, V. A.; Johnson, M.

2017-12-01

Groundwater table elevations are one of the most fundamental measurements used to characterize unconfined aquifers, groundwater flow patterns, and aquifer sustainability over time. In this study, we developed an analytical model that relies on analysis of groundwater elevation contour (equipotential) shape, aquifer transmissivity, and streambed gradient between two parallel, perennial streams. Using two existing regional water table maps, created at different times using different methods, our analysis of groundwater elevation contours, transmissivity and streambed gradient produced groundwater recharge rates (42-218 mm yr-1) that were consistent with previous independent recharge estimates from different methods. The three regions we investigated overly the High Plains Aquifer in Nebraska and included some areas where groundwater is used for irrigation. The three regions ranged from 1,500 to 3,300 km2, with either Sand Hills surficial geology, or Sand Hills transitioning to loess. Based on our results, the approach may be used to increase the value of existing water table maps, and may be useful as a diagnostic tool to evaluate the quality of groundwater table maps, identify areas in need of detailed aquifer characterization and expansion of groundwater monitoring networks, and/or as a first approximation before investing in more complex approaches to groundwater recharge estimation.

Effects of unsaturated zone on ground-water mounding

USGS Publications Warehouse

Sumner, D.M.; Rolston, D.E.; Marino, M.A.

1999-01-01

The design of infiltration basins used to dispose of treated wastewater or for aquifer recharge often requires estimation of ground-water mounding beneath the basin. However, the effect that the unsaturated zone has on water-table response to basin infiltration often has been overlooked in this estimation. A comparison was made between two methods used to estimate ground-water mounding-an analytical approach that is limited to the saturated zone and a numerical approach that incorporates both the saturated and the unsaturated zones. Results indicate that the error that is introduced by a method that ignores the effects of the unsaturated zone on ground-water mounding increases as the basin-loading period is shortened; as the depth to the water table increases, with increasing subsurface anisotropy; and with the inclusion of fine-textured strata. Additionally, such a method cannot accommodate the dynamic nature of basin infiltration, the finite transmission time of the infiltration front to the water table, or the interception of the basin floor by the capillary fringe.The design of infiltration basins used to dispose of treated wastewater or for aquifer recharge often requires estimation of ground-water mounding beneath the basin. However, the effect that the unsaturated zone has on water-table response to basin infiltration often has been overlooked in this estimation. A comparison was made between two methods used to estimate ground-water mounding - an analytical approach that is limited to the saturated zone and a numerical approach that incorporates both the saturated and the unsaturated zones. Results indicate that the error that is introduced by a method that ignores the effects of the unsaturated zone on ground-water mounding increases as the basin-loading period is shortened; as the depth to the water table increases, with increasing subsurface anisotropy; and with the inclusion of fine-textured strata. Additionally, such a method cannot accommodate the dynamic nature of basin infiltration, the finite transmission time of the infiltration front to the water, or the interception of the basin floor by the capillary fringe.

Simulated Effects of Seasonal Ground-Water Pumpage for Irrigation on Hydrologic Conditions in the Lower Apalachicola-Chattahoochee-Flint River Basin, Southwestern Georgia and Parts of Alabama and Florida, 1999-2002

USGS Publications Warehouse

Jones, L. Elliott; Torak, Lynn J.

2006-01-01

To determine the effects of seasonal ground-water pumpage for irrigation, a finite-element ground-water flow model was developed for the Upper Floridan aquifer in the lower Flint River Basin area, including adjacent parts of the Chattahoochee and Apalachicola River Basins. The model simulates withdrawal from the aquifer at 3,280 irrigation, municipal, and industrial wells; stream-aquifer flow between the aquifer and 36 area streams; leakage to and from the overlying upper semiconfining unit; regional ground-water flow at the lateral boundaries of the model; and water-table recharge in areas where the aquifer is at or near land surface. Steady-state calibration to drought conditions of October 1999 indicated that the model could adequately simulate measured groundwater levels at 275 well locations and streamflow gains and losses along 53 reaches of area streams. A transient simulation having 12 monthly stress periods from March 2001 to February 2002 incorporated time-varying stress from irrigation pumpage, stream and lake stage, head in the overlying upper semiconfining unit, and infiltration rates. Analysis of simulated water budgets of the Upper Floridan aquifer provides estimates of the source of water pumped for irrigation. During October 1999, an estimated 127 million gallons per day (Mgal/d) of irrigation pumpage from the Upper Floridan aquifer in the model area were simulated to be derived from changes in: stream-aquifer flux (about 56 Mgal/d, or 44 percent); leakage to or from the upper semiconfining unit (about 49 Mgal/d, or 39 percent); regional flow (about 18 Mgal/d, or 14 percent); leakage to or from Lakes Seminole and Blackshear (about 2.7 Mgal/d, or 2 percent); and flux at the Upper Floridan aquifer updip boundary (about 1.8 Mgal/d, or 1 percent). During the 2001 growing season (May-August), estimated irrigation pumpage ranged from about 310 to 830 Mgal/ d, about 79 percent of the 12-month total. During the growing season, irrigation pumpage was derived from decreased discharge or increased recharge of stream-aquifer flux (from about 23 to 39 percent), leakage to or from the upper semiconfining unit (from about 30 to 36 percent), regional flow (from about 8 to 11 percent), Lakes Seminole and Blackshear (about 2 percent), and flux at the Upper Floridan aquifer updip boundary (about 1 percent). Storage effects (decreased storage gain or increased storage loss) contributed from about 11 to 36 percent of irrigation pumpage during the growing season. Water managers can use the model to determine where and how much additional ground-water pumpage for irrigation should be permitted based on a variety of hydrologic constraints. For example, the model results may indicate that in some critical locations, additional ground-water pumpage during a prolonged drought might reduce stream-aquifer flux enough to cause noncompliance of established minimum instream flow conditions.

Testing mixing models of old and young groundwater in a tropical lowland rain forest with environmental tracers

USGS Publications Warehouse

Solomon, D. Kip; Genereux, David P.; Plummer, Niel; Busenberg, Eurybiades

2010-01-01

We tested three models of mixing between old interbasin groundwater flow (IGF) and young, locally derived groundwater in a lowland rain forest in Costa Rica using a large suite of environmental tracers. We focus on the young fraction of water using the transient tracers CFC‐11, CFC‐12, CFC‐113, SF6, 3H, and bomb 14C. We measured 3He, but 3H/3He dating is generally problematic due to the presence of mantle 3He. Because of their unique concentration histories in the atmosphere, combinations of transient tracers are sensitive not only to subsurface travel times but also to mixing between waters having different travel times. Samples fall into three distinct categories: (1) young waters that plot along a piston flow line, (2) old samples that have near‐zero concentrations of the transient tracers, and (3) mixtures of 1 and 2. We have modeled the concentrations of the transient tracers using (1) a binary mixing model (BMM) of old and young water with the young fraction transported via piston flow, (2) an exponential mixing model (EMM) with a distribution of groundwater travel times characterized by a mean value, and (3) an exponential mixing model for the young fraction followed by binary mixing with an old fraction (EMM/BMM). In spite of the mathematical differences in the mixing models, they all lead to a similar conceptual model of young (0 to 10 year) groundwater that is locally derived mixing with old (>1000 years) groundwater that is recharged beyond the surface water boundary of the system.

Practical aspects of prestack depth migration with finite differences

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ober, C.C.; Oldfield, R.A.; Womble, D.E.

1997-07-01

Finite-difference, prestack, depth migrations offers significant improvements over Kirchhoff methods in imaging near or under salt structures. The authors have implemented a finite-difference prestack depth migration algorithm for use on massively parallel computers which is discussed. The image quality of the finite-difference scheme has been investigated and suggested improvements are discussed. In this presentation, the authors discuss an implicit finite difference migration code, called Salvo, that has been developed through an ACTI (Advanced Computational Technology Initiative) joint project. This code is designed to be efficient on a variety of massively parallel computers. It takes advantage of both frequency and spatialmore » parallelism as well as the use of nodes dedicated to data input/output (I/O). Besides giving an overview of the finite-difference algorithm and some of the parallelism techniques used, migration results using both Kirchhoff and finite-difference migration will be presented and compared. The authors start out with a very simple Cartoon model where one can intuitively see the multiple travel paths and some of the potential problems that will be encountered with Kirchhoff migration. More complex synthetic models as well as results from actual seismic data from the Gulf of Mexico will be shown.« less

Potential effects of roadside dry wells on groundwater quality on the Island of Hawai'i-Assessment using numerical groundwater models

USGS Publications Warehouse

Izuka, Scot K.

2011-01-01

Widespread use of dry wells to dispose of roadside runoff has raised concern about the potential effects on the quality of groundwater on the Island of Hawai‘i. This study used semi-generic numerical models of groundwater flow and contaminant transport to assess the potential effect of dry wells on groundwater quality on the Island of Hawai‘i. The semi-generic models are generalized numerical groundwater-flow and solute-transport models that have a range of aquifer properties and regional groundwater gradients that are characteristic for the island. Several semi-generic models were created to study the effect of dry wells in different hydrogeologic conditions, such as different unsaturated-zone thicknesses or different aquifer characteristics. Results indicate that mixing of contaminated water from the surface with contaminant-free water in the saturated aquifer immediately reduces the contaminant concentration. The amount the concentration is reduced depends on the hydraulic properties of the aquifer in a given area, the thickness of the unsaturated zone, and whether the infiltration is focused in a small area of a dry well or spread naturally over a larger area. Model simulations indicate that focusing infiltration of contaminated runoff through a dry well can substantially increase contaminant concentrations in the underlying saturated aquifer relative to infiltration under natural conditions. Simulated concentrations directly beneath a dry well were nearly 8 times higher than the simulated concentrations directly beneath a broad infiltration area representing the natural condition. Where dry wells are present, contaminant concentrations in the underlying saturated aquifer are lower when the unsaturated zone is thicker and higher when the unsaturated zone is thinner. Contaminant concentrations decline quickly as the contaminant plume migrates, with the regional groundwater flow, away from the dry well. The differences among concentrations resulting from the various unsaturated-zone thicknesses also diminish with distance from the dry well. At a horizontal distance of about 700 ft downgradient from the dry well, all simulated maximum concentrations were less than 1 percent of the concentration in the infiltration water; at about 0.5 mi downgradient from the dry well, all simulated concentrations were equal to or less than 0.1 percent. Actual concentrations may be even lower than indicated by the models because of processes such as decay and reaction that were not simulated. Hydrologic and geologic differences from one location to the next also affect contaminant concentrations—simulations using models with properties representative of aquifers in the Hilo area resulted in lower overall concentrations than models with properties representative of aquifers in the Kona area. Results from this study can be used to assess how contaminants entering a dry well may affect receiving waters in a variety of situations on the Island of Hawai‘i. Better assessment would be obtained by using results from models having the most similar conditions (such as climate, hydraulic properties, regional groundwater gradient) to the dry well in question. The results of this study can help determine which dry wells are likely to have the greatest effect on nearby receiving waters and where more specific data and analyses may be needed.

A Multi-Methodology for improving Adelaide's Groundwater Management

NASA Astrophysics Data System (ADS)

Batelaan, Okke; Banks, Eddie; Batlle-Aguilar, Jordi; Breciani, Etienne; Cook, Peter; Cranswick, Roger; Smith, Stan; Turnadge, Chris; Partington, Daniel; Post, Vincent; Pool Ramirez, Maria; Werner, Adrian; Xie, Yueqing; Yang, Yuting

2015-04-01

Groundwater is a strategic and vital resource in South Australia playing a crucial role in sustaining a healthy environment, as well as supporting industries and economic development. In the Adelaide metropolitan region ten different aquifer units have been identified, extending to more than 500 m below sea level. Although salinity within most of these aquifers is variable, water suitable for commercial, irrigation and/or potable use is predominantly found in the deeper Tertiary aquifers. Groundwater currently contributes only 9000 ML/yr of Adelaide's total water consumption of 216,000 ML, while in the Northern Adelaide Plains 17000 ML/yr is used. However, major industries, market gardeners, golf courses, and local councils are highly dependent on this resource. Despite recent rapid expansion in managed aquifer recharge, and the potential for increased extraction of groundwater, particularly for the commercial and irrigation supplies, little is known about the sources and ages of Adelaide's groundwater. The aim of this study is therefore to provide a robust conceptualisation of Adelaide's groundwater system. The study focuses on three important knowledge gaps: 1. Does groundwater flow from the Adelaide Hills into the sedimentary aquifers on the plains? 2. What is the potential for encroachment of seawater if groundwater extraction increases? 3. How isolated are the different aquifers, or does water leak from one to the other? A multi-tool approach has been used to improve the conceptual understanding of groundwater flow processes; including the installation of new groundwater monitoring wells from the hills to the coast, an extensive groundwater sampling campaign of new and existing groundwater wells for chemistry and environmental tracers analysis, and development of a regional scale numerical model rigorously tested under different scenario conditions. The model allows quantification of otherwise hardly quantifiable quantities such as flow across fault zones and through aquitard. Risk assessment of water resources status by 2050 is achieved via uncertainty quantification of potential future scenarios. This includes several development scenarios (current or increased extraction rate) as well as different outputs from climate change predictions. It is shown that groundwater in the fractured aquifer bedrock in the hills is significantly younger than groundwater in the Adelaide plains area, indicating that the Adelaide groundwater system is, at least, partially recharged by lateral flow from water infiltrated in the hills. However, increasing ages with depth, are indicative of vertical infiltration from rainfall and possible inter-aquifer leakage. A better understanding of processes controlling these two sources of fresh groundwater, as well as evaluating their relative importance to Adelaide's groundwater budget is being thoroughly investigated using the regional numerical groundwater model. The salinity distribution along the coastline is shown not to be simply an equilibrium situation with an intruded seawater wedge extending inland. Tertiary aquifers can still contain old freshwater near the coast, and in deeper layers a hypersaline brine has been identified, which could constitute a previously-overlooked source of salinity. This study is the first comprehensive investigation of the groundwater resources within the Adelaide environment and supports strongly integrated water management of the resource.

Simulate speleogenesis processes with an approach based on fracturing and hydrogeological processes: effect of various hydraulic boundary conditions

NASA Astrophysics Data System (ADS)

Lafare, A.; Jourde, H.; Leonardi, V.; Pistre, S.; Dörfliger, N.

2012-04-01

Several numerical modeling approaches attempted to simulate the processes of karst conduit genesis. These existing methods are mainly based on the physical and chemical laws driving the carbonate dissolution processes (taking account of calcite saturation of the water and the partial pressure of carbon dioxide). As a consequence, these works bring a well-documented knowledge on the kinetics of the carbonate dissolution processes in karst systems. Nevertheless, these models are mainly applied on simplified initial void networks, which do not match the fracturing and geological reality. Considering that the initial geometry of the void network (fractures, bedding planes) would have an influence on the final pattern of the speleological network, taking account of it could improve the understanding of speleogenesis. In the aim to take into account the geometry of the initial void network (fracture networks of several orders), a numerical model is developed, which involves a pseudo-statistic fracturing generator (REZO3D, Jourde 1999, Josnin et al. 2002, Jourde et al. 2002) coupled to a finite element groundwater simulator (GROUNDWATER, F. Cornaton, CHYN, University of Neuchâtel). The principle of the modeling of the genesis of the karst drainage system is based on an analogical empirical polynomial equation considering the pore velocity and the mean age of the water as main parameters. The computation is carried out on the basis of a time step, whose duration depends on the simulated scenario (from 100 to 5000 years). The mean age of the water is used in order to simulate the decrease of the chemical dissolving potential of the water within the aquifer, in contact with the carbonate rock. The first simulator -REZO3D- allows producing three-dimensional discrete fracture networks constituted by plane fractures, whose spatial distribution respects mechanical and statistical laws. These networks are then processed in order to write finite element meshes which constitute the bases of groundwater flow and transport simulations. The polynomial parameters of the equation are calibrated with former speleogenesis studies (Dreybrodt 1996, Dreybrodt et al. 2005, Palmer 1991). The presented study involves two orthogonal families of fractures embedded in a carbonate matrix, in a mono-stratum setting. For each simulation, several settings of boundary conditions are tested, in terms of recharge (diffuse or concentrated, hydraulic head or flux limited) and discharge (spatial position, punctual or diffuse). The results are interpreted in terms of head fields, mean groundwater age distributions and total flow rates as a function of time. The aim is to assess the influence of the hydraulic boundary conditions on the finally obtained morphologies of the karstic networks, and on the velocity of the evolution of the drainage system. Results are discussed and perspectives are given on the application of such model to real case studies.

Coupled hydrogeological and geomechanical modelling for the analysis of large slope instabilities.

NASA Astrophysics Data System (ADS)

Laloui, Lyesse; Ferrari, Alessio; Bonnard, Christophe

2010-05-01

Slowly-moving landslides (average velocity between 2 and 10 cm/year) are quite frequent in mountainous or hilly areas and they may display occasional crises, generally due to exceptional climatic conditions. The hazard related to these events cannot be analysed in terms of probability analysis, as the number of recorded past events is generally very small and climate changes could significantly modify the environmental setting. Quantitative relationships relating climatic condition fluctuations and sliding area velocity must then be pursued by taking into account the most relevant physical processes involved in the landslide behaviours. Conventional stability analyses are unable to deal with such questions because they do not allow the velocity fields to be determined. With regard to the behaviour of large slope instabilities, a methodology is presented which aims to describe the behaviour of slow-moving landslides by means of a coupled hydrogeological and geomechanical modelling framework. As it is well known, the evolution of the pore water pressure within the landslide body is often recognized as the main cause for the occurrence of displacement accelerations. In this sense the interaction among the hydrological and the mechanical responses must be considered to analyse the landslide behaviour, with the aim of quantitatively relating pore water pressure variations and movements. For a given case study, pore water pressure evolutions in space and time are obtained from a duly calibrated finite element hydrogeological model, which can take into account the role of several key factors such as infiltration, preferential flows and vegetation. Computed groundwater pressures resulting from the hydrogeological simulations are introduced as nodal forces in a finite element geomechanical model in order to calculate stress evolutions and displacements. The use of advanced constitutive models based on the generalised effective stress concept allows taking into account specific behavioural features such as the effects of the changes in the degree of saturation, associated to the fluctuation of the groundwater level. The geomechanical model is calibrated comparing computed and measured displacements in relevant points of the slope. When appropriate, the outcomes from the geomechanical model can be used in an iterative way to update the hydrogeological model settings. In this way it is possible to simulate the evolution of critical factors (such as permeability or retention properties of the involved materials) associated to the cumulated displacements. Once calibrated, the coupled models can be used to assess the landslide behaviour under different scenarios, including modified climatic conditions and the implementation of mitigation measures. Applications to relevant case studies are presented in order to demonstrate the adequacy and the usefulness of the proposed modelling framework.

Hydrogeology and simulation of ground-water flow at US Marine Corps Air Station, Cherry Point, North Carolina, 1987-90

USGS Publications Warehouse

Eimers, J.L.; Daniel, C. C.; Coble, R.W.

1994-01-01

Geophysical and lithologic well-log data from 30 wells and chloride data, and water-level data from oil-test wells, supply wells, and observation wells were evaluated to define the hydrogeologic framework at the U.S. Marine Corps Air Station, Cherry Point, North Carolina. Elements of the hydrogeologic framework important to this study include six aquifers and their respective confining units. In descending order, these aquifers are the surficial, Yorktown, Pungo River, upper and lower Castle Hayne, and Beaufort. The upper and lower Castle Hayne and Beaufort aquifers and related confining units are relatively continuous throughout the study area. The surficial, Yorktown, Pungo River, and upper and lower Castle Hayne aquifers contain freshwater. The upper and lower Castle Hayne aquifers serve as the Air Station?s principal supply of freshwater. However, the lower Castle Hayne aquifer contains brackish water near its base and there is potential for upward movement of this water to supply wells completed in this aquifer. The potential for brackish-water encroachment is greatest if wells are screened too deep in the lower Castle Hayne aquifer or if pumping rates are too high. Lateral movement of brackish water into aquifers incised by estuarine streams is also possible if ground-water flow gradients toward these bodies are reversed by pumping. The potential for the reversed movement of water from the surficial aquifer downward to the water-supply aquifer is greatest in areas where clay confining units are missing. These missing clay units could indicate the presence of a paleochannel of the Neuse River. A quasi three-dimensional finite-difference ground-water flow model was constructed and calibrated to simulate conditions at and in the vicinity of the Air Station for the period of 1987-90. Comparisons of 94 observed and computed heads were made, and the average difference between them is -0.2 feet with a root mean square error of 5.7 feet. An analysis was made to evaluate the sensitivity of the model to the absence of the Yorktown and Pungo River confining units in a 1-square-mile area in the southern part of the Air Station. This analysis resulted in a maximum simulated head increase of 2 feet in one 0.11-square-mile model cell in the Pungo River aquifer.

Interactions of artificial lakes with groundwater applying an integrated MODFLOW solution

NASA Astrophysics Data System (ADS)

El-Zehairy, A. A.; Lubczynski, M. W.; Gurwin, J.

2018-02-01

Artificial lakes (reservoirs) are regulated water bodies with large stage fluctuations and different interactions with groundwater compared with natural lakes. A novel modelling study characterizing the dynamics of these interactions is presented for artificial Lake Turawa, Poland. The integrated surface-water/groundwater MODFLOW-NWT transient model, applying SFR7, UZF1 and LAK7 packages to account for variably-saturated flow and temporally variable lake area extent and volume, was calibrated throughout 5 years (1-year warm-up, 4-year simulation), applying daily lake stages, heads and discharges as control variables. The water budget results showed that, in contrast to natural lakes, the reservoir interactions with groundwater were primarily dependent on the balance between lake inflow and regulated outflow, while influences of precipitation and evapotranspiration played secondary roles. Also, the spatio-temporal lakebed-seepage pattern was different compared with natural lakes. The large and fast-changing stages had large influence on lakebed-seepage and water table depth and also influenced groundwater evapotranspiration and groundwater exfiltration, as their maxima coincided not with rainfall peaks but with highest stages. The mean lakebed-seepage ranged from 0.6 mm day-1 during lowest stages (lake-water gain) to 1.0 mm day-1 during highest stages (lake-water loss) with largest losses up to 4.6 mm day-1 in the peripheral zone. The lakebed-seepage of this study was generally low because of low lakebed leakance (0.0007-0.0015 day-1) and prevailing upward regional groundwater flow moderating it. This study discloses the complexity of artificial lake interactions with groundwater, while the proposed front-line modelling methodology can be applied to any reservoir, and also to natural lake interactions with groundwater.

Nested-scale discharge and groundwater level monitoring to improve predictions of flow route discharges and nitrate loads

NASA Astrophysics Data System (ADS)

van der Velde, Y.; Rozemeijer, J. C.; de Rooij, G. H.; van Geer, F. C.; Torfs, P. J. J. F.; de Louw, P. G. B.

2010-10-01

Identifying effective measures to reduce nutrient loads of headwaters in lowland catchments requires a thorough understanding of flow routes of water and nutrients. In this paper we assess the value of nested-scale discharge and groundwater level measurements for predictions of catchment-scale discharge and nitrate loads. In order to relate field-site measurements to the catchment-scale an upscaling approach is introduced that assumes that scale differences in flow route fluxes originate from differences in the relationship between groundwater storage and the spatial structure of the groundwater table. This relationship is characterized by the Groundwater Depth Distribution (GDD) curve that relates spatial variation in groundwater depths to the average groundwater depth. The GDD-curve was measured for a single field site (0.009 km2) and simple process descriptions were applied to relate the groundwater levels to flow route discharges. This parsimonious model could accurately describe observed storage, tube drain discharge, overland flow and groundwater flow simultaneously with Nash-Sutcliff coefficients exceeding 0.8. A probabilistic Monte Carlo approach was applied to upscale field-site measurements to catchment scales by inferring scale-specific GDD-curves from hydrographs of two nested catchments (0.4 and 6.5 km2). The estimated contribution of tube drain effluent (a dominant source for nitrates) decreased with increasing scale from 76-79% at the field-site to 34-61% and 25-50% for both catchment scales. These results were validated by demonstrating that a model conditioned on nested-scale measurements simulates better nitrate loads and better predictions of extreme discharges during validation periods compared to a model that was conditioned on catchment discharge only.

Controls on the breach geometry and flood hydrograph during overtopping of non-cohesive earthen dams

USGS Publications Warehouse

Walder, Joseph S.; Iverson, Richard M.; Godt, Jonathan W.; Logan, Matthew; Solovitz, Stephen A.

2015-01-01

Overtopping failure of non-cohesive earthen dams was investigated in 13 large-scale experiments with dams built of compacted, damp, fine-grained sand. Breaching was initiated by cutting a notch across the dam crest and allowing water escaping from a finite upstream reservoir to form its own channel. The channel developed a stepped profile, and upstream migration of the steps, which coalesced into a headcut, led to the establishment of hydraulic control (critical flow) at the channel head, or breach crest, an arcuate erosional feature that functions hydraulically as a weir. Novel photogrammetric methods, along with underwater videography, revealed that the retreating headcut maintained a slope near the angle of friction of the sand, while the cross section at the breach crest maintained a geometrically similar shape through time. That cross-sectional shape was nearly unaffected by slope failures, contrary to the assumption in many models of dam breaching. Flood hydrographs were quite reproducible--for sets of dams ranging in height from 0.55 m to 0.98 m--when the time datum was chosen as the time that the migrating headcut intersected the breach crest. Peak discharge increased almost linearly as a function of initial dam height. Early-time variability between flood hydrographs for nominally identical dams is probably a reflection of subtle experiment-to-experiment differences in groundwater hydrology and the interaction between surface water and groundwater.

Hydrogeology of parts of the Central Platte and Lower Loup Natural Resources Districts, Nebraska

USGS Publications Warehouse

Peckenpaugh, J.M.; Dugan, J.T.

1983-01-01

Water-level declines of at least 15 feet have occurred in this heavily irrigated area of central Nebraska since the 1930's, and potential for additonal declines is high. To test the effects of additional irrigation development on water levels and streamflow , computer programs were developed that represent the surface-water system, soil zone, and saturated zone. A two-dimensional, finite-difference ground-water flow model of the 3,374 square-mile study area was developed and calibrated using steady-state and transient conditions. Three management alternatives were examined. First, 125,000 acre-feet of water would be diverted annually from the Platte River. During a water year in which flows are similar to those in 1957, months of zero streamflow at Grand Island increased from the historical 2, to 7. After 5 years of such low flows, in 36 nodes (997.4 acres per node) water levels declined more than 5 feet, with a maximum decline of 10.7 feet. A second alternative would allow no new ground-water development after 1980. The third alternative would allow irrigable but unirrigated land to be developed at an annual rate of 2, 5, and 8 percent and to apply irrigation water at 80, 100, and 120 percent of consumptive irrigation requirements. The maximum projected declines by 2020 are 119 and 139 feet, respectively, for the second and third alternatives. (USGS)

Sanitary protection zoning based on time-dependent vulnerability assessment model - case examples at two different type of aquifers

NASA Astrophysics Data System (ADS)

Živanović, Vladimir; Jemcov, Igor; Dragišić, Veselin; Atanacković, Nebojša

2017-04-01

Delineation of sanitary protection zones of groundwater source is a comprehensive and multidisciplinary task. Uniform methodology for protection zoning for various type of aquifers is not established. Currently applied methods mostly rely on horizontal groundwater travel time toward the tapping structure. On the other hand, groundwater vulnerability assessment methods evaluate the protective function of unsaturated zone as an important part of groundwater source protection. In some particular cases surface flow might also be important, because of rapid transfer of contaminants toward the zones with intense infiltration. For delineation of sanitary protection zones three major components should be analysed: vertical travel time through unsaturated zone, horizontal travel time through saturated zone and surface water travel time toward intense infiltration zones. Integrating the aforementioned components into one time-dependent model represents a basis of presented method for delineation of groundwater source protection zones in rocks and sediments of different porosity. The proposed model comprises of travel time components of surface water, as well as groundwater (horizontal and vertical component). The results obtained using the model, represent the groundwater vulnerability as the sum of the surface and groundwater travel time and corresponds to the travel time of potential contaminants from the ground surface to the tapping structure. This vulnerability assessment approach do not consider contaminant properties (intrinsic vulnerability) although it can be easily improved for evaluating the specific groundwater vulnerability. This concept of the sanitary protection zones was applied at two different type of aquifers: karstic aquifer of catchment area of Blederija springs and "Beli Timok" source of intergranular shallow aquifer. The first one represents a typical karst hydrogeological system with part of the catchment with allogenic recharge, and the second one, the groundwater source within shallow intergranular alluvial aquifer, dominantly recharged by river bank filtration. For sanitary protection zones delineation, the applied method has shown the importance of introducing all travel time components equally. In the case of the karstic source, the importance of the surface flow toward ponor zones has been emphasized, as a consequence of rapid travel time of water in relation to diffuse infiltration from autogenic part. When it comes to the shallow intergranular aquifer, the character of the unsaturated zone gets more prominent role in the source protection, as important buffer of the vertical movement downward. The applicability of proposed method has been shown regardless of the type of the aquifer, and at the same time intelligible results of the delineated sanitary protection zones are possible to validate with various methods. Key words: groundwater protection zoning, time dependent model, karst aquifer, intergranular aquifer, groundwater source protection

Calibrating binary lumped parameter models

NASA Astrophysics Data System (ADS)

Morgenstern, Uwe; Stewart, Mike

2017-04-01

Groundwater at its discharge point is a mixture of water from short and long flowlines, and therefore has a distribution of ages rather than a single age. Various transfer functions describe the distribution of ages within the water sample. Lumped parameter models (LPMs), which are mathematical models of water transport based on simplified aquifer geometry and flow configuration can account for such mixing of groundwater of different age, usually representing the age distribution with two parameters, the mean residence time, and the mixing parameter. Simple lumped parameter models can often match well the measured time varying age tracer concentrations, and therefore are a good representation of the groundwater mixing at these sites. Usually a few tracer data (time series and/or multi-tracer) can constrain both parameters. With the building of larger data sets of age tracer data throughout New Zealand, including tritium, SF6, CFCs, and recently Halon-1301, and time series of these tracers, we realised that for a number of wells the groundwater ages using a simple lumped parameter model were inconsistent between the different tracer methods. Contamination or degradation of individual tracers is unlikely because the different tracers show consistent trends over years and decades. This points toward a more complex mixing of groundwaters with different ages for such wells than represented by the simple lumped parameter models. Binary (or compound) mixing models are able to represent a more complex mixing, with mixing of water of two different age distributions. The problem related to these models is that they usually have 5 parameters which makes them data-hungry and therefore difficult to constrain all parameters. Two or more age tracers with different input functions, with multiple measurements over time, can provide the required information to constrain the parameters of the binary mixing model. We obtained excellent results using tritium time series encompassing the passage of the bomb-tritium through the aquifer, and SF6 with its steep gradient currently in the input. We will show age tracer data from drinking water wells that enabled identification of young water ingression into wells, which poses the risk of bacteriological contamination from the surface into the drinking water.

A Finite Layer Formulation for Groundwater Flow to Horizontal Wells.

PubMed

Xu, Jin; Wang, Xudong

2016-09-01

A finite layer approach for the general problem of three-dimensional (3D) flow to horizontal wells in multilayered aquifer systems is presented, in which the unconfined flow can be taken into account. The flow is approximated by an integration of the standard finite element method in vertical direction and the analytical techniques in the other spatial directions. Because only the vertical discretization is involved, the horizontal wells can be completely contained in one specific nodal plane without discretization. Moreover, due to the analytical eigenfunctions introduced in the formulation, the weighted residual equations can be decoupled, and the formulas for the global matrices and flow vector corresponding to horizontal wells can be obtained explicitly. Consequently, the bandwidth of the global matrices and computational cost rising from 3D analysis can be significantly reduced. Two comparisons to the existing solutions are made to verify the validity of the formulation, including transient flow to horizontal wells in confined and unconfined aquifers. Furthermore, an additional numerical application to horizontal wells in three-layered systems is presented to demonstrate the applicability of the present method in modeling flow in more complex aquifer systems. © 2016, National Ground Water Association.

A comparative study on dynamic stiffness in typical finite element model and multi-body model of C6-C7 cervical spine segment.

PubMed

Wang, Yawei; Wang, Lizhen; Du, Chengfei; Mo, Zhongjun; Fan, Yubo

2016-06-01

In contrast to numerous researches on static or quasi-static stiffness of cervical spine segments, very few investigations on their dynamic stiffness were published. Currently, scale factors and estimated coefficients were usually used in multi-body models for including viscoelastic properties and damping effects, meanwhile viscoelastic properties of some tissues were unavailable for establishing finite element models. Because dynamic stiffness of cervical spine segments in these models were difficult to validate because of lacking in experimental data, we tried to gain some insights on current modeling methods through studying dynamic stiffness differences between these models. A finite element model and a multi-body model of C6-C7 segment were developed through using available material data and typical modeling technologies. These two models were validated with quasi-static response data of the C6-C7 cervical spine segment. Dynamic stiffness differences were investigated through controlling motions of C6 vertebrae at different rates and then comparing their reaction forces or moments. Validation results showed that both the finite element model and the multi-body model could generate reasonable responses under quasi-static loads, but the finite element segment model exhibited more nonlinear characters. Dynamic response investigations indicated that dynamic stiffness of this finite element model might be underestimated because of the absence of dynamic stiffen effect and damping effects of annulus fibrous, while representation of these effects also need to be improved in current multi-body model. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

A comparative assessment of GIS-based data mining models and a novel ensemble model in groundwater well potential mapping

NASA Astrophysics Data System (ADS)

Naghibi, Seyed Amir; Moghaddam, Davood Davoodi; Kalantar, Bahareh; Pradhan, Biswajeet; Kisi, Ozgur

2017-05-01

In recent years, application of ensemble models has been increased tremendously in various types of natural hazard assessment such as landslides and floods. However, application of this kind of robust models in groundwater potential mapping is relatively new. This study applied four data mining algorithms including AdaBoost, Bagging, generalized additive model (GAM), and Naive Bayes (NB) models to map groundwater potential. Then, a novel frequency ratio data mining ensemble model (FREM) was introduced and evaluated. For this purpose, eleven groundwater conditioning factors (GCFs), including altitude, slope aspect, slope angle, plan curvature, stream power index (SPI), river density, distance from rivers, topographic wetness index (TWI), land use, normalized difference vegetation index (NDVI), and lithology were mapped. About 281 well locations with high potential were selected. Wells were randomly partitioned into two classes for training the models (70% or 197) and validating them (30% or 84). AdaBoost, Bagging, GAM, and NB algorithms were employed to get groundwater potential maps (GPMs). The GPMs were categorized into potential classes using natural break method of classification scheme. In the next stage, frequency ratio (FR) value was calculated for the output of the four aforementioned models and were summed, and finally a GPM was produced using FREM. For validating the models, area under receiver operating characteristics (ROC) curve was calculated. The ROC curve for prediction dataset was 94.8, 93.5, 92.6, 92.0, and 84.4% for FREM, Bagging, AdaBoost, GAM, and NB models, respectively. The results indicated that FREM had the best performance among all the models. The better performance of the FREM model could be related to reduction of over fitting and possible errors. Other models such as AdaBoost, Bagging, GAM, and NB also produced acceptable performance in groundwater modelling. The GPMs produced in the current study may facilitate groundwater exploitation by determining high and very high groundwater potential zones.

Exploring Several Methods of Groundwater Model Selection

NASA Astrophysics Data System (ADS)

Samani, Saeideh; Ye, Ming; Asghari Moghaddam, Asghar

2017-04-01

Selecting reliable models for simulating groundwater flow and solute transport is essential to groundwater resources management and protection. This work is to explore several model selection methods for avoiding over-complex and/or over-parameterized groundwater models. We consider six groundwater flow models with different numbers (6, 10, 10, 13, 13 and 15) of model parameters. These models represent alternative geological interpretations, recharge estimates, and boundary conditions at a study site in Iran. The models were developed with Model Muse, and calibrated against observations of hydraulic head using UCODE. Model selection was conducted by using the following four approaches: (1) Rank the models using their root mean square error (RMSE) obtained after UCODE-based model calibration, (2) Calculate model probability using GLUE method, (3) Evaluate model probability using model selection criteria (AIC, AICc, BIC, and KIC), and (4) Evaluate model weights using the Fuzzy Multi-Criteria-Decision-Making (MCDM) approach. MCDM is based on the fuzzy analytical hierarchy process (AHP) and fuzzy technique for order performance, which is to identify the ideal solution by a gradual expansion from the local to the global scale of model parameters. The KIC and MCDM methods are superior to other methods, as they consider not only the fit between observed and simulated data and the number of parameter, but also uncertainty in model parameters. Considering these factors can prevent from occurring over-complexity and over-parameterization, when selecting the appropriate groundwater flow models. These methods selected, as the best model, one with average complexity (10 parameters) and the best parameter estimation (model 3).

Improved water resource management using three dimensional groundwater modelling for a highly complex environmental

NASA Astrophysics Data System (ADS)

Moeck, Christian; Affolter, Annette; Radny, Dirk; Auckenthaler, Adrian; Huggenberger, Peter; Schirmer, Mario

2017-04-01

Proper allocation and management of groundwater is an important and critical challenge under rising water demands of various environmental sectors but good groundwater quality is often limited because of urbanization and contamination of aquifers. Given the predictive capability of groundwater models, they are often the only viable means of providing input to water management decisions. However, modelling flow and transport processes can be difficult due to their unknown subsurface heterogeneity and typically unknown distribution of contaminants. As a result water resource management tasks are based on uncertain assumption on contaminants patterns and this uncertainty is typically not incorporated into the assessment of risks associated with different proposed management scenarios. A three-dimensional groundwater model was used to improve water resource management for a study area, where drinking water production is close to different former landfills and industrial areas. To avoid drinking water contamination, artificial groundwater recharge with surface water into the gravel aquifer is used to create a hydraulic barrier between contaminated sites and drinking water extraction wells. The model was used for simulating existing and proposed water management strategies as a tool to ensure the utmost security for drinking water. A systematic evaluation of the flow direction and magnitude between existing observation points using a newly developed three point estimation method for a large amount of scenarios was carried out. Due to the numerous observation points 32 triangles (three-points) were created which cover the entire area around the Hardwald. We demonstrated that systematically applying our developed methodology helps to identify important locations which are sensitive to changing boundary conditions and where additional protection is required without highly computational demanding transport modelling. The presented integrated approach using the flow direction between observation points can be easily transferred to a variety of hydrological settings to evaluate systematically groundwater modelling scenarios.

Estimation of lake water - groundwater interactions in meromictic mining lakes by modelling isotope signatures of lake water.

PubMed

Seebach, Anne; Dietz, Severine; Lessmann, Dieter; Knoeller, Kay

2008-03-01

A method is presented to assess lake water-groundwater interactions by modelling isotope signatures of lake water using meteorological parameters and field data. The modelling of delta(18)O and deltaD variations offers information about the groundwater influx into a meromictic Lusatian mining lake. Therefore, a water balance model is combined with an isotope water balance model to estimate analogies between simulated and measured isotope signatures within the lake water body. The model is operated with different evaporation rates to predict delta(18)O and deltaD values in a lake that is only controlled by weather conditions with neither groundwater inflow nor outflow. Comparisons between modelled and measured isotope values show whether the lake is fed by the groundwater or not. Furthermore, our investigations show that an adaptation of the Craig and Gordon model [H. Craig, L.I. Gordon. Deuterium and oxygen-18 variations in the ocean and the marine atmosphere. In Stable Isotopes in Oceanographic Studies and Paleotemperature, Spoleto, E. Tongiorgi (Ed.), pp. 9-130, Consiglio Nazionale delle Ricerche, Laboratorio di Geologia Nucleare, Pisa (1965).] to specific conditions in temperate regions seems necessary.

Linking MODFLOW with an agent-based land-use model to support decision making

USGS Publications Warehouse

Reeves, H.W.; Zellner, M.L.

2010-01-01

The U.S. Geological Survey numerical groundwater flow model, MODFLOW, was integrated with an agent-based land-use model to yield a simulator for environmental planning studies. Ultimately, this integrated simulator will be used as a means to organize information, illustrate potential system responses, and facilitate communication within a participatory modeling framework. Initial results show the potential system response to different zoning policy scenarios in terms of the spatial patterns of development, which is referred to as urban form, and consequent impacts on groundwater levels. These results illustrate how the integrated simulator is capable of representing the complexity of the system. From a groundwater modeling perspective, the most important aspect of the integration is that the simulator generates stresses on the groundwater system within the simulation in contrast to the traditional approach that requires the user to specify the stresses through time. Copyright ?? 2010 The Author(s). Journal compilation ?? 2010 National Ground Water Association.

Hydrologic and Water-Quality Responses in Shallow Ground Water Receiving Stormwater Runoff and Potential Transport of Contaminants to Lake Tahoe, California and Nevada, 2005-07

USGS Publications Warehouse

Green, Jena M.; Thodal, Carl E.; Welborn, Toby L.

2008-01-01

Clarity of Lake Tahoe, California and Nevada has been decreasing due to inflows of sediment and nutrients associated with stormwater runoff. Detention basins are considered effective best management practices for mitigation of suspended sediment and nutrients associated with runoff, but effects of infiltrated stormwater on shallow ground water are not known. This report documents 2005-07 hydrogeologic conditions in a shallow aquifer and associated interactions between a stormwater-control system with nearby Lake Tahoe. Selected chemical qualities of stormwater, bottom sediment from a stormwater detention basin, ground water, and nearshore lake and interstitial water are characterized and coupled with results of a three-dimensional, finite-difference, mathematical model to evaluate responses of ground-water flow to stormwater-runoff accumulation in the stormwater-control system. The results of the ground-water flow model indicate mean ground-water discharge of 256 acre feet per year, contributing 27 pounds of phosphorus and 765 pounds of nitrogen to Lake Tahoe within the modeled area. Only 0.24 percent of this volume and nutrient load is attributed to stormwater infiltration from the detention basin. Settling of suspended nutrients and sediment, biological assimilation of dissolved nutrients, and sorption and detention of chemicals of potential concern in bottom sediment are the primary stormwater treatments achieved by the detention basins. Mean concentrations of unfiltered nitrogen and phosphorus in inflow stormwater samples compared to outflow samples show that 55 percent of nitrogen and 47 percent of phosphorus are trapped by the detention basin. Organic carbon, cadmium, copper, lead, mercury, nickel, phosphorus, and zinc in the uppermost 0.2 foot of bottom sediment from the detention basin were all at least twice as concentrated compared to sediment collected from 1.5 feet deeper. Similarly, concentrations of 28 polycyclic aromatic hydrocarbon compounds were all less than laboratory reporting limits in the deeper sediment sample, but 15 compounds were detected in the uppermost 0.2 foot of sediment. Published concentrations determined to affect benthic aquatic life also were exceeded for copper, zinc, benz[a]anthracene, phenanthrene, and pyrene in the shallow sediment sample. Isotopic composition of water (oxygen 18/16 and hydrogen 2/1 ratios) for samples of shallow ground water, lakewater, and interstitial water from Lake Tahoe indicate the lake was well mixed with a slight ground-water signature in samples collected near the lakebed. One interstitial sample from 0.8 foot beneath the lakebed was nearly all ground water and concentrations of nitrogen and phosphorus were comparable to concentrations in shallow ground-water samples. However, ammonium represented 65 percent of filtered nitrogen in this interstitial sample, but only 10 percent of the average nitrogen in ground-water samples. Nitrate was less than reporting limits in interstitial water, compared with mean nitrate concentration of 750 micrograms per liter in ground-water samples, indicating either active dissimilative nitrate reduction to ammonium by micro-organisms or hydrolysis of organic nitrogen to ammonium with concomitant nitrate reduction. The other interstitial sample falls along a mixing line between ground water and lake water and most of the nitrogen was organic nitrogen.

Simulations of ecosystem hydrological processes using a unified multi-scale model

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Xiaofan; Liu, Chongxuan; Fang, Yilin

2015-01-01

This paper presents a unified multi-scale model (UMSM) that we developed to simulate hydrological processes in an ecosystem containing both surface water and groundwater. The UMSM approach modifies the Navier–Stokes equation by adding a Darcy force term to formulate a single set of equations to describe fluid momentum and uses a generalized equation to describe fluid mass balance. The advantage of the approach is that the single set of the equations can describe hydrological processes in both surface water and groundwater where different models are traditionally required to simulate fluid flow. This feature of the UMSM significantly facilitates modelling ofmore » hydrological processes in ecosystems, especially at locations where soil/sediment may be frequently inundated and drained in response to precipitation, regional hydrological and climate changes. In this paper, the UMSM was benchmarked using WASH123D, a model commonly used for simulating coupled surface water and groundwater flow. Disney Wilderness Preserve (DWP) site at the Kissimmee, Florida, where active field monitoring and measurements are ongoing to understand hydrological and biogeochemical processes, was then used as an example to illustrate the UMSM modelling approach. The simulations results demonstrated that the DWP site is subject to the frequent changes in soil saturation, the geometry and volume of surface water bodies, and groundwater and surface water exchange. All the hydrological phenomena in surface water and groundwater components including inundation and draining, river bank flow, groundwater table change, soil saturation, hydrological interactions between groundwater and surface water, and the migration of surface water and groundwater interfaces can be simultaneously simulated using the UMSM. Overall, the UMSM offers a cross-scale approach that is particularly suitable to simulate coupled surface and ground water flow in ecosystems with strong surface water and groundwater interactions.« less

Development of monitoring and modelling tools as basis for sustainable thermal management concepts of urban groundwater bodies

NASA Astrophysics Data System (ADS)

Mueller, Matthias H.; Epting, Jannis; Köhler, Mandy; Händel, Falk; Huggenberger, Peter

2015-04-01

Increasing groundwater temperatures observed in many urban areas strongly interfere with the demand of thermal groundwater use. The groundwater temperatures in these urban areas are affected by numerous interacting factors: open and closed-loop geothermal systems for heating and cooling, sealed surfaces, constructions in the subsurface (infrastructure and buildings), artificial groundwater recharge, and interaction with rivers. On the one hand, these increasing groundwater temperatures will negatively affect the potential for its use in the future e.g. for cooling purposes. On the other hand, elevated subsurface temperatures can be considered as an energy source for shallow geothermal heating systems. Integrated thermal management concepts are therefore needed to coordinate the thermal use of groundwater in urban areas. These concepts should be based on knowledge of the driving processes which influence the thermal regime of the aquifer. We are currently investigating the processes influencing the groundwater temperature throughout the urban area of Basel City, Switzerland. This involves a three-dimensional numerical groundwater heat-transport model including geothermal use and interactions with the unsaturated zone such as subsurface constructions reaching into the aquifer. The cantonal groundwater monitoring system is an important part of the data base in our model, which will help to develop sustainable management strategies. However, single temperature measurements in conventional groundwater wells can be biased by vertical thermal convection. Therefore, multilevel observation wells are used in the urban areas of the city to monitor subsurface temperatures reaching from the unsaturated zone to the base of the aquifer. These multilevel wells are distributed in a pilot area in order to monitor the subsurface temperatures in the vicinity of deep buildings and to quantify the influence of the geothermal use of groundwater. Based on time series of the conventional groundwater wells, the multilevel observation wells and the different boundary conditions we characterize the groundwater temperature regimes using a regional groundwater heat-transport model. In the urban area of Basel, mean annual groundwater temperatures are significantly increasing with 0.05 K per year in the period of 1994 to 2014, which is most likely due to anthropogenic influences. Overall, mean annual groundwater temperatures of Basel are 3.0

Ground-Water Flow Model of the Sierra Vista Subwatershed and Sonoran Portions of the Upper San Pedro Basin, Southeastern Arizona, United States, and Northern Sonora, Mexico

USGS Publications Warehouse

Pool, D.R.; Dickinson, Jesse

2007-01-01

A numerical ground-water model was developed to simulate seasonal and long-term variations in ground-water flow in the Sierra Vista subwatershed, Arizona, United States, and Sonora, Mexico, portions of the Upper San Pedro Basin. This model includes the simulation of details of the groundwater flow system that were not simulated by previous models, such as ground-water flow in the sedimentary rocks that surround and underlie the alluvial basin deposits, withdrawals for dewatering purposes at the Tombstone mine, discharge to springs in the Huachuca Mountains, thick low-permeability intervals of silt and clay that separate the ground-water flow system into deep-confined and shallow-unconfined systems, ephemeral-channel recharge, and seasonal variations in ground-water discharge by wells and evapotranspiration. Steady-state and transient conditions during 1902-2003 were simulated by using a five-layer numerical ground- water flow model representing multiple hydrogeologic units. Hydraulic properties of model layers, streamflow, and evapotranspiration rates were estimated as part of the calibration process by using observed water levels, vertical hydraulic gradients, streamflow, and estimated evapotranspiration rates as constraints. Simulations approximate observed water-level trends throughout most of the model area and streamflow trends at the Charleston streamflow-gaging station on the San Pedro River. Differences in observed and simulated water levels, streamflow, and evapotranspiration could be reduced through simulation of climate-related variations in recharge rates and recharge from flood-flow infiltration.

The effects of boundary conditions on the steady-state response of three hypothetical ground-water systems; results and implications of numerical experiments

USGS Publications Warehouse

Franke, O. Lehn; Reilly, Thomas E.

1987-01-01

The most critical and difficult aspect of defining a groundwater system or problem for conceptual analysis or numerical simulation is the selection of boundary conditions . This report demonstrates the effects of different boundary conditions on the steady-state response of otherwise similar ground-water systems to a pumping stress. Three series of numerical experiments illustrate the behavior of three hypothetical groundwater systems that are rectangular sand prisms with the same dimensions but with different combinations of constant-head, specified-head, no-flow, and constant-flux boundary conditions. In the first series of numerical experiments, the heads and flows in all three systems are identical, as are the hydraulic conductivity and system geometry . However, when the systems are subjected to an equal stress by a pumping well in the third series, each differs significantly in its response . The highest heads (smallest drawdowns) and flows occur in the systems most constrained by constant- or specified-head boundaries. These and other observations described herein are important in steady-state calibration, which is an integral part of simulating many ground-water systems. Because the effects of boundary conditions on model response often become evident only when the system is stressed, a close match between the potential distribution in the model and that in the unstressed natural system does not guarantee that the model boundary conditions correctly represent those in the natural system . In conclusion, the boundary conditions that are selected for simulation of a ground-water system are fundamentally important to groundwater systems analysis and warrant continual reevaluation and modification as investigation proceeds and new information and understanding are acquired.

Simulation of projected water demand and ground-water levels in the Coffee Sand and Eutaw-McShan aquifers in Union County, Mississippi, 2010 through 2050

USGS Publications Warehouse

Hutson, Susan S.; Strom, E.W.; Burt, D.E.; Mallory, M.J.

2000-01-01

Ground water from the Eutaw-McShan and the Coffee Sand aquifers is the major source of supply for residential, commercial, and industrial purposes in Union County, Mississippi. Unbiased, scientifically sound data and assessments are needed to assist agencies in better understanding and managing available water resources as continuing development and growth places more stress on available resources. The U.S. Geological Survey, in cooperation with the Tennessee Valley Authority, conducted an investigation using water-demand and ground-water models to evaluate the effect of future water demand on groundwater levels. Data collected for the 12 public-supply facilities and the self-supplied commercial and industrial facilities in Union County were used to construct water-demand models. The estimates of water demand to year 2050 were then input to a ground-water model based on the U.S. Geological Survey finite-difference computer code, MODFLOW. Total ground-water withdrawals for Union County in 1998 were estimated as 2.85 million gallons per day (Mgal/d). Of that amount, municipal withdrawals were 2.55 Mgal/d with about 1.50 Mgal/d (59 percent) delivered to residential users. Nonmunicipal withdrawals were 0.296 Mgal/d. About 80 percent (2.27 Mgal/d) of the total ground-water withdrawal is produced from the Eutaw-McShan aquifer and about 13 percent (0.371 Mgal/d) from the Coffee Sand aquifer. Between normal- and high-growth conditions, total water demand could increase from 72 to 131 percent (2.9 Mgal/d in 1998 to 6.7 Mgal/d in year 2050) with municipal demand increasing from 77 to 146 percent (2.6 to 6.4 Mgal/d). Increased pumping to meet the demand for water was simulated to determine the effect on water levels in the Coffee Sand and Eutaw- McShan aquifers. Under baseline-growth conditions, increased water use by year 2050 could result in an additional 65 feet of drawdown in the New Albany area below year 2000 water levels in the Coffee Sand aquifer and about 120 feet of maximum drawdown in the Eutaw-McShan aquifer. Under normal-growth conditions, increased water use could result in an additional 65 feet of drawdown in the New Albany area below year 2000 water levels in the Coffee Sand aquifer and about 135 feet of maximum drawdown in the Eutaw-McShan aquifer. Under high-growth conditions, increased water use could result in 75 feet of drawdown in the New Albany area below year 2000 water levels in the Coffee Sand aquifer and about 190 feet of maximum drawdown in the Eutaw-McShan aquifer. The resulting highgrowth projected water level for the year 2050 at the center of the drawdown cone in the New Albany area is between 450 and 500 feet above the top of the Eutaw-McShan aquifer.

Simulating selenium and nitrogen fate and transport in coupled stream-aquifer systems of irrigated regions

NASA Astrophysics Data System (ADS)

Shultz, Christopher D.; Bailey, Ryan T.; Gates, Timothy K.; Heesemann, Brent E.; Morway, Eric D.

2018-05-01

Elevated levels of selenium (Se) in aqueous environments can harm aquatic life and endanger livestock and human health. Although Se occurs naturally in the rocks and soils of many alluvial aquifers, mining and agricultural activities can increase its rate of mobilization and transport to surface waters. Attention is given here to regions where nonpoint source return flows from irrigated lands carry pollutant loads to aquifers and streams, contributing to concentrations that violate regulatory and performance standards. Of particular concern is the heightened level and mobilization of Se influenced by nitrate (NO3), a harmful pollutant in its own right. We present a numerical model that simulates the reactive transport of Se and nitrogen (N) species in a coupled groundwater-surface water system. Building upon a conceptual model that incorporates the major processes affecting Se and NO3 transport in an irrigated watershed, the model links the finite-difference models MODFLOW, UZF-RT3D, and OTIS, to simulate flow and reactive transport of multiple chemical species in both the aquifer and a stream network, with mass exchange between the two. The capability of the new model is showcased by calibration, testing, and application to a 500 km2 region in Colorado's Lower Arkansas River Valley using a rich data set gathered over a 10-yr period. Simulation of spatial and temporal distributions of Se concentration reveals conditions that exceed standards in groundwater for approximately 20% of the area. For the Arkansas River, standards are exceeded by 290%-450%. Simulation indicates that river concentrations of NO3 alone are near the current interim standard for the total of all dissolved N species. These results indicate the need for future use of the developed model to investigate the prospects for land and water best management practices to decrease pollutant levels.

Simulating selenium and nitrogen fate and transport in coupled stream-aquifer systems of irrigated regions

USGS Publications Warehouse

Shultz, Christopher D.; Bailey, Ryan T.; Gates, Timothy K.; Heesemann, Brent E.; Morway, Eric D.

2018-01-01

Elevated levels of selenium (Se) in aqueous environments can harm aquatic life and endanger livestock and human health. Although Se occurs naturally in the rocks and soils of many alluvial aquifers, mining and agricultural activities can increase its rate of mobilization and transport to surface waters. Attention is given here to regions where nonpoint source return flows from irrigated lands carry pollutant loads to aquifers and streams, contributing to concentrations that violate regulatory and performance standards. Of particular concern is the heightened level and mobilization of Se influenced by nitrate (NO3), a harmful pollutant in its own right. We present a numerical model that simulates the reactive transport of Se and nitrogen (N) species in a coupled groundwater-surface water system. Building upon a conceptual model that incorporates the major processes affecting Se and NO3 transport in an irrigated watershed, the model links the finite-difference models MODFLOW, UZF-RT3D, and OTIS, to simulate flow and reactive transport of multiple chemical species in both the aquifer and a stream network, with mass exchange between the two. The capability of the new model is showcased by calibration, testing, and application to a 500 km2 region in Colorado’s Lower Arkansas River Valley using a rich data set gathered over a 10-yr period. Simulation of spatial and temporal distributions of Se concentration reveals conditions that exceed standards in groundwater for approximately 20% of the area. For the Arkansas River, standards are exceeded by 290%–450%. Simulation indicates that river concentrations of NO3 alone are near the current interim standard for the total of all dissolved N species. These results indicate the need for future use of the developed model to investigate the prospects for land and water best management practices to decrease pollutant levels.

Advances in understanding river-groundwater interactions

NASA Astrophysics Data System (ADS)

Brunner, Philip; Therrien, René; Renard, Philippe; Simmons, Craig T.; Franssen, Harrie-Jan Hendricks

2017-09-01

River-groundwater interactions are at the core of a wide range of major contemporary challenges, including the provision of high-quality drinking water in sufficient quantities, the loss of biodiversity in river ecosystems, or the management of environmental flow regimes. This paper reviews state of the art approaches in characterizing and modeling river and groundwater interactions. Our review covers a wide range of approaches, including remote sensing to characterize the streambed, emerging methods to measure exchange fluxes between rivers and groundwater, and developments in several disciplines relevant to the river-groundwater interface. We discuss approaches for automated calibration, and real-time modeling, which improve the simulation and understanding of river-groundwater interactions. Although the integration of these various approaches and disciplines is advancing, major research gaps remain to be filled to allow more complete and quantitative integration across disciplines. New possibilities for generating realistic distributions of streambed properties, in combination with more data and novel data types, have great potential to improve our understanding and predictive capabilities for river-groundwater systems, especially in combination with the integrated simulation of the river and groundwater flow as well as calibration methods. Understanding the implications of different data types and resolution, the development of highly instrumented field sites, ongoing model development, and the ultimate integration of models and data are important future research areas. These developments are required to expand our current understanding to do justice to the complexity of natural systems.

Modelling of lindane transport in groundwater of metropolitan city Vadodara, Gujarat, India.

PubMed

Sharma, M K; Jain, C K; Rao, G Tamma; Rao, V V S Gurunadha

2015-05-01

Migration pattern of organochloro pesticide lindane has been studied in groundwater of metropolitan city Vadodara. Groundwater flow was simulated using the groundwater flow model constructed up to a depth of 60 m considering a three-layer structure with grid size of 40 × 40 × 40 m(3). The general groundwater flow direction is from northeast to south and southwest. The river Vishwamitri and river Jambua form natural hydrologic boundary. The constant head in the north and south end of the study area is taken as another boundary condition in the model. The hydraulic head distribution in the multilayer aquifer has been computed from the visual MODFLOW groundwater flow model. TDS has been computed though MT3D mass transport model starting with a background concentration of 500 mg/l and using a porosity value of 0.3. Simulated TDS values from the model matches well with the observed data. Model MT3D was run for lindane pesticide with a background concentration of 0.5 μg/l. The predictions of the mass transport model for next 50 years indicate that advancement of containment of plume size in the aquifer system both spatially and depth wise as a result of increasing level of pesticide in river Vishwamitri. The restoration of the aquifer system may take a very long time as seen from slow improvement in the groundwater quality from the predicted scenarios, thereby, indicating alarming situation of groundwater quality deterioration in different layers. It is recommended that all the industries operating in the region should install efficient effluent treatment plants to abate the pollution problem.

Study of Basin Recession Characteristics and Groundwater Storage Properties

NASA Astrophysics Data System (ADS)

Yen-Bo, Chen; Cheng-Haw, Lee

2017-04-01

Stream flow and groundwater storage are freshwater resources that human live on.In this study, we discuss southern area basin recession characteristics and Kao-Ping River basin groundwater storage, and hope to supply reference to Taiwan water resource management. The first part of this study is about recession characteristics. We apply Brutsaert (2008) low flow analysis model to establish two recession data pieces sifting models, including low flow steady period model and normal condition model. Within individual event analysis, group event analysis and southern area basin recession assessment, stream flow and base flow recession characteristics are parameterized. The second part of this study is about groundwater storage. Among main basin in southern Taiwan, there are sufficient stream flow and precipitation gaging station data about Kao-Ping River basin and extensive drainage data, and data about different hydrological characteristics between upstream and downstream area. Therefore, this study focuses on Kao-Ping River basin and accesses groundwater storage properties. Taking residue of groundwater volume in dry season into consideration, we use base flow hydrograph to access periodical property of groundwater storage, in order to establish hydrological period conceptual model. With groundwater storage and precipitation accumulative linearity quantified by hydrological period conceptual model, their periodical changing and alternation trend properties in each drainage areas of Kao-Ping River basin have been estimated. Results of this study showed that the recession time of stream flow is related to initial flow rate of the recession events. The recession time index is lower when the flow is stream flow, not base flow, and the recession time index is higher in low flow steady flow period than in normal recession condition. By applying hydrological period conceptual model, groundwater storage could explicitly be analyzed and compared with precipitation, by only using stream flow data. Keywords: stream flow, base flow, recession characteristics, groundwater storage

Modeling rainfall conditions for shallow landsliding in Seattle, Washington

USGS Publications Warehouse

Godt, Jonathan W.; Schulz, William H.; Baum, Rex L.; Savage, William Z.

2008-01-01

We describe the results from an application of a distributed, transient infiltration–slope-stability model for an 18 km2 area of southwestern Seattle, Washington, USA. The model (TRIGRS) combines an infinite slope-stability calculation and an analytic, one-dimensional solution for pore-pressure diffusion in a soil layer of finite depth in response to time-varying rainfall. The transient solution for pore-pressure response can be superposed on any steady-state groundwater-flow field that is consistent with model assumptions. Applied over digital topography, the model computes a factor of safety for each grid cell at any time during a rainstorm. Input variables may vary from cell to cell, and the rainfall rate can vary in both space and time. For Seattle, topographic slope derived from an airborne laser swath mapping (ALSM)–based 3 m digital elevation model (DEM), maps of soil and water-table depths derived from geotechnical borings, and hourly rainfall intensities were used as model inputs. Material strength and hydraulic properties used in the model were determined from field and laboratory measurements, and a tension-saturated initial condition was assumed. Results are given in terms of a destabilizing intensity and duration of rainfall, and they were evaluated by comparing the locations of 212 historical landslides with the area mapped as potentially unstable. Because the equations of groundwater flow are explicitly solved with respect to time, the results from TRIGRS simulations can be portrayed quantitatively to assess the potential landslide hazard based on rainfall conditions.

Analysis of confidence in continental-scale groundwater recharge estimates for Africa using a distributed water balance model

NASA Astrophysics Data System (ADS)

Mackay, Jonathan; Mansour, Majdi; Bonsor, Helen; Pachocka, Magdalena; Wang, Lei; MacDonald, Alan; Macdonald, David; Bloomfield, John

2014-05-01

There is a growing need for improved access to reliable water in Africa as population and food production increases. Currently approximately 300 million people do not have access to a secure source of safe drinking water. To meet these current and future demands, groundwater will need to be increasingly abstracted; groundwater is more reliable than surface water sources due to its relatively long response time to meteorological stresses and therefore is likely to be a more secure water resource in a more variable climate. Recent studies also quantified the volumes of groundwater potentially available which suggest that, if exploited, groundwater could help to meet the demand for fresh water. However, there is still considerable uncertainty as to how these resources may respond in the future due to changes in groundwater recharge and abstraction. Understanding and quantifying groundwater recharge is vital as it forms a primary indicator of the sustainability of underlying groundwater resources. Computational hydrological models provide a means to do this, but the complexity of recharge processes in Africa mean that these simulations are often highly uncertain. This study aims to evaluate our confidence in simulating groundwater recharge over Africa based on a sensitivity analysis using a distributed hydrological model developed by the British Geological Survey, ZOODRM. The model includes land surface, canopy, river, soil and groundwater components. Each component is able to exchange water and as such, forms a distributed water balance of Africa. The components have been parameterised using available spatial datasets of African vegetation, land-use, soil and hydrogeology while the remaining parameters have been estimated by calibrating the model to available river flow data. Continental-scale gridded precipitation and potential evapotranspiration datasets, based on remotely sensed and ground observations, have been used to force the model. Following calibration, the sensitivity analysis has been undertaken in two stages. For the first stage, individual parameters are perturbed from each component of the model. For the second stage, different methods for calculating groundwater recharge are introduced. Both stages aim to investigate which aspects of the model most impact on groundwater recharge and consequently how confidently we can simulate the complex recharge processes that occur in Africa using large scale hydrological models. Preliminary results from the analysis indicate the parameters that control runoff generation from the land surface and the choice of groundwater recharge calculation method both have a significant impact on groundwater recharge simulations.

Slope instability in complex 3D topography promoted by convergent 3D groundwater flow

NASA Astrophysics Data System (ADS)

Reid, M. E.; Brien, D. L.

2012-12-01

Slope instability in complex topography is generally controlled by the interaction between gravitationally induced stresses, 3D strengths, and 3D pore-fluid pressure fields produced by flowing groundwater. As an example of this complexity, coastal bluffs sculpted by landsliding commonly exhibit a progression of undulating headlands and re-entrants. In this landscape, stresses differ between headlands and re-entrants and 3D groundwater flow varies from vertical rainfall infiltration to lateral groundwater flow on lower permeability layers with subsequent discharge at the curved bluff faces. In plan view, groundwater flow converges in the re-entrant regions. To investigate relative slope instability induced by undulating topography, we couple the USGS 3D limit-equilibrium slope-stability model, SCOOPS, with the USGS 3D groundwater flow model, MODFLOW. By rapidly analyzing the stability of millions of potential failures, the SCOOPS model can determine relative slope stability throughout the 3D domain underlying a digital elevation model (DEM), and it can utilize both fully 3D distributions of pore-water pressure and material strength. The two models are linked by first computing a groundwater-flow field in MODFLOW, and then computing stability in SCOOPS using the pore-pressure field derived from groundwater flow. Using these two models, our analyses of 60m high coastal bluffs in Seattle, Washington showed augmented instability in topographic re-entrants given recharge from a rainy season. Here, increased recharge led to elevated perched water tables with enhanced effects in the re-entrants owing to convergence of groundwater flow. Stability in these areas was reduced about 80% compared to equivalent dry conditions. To further isolate these effects, we examined groundwater flow and stability in hypothetical landscapes composed of uniform and equally spaced, oscillating headlands and re-entrants with differing amplitudes. The landscapes had a constant slope for both headlands and re-entrants to minimize slope effects on stability. Despite these equal slopes, our analyses, given dry conditions, illustrated that the headlands can be 5-7% less stable than the re-entrants, owing to the geometry of the 3D failure mass with the lowest stability. We then simulated groundwater flow in these landscapes; flow was caused by recharge perching on a horizontal low permeability layer with discharge at the bluff faces. By systematically varying recharge, hydraulic conductivity of the material, and conductance at the bluffs, we created different 3D pore-pressure fields. Recharge rates and hydraulic conductivities controlled the height of the water table, whereas bluff conductance influenced the gradient of the water table near the bluff face. Given elevated water tables with steep gradients, bluffs in the re-entrants became unstable where flow converged. Thus, with progressively stronger effects from water flow, overall instability evolved from relatively unstable headlands to more uniform stability to relatively unstable re-entrants. Larger re-entrants led to more 3D flow convergence and greater localized instability. One- or two-dimensional models cannot fully characterize slope instability in complex topography.

Role of different types of solid models in hydrodynamic modeling and their effects on groundwater protection processes

NASA Astrophysics Data System (ADS)

Bódi, Erika; Buday, Tamás; McIntosh, Richard William

2013-04-01

Defining extraction-modified flow patterns with hydrodynamic models is a pivotal question in preserving groundwater resources regarding both quality and quantity. Modeling is the first step in groundwater protection the main result of which is the determination of the protective area depending on the amount of extracted water. Solid models have significant effects on hydrodynamic models as they are based on the solid models. Due to the legislative regulations, on protection areas certain restrictions must be applied which has firm consequences on economic activities. In Hungarian regulations there are no clear instructions for the establishment of either geological or hydrodynamic modeling, however, modeling itself is an obligation. Choosing the modeling method is a key consideration for further numerical calculations and it is decisive regarding the shape and size of the groundwater protection area. The geometry of hydrodynamic model layers is derived from the solid model. There are different geological approaches including lithological and sequence stratigraphic classifications furthermore in the case of regional models, formation-based hydrostratigraphic units are also applicable. Lithological classification is based on assigning and mapping of lithotypes. When the geometry (e.g. tectonic characteristics) of the research area is not known, horizontal bedding is assumed the probability of which can not be assessed based on only lithology. If the geological correlation is based on sequence stratigraphic studies, the cyclicity of sediment deposition is also considered. This method is more integrated thus numerous parameters (e.g. electrofacies) are taken into consideration studying the geological conditions ensuring more reliable modeling. Layers of sequence stratigraphic models can be either lithologically homogeneous or they may include greater cycles of sediments containing therefore several lithological units. The advantage of this is that the modeling can handle pinching out lithological units and lenticular bodies easier while most hydrodynamic softwares cannot handle flow units related to such model layers. Interpretation of tectonic disturbance is similar. In Hungary groundwater is extracted mainly from Pleistocene and Pannonian aquifers sediments of which were deposited in the ancient Pannonian Lake. When the basin lost its open-marine connection eustasy had no direct effects on facies changes therefore subsidence and sediment supply became the main factors. Various basin-filling related facies developed including alluvial plain facies, different delta facies types and pelitic deep-basin facies. Creating solid models based on sequence stratigraphic methods requires more raw data and also genetic approaches, in addition more working hours hence this method is seldom used in practice. Lithology-based models can be transformed into sequence stratigraphic models by extending the data base (e.g. detecting more survey data). In environments where the obtained models differ significantly notable changes can occur in the supply directions in addition the groundwater travel-time of the two models even on equal extraction terms. Our study aims to call attention to the consequences of using different solid models for typical depositional systems of the Great Hungarian Plain and to their effects on groundwater protection.

Applications of discrete element method in modeling of grain postharvest operations

USDA-ARS?s Scientific Manuscript database

Grain kernels are finite and discrete materials. Although flowing grain can behave like a continuum fluid at times, the discontinuous behavior exhibited by grain kernels cannot be simulated solely with conventional continuum-based computer modeling such as finite-element or finite-difference methods...

Analysis of the applicability of geophysical methods and computer modelling in determining groundwater level

NASA Astrophysics Data System (ADS)

Czaja, Klaudia; Matula, Rafal

2014-05-01

The paper presents analysis of the possibilities of application geophysical methods to investigation groundwater conditions. In this paper groundwater is defined as liquid water flowing through shallow aquifers. Groundwater conditions are described through the distribution of permeable layers (like sand, gravel, fractured rock) and impermeable or low-permeable layers (like clay, till, solid rock) in the subsurface. GPR (Ground Penetrating Radar), ERT(Electrical Resistivity Tomography), VES (Vertical Electric Soundings) and seismic reflection, refraction and MASW (Multichannel Analysis of Surface Waves) belong to non - invasive, surface, geophysical methods. Due to differences in physical parameters like dielectric constant, resistivity, density and elastic properties for saturated and saturated zones it is possible to use geophysical techniques for groundwater investigations. Few programmes for GPR, ERT, VES and seismic modelling were applied in order to verify and compare results. Models differ in values of physical parameters such as dielectric constant, electrical conductivity, P and S-wave velocity and the density, layers thickness and the depth of occurrence of the groundwater level. Obtained results for computer modelling for GPR and seismic methods and interpretation of test field measurements are presented. In all of this methods vertical resolution is the most important issue in groundwater investigations. This require proper measurement methodology e.g. antennas with frequencies high enough, Wenner array in electrical surveys, proper geometry for seismic studies. Seismic velocities of unconsolidated rocks like sand and gravel are strongly influenced by porosity and water saturation. No influence of water saturation degree on seismic velocities is observed below a value of about 90% water saturation. A further saturation increase leads to a strong increase of P-wave velocity and a slight decrease of S-wave velocity. But in case of few models only the relationship between differences in density and P-wave and S-wave velocity were observed. This is probably due to the way the modelling program calculates the wave field. Trace by trace should be analyzed during GPR interpretation, especially changes in signal amplitude. High permittivity of water results in higher permittivity of material and high reflection coefficient of electromagnetic wave. In case of electrical studies groundwater mineralization has the highest influence. When the layer thickness is small VES gives much better results than ERT.