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1

A QUICK AND STABLE ALGORITHM FOR GROUNDWATER FLOW PARAMETER ESTIMATION UNDER UNCERTAINTY

A quick and stable algorithm for groundwater flow parameter estimation by optimization methods under steady- state conditions is presented. A combination of gradient, Gauss-Newton and full Newton algorithms is used. The opti mization methods are directly connected with the finite element groundwater flow computations. The sensitivity matrix is computed by a differentiation of the discretized flow equation. The gradient and

B. ODENWALD; B. HERRLING

2

Parameter Estimation and Validation of Groundwater Flow Models

The reliability of model predictions is determined by the accuracy of the calibration, that is, dependent on the solution of the inverse problem of the groundwater flow equation. Provided that this problem is solved, the model can be validated. If the model is capable of reproducing the measured data for only one significantly different additional hydrologic system state, the model

Rainer Niedermeyer

1998-01-01

3

This paper proposes a composite L1 parameter estimator to solve the inverse problems in groundwater flow and solute transport modeling. The estimator is formulated using a weighted L1 norm as the error measure between the vector of the observed hydraulic heads and solute concentrations and the corresponding vector of the heads and concentrations computed from a finite element model for

Y. Xiang; J. F. Sykes; N. R. Thomson

1993-01-01

4

Regional estimation of base flow and groundwater recharge in the Upper Mississippi river basin

Groundwater recharge and discharge (base flow) estimates from two methods were compared in the Upper Mississippi River basin (USGS hydrologic cataloging unit 07). The Upper Mississippi basin drains 491,700km2 in Illinois, Iowa, Missouri, Minnesota, and Wisconsin and outlets in the Mississippi River north of Cairo, Illinois. The first method uses the water balance components from the soil and water assessment

J. G. Arnold; R. S. Muttiah; R. Srinivasan; P. M. Allen

2000-01-01

5

Estimation of regional-scale groundwater flow properties in the Bengal Basin of India and Bangladesh

NASA Astrophysics Data System (ADS)

Quantitative evaluation of management strategies for long-term supply of safe groundwater for drinking from the Bengal Basin aquifer (India and Bangladesh) requires estimation of the large-scale hydrogeologic properties that control flow. The Basin consists of a stratified, heterogeneous sequence of sediments with aquitards that may separate aquifers locally, but evidence does not support existence of regional confining units. Considered at a large scale, the Basin may be aptly described as a single aquifer with higher horizontal than vertical hydraulic conductivity. Though data are sparse, estimation of regional-scale aquifer properties is possible from three existing data types: hydraulic heads, 14C concentrations, and driller logs. Estimation is carried out with inverse groundwater modeling using measured heads, by model calibration using estimated water ages based on 14C, and by statistical analysis of driller logs. Similar estimates of hydraulic conductivities result from all three data types; a resulting typical value of vertical anisotropy (ratio of horizontal to vertical conductivity) is 104. The vertical anisotropy estimate is supported by simulation of flow through geostatistical fields consistent with driller log data. The high estimated value of vertical anisotropy in hydraulic conductivity indicates that even disconnected aquitards, if numerous, can strongly control the equivalent hydraulic parameters of an aquifer system.

Michael, Holly A.; Voss, Clifford I.

2009-09-01

6

Estimation of groundwater recharge using the soil moisture budget method and the base-flow model

Estimation of groundwater recharge is extremely important for proper management of groundwater systems. Many different approaches\\u000a exist for estimating recharge. The main purpose of this paper is to apply a water balance concept with two methods to estimate\\u000a the groundwater recharge in the Ching-Shui watershed, Taiwan. First, a soil moisture budget method is established to estimate\\u000a the infiltration, runoff, evapotranspiration,

Cheng-Haw Lee; Hsin-Fu Yeh; Jin-Fa Chen

2008-01-01

7

NASA Astrophysics Data System (ADS)

Regularized inversion of groundwater flow models can be used to delineate geological heterogeneities using subspace methods like the singular value decomposition (SVD). To characterize heterogeneity, thousands of system parameters and, with appropriate regularization, thousands of observations may be necessary. The SVD method is not practical because it requires significant memory space and is time consuming. In previous work, we demonstrated the LSQR can be used to estimate the many unknown parameters in large groundwater flow inverse problems. However, in doing so, a resolution analysis is needed to characterize the reliability of the resulting model parameters. We adopted an approach developed for large seismic tomography problems and incorporate the PROPACK package into PEST, a model independent parameter estimation program. PROPACK estimates singular values and vectors for large sparse matrices efficiently and accurately based on the Lanczos bidiagonalization, the core of LSQR, with partial reorthogonalization. Unlike other LSQR-based resolution approaches, this PROPACK-based approach calculates the full resolution matrix. We estimate the model resolution matrix for a synthetic approximation based on a regional MODFLOW model of the Trout Lake Basin, Wisconsin, and compare it with results from the more commonly used SVD approach.

Muffels, C.; Zhang, H.; Doherty, J.; Tonkin, M.; Hunt, R.; Anderson, M.

2006-12-01

8

NASA Astrophysics Data System (ADS)

Dispersivity is one of the important transport parameter for evaluating pollutant migration in shallow and deep underground aquifers. But the accurate investigation of such parameter in porous media is difficult due to the high permeability contrast within the media, and scale dependency of the parameters determined. In this paper, in-situ injection and pumping test from different depths of an aquifer using a single borehole was proposed for the estimation of the dispersivity in saturated porous media and the efficiency of the test was studied by numerical analysis. For this purpose, an idealized numerical model was developed in which Darcy's equations for groundwater flow and Advection-Dispersion equations for pollutant transport were solved by three-dimensional rectangular Finite Element Method (FEM) based on the Galerkin Technique. The model was verified with the analytical solution achieved by Leij et al. (1991) for Three-Dimensional solute transport in a homogeneous, isotropic semi-infinite porous media during steady-state unidirectional groundwater flow with rectangular source. After verification, the model was simulated for different hydraulic conductivity and dispersivity for the study of flow and transport. Simulated results of the model indicated that hydraulic conductivity significantly influenced the dispersion of the pollutant and the dispersivity could be well estimated from the sensitivity analysis of breakthrough curve obtained by single borehole in-situ test.

Regmi, G.; Watanabe, K.; Sakamoto, Y.

2006-12-01

9

Uncertainty in 1D heat-flow analysis to estimate groundwater discharge to a stream.

Temperature measurements have been used by a variety of researchers to gain insight into groundwater discharge patterns. However, much of this research has reduced the problem to heat and fluid flow in one dimension for ease of analysis. This approach is seemingly at odds with the goal of determining spatial variability in specific discharge, which implies that the temperature field will vary in more than one dimension. However, it is unclear how important the resulting discrepancies are in the context of determining groundwater discharge to surface water bodies. In this study, the importance of these variations is examined by testing two popular one-dimensional analytical solutions with stochastic models of heat and fluid flow in a two-dimensional porous medium. For cases with low degrees of heterogeneity in hydraulic conductivity, acceptable results are possible for specific discharges between 10(-7) and 10(-5) m/s. However, conduction into areas with specific discharges less than 10(-7) m/s from adjacent areas can lead to significant errors. In some of these cases, the one-dimensional solutions produced estimates of specific discharge of nearly 10(-6) m/s. This phenomenon is more likely in situations with greater degrees of heterogeneity. PMID:20646070

Ferguson, Grant; Bense, Victor

10

NASA Astrophysics Data System (ADS)

Results are presented of a detailed study into the vadose zone and shallow water table hydrodynamics of a fieldsite in Shropshire, UK. Tensiometry reveals that the loamy sand topsoil wets up via macropore flow and subsequent redistribution of moisture into the soil matrix. However, recharge does not occur until near-positive pressures are achieved at the top of the glaciofluvial outwash material that underlies the topsoil, about 1 m above the water table. Once this occurs, very rapid water table rises follow. This threshold behaviour is attributed to the vertical discontinuity in the macropore system due to seasonal ploughing of the topsoil, and a lower permeability plough/iron pan restricting matrix flow between the topsoil and the lower outwash deposits. Thus, although the wetting process in the topsoil is highly complex, a soil moisture balance model (SMBM) is shown to be skilful in predicting the initiation of preferential flow from the base of the topsoil into the lower outwash horizon. The rapidity of the response at the water table suggests that Stokes type film flow rather than Richards type capillarity dominated flow is occurring and this conjecture is tested using a range of numerical models. A variation of the source-responsive model proposed by Nimmo (2010) is shown to reproduce the observed water table dynamics well, when linked to a SMBM as the source of recharge from the topsoil. The results reveal new insights into preferential flow processes in cultivated soils. If the conceptual and numerical models can be shown to be transferable to other ploughed soils, it promises to be a very useful and practical approach to accounting for preferential flow in studies of groundwater recharge estimation. Nimmo, J. R. (2010). Theory for Source-Responsive and Free-Surface Film Modeling of Unsaturated Flow. Vadose Zone Journal, 9, 295-306.

Cuthbert, M. O.; Mackay, R.; Nimmo, J. R.

2012-04-01

11

Parameters in numerical ground-water flow models have been successfully estimated using nonlinear-optimization methods such as the modified Gauss-Newton (GN) method and conjugate-direction methods. This paper investigates the relative efficiency of GN and three conjugate-direction parameter-estimation methods on two-dimensional, steady-state and transient ground-water flow test cases. The steady-state test cases are included to compare the performance of the algorithm with published examples. The three conjugate-direction methods are the Fletcher-Reeves (FR) and quasi-Newton (QN) regression methods, and combination Fletcher-Reeves quasi-Newton (FR-QN). All three are combined with Newton's method of calculating step size. The numerical ground-water flow model is described by McDonald and Harbaugh.

Hill, M. C.

1990-01-01

12

Ground-water withdrawals from 1913 through 1998 from the Death Valley regional flow system have been compiled to support a regional, three-dimensional, transient ground-water flow model. Withdrawal locations and depths of production intervals were estimated and associated errors were reported for 9,300 wells. Withdrawals were grouped into three categories: mining, public-supply, and commercial water use; domestic water use; and irrigation water use. In this report, groupings were based on the method used to estimate pumpage. Cumulative ground-water withdrawals from 1913 through 1998 totaled 3 million acre-feet, most of which was used to irrigate alfalfa. Annual withdrawal for irrigation ranged from 80 to almost 100 percent of the total pumpage. About 75,000 acre-feet was withdrawn for irrigation in 1998. Annual irrigation withdrawals generally were estimated as the product of irrigated acreage and application rate. About 320 fields totaling 11,000 acres were identified in six hydrographic areas. Annual application rates for high water-use crops ranged from 5 feet in Penoyer Valley to 9 feet in Pahrump Valley. The uncertainty in the estimates of ground-water withdrawals was attributed primarily to the uncertainty of application rate estimates. Annual ground-water withdrawal was estimated at about 90,000 acre-feet in 1998 with an assigned uncertainty bounded by 60,000 to 130,000 acre-feet.

Moreo, Michael T.; Halford, Keith J.; La Camera, Richard J.; Laczniak, Randell J.

2003-01-01

13

The Death Valley regional ground-water flow system encompasses an area of about 43,500 square kilometers in southeastern California and southern Nevada. The study area is underlain by Quaternary to Tertiary basin-fill sediments and mafic-lava flows; Tertiary volcanic, volcaniclastic, and sedimentary rocks; Tertiary to Jurassic granitic rocks; Triassic to Middle Proterozoic carbonate and clastic sedimentary rocks; and Early Proterozoic igneous and metamorphic rocks. The rock assemblage in the Death Valley region is extensively faulted as a result of several episodes of tectonic activity. This study is comprised of published and unpublished estimates of transmissivity, hydraulic conductivity, storage coefficient, and anisotropy ratios for hydrogeologic units within the Death Valley region study area. Hydrogeologic units previously proposed for the Death Valley regional transient ground-water flow model, were recognized for the purpose of studying the distribution of hydraulic properties. Analyses of regression and covariance were used to assess if a relation existed between hydraulic conductivity and depth for most hydrogeologic units. Those analyses showed a weak, quantitatively indeterminate, relation between hydraulic conductivity and depth.

W.R. Belcher; P.E. Elliott; A.L. Geldon

2001-12-31

14

A three-layer Death Valley regional groundwater flow model was constructed to evaluate potential regional groundwater flow paths in the vicinity of Yucca Mountain, Nevada. Geoscientific information systems were used to characterize the complex surface and subsurface hydrogeological conditions of the area, and this characterization was used to construct likely conceptual models of the flow system. The high contrasts and abrupt contacts of the different hydrogeological units in the subsurface make zonation the logical choice for representing the hydraulic conductivity distribution. Hydraulic head and spring flow data were used to test different conceptual models by using nonlinear regression to determine parameter values that currently provide the best match between the measured and simulated heads and flows.

D'Agnese, F. A.; Faunt, C. C.; Hill, M. C.; Turner, A. K.

1996-01-01

15

NSDL National Science Digital Library

Students will work in groups to make observations, identify aquifers, describe aquifer properties and measure hydraulic head in a physical groundwater flow model. The information collected will be used to answer questions pertaining to the groundwater flow system. The activity serves to consolidate the key concepts covered in lecture materials. These concepts include the water cycle, hydraulic head, types of aquifers, hydraulic conductivity, permeability, Darcy's Law, hydraulic gradient, porosity and groundwater contamination.

Manda, Alex

16

Gradual Variation Analysis for Groundwater Flow

Groundwater flow in Washington DC greatly influences the surface water quality in urban areas. The current methods of flow estimation, based on Darcy's Law and the groundwater flow equation, can be described by the diffusion equation (the transient flow) and the Laplace equation (the steady-state flow). The Laplace equation is a simplification of the diffusion equation under the condition that

Li Chen

2010-01-01

17

The Death Valley regional flow system (DVRFS) is one of the larger ground-water flow systems in the southwestern United States and includes much of southern Nevada and the Death Valley region of eastern California. Centrally located within the ground-water flow system is the Nevada Test Site (NTS). The NTS, a large tract covering about 1,375 square miles, historically has been used for testing nuclear devices and currently is being studied as a potential repository for the long-term storage of high-level nuclear waste generated in the United States. The U.S. Department of Energy, as mandated by Federal and State regulators, is evaluating the risk associated with contaminants that have been or may be introduced into the subsurface as a consequence of any past or future activities at the NTS. Because subsurface contaminants can be transported away from the NTS by ground water, components of the ground-water budget are of great interest. One such component is regional ground-water discharge. Most of the ground water leaving the DVRFS is limited to local areas where geologic and hydrologic conditions force ground water upward toward the surface to discharge at springs and seeps. Available estimates of ground-water discharge are based primarily on early work done as part of regional reconnaissance studies. These early efforts covered large, geologically complex areas and often applied substantially different techniques to estimate ground-water discharge. This report describes the results of a study that provides more consistent, accurate, and scientifically defensible measures of regional ground-water losses from each of the major discharge areas of the DVRFS. Estimates of ground-water discharge presented in this report are based on a rigorous quantification of local evapotranspiration (ET). The study identifies areas of ongoing ground-water ET, delineates different ET areas based on similarities in vegetation and soil-moisture conditions, and determines an ET rate for each delineated area. Each area, referred to as an ET unit, generally consists of one or more assemblages of local phreatophytes or a unique moist soil environment. Ten ET units are identified throughout the DVRFS based on differences in spectral-reflectance characteristics. Spectral differences are determined from satellite imagery acquired June 21, 1989, and June 13, 1992. The units identified include areas of open playa, moist bare soils, sparse to dense vegetation, and open water. ET rates estimated for each ET unit range from a few tenths of a foot per year for open playa to nearly 9 feet per year for open water. Mean annual ET estimates are computed for each discharge area by summing estimates of annual ET from each ET unit within a discharge area. The estimate of annual ET from each ET unit is computed as the product of an ET unit's acreage and estimated ET rate. Estimates of mean annual ET range from 450 acre-feet in the Franklin Well area to 30,000 acre-feet in Sarcobatus Flat. Ground-water discharge is estimated as annual ET minus that part of ET attributed to local precipitation. Mean annual ground-water discharge estimates range from 350 acre-feet in the Franklin Well area to 18,000 acre-feet in Ash Meadows. Generally, these estimates are greater for the northern discharge areas (Sarcobatus Flat and Oasis Valley) and less for the southern discharge areas (Franklin Lake, Shoshone area, and Tecopa/ California Valley area) than those previously reported.

Laczniak, Randell J.; Smith, J. LaRue; Elliott, Peggy E.; DeMeo, Guy A.; Chatigny, Melissa A.; Roemer, Gaius J.

2001-01-01

18

Quantification of the contribution of groundwater flow from highland areas of mountainous watersheds to semi-arid and arid valley bottom unconsolidated aquifers is increasingly needed for the assessment of water resources in many populated areas. In mountainous environments, however, data for Darcy equation parameters are limited, leading to uncertainty in estimates of groundwater flow of up to two or more orders

L. A. Neilson-Welch; R. Allard; D. Geller; D. M. Allen

2008-01-01

19

Karstification and Groundwater Flow

One of the principal aims of hydrogeology is to propose a reasonably adequate reconstruction of the groundwater flow field, in space and in time, for a given aquifer. For example, interpretation of the chemical and isotopic composition of groundwater, understanding of the geothermal conditions (anomalies) or forecasting the possible effects of industrial waste disposals and of intensive exploitation nearly always

L. Kiraly

20

NASA Astrophysics Data System (ADS)

Water resources are strongly limited in semi-arid to arid regions and groundwater constitutes often the only possibility for fresh water for the population and industry. An understanding of the hydrological processes and the estimation of magnitude of water balance parameters also includes the knowledge of processes of groundwater recharge. For the sustainable management of water resources, it is essential to estimate the potential groundwater recharge under the given climatic conditions. We would like to present the results of a hydrological model, which is based on the HRU- concept and intersected the parameters of climatic conditions, topography, geology, soil, vegetation and land use to calculate the groundwater recharge. This model was primarily developed for humid area applications and has now been adapted to the regional conditions in the semi-arid to arid region. It was quite a challenge to understand the hydrological processes in the semi-arid to arid study area and to implement those findings (e.g. routing [Schulz (in prep.)]) into the model structure. Thus we compared the existing approaches for groundwater recharge estimations (chloride mass balance [Marei et. al 2000], empirical relations such as rainfall and base flow-relation [Goldschmidt 1960; Guttman 2000; Hughes 2008; Issar 1993; Lerner 1990; De Vries et. al 2002]) with the results of our numerical model. References: De Vries, J. J., I. Simmers (2002): Groundwater recharge: an overview of processes and challenges. Hydrogeology Journal (2002) 10: 5-17. DOI 10.1007/s10040-001-0171-7. Guttman, J., 2000. Multi-Lateral Project B: Hydrogeology of the Eastern Aquifer in the Judea Hills and Jordan Valley. Mekorot Water Company, Report 468, p. 36. Hughes, A. G., M. M. Mansour, N. S. Robins (2008): Evaluation of distributed recharge in an upland semi-arid karst system: the West Bank Mountain Aquifer, Middle East. Hydrogeology Journal (2008) 16: 845-854. DOI 10.1007/s10040-008-0273-6 Issar, A. S. (1993): Recharge and salination processes in the carbonate aquifers in Israel. Environmental Geology (1993) 21: 152-159. Lerner, D. N., A. S. Issar, I. Simmers (1990): Groundwater recharge: a guide to understanding and estimating natural recharge. International contributions to hydrogeology: Vol. 8. Marei, A., S. Khayat, S. Weise, S. Ghannam., M. Sbaih, S. Geyer (2010): Estimating groundwater recharge using chloride mass-balance method in the West Bank. Hydrol. Sc 01/2010; 55(5): 780-792.

Gräbe, Agnes; Schulz, Stephan; Rödiger, Tino; Kolditz, Olaf

2013-04-01

21

Sophocleous, M.A., 1984. Groundwater-flow parameter estimation and quality modeling of the Equus Beds aquifer in Kansas, U.S.A.J. Hydrol., 69: 197--222. The salinity problems created in the Burrton area as a result of poor oil-field brine disposal practices of the past continue to be a major concern to the area depending on the Equus Beds aquifer for water, including the City

MARIOS A. SOPHOCLEOUS

1984-01-01

22

NASA Astrophysics Data System (ADS)

The Superior Court of California recently ruled that the Antelope Valley groundwater basin is in overdraft-groundwater extractions are in excess of the "safe yield" of the groundwater basin. As defined by the Court, "safe yield is the amount of annual extractions of water from an aquifer over time equal to the amount of water needed to recharge the groundwater aquifer and maintain it in equilibrium, plus any temporary surplus." Natural recharge is an important component of total groundwater recharge in Antelope Valley; however, the exact quantity and distribution of natural recharge is uncertain with estimates ranging from 30,000 to 160,000 acre-feet per year. Weighing the evidence presented by experts, the Court determined that the "safe yield" of the adjudicated area of the basin was 110,000 acre-feet per year. Knowledge of the quantity and distribution of natural recharge is needed to evaluate whether the Court-defined "safe yield" estimate for the basin will minimize additional storage depletion, and related land subsidence, resulting from continued groundwater extraction. The objective of this study is to systematically address the uncertainty in estimates of natural recharge and related aquifer parameters using a groundwater-flow and land-subsidence model with observational data and expert knowledge. Observational data include measured water levels, land-surface deformation, and estimates of transmissivity throughout the basin. An example of expert knowledge is the distribution of artesian conditions for pre-development times. Even though a great wealth of data is available, the problem of non-uniqueness remains present throughout the calibration process. Regularization is used to systematically identify combinations of parameters that can be uniquely estimated as well as to impose expert knowledge onto the parameter identification process. Once the model was calibrated with a reasonable parameter set, the parameter null-space was identified (i.e., the combinations of parameters that cannot be estimated given the available observation data). The majority of the parameter uncertainty is represented by the parameter null-space. Uncertainty in the average annual recharge was evaluated using the null-space Monte-Carlo method. Preliminary results indicate that the total natural recharge ranges between 30,000 and 50,000 acre-ft/yr, which is significantly lower than the Court-determined "safe yield".

Siade, A. J.; Nishikawa, T.; Martin, P.

2011-12-01

23

Estimating Vertical Groundwater Velocities Using Groundwater Thermal Gradients

NASA Astrophysics Data System (ADS)

An understanding of vertical groundwater flow through unconsolidated deposits is a component for predicting fate and transport of contaminants in the saturated zone. Groundwater movement through heterogeneous glacial deposits common to northern Indiana (USA) provided a test setting for determining if measured vertical groundwater thermal gradients could aid in calculating vertical groundwater velocity estimates. Field procedure was conducted by collecting stratified groundwater temperatures from a series of cased monitoring wells previously advanced through glacial till and outwash sedimentary sequences. Groundwater thermal gradients (temperature-depth profiles) were plotted and matched using automated computer modeling software (Microsoft Excel Solver) with published type curves to derive a dimensionless parameter for estimating vertical groundwater velocities. Data results matched predictions, to include an increase in vertical groundwater velocities during the seasonally wetter Spring; and, higher calculated vertical groundwater velocities for the finer-grained till aquitards when compared to aquifers comprised of coarser-grained outwash deposits. This study shows promise and has gathered interest both in the scientific community and environmental consulting practice for estimating vertical migration rates of contaminants (specifically those affected by advection) within the saturated zone. Government agencies or consultants, for instance, could also potentially apply this estimation technique to measure and map localized recharge rates for developing more accurate wellhead protection zones.

Arriaga, M. A.; Leap, D. I.; Petruccione, J. L.

2007-05-01

24

A method was developed for making estimates of long-term, mean annual ground-water recharge from streamflow data at 80 streamflow-gaging stations in Pennsylvania. The method relates mean annual base-flow yield derived from the streamflow data (as a proxy for recharge) to the climatic, geologic, hydrologic, and physiographic characteristics of the basins (basin characteristics) by use of a regression equation. Base-flow yield is the base flow of a stream divided by the drainage area of the basin, expressed in inches of water basinwide. Mean annual base-flow yield was computed for the period of available streamflow record at continuous streamflow-gaging stations by use of the computer program PART, which separates base flow from direct runoff on the streamflow hydrograph. Base flow provides a reasonable estimate of recharge for basins where streamflow is mostly unaffected by upstream regulation, diversion, or mining. Twenty-eight basin characteristics were included in the exploratory regression analysis as possible predictors of base-flow yield. Basin characteristics found to be statistically significant predictors of mean annual base-flow yield during 1971-2000 at the 95-percent confidence level were (1) mean annual precipitation, (2) average maximum daily temperature, (3) percentage of sand in the soil, (4) percentage of carbonate bedrock in the basin, and (5) stream channel slope. The equation for predicting recharge was developed using ordinary least-squares regression. The standard error of prediction for the equation on log-transformed data was 9.7 percent, and the coefficient of determination was 0.80. The equation can be used to predict long-term, mean annual recharge rates for ungaged basins, providing that the explanatory basin characteristics can be determined and that the underlying assumption is accepted that base-flow yield derived from PART is a reasonable estimate of ground-water recharge rates. For example, application of the equation for 370 hydrologic units in Pennsylvania predicted a range of ground-water recharge from about 6.0 to 22 inches per year. A map of the predicted recharge illustrates the general magnitude and variability of recharge throughout Pennsylvania.

Risser, Dennis W.; Thompson, Ronald E.; Stuckey, Marla H.

2008-01-01

25

NASA Astrophysics Data System (ADS)

Quantification of the contribution of groundwater flow from highland areas of mountainous watersheds to semi-arid and arid valley bottom unconsolidated aquifers is increasingly needed for the assessment of water resources in many populated areas. In mountainous environments, however, data for Darcy equation parameters are limited, leading to uncertainty in estimates of groundwater flow of up to two or more orders of magnitude. An alternative method for estimating regional groundwater flow from highland to valley bottom areas was developed for the semi-arid Okanagan Basin, British Columbia, Canada. The method involved a basin-averaged water balance approach, using mean annual surface water run-off (RO) data for 9 gauged tributaries with spatially distributed estimates of mean annual precipitation (P) and actual evapotranspiration (AET), to develop basin-averaged relationships for prediction of recharge-driven groundwater flow through the bedrock highland areas. Groundwater flow from highland bedrock areas to unconsolidated valley bottom aquifers was subsequently accounted for through a calibration exercise using a spreadsheet tool developed for the project. Average annual AET was the most difficult parameter to quantify at the tributary catchment scale. Spatially distributed AET estimates were developed using temperature and precipitation data, with consideration of expected AET ranges established based on available data for the region. Results for the bedrock areas in the Okanagan Basin indicated basin-averaged partitioning of mean annual precipitation as 68% AET, 19% to surface water run-off (in streams), and 13% to net recharge (groundwater flow). The influence of AET and surface water run-off parameter uncertainty on regional bedrock groundwater flow calculations was a factor of 2 (AET range of 60-70% catchment precipitation) and 1.2 (RO range of 14 to 26%), respectively. This approach allows for preliminary estimates of water budget constrained recharge- driven groundwater flow at the catchment or basin scale.

Neilson-Welch, L. A.; Allard, R.; Geller, D.; Allen, D. M.

2008-12-01

26

Groundwater flow and transport modeling

Deterministic, distributed-parameter, numerical simulation models for analyzing groundwater flow and transport problems have come to be used almost routinely during the past decade. A review of the theoretical basis and practical use of groundwater flow and solute transport models is used to illustrate the state-of-the-art. Because of errors and uncertainty in defining model parameters, models must be calibrated to obtain a best estimate of the parameters. For flow modeling, data generally are sufficient to allow calibration. For solute-transport modeling, lack of data not only limits calibration, but also causes uncertainty in process description. Where data are available, model reliability should be assessed on the basis of sensitivity tests and measures of goodness-of-fit. Some of these concepts are demonstrated by using two case histories. ?? 1988.

Konikow, L. F.; Mercer, J. W.

1988-01-01

27

National Technical Information Service (NTIS)

Precipitation-runoff models, base-flow separation techniques, and stream gain-loss measurements were used to study recharge and ground-water surface-water interaction as part of a study of the ground-water resources of the Willamette River Basin. The stud...

K. K. Lee J. C. Risley

2002-01-01

28

NASA Astrophysics Data System (ADS)

Faults are commonplace in the subsurface and can have substantial impacts on fluid flow at multiple scales. However, there are few field data on the hydraulic properties of fault zones that can be used to quantify their impact on fluid flow, particularly at well-field to regional scales. These data are lacking in part because hydrologic test data are difficult and costly to collect, their quality is highly dependent on the spatial distribution of available wells, and permeability estimates using these data may not capture the internal heterogeneity of fault zone hydraulic properties, particularly at scales larger than the hydraulic influence of the test itself. Here we explore the advantages of supplementing traditional aquifer test data with electrical geophysical data. Self-potential data were coupled with a steady-state groundwater-flow model of the Elkhorn fault, a Laramide-aged contractional fault that juxtaposes two aquifers in South Park, Colorado; a fractured granite aquifer against the upper arkosic sandstone member of the South Park Formation. This coupled modeling approach allows us to develop estimates of fault zone permeability structure and to explore the sensitivity of the self-potential method to different hydrologic scenarios at this site. Self-potential data were collected along several transects across the Elkhorn fault in the vicinity of five monitoring wells in the hanging wall and footwall. Using the geologic structure defined by co-located electrical resistivity tomography data and geologic descriptions from the wells, a two-dimensional finite- element model was developed with three major geologic components: granite hanging wall, fault zone, and sandstone footwall. In this physical domain, groundwater-flow and electrical models were coupled to examine possible permeability structures of the fault zone. Steady-state water level data from four wells were used to calibrate the groundwater-flow model. The self-potential anomaly resulting from the modeled potentiometric surface was examined and compared to measured self-potential data from across the transect. The permeability structure of the fault zone was adjusted to optimize the model fit to both the hydrological and self-potential data. Through several iterations, possible fault zone permeability structures were identified that satisfy both datasets.

Ball, L.; Jardani, A.; Revil, A.; Ge, S.; Caine, J.

2008-12-01

29

Sensitivity Analysis of Groundwater Flow

A numerical model developed for sensitivity analysis of groundwater flow is presented. Sensitivity analysis is a useful complementary aid for groundwater flow modelling to assess the importance of various governing flow parameters to the behaviour of any specific flow problem. Two different methods are considered: One is called the direct method and the other the adjoint method. In the direct

Yung-Bing Bao; Roger Thunvik

1991-01-01

30

Technology Transfer Automated Retrieval System (TEKTRAN)

This study by the U.S. Geological Survey, in cooperation with the Agricultural Research Service (ARS), U.S. Department of Agriculture, compared multiple methods for estimating ground-water recharge and base flow (as a proxy for recharge) at sites in east-central Pennsylvania underlain by fractured b...

31

Groundwater hydrology--coastal flow

How groundwater flow varies when long-term external conditions change is little documented. Geochemical evidence shows that sea-level rise at the end of the last glacial period led to a shift in the flow patterns of coastal groundwater beneath Florida.

Sanford, Ward E.

2010-01-01

32

Parameter estimation through groundwater tracer tests

In situ estimation of parameters in chemical models describing groundwater pollutant transport and fate is considered. During tracer tests, the observed breakthrough of a conservative species yields information characterizing the hydraulic behavior of a multiple-well system. A streamline advective solute transport model incorporating the chemical model of interest is scaled so that it applies to all streamlines in the flow

Kenneth A. Rainwater; William R. Wise; Randall J. Charbeneau

1987-01-01

33

Monitoring probe for groundwater flow

A monitoring probe for detecting groundwater migration is disclosed. The monitor features a cylinder made of a permeable membrane carrying an array of electrical conductivity sensors on its outer surface. The cylinder is filled with a fluid that has a conductivity different than the groundwater. The probe is placed in the ground at an area of interest to be monitored. The fluid, typically saltwater, diffuses through the permeable membrane into the groundwater. The flow of groundwater passing around the permeable membrane walls of the cylinder carries the conductive fluid in the same general direction and distorts the conductivity field measured by the sensors. The degree of distortion from top to bottom and around the probe is precisely related to the vertical and horizontal flow rates, respectively. The electrical conductivities measured by the sensors about the outer surface of the probe are analyzed to determine the rate and direction of the groundwater flow. 4 figs.

Looney, B.B.; Ballard, S.

1994-08-23

34

Monitoring probe for groundwater flow

A monitoring probe for detecting groundwater migration. The monitor features a cylinder made of a permeable membrane carrying an array of electrical conductivity sensors on its outer surface. The cylinder is filled with a fluid that has a conductivity different than the groundwater. The probe is placed in the ground at an area of interest to be monitored. The fluid, typically saltwater, diffuses through the permeable membrane into the groundwater. The flow of groundwater passing around the permeable membrane walls of the cylinder carries the conductive fluid in the same general direction and distorts the conductivity field measured by the sensors. The degree of distortion from top to bottom and around the probe is precisely related to the vertical and horizontal flow rates, respectively. The electrical conductivities measured by the sensors about the outer surface of the probe are analyzed to determine the rate and direction of the groundwater flow.

Looney, Brian B. (Aiken, SC); Ballard, Sanford (Albuquerque, NM)

1994-01-01

35

Finite difference and finite element methods are frequently used to study aquifer flow; however, additional analysis is required when model parameters, and hence predicted heads are uncertain. Computational algorithms are presented for steady and transient models in which aquifer storage coefficients, transmissivities, distributed inputs, and boundary values may all be simultaneously uncertain. Innovative aspects of these algorithms include a new

Lloyd R. Townley; John L. Wilson

1985-01-01

36

A regional-scale, steady-state, saturated-zone ground-water flow model was constructed to evaluate potential regional ground-water flow in the vicinity of Yucca Mountain, Nevada. The model was limited to three layers in an effort to evaluate the characteristics governing large-scale subsurface flow. Geoscientific information systems (GSIS) were used to characterize the complex surface and subsurface hydrogeologic conditions of the area, and this characterization was used to construct likely conceptual models of the flow system. Subsurface properties in this system vary dramatically, producing high contrasts and abrupt contacts. This characteristic, combined with the large scale of the model, make zonation the logical choice for representing the hydraulic-conductivity distribution. Different conceptual models were evaluated using sensitivity analysis and were tested by using nonlinear regression to determine parameter values that are optimal, in that they provide the best match between the measured and simulated heads and flows. The different conceptual models were judged based both on the fit achieved to measured heads and spring flows, and the plausibility of the optimal parameter values. One of the conceptual models considered appears to represent the system most realistically. Any apparent model error is probably caused by the coarse vertical and horizontal discretization.A regional-scale, steady-state, saturated-zone ground-water flow model was constructed to evaluate potential regional ground-water flow in the vicinity of Yucca Mountain, Nevada. The model was limited to three layers in an effort to evaluate the characteristics governing large-scale subsurface flow. Geoscientific information systems (GSIS) were used to characterize the complex surface and subsurface hydrogeologic conditions of the area, and this characterization was used to construct likely conceptual models of the flow system. Subsurface properties in this system vary dramatically, producing high contrasts and abrupt contacts. This characteristic, combined with the large scale of the model, make zonation the logical choice for representing the hydraulic-conductivity distribution. Different conceptual models were evaluated using sensitivity analysis and were tested by using nonlinear regression to determine parameter values that are optimal, in that they provide the best match between the measured and simulated heads and flows. The different conceptual models were judged based both on the fit achieved to measured heads and spring flows, and the plausibility of the optimal parameter values. One of the conceptual models considered appears to represent the system most realistically. Any apparent model error is probably caused by the coarse vertical and horizontal discretization.

D'Agnese, F. A.; Faunt, C. C.; Hill, M. C.; Turner, A. K.

1999-01-01

37

We employed the ArcGIS plug-in package PRO-GRADE (Lin et al. 2009), developed for zonation of recharge/discharge (R/D) for modeling two-dimensional aquifer systems, to develop alternative R/D zonations for an existing three-dimensional groundwater flow model of a complex hydrogeologic setting. Our process began by intersecting PRO-GRADE output with the existing model's 4-zone R/D representation to develop a model having 12 R/D zones (R12) and then calibrating the resulting model using PEST. We then revised the R12 zonation using supplementary GIS data to develop a 51-zone R/D zonation (R51). From R51, we developed a series of daughter models having 40, 30, 28, and 18 R/D zones by removing zones from R51 if calibration resulted in little change in the zone's starting R/D rate and/or if the model was insensitive to the zone's R/D rate. For these models (R40N, R30N, R28N, and R18N), we used the ArcGIS Nibble tool to rapidly and consistently reassign model cells within eliminated zones of R51 to the zone of the nearest model cell in a retained zone having the same starting value. R12, R51, R40N, R30N, R28N, and R18N are all more accurate than the original model (R4), although improvements relative to stream discharge targets exceeded improvements relative to head targets. The models also executed with better numerical stability and less mass balance discrepancy than R4. These improvements demonstrate that R/D estimation in a complex shallow three-dimensional steady-state model can be improved with PRO-GRADE estimates of R/D when guided by calibration statistics and supplemental geographic data. PMID:21797853

Meyer, Scott C; Lin, Yu-Feng; Roadcap, George S

2011-07-28

38

Effects of wetlands creation on groundwater flow

Changes in groundwater flow were observed near four Experimental Wetland Areas (EWAs) constructed along a reach of the Des Plaines River in northeastern Illinois. These changes were observed during monthly monitoring of groundwater elevation in nested piezometers and shallow observation wells before and after the wetlands were filled with water. A numerical model was calibrated with observed data and used to estimate seepage from the wetlands into the Des Plaines River. After the wetlands became operational, groundwater levels in adjacent wells increased by about 0.5m, while water levels in wells distant from the wetlands decreased. The increase in groundwater levels near the wetlands is a result of seepage from the wetlands. Numerical predictions of seepage from the wetlands are 60-150 m3 day-1 for two wetlands situated over sand and gravel and less than 1 m3 day-1 for two wetlands situated over clayey till. The difference in seepage rates is attributed to two factors. First, the hydraulic conductivity of the sand and gravel unit is greater than that of the till, and thus there is less mounding and a greater capacity for transmitting water beneath the wetlands overlying this deposit. Secondly, the wetlands located over till are groundwater flow-through ponds, whereas the wetlands over the sand and gravel are primarily groundwater recharge areas. The model was used to estimate that seepage from the wetlands will double groundwater discharge into the Des Plaines River and a tributary relative to pre-operational discharge from the study area. Overall, the wetlands have acted as a constant head boundary, stabilizing groundwater flow patterns. ?? 1991.

Hensel, B. R.; Miller, M. V.

1991-01-01

39

NASA Astrophysics Data System (ADS)

A numerical groundwater fate and transport model was developed for analyses of data from field experiments evaluating the impacts of ethanol on the natural attenuation of benzene, toluene, ethylbenzene, and xylenes (BTEX) and methyl tert-butyl ether (MTBE) at Vandenberg Air Force Base, Site 60. We used the U.S. Geological Survey (USGS) groundwater flow (MODFLOW2000) and transport (MT3DMS) models in conjunction with the USGS universal inverse modeling code (UCODE) to jointly determine flow and transport parameters using bromide tracer data from multiple experiments in the same location. The key flow and transport parameters include hydraulic conductivity of aquifer and aquitard layers, porosity, and transverse and longitudinal dispersivity. Aquifer and aquitard layers were assumed homogenous in this study. Therefore, the calibration parameters were not spatially variable within each layer. A total of 162 monitoring wells in seven transects perpendicular to the mean flow direction were monitored over the course of ten months, resulting in 1,766 bromide concentration data points and 149 head values used as observations for the inverse modeling. The results showed the significance of the concentration observation data in predicting the flow model parameters and indicated the sensitivity of the hydraulic conductivity of different zones in the aquifer including the excavated former contaminant zone. The model has already been used to evaluate alternative designs for further experiments on in situ bioremediation of the tert-butyl alcohol (TBA) plume remaining at the site. We describe the recent applications of the model and future work, including adding reaction submodels to the calibrated flow model.

Rasa, E.; Foglia, L.; Mackay, D. M.; Ginn, T. R.; Scow, K. M.

2009-12-01

40

Real-time groundwater flow modeling with filter methods is interesting for dynamical groundwater flow systems, for which measurement data in real-time are available. The Ensemble Kalman Filter (EnKF) approach is used here to update states together with parameters by adopting an augmented state vector approach. The performance of EnKF is investigated in a synthetic study with a two-dimensional transient groundwater flow

H. J. Hendricks Franssen; W. Kinzelbach

2008-01-01

41

Groundwater flow into Lake Michigan from Wisconsin

Detailed hydrogeological study has been done at six sites along the Lake Michigan shoreline in Wisconsin. At each site a flux of groundwater to the lake has been calculated for both natural conditions and the existing conditions created by pumping. The values from each site have then been extrapolated to the entire portion of the total shoreline having similar hydrogeology in order to calculate a total flow of groundwater to the lake. Sensitivity analysis with a digital model was used to define limits on the similarity of hydrogeologic conditions. The net flow calculated is 580-880 m3 day-1 km-1 of shoreline, which falls within the previously published range of 110-8200 m3 day-1 km-1. Human activity may have reduced the natural flow as much as 15%. The estimated natural flow is between 7 and 11% of the surface water contribution to the lake from the study area. ?? 1986.

Cherkauer, D. S.; Hensel, B. R.

1986-01-01

42

In order to evaluate effective hydraulic conductivities of aquifers and aquitards in shallow coal-bearing rocks of the Allegheny Plateau, an inverse solution modeling approach is proposed. A two-dimensional finite element technique is employed to simulate steady-state groundwater flow through a typical structural and lithological framework for deeply dissected areas of the plateau, as defined by exploratory drilling at a number of surface mine sites. The lenses recharge through surface infiltration and discharge through downward leakage across the underclay and lateral flow to the cropline. Domain variables (saturated geometry, lithologic variation, and piezometric conditions) were derived from drilling records, monitoring wells, field surveys, water quality analyses, and surface discharge data. Through trial and error, steady-state heads of perched groundwater lenses are calibrated to observed heads by adjusting coal and underclay hydraulic conductivities. To evaluate the sensitivity of the lens shape to boundary and domain variables, such as recharge rate, overburden hydraulic conductivity and structural dip, model scenarios have been run to define dh/dk over the parameter range. Results indicate (1) effective underclay hydraulic conductivity must be less than 0.00001 ft/day for perched water to exist (2) coal hydraulic conductivity can range from 0.01 to 0.5 ft/day, the latter matching the upper range of field values obtained through single well drawdown tests and (3) calibrations were relatively insensitive to variations in recharge rate but were sensitive to scale of the domain and dip of the coal-underclay contact, and (4) the ratio of lateral discharge to vertical leakage through the underclay is determined.

Abate, C.; Parizek, R.R. (Pennsylvania State Univ., University Park, PA (United States). Dept. of Geosciences)

1992-01-01

43

Using groundwater levels to estimate recharge

. Accurate estimation of groundwater recharge is extremely important for proper management of groundwater systems. Many different\\u000a approaches exist for estimating recharge. This paper presents a review of methods that are based on groundwater-level data.\\u000a The water-table fluctuation method may be the most widely used technique for estimating recharge; it requires knowledge of\\u000a specific yield and changes in water levels

Richard W. Healy; Peter G. Cook

2002-01-01

44

Regionally compartmented groundwater flow on Mars

Groundwater flow on Mars likely contributed to the formation of several types of morphologic and mineralogic features, including chaotic terrains, valley networks, Meridiani Planum geologic units and, potentially, sulfate and phyllosilicate deposits. A central issue for these features is the spatial scale of groundwater flow required for their formation. For groundwater simulation purposes, a global Martian aquifer has frequently been

Keith P. Harrison; Robert E. Grimm

2009-01-01

45

This study by the U.S. Geological Survey (USGS), in cooperation with the Agricultural Research Service (ARS), U.S. Department of Agriculture, compared multiple methods for estimating ground-water recharge and base flow (as a proxy for recharge) at sites in east-central Pennsylvania underlain by fractured bedrock and representative of a humid-continental climate. This study was one of several within the USGS Ground-Water Resources Program designed to provide an improved understanding of methods for estimating recharge in the eastern United States. Recharge was estimated on a monthly and annual basis using four methods?(1) unsaturated-zone drainage collected in gravity lysimeters, (2) daily water balance, (3) water-table fluctuations in wells, and (4) equations of Rorabaugh. Base flow was estimated by streamflow-hydrograph separation using the computer programs PART and HYSEP. Estimates of recharge and base flow were compared for an 8-year period (1994-2001) coinciding with operation of the gravity lysimeters at an experimental recharge site (Masser Recharge Site) and a longer 34-year period (1968-2001), for which climate and streamflow data were available on a 2.8-square-mile watershed (WE-38 watershed). Estimates of mean-annual recharge at the Masser Recharge Site and WE-38 watershed for 1994-2001 ranged from 9.9 to 14.0 inches (24 to 33 percent of precipitation). Recharge, in inches, from the various methods was: unsaturated-zone drainage, 12.2; daily water balance, 12.3; Rorabaugh equations with PULSE, 10.2, or RORA, 14.0; and water-table fluctuations, 9.9. Mean-annual base flow from streamflow-hydrograph separation ranged from 9.0 to 11.6 inches (21-28 percent of precipitation). Base flow, in inches, from the various methods was: PART, 10.7; HYSEP Local Minimum, 9.0; HYSEP Sliding Interval, 11.5; and HYSEP Fixed Interval, 11.6. Estimating recharge from multiple methods is useful, but the inherent differences of the methods must be considered when comparing results. For example, although unsaturated-zone drainage from the gravity lysimeters provided the most direct measure of potential recharge, it does not incorporate spatial variability that is contained in watershed-wide estimates of net recharge from the Rorabaugh equations or base flow from streamflow-hydrograph separation. This study showed that water-level fluctuations, in particular, should be used with caution to estimate recharge in low-storage fractured-rock aquifers because of the variability of water-level response among wells and sensitivity of recharge to small errors in estimating specific yield. To bracket the largest range of plausible recharge, results from this study indicate that recharge derived from RORA should be compared with base flow from the Local-Minimum version of HYSEP.

Risser, Dennis W.; Gburek, William J.; Folmar, Gordon J.

2005-01-01

46

Chaotic solute advection by unsteady groundwater flow

Solute mixing in fluids is enhanced significantly by chaotic advection, the phenomenon in which fluid pathlines completely fill the spatial domain explored by a laminar flow. Steady groundwater flows are, in general, not well conditioned for this phenomenon because Darcy's law confines them spatially to nonintersecting stream surfaces. Unsteady groundwater flows, however, may, in principle, induce chaotic solute advection if

Garrison Sposito

2006-01-01

47

Uncertainty in Climatology-Based Estimates of Shallow Groundwater Recharge

The groundwater recharge (GR) estimates for flow and transport projections are often evaluated as a fixed percentage of average annual precipitation. The chemical transport in variably saturated heterogeneous porous media is not linearly related to the average velocity. The objective of this study was to estimate the variability in annual, seasonal, and event-based GR at the field scale and to

A. K. Guber; Y. Pachepsky; T. J. Gish; T. J. Nicholson; R. R. Cady

2007-01-01

48

Geomorphic aspects of groundwater flow

NASA Astrophysics Data System (ADS)

The many roles that groundwater plays in landscape evolution are becoming more widely appreciated. In this overview, three major categories of groundwater processes and resulting landforms are considered: (1) Dissolution creates various karst geometries, mainly in carbonate rocks, in response to conditions of recharge, geologic setting, lithology, and groundwater circulation. Denudation and cave formation rates can be estimated from kinetic and hydraulic parameters. (2) Groundwater weathering generates regoliths of residual alteration products at weathering fronts, and subsequent exhumation exposes corestones, flared slopes, balanced rocks, domed inselbergs, and etchplains of regional importance. Groundwater relocation of dissolved salts creates duricrusts of various compositions, which become landforms. (3) Soil and rock erosion by groundwater processes include piping, seepage erosion, and sapping, important agents in slope retreat and headward gully migration. Thresholds and limits are important in many chemical and mechanical groundwater actions. A quantitative, morphometric approach to groundwater landforms and processes is exemplified by selected studies in carbonate and clastic terrains of ancient and recent origins. Résumé Les rôles variés joués par les eaux souterraines dans l'évolution des paysages deviennent nettement mieux connus. La revue faite ici prend en considération trois grandes catégories de processus liés aux eaux souterraines et les formes associées: (1) La dissolution crée des formes karstiques variées, surtout dans les roches carbonatées, en fonction des conditions d'alimentation, du cadre géologique, de la lithologie et de la circulation des eaux souterraines. Les taux d'érosion et de formation des grottes peuvent être estimés à partir de paramètres cinétiques et hydrauliques. (2) L'érosion par les eaux souterraines donne naissance à des régolites, résidus d'altération sur des fronts d'altération, et l'exhumation résultante fait apparaître des rognons, des pentes qui s'évasent, des roches en équilibre, des inselbergs et des plaines de corrosion d'extension régionale. La migration des sels dissous des eaux souterraines crée des croûtes de compositions variées, qui constituent des paysages particuliers. (3) Les processus d'érosion des sols et des roches par les eaux souterraines comprennent les phénomènes suivants: la chenalisation, l'érosion par suintement, le sapement, qui tous sont des agents notables du recul des versants et d'érosion régressive vers l'amont. Les seuils et les limites sont importants dans de nombreuses actions chimiques et mécaniques des eaux souterraines. Une approche morphométrique quantitative des formes et des processus liés aux eaux souterraines est donnée en exemple à partir d'études choisies dans les terrains carbonatés et détritiques d'origine aussi bien ancienne que récente. Resumen Las aguas subterráneas tienen una importancia fundamental en la evolución de los paisajes geomorfológicos. En este artículo se consideran tres grandes categorías de procesos ligados al agua subterránea y sus correspondientes paisajes resultantes: (1) La disolución crea distintas geometrías kársticas, fundamentalmente en rocas carbonatadas, como respuesta a las condiciones de recarga, condicionantes geológicos, litologías y al propio flujo de agua subterránea. La velocidad de denudación y formación de cavernas se puede estimar a partir de los parámetros cinéticos e hidráulicos. (2) La erosión producida por las aguas subterráneas genera regolitas de alteración residual en los frentes de erosión, con los subsiguientes afloramientos de rocas inalteradas, inselbergs, rocas oscilantes o llanuras de corrosión de carácter regional. La recolocación de las sales disueltas crea costras superficiales de diferente composición. (3) La erosión de rocas y suelos por procesos ligados al agua subterránea, como filtración y arrastre de finos da lugar a un movimiento de retroceso de taludes y barrancos. La existencia de umbrales y lím

LaFleur, Robert G.

49

Unsteady groundwater flow on sloping bedrock

A numerical model based on the equation describing the unsteady groundwater flow on impervious sloping bedrock has been herewith formulated. The case which has been studied concerns the groundwater flow from one canal to another with a sudden rising of the canal level as an upstream boundary condition, while the downstream level remains constant. Initially, at time t = 0,

C. N. Frangakis; C. Tzimopoulos

1979-01-01

50

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

Edited by: Belcher, Wayne R.; Sweetkind, Donald S.

2010-01-01

51

Groundwater flow in layered aquifer systems

NSDL National Science Digital Library

Four groundwater modeling programs are available from this site. Trial versions of the software are downloadable for free. The programs are MicroFEM, for multiple-aquifer steady-state and transient groundwater flow modeling; MLU for drawdown calculations and inverse modeling of transient well flow in layered aquifer systems; SchlumBG for the automatic interpretation of geo-electrical measurements; and FlowNet for modeling of two-dimensional steady-state flow in a heterogeneous, anisotropic aquifer.

Hemker, C. J.; Microfem

52

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

edited by Belcher, Wayne R.

2004-01-01

53

Faults are commonplace in the subsurface and can have substantial impacts on fluid flow at multiple scales. However, there are few field data on the hydraulic properties of fault zones that can be used to quantify their impact on fluid flow, particularly at well-field to regional scales. These data are lacking in part because hydrologic test data are difficult and

L. Ball; A. Jardani; A. Revil; S. Ge; J. Caine

2008-01-01

54

NASA Astrophysics Data System (ADS)

The Southern Nevada Water Authority’s (SNWA) proposal to develop groundwater resources in Snake Valley and adjacent basins in eastern Nevada has focused attention on understanding the links between basin-fill and carbonate aquifer systems, groundwater flow paths, and the movement of groundwater between basins. The SNWA development plans are contentious in part because (1) there are few perennial streams that flow into the basins and these surface-water resources are fully appropriated; (2) groundwater resources that sustain streams, springs, wetlands, and the local agricultural economy are also limited; and (3) because Snake Valley straddles the Utah-Nevada state line. We report groundwater temperatures and estimates of heat flow used to constrain estimates of groundwater flow into and through Snake Valley. Thermal logs have been collected from 24 monitoring wells in the Utah part of the valley. Natural, undisturbed geothermal gradients within the Basin and Range are generally 30 °C/km, which correspond to heat flow values of approximately 90 mW/m2. Geothermal gradients in the southern portion of Snake Valley are lower than typical Basin and Range geothermal gradients, with the majority ranging between 10 and 20 °C/km, corresponding to heat flow values of 30 to 60 mW/m2. In the northern portion of the basin, however, geothermal gradients are generally higher than typical Basin and Range geothermal gradients, with thermal logs of two wells indicating gradients of 39 °C/km and 51 °C/km, which correspond to heat flow values of approximately 117 and 153 mW/m2, respectively. These observations suggest heat is being redistributed by groundwater flow to discharge points in northern Snake Valley. This interpretation is also supported by spring temperatures in northern Snake Valley and at Fish Springs National Wildlife Refuge to the northeast that are higher than ambient (12 °C) surface temperature. These thermal data are being used together with water levels and discharge observations in a three-dimensional, coupled groundwater flow/thermal transport model to evaluate groundwater flow within Snake Valley and adjacent basins. Advantages of using a coupled flow/thermal model approach include the incorporation of spatial variations in thermal gradients and heat flow observations as additional constraints to assess model performance beyond typical groundwater flow models, which generally only test water levels and discharge observations.

Masbruch, M. D.; Chapman, D. S.

2009-12-01

55

The recharge and discharge components of the Death Valley regional groundwater flow system were defined by remote sensing and GIS techniques that integrated disparate data types to develop a spatially complex representation of near-surface hydrological processes. Image classification methods were applied to multispectral satellite data to produce a vegetation map. This map provided a basis for subsequent évapotranspiration and infiltration

FRANK A. D'AGNESE; CLAUDIA C. FAUNT; A. KEITH TURNER

1996-01-01

56

A 3-D finite element model (Feflow) has been used for regional groundwater flow modelling of Upper Chaj Doab in Indus Basin, Pakistan. The thematic layers of soils, landuse, hydrology, infrastructure and climate were developed using Geographic Information System (GIS). The numerical groundwater flow model is developed to configure the groundwater equipotential surface, hydraulic head gradient and estimation of the groundwater

A. Ashraf; Z. Ahmad

2008-01-01

57

Effect of groundwater flow on forming arsenic contaminated groundwater in Sonargaon, Bangladesh

NASA Astrophysics Data System (ADS)

We examine the As-contaminated groundwater flow paths in the Blamaptra delta plain. Water recharged from ground surface moves vertically downward beneath flood plain. As-hotspot groundwaters are formed on the vertical groundwater flow paths. Reducing groundwater condition is not essential for the As-hotspot groundwaters.

Nakaya, Shinji; Natsume, Haruyasu; Masuda, Harue; Mitamura, Muneki; Biswas, Dipak Kumar; Seddique, Ashraf A.

2011-11-01

58

Geochemical interpretation of groundwater flow in the southern Great Basin

The study of geochemical processes and integrated water flow can help identify groundwater sources and improve predic- tions of contaminant fate and transport in groundwater systems. Understanding groundwater flow paths in and around the Nevada Test Site (NTS) is important due to the possible migration of contaminated groundwater to the neighboring communi- ties. A total of 118 groundwater samples from

J. E. Koonce; I. M. Farnham; K. J. Stetzenbach

2006-01-01

59

Steady State Groundwater Flow Across Idealized Faults

NASA Astrophysics Data System (ADS)

The effects of vertical faults on steady state groundwater flow are simulated using simple analytical solutions for horizontal flow across three domains that are linked by requiring continuity of head and flux. Hydraulic properties are vertically averaged, so that changes in transmissivity can be used to account for changes in aquifer thickness, juxtaposition of different aquifers across the fault, or some combination of the two. Vertical flow along the fault can be included through the use of a source-sink term. Different combinations of transmissivity contrast and recharge/discharge produce distinct head profiles, which can be used to qualitatively infer the nature of real hydrogeologic systems. Observed hydraulic gradient ratios can also be used to calculate transmissivity ratios, and if information about fault zone thickness and an independent estimate for one of the three transmissivities is known, the magnitudes of the remaining two transmissivities can be calculated. Use of the model to interpret real flow systems is demonstrated using an example from the Albuquerque Basin, New Mexico.

Haneberg, William C.

1995-07-01

60

Groundwater Recharge Rate and Zone Structure Estimation Using PSOLVER Algorithm.

The quantification of groundwater recharge is an important but challenging task in groundwater flow modeling because recharge varies spatially and temporally. The goal of this study is to present an innovative methodology to estimate groundwater recharge rates and zone structures for regional groundwater flow models. Here, the unknown recharge field is partitioned into a number of zones using Voronoi Tessellation (VT). The identified zone structure with the recharge rates is associated through a simulation-optimization model that couples MODFLOW-2000 and the hybrid PSOLVER optimization algorithm. Applicability of this procedure is tested on a previously developed groundwater flow model of the Tahtal? Watershed. Successive zone structure solutions are obtained in an additive manner and penalty functions are used in the procedure to obtain realistic and plausible solutions. One of these functions constrains the optimization by forcing the sum of recharge rates for the grid cells that coincide with the Tahtal? Watershed area to be equal to the areal recharge rate determined in the previous modeling by a separate precipitation-runoff model. As a result, a six-zone structure is selected as the best zone structure that represents the areal recharge distribution. Comparison to results of a previous model for the same study area reveals that the proposed procedure significantly improves model performance with respect to calibration statistics. The proposed identification procedure can be thought of as an effective way to determine the recharge zone structure for groundwater flow models, in particular for situations where tangible information about groundwater recharge distribution does not exist. PMID:23746002

Ayvaz, M Tamer; Elçi, Alper

2013-06-01

61

Calibration is crucial to improving the performance of a groundwater flow model. In most cases, if historical groundwater data are available, the model is effectively calibrated before it is used for predictive simulations. That is, the model must be able to simulate observed historical groundwater conditions (e.g., groundwater elevations and flux rates). Groundwater elevation data used for model calibration typically

J. Zhang; L. Elliot; G. Muehleck

2008-01-01

62

Estimated ground-water recharge from streamflow in Fortymile Wash near Yucca Mountain, Nevada

The two purposes of this report are to qualitatively document ground-water recharge from stream-flow in Fortymile Wash during the period 1969--95 from previously unpublished ground-water levels in boreholes in Fortymile Canyon during 1982--91 and 1995, and to quantitatively estimate the long-term ground-water recharge rate from streamflow in Fortymile Wash for four reaches of Fortymile Wash (Fortymile Canyon, upper Jackass Flats, lower Jackass Flats, and Amargosa Desert). The long-term groundwater recharge rate was estimated from estimates of the volume of water available for infiltration, the volume of infiltration losses from streamflow, the ground-water recharge volume from infiltration losses, and an analysis of the different periods of data availability. The volume of water available for infiltration and ground-water recharge in the four reaches was estimated from known streamflow in ephemeral Fortymile Wash, which was measured at several gaging station locations. The volume of infiltration losses from streamflow for the four reaches was estimated from a streamflow volume loss factor applied to the estimated streamflows. the ground-water recharge volume was estimated from a linear relation between infiltration loss volume and ground-water recharge volume for each of the four reaches. Ground-water recharge rates were estimated for three different periods of data availability (1969--95, 1983--95, and 1992--95) and a long-term ground-water recharge rate estimated for each of the four reaches.

Savard, C.S.

1998-10-01

63

Estimating hyperconcentrated flow discharge

NASA Astrophysics Data System (ADS)

Determining flow discharge in torrential mountain floods can help in managing flood risk. However, standard methods of estimating discharge have significant uncertainties. To reduce these uncertainties, Bodoque et al. developed an iterative methodological approach to flow estimation based on a method known as the critical depth method along with paleoflood evidence. They applied the method to study a flash flood that occurred on 17 December 1997 in the Arroyo Cabrera catchment in central Spain. This large flow event, triggered by torrential rains, was complex and included hyperconcentrated flows, which are flows of water mixed with significant amounts of sediment.

Balcerak, Ernie

2012-02-01

64

Estimating Regional Groundwater Recharge Using a Hydrological Budget Method

Estimating groundwater recharge is a key component in determining the sustainable yield of groundwater resources in arid and\\u000a semi-arid areas such as southern California. Estimating groundwater recharge on a regional scale requires developing a water\\u000a budget that incorporates data on boundary conditions, aquifer properties, groundwater levels, and groundwater production.\\u000a The hydrological budget method proposed herein is simple, cost-effective, and easy

Fakhri Manghi; Behrooz Mortazavi; Christie Crother; Moshrik R. Hamdi

2009-01-01

65

Numerical simulation of groundwater flow in regional rock aquifers, southwestern Quebec, Canada

The St. Lawrence Lowlands platform, Quebec, Canada, is a densely-populated area, heavily dependent on groundwater resources. In 1999, the Geological Survey of Canada initiated a large-scale hydrogeological assessment study over a 1,500 km2 region northwest of Montreal. The objectives were to define the regional groundwater flow, and to give quantitative estimates of the groundwater dynamic parameters and of the available groundwater

M. Nastev; A. Rivera; R. Lefebvre; R. Martel; M. Savard

2005-01-01

66

GROUNDWATER FLOW IN LOW-PERMEABILITY ENVIRONMENTS.

Certain geologic media are known to have small permeability; subsurface environments composed of these media and lacking well developed secondary permeability have groundwater flow systems with many distinctive characteristics. Moreover, groundwater flow in these environments appears to influence the evolution of certain hydrologic, geologic, and geochemical systems, may affect the accumulation of petroleum and ores, and probably has a role in the structural evolution of parts of the crust. Such environments are also important in the context of waste disposal. This review attempts to synthesize the diverse contributions of various disciplines to the problem of flow in low-permeability environments. Problems hindering analysis are enumerated together with suggested approaches to overcoming them. A common thread running through the discussion is the significance of size- and time-scale limitations of the ability to directly observe flow behavior and make significance of size- and time-scale limitations of the ability to directly observe flow behavior and make measurements of parameters.

Neuzil, C. E.

1986-01-01

67

National Technical Information Service (NTIS)

Isotopic tracers, such as stable isotopes of the water molecule and tritium, have been used in investigations of groundwater flow and transport and recharge water source for several decades. While these data can place hard constraints on groundwater flow ...

J. E. Moran G. B. Hudson

2005-01-01

68

A methodology was proposed to determine the groundwater flow direction from a thermal response test analysis using three boreholes. The methodology was verified using sample test data generated from a three-dimensional numerical model for the borehole ground heat exchangers. It was found that the groundwater flow velocity and the borehole separation had significant effects on the correctness of the estimated

C. K. Lee; H. N. Lam

2011-01-01

69

Simulated changes in ground-water flow caused by hypothetical pumping in East Carson City, Nevada

An existing groundwater model of Carson Valley was used to simulate changes in groundwater flow on the east side of Carson Valley, Nevada, in response to hypothetical increases in groundwater pumpage. Pumpage scenarios that reflect State groundwater permits and pending applications were used in four different simulations to estimate the effect of hypothetical development on groundwater levels and storage, groundwater flow to the Carson River, and groundwater levels and storage, groundwater flow to the Carson River, and groundwater consumed by evapotranspiration over a 45-yr period. The four simulations were based on pumpage rates ranging from 0.13 to 6.4 cu ft/sec (92 to 4,590 acre-ft/year). Changes in groundwater flow and water levels caused by the lowest rate were minimal and at the limit of accuracy of the groundwater model. The highest pumping rate caused water level declines as much as 15 ft, decreased groundwater storage by 27,000 acre/ft, decreased groundwater to the Carson River by 4.3 cu ft/sec (3,100 acre-ft/year), and reduced evapotranspiration losses by about 1,200 acre-ft/year. (Author 's abstract)

Maurer, D. K.

1988-01-01

70

IN SITU FLOW METERS AROUND A GROUNDWATER CIRCULATION WELL (ABSTRACT)

The primary benefit of groundwater circulation well (GCW) technology is the development of strong vertical flows surrounding the treatment well. The extent of significant vertical flow surrounding a circulation well is difficult to establish from traditional groundwater elevation...

71

IN SITU FLOW METERS AROUND A GROUNDWATER CIRCULATION WELL (PAPER)

72

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. PMID:20213054

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

2010-03-07

73

NSDL National Science Digital Library

Presented by West Virginia University, this site addresses flow rates in streams and how to accurately estimate these rates. The site contains thorough diagrams along with solid explanatory text. Overall, the presentation is strong and easily comprehended.

Porter, Dana O.

2008-10-14

74

Continuous transmissivity transitions for horizontal groundwater flow models

In the southern part of Germany, shallow and mostly unconfined valley aquifers are widespread. The differential equation describing groundwater flow and its boundary conditions varies for different flow situations due to the transient nature of the groundwater table. The authors present a continuous physical-mathematical formulation of two-dimensional horizontal groundwater flow, which allows for a simultaneous computation of saturated unconfined, partially

B. Odenwald; J. Stamm; B. Herrling

1995-01-01

75

Numerical errors in groundwater and overland flow models

NASA Astrophysics Data System (ADS)

Numerical error estimates are useful to evaluate the applicability of overland and groundwater flow models and verify the validity of their results. In this paper, methods of estimating numerical errors are developed and then applied to evaluate the numerical accuracy of the South Florida Water Management Model. Analytical expressions for errors generated during the propagation of disturbances due to well pumping, boundary water level changes, and rainfall are obtained for steady and transient conditions using Fourier analysis of the linearized governing equations. Different situations under which truncation errors are introduced into models and their variation with the spatial and temporal discretization are discussed. Numerical experiments are carried out with the three-dimensional groundwater flow model MODFLOW and a number of implicit and explicit models to verify the results. Dimensionless parameters are used in the expressions so that the results can be used to determine discretization errors in any existing or new finite difference model of regional or local scale.

Lal, A. M. Wasantha

2000-05-01

76

Flow Of Groundwater From Soil To Crystalline Rock

NASA Astrophysics Data System (ADS)

Knowledge of groundwater flow from soil or surface water to crystalline bedrock has usually been derived from indirect studies of drawdown in soil due to underground constructions, as well as from analysis of water chemistry and from tracer experiments. Infiltration into the bedrock occurs at specific sites where suitable combinations of geological and hydrological variables exist. Flow from soil to rock in the saturated zone occurs where conductors in the bedrock, such as fractures and fracture zones, are hydraulically connected to a groundwater reservoir in permeable soil or to horizons of permeable and constructive material in heterogeneous soil. Of particular importance for infiltration are the hydraulic conditions of the contact zone between soil and rock. A thin layer of silt on the bedrock surface often blocks the water flow. The micro-topography of the bedrock surface is important since fracture zones usually give depressions in the surface, in which accumulations of sorted and conductive material often can be found. A strong heterogeneity in the infiltration from soil to rock is evidenced by statistical analyses of the flow related to various geological and hydrogeological variables, as well as from analyses of groundwater chemistry and tracer experiments. In order to estimate the infiltration from soil to rock and to carry out mathematical modelling of the groundwater flow, it is necessary to have a good knowledge of the hydraulic conditions of the superficial rock and soil as well as of the conditions at the soil/bedrock contact zone. Information on the saturated flow from soil to rock is essential for calculation of water budgets, for assessments of spread of pollutants and for estimations of leakage into underground constructions.

Olofsson, B.

1994-03-01

77

Regional changes and effects on in groundwater flow patterns groundwater composition

Schot, P.P. and Molenaar, A., 1992. Regional changes in groundwater flow patterns and effects on groundwater composition. J. Hydrol., 130: 151-170. Wetlands on the Vecht river plain in the Netherlands are threatened by pollution of ground water on the adjacent ridge 'Het Gooi'. To assess the impact of this pollution, information is needed on the present groundwater flow pattern and

P. P. Schot; A. Molenaar

78

Effects of intraborehole flow on groundwater age distribution

Environmental tracers are used to estimate groundwater ages and travel times, but the strongly heterogeneous nature of many subsurface environments can cause mixing between waters of highly disparate ages, adding additional complexity to the age-estimation process. Mixing may be exacerbated by the presence of wells because long open intervals or long screens with openings at multiple depths can transport water and solutes rapidly over a large vertical distance. The effect of intraborehole flow on groundwater age was examined numerically using direct age transport simulation coupled with the Multi-Node Well Package of MODFLOW. Ages in a homogeneous, anisotropic aquifer reached a predevelopment steady state possessing strong depth dependence. A nonpumping multi-node well was then introduced in one of three locations within the system. In all three cases, vertical transport along the well resulted in substantial changes in age distributions within the system. After a pumping well was added near the nonpumping multi-node well, ages were further perturbed by a flow reversal in the nonpumping multi-node well. Results indicated that intraborehole flow can substantially alter groundwater ages, but the effects are highly dependent on local or regional flow conditions and may change with time. ?? Springer-Verlag 2007.

Zinn, B. A.; Konikow, L. F.

2007-01-01

79

Groundwater velocities at the Nevada Test Site: {sup 14}Carbon-based estimates

Chemical and isotopic data can be used to constrain and validate groundwater flow models. This study examines probable groundwater flowpaths at the Nevada Test Site (NTS) and estimates groundwater velocities for these flowpaths using water chemistry and carbon isotopes. These velocities are provided for comparison to velocities calculated by a numerical flow model developed by GeoTrans, Inc. Similar to numerical flow models, models of chemical and isotopic evolution are not unique; any number of combinations of reactions can simulate evolution from one water to another, but are no guarantee that the simulation is correct. Knowledge of the hydrology, mineralogy, and chemistry must be combined to produce feasible evolutionary paths.

Chapman, J.B.; Hershey, R.L.; Lyles, B.F.

1995-07-01

80

Groundwater flow modeling was used to quantitatively assess the hydrologic processes affecting ground water and solute movement to drain laterals. Modeling results were used to calculate the depth distribution of groundwater flowing into drain laterals at 1.8 m (drain lateral 1) and 2.7 m (drain lateral 2) below land surface. The simulations indicated that under nonirrigated conditions about 89% of the flow in drain lateral 2 was from groundwater originating from depths greater than 6 m below land surface. The deep groundwater has higher selenium concentrations than shallow groundwater. Simulation of irrigated conditions indicates that as recharge (deep percolation) increases, the proportional contribution of deep groundwater to drain lateral flow decreases. Groundwater flow paths and travel times estimated from the simulation results indicate that groundwater containing high concentrations of selenium (greater than 780 ?g L?1) probably will continue to enter drain lateral 2 for decades.

Fio, John L.; Deverel, S. J.

1991-01-01

81

Coupled Groundwater and Heat Flow in the Tahoe Basin Region

NASA Astrophysics Data System (ADS)

We propose that recent developments in available temperature probe technology and improvements in appropriate modeling software, together with the advent of desktop high-speed computing, have enabled the thermal analysis approach to be an inexpensive, robust, and practical way to constrain groundwater flow fields in a wide variety of environments. We present field measurements and numerical models of coupled heat and groundwater flow in the Tahoe Basin region. In montane regions such as the Tahoe Basin, steep topography provides a driving force for deep groundwater flow. Deep groundwater flow re-routes subsurface heat flow, impacting temperature gradients to depth, including the shallow subsurface (<100m depth). In the Tahoe Basin region, the magnitude of deep groundwater flow on the areal or regional scale has been largely unknown. We present examples of borehole temperature profiles that constrain possible areal groundwater flow patterns, including the magnitude of flow beneath the bottom of boreholes probed.

Trask, J. C.

2002-12-01

82

Unified Numerical Model for Saturated--Unsaturated Groundwater Flow.

National Technical Information Service (NTIS)

A numerical model for analyzing the transient flow of groundwater in fully or partially saturated, multidimensional heterogeneous porous media is developed. The motivation for this effort originated with studies of the occurrence of groundwater in the har...

T. N. Narasimhan

1975-01-01

83

Numerical simulation of groundwater flow on MPPs

Mathematical models are often used to aid in the design and management of engineered remediation procedures. This paper discusses the numerical simulation of groundwater flow in three-dimensional heterogeneous porous media. A portable and scalable code called PARFLOW is being developed for massively parallel computers to enable the detailed modeling of large sites. This code uses a turning bands algorithm to generate a statistically accurate subsurface realization, and preconditioned conjugate gradients to solve the linear system that yields the flow velocity field. Preliminary numerical results for the LLNL site are presented.

Ashby, S.; Falgout, R.; Tompson, A. [Lawrence Livermore National Lab., CA (United States); Fogwell, T. [International Technology Corp., Martinez, CA (United States)

1994-03-01

84

Patterns in groundwater chemistry resulting from groundwater flow

NASA Astrophysics Data System (ADS)

Groundwater flow influences hydrochemical patterns because flow reduces mixing by diffusion, carries the chemical imprints of biological and anthropogenic changes in the recharge area, and leaches the aquifer system. Global patterns are mainly dictated by differences in the flux of meteoric water passing through the subsoil. Within individual hydrosomes (water bodies with a specific origin), the following prograde evolution lines (facies sequence) normally develop in the direction of groundwater flow: from strong to no fluctuations in water quality, from polluted to unpolluted, from acidic to basic, from oxic to anoxic-methanogenic, from no to significant base exchange, and from fresh to brackish. This is demonstrated for fresh coastal-dune groundwater in the Netherlands. In this hydrosome, the leaching of calcium carbonate as much as 15m and of adsorbed marine cations (Na+, K+, and Mg2+) as much as 2500m in the flow direction is shown to correspond with about 5000yr of flushing since the beach barrier with dunes developed. Recharge focus areas in the dunes are evidenced by groundwater displaying a lower prograde quality evolution than the surrounding dune groundwater. Artificially recharged Rhine River water in the dunes provides distinct hydrochemical patterns, which display groundwater flow, mixing, and groundwater ages. Résumé Les écoulements souterrains influencent les différents types hydrochimiques, parce que l'écoulement réduit le mélange par diffusion, porte les marques chimiques de changements biologiques et anthropiques dans la zone d'alimentation et lessive le système aquifère. Ces types dans leur ensemble sont surtout déterminés par des différences dans le flux d'eau météorique traversant le sous-sol. Dans les "hydrosomes" (masses d'eau d'origine déterminée), les lignes marquant une évolution prograde (séquence de faciès) se développent normalement dans la direction de l'écoulement souterrain : depuis des fluctuations fortes de la qualité de l'eau vers une absence de fluctuations, de polluées vers non polluées, d'acides vers basiques, d'oxygénées vers anoxiques et méthanogènes, depuis des échanges de base inexistants vers des échanges significatifs, de l'eau douce vers l'eau saumâtre. Ceci est montré pour une nappe d'eau douce dans une dune côtière des Pays-Bas. Dans "l'hydrosome", on montre que la disparition du carbonate de calcium par lessivage à plus de 15m et celle de cations adsorbés d'origine marine (Na+, K+ et Mg2+) à plus de 2500m vers l'aval-gradient correspond à environ 5000 ans d'écoulement, depuis que la barrière de la plage avec les dunes s'est mise en place. Les zones d'alimentation ponctuelle dans les dunes sont mises en évidence par l'eau souterraine montrant une plus faible évolution prograde de sa qualité que l'eau souterraine de la dune alentour. L'eau du Rhin utilisée pour la réalimentation artificielle dans les dunes a fourni des types hydrochimiques distincts, qui marquent l'écoulement, le mélange et les âges de l'eau souterraine. Resumen El flujo subterráneo tiene una gran importancia sobre la hidroquímica de un sistema ya que reduce la mezcla por difusión, transporta las huellas químicas y biológicas de las acciones antrópicas en la zona de recarga y drena el sistema acuífero. Las tendencias globales vienen regidas por las diferencias en el flujo de agua meteórica que atraviesa el subsuelo. En un hidrosoma individual (cuerpo de agua de un origen específico), se suele desarrollar la siguiente línea de evolución (secuencia de facies) en la dirección del flujo: de gran a nula fluctuación en la calidad del agua, de agua contaminada a no contaminada, de ácida a básica, de óxica a anóxica-metanogénica, de nulo a importante cambio de base y de agua dulce a salobre. Esto puede verse, por ejemplo, en las aguas dulces presentes en las dunas costeras de Holanda. En este hidrosoma, el lixiviado de carbonato cálcico, hasta 15m, y de cationes de adsorción marina (Na+, K+ and Mg2+), hasta 2500m en la dirección

Stuyfzand, Pieter J.

85

Guidelines for Evaluating Ground-Water Flow Models

Ground-water flow modeling is an important tool frequently used in studies of ground-water systems. Reviewers and users of these studies have a need to evaluate the accuracy or reasonableness of the ground-water flow model. This report provides some guidelines and discussion on how to evaluate complex ground-water flow models used in the investigation of ground-water systems. A consistent thread throughout these guidelines is that the objectives of the study must be specified to allow the adequacy of the model to be evaluated.

Reilly, Thomas E.; Harbaugh, Arlen W.

2004-01-01

86

Groundwater support of stream flows in the Cambridge area, UK

This paper describes a feasibility study for the maintenance of stream flows during dry summer months in an area of Cambridgeshir e. Groundwater pumped from boreholes is used for augmentation. A mathematical model was used to represent the study area and led to an improved understanding of the aquifer flow mechanisms. Groundwater flow within horizons of high hydraulic conductivity is

K. R. RUSHTON

87

Using Groundwater Age and Other Isotopic Signatures to Delineate Groundwater Flow and Stratification

Isotopic tracers, such as stable isotopes of the water molecule and tritium, have been used in investigations of groundwater flow and transport and recharge water source for several decades. While these data can place hard constraints on groundwater flow rates, the degree of vertical flow between aquifers and across aquitards, and recharge source area(s), they are rarely used, even for validation, in conceptual or numerical models of groundwater flow. The Groundwater Ambient Monitoring and Assessment Program, sponsored by the California State Water Resources Control Board, and carried out in collaboration with the U.S. Geological Survey, has provided the means to gather an unprecedented number of tritium-helium groundwater ages in the basins of California. As the examples below illustrate, a collection of groundwater ages in a basin allows delineation of recharge areas (youngest ages), bulk flow rates and flowpaths, as well as a means of assessing susceptibility to anthropogenic contaminants.

Moran, J E; Hudson, G B

2005-08-31

88

Groundwater flow system study in volcanic low permeability bedrock basin

In Japan, the groundwater aquifer for pumping purposes are mostly in alluvium and diluvium deposits and the general concept and methodology for those aquifers has been already established. However, little study has been conducted for the groundwater flow system in relatively low permeability igneous and sedimentary rocks and it was not yet well understood. Although the groundwater of those aquifers

D. Inoue; J. Shimada; Y. Hase; K. Miyaoka

2005-01-01

89

Confidence Region Estimation for Groundwater Parameter Identification Problems

NASA Astrophysics Data System (ADS)

This presentation focuses on different methods to generate confidence regions for nonlinear parameter identification problems. Three methods for confidence region estimation are considered: a linear approximation method, an F--test method, and a Log--Likelihood method. Each of these methods are applied to three case studies. One case study is a problem with synthetic data, and the other two case studies identify hydraulic parameters in groundwater flow problems based on experimental well--test results. The confidence regions for each case study are analyzed and compared. Each of the three methods produce similar and reasonable confidence regions for the case study using synthetic data. The linear approximation method grossly overestimates the confidence region for the first groundwater parameter identification case study. The F--test and Log--Likelihood methods result in similar reasonable regions for this test case. For the second groundwater parameter identification case study, the linear approximation method produces a confidence region of reasonable size. In this test case, the F--test and Log--Likelihood methods generate disjoint confidence regions of reasonable size. The differing results, capabilities, and drawbacks of all three methods are discussed. Sandia is a multi program laboratory operated by Sandia Corporation, a Lockheed Martin Company, for the United States Department of Energy's National Nuclear Security Administration under Contract DE-AC04- 94AL85000. This research is funded by WIPP programs administered by the Office of Environmental Management (EM) of the U.S Department of Energy.

Vugrin, K. W.; Swiler, L. P.; Roberts, R. M.

2007-12-01

90

Relation of streams, lakes, and wetlands to groundwater flow systems

Surface-water bodies are integral parts of groundwater flow systems. Groundwater interacts with surface water in nearly all\\u000a landscapes, ranging from small streams, lakes, and wetlands in headwater areas to major river valleys and seacoasts. Although\\u000a it generally is assumed that topographically high areas are groundwater recharge areas and topographically low areas are groundwater\\u000a discharge areas, this is true primarily for

Thomas C. Winter

1999-01-01

91

The potential of hydrothermal boiling in groundwater flow channels for generating harmonic tremor (a relatively monochromatic ground vibration associated with volcanic activity) is examined. We use simple ``organ pipe'' theory of normal-mode fluid vibration and fundamental energy considerations to develop a first-order analytical model of a hydrothermal-boiling souce of harmonic tremor. We use this model to estimate order-of-magnitude groundwater flow

Robert C. Leet

1988-01-01

92

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

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,

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

1986-01-01

93

Tracing Groundwater Flow on a Barrier Island in the North-east Gulf of Mexico

NASA Astrophysics Data System (ADS)

Groundwater flow on St. George Island, a barrier island in the north-east Gulf of Mexico, was monitored downfield from wastewater systems using artificial tracer techniques. Sulphur hexafluoride and fluorescein dye were used to determine groundwater flow velocity, hydraulic conductivity, and dispersivity at selected sites on the island. Monthly hydraulic head measurements illustrate the aquifer's dependence on recharge associated with rainfall. However, during periods of little rain, tidal stage also influences the direction and magnitude of groundwater flow within approximately 30 m of the waters edge. Estimated hydraulic conductivities ranged from 3 to 180 m day -1, with an overall estimate of 36 m day -1. Groundwater tracers showed very little dilution and calculated longitudinal dispersivities were approximately 0·1 to 0·5 m, which is in the same range as previous studies of sandy aquifers. The total groundwater flux into adjacent Apalachicola Bay was also evaluated using two independent techniques. Darcy's law was applied using an estimated cross sectional area and the experimental horizontal transport rates to estimate the volumetric flow. In addition, a simple water balance calculation was used, which accounted for all known sources and sinks of water to the aquifer. The two independent approaches agreed very well, with an estimated groundwater flux from the surficial aquifer to Apalachicola Bay between 1-9×10 6 m 3 year -1.

Reide Corbett, D.; Dillon, K.; Burnett, W.

2000-08-01

94

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

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. PMID:23036222

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

2012-10-04

95

Regional groundwater-flow simulations for a 30,000-square-mile area of the High Plains aquifer, referred to collectively as the Elkhorn-Loup Model, were developed to predict the effects of groundwater irrigation on stream base flow in the Elkhorn and Loup River Basins, Nebraska. Simulations described the stream-aquifer system from predevelopment through 2005 [including predevelopment (pre-1895), early development (1895-1940), and historical development (1940 through 2005) conditions] and future hypothetical development conditions (2006 through 2033 or 2055). Predicted changes to stream base flow that resulted from simulated changes to groundwater irrigation will aid development of long-term strategies for management of hydrologically connected water supplies. The predevelopment through 2005 simulation was calibrated using an automated parameter-estimation method to optimize the fit to pre-1940 groundwater levels and base flows, 1945 through 2005 decadal groundwater-level changes, and 1940 through 2005 base flows. The calibration results of the pre-1940 period indicated that 81 percent of the simulated groundwater levels were within 30 feet of the measured water levels. The results did not indicate large areas of simulated groundwater levels that were biased too high or too low, indicating that the simulation generally captures the regional trends. Calibration results using 1945 through 2005 decadal groundwater-level changes indicated that a majority of the simulated groundwater-level changes were within 5 feet of the changes calculated from measured groundwater levels. Simulated groundwater-level rises generally were smaller than measured rises near surface-water irrigation districts. Simulated groundwater-level declines were larger than measured declines in several parts of the study area having large amounts of irrigated crops. Base-flow trends and volumes generally were reproduced by the simulation at most sites. Exceptions include downward trends of simulated base flow from the 1970s to the end of the calibration period for the Elkhorn River at Norfolk, Beaver Creek at Genoa, and Cedar River near Fullerton. Effects of groundwater irrigation on stream base flow were predicted using several methods: (1) simulated base-flow depletion was mapped to represent the percentage of water pumped from a hypothetical well during 2006 through 2055 that corresponds to base-flow depletions at the end of that 50-year period; (2) the groundwater-flow simulation predicted changes in stream base flow that result from modifying the number of irrigated acres in a 25-year period (2009 through 2033); and (3) a simulation-optimization model determined the minimum reduction of groundwater pumpage that would be necessary in the Elkhorn River Basin in a 25-year period (2009 through 2033) to comply with various hypothetical base-flow requirements for the Elkhorn River. The results are not intended to determine specific management plans that must be adopted, but rather to improve the understanding of how base flow is affected by irrigation. A 50-year simulation (2006-55) indicated that depletions of less than 10 percent of pumpage mainly occur in areas that are about 10 miles or farther from the Elkhorn and Loup Rivers and their tributaries. The calibrated simulation was used to predict the 25-year effect on base flow of a 10 percent decrease in irrigated acres and the effect of increasing acres at the presently (2010) allowed rate. Hypothesized changes to irrigated acres were applied only to areas where mapped base-flow depletions were at least 10 percent of pumpage. The effect of changes in irrigated acres includes the combined effects of changes to pumpage and additional recharge from irrigated acres. When irrigated acres were decreased by 10 percent within selected areas of four Natural Resources Districts (a total reduction of about 120,000 acres and a 5 percent reduction in irrigation pumpage), simulated base flow was predicted to inc

Stanton, Jennifer S.; Peterson, Steven M.; Fienen, Michael N.

2010-01-01

96

Stream functions in three-dimensional groundwater flow

Development of the partial differential equation of stream function ? in two-dimensional groundwater flow is based on the assumption that the curl of hydraulic gradient vector (?×??) is equal to zero. The equation of ? is expressed in terms of hydraulic conductivity. This equation is valid for steady state groundwater flow only. In this paper, two partial differential equations of

George B. Matanga

1993-01-01

97

Stream functions in three-dimensional groundwater flow

Development of the partial differential equation of stream function psi in two-dimensional groundwater flow is based on the assumption that the curl of hydraulic gradient vector (?×?varphi) is equal to zero. The equation of psi is expressed in terms of hydraulic conductivity. This equation is valid for steady state groundwater flow only. In this paper, two partial differential equations of

George B. Matanga

1993-01-01

98

Modeling groundwater flow by the natural element method

The finite difference and the finite element methods have difficulties in modeling groundwater flows with complicated shaped or moving boundary conditions. In order to resolve the difficulties, this study introduces the natural element method (NEM), one of the meshless methods, and applied the NEM to modeling groundwater flow for the first time. The NEM has been developed to solve efficiently

2006-01-01

99

Stochastic groundwater flow modeling using the second-order method

Stochastic groundwater flow modeling by means of a second-order uncertainty analysis technique is discussed. This technique is based on a Taylor series expansion of the state variables of interest (hydraulic heads and Darcian velocities) about the expected values of the model parameters. The method has been incorporated into the computer code PORSTAT, which solves the two-dimensional stochastic groundwater flow equation

B. Sagar; P. M. Clifton

1984-01-01

100

CONCEPTUAL FRAMEWORK FOR REGRESSION MODELING OF GROUND-WATER FLOW.

The author examines the uses of ground-water flow models and which classes of use require treatment of stochastic components. He then compares traditional and stochastic procedures for modeling actual (as distinguished from hypothetical) systems. Finally, he examines the conceptual basis and characteristics of the regression approach to modeling ground-water flow.

Cooley, Richard, L.

1985-01-01

101

NASA Astrophysics Data System (ADS)

Calibration is crucial to improving the performance of a groundwater flow model. In most cases, if historical groundwater data are available, the model is effectively calibrated before it is used for predictive simulations. That is, the model must be able to simulate observed historical groundwater conditions (e.g., groundwater elevations and flux rates). Groundwater elevation data used for model calibration typically are collected from observation wells (i.e., monitoring wells), not from active pumping wells. However, some sites have few or no observation wells and only groundwater elevations from active pumping wells are available. In this circumstance, using groundwater elevations from active pumping wells becomes necessary in model calibration. Directly using observation data from pumping wells to calibrate a model often leads to inaccurate model parameters because 1) groundwater elevations at pumping wells are affected by well efficiency (i.e., well loss), which is not accounted for in flow models, and 2) groundwater elevations change significantly in areas adjacent to pumping wells. As such, simulated groundwater elevations in a model cell where a well is located (i.e., the well-cell) are not representative of observed groundwater elevations in the wells. Consequently, observed pumping well groundwater elevations should be adjusted before being used as calibration targets by correcting for well losses and adjusting to spatially-averaged well-cell groundwater elevations. A method of calculating the spatially-averaged well-cell groundwater elevations based on the Thiem solution for a two-dimensional, steady-state flow condition has been developed. The derived formulation shows that the spatially-averaged well-cell groundwater elevations depend on pumping rate, aquifer transmissivity, well radius, and well-cell size. Using spatially-averaged well-cell groundwater elevations as the calibration targets improves flow model calibration, especially if little groundwater elevation data are available from observation wells and groundwater elevation data from pumping wells are abundant. MODFLOW test runs show that model calibration improves significantly when using groundwater elevation data from pumping wells. Calibration errors associated with direct use of pumping well groundwater elevation data also are addressed.

Zhang, J.; Elliot, L.; Muehleck, G.

2008-12-01

102

The influence of groundwater flow on thermal regimes in mountainous terrain: A model study

Groundwater flow in high-relief mountainous terrain is modeled to examine how geology, surface topography, climate, and regional heat flow influence the pattern and magnitude of an advective thermal disturbance. A numerical procedure is used to estimate the position of the water table within constraints provided by the available infiltration rate and the permeability of the mountain massif. Results show that

Craig Forster; Leslie Smith

1989-01-01

103

Automatic Time Stepping with Global Error Control for Groundwater Flow Models

An automatic time stepping with global error control is proposed for the time integration of the diffusion equation to simulate groundwater flow in confined aquifers. The scheme is based on an a posteriori error estimate for the discontinuous Galerkin (dG) finite element methods. A stability factor is involved in the error estimate and it is used to adapt the time

Guoping Tang; Guoping; Melanie A. Mayes

2008-01-01

104

Using Springs to Study Groundwater Flow and Active Geologic Processes

NASA Astrophysics Data System (ADS)

Spring water provides a unique opportunity to study a range of subsurface processes in regions with few boreholes or wells. However, because springs integrate the signal of geological and hydrological processes over large spatial areas and long periods of time, they are an indirect source of information. This review illustrates a variety of techniques and approaches that are used to interpret measurements of isotopic tracers, water chemistry, discharge, and temperature. As an example, a set of springs in the Oregon Cascades is considered. By using tracers, temperature, and discharge measurements, it is possible to determine the mean-residence time of water, infer the spatial pattern and extent of groundwater flow, estimate basin-scale hydraulic properties, calculate the regional heat flow, and quantify the rate of magmatic intrusion beneath the volcanic arc.

Manga, Michael

105

Development of a numerical groundwater flow model using SRTM elevations

Remotely-sensed elevation data are potentially useful for constructing regional scale groundwater models, particularly in\\u000a regions where ground-based data are poor or sparse. Surface-water elevations measured by the Shuttle Radar Topography Mission\\u000a (SRTM) were used to develop a regional-groundwater flow model by assuming that frozen surface waters reflect local hydraulic\\u000a head (or groundwater potential). Drainage lakes (fed primarily by surface water)

Kyle C. Fredrick; Matthew W. Becker; L. Shawn Matott; Ashish Daw; Karl Bandilla; Douglas M. Flewelling

2007-01-01

106

NSDL National Science Digital Library

Groundwater plays a central role in the environment and many communities around the world depend on it. This radio broadcast explores the importance of groundwater in our lives. Most freshwater resources are stored naturally as groundwater, a substantial portion of the public water supply is taken from this source, and in drier regions, many communities are totally dependent upon it. Although totally hidden from view, groundwater plays a central role in the environment, maintaining wetlands and river flows through prolonged dry periods. However, to many people who rely upon it, groundwater remains a subject of mystery. How does groundwater occur and where can it be found? How is it used and how do people care for it? Is the way that people behave on the land posing a huge risk to its natural pristine quality and how can science and technology help in the way we treat, use, and preserve groundwater? The broadcast is 30 minutes in length.

107

A local-scale groundwater flow model for groundwater resources management in Dakhla Oasis, SW Egypt

Dakhla Oasis is located in the Western Desert of Egypt. Groundwater exploited from the Nubian Sandstone aquifer is the only available water resource in this area. This resource has been heavily exploited since 1960, which has led to a substantial decline in the potentiometric surface of the aquifer. A regional numerical groundwater flow model, calibrated under unsteady-state conditions, has been

A. M. Ebraheem; S. Riad; P. Wycisk; A. M. Sefelnasr

2004-01-01

108

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.

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

2000-01-01

109

Mathematical modelling of saturated and unsaturated groundwater flow

Lectures concerning the practical application of mathematical models for ground water resources evaluation and their theoretical analysis are presented. The occurrence of groundwater in the Earth's subsurface, the distinction between saturated and unsaturated soils, and the derivation of an equation of motion for groundwater flow, are discussed. From the latter, it is shown how equations which are practical for modeling

B. H. Gilding

1991-01-01

110

NASA Astrophysics Data System (ADS)

Sound water management in wetlands requires knowledge of on-going processes and estimates of the water balance components. Specifically evapotranspiration is of crucial importance, as it is often the main water extracting quantity. To avoid elaborate and expensive equipment, which is often required for estimating actual values, potential evapotranspiration is frequently used, which can be easily derived from standard meteorological measurements. However, the potential values may under- or overestimate actual evapotranspiration significantly. A cheap and easy-to-use method for estimating actual values in shallow groundwater environments relies on diurnal groundwater fluctuation. Basically the 24 hours groundwater level decline, considering in some way the prevalent groundwater recovery, is multiplied by the readily available specific yield. Various varieties of this approach have been employed for that purpose, above all differing in their assumptions on groundwater recovery, i.e. lateral or vertical in- or outflow. The objective of our study is therefore to compare these different methods. For this purpose we use data of a weighable groundwater lysimeter situated at a ditch drained grassland site in the Spreewald wetland in Northeastern Germany. The groundwater level in the lysimeter was adjusted to a reference gauge and simulated the conditions of the surrounding area. Hence the lysimeter reflected near natural conditions and provided measurements of all water balance components with high temporal resolution (up to 10 minute intervals). Suitable days, i.e. with a pronounced diurnal fluctuation, of the vegetation periods 2011 and 2012 are chosen and used to prove common assumptions about groundwater recharge, e.g. if the values remain constant during the day or if diurnal variations resulting from gradient changes exist. Finally, based on the lysimeter measurements, the evapotranspiration estimates gained from different approaches that employ diurnal groundwater fluctuation are evaluated.

Fahle, Marcus; Dietrich, Ottfried; Lischeid, Gunnar

2013-04-01

111

Estimating Ground-Water Recharge from Stream Hydrographs

It is possible to separate graphically the base flow on stream hydrographs by plo). ting the logarithm of the discharge against time. Total potential ground-water discharge (Q,) at the beginning of any given base-flow recession is Q,, -- KK,\\/2.3

P. Meyboom

1961-01-01

112

NSDL National Science Digital Library

The resource describes groundwater. It includes a diagram of mountains, ocean, streams and lakes with red arrows indicating the flow of groundwater into the soil and into the ocean. Accompanying text describes ground water, the water table, porosity, saturation, runoff and flooding.

113

The effect of turbulent groundwater flow on hydraulic heads and parameter sensitivities was examined for the Biscayne aquifer in southern Florida using the Conduit Flow Process (CFP) for MODFLOW-2005. Turbulent flow was spatially extensive in preferential groundwater flow layers with mean void diameters equal to about 3.5 centimeters, groundwater temperature equal to about 25 degrees Celsius, and critical Reynolds numbers

W. B. Shoemaker

2009-01-01

114

Fracture Flow of Groundwater in Coal-Bearing Strata.

National Technical Information Service (NTIS)

Fractures are of considerable importance to groundwater flow through lithified coal-bearing strata. Laboratory tests on core samples in many different studies in the northern Appalachians and northern Great Plains show sandstones, siltstones, shales, and ...

J. P. Schubert

1980-01-01

115

Permafrost thaw in a nested groundwater-flow system

NASA Astrophysics Data System (ADS)

Groundwater flow in cold regions containing permafrost accelerates climate-warming-driven thaw and changes thaw patterns. Simulation analyses of groundwater flow and heat transport with freeze/thaw in typical cold-regions terrain with nested flow indicate that early thaw rate is particularly enhanced by flow, the time when adverse environmental impacts of climate-warming-induced permafrost loss may be severest. For the slowest climate-warming rate predicted by the Intergovernmental Panel on Climate Change (IPCC), once significant groundwater flow begins, thick permafrost layers can vanish in several hundred years, but survive over 1,000 years where flow is minimal. Large-scale thaw depends mostly on the balance of heat advection and conduction in the supra-permafrost zone. Surface-water bodies underlain by open taliks allow slow sub-permafrost flow, with lesser influence on regional thaw. Advection dominance over conduction depends on permeability and topography. Groundwater flow around permafrost and flow through permafrost impact thaw differently; the latter enhances early thaw rate. Air-temperature seasonality also increases early thaw. Hydrogeologic heterogeneity and topography strongly affect thaw rates/patterns. Permafrost controls the groundwater/surface-water-geomorphology system; hence, prediction and mitigation of impacts of thaw on ecology, chemical exports and infrastructure require improved hydrogeology/permafrost characterization and understanding.

McKenzie, Jeffrey M.; Voss, Clifford I.

2013-02-01

116

Groundwater Flow Model of the General Separations Area Using PORFLOW

The E Area PA (McDowell-Boyer et al. 2000) includes a steady-state simulation of groundwater flow in the General Separations Area as a prerequisite for saturated zone contaminant transport analyses. The groundwater flow simulations are based on the FACT code (Hamm and Aleman2000). The FACT-based GSA model was selected during preparation of the original PA to take advantage of an existing

2004-01-01

117

PUMa - modelling the groundwater flow in Baltic Sedimentary Basin

NASA Astrophysics Data System (ADS)

In 2009-2012 at University of Latvia and Latvia University of Agriculture project "Establishment of interdisciplinary scientist group and modelling system for groundwater research" is implemented financed by the European Social Fund. The aim of the project is to develop groundwater research in Latvia by establishing interdisciplinary research group and modelling system covering groundwater flow in the Baltic Sedimentary Basin. Researchers from fields like geology, chemistry, mathematical modelling, physics and environmental engineering are involved in the project. The modelling system is used as a platform for addressing scientific problems such as: (1) large-scale groundwater flow in Baltic Sedimentary Basin and impact of human activities on it; (2) the evolution of groundwater flow since the last glaciation and subglacial groundwater recharge; (3) the effects of climate changes on shallow groundwater and interaction of hydrographical network and groundwater; (4) new programming approaches for groundwater modelling. Within the frame of the project most accessible geological information such as description of geological wells, geological maps and results of seismic profiling in Latvia as well as Estonia and Lithuania are collected and integrated into modelling system. For example data form more then 40 thousands wells are directly used to automatically generate the geological structure of the model. Additionally a groundwater sampling campaign is undertaken. Contents of CFC, stabile isotopes of O and H and radiocarbon are the most significant parameters of groundwater that are established in unprecedented scale for Latvia. The most important modelling results will be published in web as a data set. Project number: 2009/0212/1DP/1.1.1.2.0/09/APIA/VIAA/060. Project web-site: www.puma.lu.lv

Kalvane, G.; Marnica, A.; Bethers, U.

2012-04-01

118

Application of the discontinuous spectral Galerkin method to groundwater flow

The discontinuous spectral Galerkin method uses a finite-element discretization of the groundwater flow domain with basis functions of arbitrary order in each element. The independent choice of the basis functions in each element permits discontinuities in transmissivity in the flow domain. This formulation is shown to be of high order accuracy and particularly suitable for accurately calculating the flow field

Sergio Fagherazzi; David Jon Furbish; Patrick Rasetarinera; M. Youssuff Hussaini

2004-01-01

119

A study was undertaken to quantitatively evaluate the hydrologic processes affecting the chemical and isotopic composition of drain lateral water in a drained agricultural field in the western San Joaquin Valley, California. The results elucidate the process of mixing of deep and shallow groundwater (below and within 6 m from land surface) entering the drain laterals. The deep groundwater was subject to evapoconcentration prior to drainage system installation and has been displaced downward (to depths greater than 6 m) in the groundwater system. The proportions of deep and shallow groundwater entering the drain laterals was calculated from the end-member oxygen 18 compositions determined in groundwater samples. The percentage of total drain lateral flow which is deep groundwater flow is about 30% for the shallow drain lateral (1.8 m below land surface) (drain lateral 1)) and 60% for the deep drain lateral (2.7 m below land surface (drain lateral 2)). During irrigation, the percentages of deep groundwater flow decrease to 0 and 30% for the shallow and deep drain laterals, respectively. Selenium concentrations in drain lateral waters decrease during irrigation but selenium loads increase. Total estimated annual loads were 1.1 and 5.4 kg of selenium for drain laterals 1 and 2, respectively. Substantial percentages of the annual load occurred during 8 days of irrigation, 23 and 9% for drain laterals 1 and 2, respectively.

Deverel, S. J.; Fio, John L.

1991-01-01

120

NASA Astrophysics Data System (ADS)

The Independence Basin in the semi-arid Guanajuato state of central Mexico is facing serious groundwater resources deficiency due to an increasing demand linked to a rapid population growth and agricultural development. This problem is aggravated by an inadequate evaluation of groundwater resources in the region. Geochemistry and isotopic tracers were used in order to investigate the groundwater flow system and estimate the groundwater residence time. The groundwater is characterized by low salinity with some exceptions associated to a contribution of more saline groundwater from deep formations. The predominant reactions are CO2 gas dissolution, carbonate dissolution, albite weathering, kaolinite and chalcedony precipitation. Six principal hydrochemical zones were recognized, which provided information on plausible recharge sources and groundwater chemical evolution. The 14C concentration varies between 19 and 94 pmc. The high 14C values indicating recent recharge are observed at the basin margins and a trend to lower 14C values is observed along the modern groundwater flow paths. The groundwater residence time according to radiocarbon estimations ranges between recent and ˜11 ka. The residence time distribution matches the regional important discharge zones west in the basin center (from Dolores Hidalgo and southwest from Doctor Mora). Hydrochemical tracers are in general agreement with the predeveloped and current hydraulic-head configuration, however, show some inconsistencies with the predeveloped head in the downgradient areas, which means that the impact by gradually increasing groundwater extraction during the last decades is reflected on radiocarbon age distribution. Geochemical evidences imply that the recharge input from the northern basin area is insignificant.

Mahlknecht, J.; Gárfias-Solis, J.; Aravena, R.; Tesch, R.

2006-06-01

121

Estimation of groundwater residence time using the 36Cl bomb pulse.

We propose a methodology for estimating the residence time of groundwater based on bomb-produced (36)Cl. Water samples were collected from 28 springs and 2 flowing wells located around Mt. Fuji, Central Japan. (36)Cl/Cl ratios in the water samples, determined by accelerator mass spectrometry (AMS), were between 43 × 10(-15) and 412 × 10(-15). A reference time series of the above-background (i.e., bomb-derived) (36)Cl concentration was constructed by linearly scaling the background-corrected Dye-3 data according to the estimated total bomb-produced (36)Cl fallout in the Mt. Fuji area. Assuming piston flow transport, estimates of residence time were obtained by comparing the measured bomb-derived (36)Cl concentrations in spring water with the reference curve. The distribution of (36)Cl-based residence times is basically consistent with that of tritium-based estimates calculated from data presented in previous studies, although the estimated residence times differ between the two tracers. This discrepancy may reflect chlorine recycling via vegetation or the relatively small change in fallout rate, approximately since 1975, which would give rise to large uncertainties in (36)Cl-based estimates of recharge for the period, approximately since 1975. Given the estimated ages for groundwater from flowing wells, dating based on a (36)Cl bomb pulse may be more reliable and sensitive for groundwater recharged before 1975, back as far as the mid-1950s. PMID:21309769

Tosaki, Yuki; Tase, Norio; Sasa, Kimikazu; Takahashi, Tsutomu; Nagashima, Yasuo

2011-02-10

122

NASA Astrophysics Data System (ADS)

A regional groundwater flow model was developed, in order to evaluate the water table behavior in the region of the Guadalupe Valley, in Baja California, Mexico. The State of Baja California has been subject to an increment of the agricultural, urban and industrials activities, implicating a growing water-demand. However, the State is characterized by its semi-arid climate with low surface water availability; therefore, has resulted in an extensive use of groundwater in local aquifer. Water level measurements indicate there has been a decline in water levels in the Guadalupe Valley for the past 20 years. This study describes the use of groundwater optimization modeling to efficiently allocate the groundwater resources in the Guadalupe Valley. A 2- Dimensional groundwater flow was used along with optimization techniques to evaluate the effects of the current groundwater management alternative and to determine the optimal withdrawal rates for a variety of management alternatives in the Guadalupe Valley Aquifer. For all simulations, the objective of the optimization was to maximize total groundwater withdrawals. Both steady-state and transient calibration were carried out in order to obtain the best possible match to measured levels in the Guadalupe Valley Aquifer. The results of this simulation-optimization are as follows: (1) probably this should be an integrated hydrogeological evaluation that determines the conditions of the groundwater resource and permits planning a management of the Guadalupe Valley Aquifer; (2) a satisfactory match between calculated and measured water levels in the Guadalupe Valley Aquifer.

Campos, R.; Kretzschmar, T.

2006-12-01

123

Ground-water withdrawal estimates from 1913 through 2003 for the Death Valley regional ground-water flow system are compiled in an electronic database to support a regional, three-dimensional, transient ground-water flow model. This database updates a previously published database that compiled estimates of ground-water withdrawals for 1913–1998. The same methodology is used to construct each database. Primary differences between the 2 databases are an additional 5 years of ground-water withdrawal data, well locations in the updated database are restricted to Death Valley regional ground-water flow system model boundary, and application rates are from 0 to 1.5 feet per year lower than original estimates. The lower application rates result from revised estimates of crop consumptive use, which are based on updated estimates of potential evapotranspiration. In 2003, about 55,700 acre-feet of ground water was pumped in the DVRFS, of which 69 percent was used for irrigation, 13 percent for domestic, and 18 percent for public supply, commercial, and mining activities.

Michael T. Moreo; and Leigh Justet

2008-07-02

124

Optimal Management of Flow in Groundwater Systems

NASA Astrophysics Data System (ADS)

Groundwater simulation models are physically based mathematical models derived from Darcy's law and the law of conservation of mass. Various established solution techniques utilizing either the finite difference or the finite element method, or a combination of both, are available for solving the governing equation of the model, provided that model parameters and initial and boundary conditions are properly specified. With the advancement of numerical computing and various user-friendly interface software, groundwater simulation models are now commonly used by groundwater planners to assist in the decision making in a variety of water resources management problems.In simulation,groundwater models are used to predict (1) the hydraulic or water quality response of the aquifer system to a set of pumping and recharge schedules and (2) the probable hydrologic and environmental impacts associated with groundwater development. Because it can only consider a limited number of management alternatives, the simulation approach generally does not identify the optimal pumping/recharge schedules in the context of all the objectives and constraints. A recent advancement in groundwater modeling has been the development of management models that combine optimization and simulation. In contrast to simulation, optimization models identify optimal planning, design,and operational policies for the groundwater system. And because the simulation model is incorporated in a constraint set of the management model, the optimal decisions not only define the optimal pumping/recharge schedules, but also predict the time and spatial variation in the hydraulic head.

Yeh, William W.-G.

125

A three-dimensional groundwater flow and solute transport model was calibrated to a plume of water described by measurements of Î´Â¹â¸O and used to calculate groundwater inflow and outflow rates at a lake in northern Wisconsin. The flow model was calibrated to observed hydraulic gradients and estimated recharge rates. Calibration of the solute transport submodel to the configuration of a stable

David P. Krabbenhoft; Mary P. Anderson; Carl J. Bowser

1990-01-01

126

NASA Astrophysics Data System (ADS)

A 3-D finite element model (Feflow) has been used for regional groundwater flow modelling of Upper Chaj Doab in Indus Basin, Pakistan. The thematic layers of soils, landuse, hydrology, infrastructure and climate were developed using Geographic Information System (GIS). 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. Integration of GIS with groundwater modelling and satellite remote sensing capabilities has provided an efficient way of analysing and monitoring groundwater status and its associated land conditions. The Arcview GIS software is used as additive tool to develop supportive data for numerical groundwater modelling, integration and presentation of image processing and modelling results. The groundwater behaviour of the regional model shows a gradual decline in watertable from year 1999 onward. The persistent dry condition and high withdrawal rates play an influential role in lowering down the groundwater levels. Different scenarios were developed to study the impact of extreme climatic conditions (drought/flood) and variable groundwater abstraction on the regional groundwater system. The results of the study provide useful information regarding the behaviour of aquifer in order to organize management schemes on local and regional basis to monitor future groundwater development in the area.

Ashraf, A.; Ahmad, Z.

2008-04-01

127

Geochemical and isotopic data from groundwater sampling locations can be used to estimate groundwater flow velocities for independent comparison to velocities calculated by other methods. The objective of this study was to calculate groundwater flow velocities using geochemistry and environmental isotopes from the southern end of Yucca Flat to the Amargosa Desert, considering mixing of different groundwater inputs from sources each and southeast of the Nevada Test Site (NTS). The approach used to accomplish the objective of this study consisted of five steps: (1) reviewing and selecting locations where carbon isotopic groundwater analyses, reliable ionic analysis, and well completion information are available; (2) calculating chemical speciation with the computer code WATEQ4F (Ball and Nordstrom, 1991) to determine the saturation state of mineral phases for each ground water location; (3) grouping wells into reasonable flowpaths and mixing scenarios from different groundwater sources; (4) using the computer code NETPATH (Plummer et al., 1991) to simulate mixing and the possible chemical reactions along the flowpath, and to calculate the changes in carbon-13/carbon-12 isotopic ratios ({delta}{sup 13}C) as a result of these reactions; and (5) using carbon-14 ({sup 14}C) data to calculate velocity.

Hershey, R.L.; Acheampong, S.Y. [Nevada Univ., Reno, NV (United States). Water Resources Center

1997-06-01

128

The computational cost of groundwater flow simulation can be crucial when analyzing complex conjunctive use water resources systems that need to simulate simultaneously surface and groundwater components. A general methodology for accurate simulation of unconfined groundwater flow with low computational cost is presented. It requires linearizing the unconfined groundwater flow problem governed by the Boussinesq equation. The technique is based

David Pulido-Velazquez; Andrés Sahuquillo; Joaquín Andreu; Manuel Pulido-Velazquez

2007-01-01

129

Glaciation and regional groundwater flow in the Fennoscandian shield

Regional-scale groundwater flow modeling of the Fennoscandian shield suggests that groundwater flow can be strongly affected by future climate change and glaciation. We considered variable-density groundwater flow in a 1500-km-long and approximately 10-km-deep cross-section through southern Sweden. Groundwater flow and shield brine transport in the cross-sectional model were analyzed under projected surface conditions for the next 140 ka. Simulations suggest that blockage of recharge and discharge by low-permeability permafrost or cold-based ice causes sinking of brine and consequent freshening of near-surface water in areas of natural discharge. Although recharge of basal meltwater is limited by the requirement that water pressure at the base of the ice sheet not exceed the pressure exerted by the weight of the ice, warm-based ice with basal melting creates a potential for groundwater recharge rates much larger than those of present, ice-free conditions. In the simulations, regional-scale redistribution of recharged water by subsurface flow is minor over the duration of a glacial advance (approximately 10 ka). During glacial retreat, significant upward flow of groundwater may occur below the ice sheet owing to pressure release. If the mechanical loading efficiency of the rocks is high, both subsurface penetration of meltwater during glacial advance and up-flow during glacial retreat are reduced because of loading-induced pressure changes. The maximum rate of groundwater discharge in the simulations occurs at the receding ice margin, and some discharge occurs below incursive postglacial seas. Recharge of basal meltwater could decrease the concentration of dissolved solids significantly below present-day levels at depths of up to several kilometers and may bring oxygenated conditions to an otherwise reducing chemical environment for periods exceeding 10 ka.

Provost, A. M.; Voss, C. I.; Neuzil, C. E.

2012-01-01

130

Regional ground-water flow in the Lower Peninsula of Michigan

A steady-state, numerical model is being developed to simulate groundwater flow in four regional aquifers in Michigan's Lower Peninsula. The uppermost layer in the model simulates flow in the glaciofluvial aquifer and the second layer simulates flow in the Saginaw aquifer, both of which contain freshwater. The lower two modeled units simulate flow in the Parma-Bayport and Marshall aquifers, both of which contain saline water or brine, except at or near their subcrop, where they contain freshwater. The US Geological Survey's Modular Model (MODFLOW) was modified to simulate variable-density groundwater flow in the lower two aquifers by assuming that groundwater density and viscosity differ from place to place but do not change over time. The model simulates groundwater conditions prior to large-scale withdrawals from the aquifer. Boundaries for the model include constant-head boundaries at the shorelines of Lakes Michigan, Huron, St. Clair, and Erie, as well as the St. Clair and Detroit Rivers. The southern boundary is simulated as a no-flow condition along several major stream divides in Michigan and Indiana. Recharge to the glaciofluvial aquifer is estimated to range from 0.2 to 22 inches per year and averages 8.4 inches per year. Regional groundwater flow occurs in areas where the bedrock aquifers are confined and in parts of the glaciofluvial aquifer, such as in the north-central part of the Lower Peninsula. Regional discharge primarily occurs to Saginaw Bay and to streams in the Saginaw and Michigan Lowlands. Parts of the Grand and Maple rivers may also receive discharge on a regional scale. Local flow systems control the direction and rate of groundwater flow in areas where aquifers are unconfined or hydraulically connected to overlying glacial deposits.

Grannemann, N.G.; Huffman, G.C. (Geological Survey, Lansing, MI (United States))

1994-04-01

131

Estimation of ecological high flow

NASA Astrophysics Data System (ADS)

Floods can destroy fish habitat. During a flood a fish has to seek shelters (refuges) to survive. It is necessary to know the maximum discharge that the fish can sustain against the strong current. Ecological and hydraulic engineers can simulate the flow condition of high flow for designing the refuge when restoring and enhancing the rivers are needed. Based on the average ratio of the mean and maximum velocities invariant with time, discharge and water level, this paper tries to introduce the concept of ecological high flow. The mean-maximum velocity ratio can be used to estimate the mean velocity of the river. If the maximum velocity of the cross section is replaced by the maximum sustained swimming speeds of fish, the mean velocity of ecological high flow can be calculated with the constant ratio. The cross-sectional area can be estimated by the gage height. Then the ecological high flow can be estimated as the product of mean velocity of ecological high flow multiplied by the cross-sectional area. The available data of the upstream of the Dacha River where is the habitat of the Formosan landlocked salmon were used to illustrate the estimation of the ecological high flow. Any restoration project at Sonmou that try to improve the stream habitat can use the ecological high flow to design the hydraulic structure at suitable location to offer refuges for the Formosan landlocked salmon that is an endangered species in Taiwan

Lin, Jen-Yang; Chen, Yen-Chang; Hsienshao Tsao, Eric

2006-02-01

132

The San Juan structural basin northwestern New Mexico was modeled in three dimensions using a finite-difference, steady-state model. The modeled space was divided into seven layers of square prisms that were 6 miles on a side in the horizontal directions. In the vertical direction, the layers of prisms ranged in thickness from 300 to 1,500 feet. The model included the geologic section between the base of the Entrada Sandstone and the top of Mesaverde Group. Principal aquifers in this section are mostly confined and include the Entrada Sandstone, the Westwater Canyon Member of the Morrison Formation , and the Gallup Sandstone. Values for vertical hydraulic conductivities from 10 to the minus 12th power to 10 to the minus 11th power feet per second for the confining layers gave a good simulation of head differences between layers, but a sensitivity analysis indicated that these values could be between 10 and 100 times greater. The model-derived steady-state flow was about 30 cubic feet per second. About one-half of the flow was in the San Juan River drainage basin about one-third in the Rio Grande drainage basin, and one-sixth in the Puerco River drainage basin. (USGS)

Frenzel, P. F.; Lyford, F. P.

1982-01-01

133

In situ permeable flow sensor: A device for measuring groundwater flow velocity.

National Technical Information Service (NTIS)

A new technology called the In Situ Permeable Flow Sensor has been developed at Sandia National Laboratories. These sensors use a thermal perturbation technique to directly measure the direction and magnitude of the full three dimensional groundwater flow...

S. Ballard G. T. Barker R. L. Nichols

1994-01-01

134

The purpose of the flow boundary conditions analysis is to provide specified-flux boundary conditions for the saturated zone (SZ) site-scale flow and transport model. This analysis is designed to use existing modeling and analysis results as the basis for estimated groundwater flow rates into the SZ site-scale model domain, both as recharge at the upper (water table) boundary and as underflow at the lateral boundaries. The objective is to provide consistency at the boundaries between the SZ site-scale flow model and other groundwater flow models. The scope of this analysis includes extraction of the volumetric groundwater flow rates simulated by the SZ regional-scale flow model to occur at the lateral boundaries of the SZ site-scale flow model and the internal qualification of the regional-scale model for use in this analysis model report (AMR). In addition, the scope includes compilation of information on the recharge boundary condition taken from three sources: (1) distributed recharge as taken from the SZ regional-scale flow model, (2) recharge below the area of the unsaturated zone (UZ) site-scale flow model, and (3) focused recharge along the Fortymile Wash channel.

B. Arnold; T. Corbet

2001-12-18

135

Storm-driven groundwater flow in a salt marsh

NASA Astrophysics Data System (ADS)

Storms can cause significant groundwater flow in coastal settings, but prior studies of the effects of storms on groundwater flow and transport have largely focused on very large storms and used salinity as a tracer. We have little information about the effects of smaller storms on coastal flow and how storm-induced variability affects key tidal wetlands like salt marshes, which may remain saline throughout a storm. Here we show that even the distant passage of a moderate storm can strongly increase groundwater flow and transport in salt marsh ecosystems and adjacent barrier islands. Groundwater monitoring and radium isotope tracer analyses revealed significant influx of saline creek water into the confined aquifer below the marsh platform, driven by storm surge. This pulse of fluids reached depths exceeding 5 m, and surge-enhanced tides propagated through the aquifer to affect flow in the upland >100 m from the creek bank. Groundwater discharge from the marsh varied significantly prior to the storm, doubling during inundating tides compared to a period of noninundating neap tides. Storm surge then caused groundwater discharge to decline ˜50% compared to similar inundating tides. Ra- and nutrient-poor creek water that entered the confined aquifer below the marsh was quickly enriched in nutrients and carbon, even on 12 h tidal cycles, so that nutrient discharge was likely proportional to groundwater discharge. Storm-related flow could also drive significant contaminant discharge from developed coastlines. The enhanced transport and variability observed here likely affected hundreds of kilometers of the coastline impacted by the storm.

Wilson, Alicia M.; Moore, Willard S.; Joye, Samantha B.; Anderson, Joseph L.; Schutte, Charles A.

2011-02-01

136

Mathematical and numerical models for coupling surface and groundwater flows

In this paper we present some results about the coupling of Navier–Stokes and Shallow Water equations for surface flows and Darcy's equation for groundwater flows. We discuss suitable interface conditions and show the well-posedness of the coupled problem in the case of a linear Stokes problem. An iterative method to compute the solution is proposed. At each step this method

Marco Discacciati; Edie Miglio; Alfio Quarteroni

2002-01-01

137

Heat transfer from a solar pond through saturated groundwater flow

Heat losses from a salt gradient solar pond through saturated groundwater flow was studied by developing a finite difference computer model. The first part of the model calculates the rate of the seepage from the solar pond and measures the velocity components for the nodes of the hydraulic flownet created by the seepage flow. The second part of the model

Dadkhah

1985-01-01

138

NASA Astrophysics Data System (ADS)

The present work deals with determination groundwater flows in the Amazon region, based on analysis of geothermal data acquired in shallow and deep wells. The method employed is based on the model of simultaneous heat transfer by conduction and advection in permeable media. Analysis of temperature data acquired in water wells indicates down flows of groundwaters with velocities in excess of 10-7 m/s at depths less than 300 m in the Amazonas basin. Bottom-hole temperature (BHT) data sets have been used in determining characteristics of fluid movements at larger depths in the basins of Acre, Solimões, Amazonas, Marajó and Barreirinhas. The results of model simulations point to down flow of groundwaters with velocities of the order of 10-8 to 10-9 m/s, at depths of up to 4000 m. No evidence has been found for up flow typical of discharge zones. The general conclusion compatible with such results is that large-scale groundwater recharge systems operate at both shallow and deep levels in all sedimentary basins of the Amazon region. However, the basement rock formations of the Amazon region are relatively impermeable and hence extensive down flow systems through the sedimentary strata are possible only in the presence of generalized lateral movement of groundwater in the basal parts of the sedimentary basins. The direction of this lateral flow, inferred from the basement topography and geological characteristics of the region, is from west to east, following roughly the course of surface drainage system of the Amazon River, with eventual discharge into the Atlantic Ocean. The estimated flow rate at the continental margin is 3287 m3/s, with velocities of the order of 218 m/year. It is possible that dynamic changes in the fluvial systems in the western parts of South American continent have been responsible for triggering alterations in the groundwater recharge systems and deep seated lateral flows in the Amazon region.

Pimentel, Elizabeth T.; Hamza, Valiya M.

2012-08-01

139

This report is a guide for executing numerical simulations with the transient ground-water flow model of the Death Valley regional ground-water flow system, Nevada and California using the U.S. Geological Survey modular finite-difference ground-water flow model, MODFLOW-2000. Model inputs, including observations of hydraulic head, discharge, and boundary flows, are summarized. Modification of the DVRFS transient ground-water model is discussed for two common uses of the Death Valley regional ground-water flow system model: predictive pumping scenarios that extend beyond the end of the model simulation period (1998), and model simulations with only steady-state conditions.

Joan B. Blainey; Claudia C. Faunt, and Mary C. Hill

2006-05-16

140

NASA Astrophysics Data System (ADS)

The Tongue Creek watershed lies on the south flank of Grand Mesa in western Colorado, USA and is a site with 1.5 km of topographic relief, heat flow of 100 mW/m2, thermal conductivity of 3.3 W m-1 °C-1, hydraulic conductivity of 10-8 m/s, a water table that closely follows surface topography, and groundwater temperatures 3-15°C above mean surface temperatures. These data suggest that convective heat transport by groundwater flow has modified the thermal regime of the site. Steady state three-dimensional numerical simulations of heat flow, groundwater flow, and convective transport were used to model these thermal and hydrological data. The simulations provided estimates for the scale of hydraulic conductivity and bedrock base flow discharge within the watershed. The numerical models show that (1) complex three-dimensional flow systems develop with a range of scales from tens of meters to tens of kilometers; (2) mapped springs are frequently found at locations where contours of hydraulic head indicate strong vertical flow at the water table, and; (3) the distribution of groundwater temperatures in water wells as a function of surface elevation is predicted by the model.

Lazear, Gregory D.

2006-12-01

141

Ground water is the primary source of water for domestic, municipal, and industrial use within the northwest section of Michigan's Lower Peninsula. Because of the importance of this resource, numerous communities including the city of Cadillac in Wexford County, Michigan, have begun local wellhead protection programs. In these programs, communities protect their ground-water resources by identifying the areas that contribute water to production wells, identifying potential sources of contamination, and developing methods to cooperatively manage and minimize threats to the water supply. The U.S. Geological Survey, in cooperation with the city of Cadillac, simulated regional ground-water flow and estimated areas contributing recharge and zones of transport to the production well field. Ground-water flow models for the Clam River watershed, in Wexford and Missaukee Counties, were developed using the U.S. Geological Survey modular three-dimensional finite-difference ground-water flow model (MODFLOW 2000). Ground-water flow models were calibrated using the observation, sensitivity, and parameter estimation packages of MODFLOW 2000. Ground-water-head solutions from calibrated flow models were used in conjunction with MODPATH, a particle-tracking program, to simulate regional ground-water flow and estimate areas contributing recharge and zones of transport to the Cadillac production-well field for a 10-year period. Model simulations match the conceptual model in that regional ground-water flow in the deep ground-water system is from southeast to northwest across the watershed. Areas contributing water were determined for the optimized parameter set and an alternate parameter set that included increased recharge and hydraulic conductivity values. Although substantially different hydrologic parameters (assumed to represent end-member ranges of realistic hydrologic parameters) were used in alternate numerical simulations, simulation results differ little in predictions of the size of the contributing area to the city well field. However, increasing recharge and hydraulic conductivity values appreciably affected the shape of the contributing area and zone of contribution of reacharge. Simulation results indicate that the region immediately to the south and southeast of the well field is contributing water to the production wells. Detailed aquifer characterization would be needed to describe and simulate the heterogeneous glacial deposits in the watershed.

Hoard, Christopher J.; Westjohn, David B.

2005-01-01

142

Regional groundwater flow modeling in Zhangye Basin a of Heihe river watershed, China

Groundwater in Zhangye Basin accounts for a large amount of quantities during supplying water for Zhangye City. In order to find out the optimal groundwater development plan to achieve the sustainable development, a regional groundwater flow model was constructed for the study area. Hydrogeological parameters were calibrated against observed groundwater level hydrographs and flow field. Then, the model was used

S. H. X. Wang; J. Qian; X. L. Hu

2011-01-01

143

Impact of Groundwater Discharge on Hyporheic Exchange Flow using a Multi-scale Model

NASA Astrophysics Data System (ADS)

Groundwater - surface water interactions in streams affect nutrient uptake, contaminant deposition, biogeochemistry, and thus water quality. The region of the subsurface through which surface water flows (hyporheic zone) is rich in biological activity transforming many substances and making it an important focus for scholarly inquiry. Groundwater discharge levels can significantly affect the shape and extent of the hyporheic zone. In order to investigate the importance of and interactions between features of the system, we developed a predictive multi-scale model of stream-subsurface exchange based on easily measured a priori system characteristics and stream bathymetry. This model is spatially explicit and includes both the lateral and subsurface hyporheic regions. Exchange due to features ranging from small ripples to meanders can be incorporated into the model, which produces water exchange flux across the sediment boundary, subsurface residence time distributions, and three-dimensional flow paths. In prior work, this multi-scale model has been tested on laboratory flume datasets. In this study we apply the model to Sugar Creek, a small gaining agricultural steam in Indiana, which exemplifies streams found throughout the Midwestern United States. Within the modeling framework, we varied the groundwater discharge by increasing the groundwater levels along the lateral boundaries of the system. We found that increases in groundwater discharge inhibited flow into the subsurface preferentially near the edges of the system and that the flux into the subsurface was a nonlinear function of groundwater discharge. We also simulated the system with and without ripple/dune scale bedforms in order to investigate the complex interactions between these bedforms and groundwater discharge. Our results show that the presence of bedforms increased exchange to a greater extent in the scenarios with groundwater discharge. Insights gained from this study suggest several areas for future work and offer recommendations to research practitioners. First, because of the system's sensitivity to groundwater discharge rate, future field studies should strive to improve groundwater discharge measurements through focused tracer studies or detailed peizometer measurements. Second, simulation and modeling studies should include the best estimates obtainable for groundwater discharge; it is an influential parameter that must not be neglected. Finally, further investigations should be made into the effect of spatial variations in groundwater levels in order to determine the level of detail required to adequately characterize a field site.

Stonedahl, S. H.

2011-12-01

144

Stream Flow Estimation via Belief Propagation for Sparsely Instrumented Watersheds

NASA Astrophysics Data System (ADS)

Knowledge of stream flow rates is critical for management of in-stream flows and mitigation of flooding and drought events. Unfortunately, spatially dense networks of in situ stream flow measurements are not generally available and would be prohibitively expensive to deploy and maintain. Since measurements are only available at relatively sparse spatial frequencies, a data assimilation technique that best utilizes available measurements in a computationally efficient manner is required. Complexities in underlying geology, groundwater-surface water interactions, and rainfall patterns also need to be captured for optimal performance. In this study, a probabilistic technique based on Bayesian Networks and belief propagation is used to estimate and forecast stream flow based on flow at surrounding locations, rainfall, and groundwater levels, and to quantify the uncertainty of the estimates. The causal nature and inherent tree-like structure of stream flow suggests that belief propagation based on message passing is a computationally efficient method to propagate partial observations to improve flow estimates at other stations across the watershed. Stations are considered as part of an array of nodes that communicate evidence of flow measurements to their neighbors via conditional probability densities defining the links between the nodes. The probability density functions are generated based on the relationship between estimates of flow from the Watershed Assessment Model (WAM), calibrated for our study site at the Santa Fe River Watershed in North Central Florida, USA from 1990 through 2008. Rainfall values were obtained from NEXRAD datasets, while Suwannee River Water Management District provided groundwater levels at a network of wells in the watershed. Performance of the proposed method is evaluated by comparing the results to flow measured at several USGS gage stations along the river not used to develop the algorithm, using various metrics such as Nash-Sutcliffe Coefficient, mean and standard deviations of error, and error entropies.

Krekeler, C. R.; Nagarajan, K.; Graham, W. D.; Slatton, K. C.

2009-12-01

145

Groundwater Table Estimation Using MODFLOW and Artificial Neural Networks

The use of numerical models to simulate groundwater flow has been addressed in many research studies during the past decade.\\u000a The main drawback with these models is their enormous and generally difficult or costly data requirements. On the other hand,\\u000a artificial neural networks (ANNs) are offering a simple but precise solution to many simulation problems. In this chapter,\\u000a the applicability

K. Mohammadi

146

Automatic Time Stepping with Global Error Control for Groundwater Flow Models

An automatic time stepping with global error control is proposed for the time integration of the diffusion equation to simulate groundwater flow in confined aquifers. The scheme is based on an a posteriori error estimate for the discontinuous Galerkin (dG) finite element methods. A stability factor is involved in the error estimate and it is used to adapt the time step and control the global temporal error for the backward difference method. The stability factor can be estimated by solving a dual problem. The stability factor is not sensitive to the accuracy of the dual solution and the overhead computational cost can be minimized by solving the dual problem using large time steps. Numerical experiments are conducted to show the application and the performance of the automatic time stepping scheme. Implementation of the scheme can lead to improvement in accuracy and efficiency for groundwater flow models.

Tang, Guoping [ORNL

2008-09-01

147

Study on the groundwater flow and hydrogeochemical interaction in fractured rock masses.

National Technical Information Service (NTIS)

Since the major transport mechanism of radionuclides leaching from a repository is by flowing groundwater, the flow paths, volume and travel time of groundwater in rock mass should be evaluated and convincingly predicted. Hence, the main objectives of thi...

J. S. Ahn J. W. Kim C. S. Kim J. H. Kim S. T. Yun

1990-01-01

148

Comparison of groundwater flow in Southern California coastal aquifers

Development of the coastal aquifer systems of Southern California has resulted in overdraft, changes in streamflow, seawater intrusion, land subsidence, increased vertical flow between aquifers, and a redirection of regional flow toward pumping centers. These water-management challenges can be more effectively addressed by incorporating new understanding of the geologic, hydrologic, and geochemical setting of these aquifers. Groundwater and surface-water flow are controlled, in part, by the geologic setting. The physiographic province and related tectonic fabric control the relation between the direction of geomorphic features and the flow of water. Geologic structures such as faults and folding also control the direction of flow and connectivity of groundwater flow. The layering of sediments and their structural association can also influence pathways of groundwater flow and seawater intrusion. Submarine canyons control the shortest potential flow paths that can result in seawater intrusion. The location and extent of offshore outcrops can also affect the flow of groundwater and the potential for seawater intrusion and land subsidence in coastal aquifer systems. As coastal aquifer systems are developed, the source and movement of groundwater and surface-water resources change. In particular, groundwater flow is affected by the relative contributions of different types of inflows and outflows, such as pumpage from multi-aquifer wells within basal or upper coarse-grained units, streamflow infiltration, and artificial recharge. These natural and anthropogenic inflows and outflows represent the supply and demand components of the water budgets of groundwater within coastal watersheds. They are all significantly controlled by climate variability related to major climate cycles, such as the El Ni??o-Southern Oscillation and the Pacific Decadal Oscillation. The combination of natural forcings and anthropogenic stresses redirects the flow of groundwater and either mitigates or exacerbates the potential adverse effects of resource development, such as declining water levels, seawater intrusion, land subsidence, and mixing of different waters. Streamflow also has been affected by development of coastal aquifer systems and related conjunctive use. Saline water is the largest water-quality problem in Southern California coastal aquifer systems. Seawater intrusion is a significant source of saline water, but saline water is also known to come from other sources and processes. Seawater intrusion is typically restricted to the coarse-grained units at the base of fining-upward sequences of terrestrial deposits, and at the top of coarsening upward sequences of marine deposits. This results in layered and narrow intrusion fronts. Maintaining the sustainability of Southern California coastal aquifers requires joint management of surface water and groundwater (conjunctive use). This requires new data collection and analyses (including research drilling, modern geohydrologic investigations, and development of detailed computer groundwater models that simulate the supply and demand components separately), implementation of new facilities (including spreading and injection facilities for artificial recharge), and establishment of new institutions and policies that help to sustain the water resources and better manage regional development. ?? 2009 Geological Society of America.

Hanson, R. T.; Izbicki, J. A.; Reichard, E. G.; Edwards, B. D.; Land, M.; Martin, P.

2009-01-01

149

The Marine Corps Air Ground Combat Center (MCAGCC) Twentynine Palms, California, overlies the Surprise Spring, Deadman, Mesquite, and Mainside subbasins of the Morongo groundwater basin in the southern Mojave Desert. Historically, the MCAGCC has relied on groundwater pumped from the Surprise Spring subbasin to provide all of its potable water supply. Groundwater pumpage in the Surprise Spring subbasin has caused groundwater levels in the subbasin to decline by as much as 190 feet (ft) from 1953 through 2007. Groundwater from the other subbasins contains relatively high concentrations of fluoride, arsenic, and (or) dissolved solids, making it unsuitable for potable uses without treatment. The potable groundwater supply in Surprise Spring subbasin is diminishing because of pumping-induced overdraft and because of more restrictive Federal drinking-water standards on arsenic concentrations. The U.S. Geological Survey, in cooperation with the MCAGCC, completed this study to better understand groundwater resources in the area and to help establish a long-term strategy for regional water-resource development. The Surprise Spring, Deadman, Mesquite, and Mainside subbasins are filled with sedimentary deposits of Tertiary age, alluvial fan deposits of Quaternary-Tertiary age, and younger alluvial and playa deposits of Quaternary age. Combined, this sedimentary sequence reaches a maximum thickness of more than 16,000 ft in the Deadman and Mesquite subbasins. The sedimentary deposits of Tertiary age yield a small amount of water to wells, and this water commonly contains high concentrations of fluoride, arsenic, and dissolved solids. The alluvial fan deposits form the principal water-bearing unit in the study area and have a combined thickness of 250 to more than 1,000 ft. The younger alluvial and playa deposits are unsaturated throughout most of the study area. Lithologic and downhole geophysical logs were used to divide the Quaternary/ Tertiary alluvial fan deposits into two aquifers (referred to as the upper and the middle aquifers) and the Tertiary sedimentary deposits into a single aquifer (referred to as the lower aquifer). In general, wells perforated in the upper aquifer yield more water than wells perforated in the middle and lower aquifers. The study area is dominated by extensive faulting and moderate to intense folding that has displaced or deformed the pre-Tertiary basement complex as well as the overlying Tertiary and Quaternary deposits. Many of these faults act as barriers to the lateral movement of groundwater flow and form many of the boundaries of the groundwater subbasins. The principal recharge to the study area is groundwater underflow across the western and southern boundaries that originates as runoff in the surrounding mountains. Groundwater discharges naturally from the study area as spring flow, as groundwater underflow to downstream basins, and as water vapor to the atmosphere by transpiration of phreatophytes and direct evaporation from moist soil. The annual volume of water that naturally recharged to or discharged from the groundwater flow system in the study area during predevelopment conditions was estimated to be 1,010 acre-feet per year (acre-ft/yr). About 90 percent of this recharge originated as runoff from the Little San Bernardino and the Pinto Mountains to the south, and the remainder originated as runoff from the San Bernardino Mountains to the west. Evapotranspiration by phreatophytes near Mesquite Lake (dry) was the primary form of predevelopment groundwater discharge. From 1953 through 2007, approximately 139,400 acre-feet (acre-ft) of groundwater was pumped by the MCAGCC from the Surprise Spring subbasin. A regional-scale numerical groundwater flow model was developed using MODFLOW-2000 for the Surprise Spring, Deadman, Mesquite, and Mainside subbasins. The aquifer system was simulated by using three model layers representing the upper, middle, and lower aquifers. Measured groundwater levels

Li, Zhen; Martin, Peter

2011-01-01

150

Steady state groundwater flow simulation with imprecise parameters

A methodology based on fuzzy set theory is developed to incorporate imprecise parameters into steady state groundwater flow models. In this case, fuzzy numbers are used to represent parameter imprecision. As such, they are also used as a measure for the uncertainty associated with the hydraulic heads due to the imprecision in the input parameters. The imprecise input parameters may

Chunhua Dou; Wayne Woldt; Istvan Bogardi; Mohamed Dahab

1995-01-01

151

Steady two-dimensional groundwater flow through many elliptical inhomogeneities

A new analytic element solution has been derived for steady two-dimensional groundwater flow through an aquifer that contains an arbitrary number of elliptical inhomogeneities. The hydraulic conductivity of each inhomogeneity is homogeneous and differs from the conductivity of the homogeneous background. In addition to elliptical inhomogeneities, other elements (such as wells and line sinks) may be present. The method is

Raghavendra Suribhatla; Mark Bakker; Karl Bandilla; Igor Jankovic

2004-01-01

152

Steady State Groundwater Flow Simulation With Imprecise Parameters

A methodology based on fuzzy set theory is developed to incorporate imprecise parameters into steady state groundwater flow models. In this case, fuzzy numbers are used to represent parameter imprecision. As such, they are also used as a measure for the uncertainty associated with the hydraulic heads due to the imprecision in the input parameters. The imprecise input parameters may

Chunhua Dou; Wayne Woldt; Istvan Bogardi; Mohamed Dahab

1995-01-01

153

Groundwater flow beneath ice sheets: Part I — Large scale patterns

Ice sheets melting basally will inject water into subglacial permeable beds under a maximum head equivalent to the total ice pressure. Melting beneath the European Ice Sheet is simulated for the last two glacial cycles and the consequences for groundwater flow computed along an ice sheet flowline stretching from the low permeability basement rocks of Sweden to the thick Mesozoic

G. S. Boulton; P. E. Caban; K. Van Gijssel

1995-01-01

154

Finite element techniques for modeling groundwater flow in fractured aquifers

A mathematical description of groundwater flow in fractured aquifers is presented. Four alternative conceptual models are considered. The first three are based on the dual-porosity approach with different representations of fluid interactions between the fractures and porous matrix blocks, and the fourth is based on the discrete fracture approach. Two numerical solution techniques are presented for solving the governing equations

Peter S. Huyakorn; Barry H. Lester; Charles R. Faust

1983-01-01

155

Groundwater Flow Effects in Processes of Soil Freezing

The influence of groundwater flow effects on freezing processes in soil is analyzed by means of finite element method. The latent heat involved in a phase change is taken into account by virtue of the enthalpy, which is defined as the integral of heat capacity with respect to temperature. The analyses are carried out in an example of a two-dimensional

Andrzej Stuizalec

1989-01-01

156

Numerical simulation of waste movement in steady groundwater flow systems

The finite element method based on a Galerkin technique is used to formulate the problem of simulating the two-dimensional transient movement of conservative or nonconservative wastes in a steady state saturated groundwater flow system. The convection-dispersion equation is solved in two ways: in the conventional Cartesian coordinate system and in a transformed coordinate system equivalent to the orthogonal curvilinear coordinate

John F. Pickens; William C. Lennox

1976-01-01

157

Numerical error in groundwater flow and solute transport simulation

Models of groundwater flow and solute transport may be affected by numerical error, leading to quantitative and qualitative changes in behavior. In this paper we compare and combine three methods of assessing the extent of numerical error: grid refinement, mathematical analysis, and benchmark test problems. In particular, we assess the popular solute transport code SUTRA [Voss, 1984] as being a

Juliette A. Woods; Michael D. Teubner; Craig T. Simmons; Kumar A. Narayan

2003-01-01

158

Numerical error in groundwater flow and solute transport simulation

Models of groundwater flow and solute transport may be affected by numerical error, leading to quantitative and qualitative changes in behavior. In this paper we compare and combine three methods of assessing the extent of numerical error: grid refinement, mathematical analysis, and benchmark test problems. In particular, we assess the popular solute transport code SUTRA [ Voss, 1984] as being

Juliette A. Woods; Michael D. Teubner; Craig T. Simmons; Kumar A. Narayan

2003-01-01

159

Perturbation of ground surface temperature reconstructions by groundwater flow?

NASA Astrophysics Data System (ADS)

Subsurface temperatures have been shown to be a robust source of information on past climates. Most analyses neglect groundwater flow (GWF) and assume purely conductive heat flow. However, in many situations GWF has not been fully considered and to date there are no general GWF criteria for either accepting or rejecting a temperature profile for paleoclimate analysis. Here we examine the transition from conduction dominated environments to environments where advection has a significant effect on the subsurface temperature regime and thus ground surface temperature (GST) histories. We provide guidelines indicating when advection is important and conclude that it is unlikely that groundwater flow is a significant source of error in the global data set maintained by the International Heat Flow Commission.

Ferguson, Grant; Beltrami, Hugo; Woodbury, Allan D.

2006-07-01

160

2007 Estimated International Energy Flows

An energy flow chart or 'atlas' for 136 countries has been constructed from data maintained by the International Energy Agency (IEA) and estimates of energy use patterns for the year 2007. Approximately 490 exajoules (460 quadrillion BTU) of primary energy are used in aggregate by these countries each year. While the basic structure of the energy system is consistent from country to country, patterns of resource use and consumption vary. Energy can be visualized as it flows from resources (i.e. coal, petroleum, natural gas) through transformations such as electricity generation to end uses (i.e. residential, commercial, industrial, transportation). These flow patterns are visualized in this atlas of 136 country-level energy flow charts.

Smith, C A; Belles, R D; Simon, A J

2011-03-10

161

MODIS-Aided Statewide Net Groundwater-Recharge Estimation in Nebraska.

Monthly evapotranspiration (ET) rates (2000 to 2009) across Nebraska at about 1-km resolution were obtained by linear transformations of the MODIS (MODerate resolution Imaging Spectroradiometer) daytime surface temperature values with the help of the Priestley-Taylor equation and the complementary relationship of evaporation. For positive values of the mean annual precipitation and ET differences, the mean annual net recharge was found by an additional multiplication of the power-function-transformed groundwater vulnerability DRASTIC-code values. Statewide mean annual net recharge became about 29 mm (i.e., 5% of mean annual precipitation) with the largest recharge rates (in excess of 100 mm/year) found in the eastern Sand Hills and eastern Nebraska. Areas with the largest negative net recharge rates caused by declining groundwater levels due to large-scale irrigation are found in the south-western region of the state. Error bounds of the estimated values are within 10% to 15% of the corresponding precipitation rates and the estimated net recharge rates are sensitive to errors in the precipitation and ET values. This study largely confirms earlier base-flow analysis-based statewide groundwater recharge estimates when considerations are made for differences in the recharge definitions. The current approach not only provides better spatial resolution than available earlier studies for the region but also quantifies negative net recharge rates that become especially important in numerical modeling of shallow groundwater systems. PMID:23216050

Szilagyi, Jozsef; Jozsa, Janos

2012-12-05

162

Characterization and conceptualization of groundwater flow systems: Chapter 2

This chapter discusses some of the fundamental concepts, data needs and approaches that aid in developing a general understanding of a groundwater system. Principles of the hydrological cycle are reviewed; the processes of recharge and discharge in aquifer systems; types of geological, hydrological and hydraulic data needed to describe the hydrogeological framework of an aquifer system; factors affecting the distribution of recharge to aquifers; and uses of groundwater chemistry, geochemical modelling, environmental tracers and age interpretations in groundwater studies. Together, these concepts and observations aid in developing a conceptualization of groundwater flow systems and provide input to the development of numerical models of a flow system. Conceptualization of the geology, hydrology, geochemistry, and hydrogeological and hydrochemical framework can be quite useful in planning, study design, guiding sampling campaigns, acquisition of new data and, ultimately, developing numerical models capable of assessing a wide variety of societal issues — for example, sustainability of groundwater resources in response to real or planned withdrawals from the system, CO2 sequestration or other waste isolation issues (such as nuclear waste disposal).

Plummer, L. N.; Sanford, W. E.; Glynn, P. D.

2013-01-01

163

Approaches to the simulation of unconfined flow and perched groundwater flow in MODFLOW.

Various approaches have been proposed to manage the nonlinearities associated with the unconfined flow equation and to simulate perched groundwater conditions using the MODFLOW family of codes. The approaches comprise a variety of numerical techniques to prevent dry cells from becoming inactive and to achieve a stable solution focused on formulations of the unconfined, partially-saturated, groundwater flow equation. Keeping dry cells active avoids a discontinuous head solution which in turn improves the effectiveness of parameter estimation software that relies on continuous derivatives. Most approaches implement an upstream weighting of intercell conductance and Newton-Raphson linearization to obtain robust convergence. In this study, several published approaches were implemented in a stepwise manner into MODFLOW for comparative analysis. First, a comparative analysis of the methods is presented using synthetic examples that create convergence issues or difficulty in handling perched conditions with the more common dry-cell simulation capabilities of MODFLOW. Next, a field-scale three-dimensional simulation is presented to examine the stability and performance of the discussed approaches in larger, practical, simulation settings. PMID:21635246

Bedekar, Vivek; Niswonger, Richard G; Kipp, Kenneth; Panday, Sorab; Tonkin, Matthew

2011-06-02

164

Apparent dispersion in transient groundwater flow

This paper investigates the effects of large-scale temporal velocity fluctuations, particularly changes in the direction of flow, on solute spreading in a two-dimensional aquifer. Relations for apparent longitudinal and transverse dispersivity are developed through an analytical solution for dispersion in a fluctuating, quasi-steady uniform flow field, in which storativity is zero. For transient flow, spatial moments are evaluated from numerical

Daniel J. Goode; Leonard F. Konikow

1990-01-01

165

A regional-scale groundwater flow model for the Leon-Chinandega aquifer, Nicaragua

Groundwater flow in the Leon-Chinandega aquifer was simulated using transient and steady-state numerical models. This unconfined\\u000a aquifer is located in an agricultural plain in northwest Nicaragua. Previous studies were restricted to determining groundwater\\u000a availability for irrigation, overlooking the impacts of groundwater development. A sub-basin was selected to study the groundwater\\u000a flow system and the effects of groundwater development using a

Heyddy Calderón Palma; Laurence R. Bentley

2007-01-01

166

Steady State Groundwater Flow Simulation With Imprecise Parameters

NASA Astrophysics Data System (ADS)

A methodology based on fuzzy set theory is developed to incorporate imprecise parameters into steady state groundwater flow models. In this case, fuzzy numbers are used to represent parameter imprecision. As such, they are also used as a measure for the uncertainty associated with the hydraulic heads due to the imprecision in the input parameters. The imprecise input parameters may come from indirect measurements, subjective interpretation, and expert judgment of available information. In the methodology, a finite difference method is combined with level set operations to formulate the fuzzy groundwater flow model. This fuzzy modeling technique can handle imprecise parameters in a direct way without generating a large number of realizations. Two numerical solution methods are used to solve the fuzzy groundwater flow model: the groundwater model operator method proposed in this methodology and the iterative algorithm based on conventional interval arithmetics. The iterative method is simple but may overestimate the uncertainty of hydraulic heads. The groundwater model operator method not only provides the hull of the solution set for the hydraulic heads but also considers the dependence of hydraulic head coefficients which are functions of imprecise parameters. Sensitivity analysis shows that the dependence of hydraulic head coefficients has a critical impact on the model results, and neglecting this dependence may result in significant overestimation of the uncertainty of hydraulic heads. A numerical model based on the methodology is tested by comparing it with the analytical solution for a homogeneous radial flow problem. It is also applied to a simplified two-dimensional heterogeneous flow case to demonstrate the methodology.

Dou, Chunhua; Woldt, Wayne; Bogardi, Istvan; Dahab, Mohamed

1995-01-01

167

Validation Analysis of the Shoal Groundwater Flow and Transport Model

Environmental restoration at the Shoal underground nuclear test is following a process prescribed by a Federal Facility Agreement and Consent Order (FFACO) between the U.S. Department of Energy, the U.S. Department of Defense, and the State of Nevada. Characterization of the site included two stages of well drilling and testing in 1996 and 1999, and development and revision of numerical models of groundwater flow and radionuclide transport. Agreement on a contaminant boundary for the site and a corrective action plan was reached in 2006. Later that same year, three wells were installed for the purposes of model validation and site monitoring. The FFACO prescribes a five-year proof-of-concept period for demonstrating that the site groundwater model is capable of producing meaningful results with an acceptable level of uncertainty. The corrective action plan specifies a rigorous seven step validation process. The accepted groundwater model is evaluated using that process in light of the newly acquired data. The conceptual model of ground water flow for the Project Shoal Area considers groundwater flow through the fractured granite aquifer comprising the Sand Springs Range. Water enters the system by the infiltration of precipitation directly on the surface of the mountain range. Groundwater leaves the granite aquifer by flowing into alluvial deposits in the adjacent basins of Fourmile Flat and Fairview Valley. A groundwater divide is interpreted as coinciding with the western portion of the Sand Springs Range, west of the underground nuclear test, preventing flow from the test into Fourmile Flat. A very low conductivity shear zone east of the nuclear test roughly parallels the divide. The presence of these lateral boundaries, coupled with a regional discharge area to the northeast, is interpreted in the model as causing groundwater from the site to flow in a northeastward direction into Fairview Valley. Steady-state flow conditions are assumed given the absence of groundwater withdrawal activities in the area. The conceptual and numerical models were developed based upon regional hydrogeologic investigations conducted in the 1960s, site characterization investigations (including ten wells and various geophysical and geologic studies) at Shoal itself prior to and immediately after the test, and two site characterization campaigns in the 1990s for environmental restoration purposes (including eight wells and a year-long tracer test). The new wells are denoted MV-1, MV-2, and MV-3, and are located to the northnortheast of the nuclear test. The groundwater model was generally lacking data in the north-northeastern area; only HC-1 and the abandoned PM-2 wells existed in this area. The wells provide data on fracture orientation and frequency, water levels, hydraulic conductivity, and water chemistry for comparison with the groundwater model. A total of 12 real-number validation targets were available for the validation analysis, including five values of hydraulic head, three hydraulic conductivity measurements, three hydraulic gradient values, and one angle value for the lateral gradient in radians. In addition, the fracture dip and orientation data provide comparisons to the distributions used in the model and radiochemistry is available for comparison to model output. Goodness-of-fit analysis indicates that some of the model realizations correspond well with the newly acquired conductivity, head, and gradient data, while others do not. Other tests indicated that additional model realizations may be needed to test if the model input distributions need refinement to improve model performance. This approach (generating additional realizations) was not followed because it was realized that there was a temporal component to the data disconnect: the new head measurements are on the high side of the model distributions, but the heads at the original calibration locations themselves have also increased over time. This indicates that the steady-state assumption of the groundwater model is in error. To test the robustness of the model d

A. Hassan; J. Chapman

2008-11-01

168

NASA Astrophysics Data System (ADS)

The purpose of this report is to describe (1) the geologic and hydrologic setting of Tinian, (2) the numerical ground-water flow model developed, (3) the results of the model simulations that assess the hydrologic effects of drought on the freshwater lens, and (4) data needs. No new data were collected for this report; only existing data were used to develop the conceptual framework of the ground-water flow system. A numerical ground-water flow model of Tinian was used to refine the conceptual framework and to estimate the effects of different withdrawal scenarios and drought on ground-water levels, the freshwater/saltwater interface, and coastal discharge.

Gingerich, S. B.

2002-01-01

169

A preliminary study has been made of the effects of groundwater flow on the heat transfer characteristics of vertical closed-loop heat exchangers and the ability of current design and in-situ thermal conductivity measurement techniques to deal with these effects. It is shown that an initial assessment of the significance of groundwater flow can be made by examining the Peclet number of the flow. A finite-element numerical groundwater flow and heat transfer model has been used to simulate the effects of groundwater flow on a single closed-loop heat exchanger in various geologic materials. These simulations show that advection of heat by groundwater flow significantly enhances heat transfer in geologic materials with high hydraulic conductivity, such as sands, gravels, and rocks exhibiting fractures and solution channels. Simulation data were also used to derive effective thermal conductivities with an in-situ thermal conductivity estimation procedure. These data were used to design borehole fields of different depths for a small commercial building. The performance of these borehole field designs was investigated by simulating each borehole field using the pre-calculated building loads over a ten-year period. Results of these simulations, in terms of the minimum and peak loop temperatures, were used to examine the ability of current design methods to produce workable and efficient designs under a range of groundwater flow conditions.

Chiasson, A.D.; Rees, S.J.; Spitler, J.D.

2000-07-01

170

Groundwater flow is influenced by topography, but in fractured and dipping sedimentary rocks, it is also influenced by structure. Field evidence indicates that groundwater is older on the downdip side of a stream (asymmetry) and that dip-aligned streams receive more base flow than strike-aligned streams (anisotropy). We present detailed numerical models to evaluate the effects of various factors that influence

Ying Fan; Laura Toran; Roy W. Schlische

2007-01-01

171

Simulation of groundwater flow around a pilot waste tire site

The groundwater system in the area contains several aquifers divided by underclays as confining layers. The three aquifers addressed under this research include the upper aquifer above the No. 6 underclay, the middle aquifer above the No. 5 underclay and the lower aquifer above the No. 4 underclay. A quasi-3D conceptual model is used in simulating groundwater flow and MODFLOW is used for the actual modeling. The boundary of the model area is defined by a local divide on the north, the Hugle Run on the west and the Temple Ditch on the east and the Sandy Creek on the south. The model consists of three aquifer layers and two confining layers. The upper one is unconfined, the middle one is a hybrid, and the lower one is confined. In the simulation of the upper aquifer, drain boundary condition is defined to include seepage. In the simulation of the middle aquifer, the Hugle Run and the Temple ditch associated with the alluvium represent a drain boundary and the Sand Creek to the south represents a constant head. The lower aquifer does not have a natural hydrogeologic boundary. The equipotential contours are assigned as constant head boundary. Simulation has indicated that minimal groundwater flow existed in the upper aquifer and it is flowing toward the southwest. Groundwater flow in the middle aquifer near the pilot waste site is somewhat divergent to the south. The velocity is slow near the site but increases quickly toward the southwest. Leakage from the upper aquifer appears to be predominant over the regional flow in the recharge of the middle aquifer. The lower aquifer is recharged mainly by the regional flow and is flowing almost due south.

Lin, Y.; Chyi, L.L. (Univ. of Akron, OH (United States). Dept. of Geology)

1994-04-01

172

Global estimates of submarine groundwater discharge using numerical modeling and geomatics

NASA Astrophysics Data System (ADS)

Submarine groundwater discharge (SGD), the flow of fresh or saline groundwater to an ocean, may be a significant contributor to the water and chemical budgets of the world oceans. SGD consists of fresh, terrestrial groundwater driven by hydraulic gradients, the focus of this research, and re-circulated seawater driven by tidal pumping, wave set-up, convection and hydraulic gradients. We couple density-dependent analytical and numerical simulations of generic models of coastal topography and geology with geomatic data bases to resolve the rate and driving mechanisms of terrestrially-derived submarine groundwater discharge globally. Two analytical models lead to linear relationships between SGD and the key predictive parameters: hydraulic gradients, hydraulic conductivities, aquifer thickness and recharge. Average global geomatic parameters suggest global SGD ranges from 0.01% to 0.2% of global river run off which much lower than most previous estimates of global SGD. Quantifying submarine groundwater discharge is critical because SGD is a poorly constrained flux that can significantly contribute to eutrophication or water quality decline in coastal areas.

Luijendijk, E.; Gleeson, T.; Ferguson, G. A.

2011-12-01

173

Groundwater Flow Demonstration Model Activities for Grades 6-12

NSDL National Science Digital Library

This set of activities is designed to use a demonstration model available through the Uath County Cooperative Extension Services or from Project WET. They demonstrate such concepts as aquifers, groundwater flow, water table, the relationship between groundwater and surface water, recharge, and others. A glossary and standards correlations to the Utah Core Curriculum for Science are included. The physical model can be obtained through the Utah County Cooperative Extension Service, the Utah Water Resources Education Program, or for sale from Project WET (Water Education for Teachers).

Farrell-Poe, Kitt

174

Groundwater Flow and Transport Modeling With Correlated Possibilistic Data

Stochastic groundwater modeling involves the propagation of probabilistic uncertainty from model input parameters to model estimates, usually via a Monte Carlo method. With the increasing reliance upon expert knowledge to define model inputs, and both fuzzy set and possibility theories to characterize this expert knowledge, alternative means of executing model equations are needed. While the fuzzy extension principle is commonly

M. Ozbek; J. Ross; G. Pinder

2008-01-01

175

NASA Astrophysics Data System (ADS)

The computational cost of groundwater flow simulation can be crucial when analyzing complex conjunctive use water resources systems that need to simulate simultaneously surface and groundwater components. A general methodology for accurate simulation of unconfined groundwater flow with low computational cost is presented. It requires linearizing the unconfined groundwater flow problem governed by the Boussinesq equation. The technique is based on a change of variable and depends on the reference level adopted. Some recommendations have been provided to set the reference level to estimate the spatially variant parameters required to define the linearized problem. Using this linearization, more accurate results can be obtained than those derived with the classical assumption of invariant transmissivity. Solving the problem with eigenvalue techniques, the solution can be defined with a semi-explicit state equation with low computational cost. Some case studies have been analyzed in order to demonstrate that the methodology can be applied to any aquifer geometry (including non-horizontal bottoms), hydrodynamic properties and boundary conditions (even different prescribed head values). The results have been compared with those obtained with other linearization methods and MODFLOW [McDonald, M.G., Harbaugh, A.W., 1988. A modular three dimensional finite difference ground water flow model. Open File Report 83-875, US Geological Survey, Washington DC] for unconfined aquifers. A case study defined from a previously calibrated finite-difference model of the “Delta Adra” aquifer, located in southern Spain, has been also analyzed.

Pulido-Velazquez, David; Sahuquillo, Andrés; Andreu, Joaquín; Pulido-Velazquez, Manuel

2007-05-01

176

NASA Astrophysics Data System (ADS)

The distribution of groundwater fluxes in aquifers is strongly influenced by topography, and organized between hillslope and regional scales. The objective of this study is to provide new insights regarding the compartmentalization of aquifers at the regional scale and the partitioning of recharge between shallow/local and deep/regional groundwater transfers. A finite-difference flow model was implemented, and the flow structure was analyzed as a function of recharge (from 20 to 500 mm/yr), at the regional-scale (1400 km2), in three dimensions, and accounting for variable groundwater discharge zones; aspects which are usually not considered simultaneously in previous studies. The model allows visualizing 3-D circulations, as those provided by Tothian models in 2-D, and shows local and regional transfers, with 3-D effects. The probability density function of transit times clearly shows two different parts, interpreted using a two-compartment model, and related to regional groundwater transfers and local groundwater transfers. The role of recharge on the size and nature of the flow regimes, including groundwater pathways, transit time distributions, and volumes associated to the two compartments, have been investigated. Results show that topography control on the water table and groundwater compartmentalization varies with the recharge rate applied. When recharge decreases, the absolute value of flow associated to the regional compartment decreases, whereas its relative value increases. The volume associated to the regional compartment is calculated from the exponential part of the two-compartment model, and is nearly insensitive to the total recharge fluctuations.

Goderniaux, Pascal; Davy, Philippe; Bresciani, Etienne; Dreuzy, Jean-Raynald; Borgne, Tanguy

2013-04-01

177

Technology Transfer Automated Retrieval System (TEKTRAN)

The GRAPHIC Project has identified priority research topics related to groundwater recharge, discharge, storage, and water quality. This presentation focuses on some physical aspects affecting spatial groundwater recharge estimation and uncertainty associated with spatial variability. Previous wor...

178

Understanding the relative importance of climate, vegetation, and soils in controlling groundwater recharge is important for estimating effects of climate variability and land use\\/land cover change on recharge\\/water resources. The purpose of this study was to evaluate the sensitivity of groundwater recharge to variations in climate, soil type, and vegetation type using unsaturated-flow modeling and to further assess the sensitivity

K. E. Keese; B. R. Scanlon; R. C. Reedy

2004-01-01

179

Climate proxy data as groundwater tracers in regional flow systems

NASA Astrophysics Data System (ADS)

The isotopic and chemical signatures of groundwater reflect local climate conditions. By systematically analyzing groundwater and determining their hydrologic setting, records of past climates can be constructed. Because of their chemistries and relatively uncomplicated source functions, dissolved noble gases have yielded reliable records of continental temperatures for the last 30,000 to 50,000 years. Variations in the stable isotope compositions of groundwater due to long term climate changes have also been documented over these time scales. Because glacial - interglacial climate changes are relatively well known, these climate proxies can be used as "stratigraphic" markers within flow systems and used to distinguish groundwaters that have recharged during the Holocene from those recharged during the last glacial period, important time scales for distinguishing regional and local flow systems in many aquifers. In southern Georgia, the climate proxy tracers were able to identify leakage from surface aquifers into the Upper Floridan aquifer in areas previously thought to be confined. In south Florida, the transition between Holocene and glacial signatures in the Upper Floridan aquifer occurs mid-way between the recharge area and Lake Okeechobee. Down gradient of the lake, the proxies are uniform, indicating recharge during the last glacial period. Furthermore, there is no evidence for leakage from the shallow aquifers into the Upper Floridan. In the Lower Floridan, the climate proxies indicate that the saline water entered the aquifer after sea level rose to its present level.

Clark, J. F.; Morrissey, S. K.; Stute, M.

2008-05-01

180

NASA Astrophysics Data System (ADS)

Interpolation of solute concentration measurements often yields disappointing results, especially when it fails to incorporate some knowledge relative to the underlying physics of groundwater flow and solute transport. Concentration maps, however, are required in several applications such as plume monitoring, evaluation of total dissolved mass, design of hydraulic containment and pump-and-treat systems, source identification and natural attenuation assessment. Kriged concentration maps can be improved by a coordinate transformation based on natural flow coordinates, as this allows to consider variations in the local anisotropy direction produced by heterogeneous groundwater flow. On the other hand, this does not consider nonstationarity induced by local dispersion. This paper presents a flexible kriging approach that combines a coordinate transformation based on groundwater flow and a class of nonstationary (NS) covariance functions that can be parameterized to account for the evolution of concentration correlation and variance with travel time/distance. We also propose an alternative flow coordinate transformation that does not rely on the stream function, enabling the computation of approximate 3-D flow coordinates. Nonstationary covariance parameters are estimated using maximum likelihood, and candidate parametrizations are compared by the likelihood ratio test and Akaike Information Criterion. The approach is tested on simple 2-D and 3-D synthetic plumes shaped by heterogeneous flow and local dispersion. Results show that: (1) NS covariance parameterizations improve significantly the likelihood compared to the stationary models, (2) the combined coordinate transformation and NS covariance approach enhances kriging of solute concentrations. Although the flow fields are considered known in the case studies, the approach can be modified to incorporate flow uncertainty and lends itself to various useful extensions, such as mass flux estimation.

Rivest, M.; Marcotte, D.

2012-11-01

181

NASA Astrophysics Data System (ADS)

An optimum groundwater management which achieved a good balance between conservation and utilization is required to use the groundwater as sustainable water resources. On the recent groundwater management which uses a numerical simulation, it is important to understand the full breadth of groundwater basin and groundwater storage for evaluation the extent of human impact. However, previous study has not been clarified the full breadth of them throughout Japan, because basic information on the groundwater has not maintained still enough. The present work developed the three dimensional hydrogeological model in Japanese islands using the related database. And the groundwater storage was estimated based on the three dimensional hydrogeological model. As a result, to evaluate the full breadth of groundwater basin became possible from the sharply wide-range distribution of stratum. Moreover, we succeeded in providing the useful information such as development potential of unused groundwater resources for groundwater conservation and development.

Koshigai, Masaru; Marui, Atsunao; Ito, Narimitsu; Yoshizawa, Takuya

182

This analysis is designed to use existing modeling and analysis results as the basis for estimated groundwater flow rates into the saturated zone (SZ) site-scale model domains, both as recharge (infiltration) at the upper boundary (water table), and as underflow at the lateral boundaries. Specifically, this work compiles information on the recharge boundary conditions supplied to the base-case and alternate SZ site-scale flow models taken from (1) distributed recharge from the 1997 (D'Agnese et al. 1997 [DIRS 100131]) or 2001 (D'Agnese et al. 2002 [DIRS 158876]) SZ regional-scale (Death Valley Regional Flow System [DVRFS]) model; (2) recharge below the area of the 1997 (Wu et al. 1997 [DIRS 156453]) or 2003 (BSC 2004 [DIRS 169861]) unsaturated zone (UZ) site-scale flow model; and (3) focused recharge along Fortymile Wash. In addition, this analysis includes extraction of the groundwater flow rates simulated by the 1997 and 2001 DVRFS models coincident with the lateral boundaries of the SZ site-scale flow models. The fluxes from the 1997 DVRFS were used to calibrate the base-case SZ site-scale flow model. The 2001 DVRFS fluxes are used in the alternate SZ site-scale flow model.

S. James

2004-10-06

183

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

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.

Gannett, Marshall W.; Lite, Kenneth E., Jr.

2004-01-01

184

Using Visual MODFLOW to Simulate Groundwater Flow and Transport

NSDL National Science Digital Library

Students are trained to use the Visual MODFLOW computer program (Waterloo Hydrogeologic, Inc.) and they learn first-hand how to apply the Dupuit Approximation to groundwater flow and transport problems in unconfined aquifers. The students apply the Dupuit Approximation (Fetter, 2001) to a case study developed from Anderson and Woessner (1992) in which they are given system dimensions, aquifer properties, and well water levels. Learning objectives include (1) prediction of groundwater flow and transport and (2) model calibration (e.g., getting the model output to match well water level data). Students also learn how to solve the equations using a computer spreadsheet program, further expanding their ability to understand and work with the equations.

Callahan, Tim

185

Free boundary problems in fresh-salt groundwater flow

NASA Astrophysics Data System (ADS)

Contribution density induced (that is, gravity driven, groundwater flow) problems in fluids with a low relative density difference are studied. This allows the assumption that the flow is incompressible. This situation occurs in the case of fresh and salt groundwater flow. It is also assumed that the scale of the problems is such that a description in terms of an abrupt transition between the fluids, an interface or free boundary between the fresh and salt water, is possible. The necessary physical properties of groundwater flow are discussed, Darcy's law is introduced and differential equations for the pressure and stream function are derived to describe the flow of a fluid with a variable density through a porous material. Some mathematical preliminaries are given, in particular the concepts of test functions and distributions are introduced. Also, expressions for the divergence and the curl of a vector field across a discontinuity are derived. The interface models are set up, two cases being treated in detail: a two dimensional fresh salt problem in a horizontal aquifer and an axially symmetric flow problem in which fresh water, on top of the heavier salt water, flows towards a well (the coning problem). For both cases a numerical method is given. A simplification which arises in many practical situations and which is called the Dupuit approximation is considered. In this approximation, it is assumed that the horizontal component of the specific discharge is constant (in the vertical direction) in each fluid and has a jump at the interface. It leads to a description in terms of a nonlinear diffusion equation. The mathematical theory for this equation is summarized, and some extensions, in particular adding convection terms, are discussed.

Vanduijn, C. J.; Dejisselinedejong, G.

186

Fracture flow of groundwater in coal-bearing strata

Fractures are of considerable importance to groundwater flow through lithified coal-bearing strata. Laboratory tests on core samples in many different studies in the northern Appalachians and northern Great Plains show sandstones, siltstones, shales, and claystones with air permeabilities ranging from less than 10â»Â¹Â° to 2.4 x 10â»â¶ m\\/s. Generally, the air permeabilities were less than 10â»â¸ m\\/s Equivalent hydraulic conductivities

Schubert

1980-01-01

187

MODOPTIM is a non-linear ground-water model calibration and management tool that simulates flow with MODFLOW-96 as a subroutine. A weighted sum-of-squares objective function defines optimal solutions for calibration and management problems. Water levels, discharges, water quality, subsidence, and pumping-lift costs are the five direct observation types that can be compared in MODOPTIM. Differences between direct observations of the same type can be compared to fit temporal changes and spatial gradients. Water levels in pumping wells, wellbore storage in the observation wells, and rotational translation of observation wells also can be compared. Negative and positive residuals can be weighted unequally so inequality constraints such as maximum chloride concentrations or minimum water levels can be incorporated in the objective function. Optimization parameters are defined with zones and parameter-weight matrices. Parameter change is estimated iteratively with a quasi-Newton algorithm and is constrained to a user-defined maximum parameter change per iteration. Parameters that are less sensitive than a user-defined threshold are not estimated. MODOPTIM facilitates testing more conceptual models by expediting calibration of each conceptual model. Examples of applying MODOPTIM to aquifer-test analysis, ground-water management, and parameter estimation problems are presented.

Halford, Keith J.

2006-01-01

188

Dolomitization by ground-water flow systems in carbonate platforms

Dolomite occurs throughout the subsurface of modern carbonate platforms such as the Bahamas. Groundwater flow systems must be responsible for delivery of reactants needed for dolomitization. Reflux, freshwater lens flows, and thermal convection are large-scale flow systems that may be widespread in active platforms. The author has evaluated some aspects of the dynamics and characteristics of these processes with ground-water flow theory and by scaled sandbox experiments. Reflux is not restricted to hypersaline brines, but can occur with bankwaters of only slightly elevated salinity such as those found on the Bahama Banks today (42%). The lack of evaporites in a stratigraphic section, therefore, does not rule out the possibility that reflux may have operated. Flows associated with freshwater lenses include flow in the lens, in the mixing zone, and in the seawater beneath and offshore of the lens. Upward transfer of seawater through the platform margins occurs when surrounding cold ocean water migrates into the platform and is heated. This type of thermal convection (Kohout convection) has been studied by Francis Kohout in south Florida. The ranges of mass flux of magnesium in these processes are all comparable and are all sufficient to account for young dolomites beneath modern platforms. Each process yields dolomitized zones of characteristic shape and location and perhaps may be distinguishable in ancient rocks. The concepts presented here may have application to exploration for dolomite reservoirs in the Gulf Coast and elsewhere.

Simms, M.

1984-09-01

189

Based on analysis of groundwater hydrochemical and isotopic indicators, this article aims to identify the groundwater flow\\u000a systems in the Yangwu River alluvial fan, in the Xinzhou Basin, China. Groundwater ?2H and ?18O values indicate that the origin of groundwater is mainly from precipitation, with local evaporative influence. d-excess values lower than 10% in most groundwaters suggest a cold climate

Dongmei Han; Xing Liang; Menggui Jin; Matthew J. Currell; Ying Han; Xianfang Song

2009-01-01

190

Long-term groundwater monitoring has been carried in the model locality of the landslide area at T?ebenice, situated in the\\u000a northern part of the Czech Republic in Cretaceous claystones to marlstones. Primarily, long-term fluctuation of the groundwater\\u000a and piezometric levels has been monitored. Monitoring of groundwater flow was carried out in selected wells also by the photometry\\u000a logging method using a

Jan Novotný; Miroslav Kobr

2009-01-01

191

Regional stochastic estimation of the groundwater catchment for distributed hydrological modelling

NASA Astrophysics Data System (ADS)

Rainfall-runoff modeling typically assumes that the groundwater catchment boundary coincide with the topographic one. While this is often a reasonable assumption for large and and mesoscale catchments (> 103 km2), this assumption may lead to large errors of streamflow in small scale catchments (? 102 km2), in particular in certain geological settings. The Ammer catchment (135 km2) in the upper Neckar river basin (Germany) is a prime example where groundwater and topographic catchment boundaries are significantly distinct from each other. The catchment is characterized by a complex sequence of fractured, karstic Triassic rock formations. These strata gently dip into ESE direction governing groundwater flow. Analysis of tracer experiments conducted in the 1970s indicates that the boundary overlap could be less than 80 percent. Further, a modelling study of the upper Neckar river basin using the distributed hydrological model mHM showed Nash-Sutcliff efficiencies (NSE) < 0.4 for simulated runoff in the Ammer sub-basin whereas higher efficiencies (NSE ~ 0.7) were obtained for most of the other 21 sub basins in the region. In this study we present a methodology to simultaneously estimate the regional groundwater catchment boundaries of the Ammer and its surrounding basins. In a first step we derive the best possible fit between mHM simulated and observed runoff for the individual sub-basins in the Ammer region and determine the trade-off between the fits of the individual basins using the muliobjective optimization method AMALGAM. We further present a strategy to estimate the regional groundwater catchment boundaries with the aim to improve runoff predictions in the Ammer catchment while not deteriorating runoff predictions in the surrounding basins. Our strategy involves a modification of the mHM model to account for ground water import/export from neighboring catchments while maintaining full mass balance of the surrounding basins. Groundwater catchment boundaries are then obtained by innovative stochastic optimization techniques based on Simulated Annealing that are constrained by expert knowledge about the hydrological system, e.g. a minimum overlap of groundwater and topographical catchment boundaries. The methods developed herein are useful for both plausibility and hypothesis testing as well as hydrological modelling of small scale catchments where conventional models fail due to the mismatch between groundwater and topographical catchment boundaries.

Wöhling, Th.; Samaniego, L.; Selle, B.; Kumar, R.; Zink, M.

2012-04-01

192

NASA Astrophysics Data System (ADS)

Extensive hydrogeological investigations followed by three-dimensional groundwater flow and contaminant transport modelling were carried out around a proposed uranium tailings pond at Seripalli in Andhra Pradesh, India, to estimate its radiological impact. The hydrogeological parameters and measured groundwater level were used to model the groundwater flow and contaminant transport from the uranium tailings pond using a finite-element-based model. The simulated groundwater level compares reasonably with the observed groundwater level. Subsequently, the transport of long-lived radionuclides such as 238U, 234U, 230Th and 226Ra from the proposed tailings pond was modelled. The ingrowths of progenies were also considered in the modelling. It was observed that these radionuclides move very little from the tailings pond, even at the end of 10,000 y, due to their high distribution coefficients and low groundwater velocities. These concentrations were translated into committed effective dose rates at different distances in the vicinity of the uranium tailings pond. The results indicated that the highest effective dose rate to members of the public along the groundwater flow pathway is 2.5 times lower than the drinking water guideline of 0.1 mSv/y, even after a long time period of 10,000 y.

Elango, L.; Brindha, K.; Kalpana, L.; Sunny, Faby; Nair, R. N.; Murugan, R.

2012-06-01

193

New approximation for free surface flow of groundwater: capillarity correction

NASA Astrophysics Data System (ADS)

An existing capillarity correction for free surface groundwater flow as modelled by the Boussinesq equation is re-investigated. Existing solutions, based on the shallow flow expansion, have considered only the zeroth-order approximation. Here, a second-order capillarity correction to tide-induced watertable fluctuations in a coastal aquifer adjacent to a sloping beach is derived. A new definition of the capillarity correction is proposed for small capillary fringes, and a simplified solution is derived. Comparisons of the two models show that the simplified model can be used in most cases. The significant effects of higher-order capillarity corrections on tidal fluctuations in a sloping beach are also demonstrated.

Jeng, D.-S.; Seymour, B. R.; Barry, D. A.; Li, L.; Parlange, J.-Y.

2005-10-01

194

Estimating contaminant attenuation half-lives in alluvial groundwater systems.

One aspect of describing contamination in an alluvial aquifer is estimating changes in concentrations over time. A variety of statistical methods are available for assessing trends in contaminant concentrations. We present a method that extends trend analysis to include estimating the coefficients for the exponential decay equation and calculating contaminant attenuation half-lives. The conceptual model for this approach assumes that the rate of decline is proportional to the contaminant concentration in an aquifer. Consequently, the amount of time to remove a unit quantity of the contaminant inventory from an aquifer lengthens as the concentration decreases. Support for this conceptual model is demonstrated empirically with log-transformed time series of contaminant data. Equations are provided for calculating system attenuation half-lives for non-radioactive contaminants. For radioactive contaminants, the system attenuation half-life is partitioned into the intrinsic radioactive decay and the concentration reduction caused by aquifer processes. Examples are presented that provide the details of this approach. In addition to gaining an understanding of aquifer characteristics and changes in constituent concentrations, this method can be used to assess compliance with regulatory standards and to estimate the time to compliance when natural attenuation is being considered as a remediation strategy. A special application of this method is also provided that estimates the half-life of the residence time for groundwater in the aquifer by estimating the half life for a conservative contaminant that is no longer being released into the aquifer. Finally, the ratio of the half-life for groundwater residence time to the attenuation half-life for a contaminant is discussed as a system-scale retardation factor which can be used in analytical and numerical modeling. PMID:17344953

Tardiff, Mark F; Katzman, Danny

2007-02-09

195

CFCs (chlorofluorocarbons) concentrations of groundwater in the Kurobe alluvial fan, Japan were measured. Water samples from 15 wells were obtained from 2006 Feb. 21st to 23rd and their CFCs concentrations were analyzed with GC-ECD. Then, the atmospheric concentrations of CFCs were calculated using the groundwater CFCs concentration in order to estimate the groundwater residence time. Using the annual mean air

Y. Maeda; T. Tokunaga; K. Asai

2006-01-01

196

Statistical analysis of hydrographs and water-table fluctuation to estimate groundwater recharge

Using water-table monitoring data from the National Groundwater Monitoring Network in Korea, groundwater hydrographs were classified into five typical groups. Then, to estimate groundwater recharge, a modified water-table fluctuation (WTF) method was developed from the relation between the cumulative WTF and corresponding precipitation records. Applying this method to different types of hydrographs, the spatial variability of recharge in river basins

Sang-Ki Moon; Nam C Woo; Kwang S Lee

2004-01-01

197

. Groundwater mounds and hinge lines are important features related to the interaction of groundwater and lakes. In contrast\\u000a to the transient formation of groundwater mounds, numerical simulations indicate that permanent groundwater mounds form between\\u000a closely spaced lakes as the natural consequence of adding two net sinks to a groundwater flow system. The location of the\\u000a groundwater mound and the

David C. Gosselin; Mohan J. Khisty

2001-01-01

198

Tide-induced fingering flow during submarine groundwater discharge

NASA Astrophysics Data System (ADS)

Submarine groundwater discharge (SGD) is a relevant component of the hydrological cycle (Moore, 2010). The discharge of fresh groundwater that originated from precipitation on the land typically occurs at the near shore scale (~ 10m-100m) and the embayment scale (~ 100m - 10km) (Bratton, 2010). In the recent years a number of studies revealed that tidal forcing has an important effect on the fresh SGD pattern in the beach zone, i.e., it leads to the formation of an upper saline recirculation cell and a lower "freshwater discharge tube" (Boufadel, 2000, Robinson et al., 2007; Kuan et al., 2012). Thereby the discharge of the fresh groundwater occurs near the low-tide mark. The shape and extent of the upper saline recirculation cell is mainly defined by the tidal amplitude, beach slope, fresh groundwater discharge rate and hydraulic conductivity (Robinson et al., 2007). In spite of fact that in this case sea water overlies less denser freshwater, all previous modeling studies suggested that the saline recirculation cell and the freshwater tube are rather stable. However, new numerical investigations indicate that there maybe realistic cases where the upper saline recirculation cell becomes unstable as a result of the density contrast to the underlying freshwater tube. In these cases salt water fingers develop and move downward, thereby penetrating the freshwater tube. To the author's knowledge, the present study is the first that illustrate the possibility of density induced fingering flow during near shore SGD. A total of 240 high resolution simulations with the density dependent groundwater modelling software SEAWAT-2000 (Langevin et al., 2007) has been carried out to identify the conditions under which salt water fingering starts to occur. The simulations are based on the field-scale model setup employed in Robinson et al. (2007). The simulation results indicate that a very flat beach slope of less than 1:35, a hydraulic conductivity of 10 m/d and already a tidal range of 2 m initiates fingering flow. Flatter beach slope, higher hydraulic conductivity and increasing tidal range support this behavior. In the cases of fingering flow, freshwater is squeezed upward and pinches out within the inter-tidal zone. Once pinched out, the discharge point slowly moves along at the beach surface towards the low-tide mark. Overall, the fingering process further complicates the flow pattern and the mixing of salt and freshwater in the inter-tidal zone compared to the cases where the saline recirculation cell remains stable. This may have an important implication for the hydrogeochemical processes in this zone and thus the mass flux of reactive chemicals from the land to the ocean. Boufadel, M. C. (2000). A mechanistic study of nonlinear solute transport in a groundwater-surface water system under steady state and transient hydraulic conditions, Water Resour. Res., 36(9), 2549 2565. Bratton, J.F. (2010). The Three Scales of Submarine Groundwater Flow and Discharge across Passive Continental Margins, The Journal of Geology, 2010, 118, 565-575. Kuan, W. K., G. Jin, P. Xin, C. Robinson, B. Gibbes, and L. Li (2012). Tidal influence on seawater intrusion in unconfined coastal aquifers, Water Resour. Res., 48, W02502, doi:10.1029/2011WR010678. Langevin, C.D., D.T. Thorne, Jr., A.M. Dausman, M.C. Sukop, and G. Weixing (2007). Seawat version 4: a computer program for simulation of multi-species solute and heat transport, Technical Report, U.S. Geological Survey Techniques and Methods Book 6, Chapter A22, 39 pp. Robinson, C., L. Li, and H. Prommer (2007). Tide-induced recirculation across the aquifer-ocean interface, Water Resour. Res., 43, W07428, doi:10.1029/2006WR005679. Moore, W.S. (2010). The Effect of Submarine Groundwater Discharge on the Ocean, Annu. Rev. Mar. Sci., 2, 59-88.

Greskowiak, Janek

2013-04-01

199

In 2005, the U.S. Geological Survey began a pilot study for the National Assessment of Water Availability and Use Program to assess the availability of water and water use in the Great Lakes Basin. Part of the study involves constructing a ground-water flow model for the Lake Michigan part of the Basin. Most ground-water flow occurs in the glacial sediments above the bedrock formations; therefore, adequate representation by the model of the horizontal and vertical hydraulic conductivity of the glacial sediments is important to the accuracy of model simulations. This work processed and analyzed well records to provide the hydrogeologic parameters of horizontal and vertical hydraulic conductivity and ground-water levels for the model layers used to simulated ground-water flow in the glacial sediments. The methods used to convert (1) lithology descriptions into assumed values of horizontal and vertical hydraulic conductivity for entire model layers, (2) aquifer-test data into point values of horizontal hydraulic conductivity, and (3) static water levels into water-level calibration data are presented. A large data set of about 458,000 well driller well logs for monitoring, observation, and water wells was available from three statewide electronic data bases to characterize hydrogeologic parameters. More than 1.8 million records of lithology from the well logs were used to create a lithologic-based representation of horizontal and vertical hydraulic conductivity of the glacial sediments. Specific-capacity data from about 292,000 well logs were converted into horizontal hydraulic conductivity values to determine specific values of horizontal hydraulic conductivity and its aerial variation. About 396,000 well logs contained data on ground-water levels that were assembled into a water-level calibration data set. A lithology-based distribution of hydraulic conductivity was created by use of a computer program to convert well-log lithology descriptions into aquifer or nonaquifer categories and to calculate equivalent horizontal and vertical hydraulic conductivities (K and KZ, respectively) for each of the glacial layers of the model. The K was based on an assumed value of 100 ft/d (feet per day) for aquifer materials and 1 ft/d for nonaquifer materials, whereas the equivalent KZ was based on an assumed value of 10 ft/d for aquifer materials and 0.001 ft/d for nonaquifer materials. These values were assumed for convenience to determine a relative contrast between aquifer and nonaquifer materials. The point values of K and KZ from wells that penetrate at least 50 percent of a model layer were interpolated into a grid of values. The K distribution was based on an inverse distance weighting equation that used an exponent of 2. The KZ distribution used inverse distance weighting with an exponent of 4 to represent the abrupt change in KZ that commonly occurs between aquifer and nonaquifer materials. The values of equivalent hydraulic conductivity for aquifer sediments needed to be adjusted to actual values in the study area for the ground-water flow modeling. The specific-capacity data (discharge, drawdown, and time data) from the well logs were input to a modified version of the Theis equation to calculate specific capacity based horizontal hydraulic conductivity values (KSC). The KSC values were used as a guide for adjusting the assumed value of 100 ft/d for aquifer deposits to actual values used in the model. Water levels from well logs were processed to improve reliability of water levels for comparison to simulated water levels in a model layer during model calibration. Water levels were interpolated by kriging to determine a composite water-level surface. The difference between the kriged surface and individual water levels was used to identify outlier water levels. Examination of the well-log lithology data in map form revealed that the data were not only useful for model input, but also were useful for understanding th

Arihood, Leslie D.

2009-01-01

200

Shallow land burial of low-level radioactive waste has been practiced since 1951 in Melton Valley. Groundwater flow modeling was used to better understand the geohydrology of the valley, and to provide a foundation for future contaminant transport modeling. The three-dimensional, finite difference model simulates the aquifer as a two layer system that represents the regolith and bedrock. Transmissivities, which were adjusted during model calibration, range from 8 to 16 sq ft/day for the regolith, and from 0.2 to 1.5 sq ft/day for bedrock. An anisotropy ratio of 1:3 for strike-normal to strike-parallel transmissivity values, in conjunction with recharge rate = 6% of precipitation that is uniformly distributed over the model area, produces the best match between simulated and observed water levels. Simulated water levels generally compare well to observed or estimated 1978 groundwater conditions. Simulated water levels for the regolith for 39 of 69 comparison points are within +/- 10 ft of average 1978 levels. Simulated vertical flow components are in the observed direction for 9 of 11 comparison points. Preliminary simulations indicate that nearly all groundwater flow is within the regolith and discharges to either the Clinch River or the White Oak Creek-Melton Branch drainage systems. Less than 3% of the flow is between the regolith and bedrock, and < 1% of total groundwater flow discharges to the Clinch River through bedrock. Additional data needed to refine and further calibrate the model, include: (1) quantity and areal distribution of recharge; (2) water levels in the regolith near the model boundaries and beyond the Clinch River; (3) water levels and aquifer characteristics for bedrock; and (4) additional surface water data. (Author 's abstract)

Tucci, Patrick

1986-01-01

201

Nitrate Discharge to Coastal Waters in Response to Variable-Density Groundwater Flow

NASA Astrophysics Data System (ADS)

Flow dynamics and velocities within coastal aquifers can be complicated by the influence of the saltwater wedge. As a proxy for a number of contaminant types, the variable-density SEAWAT code was used to evaluate the groundwater flow and nutrient fluxes from a coastal aquifer to the sea in response to variable density flow caused by the presence of seawater at the coast. A regional scale coupled variable-density groundwater flow and transport model was developed to characterize and enhance the understanding of complex groundwater flow dynamics, contaminant transport processes, and contaminant flux from the coastal aquifers of southern Baldwin County to coastal surface waters and to the Gulf of Mexico. Simulation results indicate that groundwater flow dynamics and contaminant transport are additionally influenced by density variations that can occur from the incursion of saltwater from the Gulf of Mexico. Residual nitrate concentrations in the saturated zone were estimated to range between 30 and 160 mg/L for the contamination source zones. Simulation results indicate that nitrate concentrations as high as 5 mg/L extend to the deeper Gulf Shores Aquifer. Furthermore, the model indicates that nitrate sources at this depth were released approximately 100 years ago. Vertical and horizontal nitrate transport is attenuated as a result of dilution by dispersion. Simulated nitrate transport trends and concentrations closely resemble the observed ones. Vertical gradients and mixing appear to be significant in this system. The SEAWAT model results reveal the importance of the Intracoastal Waterway in acting as a groundwater and contaminant sink for the Beach Sand and Gulf Shores Aquifers. The model predicts that the Beach Sand and Gulf Shores Aquifers will be impacted by severe saltwater intrusion, whereas the deeper 350 and 500-foot Aquifers will experience no saltwater intrusion for the entire 1,000 year simulation period. Consequently, nitrate discharge to the Gulf of Mexico originates from the lower part of the aquifer system through submarine groundwater discharge. Besides its importance at a regional level, this study represents a basis for decision-making processes in water resources management of other similar coastal aquifer systems of the United States and around the world.

Murgulet, D.; Tick, G. R.

2010-12-01

202

Evaluation of groundwater travel time (GWTT) is required as part of the investigation of the suitability of Yucca Mountain as a potential high-level nuclear-waste repository site. The Nuclear Regulatory Commission`s GWTT regulation is considered to be a measure of the intrinsic ability of the site to contain radionuclide releases from the repository. The work reported here is the first step in a program to provide an estimate of GWTT at the Yucca Mountain site in support of the DOE`s Technical Site Suitability and as a component of a license application. Preliminary estimation of the GWTT distribution in the unsaturated zone was accomplished using a numerical model of the physical processes of groundwater flow in the fractured, porous medium of the bedrock. Based on prior investigations of groundwater flow at the site, fractures are thought to provide the fastest paths for groundwater flow; conditions that lead to flow in fractures were investigated and simulated. Uncertainty in the geologic interpretation of Yucca Mountain was incorporated through the use of geostatistical simulations, while variability of hydrogeologic parameters within each unit was accounted for by the random sampling of parameter probability density functions. The composite-porosity formulation of groundwater flow was employed to simulate flow in both the matrix and fracture domains. In this conceptualization, the occurrence of locally saturated conditions within the unsaturated zone is responsible for the initiation of fast-path flow through fractures. The results of the GWTT-94 study show that heterogeneity in the hydraulic properties of the model domain is an important factor in simulating local regions of high groundwater saturation. Capillary-pressure conditions at the surface boundary influence the extent of the local saturation simulated.

Arnold, B.W.; Altman, S.J. [Sandia National Labs., Albuquerque, NM (United States); Robey, T.H. [Spectra Research Institute, Albuquerque, NM (United States)] [and others

1995-08-01

203

Unsaturated flow has been modeled through four cross-sections at Yucca Mountain, Nevada, for the purpose of determining groundwater particle travel times from the potential repository to the water table. This work will be combined with the results of flow modeling in the saturated zone for the purpose of evaluating the suitability of the potential repository under the criteria of 10CFR960. One criterion states, in part, that the groundwater travel time (GWTT) from the repository to the accessible environment must exceed 1,000 years along the fastest path of likely and significant radionuclide travel. Sensitivity analyses have been conducted for one geostatistical realization of one cross-section for the purpose of (1) evaluating the importance of hydrological parameters having some uncertainty and (2) examining conceptual models of flow by altering the numerical implementation of the conceptual model (dual permeability (DK) and the equivalent continuum model (ECM). Results of comparisons of the ECM and DK model are also presented in Ho et al.

Altman, S.J.; Ho, C.K.; Arnold, B.W.; McKenna, S.A.

1995-12-31

204

Based on analysis of groundwater hydrochemical and isotopic indicators, this article aims to identify the groundwater flow systems in the Yangwu River alluvial fan, in the Xinzhou Basin, China. Groundwater delta(2)H and delta(18)O values indicate that the origin of groundwater is mainly from precipitation, with local evaporative influence. d-excess values lower than 10% in most groundwaters suggest a cold climate during recharge in the area. Major ion chemistry, including rCa/rMg and rNa/rCl ratios, show that groundwater salinization is probably dominated by water-rock interaction (e.g., silicate mineral weathering, dissolution of calcite and dolomite and cation exchange) in the Yangwu River alluvial fan, and locally by intensive evapotranspiration in the Hutuo River valley. Cl and Sr concentrations follow an increasing trend in shallow groundwater affected by evaporation, and a decreasing trend in deep groundwater. (87)Sr/(86)Sr ratios reflect the variety of lithologies encountered during throughflow. The groundwater flow systems (GFS) of the Yangwu River alluvial fan include local and intermediate flow systems. Hydrogeochemical modeling results, simulated using PHREEQC, reveal water-rock interaction processes along different flow paths. This modeling method is more effective for characterizing flow paths in the intermediate system than in the local system. Artificial exploitation on groundwater in the alluvial fan enhances mixing between different groundwater flow systems. PMID:19548025

Han, Dongmei; Liang, Xing; Jin, Menggui; Currell, Matthew J; Han, Ying; Song, Xianfang

2009-06-23

205

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

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

2009-01-01

206

NASA Astrophysics Data System (ADS)

A three-dimensional (3D) groundwater flow and radionuclide transport model with a domain of 6400 square kilometers was developed for the Idaho National Laboratory (INL). The model provides a comprehensive evaluation of environmental impacts from operations at the INL on the underlying Snake River Plain Aquifer. The aquifer consists of highly heterogeneous fractured basalt rocks and discontinuous sedimentary interbeds. A multi-objective automated inverse simulation was applied to simultaneously calibrate the model to measured heads, groundwater velocities estimated from isotope studies and derived total water fluxes across model boundaries. A total of 225 wells were used during the calibration of the flow model. A pilot point approach was adopted in the inverse simulations in order to model spatial heterogeneity in the aquifer. This approach resulted in a large inverse problem with more than 350 model parameters to be estimated. A regularization procedure was used to reduce the non-uniqueness of the inverse problem. The transport simulation of tritium transport at the INL over the past 56 years was found to be in agreement with groundwater monitoring data.

Huang, H.; Magnuson, S.; Podgorney, R.; Sondrup, J.; Wood, T.

2007-12-01

207

This paper presents the construction, verification, and application of two groundwater flow and contaminant transport models: A Finite Element Model of Water Flow through Aquifers (FEWA) and A Finite Element Model of Material Transport through Aquifers (FEMA). The construction is based on the finite element approximation of partial differential equations of groundwater flow (FEWA) and of solute movement (FEMA). The

G. T. Yeh; K. V. Wong; P. M. Craig; E. C. Davis

1985-01-01

208

Groundwater flow in an arsenic-contaminated aquifer, Mekong Delta, Cambodia

To advance understanding of hydrological influences on As concentrations within groundwaters of Southeast Asia, the flow system of an As-rich aquifer on the Mekong Delta in Cambodia where flow patterns have not been disturbed by irrigation well pumping was examined. Monitoring of water levels in a network of installed wells, extending over a 50km2 area, indicates that groundwater flow is

Shawn G. Benner; Matthew L. Polizzotto; Benjamin D. Kocar; Somenath Ganguly; Kongkea Phan; Kagna Ouch; Michael Sampson; Scott Fendorf

2008-01-01

209

We study the applicability of Proper Orthogonal Decomposition (POD) techniques to reduce the computational burden associated with Monte Carlo (MC) iterations, which are typically used in the solution of the stochastic groundwater flow problem. We consider a two-dimensional saturated flow scenario, depicting steady-state groundwater flow around a pumping well within an aquifer characterized by deterministic distributions of transmissivity and boundary

D. Pasetto; A. Guadagnini; M. Putti

2010-01-01

210

Ground water is the primary source of water in the Wright-Patterson Air Force Base area. The aquifer consists of glacial sands and gravels that fill a buried bedrock-valley system. Consolidated rocks in the area consist of poorly permeable Ordovician shale of the Richmondian stage, in the upland areas, the Brassfield Limestone of Silurian age. The valleys are filled with glacial sediments of Wisconsinan age consisting of clay-rich tills and coarse-grained outwash deposits. Estimates of hydraulic conductivity of the shales based on results of displacement/recovery tests range from 0.0016 to 12 feet per day; estimates for the glacial sediments range from less than 1 foot per day to more than 1,000 feet per day. Ground water flow from the uplands towards the valleys and the major rivers in the region, the Great Miami and the Mad Rivers. Hydraulic-head data indicate that ground water flows between the bedrock and unconsolidated deposits. Data from a gain/loss study of the Mad River System and hydrographs from nearby wells reveal that the reach of the river next to Wright-Patterson Air Force Base is a ground-water discharge area. A steady-state, three-dimensional ground-water-flow model was developed to simulate ground-water flow in the region. The model contains three layers and encompasses about 100 square miles centered on Wright-Patterson Air Force Base. Ground water enters the modeled area primarily by river leakage and underflow at the model boundary. Ground water exits the modeled area primarily by flow through the valleys at the model boundaries and through production wells. A model sensitivity analysis involving systematic changes in values of hydrologic parameters in the model indicates that the model is most sensitive to decreases in riverbed conductance and vertical conductance between the upper two layers. The analysis also indicates that the contribution of water to the buried-valley aquifer from the bedrock that forms the valley walls is about 2 to 4 percent of the total ground-water flow in the study area. Ground waters in the vicinity of Wright-Patterson Air Force Base can be classified into two compositional groups on the basis of their chemical composition: calcium magnesium bicarbonate-type and sodium chloride-type waters. Calcium magnesium bicarbonate-type waters are found in the glacial deposits and the Brassfield Limestone, whereas the sodium chloride waters are exclusively associated with the shales. Equilibrium speciation calculations indicate that ground water of the glacial drift aquifer is in equilibrium with calcite, dolomite, and chalcedony, but is undersaturated with respect to gypsum and fluorite. Waters from the shales are slightly supersaturated with respect to calcite, dolomite, and siderite but are undersaturated with respect to chalcedony. Simple-mass balance calculations treating boron as a conservative species indicate that little (< 5 percent) or no recharge from the shales to the glacial drift aquifer takes place. Data on the stable isotopes of oxygen and hydrogen indicate a meteoric origin for all ground water beneath Wright-Patterson Air Force Base, but the data were inconclusive with respect to identification of distinct isotopic differences between water collected from the glacial drift and bedrock aquifers. Tritium concentrations used to distinguish waters having a pre-and post-1953 recharge component indicate that most water entered the glacial drift aquifer after 1953. This finding indicates that recharge from shallow to deep parts (greater than 150 feet) of the aquifer takes place over time intervals of a few years or decades. However, the fact that some deep parts of the glacial aquifer did not contain measurable tritium indicates that ground-water flow from recharge zones to these parts of the aquifer takes decades or longer.

Dumouchelle, D. H.; Schalk, C. W.; Rowe, G. L.; de Roche, J. T.

1993-01-01

211

Relation of streams, lakes, and wetlands to groundwater flow systems

NASA Astrophysics Data System (ADS)

Surface-water bodies are integral parts of groundwater flow systems. Groundwater interacts with surface water in nearly all landscapes, ranging from small streams, lakes, and wetlands in headwater areas to major river valleys and seacoasts. Although it generally is assumed that topographically high areas are groundwater recharge areas and topographically low areas are groundwater discharge areas, this is true primarily for regional flow systems. The superposition of local flow systems associated with surface-water bodies on this regional framework results in complex interactions between groundwater and surface water in all landscapes, regardless of regional topographic position. Hydrologic processes associated with the surface-water bodies themselves, such as seasonally high surface-water levels and evaporation and transpiration of groundwater from around the perimeter of surface-water bodies, are a major cause of the complex and seasonally dynamic groundwater flow fields associated with surface water. These processes have been documented at research sites in glacial, dune, coastal, mantled karst, and riverine terrains. Résumé Les eaux de surface sont parties intégrantes des systèmes aquifères. Les eaux souterraines interagissent avec les eaux de surface dans presque tous les types d'environnements, depuis les petits ruisseaux, les lacs et les zones humides jusqu'aux bassins versants des vallées des grands fleuves et aux lignes de côte. Il est en général admis que les zones topographiquement hautes sont des lieux de recharge des aquifères et les zones basses des lieux de décharge, ce qui est le cas des grands systèmes aquifères régionaux. La superposition de systèmes locaux, associés à des eaux de surface, à l'organisation régionale d'écoulements souterrains résulte d'interactions complexes entre les eaux souterraines et les eaux de surface dans tous les environnements, quelle que soit la situation topographique régionale. Les processus hydrologiques associés aux eaux de surface elles-mêmes, tels que des niveaux d'eau de surface saisonnièrement hauts et l'évaporation et la transpiration de l'eau souterraine à la périphérie des eaux de surface, sont les causes essentielles de la dynamique complexe et saisonnière des nappes associées aux eaux de surface. Ces processus ont été mis en évidence sur des sites de recherche dans des formations glaciaires, dunaires, littorales, fluviales et de karst couvert. Resumen Los cuerpos de aguas superficiales son partes integrales de los sistemas de flujo subterráneo. El agua subterránea interactúa con la superficial en prácticamente todo tipo de paisajes, desde pequeños torrentes, lagos y humedales, hasta grandes valles fluviales y costas. Aunque se suele asumir que las áreas topográficamente elevadas son zonas de recarga de aguas subterráneas, mientras las áreas topográficamente más bajas lo son de descarga, esto es cierto básicamente para los sistemas de flujo regional. Al superponer los sistemas de flujo local, asociados a los cuerpos de agua superficial, a las condiciones regionales, resultan interacciones complejas, y esto ocurre independientemente de su posición topográfica. Los procesos hidrológicos asociados con los propios cuerpos de agua superficial, como los niveles superficiales máximos estacionales y la evapotranspiración de agua subterránea en los perímetros de cuerpos superficiales, son una de las principales causas de la complejidad y de las variaciones dinámicas de las interacciones entre aguas subterráneas y superficiales. Estos procesos se han documentado en distintas zonas investigadas, incluyendo depósitos glaciares, dunas, áreas costeras, karsts y terrazas fluviales.

Winter, Thomas C.

212

Groundwater Flow Model of the General Separations Area Using PORFLOW

The E Area PA (McDowell-Boyer et al. 2000) includes a steady-state simulation of groundwater flow in the General Separations Area as a prerequisite for saturated zone contaminant transport analyses. The groundwater flow simulations are based on the FACT code (Hamm and Aleman2000). The FACT-based GSA model was selected during preparation of the original PA to take advantage of an existing model developed for environmental restoration applications at the SRS (Flach and Harris 1997, 1999; Flach 1999). The existing GSA/FACT model was then slightly modified for PA use, as described in the PA document. FACT is a finite-element code utilizing deformed brick elements. Material properties are defined at element centers, and state variables such as hydraulic head are located at element vertices. The PORFLOW code (Analytic and Computational Research, Inc. 2000) was selected for performing saturated zone transport simulations of source zone radionuclides and their progeny. PORFLOW utilizes control volume discretization and the nodal point integration method, with all properties and state variables being defined at the center of an interior grid cell. The groundwater flow calculation includes translating the Darcy velocity field computed by FACT into a form compatible for input to PORFLOW. The FACT velocity field is defined at element vertices, whereas PORFLOW requires flux across cell faces. For the present PA, PORFLOW cell face flux is computed in a two-step process. An initial face flux is computed from FACT as an average of the normal components of Darcy velocity at the four corners. The derived flux field approximately conserves mass, but not rigorously. Thus, the flux field is subsequently perturbed to force rigorous mass conservation on a cell-by-cell basis. The undocumented process used is non-unique and can introduce significant artifacts into the final flux field.

FLACH, GREGORY

2004-07-15

213

Evaluation of ground-water flow by particle tracking, Wright-Patterson Air Force Base, Ohio

The U.S. Geological Survey (USGS) and Wright-Patterson Air Force Base (WPAFB) began a Basewide Monitoring Program (BMP) in 1992. The purpose of the BMP was to establish a long-term ground-water and surface- water sampling network in order to (1) characterize current ground-water and surface-water quality; (2) describe water-quality changes as water enters, flows across, and exits Base boundaries; (3) conduct statistical analyses of water quality; and (4) estimate the effect of WPAFB on regional water quality. As part of the BMP, the USGS conducted ground-water particle-tracking analyses based on a ground-water-flow model produced during a previous USGS study. This report briefly describes the previous USGS study, the inherent assumptions of particle-tracking analyses, and information on the regional ground-water-flow field as inferred from particle pathlines. Pathlines for particles placed at the Base boundary and particles placed within identified Installation Restoration Program sites are described.

Cunningham, W. L.; Sheets, R. A.; Schalk, C. W.

1994-01-01

214

Groundwater Flow with Freeze-Thaw in Dynamic Permafrost Systems: Numerical Simulation

Rapid warming of continuous and discontinuous permafrost regions is changing cold regions hydrology, but the effect of these changes on groundwater hydrology is complex and difficult to observe and quantify. Subsurface freezing and thawing involves complex feedbacks between the coupled subsurface ice and groundwater flow systems. Numerical groundwater simulation allows elucidation of some of these processes. Two approaches are presented.

C. I. Voss; J. M. McKenzie; M. A. Walvoord

2009-01-01

215

The Independence Basin in the semi-arid Guanajuato state of central Mexico is facing serious groundwater resources deficiency due to an increasing demand linked to a rapid population growth and agricultural development. This problem is aggravated by an inadequate evaluation of groundwater resources in the region. Geochemistry and isotopic tracers were used in order to investigate the groundwater flow system and

J. Mahlknecht; J. Gárfias-Solis; R. Aravena; R. Tesch

2006-01-01

216

This study used a two-dimensional steady-state finite-element groundwater flow model to simulate groundwater flow in two Newfoundland blanket peat complexes and to examine flow system sensitivity to changes in water table recharge and aquifer properties. The modelling results were examined within the context of peat-forming processes in the two complexes. Modelled flow compared favourably with observed flow. The sensitivity analyses

D. R. Lapen; J. S. Price; R. Gilbert

2005-01-01

217

NASA Astrophysics Data System (ADS)

A better understanding of multidimensional unsaturated and saturated flow and transport under boundary conditions typical of on-site wastewater disposal systems is required to assess the risk to groundwater contamination. The main objective of this research is to characterize in-situ wastewater flow and transport from at-grade line sources on a shallow groundwater conditions. The research site was conducted at Wetaskiwin Rest Stop, Alberta, Canada, where ultraviolet disinfected wastewater has been disposed off to the ground via pressurized at-grade line sources since 2007. The site was characterized for wastewater plume and temporal groundwater fluctuation by using Electromagnetic induction (EM31) and (EM38); and by grid of 74 water table wells, 14 piezometers and 11 transducers. Groundwater was analyzed for selected tracers (pH, EC and Cl) and some microbiology (e.g. E. coli). From the results wastewater plume was identified; and wastewater plume center of mass and average flow direction were estimated. Along the horizontal plume center of mass, 30 monitoring wells in 10 nests and 31 temperature sensors in 5 nests were installed to get vertical resolution of the wastewater plume and to track contaminant transport over time. Results, implications and plans for future investigations will be presented. The research output will benefit future research on contaminant fate and transport and groundwater risk assessment plans. Key words: On-site wastewater treatment/disposal system, Wastewater plume, Groundwater contamination.

Weldeyohannes, A. O.; Kachanoski, R. G.; Dyck, M. F.

2011-12-01

218

Satellite-based estimates of groundwater depletion in India

Groundwater is a primary source of fresh water in many parts of the world. Some regions are becoming overly dependent on it, consuming groundwater faster than it is naturally replenished and causing water tables to decline unremittingly. Indirect evidence suggests that this is the case in northwest India, but there has been no regional assessment of the rate of groundwater

Matthew Rodell; Isabella Velicogna; James S. Famiglietti

2009-01-01

219

ERIC Educational Resources Information Center

Presents a literature review of groundwater quality covering publications of 1977. This review includes: (1) sources of groundwater contamination; and (2) management of groundwater. A list of 59 references is also presented. (HM)

Braids, Olin C.; Gillies, Nola P.

1978-01-01

220

The U.S. Geological Survey created a Conduit Flow Process (CFP) (Shoemaker and others, 2008) for the Modular Finite-Difference Ground-Water Flow Model, MODFLOW-2005. An application of the CFP on the Biscayne aquifer in southern Florida is described that examines (1) the potential for turbulent groundwater flow, and (2) the effects of turbulent flow on hydraulic heads and parameter sensitivities. Turbulent flow

W. Barclay Shoemaker; Kevin J. Cunningham; Eve L. Kuniansky; Joann Dixon

2008-01-01

221

A hydrogeomechanical numerical model is presented to evaluate three-dimensional groundwater flow and land deformation in unsaturated true anisotropic aquifers due to groundwater pumping. This multidimensional numerical model is developed on the basis of the fully coupled poroelastic governing equations for saturated-unsaturated groundwater flow in deforming true anisotropic geologic media and the Galerkin finite element method. A series of true anisotropic

Jun-Mo Kim

2005-01-01

222

Estimated International Energy Flows 2007

NSDL National Science Digital Library

This Energy Flow Charts website is a set of energy Sankey diagrams or flow charts for 136 countries constructed from data maintained by the International Energy Agency (IEA) and reflects the energy use patterns for 2007.

Smith, Clara; Laboratory, Lawrence L.

223

RELIABILITY ANALYSES FOR GROUNDWATER FLOW IN OPEN PIT MINES - QUANTITY OF FLOW

Seepage considerations are a key element in analyzing the geotechnical stability performance of soil and rock slopes in open pit mines. Two effects need to be considered: the quantity of flow (operational) and the reduction in the soil\\/rock mass shear strength resulting from water pore pressures within the rock and\\/or soil masses. Groundwater flow through soil\\/rock masses is mainly controlled

Esteban Hormazábal; Alfredo Urzúa

224

Stream and Pseudopotential Functions in Visualizing Groundwater Flow and Transport Processes

NASA Astrophysics Data System (ADS)

Scientific visualization is increasingly being applied in many large-scale groundwater modeling efforts as an effective means of presentation and interpretation of model results. An interpolation or statistical approach is applied to develop three-dimensional spatial distributions of geologic, hydraulic, and chemical data from a model or field measurements. The distributions become the basis for evaluating spatial variation of data. The evaluation is accomplished by displaying data in the form of isosurfaces of values of data Or as contours of data on a surface or plane. This approach of analyzing data is known as data visualization. In addition to data visualization, some of the problems encountered in groundwater hydrology require visualization of groundwater flow and transport processes. Display of hydraulic and chemical data for analysis of groundwater flow and transport processes is herein referred to as process visualization. In both data and process visualization, hydraulic and chemical data are displayed as color contours or isolines on surfaces. However, in data visualization the surface on which data are displayed may be oriented in any direction, whereas in process visualization the surfaces need to be tangential or orthogonal to the direction of groundwater flow. In three-dimensional groundwater flow, stream surfaces and pseudopotential surfaces are tangential and orthogonal, respectively, to the direction of groundwater flow. Therefore stream and pseudopotential surfaces provide natural platforms on which to visualize groundwater flow and transport processes. To demonstrate application of stream and pseudopotential surfaces in process visualization, the three-dimensional groundwater flow beneath the Borden Landfill is considered.

Matanga, George B.

1996-04-01

225

A Flexible Python Design for Analytic Modeling of Groundwater Flow

NASA Astrophysics Data System (ADS)

We present a simple and flexible, object-oriented design for the modeling of groundwater flow using analytic elements in Python. The primary feature is that new analytic elements may be added to the code without the need to make any changes in the existing part of the code. The code consists of a Model class and an Element base class. Each new element is derived from the Element base class (or a derived class) and added to the model. Boundary conditions are implemented by each element itself, because they generate their own equations. Significant speed-up may be obtained through the use of FORTRAN extensions of the computationally intensive functions. Another way to increase performance is by grouping elements with same-type boundary conditions, although that requires changes to the existing code when elements with new boundary conditions are implemented. The described design has been applied successfully to three types of flow: steady multi-aquifer flow, transient periodic flow, and steady unsaturated flow. All systems include wells (point-sinks), line-sinks and circular inhomogeneities. Heads and velocities can be computed analytically at any point; path lines may be computed through numerical integration of the velocity field. The multi-aquifer code is the most extensive and includes many other features such as polygonal inhomogeneities and impermeable walls. Additional Python features make it very easy to create models; input scripts can be generated from GIS coverages of elements; high-quality and interactive graphical output is generated with the matplotlib package.

Bakker, M.

2008-12-01

226

NASA Astrophysics Data System (ADS)

We study the applicability of Proper Orthogonal Decomposition (POD) techniques to reduce the computational burden associated with Monte Carlo (MC) iterations, which are typically used in the solution of the stochastic groundwater flow problem. We consider a two-dimensional saturated flow scenario, depicting steady-state groundwater flow around a pumping well within an aquifer characterized by deterministic distributions of transmissivity and boundary conditions and subject to uncertain and spatially distributed areal recharge. The latter is modeled as a stochastic random process which is fully characterized by its mean and variogram. Key moments and the complete probability distribution of state variables, i.e., hydraulic head and flux, are typically computed by means of computationally intensive MC simulations. Our strategy is to substitute a reduced model in place of the full groundwater model in the MC iterations, thus achieving computational savings while keeping the accuracy of the calculated statistics under control. To this aim, a reduced model is developed by employing POD to project the model equations onto the space generated by a small number of (randomly selected) full model MC realizations (snapshots). The reduced model is then used to generate the remaining subset of the ensemble. Our preliminary results show that the eigenvalues generated by principal component analysis of the snapshot set tend to zero as the dimension of the snapshot set increases. This suggests that a sufficiently large number of snapshots can control the accuracy of the reduced model. Our tests show that POD-based MC allows obtaining accurate estimates of the probability distribution and leading moments of hydraulic heads by means of only a few MC full model runs: in our cases only 5% of the MC ensemble size (200 snapshots instead of a 5000 realizations ensemble) allows reliable characterization of the hydraulic head probability distribution. This results in considerable CPU time savings in the presence of moderate to large spatial variability of groundwater recharge.

Pasetto, D.; Guadagnini, A.; Putti, M.

2010-12-01

227

NASA Astrophysics Data System (ADS)

Submarine groundwater discharge was quantified by a variety of methods in Salt Pond, adjacent to Nauset Marsh on Cape Cod, USA. Discharge estimates based on radon and salinity took advantage of the presence of the narrow channel connecting Salt Pond to Nauset Marsh, which allowed constructing whole-pond mass balances as water flowed in and out due to tidal fluctuations. A box model was used to estimate discharge separately to Salt Pond and to the channel by simulating the timing and magnitude of variations in the radon and salinity data in the channel. Discharge to the pond is estimated to be 2200±1100 m3d-1, while discharge to the channel is estimated to be 300±150 m3d-1, for a total discharge of 2500±1250 m3d-1 to the Salt Pond system. This translates to an average groundwater flow velocity of 3±1.5 cm d-1 Seepage meter flow estimates are broadly consistent with this figure, provided discharge is confined to shallow sediments (water depth <1 m). The radon data can be modeled assuming all groundwater fluxes to both the channel and to the pond are fresh, with no need to invoke a saline component. The absence of a saline component in the radon flux may be due to removal of radon from saline groundwater by recent advection of seawater or it may to due to the presence of impermeable sediments in the center of the pond that limit seawater recirculation. This groundwater flux estimated from the radon and salinity data is comparable to a value of 3200-4500 m3d-1 predicted by a recent hydrologic model (Masterson, 2004; Colman and Masterson, 2004). Additional work is needed to determine if the measured rate of discharge is representative of the long-term average, and to determine the rate of groundwater discharge seaward of Salt Pond. Data also suggest a TDN flux from groundwater to Salt Pond of ~2.6 mmol m-2d-1, a figure comparable to fluxes observed in other eutrophic settings.

Crusius, J.; Koopmans, D.; Bratton, J. F.; Charette, M. A.; Kroeger, K. D.; Henderson, P.; Ryckman, L.; Halloran, K.; Colman, J. A.

2005-01-01

228

Submarine groundwater discharge was quantified by a variety of methods in Salt Pond, adjacent to Nauset Marsh on Cape Cod, USA. Discharge estimates based on radon and salinity took advantage of the presence of the narrow channel connecting Salt Pond to Nauset Marsh, which allowed constructing whole-pond mass balances as water flowed in and out due to tidal fluctuations. A box model was used to estimate discharge separately to Salt Pond and to the channel by simulating the timing and magnitude of variations in the radon and salinity data in the channel. Discharge to the pond is estimated to be 2200??1100 m3 d-1, while discharge to the channel is estimated to be 300??150m3 d-1, for a total discharge of 2500??1250 m3 d-1 to the Salt Pond system. This translates to an average groundwater flow velocity of 3??1.5 cm d -1. Seepage meter flow estimates are broadly consistent with this figure, provided discharge is confined to shallow sediments (water depth <1 m). The radon data can be modeled assuming all groundwater fluxes to both the channel and to the pond are fresh, with no need to invoke a saline component. The absence of a saline component in the radon flux may be due to removal of radon from saline groundwater by recent advection of seawater or it may to due to the presence of impermeable sediments in the center of the pond that limit seawater recirculation. This groundwater flux estimated from the radon and salinity data is comparable to a value of 3200-4500 m3 d-1 predicted by a recent hydrologic model (Masterson, 2004; Colman and Masterson, 20041). Additional work is needed to determine if the measured rate of discharge is representative of the long-term average, and to determine the rate of groundwater discharge seaward of Salt Pond. Data also suggest a TDN flux from groundwater to Salt Pond of ???2.6 mmol m-2 d-1, a figure comparable to fluxes observed in other eutrophic settings.

Crusius, J.; Koopmans, D.; Bratton, J. F.; Charette, M. A.; Kroeger, K. D.; Henderson, P.; Ryckman, L.; Halloran, K.; Colman, J. A.

2005-01-01

229

Controls on Groundwater Flow in an Alpine Talus-Moraine Complex

NASA Astrophysics Data System (ADS)

Since alpine watersheds are the headwaters of rivers acting as major sources of water, there is growing concern over water shortages in areas dependent on mountain runoff. Talus and moraine complexes, as well as fractured bedrock, are a dominant hydrologic response unit within the Lake O'Hara Research Basin (LORB) in Yoho National Park, British Columbia. In this alpine environment, previous studies have shown that groundwater plays an important hydrological role. Although little is known about groundwater storage in these media, they are likely a significant groundwater reservoir and an important control on groundwater flow. The goals of this study are to develop a conceptual model of the talus and moraine complex and the fractured bedrock. The approximately 0.3km2 Babylon drainage basin within the LORB was chosen as the study site as it contains a talus and moraine complex that drains into one gaugeable stream. The conceptual model of this basin has been developed using geophysical, hydrological and hydrogeological methods. Three Ground Penetrating Radar (GPR) and Electrical Resistivity Imaging (ERI) surveys were used to characterize the subsurface structure and water distribution within the talus and moraine complex. The bedrock surface is clearly defined in the GPR profiles and its elevation agrees with that in the ERI inversions. Highly resistive talus material is observable in the ERI results, and areas of low resistivity are found within the bedrock. Hydraulic conductivity estimates of the geologic media, calculated using tracer slug injection and baseflow recession analysis methods, fall within the ranges from gravel to fractured rock. Isotopic hydrograph separations indicate that groundwater is a significant contributor to stream discharge. Linear reservoir models show basin response times of up to 16 hours. The geophysical and hydrological evidence points toward two flow systems operating in the Babylon basin, those of flow through the fractured bedrock and flow through the talus and moraine complex. Understanding the hydrologic characteristics of alpine talus and moraine complexes and fractured bedrock is of great importance to increasing our knowledge of alpine hydrology. The results from this study will enable the estimation of hydrologic parameters of these geologic media and provide valuable information for the predictive modelling of mountain streams.

Muir, D. L.; Hayashi, M.; Bentley, L. R.

2009-05-01

230

NASA Astrophysics Data System (ADS)

The potential of hydrothermal boiling in groundwater flow channels for generating harmonic tremor (a relatively monochromatic ground vibration associated with volcanic activity) is examined. We use simple "organ pipe" theory of normal-mode fluid vibration and fundamental energy considerations to develop a first-order analytical model of a hydrothermal-boiling source of harmonic tremor. We use this model to estimate order-of-magnitude groundwater flow channel lengths and boiling heat transfer rates required to produce harmonic tremor with dominant frequencies in the range 0.5-5 Hz and surface wave reduced displacements of up to 100 cm2. Depending on groundwater sound speed, flow channel lengths of the order of 1-1000 m are required to produce fluid vibration eigenfrequencies in the range 0.5-5 Hz. The boiling heat transfer rate required to produce tremor with a given surface wave reduced displacement depends on the tremor frequency and on whether saturated boiling or subcooled boiling is the cause of the tremor. Saturated boiling produces groundwater vibration via steam bubble growth, whereas subcooled boiling produces groundwater vibration via steam bubble collapse. We find that subcooled hydrothermal boiling is from 102 to 104 times more efficient than saturated boiling in converting boiling "thermal" power to seismic power. For example, the boiling heat transfer rates required to produce 1-Hz tremor with reduced displacements of up to 100 cm2 via subcooled boiling are generally less than a few thousand megawatts; for saturated boiling, the required boiling heat transfer rates are several orders of magnitude larger than this. The highest values of heat flow reported in the literature for volcanic crater lakes and terrestrial and ocean floor geothermal areas are of the order of 1000 MW. Taking this value as a first-order estimate of an upper limit on possible boiling heat transfer rates in volcanic hydrothermal systems, our results suggest that saturated hydrothermal boiling is capable of generating only low-amplitude harmonic tremor, with surface wave reduced displacements no higher than a few square centimeters. However, subcooled hydrothermal boiling could potentially generate high-amplitude harmonic tremor, with reduced displacements as large as several hundred square centimeters. As a specific application of our model, we evaluate the potential of hydrothermal boiling for generating harmonic tremor at recently active Mount St. Helens and Nevado Del Ruiz volcanoes. We conclude that subcooled boiling likely could have produced the tremor episodes considered at both volcanoes. Saturated boiling also could explain the Nevado Del Ruiz tremor but probably not the more powerful Mount St. Helens tremor.

Leet, Robert C.

1988-05-01

231

Numerical Groundwater Flow Modeling of the Arsenic Contaminated Gotra Aquifer, West Bengal, India

NASA Astrophysics Data System (ADS)

We present results of a groundwater flow study in a 7 square kilometer region centered on our field site in the village of Gotra, West Bengal, India, where naturally occurring arsenic contaminates shallow groundwater (mostly < 40 m below surface) at levels that exceed World Health Organization limits. Field investigations since 2004 include sediment coring, geochemical surveys of domestic wells and dedicated piezometers, and monitoring of piezometric levels with dataloggers in several wells over a period of three years. The village itself is situated upon the natural levee of a sinuous abandoned channel, which terminates a classical fluvio-deltaic depositional sequence originating from the north east. The formerly prograding meander bend deposited point bar sands that now comprise the 25-30m-thick shallow aquifer, while incising a deeper sand unit as well as a floodplain sequence to the south west. Hand-pumped domestic tubewells are restricted to the point bar sands, whereas the majority of irrigation wells are screened within the deeper aquifer. Both steady-state and transient simulations were used to estimate aquifer recharge and boundary fluxes, as well as to distinguish groundwater flow paths and average residence times under the influence of irrigation and seasonal stresses. The hydrogeology of the deeper aquifer, as well as the thickness and continuity of the low permeable paleosol separating shallow and deep flow systems are major uncertainties that are explored through model sensitivity testing. Recharge to the shallow flow system is estimated at ~170mm/yr, predominantly by monsoon precipitation. Groundwater in the arsenic affected area generally flows downward through the fine-grained channel-fill deposits, then horizontally through the point bar sands perpendicular to the trend of the abandoned channel. This flowpath coincides with observed geochemical gradients from surveys of domestic well quality conducted in previous years, and supports a model of arsenic release from the low permeability unit. Average residence times in the point bar sands and channel-fill deposits are estimated at 50 and 310 years, respectively, and are highly sensitive to variations in recharge, shallow aquifer conductivity, and hydraulic conductivity of seepage layers that line surface water bottoms.

Koenig, C. E.; Desbarats, A. J.; Beckie, R. D.; Pal, T.; Mukherjee, P. K.

2009-12-01

232

Uncertainty Analysis Framework - Hanford Site-Wide Groundwater Flow and Transport Model

Pacific Northwest National Laboratory (PNNL) embarked on a new initiative to strengthen the technical defensibility of the predictions being made with a site-wide groundwater flow and transport model at the U.S. Department of Energy Hanford Site in southeastern Washington State. In FY 2000, the focus of the initiative was on the characterization of major uncertainties in the current conceptual model that would affect model predictions. The long-term goals of the initiative are the development and implementation of an uncertainty estimation methodology in future assessments and analyses using the site-wide model. This report focuses on the development and implementation of an uncertainty analysis framework.

Cole, Charles R.; Bergeron, Marcel P.; Murray, Christopher J.; Thorne, Paul D.; Wurstner, Signe K.; Rogers, Phillip M.

2001-11-09

233

A chlorine-36 study of regional groundwater flow and vertical transport in southern Nevada

Chlorine-36 data for groundwater from the Death Valley regional flow system is interpreted in the context of existing conceptual models for regional groundwater flow in southern Nevada. Chlorine-36 end member compositions are defined for both recharge and chemically evolved groundwater components. The geochemical evolution of 36Cl is strongly controlled by water-rock interaction with Paleozoic carbonate rocks that comprise the regional

Jean E. Moran; Timothy P. Rose

2003-01-01

234

Model Reduction of a Transient Groundwater-Flow Model for Bayesian Inverse Problems

NASA Astrophysics Data System (ADS)

A Bayesian inverse problem requires many repeated model simulations to characterize an unknown parameter's posterior probability distribution. It is computationally infeasible to solve a Bayesian inverse problem of a discretized groundwater flow model with a high dimension parameter and state space. Model reduction has been shown to reduce the dimension of a groundwater model by several orders of magnitude and is well suited for Bayesian inverse problems. A projection-based model reduction approach is proposed to reduce the parameter and state dimensions of a groundwater model. Previous work has done this by using a greedy algorithm for the selection of parameter vectors that make up a basis and their corresponding steady-state solutions for a state basis. The proposed method extends this idea to include transient models by assembling sequentially though the greedy algorithm the parameter and state projection bases. The method begins with the parameter basis being a single vector that is equal to one or an accepted series of values. A set of state vectors that are solutions to the groundwater model using this parameter vector at appropriate times is called the parameter snapshot set. The appropriate times for the parameter snapshot set are determined by maximizing the set's minimum singular value. This optimization is a similar to those used in experimental design for maximizing information. The two bases are made orthonormal by a QR decomposition and applied to the full groundwater model to form a reduced model. The parameter basis is increased with a new parameter vector that maximizes the error between the full model and the reduced model at a set of observation times. The new parameter vector represents where the reduced model is least accurate in representing the original full model. The corresponding parameter snapshot set's appropriate times are found using a greedy algorithm. This sequentially chooses times that have maximum error between the full and reduced models. The new parameter vector is added to the parameter basis and its corresponding parameter snapshot set is added to the state basis. Additional parameter vectors and parameter snapshot sets are added to their corresponding bases until adding a new parameter vector has little impact on the error between the reduced model and the full model. The resulting parameter and state bases are used directly to reduce the parameter and state dimensions of the groundwater flow model. We apply the proposed model reduction technique to a synthetic example that estimates the posterior probability distribution of hydraulic conductivity using a one-dimensional confined groundwater model and the Markov Chain Monte Carlo method. Several cases will be explored that depend on the number of hydraulic conductivity values that represent the synthetic system and their impact on management decisions.

Boyce, S. E.; Yeh, W. W.

2011-12-01

235

Topographically driven groundwater flow and the San Andreas heat flow paradox revisited

Evidence for a weak San Andreas Fault includes (1) borehole heat flow measurements that show no evidence for a frictionally generated heat flow anomaly and (2) the inferred orientation of ??1 nearly perpendicular to the fault trace. Interpretations of the stress orientation data remain controversial, at least in close proximity to the fault, leading some researchers to hypothesize that the San Andreas Fault is, in fact, strong and that its thermal signature may be removed or redistributed by topographically driven groundwater flow in areas of rugged topography, such as typify the San Andreas Fault system. To evaluate this scenario, we use a steady state, two-dimensional model of coupled heat and fluid flow within cross sections oriented perpendicular to the fault and to the primary regional topography. Our results show that existing heat flow data near Parkfield, California, do not readily discriminate between the expected thermal signature of a strong fault and that of a weak fault. In contrast, for a wide range of groundwater flow scenarios in the Mojave Desert, models that include frictional heat generation along a strong fault are inconsistent with existing heat flow data, suggesting that the San Andreas Fault at this location is indeed weak. In both areas, comparison of modeling results and heat flow data suggest that advective redistribution of heat is minimal. The robust results for the Mojave region demonstrate that topographically driven groundwater flow, at least in two dimensions, is inadequate to obscure the frictionally generated heat flow anomaly from a strong fault. However, our results do not preclude the possibility of transient advective heat transport associated with earthquakes.

Saffer, D. M.; Bekins, B. A.; Hickman, S.

2003-01-01

236

Groundwater flow, quality (2007-10), and mixing in the Wind Cave National Park area, South Dakota

A study of groundwater flow, quality, and mixing in relation to Wind Cave National Park in western South Dakota was conducted during 2007-11 by the U.S. Geological Survey in cooperation with the National Park Service because of water-quality concerns and to determine possible sources of groundwater contamination in the Wind Cave National Park area. A large area surrounding Wind Cave National Park was included in this study because to understand groundwater in the park, a general understanding of groundwater in the surrounding southern Black Hills is necessary. Three aquifers are of particular importance for this purpose: the Minnelusa, Madison, and Precambrian aquifers. Multivariate methods applied to hydrochemical data, consisting of principal component analysis (PCA), cluster analysis, and an end-member mixing model, were applied to characterize groundwater flow and mixing. This provided a way to assess characteristics important for groundwater quality, including the differentiation of hydrogeologic domains within the study area, sources of groundwater to these domains, and groundwater mixing within these domains. Groundwater and surface-water samples collected for this study were analyzed for common ions (calcium, magnesium, sodium, bicarbonate, chloride, silica, and sulfate), arsenic, stable isotopes of oxygen and hydrogen, specific conductance, and pH. These 12 variables were used in all multivariate methods. A total of 100 samples were collected from 60 sites from 2007 to 2010 and included stream sinks, cave drip, cave water bodies, springs, and wells. In previous approaches that combined PCA with end-member mixing, extreme-value samples identified by PCA typically were assumed to represent end members. In this study, end members were not assumed to have been sampled but rather were estimated and constrained by prior hydrologic knowledge. Also, the end-member mixing model was quantified in relation to hydrogeologic domains, which focuses model results on major hydrologic processes. Finally, conservative tracers were weighted preferentially in model calibration, which distributed model errors of optimized values, or residuals, more appropriately than would otherwise be the case The latter item also provides an estimate of the relative effect of geochemical evolution along flow paths in comparison to mixing. The end-member mixing model estimated that Wind Cave sites received 38 percent of their groundwater inflow from local surface recharge, 34 percent from the upgradient Precambrian aquifer, 26 percent from surface recharge to the west, and 2 percent from regional flow. Artesian springs primarily received water from end members assumed to represent regional groundwater flow. Groundwater samples were collected and analyzed for chlorofluorocarbons, dissolved gasses (argon, carbon dioxide, methane, nitrogen, and oxygen), and tritium at selected sites and used to estimate groundwater age. Apparent ages, or model ages, for the Madison aquifer in the study area indicate that groundwater closest to surface recharge areas is youngest, with increasing age in a downgradient direction toward deeper parts of the aquifer. Arsenic concentrations in samples collected for this study ranged from 0.28 to 37.1 micrograms per liter (?g/L) with a median value of 6.4 ?g/L, and 32 percent of these exceeded 10 ?g/L. The highest arsenic concentrations in and near the study area are approximately coincident with the outcrop of the Minnelusa Formation and likely originated from arsenic in shale layers in this formation. Sample concentrations of nitrate plus nitrite were less than 2 milligrams per liter for 92 percent of samples collected, which is not a concern for drinking-water quality. Water samples were collected in the park and analyzed for five trace metals (chromium, copper, lithium, vanadium, and zinc), the concentrations of which did not correlate with arsenic. Dye tracing indicated hydraulic connection between three water bodies in Wind Cave.

Long, Andrew J.; Ohms, Marc J.; McKaskey, Jonathan D. R. G.

2012-01-01

237

Simulation of groundwater flow in unconfined aquifer using meshfree point collocation method

For appropriate management of available groundwater, the flow behavior in the porous media has to be analyzed. The complex problem of groundwater flow can be studied by solving the governing equations analytically or by using numerical methods. As the analytical solutions are available only for simple idealized cases, numerical methods such as finite difference method (FDM) and finite element method

Mategaonkar Meenal; T. I. Eldho

2011-01-01

238

The study focused on the assessment of groundwater flow from over exploitation of water table in the northern part of Niger Delta in Nigeria. Due to semi arid climate and water shortage, the effect of abstraction with respect to recharge is not well assessed and the aquifer storativity and groundwater flow pattern is not known. The local litho-stratigraphy of the

S. Roy; D. Ophori

2010-01-01

239

Groundwater Flow Model for the R-Reactor Area Final Report.

National Technical Information Service (NTIS)

A detailed numerical groundwater flow model has been developed for the R- Area of the Savannah River Site in Aiken, South Carolina. The three-dimensional, finite-element groundwater modeling code Flow and Contaminant Transport (FACT) has been used for thi...

M. K. Harris

1997-01-01

240

Application of the Lanczos algorithm to the simulation of groundwater flow in dual-porosity media

Groundwater flow in fractured porous media can be realistically described using a dual-porosity approach. A popular numerical approach for simulation of groundwater flow in dual-porosity media is the use of spatial discretization procedures based upon the finite element techniques. The computational effort for this technique strongly depends on both the number of unknowns and the number of time steps required

K. Zhang; A. D. Woodbury; W. S. Dunbar

2000-01-01

241

Groundwater Flow Model for the R-Reactor Area Final Report

A detailed numerical groundwater flow model has been developed for the R-Area of the Savannah River Site in Aiken, South Carolina. The three-dimensional, finite-element groundwater modeling code Flow and Contaminant Transport (FACT) has been used for this study.

1997-01-01

242

Lanczos method for the solution of groundwater flow in discretely fractured porous media

One of the more advanced approaches for simulating groundwater flow in fractured porous media is the discrete-fracture approach. This approach is limited by the large computational overheads associated with traditional modeling methods. In this work, we apply the Lanczos reduction method to the modeling of groundwater flow in fractured porous media using the discrete-fracture approach. The Lanczos reduction method reduces

Allan Woodbury; Keni Zhang

2001-01-01

243

Groundwater Flow Model for the R-Reactor Area Final Report

A detailed numerical groundwater flow model has been developed for the R-Area of the Savannah River Site in Aiken, South Carolina. The three-dimensional, finite-element groundwater modeling code Flow and Contaminant Transport (FACT) has been used for this study.

Harris, M.K. [Westinghouse Savannah River Company, AIKEN, SC (United States)

1997-11-01

244

National Technical Information Service (NTIS)

This paper presents the construction, verification, and application of two groundwater flow and contaminant transport models: A Finite Element Model of Water Flow through Aquifers (FEWA) and A Finite Element Model of Material Transport through Aquifers (F...

G. T. Yeh K. V. Wong P. M. Craig E. C. Davis

1985-01-01

245

NASA Astrophysics Data System (ADS)

We show how fully distributed space-time measurements with Fiber-Optic Distributed Temperature Sensing (FO-DTS) can be used to investigate groundwater flow and heat transport in fractured media. Heat injection experiments are combined with temperature measurements along fiber-optic cables installed in boreholes. Thermal dilution tests are shown to enable detection of cross-flowing fractures and quantification of the cross flow rate. A cross borehole thermal tracer test is then analyzed to identify fracture zones that are in hydraulic connection between boreholes and to estimate spatially distributed temperature breakthrough in each fracture zone. This provides a significant improvement compared to classical tracer tests, for which concentration data are usually integrated over the whole abstraction borehole. However, despite providing some complementary results, we find that the main contributive fracture for heat transport is different to that for a solute tracer.

Read, T.; Bour, O.; Bense, V.; Le Borgne, T.; Goderniaux, P.; Klepikova, M. V.; Hochreutener, R.; Lavenant, N.; Boschero, V.

2013-05-01

246

Uncertainty Estimation In Groundwater Modelling Using Kalman Filtering

NASA Astrophysics Data System (ADS)

One of the most comprehensive data assimilation schemes is Kalman Filtering. Given a set of measurements, a model prediction of the considered system and their as- sociated uncertainties, the Kalman filter provides the best linear unbiased estimator (BLUE) of the state of the system. This prediction is associated with an updated uncer- tainty estimate. In its original version, however, it can be used only in linear systems, such as saturated zone modelling with constant hydraulic conductivities and specific storage. For more complex problems where non-linearities cannot be neglected, the extended Kalman filter (EKF) has been developed that linearizes the model in the neighbourhood of the system state. The main problem with these optimal schemes is the large computational and memory requirements for systems of high dimension. For example, the propagation of the uncertainty through time requires as many evaluations of the model as the number of variables in the system. Sub-optimal schemes have been developed that reduce significantly the computational requirements. The most successful techniques are based on the reduction of the rank of the covariance matrix. The ensemble Kalman filter (EnKF) relies on Monte Carlo sim- ulations to approximate the covariance matrix. The reduced rank square root Kalman filter (RRSQRT) captures the main features of the covariance matrix using a lower rank approximation. Some more advanced techniques have recently been developed that combine the two approaches to prevent the loss of information The goal of this study is to assess the effect of different uncertainty representations on the performance of data assimilation in groundwater modelling using Kalman filter- ing. The assessment of the uncertainty pattern is probably the most difficult problem of data assimilation since it requires taking into account all the possible causes of er- rors. The study is an attempt to identify the main causes of uncertainty in groundwater saturated zone modelling (for example, on hydraulic conductivities, rainfall estima- tion, piezometric head measurement) and their respective effects on the update of the spatial representation of the piezometric head.

Drecourt, J. P.; Madsen, H.; Rosbjerg, D.

247

The fact that groundwater exploitation has largely increased since 1997 in the Dar-es-Salaam aquifer, calls for a directed attention towards possible problems of aquifer overexploitation that may arise in the near future. Hydraulic parameters are important for developing local and regional water plans as well as developing numerical groundwater flow models to predict the future availability of the water resource.

Ibrahimu Chikira Mjemah; Marc Van Camp; Kristine Walraevens

2009-01-01

248

Concurrent use of multiple observation types: impact on ground-water model parameter estimates

NASA Astrophysics Data System (ADS)

For inverse modeling, simultaneous use of different types of field observation data can improve ground-water model structure, features, and parameter values. However, such simultaneous use is neither always successful nor always desirable. With regard to coupled flow and transport modeling, there can be significant advantages to concurrent use of both hydraulic head (or pressure) and concentration (or temperature) data for model refinement and parameter estimation. Transport always depends on flow, thus, for both constant- and variable-density flow, measurements of concentration can be used to help estimate classical flow-model parameters such as hydraulic conductivity. When flow processes depend on transport processes, such as in variable-density flow, measurements of pressure can provide information to help estimate transport parameters such as dispersivity that are normally assumed to be estimatable only from measurements of concentration. In some cases, however, use of atypical observation types can give unexpected results. For example, in heterogeneous aquifers, drawdown propagates diffusively through all heterogeneities in the fabric, whereas plumes eventually select the most conductive-connected propagation paths, in effect sub-sampling the fabric. Parameter estimation separately using head and concentration observations thus gives two different sets of estimates for a homogeneous effective model of the same system. Because models never completely represent aquifer heterogeneity in a field area, this dilemma must be recognized in order to employ inverse modeling in a meaningful manner when concurrently using head and concentration observations. Indeed, different relative weightings of observation data types in an inverse model can result in disturbingly different estimates of parameters for the same model. There is no "correct" weighting to balance the influence of different observation types on the parameter estimation. Selection of such weights should depend on the practitioner's needs and insights. Further, selection of the error model for observations (e.g. normally- or log-normally-distributed errors) can imply significantly different parameter estimates when using the same observations. The differences implied by these error models can equivalently be achieved via appropriate selection of weights on the observations in this case. Moreover, the most effective observation networks for parameter estimation can be very different for the different error models, suggesting that the error model must be known a priori for network design.

Voss, C. I.; Sanz, E.; Nordqvist, R.

2004-12-01

249

A conduit flow process (CFP) for the Modular Finite Difference Ground-Water Flow model, MODFLOW-2005, has been created by the U.S. Geological Survey. An application of the CFP on a carbonate aquifer in southern Florida is described; this application examines (1) the potential for turbulent groundwater flow and (2) the effects of turbulent flow on hydraulic heads and parameter sensitivities. Turbulent

W. Barclay Shoemaker; Kevin J. Cunningham; Eve L. Kuniansky; Joann Dixon

2008-01-01

250

Regional Groundwater Flow in Quaternary Aquifers in the Kanto Plain, central Japan

NASA Astrophysics Data System (ADS)

The Kanto Plain located in the Pacific side of central Japan is the largest groundwater basin in Japan. Tokyo metropolitan district is situated in this plain, and approximately 30 % of the whole population of Japan lives here. Urbanization and various human activities have affected groundwater environment in each part of the plain; e.g. land subsidence, decline of piezometric head and pollution. It is necessary to make clear the present groundwater environment and the process of environmental changes to maintain and manage groundwater environment. In this study, groundwater samples were taken in Quaternary aquifers (shallower than GL-400m) and analyzed major dissolved ions and delta-18O, D to clarify the present regional groundwater flow system. Also, long term data of piezometric head in various aquifers observed by the local administrations were collected. From the three dimensional distribution of groundwater quality and delta-18O, D, groundwater with relatively high Cl- concentration (up to about 200mg/l) and low isotopic ratios was found in the aquifer that was situated between 200m and 400m depth of the central part. This groundwater area was distributed in the direction of northwest-southeast, and boundary of it was clear. Considering the hydrogeological setting and isotopic ratios of precipitation, the groundwater was considered to have been supplied to this area by regional groundwater flow. On the other hand, the southwestern boundary was well corresponded to the location of Ayasegawa fault system that deformed Quaternary sediments approximately 100m at the depth GL-200m. In addition, piezometric head in each aquifer differed bordering on the fault. These differences strongly suggested the fault system divides the regional groundwater flow system, that is, the fault system acts as barrier to groundwater flow from southwestern part to central part of the plain. Also, this barrier was fully functioning in the period when the groundwater was pumped in large quantities.

Hayashi, T.; Miyakoshi, A.; Yasuhara, M.; Sakura, Y.

2006-12-01

251

National Technical Information Service (NTIS)

A calibrated groundwater flow model for a contaminated site can provide substantial information for assessing and improving hydraulic measures implemented for remediation. A three-dimensional transient groundwater flow model was developed for a contaminat...

Q. Zhou J. T. Birkholzer I. Javandel P. D. Jordan

2005-01-01

252

NASA Astrophysics Data System (ADS)

The theory of regional groundwater flow is critical for understanding many geologic processes. It is known that heterogeneity and anisotropy in hydraulic conductivity caused by varying lithology and faults affect the pattern of nested flow systems in complex basin. In addition, depth-decaying hydraulic conductivity, a widely observed phenomenon in the earth’s crust, cannot be neglected in studies related to regional groundwater flow. As hydraulic conductivity decays with depth, the regional flow system becomes weaker and the local flow systems penetrate deeper. Moreover, the co-existence of depth-decaying trend and anisotropy of hydraulic conductivity can lead to more complex patterns of nested flow system. Closely related to groundwater flow is groundwater age, the amount of time groundwater has been in subsurface since recharge The distribution of groundwater age is sensitive to the depth-decaying hydraulic conductivity and porosity. Depth-decaying hydraulic conductivity mostly leads to aging while depth-decaying porosity leads to rejuvenation of groundwater. Acting together, these factors cause aging in deeper parts and rejuvenation near the discharge zones in the unit basin. In the complex basin with nested flow systems, the geometry and size of rejuvenated zones are very sensitive to the decay of hydraulic conductivity and porosity. The theoretical framework is applied to the Ordos basin in northern China to examine the influence of varying lithology, permeability contrast caused by faults, depth-decaying hydraulic conductivity, and anisotropy on regional groundwater flow. Using a 2D west-east cross section of approximately 240 km, the groundwater flow field and distribution of groundwater age are modeled using COMSOL Multiphysics, a finite element program. Model results suggest that local, intermediate and regional flow systems are well developed. Since increasing anisotropic ratio would lead the stagnation points which divides the intermediate flow system, local flow system and regional flow system to move towards the basin surface and increasing decay exponent would lead the stagnation points to move towards the basin bottom, the uncertainties of position of stagnation points due to anisotropic ratio and decay exponent, which would cause a possible area for a specific stagnation point, is discussed. Moreover, the modeled groundwater age is well correlated with isotopic age from Carbon-14 dating in two double-packered wells that enable groundwater sampling from isolated depth intervals between packers. For the borehole around the divide of the regional flow system, the age of groundwater is several hundred years in the shallow part, but reaches approximately 19 million years in the deep part near the stagnant zone below the divide.

Jiang, X.; Wan, L.; Wang, X.; Ge, S.; Cao, G.; Hu, F.

2010-12-01

253

Groundwater Flow and Sand Body Interconnectedness in a Thick, Multiple-Aquifer System

NASA Astrophysics Data System (ADS)

Many so-called sandstone aquifers are actually multiple-aquifer systems consisting of discontinuous sand bodies distributed complexly in a matrix of lower-permeability silts and clays. The arrangement and Interconnectedness of these various lithofacies strongly influence spatial patterns of hydraulic conductivity (K) and, in turn, groundwater flow and mass transport. A promising technique of estimating such patterns of K involves careful analysis of both subsurface geologic and subsurface hydrologic data. In this study the three-dimensional distribution of K was estimated for a numerical flow model of part of the Wilcox aquifer system in Texas, using K data from core samples and pumping tests and more than 100 geophysical logs. The aquifer system, which is up to 320 m thick, consists of multiple, elongate sand bodies and silts and clays deposited in a fluvial environment and is similar to many other systems found in the Gulf Coast and other sedimentary basins. The resulting deterministic-conceptual flow model demonstrates the importance and methods of incorporating geologic information in groundwater models. Flow in the aquifer is shown to be controlled not so much by K of the sands as by their continuity and Interconnectedness. Much of the aquifer system consists of large zones in which the fluvial channel-fill sands are sparse and apparently disconnected, resulting in groundwater flow rates lower by a factor of 101 to 103 than in adjacent, well-interconnected belts of fluvial channel-fill sand belts. Modeling results also raise serious doubts regarding our ability to predict regional scale flow and mass transport in complex aquifers such as the Wilcox, using current technology. Though sand body Interconnectedness is critically important, it is also very difficult to estimate. One or two well-connected sands among a system of otherwise disconnected sands can completely alter a velocity field. This is particularly true if the sands are connected vertically and nonzero vertical hydraulic gradients exist. Because the model is three-dimensional, sensitivity of hydraulic head to heterogeneity or Interconnectedness is much less than normally observed in two-dimensional models, and therefore heads computed by the model give little to no indication of the location of well-interconnected zones. Thus such zones can easily go undetected, even in carefully calibrated models which yield reasonably accurate hydraulic heads. This is a significant point for modeling of solute transport.

Fogg, Graham E.

1986-05-01

254

Interactions between surface and groundwater are a key component of the hydrologic budget on the watershed scale. Models that honor these interactions are commonly based on the conductance concept that presumes a distinct interface at the land surface, separating the surface from the subsurface domain. These types of models link the subsurface and surface domains via an exchange flux that

Stefan J. Kollet; Reed M. Maxwell

2006-01-01

255

NASA Astrophysics Data System (ADS)

Vertical circulation flow fields in groundwater could be established by a groundwater circulation well (GCW). Such flow fields are artificially induced by a well with at least two screen sections one for injection and one for extraction. GCWs have been developed as an in-situ technique used for the remediation of volatile contaminants in groundwater. Recently, they have been used also for the injection of nutrients and co-solvents for enhanced groundwater remediation. Furthermore, this technique has used for aquifer characterization in several cases. The hydraulics of such circulation flow fields are determined by strongly non-uniform flow even in homogeneous aquifers. This strongly non-uniform circulation flow introduces additional dispersion effect to a tracer break through apart from the aquifer dispersivity. The analysis of tracer experiments in a circulation flow field induced by a GCW is presented. The tracer was injected at only a certain part of the GCW injection filter defining a certain stream tube. The tracer break through was observed at several sampling points within the circulation flow field and at the extraction filter that has been divided into several segments. From these results the shape of the stream tube could be derived. By calibration of a numerical model using MODFLOW/MT3D the major aquifer and transport parameters could be estimated. The obtained parameter values were compared with the values that were assumed a priori for the experimental set-up.

Mohrlok, U.

2012-04-01

256

The landfill construction has caused many negative impacts on the surrounding environment, particularly groundwater. Evaluation of the function of the leachate collection pipe at the landfill site is indispensable for managing the landfill operation. 3D groundwater flow simulation may be applicable but it requires much capacity of computer and time consumption comparing with 2D groundwater flow simulation due to the

DANG Thuong Huyen; Kenji JINNO; Atsushi TSUTSUMI

2009-01-01

257

A karst aquifer is a carbonate aquifer where groundwater flow dominantly occurs through bedding planes, fractures, conduits, and caves created by and\\/or enlarged by dissolution. Conventional groundwater modeling methods assume that groundwater flow can be described by Darcian principles where primary porosity (i.e. matrix porosity) and laminar flow are dominant in the aquifer. However, in karst aquifers this assumption is

Josue Jacob Gallegos

2011-01-01

258

A three-dimensional numerical model for groundwater flow and heat transport is used to analyze an aquifer thermal energy storage system operating under a continuous flow regime. This study emphasizes the influence of regional groundwater flow on the performance of the system under various operation scenarios. The pressure gradient across the system, which determines the direction and velocity of regional groundwater

K. S. Lee

2011-01-01

259

Model Refinement and Simulation of Groundwater Flow in Clinton, Eaton, and Ingham Counties, Michigan

A groundwater-flow model that was constructed in 1996 of the Saginaw aquifer was refined to better represent the regional hydrologic system in the Tri-County region, which consists of Clinton, Eaton, and Ingham Counties, Michigan. With increasing demand for groundwater, the need to manage withdrawals from the Saginaw aquifer has become more important, and the 1996 model could not adequately address issues of water quality and quantity. An updated model was needed to better address potential effects of drought, locally high water demands, reduction of recharge by impervious surfaces, and issues affecting water quality, such as contaminant sources, on water resources and the selection of pumping rates and locations. The refinement of the groundwater-flow model allows simulations to address these issues of water quantity and quality and provides communities with a tool that will enable them to better plan for expansion and protection of their groundwater-supply systems. Model refinement included representation of the system under steady-state and transient conditions, adjustments to the estimated regional groundwater-recharge rates to account for both temporal and spatial differences, adjustments to the representation and hydraulic characteristics of the glacial deposits and Saginaw Formation, and updates to groundwater-withdrawal rates to reflect changes from the early 1900s to 2005. Simulations included steady-state conditions (in which stresses remained constant and changes in storage were not included) and transient conditions (in which stresses changed in annual and monthly time scales and changes in storage within the system were included). These simulations included investigation of the potential effects of reduced recharge due to impervious areas or to low-rainfall/drought conditions, delineation of contributing areas with recent pumping rates, and optimization of pumping subject to various quantity and quality constraints. Simulation results indicate potential declines in water levels in both the upper glacial aquifer and the upper sandstone bedrock aquifer under steady-state and transient conditions when recharge was reduced by 20 and 50 percent in urban areas. Transient simulations were done to investigate reduced recharge due to low rainfall and increased pumping to meet anticipated future demand with 24 months (2 years) of modified recharge or modified recharge and pumping rates. During these two simulation years, monthly recharge rates were reduced by about 30 percent, and monthly withdrawal rates for Lansing area production wells were increased by 15 percent. The reduction in the amount of water available to recharge the groundwater system affects the upper model layers representing the glacial aquifers more than the deeper bedrock layers. However, with a reduction in recharge and an increase in withdrawals from the bedrock aquifer, water levels in the bedrock layers are affected more than those in the glacial layers. Differences in water levels between simulations with reduced recharge and reduced recharge with increased pumping are greatest in the Lansing area and least away from pumping centers, as expected. Additionally, the increases in pumping rates had minimal effect on most simulated streamflows. Additional simulations included updating the estimated 10-year wellhead-contributing areas for selected Lansing-area wells under 2006-7 pumping conditions. Optimization of groundwater withdrawals with a water-resource management model was done to determine withdrawal rates while minimizing operational costs and to determine withdrawal locations to achieve additional capacity while meeting specified head constraints. In these optimization scenarios, the desired groundwater withdrawals are achieved by simulating managed wells (where pumping rates can be optimized) and unmanaged wells (where pumping rates are not optimized) and by using various combinations of existing and proposed well locations.

Luukkonen, Carol L.

2010-01-01

260

Modeling Steady-State Groundwater Flow Using Microcomputer Spreadsheets.

ERIC Educational Resources Information Center

Describes how microcomputer spreadsheets are easily adapted for use in groundwater modeling. Presents spreadsheet set-ups and the results of five groundwater models. Suggests that this approach can provide a basis for demonstrations, laboratory exercises, and student projects. (ML)

Ousey, John Russell, Jr.

1986-01-01

261

NASA Astrophysics Data System (ADS)

Submarine groundwater discharge (SGWD) is an important discharge process occurring in the vicinity of the saltwater-freshwater boundary in coastal unconfined aquifers. It is now well established that the SGWD has a regional freshwater flow component and a re-circulated saltwater flow component. In an unconfined aquifer, the freshwater and saltwater regions are separated by a distinct interface and freshwater flow occurs above the interface and saltwater flow occurs beneath the interface. Under natural conditions, the interface is at a dynamic equilibrium established by the movement of fresh and saltwater flows. Currently, there is a considerable controversy in the estimated values of these fresh and saltwater flow rates. For example, in a classic field study, Moore (Nature, v.380, p.612-614, 1996) discovered very high rates (much higher than estimated regional freshwater flux) of SGWD into a coastal aquifer. Younger (Nature, v.382, p.121-122, 1996) argued that only four percent of the SGWD estimated by Moore is from the land (fresh groundwater) and the rest of SGWD is of marine origin. The objective of this work is develop a physical model for a coastal unconfined aquifer and perform careful studies to visualize the freshwater and saltwater flow patterns near a coastal interface. We conducted laboratory studies of the saltwater intrusion phenomenon in two flow tanks filled with a homogeneous porous medium. Our small tank has dimensions of 53 cm x 32 cm x 2.7 cm, and our large tank has dimensions of 110 cm x 65 cm x 5 cm. By completing experiments in two difference scales we hope to address the scaling issues related to this complex flow problem. Our experimental setup allowed us to quantify both freshwater and seawater fluxes; further, the circulation patterns of seawater and the discharge patterns of freshwater were also observed. Tracer studies were conducted to quantify the residence times. In this presentation, we will present the data collected from our experiments and correlate the observed fluxes and circulation patterns with certain dimensional parameters. SGWD can be an important phenomenon that controls the overall nutrient budgets of coastal water. Our study would aid in developing a better understanding of seawater circulation and its relationship to SGWD.

Clement, P.; Goswami, R. R.; Hogan, M. B.

2005-12-01

262

Ash Meadows is one of the major discharge areas within the regional Death Valley ground-water flow system of southern Nevada and adjacent California. Ground water discharging at Ash Meadows is replenished from inflow derived from an extensive recharge area that includes the eastern part of the Nevada Test Site (NTS). Currently, contaminants introduced into the subsurface by past nuclear testing at NTS are the subject of study by the U.S. Department of Energy's Environmental Restoration Program. The transport of any contaminant in contact with ground water is controlled in part by the rate and direction of ground-water flow, which itself depends on the location and quantity of ground water discharging from the flow system. To best evaluate any potential risk associated with these test-generated contaminants, studies were undertaken to accurately quantify discharge from areas downgradient from the NTS. This report presents results of a study to refine the estimate of ground-water discharge at Ash Meadows. The study estimates ground-water discharge from the Ash Meadows area through a rigorous quantification of evapotranspiration (ET). To accomplish this objective, the study identifies areas of ongoing ground-water ET, delineates unique areas of ET defined on the basis of similarities in vegetation and soil-moisture conditions, and computes ET rates for each of the delineated areas. A classification technique using spectral-reflectance characteristics determined from satellite images recorded in 1992 identified seven unique units representing areas of ground-water ET. The total area classified encompasses about 10,350 acres dominated primarily by lush desert vegetation. Each unique area, referred to as an ET unit, generally consists of one or more assemblages of local phreatophytes. The ET units identified range from sparse grasslands to open water. Annual ET rates are computed by energy-budget methods from micrometeorological measurements made at 10 sites within six of the seven identified ET units. Micrometeorological data were collected for a minimum of 1 year at each site during 1994 through 1997. Evapotranspiration ranged from 0.6 foot per year in a sparse, dry saltgrass environment to 8.6 feet per year over open water. Ancillary data, including water levels, were collected during this same period to gain additional insight into the evapotranspiration process. Water levels measured in shallow wells showed annual declines of more than 10 feet and daily declines as high as 0.3 foot attributed to water losses associated with evapotranspiration. Mean annual ET from the Ash Meadows area is estimated at 21,000 acre-feet. An estimate of ground-water discharge, based on this ET estimate, is presented as a range to account for uncertainties in the contribution of local precipitation. The estimates given for mean annual ground-water discharge range from 18,000 to 21,000 acre-feet. The low estimate assumes a large contribution from local precipitation in computed ET rates; whereas, the high estimate assumes no contribution from local precipitation. The range presented is only slightly higher than previous estimates of ground-water discharge from the Ash Meadows area based primarily on springflow measurements.

Laczniak, R. J.; DeMeo, G. A.; Reiner, S. R.; Smith, J. L.; Nylund, W. E.

1999-01-01

263

The use of temperature profiles beneath streams to determine rates of vertical ground-water flow and effective vertical hydraulic conductivity of sediments was evaluated at three field sites by use of a model that numerically solves the partial differential equation governing simultaneous vertical flow of fluid and heat in the Earth. The field sites are located in Hardwick and New Braintree, Mass., and in Dover, N.J. In New England, stream temperature varies from about 0 to 25 ?C (degrees Celsius) during the year. This stream-temperature fluctuation causes ground-water temperatures beneath streams to fluctuate by more than 0.1 ?C during a year to a depth of about 35 ft (feet) in fine-grained sediments and to a depth of about 50 ft in coarse-grained sediments, if ground-water velocity is 0 ft/d (foot per day). Upward flow decreases the depth affected by stream-temperature fluctuation, and downward flow increases the depth. At the site in Hardwick, Mass., ground-water flow was upward at a rate of less than 0.01 ft/d. The maximum effective vertical hydraulic conductivity of the sediments underlying this site is 0.1 ft/d. Ground-water velocities determined at three locations at the site in New Braintree, Mass., where ground water discharges naturally from the underlying aquifer to the Ware River, ranged from 0.10 to 0.20 ft/d upward. The effective vertical hydraulic conductivity of the sediments underlying this site ranged from 2.4 to 17.1 ft/d. Ground-water velocities determined at three locations at the Dover, N.J., site, where infiltration from the Rockaway River into the underlying sediments occurs because of pumping, were 1.5 ft/d downward. The effective vertical hydraulic conductivity of the sediments underlying this site ranged from 2.2 to 2.5 ft/d. Independent estimates of velocity at two of the three sites are in general agreement with the velocities determined using temperature profiles. The estimates of velocities and conductivities derived from the temperature measurements generally fall within the ranges of expected rates of flow in, and conductivities of, the sediments encountered at the test sites. Application of the method at the three test sites demonstrates the feasibility of using the method to determine the rate of ground-water flow between a stream and underlying sediments and the effective vertical hydraulic conductivity of the sediments.

Lapham, Wayne W.

1989-01-01

264

A new approach to calibrate steady groundwater flow models with time series of head observations

NASA Astrophysics Data System (ADS)

We developed a new method to calibrate aquifer parameters of steady-state well field models using measured time series of head fluctuations. Our method is an alternative to standard pumping tests and is based on time series analysis using parametric impulse response functions. First, the pumping influence is isolated from the overall groundwater fluctuation observed at monitoring wells around the well field, and response functions are determined for each individual well. Time series parameters are optimized using a quasi-Newton algorithm. For one monitoring well, time series model parameters are also optimized by means of SCEM-UA, a Markov Chain Monte Carlo algorithm, as a control on the validity of the parameters obtained by the faster quasi-Newton method. Subsequently, the drawdown corresponding to an average yearly pumping rate is calculated from the response functions determined by time series analysis. The drawdown values estimated with acceptable confidence intervals are used as calibration targets of a steady groundwater flow model. A case study is presented of the drinking water supply well field of Waalwijk (Netherlands). In this case study, a uniform aquifer transmissivity is optimized together with the conductance of ditches in the vicinity of the well field. Groundwater recharge or boundary heads do not have to be entered, which eliminates two import sources of uncertainty. The method constitutes a cost-efficient alternative to pumping tests and allows the determination of pumping influences without changes in well field operation.

Obergfell, C.; Bakker, M.; Maas, C.

2012-04-01

265

Groundwater is a vital water resource in the arid to semi-arid southwestern United States. Accurate accounting of inflows to and outflows from the groundwater system is necessary to effectively manage this shared resource, including the important outflow component of groundwater discharge by vegetation. A simple method for estimating basin-scale groundwater discharge by vegetation is presented that uses remote sensing data from satellites, geographic information systems (GIS) land cover and stream location information, and a regression equation developed within the Southern Arizona study area relating the Enhanced Vegetation Index from the MODIS sensors on the Terra satellite to measured evapotranspiration. Results computed for 16-day composited satellite passes over the study area during the 2000 through 2007 time period demonstrate a sinusoidal pattern of annual groundwater discharge by vegetation with median values ranging from around 0.3 mm per day in the cooler winter months to around 1.5 mm per day during summer. Maximum estimated annual volume of groundwater discharge by vegetation was between 1.4 and 1.9 billion m3 per year with an annual average of 1.6 billion m3. A simplified accounting of the contribution of precipitation to vegetation greenness was developed whereby monthly precipitation data were subtracted from computed vegetation discharge values, resulting in estimates of minimum groundwater discharge by vegetation. Basin-scale estimates of minimum and maximum groundwater discharge by vegetation produced by this simple method are useful bounding values for groundwater budgets and groundwater flow models, and the method may be applicable to other areas with similar vegetation types.

Tillman, F. D.; Callegary, J. B.; Nagler, P. L.; Glenn, E. P.

2012-01-01

266

Various equations have been derived and applied in the study of groundwater base flows. Many studies have confirmed the applicability of a linear storage-discharge relationship in describing groundwater outflows into stream channels from adjoining aquifers. This result has been used in studies of base flow to estimate various catchment-scale, effective hydraulic parameters such as saturated hydraulic conductivity, drainable porosity, and

R. Anderson; V. Koren; M. Smith; D. Seo

2003-01-01

267

A novel approach for direct estimation of fresh groundwater discharge to an estuary

NASA Astrophysics Data System (ADS)

Coastal groundwater discharge is an important source of freshwater and nutrients to coastal and estuarine systems. Directly quantifying the spatially integrated discharge of fresh groundwater over a coastline is difficult due to spatial variability and limited observational methods. In this study, I applied a novel approach to estimate net freshwater discharge from a groundwater-fed tidal creek over a spring-neap cycle, with high temporal resolution. Acoustic velocity instruments measured tidal water fluxes while other sensors measured vertical and lateral salinity to estimate cross-sectionally averaged salinity. These measurements were used in a time-dependent version of Knudsen's salt balance calculation to estimate the fresh groundwater contribution to the tidal creek. The time-series of fresh groundwater discharge shows the dependence of fresh groundwater discharge on tidal pumping, and the large difference between monthly mean discharge and instantaneous discharge over shorter timescales. The approach developed here can be implemented over timescales from days to years, in any size estuary with dominant groundwater inputs and well-defined cross-sections. The approach also directly links delivery of groundwater from the watershed with fluxes to the coastal environment.

Ganju, Neil K.

2011-06-01

268

Both topography and buoyancy can drive groundwater flow; however, the interactions between them are still poorly understood.\\u000a In this paper, the authors conduct numerical simulations of variable-density fluid flow and heat transport to quantify their\\u000a relative importance. The finite element modeling experiments on a 2-D conceptual model reveal that the pattern of groundwater\\u000a flow depends largely upon the relative magnitude

JianWen Yang; ZuoHai Feng; XianRong Luo; YuanRong Chen

2010-01-01

269

A conceptual model of a Coastal Wetlands system (Lake Warden wetlands system, Western Australia) has been developed using hydraulic, chemical and stable isotopic data and this has been used as the basis to develop a groundwater flow model using the finite element numerical code (FEFLOW). The model was utilised to identify the role of groundwater within the system and assist

S. Marimuthu; D. A. Reynold

2005-01-01

270

The integration of the Geographic Information System (GIS) with groundwater modeling and satellite remote sensing capabilities\\u000a has provided an efficient way of analyzing and monitoring groundwater behavior and its associated land conditions. A 3-dimensional\\u000a finite element model (Feflow) has been used for regional groundwater flow modeling of Upper Chaj Doab in Indus Basin, Pakistan.\\u000a The approach of using GIS techniques

Zulfiqar Ahmad; Arshad Ashraf; Alan Fryar; Gulraiz Akhter

2011-01-01

271

Complexity in the validation of ground-water travel time in fractured flow and transport systems

Ground-water travel time is a widely used concept in site assessment for radioactive waste disposal. While ground-water travel time was originally conceived to provide a simple performance measure for evaluating repository sites, its definition in many flow and transport environments is ambiguous. The US Department of Energy siting guidelines (10 CFR 960) define ground-water travel time as the time required

P. B Davies; R. L. Hunter; J. F. Pickens

1991-01-01

272

This report documents the application of nonlinear-regression methods to a numerical model of ground-water flow in the Albuquerque Basin, New Mexico. In the Albuquerque Basin, ground water is the primary source for most water uses. Ground-water withdrawal has steadily increased since the 1940's, resulting in large declines in water levels in the Albuquerque area. A ground-water flow model was developed in 1994 and revised and updated in 1995 for the purpose of managing basin ground- water resources. In the work presented here, nonlinear-regression methods were applied to a modified version of the previous flow model. Goals of this work were to use regression methods to calibrate the model with each of six different configurations of the basin subsurface and to assess and compare optimal parameter estimates, model fit, and model error among the resulting calibrations. The Albuquerque Basin is one in a series of north trending structural basins within the Rio Grande Rift, a region of Cenozoic crustal extension. Mountains, uplifts, and fault zones bound the basin, and rock units within the basin include pre-Santa Fe Group deposits, Tertiary Santa Fe Group basin fill, and post-Santa Fe Group volcanics and sediments. The Santa Fe Group is greater than 14,000 feet (ft) thick in the central part of the basin. During deposition of the Santa Fe Group, crustal extension resulted in development of north trending normal faults with vertical displacements of as much as 30,000 ft. Ground-water flow in the Albuquerque Basin occurs primarily in the Santa Fe Group and post-Santa Fe Group deposits. Water flows between the ground-water system and surface-water bodies in the inner valley of the basin, where the Rio Grande, a network of interconnected canals and drains, and Cochiti Reservoir are located. Recharge to the ground-water flow system occurs as infiltration of precipitation along mountain fronts and infiltration of stream water along tributaries to the Rio Grande; subsurface flow from adjacent regions; irrigation and septic field seepage; and leakage through the Rio Grande, canal, and Cochiti Reservoir beds. Ground water is discharged from the basin by withdrawal; evapotranspiration; subsurface flow; and flow to the Rio Grande, canals, and drains. The transient, three-dimensional numerical model of ground-water flow to which nonlinear-regression methods were applied simulates flow in the Albuquerque Basin from 1900 to March 1995. Six different basin subsurface configurations are considered in the model. These configurations are designed to test the effects of (1) varying the simulated basin thickness, (2) including a hypothesized hydrogeologic unit with large hydraulic conductivity in the western part of the basin (the west basin high-K zone), and (3) substantially lowering the simulated hydraulic conductivity of a fault in the western part of the basin (the low-K fault zone). The model with each of the subsurface configurations was calibrated using a nonlinear least- squares regression technique. The calibration data set includes 802 hydraulic-head measurements that provide broad spatial and temporal coverage of basin conditions, and one measurement of net flow from the Rio Grande and drains to the ground-water system in the Albuquerque area. Data are weighted on the basis of estimates of the standard deviations of measurement errors. The 10 to 12 parameters to which the calibration data as a whole are generally most sensitive were estimated by nonlinear regression, whereas the remaining model parameter values were specified. Results of model calibration indicate that the optimal parameter estimates as a whole are most reasonable in calibrations of the model with with configurations 3 (which contains 1,600-ft-thick basin deposits and the west basin high-K zone), 4 (which contains 5,000-ft-thick basin de

Tiedeman, C. R.; Kernodle, J. M.; McAda, D. P.

1998-01-01

273

Because of their low solubility, waste chemicals in the form of nonaqueous phase liquids (NAPLs) that are entrapped in subsurface formations act as long-term sources of groundwater contamination. In the design of remediation schemes that use surfactants, it is necessary to estimate the mass transfer rate coefficients under multi-dimensional flow fields that exit at field sites. In this study, we investigate mass transfer under a two-dimensional flow field to obtain an understanding of the basic mechanisms of surfactant-enhanced dissolution and to quantify the mass transfer rates. Enhanced dissolution experiments in a two-dimensional test cell were conducted to measure rates of mass depletion from entrapped NAPLs to a flowing aqueous phase containing a surfactant. In situ measurement of transient saturation changes using a gamma attenuation system revealed dissolution patterns that are affected by the dimensionality of the groundwater flow field. Numerical modeling of local flow fields that changed with time, due to depletion of NAPL sources, enabled the examination of the basic mechanisms of NAPL dissolution in complex groundwater systems. Through nonlinear regression analysis, mass transfer rates were correlated to porous media properties, NAPL saturation and aqueous phase velocity. Results from the experiments and numerical analyses were used to identify deficiencies in existing methods of analysis that uses assumptions of one-dimensional flow, homogeneity of aquifer properties, local equilibrium and idealized transient mass transfer. PMID:11530927

Saba, T; Illangasekare, T H; Ewing, J

2001-09-01

274

Comparison of a karst groundwater model with and without discrete conduit flow

NASA Astrophysics Data System (ADS)

Karst aquifers exhibit a dual flow system characterized by interacting conduit and matrix domains. This study evaluated the coupled continuum pipe-flow framework for modeling karst groundwater flow in the Madison aquifer of western South Dakota (USA). Coupled conduit and matrix flow was simulated within a regional finite-difference model over a 10-year transient period. An existing equivalent porous medium (EPM) model was modified to include major conduit networks whose locations were constrained by dye-tracing data and environmental tracer analysis. Model calibration data included measured hydraulic heads at observation wells and estimates of discharge at four karst springs. Relative to the EPM model, the match to observation well hydraulic heads was substantially improved with the addition of conduits. The inclusion of conduit flow allowed for a simpler hydraulic conductivity distribution in the matrix continuum. Two of the high-conductivity zones in the EPM model, which were required to indirectly simulate the effects of conduits, were eliminated from the new model. This work demonstrates the utility of the coupled continuum pipe-flow method and illustrates how karst aquifer model parameterization is dependent on the physical processes that are simulated.

Saller, Stephen P.; Ronayne, Michael J.; Long, Andrew J.

2013-09-01

275

Simulating the effect of climate extremes on groundwater flow through a lakebed.

Groundwater exchanges with lakes resulting from cyclical wet and dry climate extremes maintain lake levels in the environment in ways that are not well understood, in part because they remain difficult to simulate. To better understand the atypical groundwater interactions with lakes caused by climatic extremes, an original conceptual approach is introduced using MODFLOW-2005 and a kinematic-wave approximation to variably saturated flow that allows lake size and position in the basin to change while accurately representing the daily lake volume and three-dimensional variably saturated groundwater flow responses in the basin. Daily groundwater interactions are simulated for a calibrated lake basin in Florida over a decade that included historic wet and dry departures from the average rainfall. The divergent climate extremes subjected nearly 70% of the maximum lakebed area and 75% of the maximum shoreline perimeter to both groundwater inflow and lake leakage. About half of the lakebed area subject to flow reversals also went dry. A flow-through pattern present for 73% of the decade caused net leakage from the lake 80% of the time. Runoff from the saturated lake margin offset the groundwater deficit only about half of that time. A centripetal flow pattern present for 6% of the decade was important for maintaining the lake stage and generated 30% of all net groundwater inflow. Pumping effects superimposed on dry climate extremes induced the least frequent but most cautionary flow pattern with leakage from over 90% of the actual lakebed area. PMID:22891702

Virdi, Makhan L; Lee, Terrie M; Swancar, Amy; Niswonger, Richard G

2012-08-14

276

Distributions of stable isotopes of water, radiocarbon, noble gases, and chloride (Cl) in groundwater from the Upper Floridan aquifer in southeastern Georgia suggest that down gradient of the Gulf Trough this aquifer contains waters representative of both regional and local groundwater flow systems. In this area, locally recharged waters tend to remain near the top of the aquifer and do

Jordan F. Clark; Martin Stute; Peter Schlosser; Stefan Drenkard; Georges Bonani

1997-01-01

277

Distributions of stable isotopes of water, radiocarbon, noble gases, and chloride (Cl) in groundwater from the Upper Floridan aquifer in southeastern Georgia suggest that down gradient of the Gulf Trough this aquifer contains waters representative of both regional and local groundwater flow systems. In this area, locally recharged waters tend to remain near the top of the aquifer and do

Jordan F. Clark; Martin Stute; Peter Schlosser; Stefan Drenkard; Georges Bonani

1997-01-01

278

Application of muti-quadric interpolation in numerical simulation of 2D groundwater flow

Multi-quadric (MQ) interpolation is a numerical method to solve partial differential equations (PDEs). The purpose of this paper was to discuss the effectiveness of the method applied in groundwater flow simulation, and the influence of shape parameters, support domain, node spacing, and time steps on results. We used MQ method for the numerical solution of four cases of 2D groundwater

Yu-qiao Long; Li-li Hou; Zhong-ping Yang; Wei Li; Yan-ge Li

2011-01-01

279

Storm-Driven Groundwater Flow and Nutrient Transport in a Barrier Island

Porewaters in coastal sediments are significantly enriched in nutrients compared to adjacent surface waters, but groundwater fluxes, and hence nutrient fluxes, are poorly known. Here observations from a barrier island in the U.S. Southeast suggest significant groundwater flow and nutrient transport during a storm. In August 2008 Tropical Storm Fay passed 200 km to the south of Cabretta Island, GA.

A. M. Wilson; J. Anderson; W. S. Moore; C. Schutte; S. B. Joye

2009-01-01

280

Regional groundwater flow in the Atikokan research area : model development and calibration.

National Technical Information Service (NTIS)

The flow of groundwater in the crystalline rocks at the Atikokan Research Area (ARA) has been simulated on the regional scale in order to understand the groundwater conditions in the area and refine our knowledge of the hydraulic parameters of the rock th...

D. U. Ophori T. Chan

1996-01-01

281

Rapid intrusion of magma into wet rock: groundwater flow due to pore pressure increases

Analytical and numerical solutions are developed to simulate the pressurization, expansion, and flow of groundwater contained within saturated, intact host rocks subject to sudden heating from the planar surface of an igneous intrusion. For most rocks, water diffuses more rapidly than heat, assuring that groundwater is not heated along a constant-volume pressure path and that thermal expansion and pressurization adjacent

Paul T. Delaney

1982-01-01

282

Simulation of Regional Ground-Water Flow in the Upper Deschutes Basin, Oregon.

National Technical Information Service (NTIS)

This report describes the mathematical simulation of regional ground-water flow in the upper Deschutes Basin in central Oregon. The report includes a description of the ground-water hydrology of the upper Deschutes Basin and how the hydrologic system was ...

M. W. Gannett K. E. Lite

2004-01-01

283

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

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, the authors 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

Richard M. Iverson; Mark E. Reid

1992-01-01

284

Gravity-driven groundwater flow and slope failure potential: 1. Elastic Effective-Stress Model

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

Richard M. Iverson; Mark E. Reid

1992-01-01

285

Gravity-Driven Groundwater Flow and Slope Failure Potential 1. Elastic Effective-Stress Model

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

Richard M. Iverson; Mark E. Reid

1992-01-01

286

Quantification of ground-water flow in fractured rock, Oak Ridge, Tennessee

The theory of ground-water flow in fractured rocks has been used to interpret aquifer tests and streamflow data for the Oak Ridge Reservation of US Department of Energy. This interpretation has resulted in a better understanding of the data needed for ground-water models. The hydraulic conductivity values calculated from most aquifer tests are meaningless. Slug tests and early data from

Gerald K. Moore

1997-01-01

287

Using fuzzy set methods to consider parameter imprecision in groundwater flow models

Numerical simulation of groundwater flow under both steady state and transient conditions involves the prediction of hydraulic head in both space and time. In the modeling process, parameter uncertainty is one of the major barriers to reliable prediction of groundwater system response. Stochastic modeling techniques have been used extensively for consideration of uncertainty that stems from few measurement data in

WAYNE WOLDT; CHUNHUA DOU; ISTVAN BOGARDI; MOHAMED DAHAB

1995-01-01

288

How to model groundwater flow on the regional scale in hydrogeologically complex regions?

This contribution deals with the question of whether deterministic, three-dimensional numerical groundwater flow models are the appropriate and only means to meaningfully represent groundwater resources on the river basin scale in the context of Integrated Water Resources Management. The discussion is based on two case studies from the Upper Danube catchment (77 000 km2) and the Neckar catchment (14 000

Roland BARTHEL; Jens WOLF; Vlad ROJANSCHI; Johanna JAGELKE; Marco BORCHERS; Thomas GAISER; Wolfram MAUSER

289

Unsaturated Groundwater Flow Beneath Upper Mortandad Canyon, Los Alamos, New Mexico

Mortandad Canyon is a discharge site for treated industrial effluents containing radionuclides and other chemicals at Los Alamos National Laboratory, New Mexico. This study was conducted to develop an understanding of the unsaturated hydrologic behavior below the canyon floor. The main goal of this study was to evaluate the hypothetical performance of the vadose zone above the water table. Numerical simulations of unsaturated groundwater flow at the site were conducted using the Finite Element Heat and Mass Transfer (FEHM) code. A two-dimensional cross-section along the canyon's axis was used to model flow between an alluvial groundwater system and the regional aquifer approximately 300 m below. Using recharge estimated from a water budget developed in 1967, the simulations showed waters from the perched water table reaching the regional aquifer in 13.8 years, much faster than previously thought. Additionally, simulations indicate that saturation is occurring in the Guaje pumice bed an d that the Tshirege Unit 1B is near saturation. Lithologic boundaries between the eight materials play an important role in flow and solute transport within the system. Horizontal flow is shown to occur in three thin zones above capillary barriers; however, vertical flow dominates the system. Other simulations were conducted to examine the effects of changing system parameters such as varying recharge inputs, varying the distribution of recharge, and bypassing fast-path fractured basalt of uncertain extent and properties. System sensitivity was also explored by changing model parameters with respect to size and types of grids and domains, and the presence of dipping stratigraphy.

Dander, D.C.

1998-10-15

290

Autoregressive spectral estimation in transitional pulsatile flow

NASA Astrophysics Data System (ADS)

An autoregressive spectral estimation technique is applied to describe the frequency content of velocity disturbances created by pulsatile flow through a constricted tube. The Reynolds number and frequency parameter are such that transitional phenomena, including vortex formation and coherent disturbances, as well as turbulence, are created during various phases of the pulsatile cycle. Although under some circumstances Fourier methods of spectral estimation suffer from poor frequency resolution and large variance under these unsteady flow conditions, the autoregressive technique is shown to be capable of identifying essential flow disturbance features with good resolution and considerably smaller statistical variation. This method should be particularly useful in analyzing energy spectra of flow disturbance variables under unsteady mean flow conditions or when a limited amount of data is available.

Lieber, B. B.; Giddens, D. P.

1989-12-01

291

Simplified groundwater flow modeling: an application of Kalman filter based identification

The need exists for methods to simplify groundwater contaminant transport models. Reduced-order models are needed in risk assessments for licensing and regulating long-term nuclear waste repositories. Such models will be used in Monte Carlo simulations to generate probabilities of nuclear waste migration in aquifers at candidate repository sites in the United States. In this feasibility study we focused on groundwater flow rather than contaminant transport because the flow problem is more simple. A pump-drawdown test is modeled with a reduced-order set of ordinary differential equations obtained by differencing the partial differential equation. We determined the accuracy of the reduced model by comparing it with the analytic solution for the drawdown test. We established an accuracy requirement of 2% error at the single observation well and found that a model with only 21 states satisfied that criterion. That model was used in an extended Kalman filter with synthesized measurement data from one observation well to identify transmissivity within 1% error and storage coefficient within 10% error. We used several statistical tests to assess the performance of the estimator/identifier and found it to be satisfactory for this application.

Pimentel, K.D.; Candy, J.V.; Azevedo, S.G.; Doerr, T.A.

1980-05-01

292

A Controlled Experiment for Investigating Uncertainty Measures in Groundwater Flow Modeling

NASA Astrophysics Data System (ADS)

Prediction uncertainty and reliability are important to any analysis of risk and decision making, and are often measured using confidence intervals. Confidence intervals are easy to calculate using linear gradient-based (first-order, second moment) methods because they require few additional model runs. However, the resulting linear intervals may not be accurate for groundwater flow problems, which can be highly nonlinear with respect to defined model parameters. Alternative methods considered in this work include nonlinear gradient-based intervals and Markov-Chain Monte Carlo. All methods only technically apply when the model accurately represents the true system, which often is not achieved. Also, if the estimated and unestimated parameters included in the uncertainty analysis do not include aspects or characteristics of the physical system that are important to predicted quantities, the confidence intervals will not reflect the related uncertainties and will tend to be too narrow. This study conducts a controlled experiment in groundwater flow modeling developed based on Hill et al. (1998) to investigate (1) accuracy of the linear measures of prediction uncertainty in the presence and absence of (a) model nonlinearity, (b) model errors, and (c) observation errors; (2) the effect of parameter definition on whether these measures of prediction uncertainty reflect the actual uncertainty.

Lu, D.; Hill, M. C.; Ye, M.

2010-12-01

293

The U.S. Air Force at Arnold Air Force Base (AAFB), in Coffee and Franklin Counties, Tennessee, is investigating ground-water contamination in selected areas of the base. This report documents the results of a comprehensive investigation of the regional hydrogeology of the AAFB area. Three aquifers within the Highland Rim aquifer system, the shallow aquifer, the Manchester aquifer, and the Fort Payne aquifer, have been identified in the study area. Of these, the Manchester aquifer is the primary source of water for domestic use. Drilling and water- quality data indicate that the Chattanooga Shale is an effective confining unit, isolating the Highland Rim aquifer system from the deeper, upper Central Basin aquifer system. A regional ground-water divide, approximately coinciding with the Duck River-Elk River drainage divide, underlies AAFB and runs from southwest to northeast. The general direction of most ground-water flow is to the north- west or to the northwest or to the southeast from the divide towards tributary streams that drain the area. Recharge estimates range from 4 to 11 inches per year. Digital computer modeling was used to simulate and provide a better understanding of the ground-water flow system. The model indicates that most of the ground-water flow occurs in the shallow and Manchester aquifers. The model was most sensitive to increases in hydraulic conductivity and changes in recharge rates. Particle-tracking analysis from selected sites of ground-water contamination indicates a potential for contami- nants to be transported beyond the boundary of AAFB.

Haugh, C. J.; Mahoney, E. N.

1994-01-01

294

Microsphere estimates of blood flow: Methodological considerations

The microsphere technique is a standard method for measuring blood flow in experimental animals. Sporadic reports have appeared outlining the limitations of this method. In this study the authors have systematically assessed the effect of blood withdrawals for reference sampling, microsphere numbers, and anesthesia on blood flow estimates using radioactive microspheres in dogs. Experiments were performed on 18 conscious and 12 anesthetized dogs. Four blood flow estimates were performed over 120 min using 1 {times} 10{sup 6} microspheres each time. The effects of excessive numbers of microspheres pentobarbital sodium anesthesia, and replacement of volume loss for reference samples with dextran 70 were assessed. In both conscious and anesthetized dogs a progressive decrease in gastric mucosal blood flow and cardiac output was observed over 120 min. This was also observed in the pancreas in conscious dogs. The major factor responsible for these changes was the volume loss due to the reference sample withdrawals. Replacement of the withdrawn blood with dextran 70 led to stable blood flows to all organs. The injection of excessive numbers of microspheres did not modify hemodynamics to a greater extent than did the injection of 4 million microspheres. Anesthesia exerted no influence on blood flow other than raising coronary flow. The authors conclude that although blood flow to the gastric mucosa and the pancreas is sensitive to the minor hemodynamic changes associated with the microsphere technique, replacement of volume loss for reference samples ensures stable blood flow to all organs over a 120-min period.

von Ritter, C.; Hinder, R.A.; Womack, W.; Bauerfeind, P.; Fimmel, C.J.; Kvietys, P.R.; Granger, D.N.; Blum, A.L. (Univ. of the Witwatersrand, Johannesburg (South Africa) Louisianna State Univ. Medical Center, Shreveport (USA) Universitaire Vaudois (Switzerland))

1988-02-01

295

Flow Estimation by Indicator Dilution (Bolus Injection)

Indicator dilution techniques used for the estimation of flow (F), mean transit time (t?), dispersion (?), and mean transit time volume (V) in the circulation are subject to error when (1) flow is not steady and (2) concentrations are obtained by sampling at a constant rate (time averaging) rather than at rates proportional to the instantaneous flow past the sampling site (volume averaging). Using a simple descriptive model for indicator transport, the effects of simulated aortic flow or of sinusoidal flow of widely variable frequency were assessed. Errors in estimates of F, t?, ?, and V are greater with bolus injections than with constant-rate injections. Errors are roughly proportional to the amplitude of variation in flow. They are maximal when the period of flow fluctuation is similar to the passage time of dye dilution curve, which, for the human central circulation, is about the time for one respiratory cycle. With sinusoidal flow between 50% and 150% of the mean flow, errors were at worst up to 60% in F, 30% in t?, 50% in ?, and 70% in V, with a bimodal distribution. Errors are minimal at cardiac frequencies. The troublesome lower frequencies can be avoided. Preliminary tests of a method for converting time- to volume-averaged concentrations gave encouraging results

Bassingthwaighte, James B.; Knopp, Thomas J.; Anderson, Dennis U.

2010-01-01

296

Using MODFLOW drains to simulate groundwater flow in a karst environment.

National Technical Information Service (NTIS)

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 ...

J. Quinn D. Tomasko M. A. Glennon S. F. Miller L. D. McGinnis

1998-01-01

297

Evolution of 3-D geologic framework modeling and its application to groundwater flow studies

In this Fact Sheet, the authors discuss the evolution of project 3-D subsurface framework modeling, research in hydrostratigraphy and airborne geophysics, and methodologies used to link geologic and groundwater flow models.

Blome, Charles D.; Smith, David V.

2012-01-01

298

Application of First-Order Reliability to Stochastic Finite Element Analysis of Groundwater Flow,

National Technical Information Service (NTIS)

A method for stochastic analysis of groundwater flow based on the first-order reliability approach is presented. The method can fully utilize any level of probabilistic information from the minimum knowledge of first and second statistical moments to the ...

J. D. Cawlfield N. Sitar

1987-01-01

299

National Technical Information Service (NTIS)

The subject of investigation of the present thesis is the application of the boundary-integral-equation method to the computational modeling of three-dimensional, steady groundwater flow problems. The authors have investigated a particular type of integra...

R. M. van der Weiden

1988-01-01

300

NASA Astrophysics Data System (ADS)

It has been estimated that, at the time of peak outflow channel activity, ~2-3 Gya, Mars possess a planetary inventory of water equivalent to a global ocean 0.5-1 km deep (M. Carr, Icarus. 68, 187, 1986). Because this peak post-dates the period when the most efficient mechanisms of planetary water loss (impact erosion and hydrodynamic escape) are thought to be active (>4 Gya), the bulk of this water is likely to still suvive as in the PLD and in the subsurface, as ground ice and groundwater. How much groundwater survives on Mars today depends on the relative size of the planetary inventory of H2O vs. the pore volume of the cryosphere (that region of the crust where the temperature remains below freezing). If the planetary inventory exceeds what can be stored as ice within the cryosphere, then the excess will exist as a groundwater, saturating the lowermost porous regions of the crust. Previous best estimates of mean global heat flow, crustal thermal conductivity, and freezing-point depression, suggested that the nominal depth of the cryosphere varied from ~2.5 km at the equator to ~6.5 km at the poles, with the natural heteorgenity of the crust expected to give rise to significant (±50%) local variations (Clifford (JGR 98, 10973, 1993). Here we revisit these previousr estimates, examining the potential consequences and implications of our evolving understanding of crustal heat flow, thermal conductivity and the effects of groundwater composition on freezing-point depression -- as deduced from recent Mars' surface, orbital, and Earth-based investigations. We conclude that the present day cryosphere may be up to twice as deep as previously thought, raising questions about the continued survival of subpermafrost groundwater -- as a once large inventory may have been cold-trapped into the thickening cryosphere, as the planet's internal heat flow declined with time. If groundwater does continue to persist on Mars, the locations that are likely to provide the best opportunity for its detection are those that combine low latitude (minimizing the thickness of frozen ground) and low elevation (minimizing the depth to a water table in hydrostatic equilibrium). The results of MARSIS radar soundings obtained over several of these areas will be discussed.

Clifford, S. M.; Heggy, E.; Boisson, J.; McGovern, P.; Max, M. D.; Marsis Team

2009-04-01

301

A numerical modeling case study of groundwater flow in a diffuse pollution prone area is presented. The study area is located within the metropolitan borders of the city of Izmir, Turkey. This groundwater flow model was unconventional in the application since the groundwater recharge parameter in the model was estimated using a lumped, transient water-budget based precipitation-runoff model that was executed independent of the groundwater flow model. The recharge rate obtained from the calibrated precipitation-runoff model was used as input to the groundwater flow model, which was eventually calibrated to measured water table elevations. Overall, the flow model results were consistent with field observations and model statistics were satisfactory. Water budget results of the model revealed that groundwater recharge comprised about 20% of the total water input for the entire study area. Recharge was the second largest component in the budget after leakage from streams into the subsurface. It was concluded that the modeling results can be further used as input for contaminant transport modeling studies in order to evaluate the vulnerability of water resources of the study area to diffuse pollution. PMID:20595769

Elçi, A; Karada?, D; Fistiko?lu, O

2010-01-01

302

NASA Astrophysics Data System (ADS)

Results are presented of a detailed study into the vadose zone and shallow water table hydrodynamics of a field site in Shropshire, UK. A conceptual model is presented and tested using a range of numerical models, including a modified soil moisture balance model (SMBM) for estimating groundwater recharge in the presence of both diffuse and preferential flow components. Tensiometry reveals that the loamy sand topsoil wets up via preferential flow and subsequent redistribution of moisture into the soil matrix. Recharge does not occur until near-positive pressures are achieved at the top of the sandy glaciofluvial outwash material that underlies the topsoil, about 1 m above the water table. Once this occurs, very rapid water table rises follow. This threshold behaviour is attributed to the vertical discontinuity in preferential flow pathways due to seasonal ploughing of the topsoil and to a lower permeability plough/iron pan restricting matrix flow between the topsoil and the lower outwash deposits. Although the wetting process in the topsoil is complex, a SMBM is shown to be effective in predicting the initiation of preferential flow from the base of the topsoil into the lower outwash horizon. The rapidity of the response at the water table and a water table rise during the summer period while flow gradients in the unsaturated profile were upward suggest that preferential flow is also occurring within the outwash deposits below the topsoil. A variation of the source-responsive model proposed by Nimmo (2010) is shown to reproduce the observed water table dynamics well in the lower outwash horizon when linked to a SMBM that quantifies the potential recharge from the topsoil. The results reveal new insights into preferential flow processes in cultivated soils and provide a useful and practical approach to accounting for preferential flow in studies of groundwater recharge estimation.

Cuthbert, M. O.; Mackay, R.; Nimmo, J. R.

2013-03-01

303

Groundwater flow modelling of the regional aquifer of the Pampa del Tamarugal, northern Chile

The Pampa del Tamarugal Aquifer (PTA) is an important source of groundwater in northern Chile. In this study, a groundwater\\u000a flow model of this aquifer is developed and calibrated for the period 1983–2004. The model reproduces the observed flow-field\\u000a and the water balance components reasonably well. Five scenarios are defined to evaluate the response to different pumping\\u000a situations. These scenarios

Rodrigo Rojas; Alain Dassargues

2007-01-01

304

CUDA-based solver for large-scale groundwater flow simulation

This article presents a parallel simulation solver for groundwater flow on CUDA. Preconditioned conjugate gradient (PCG) algorithm\\u000a is used to solve the large linear systems arising from the finite-difference discretization of three-dimensional groundwater\\u000a flow problems. CUDA implementing methods for the two most time-consuming operations in PCG, sparse matrix–vector multiplication\\u000a and vector inner-product, are given. The experimental results show that CUDA

Xiaohui Ji; Tangpei Cheng; Qun Wang

305

Modeling of three-dimensional groundwater flow using the method to calculate fractal dimension

A three-dimensional finite-difference groundwater flow model was developed by the use of fractal theory. The model developed\\u000a in this study can simulate the groundwater flow in fractured aquifers as well as in porous aquifers. The model was designed\\u000a to be able to use other parameters, such as permeability, hydraulic conductivity, porosity and fractal dimension besides hydraulic\\u000a parameters which are used

Bohyun Chon; Yong-Suk Choi

2001-01-01

306

A three-dimensional finite-difference groundwater flow model was implemented to investigate the variety of hydrogeological conditions and to simulate the behavior of the flow system under different stresses in the unconfined aquifer of Bou-Areg. The modelling package MODFLOW, employed in the Groundwater Modelling System (GMS), was applied for this purpose. The plain of Bou-Areg, located on the Mediterranean coast of northeastern

F. El Yaouti; A. El Mandour; D. Khattach; O. Kaufmann

2008-01-01

307

Linear hydrologic features such as rivers are important external stresses in groundwater flow systems that are implemented numerically as head-dependent flux boundaries. In MODFLOW, the USGS modular finite difference saturated groundwater flow model, information for cells designated as these types of boundaries are contained in input files, where the only spatial reference are the grid coordinates (Layer-Row-Column). Linear hydrologic spatial

R. D. Patterson

2001-01-01

308

Starting with regional geographic, geologic, surface and subsurface hydrologic, and geophysical data for the Tono area in Gifu, Japan, we develop an effective continuum model to simulate subsurface flow and transport in a 4 km by 6 km by 3 km thick fractured granite rock mass overlain by sedimentary layers. Individual fractures are not modeled explicitly. Rather, continuum permeability and porosity distributions are assigned stochastically, based on well-test data and fracture density measurements. Lithologic layering and one major fault, the Tsukiyoshi Fault, are assigned deterministically. We conduct three different studies: (1) the so-called base case, in which the model simulates the steady-state groundwater flow through the site, and then stream trace analysis is used to calculate travel times to the model boundary from specified release points; (2) simulations of transient flow during long term pump tests (LTPT) using the base-case model; and (3) thermal studies in which coupled heat flow and fluid flow are modeled, to examine the effects of the geothermal gradient on groundwater flow. The base-case study indicates that the choice of open or closed lateral boundaries has a strong influence on the regional groundwater flow patterns produced by the models, but no field data exist that can be used to determine which boundary conditions are more realistic. The LTPT study cannot be used to distinguish between the alternative boundary conditions, because the pumping rate is too small to produce an analyzable pressure response at the model boundaries. In contrast, the thermal study shows that the temperature distributions produced by the open and closed models differ greatly. Comparison with borehole temperature data may be used to eliminate the closed model from further consideration.

Doughty, Christine; Karasaki, Kenzi

2002-12-11

309

Comparison of groundwater recharge estimation methods for the semi-arid Nyamandhlovu area, Zimbabwe

NASA Astrophysics Data System (ADS)

The Nyamandhlovu aquifer is the main water resource in the semi-arid Umguza district in Matebeleland North Province in Zimbabwe. The rapid increase in water demand in the city of Bulawayo has prompted the need to quantify the available groundwater resources for sustainable utilization. Groundwater recharge estimation methods and results were compared: chloride mass balance method (19-62 mm/year); water-table fluctuation method (2-50 mm/year); Darcian flownet computations (16-28 mm/year); 14C age dating (22-25 mm/year); and groundwater modeling (11-26 mm/year). The flownet computational and modeling methods provided better estimates for aerial recharge than the other methods. Based on groundwater modeling, a final estimate for recharge (from precipitation) on the order of 15-20 mm/year is believed to be realistic, assuming that part of the recharge water transpires from the water table by deep-rooted vegetation. This recharge estimate (2.7-3.6% of the annual precipitation of 555 mm/year) compares well with the results of other researchers. The advantages/disadvantages of each recharge method in terms of ease of application, accuracy, and costs are discussed. The groundwater model was also used to quantify the total recharge of the Nyamandhlovu aquifer system (20 × 106-25 × 106 m3/year). Groundwater abstractions exceeding 17 × 106 m3/year could cause ecological damage, affecting, for instance, the deep-rooted vegetation in the area.

Sibanda, Tenant; Nonner, Johannes C.; Uhlenbrook, Stefan

2009-09-01

310

Using environmental isotopes for groundwater flow analysis in basinal structures

Isotope data on environmental isotopes (radiocarbon, tritium, oxygen 18 and carbon 13) were collected in different geological forma tions in the territory of the Czech Republic. The majority come from basinal structures of the Upper Cretaceous sediments, which are part of the platform cover of the basement of the Bohemian Massif. Radiocarbon groundwater ages which are considered groundwater residence times

JAN SILAR; JAKUB SILAR

1995-01-01

311

Simulation of groundwater flow and environmental effects resulting from pumping

In coastal lowland plains, increased water demand on a limited water resource has resulted in declining groundwater levels, land subsidence and saltwater encroachment. In southwestern Kyushu, Japan, a sinking of the land surface due to over pumping of groundwater has long been recognized as a problem in the Shiroishi lowland plain. In this paper, an integrated model was established for

Nguyen Cao Don; Hiroyuki Araki; Hiroyuki Yamanishi; Kenichi Koga

2005-01-01

312

A finite element formulation is developed for the simulation of groundwater flow and solute transport in multilayer systems of several aquifers and aquitards. This formulation is general, flexibile, and capable of taking full advantage of the nature of flow in such multilayer systems. A fully three-dimensional spatial representation can be performed for certain aquifers or for the entire flow system

Peter S. Huyakorn; B. Geoffrey Jones; Peter F. Andersen

1986-01-01

313

Nitrate Discharge to Coastal Waters in Response to Variable-Density Groundwater Flow

Flow dynamics and velocities within coastal aquifers can be complicated by the influence of the saltwater wedge. As a proxy for a number of contaminant types, the variable-density SEAWAT code was used to evaluate the groundwater flow and nutrient fluxes from a coastal aquifer to the sea in response to variable density flow caused by the presence of seawater at

D. Murgulet; G. R. Tick

2010-01-01

314

Submarine groundwater discharge (SGWD) is an important discharge process occurring in the vicinity of the saltwater-freshwater boundary in coastal unconfined aquifers. It is now well established that the SGWD has a regional freshwater flow component and a re-circulated saltwater flow component. In an unconfined aquifer, the freshwater and saltwater regions are separated by a distinct interface and freshwater flow occurs

P. Clement; R. R. Goswami; M. B. Hogan

2005-01-01

315

Stable isotopes, radiogenic isotopes, and major ion chemistry are used to constrain flow paths in a fracture-controlled regional groundwater flow system in far west Texas. The flow system occurs in Permian and Cretaceous sedimentary rocks and Cenozoic alluvial basin fill. Samples from springs and wells in the study area were analyzed for major ions and hydrogen, oxygen, and strontium isotopes.

Matthew M. Uliana; Jay L. Banner; John M. Sharp

2007-01-01

316

Numerical modeling of deep groundwater flow and heat transport in the Williston Basin

A numerical modeling approach has been used to evaluate quantitatively the effects of fluid flow on contemporary heat flow in an intracratonic basin. The authors have selected the Williston basin for this hydrodynamic study because of the opportunity it presents to assess the relation of deep groundwater flow to basin geothermics and the associated features of diagenesis and petroleum accumulation.

G. Garven; L. Vigrass

1985-01-01

317

NASA Astrophysics Data System (ADS)

Temperature logs and heat-flow data from wells in the northern San Juan basin, Colorado-New Mexico, suggest that coals of the Fruitland Formation are an aquifer with appreciable horizontal ground-water movement. Calculated hydraulic conductivities, based on ground water flow rates estimated from heat-flow data, are several orders of magnitude greater than hydraulic conductivities measured in laboratory or pumping tests. Fractures and other preferential pathways probably create high regional hydraulic conductivity that allows significant heat advection.

McCord, John; Reiter, Marshall; Phillips, Fred

1992-05-01

318

We have developed a program for inverse analysis of two-dimensional linear or radial groundwater flow problems. The program, lr2dinv, 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

Geoffrey C. Bohling; James J. Butler

2001-01-01

319

Quantification of ground-water flow in fractured rock, Oak Ridge, Tennessee

The theory of ground-water flow in fractured rocks has been used to interpret aquifer tests and streamflow data for the Oak Ridge Reservation of US Department of Energy. This interpretation has resulted in a better understanding of the data needed for ground-water models. The hydraulic conductivity values calculated from most aquifer tests are meaningless. Slug tests and early data from pumping tests measure the total transmissivity of all fractures within the area of influence; this value can be used to calculate rates of ground-water flow and transport near the well. Larger transmissivity values are calculated form late aquifer-test data and from an analysis of streamflow hydrographs because most ground-water flow occurs in a thin layer at the water table. This layer supplies most ground-water discharge to streams and apparently is a late-time water source for pumpage from deeper wells. The calibration of distributed flow and transport models will be difficult, if not impossible, because about 90% of the ground-water flow occurs in only 10% of the area, and the locations of these flow paths are unknown. Also, large changes in transmissivity occur with recharge and discharge cycles that change the saturated thickness of the permeable layer near the water table.

Moore, G.K. [Univ. of Tennessee, Knoxville, TN (United States)

1997-05-01

320

Conduit and diffuse type groundwater flow regimes in young volcanic terrain

The Big Butte Springs Watershed Geohydrologic Study (Medford Water Commission and Rogue River National Forest, Medford, OR, 1990) compares the movement of the groundwater supplying these major domestic springs to karstic terrain groundwater flow regimes. The similarity of groundwater velocities and the characteristics of responses to precipitation events in young volcanic groundwater systems warrants the use of conduit-like (and diffuse-like) for volcanic terrain to clearly differentiate from the karstic hydrogeologic terms turbulent solution conduit flow and diffuse darcian flow''. The conduit-like systems in young volcanic terrain includes both the clinkery, rubbly interflow zones and the high hydraulic conductivity (K) basal zones. The basal zones are interpreted to originate as follows: (1) thin lava flows onto rivers/streams yielding through-going continuous groundwater passages by steam explosion and thermal shock, and (2) lava flows cover high K river gravel sequences. The (volcanic) diffuse component originates from fracture systems, minor interflow zones or from streams which were tributary to the pre-lava flow main river system. The presentation will highlight comparisons of data from karstic and volcanic terrain and include descriptions of several world-wide high velocity and high K volcanic groundwater systems.

Hicks, B.G. (Consulting Engineering Geologist, Ashland, OR (United States))

1993-04-01

321

Motion detail preserving optical flow estimation.

A common problem of optical flow estimation in the multiscale variational framework is that fine motion structures cannot always be correctly estimated, especially for regions with significant and abrupt displacement variation. A novel extended coarse-to-fine (EC2F) refinement framework is introduced in this paper to address this issue, which reduces the reliance of flow estimates on their initial values propagated from the coarse level and enables recovering many motion details in each scale. The contribution of this paper also includes adaptation of the objective function to handle outliers and development of a new optimization procedure. The effectiveness of our algorithm is demonstrated by Middlebury optical flow benchmarkmarking and by experiments on challenging examples that involve large-displacement motion. PMID:22156095

Xu, Li; Jia, Jiaya; Matsushita, Yasuyuki

2012-09-01

322

\\u000a Groundwater modelling by numerical methods has been widely used around the world to study and understand the various aquifer\\u000a systems. Modelling techniques has been successfully used to study the groundwater flow patterns and migration of particles\\u000a along with flow in a number of mining sites. The present study was carried out to develop a groundwater model and study the\\u000a groundwater

Lakshmanan Elango

323

NASA Astrophysics Data System (ADS)

A case study of an unconfined aquifer in the Grand Forks valley in south-central BC was used to develop methodology for linking climate models, hydrologic models, and groundwater models to investigate future impacts of climate change on groundwater resources. A three dimensional groundwater flow model of variable spatial resolution (constrained by borehole spacing) was implemented in MODFLOW, and calibrated to observation well data. Multiple scenarios of the hydraulic conductivity fields were used in a sensitivity analysis. A new methodology was developed for generating spatially-distributed and temporally-varying recharge zonation for the surficial aquifer, using GIS linked to the one-dimensional HELP (USEPA) hydrologic model that estimates aquifer recharge. The recharge model accounts for soil distribution, vadose zone depth and hydraulic conductivity, extent of impermeable areas, surficial geology, and vadose zone thickness. Production well pumping and irrigation return flow during the summer season were included in recharge computations. Although recharge was computed as monthly averages per climate scenario, it is driven by physically-based daily weather inputs generated by a stochastic weather generator and calibrated to local observed climate. Four year long climate scenarios were run, each representing one typical year in the present and future (2020s, 2050s, and 2080s), by perturbing the historical weather according to the downscaled CGCM1 general circulation model results (Environment Canada). CGCM1 model outputs were calibrated for local conditions during the downscaling procedure. These include absolute and relative changes in precipitation; including indirect measures of precipitation intensity, dry and wet spell lengths, temperature, and solar radiation for the evapotranspiration model. CGCM1 downscaling was also used to predict basin-scale runoff for the Kettle River upstream of Grand Forks. This river exerts strong control on the groundwater levels in the aquifer and physically-based discharge predictions were used in the transient groundwater flow model. Modeled discharge hydrographs were converted to river stage hydrographs at each of 123 river segments, and interpolated between known river channel cross-sections. Stage-discharge curves were estimated using the BRANCH model and calibrated to observed historical data. River channels were represented in three-dimensions using a high grid density (14 to 25 m) in MODFLOW, which were mapped onto river segments. River stage schedules along the 26 km long meandering channel were imported at varying, but high, temporal resolution (1 to 5 days) for every cell location independently. Head differences were computed at each time step for historical and future, mapped in GIS and linked to the MODFLOW model. Temporal changes in mass balance components show relations between pumping, storage, recharge, and flow. Within an annual cycle and between climate scenarios the results show different spatial and temporal distributions in groundwater conditions. Groundwater levels near the river floodplain are predicted to be lower earlier in the year under future climate scenarios, but away from rivers, groundwater levels increase slightly due to the predicted increase in recharge.

Scibek, J.; Allen, D. M.; Whitfield, P.; Wei, M.

2004-05-01

324

Using MODFLOW drains to simulate groundwater flow in a karst environment

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 stream 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.

Quinn, J.; Tomasko, D.; Glennon, M.A.; Miller, S.F.; McGinnis, L.D.

1998-07-01

325

Results are presented of a detailed study into the vadose zone and shallow water table hydrodynamics of a field site in Shropshire, UK. A conceptual model is developed and tested using a range of numerical models, including a modified soil moisture balance model (SMBM) for estimating groundwater recharge in the presence of both diffuse and preferential flow components. Tensiometry reveals that the loamy sand topsoil wets up via macropore flow and subsequent redistribution of moisture into the soil matrix. Recharge does not occur until near-positive pressures are achieved at the top of the sandy glaciofluvial outwash material that underlies the topsoil, about 1 m above the water table. Once this occurs, very rapid water table rises follow. This threshold behaviour is attributed to the vertical discontinuity in the macropore system due to seasonal ploughing of the topsoil, and a lower permeability plough/iron pan restricting matrix flow between the topsoil and the lower outwash deposits. Although the wetting process in the topsoil is complex, a SMBM is shown to be effective in predicting the initiation of preferential flow from the base of the topsoil into the lower outwash horizon. The rapidity of the response at the water table and a water table rise during the summer period while flow gradients in the unsaturated profile were upward suggest that preferential flow is also occurring within the outwash deposits below the topsoil. A variation of the source-responsive model proposed by Nimmo (2010) is shown to reproduce the observed water table dynamics well in the lower outwash horizon when linked to a SMBM that quantifies the potential recharge from the topsoil. The results reveal new insights into preferential flow processes in cultivated soils and provide a useful and practical approach to accounting for preferential flow in studies of groundwater recharge estimation.

Cuthbert, M. O.; Mackay, R.; Nimmo, J. R.

2012-01-01

326

NASA Astrophysics Data System (ADS)

A flow pattern is characterized by aquifer features and the number, type, and distribution of stagnation points (locations where the discharge is zero). This article identifies a condition for transition of flow patterns in two-dimensional groundwater flow obeying Darcy's law by examining changes in stagnation points, using the Taylor series expansion of the discharge vector. It is found that the three standard types of stagnation points (minimums, maximums, and saddle points) are completely characterized by the first-order term containing the discharge gradient tensor. However, when the determinant of the tensor becomes zero, stagnation points of other types characterized by higher-order terms come into existence. In this article, we call these zero-determinant stagnation points as critical stagnation points; they may emerge suddenly, split to a set of new stagnation points, or disappear from the flow, resulting in transitions of flow patterns. Examples of both transient and steady flows are used to illustrate the usefulness and significance of critical stagnation points.

Jin, Wei; Steward, David R.

2007-01-01

327

Parameter estimation techniques and uncertainty in ground water flow model predictions

Quantification of uncertainty in predictions of nuclear waste repository performance is a requirement of Nuclear Regulatory Commission regulations governing the licensing of proposed geologic repositories for high-level radioactive waste disposal. One of the major uncertainties in these predictions is in estimating the ground-water travel time of radionuclides migrating from the repository to the accessible environment. The cause of much of this uncertainty has been attributed to a lack of knowledge about the hydrogeologic properties that control the movement of radionuclides through the aquifers. A major reason for this lack of knowledge is the paucity of data that is typically available for characterizing complex ground-water flow systems. Because of this, considerable effort has been put into developing parameter estimation techniques that infer property values in regions where no measurements exist. Currently, no single technique has been shown to be superior or even consistently conservative with respect to predictions of ground-water travel time. This work was undertaken to compare a number of parameter estimation techniques and to evaluate how differences in the parameter estimates and the estimation errors are reflected in the behavior of the flow model predictions. That is, we wished to determine to what degree uncertainties in flow model predictions may be affected simply by the choice of parameter estimation technique used. 3 refs., 2 figs.

Zimmerman, D.A. (GRAM, Inc., Albuquerque, NM (USA)); Davis, P.A. (Sandia National Labs., Albuquerque, NM (USA))

1990-01-01

328

Stream Restoration Flow Estimation for Kentucky Streams

NASA Astrophysics Data System (ADS)

Stream restoration analysis and natural stream design include components of channel analysis related to flow magnitude and estimation of bank-full flow return period events. The more frequent flood events, associated with return periods less than 5 years, are important in restoration project planning and channel stability. Concepts proposed by Costa and O'Connor (1995) including components of flow duration, stream power per unit area, flood energy, and other characteristics indicate flood effectiveness as a source of geomorphic change in channels and floodplains. This study considers stream gage sites in the Cumberland, Tennessee and Mississippi watersheds of Kentucky. The magnitude and variability of recorded flood events is described, as well as the frequency of observed peak flow record. The importance of the higher frequency events is presented in the context of channel forming flow, bank-full discharge, effective discharge, and mean annual discharge (FISRWG 1998). Comparison of historical flow records, estimated bank-full flow derived from observed conditions is presented as a link between these information resources.

French, M.; Connelly, A.

2005-05-01

329

NASA Astrophysics Data System (ADS)

The San Joaquin Valley, California is one of the most productive agricultural areas in the world. The application of fertilizer and manure to the land over decades has led to extensive nitrate contamination in Valley aquifer. Groundwater-surface water exchanges in the region have can result in significant nitrate fluxes into Valley rivers. This work examines groundwater-surface water interactions at a USGS NAWQA site on the Merced River, near Livingston, CA. Hydrologic infrastructure at the site includes deep observation wells leading to shallow riparian wells and sampling points. The infrastructure is being instrumented as an agricultural flow path sensor network linking agricultural management practices to chemical transport and fate along a flow path through the vadose zone, groundwater and surface water. This work examines the movement of nitrate rich water into the Merced River through the hyporheic zone, and the denitrification rates associated with this transfer. Small inexpensive loggers self-logging thermistors are used to map temperature gradients in the streambed which are used estimate spatially distributed groundwater losses and gains within a roughly 300 m reach of the Merced River. In addition, samples collected from drive points installed at multiple depths in the riverbed are used to characterize the nitrate gradient across two transects within the same reach.

Butler, C.; Fisher, J.; Pai, H.; Villamizar Amaya, S.; Harmon, T. C.

2008-12-01

330

Because mixing of groundwater commonly occurs in geologically active regions such as subduction zones, sole use of a conventional method for groundwater dating is not applicable. Here we present a new model using dissolved 4He concentration and He isotopic ratio as well as crustal He flux to estimate the very long residence time of groundwater where mixing of waters of

N. Morikawa; K. Kazahaya; M. Yasuhara; A. Inamura; K. Nagao; H. Sumino; M. Ohwada

2005-01-01

331

Fire Island National Seashore (FIIS) occupies 42 kilometers of the barrier island for which it is named that lies off the southern shore of Suffolk County, N.Y. Freshwater in the highly permeable, sandy aquifer underlying Fire Island is bounded laterally by marine surface waters and at depth by saline groundwater. Interspersed throughout FIIS are 17 pre-existing residential communities that in summer months greatly increase in population through the arrival of summer residents and vacationers; in addition, the National Park Service (NPS) has established several facilities on the island to accommodate visitors to FIIS. The 2.2 million people estimated by the NPS to visit Fire Island annually impact groundwater quality through the release of waste-derived contaminants, such as nutrients, pathogens, and organic compounds, into the environment. Waste-contaminated groundwater can move through the aquifer and threaten the ecological health of the adjacent back-barrier estuaries to which much of the groundwater ultimately discharges. In 2004, the U.S. Geological Survey (USGS), in cooperation with the NPS, began a 3-year investigation to (1) collect groundwater levels and water-quality (nutrient) samples, (2) develop a three-dimensional model of the shallow (water-table) aquifer system and adjacent marine surface waters, and (3) calculate nitrogen loads in simulated groundwater discharges from the aquifer to back-barrier estuaries and the ocean. The hydrogeology of the shallow aquifer system was characterized from the results of exploratory drilling, geophysical surveying, water-level monitoring, and water-quality sampling. The investigation focused on four areas-the communities of Kismet and Robbins Rest, the NPS Visitor Center at Watch Hill, and the undeveloped Otis Pike Fire Island High Dune Wilderness. Thirty-five observation wells were installed within FIIS to characterize subsurface hydrogeology and establish a water-table monitoring network in the four study areas. A variable-density model of the shallow aquifer system and adjacent marine surface waters was developed to simulate groundwater flow patterns and rates. Nitrogen loads from the shallow aquifer system were calculated from representative total nitrogen (TN) concentrations and simulated groundwater discharges to back-barrier estuaries and the ocean. The model simulates groundwater directions, velocities, and discharge rates under 2005 mean annual conditions. Groundwater budgets were developed for recharge areas of similar land use that contribute freshwater to back-barrier estuaries, the ocean, and subsea-discharge zones. Total freshwater discharge from the shallow aquifer system is about 43,500 cubic meters per day (m3/d) (79.8 percent) to back-barrier estuaries and about 10,200 m3/d (18.7 percent) to the ocean; about 836 m3/d (1.5 percent) may exit the system as subsea underflow. The total contribution of fresh groundwater to shoreline discharge zones amounts to about 53,700 m3/d (98.5 percent). The median age of freshwater discharged to back-barrier estuaries and the ocean was 3.4 years, and the 95th-percentile age was 20 years. The TN concentrations and loads under 2005 mean annual conditions for areas that contribute fresh groundwater to back-barrier estuaries and the ocean were calculated for the principal land uses on Fire Island. The overall TN load from the shallow aquifer system to shoreline discharge zones is about 16,200 kilograms per year (kg/yr) (82.2 percent) to back-barrier estuaries and about 3,500 kg/yr (17.8 percent) to the ocean. The overall TN load to marine surface waters amounts to about 19,700 kg/yr-roughly 6 percent of the annual TN load from shallow groundwater entering the South Shore Estuary Reserve (SSER) from the Suffolk County mainland, which is about 345,000 kg/yr. In contrast to the TN load from shallow groundwater for the SSER watershed, which annually yields about 353 kilograms per square kilometer (kg/km2), the overall TN loa

Schubert, Christopher E.

2010-01-01

332

Estimation of submarine groundwater discharge from bulk ground electrical conductivity measurements

NASA Astrophysics Data System (ADS)

The utility of bulk ground conductivity (BGC) measurements in the estimation of submarine groundwater discharge (SGD) was investigated at four sites covering a range of hydrogeological settings, namely Cockburn Sound (Australia); Shelter Island (USA); Ubatuba Bay (Brazil) and Flic-en-Flac Bay (Mauritius). At each of the sites, BGC was surveyed in the intertidal zone, and seepage meters were used for direct measurements of SGD flow rates. In the presence of detectable salinity gradients in the sediment, a negative correlation between SGD and BGC was recorded. The correlation is site-specific and is dependent on both the type of sediment and the mixing processes. For example, at Shelter Island the maximum mean flow rates were 65 cm d-1 at a BGC of ˜0 mS cm-1 while at Mauritius maximum mean flow rates were 364 cm d-1 at a BGC of ˜0 mS cm-1. BGC measurements are used to estimate SGD over a large scale, and to separate its fresh and saline components. Extrapolating BGC measurements throughout the study sites yields a total discharge of 2.91, 1.59, 7.16, and 25.4 103 m3 d-1 km-1 of shoreline with a freshwater fraction of 41, 24, 29, and 63% at Cockburn Sound, Shelter Island, Ubatuba Bay, and Flic-en-Flac Bay respectively. The results demonstrate that ground conductivity is a useful tracer to survey and separate freshwater and recirculated seawater component of SGD. The presented investigation is a subset within a series of experiments designed to compare different methods to investigate SGD co-organized and carried out by SCOR, LOICZ, IOC and IAEA.

Stieglitz, Thomas; Rapaglia, John; Bokuniewicz, Henry

2008-08-01

333

ADAPTATION OF THE CARTER-TRACY WATER INFLUX CALCULATION TO GROUNDWATER FLOW SIMULTATION.

The Carter-Tracy calculation for water influx is adapted to groundwater flow simulation with additional clarifying explanation not present in the original papers. The Van Everdingen and Hurst aquifer-influence functions for radial flow from an outer aquifer region are employed. This technique, based on convolution of unit-step response functions, offers a simple but approximate method for embedding an inner region of groundwater flow simulation within a much larger aquifer region where flow can be treated in an approximate fashion. The use of aquifer-influence functions in groundwater flow modeling reduces the size of the computational grid with a corresponding reduction in computer storage and execution time. The Carter-Tracy approximation to the convolution integral enables the aquifer influence function calculation to be made with an additional storage requirement of only two times the number of boundary nodes more than that required for the inner region simulation.

Kipp, Jr. , Kenneth, L.

1986-01-01

334

Modeling regional groundwater flow in a peat bog complex in Ontario, Canada

NASA Astrophysics Data System (ADS)

Peatlands are important ecohydrological systems and contribute significantly to the global carbon cycle. They function as carbon sinks through CO2-sequestration but also emit methane depending i.a. on the prevailing hydrological structures. Knowledge of their hydrology including exchange between the groundwater and surface water domain is thus necessary to understand wetland environments and to determine their vulnerability to climate changes. The impact of proposed wetter conditions on wetland hydrological homeostastis in northern bogs is uncertain to this date. Elevated water tables due to changing hydrological flow patterns may affect the characteristics of wetlands as a carbon reservoir. Modeling approaches allow quantifying and qualifying of these flow patterns on a longer time scale. Luther Bog is located in Southern Ontario. The ombotrophic bog to poor fen is partially bordered by Luther Lake which inundates the area since its creation in 1952. In this study the interaction between the wetland and the adjacent lake is modeled using the fully-integrated HydroGeoSphere model. A transient three-dimensional groundwater mode is set up for a small catchment with the lake level implemented as a constant-head boundary condition. Hydraulic properties of the peat were estimated executing bail tests on multilevel piezometers at different sites within the wetland. The first hypothesis is that the wet conditions in the runoff network keep the water table in the wetland high over a specific transition zone. The Second is that there may be a reversal of flow directions over the hydrological year, due to varying boundary conditions, e.g. evapotranspiration and precipitation. First results indicate that exchange rates may be very slow. This is supported by manual measurements of little hydraulic gradients and little topographic gradients. The results also show a seasonal effect in flow directions in both, the groundwater and the surface water domain. The model will be tested upon its sensitivity to variations in the anisotropy of hydraulic conductivities as this is difficult to determine in the field using known approaches, e.g. bail tests. A transport simulation will be conducted to determine the exact amount of exchange water and the extent of the exchange zone.

Durejka, Stefan; Knorr, KLaus-Holger; Blodau, Christian; Frei, Sven

2013-04-01

335

Estimating the effect of phreatophytes on the groundwater flow field is critical in the design or evaluation of a phytoremediation system. Complex hydrogeological conditions and the transient water use rates of trees require the application of numerical modeling to address such issues as hydraulic containment, seasonality, and system design.In 1999, 809 hybrid poplars and willows were planted to phytoremediate the

J. J. Quinn; M. C. Negri; R. R. Hinchman; L. P. Moos; J. B. Wozniak; E. G. Gatliff

2001-01-01

336

Groundwater level monitoring and recharge estimation in the White Volta River basin of Ghana

NASA Astrophysics Data System (ADS)

Recharge quantification is an important pre-requisite for effectively managing groundwater resources as recharge estimates are needed to determine sustainable yields of groundwater aquifers for rational and sustainable exploitation of the resource. In this study, the water table fluctuation method has been applied in the White Volta River basin of Ghana (approx. 46,000 km2) to estimate seasonal fluctuations in groundwater levels in the basin and subsequently to estimate recharge to the groundwater for the 2006 and 2007 water years. Results show high seasonal and spatial variability in the water level, with a range of 1240-5000 mm in 2006, and 1600-6800 mm in 2007. Seasonal rainfall was found to be the main source of recharge to the aquifers in the basin as water level rise occurred only in the rainfall season. Recharge to groundwater in the White Volta basin was estimated to vary between 2.5% and 16.5% of the mean annual rainfall, with a mean recharge of 7-8%.

Obuobie, Emmanuel; Diekkrueger, Bernd; Agyekum, William; Agodzo, Sampson

2012-08-01

337

A conceptual model of the Lake Warden coastal wetlands system, Western Australia, was developed using hydraulic, chemical\\u000a and stable isotopic data, and formed the basis for a groundwater flow model using the finite element numerical code (FEFLOW).\\u000a The system to be modeled is complex. The surface water and groundwater within the wetlands system show varying salinity and\\u000a isotopic composition over

D. A. Reynolds; S. Marimuthu

2007-01-01

338

NASA Astrophysics Data System (ADS)

Widespread arsenic poisoning is occurring in large areas of Bangladesh and West Bengal, India due to high arsenic levels in shallow groundwater, which is the primary source of irrigation and drinking water in the region. The high-arsenic groundwater exists in aquifers of the Bengal Basin, a huge sedimentary system approximately 500km x 500km wide and greater than 15km deep in places. Deeper groundwater (>150m) is nearly universally low in arsenic and a potential source of safe drinking water, but evaluation of its sustainability requires understanding of the entire, interconnected regional aquifer system. Numerical modeling of flow and arsenic transport in the basin introduces problems of scale: challenges in representing the system in enough detail to produce meaningful simulations and answer relevant questions while maintaining enough simplicity to understand controls on processes and operating within computational constraints. A regional groundwater flow and transport model of the Bengal Basin was constructed to assess the large-scale functioning of the deep groundwater flow system, the vulnerability of deep groundwater to pumping-induced migration from above, and the effect of chemical properties of sediments (sorption) on sustainability. The primary challenges include the very large spatial scale of the system, dynamic monsoonal hydrology (small temporal scale fluctuations), complex sedimentary architecture (small spatial scale heterogeneity), and a lack of reliable hydrologic and geologic data. The approach was simple. Detailed inputs were reduced to only those that affect the functioning of the deep flow system. Available data were used to estimate upscaled parameter values. Nested small-scale simulations were performed to determine the effects of the simplifications, which include treatment of the top boundary condition and transience, effects of small-scale heterogeneity, and effects of individual pumping wells. Simulation of arsenic transport at the large scale adds another element of complexity. Minimization of numerical oscillation and mass balance errors required experimentation with solvers and discretization. In the face of relatively few data in a very large-scale model, sensitivity analyses were essential. The scale of the system limits evaluation of localized behavior, but results clearly identified the primary controls on the system and effects of various pumping scenarios and sorptive properties. It was shown that limiting deep pumping to domestic supply may result in sustainable arsenic-safe water for 90% of the arsenic-affected region over a 1000 year timescale, and that sorption of arsenic onto deep, oxidized Pleistocene sediments may increase the breakthrough time in unsustainable zones by more than an order of magnitude. Thus, both hydraulic and chemical defenses indicate the potential for sustainable, managed use of deep, safe groundwater resources in the Bengal Basin.

Michael, H. A.; Voss, C. I.

2009-12-01

339

Regional ground-water flow near Richton Dome, Mississippi. Annual status report for fiscal year 1982

This report presents the analyses and preliminary results of the ground-water modeling program for the regional assessment of Richton Dome, Mississippi. The reported work is part of an ongoing evaluation of Richton Dome as a potential repository for high-level radioactive waste. As such, the results are to be considered preliminary and subject to modification by further analyses that are recommended in the conclusions of this report. The bases of the report are developed in three major sections that describe the regional geology and hydrology, present the available basic data utilized in the study and develop the conceptual and numerical models of the ground-water flow system. Appendix A describes previous hydrologic and geologic investigations in the study area. Appendix B documents changes made to the input data of the regional ground-water flow model of Richton Dome during the first quarter of FY 1983, presents new mass balance calculations, and updates comparisons between measured and calculated heads at calibration well locations. The results of the ground-water modeling process are discussed in two sections addressing the model calibration procedure, the model sensitivity analyses, and the preliminary, quantitative description of the operation of the regional ground-water flow system. The concluding sections of the report qualify the preliminary nature of the modeling results and suggest improvements in the data base and the conceptual model utilized in the study to improve the current understanding of the regional ground-water flow. 57 references, 18 figures, 9 tables.

Not Available

1983-11-01

340

A numerical method is presented to simulate groundwater flow and transport using the Boundary-Fitted Coordinate (BFC) systems approach initially developed for aerodynamics. An irregularly-shaped physical domain is transformed to a simple computational domain with uniform grids. Governing equations defined in the physical domain are transformed into the computational domain, wherein all transformed equations are solved by the Finite Difference Method (FDM). This study developed three FORTRAN 77 computer programs: (1) BFCGW, which simulates groundwater flow and transport, (2) SEEPAGE, which simulates free-surface and seepage face, and (3) Q3D, which simulates multi-layered flow. A series of plotting programs using [open quotes]DISSPLA,[close quotes] an IBM FORTRAN graphics package, was also developed to plot grid lines, contour lines, and flow vectors in an irregularly-shaped physical domain with non-uniform grids. Each of the three programs was verified by solving an idealized problem for which the analytical solution was known and/or a realistic problem for which field measurements could be obtained. The computer program BFCGW was employed to simulate an idealized well flow in a triangular physical domain and actual groundwater flows in the area of West Lafayette, Indiana. The numerical solutions in both cases closely matched the analytical solutions and/or numerical simulations by other computer codes such as AQUA and MODFLOW. The program BFCGW performs rotation and stretching of local coordinates prior to BFC transformations to simulate heterogeneous and anisotropic groundwater flow. The rotation and stretching technique simplifies transformed governing equations of anisotropic groundwater flow. With the program BFCGW, the groundwater flow and the transport equations are solved sequentially to simulate solute concentration distributions.

Lee, K.K.

1992-01-01

341

Concentrations of chloride in excess of State of New Hampshire water-quality standards (230 mg/l) have been measured in watersheds adjacent to an interstate highway (I-93) in southern New Hampshire. A proposed widening plan for I-93 has raised concerns over further increases in chloride. As part of this effort, road-salt-contaminated groundwater discharge was mapped with terrain electrical conductivity (EC) electromagnetic (EM) methods in the fall of 2006 to identify potential sources of chloride during base-flow conditions to a small stream, Policy Brook. Three different EM meters were used to measure different depths below the streambed (ranging from 0 to 3 m). Results from the three meters showed similar patterns and identified several reaches where high EC groundwater may have been discharging. Based on the delineation of high (up to 350 mmhos/m) apparent terrain EC, seven-streambed piezometers were installed to sample shallow groundwater. Locations with high specific conductance in shallow groundwater (up to 2630 mmhos/m) generally matched locations with high streambed (shallow subsurface) terrain EC. A regression equation was used to convert the terrain EC of the streambed to an equivalent chloride concentration in shallow groundwater unique for this site. Utilizing the regression equation and estimates of onedimensional Darcian flow through the streambed, a maximum potential groundwater chloride load was estimated at 188 Mg of chloride per year. Changes in chloride concentration in stream water during streamflow recessions showed a linear response that indicates the dominant process affecting chloride is advective flow of chloride-enriched groundwater discharge. Published in 2010 by John Wiley & Sons, Ltd.

Harte, P. T.; Trowbridge, P. R.

2010-01-01

342

The report presents the results of a study to provide a quantitative evaluation of the ground-water flow system at the Julietta and Tibbs-Banta landfills and provide a general description of the ground-water quality beneath and near the two landfills. These objectives provide the information necessary to evaluate the effects of the landfills on ground-water quality. Geologic, hydrologic, and water-quality data

R. F. Duwelius; T. K. Greeman

1989-01-01

343

A regional groundwater flow model encompassing approximately 100 mi{sup 2} surrounding the C, K. L. and P reactor areas has been developed. The Reactor flow model is designed to meet the planning objectives outlined in the General Groundwater Strategy for Reactor Area Projects by providing a common framework for analyzing groundwater flow, contaminant migration and remedial alternatives within the Reactor Projects team of the Environmental Restoration Department.

Flach, G.P.

1999-02-24

344

A calibrated groundwater flow model for a contaminated site can provide substantial information for assessing and improving hydraulic measures implemented for remediation. A three-dimensional transient groundwater flow model was developed for a contaminated mountainous site, at which interim corrective measures were initiated to limit further spreading of contaminants. This flow model accounts for complex geologic units that vary considerably in

Quanlin Zhou; Jens T. Birkholzer; Iraj Javandel; Preston D. Jordan

2004-01-01

345

In this paper, we investigate the effects of systematic and local heterogeneity on groundwater flow, transport, and residence time distributions (RTDs) of basins where groundwater flow is topography driven. Systematic heterogeneity is represented by an exponentially depth-decreasing hydraulic conductivity and porosity, and local heterogeneity is represented by the dispersivity. The RTDs for both a simple basin with one flow system

M. Bayani Cardenas; Xiao-Wei Jiang

2010-01-01

346

Groundwater flow behaviour during the initial development phase of an artificial catchment

NASA Astrophysics Data System (ADS)

Artificially created, spatially and structurally well defined hydrological catchments are suitable study sites for hydrological and ecosystem research. One of the largest artificial catchments named "Chicken Creek" with clearly defined boundary conditions and extended monitoring facilities was set up on a dump site from opencast mining activities in Eastern Germany. The catchment, left to undisturbed succession, enables the observation of ecosystem development from the very beginning. Precipitation as the only source of water input is the dominating driving force for the hydrological processes in the initial development phase. Due to the initial absence of vegetation or organic structures, the morphological and hydrogeological properties of the artificial catchment control the runoff and storage processes. In case of the Chicken Creek catchment, they are given by the construction design and technology. In mature natural catchments, the groundwater flow system has normally achieved a dynamic equilibrium stage. In the newly constructed artificial catchment, the groundwater body is just evolving by infiltrating and percolating precipitation which fills the pore volume of the initially unsaturated catchment body. The saturation process has started above the underlying horizontal clay layer that is acting as lower catchment boundary. The observed trend of rising groundwater table superposed by seasonal fluctuations indicates a groundwater recharge higher than the drainage. During the last four years, the filling process is extenuating and an equilibrium between groundwater recharge and drainage is establishing. Groundwater exfiltration preferentially occurs in new gully structures formed by precipitation induced erosion processes. A groundwater model is set up to simulate the groundwater dynamics during the initial phase of the catchment development. Based on the theoretical consideration of initial homogeneity and isotropy, hydrogeologically relevant structures, patterns and their effects on the groundwater system shall be introduced and their effects evaluated in comparison with the field observations. The modelling aims at the identification and description of different flow statuses, threshold behaviour and flow patterns. Observation and simulation results shall be presented.

Mazur, Kai; Schoenheinz, Dagmar; Biemelt, Detlef; Grünewald, Uwe

2010-05-01

347

The Dixie Valley area includes seven valleys in west-central Nevada (Dixie, Fairview, Stingaree, Cowkick, Eastgate, Pleasant, and Jersey Valleys; total, 2,380 square miles). Dixie Valley receives surface-water and ground-water flow from Stingaree, Cowkick, Eastgate, Pleasant, and Jersey Valleys and subsurface flow from Fairview Valley, which is a topographically closed basin. The relation between precipitation and altitude was re-evaluated for the Dixie Valley area using new data, and empirical estimates of recharge were revised accordingly. The revised estimate of total recharge is 23,000 acre-feet per Re-evaluation of ground-water discharge focused on Dixie Valley as the largest basin in the study area. Phreatophytic vegetation was mapped and partitioned into nine zones on the basis of species composition and foliage density. For woody phreatophytes, annual evapotranspiration rates of 0.7 cubic feet of water per cubic foot of foliage for greasewood and 1.1 cubic feet of water per cubic foot of foliage for rabbitbrush were adapted from lysimeter studies near Winnemucca, Nevada. These rates were multiplied by the foliage density of the respective phreatophytes in each zone to estimate a specific rate for that zone. Rates for salt-grass (0.5 to 0.8 foot per year) and the playa surface (0.1 to 0.3 foot per year) were based on a range of rates. used in other recent studies in western and central Nevada. These rates were multiplied by the areas of the zones to produce estimates of the annual volume of ground water discharged. The discharge estimated for Dixie Valley is between 17,000 and 28,000 acre-feet per year. The revised discharge estimate for the entire Dixie Valley area is between 20,000 and 31,000 acre-feet per year. The revised ground-water budget for the entire Dixie Valley study area has a total recharge of about 23,000 acre-feet per year. This is within the range of estimates of natural discharge--from 20,000 to 31,000 acre-feet per year. For Dixie Valley alone, the total recharge of about 8,900 acre-feet per year and the estimated subsurface inflow from tributary areas of about 11,000 acre-feet per year produce an estimated total inflow of about 20,000 acre-feet per year. This compares with the discharge estimate of 17,000 to 28,000 acre-feet per year.

Harrill, J. R.; Hines, L. B.

1995-01-01

348

Flow Model Development for the Idaho National Laboratory OU 10-08 Sitewide Groundwater Model

A two-dimensional (2D), steady-state groundwater flow model was developed for the Idaho National Laboratory (INL) sitewide groundwater model. A total of 224 wells inside the model domain were used to calibrate the 2D flow model. Three different calibration techniques, zonation approach, pilot point approach and coupled zonation/pilot point approach, were explored and applied during the model development. The pilot point approach allows modelers to model aquifer heterogeneities at various scales, and extract the maximum amount of data from available monitoring data, permitting the best possible representation of flow and transport at the INL.

Hai Huang; Swen Magnuson; Thomas Wood

2005-09-01

349

During 2007 a Feasibility Study and Proposed Plan were completed that describe the selection of a combined groundwater pump-and-treat, monitored natural attenuation, and flow-path-control remedy for contaminants present in the Hanford 200-ZP-1 groundwater operable unit. In anticipation of the September 2008 signing of the final record of decision, work began on the development of a groundwater flow and contaminant transport model encompassing the 200-ZP-1 OU. The model was developed to support the preparation of the remedial design/remedial action work plan and subsequent design documents; to provide estimates of influent concentrations and mass removal rates for several contaminants of concern, including carbon tetrachloride, technetium-99, and hexavalent chromium; and to assist in the integration of remedial decision making across the Hanford Central Plateau. This paper describes the initial development and application of the flow and transport model, through Spring 2009.

Tonkin, Matthew J.; Karanovic, Marinko; Byrnes, Mark E.; Morse, John G.; Murray, Christopher J.; Clement, Paul

2010-03-08

350

Groundwater flow analyses in preliminary site investigations. Modelling strategy and computer codes.

National Technical Information Service (NTIS)

The analyses of groundwater flow comprised a part of the preliminary site investigations which were carried out by Teollisuuden Voima Oy (TVO) for five areas in Finland during 1987 -1992. The main objective of the flow analyses was to characterize groundw...

V. Taivassalo L. Koskinen K. Meling

1994-01-01

351

A Finite Element Model for the Unsteady Groundwater Flow over Sloping Beds

A numerical solution of the nonlinear two-dimensional unsteady groundwater flow over sloping beds, using the Galerkin finite element method, is presented. The applied differential equation is based on the assumption that the streamlines are parallel to the sloping bed while the conventional differential equation is based on the Dupuit–Forchheimer assumption of horizontal flow. Furthermore, the gradient of the piezometric head

N. Kalaidzidou-Paikou; D. Karamouzis; D. Moraitis

1997-01-01

352

Modeling three-dimensional groundwater flows by the body-fitted coordinate (BFC) method

The purpose of this research was to determine if the body-fitted coordinate (BFC) method could be utilized to model three-dimensional groundwater flows and what advantages it offers. This method was initially developed and used in aerodynamics and heat transfer areas to simulate air and heat flows in irregular domains. Chapter 1 introduces the BFC method as an alternative to two

Min-Ho Koo

1996-01-01

353

On the thermal effects of groundwater flow. 1. Regional scale systems

Numerical solutions of the equations of fluid flow and heat transport are used to quantify the effects of groundwater flow on the subsurface thermal regime. Simulations are carried out for a vertical section through a basin with a distance of 40 km separating the regional topographic high and low. Emphasis is placed on understanding the conditions under which advective effects

Leslie Smith; David S. Chapman

1983-01-01

354

The analysis of groundwater flows in unconfined aquifers with nonuniform hydraulic conductivity

Horizontal groundwater flows in unconfined aquifers with horizontal lower boundaries can be found exactly by the seepage analysis that allows the hydraulic conductivity to vary in the vertical direction. The exact analysis of flows when the lower boundary of the aquifer is not a horizontal plane, requires the soil-water pressure on this boundary to be known, and this is not

E. G. Youngs

1986-01-01

355

The mathematical development of a two-dimensional finite volume model for groundwater flow is described. Based on the hydraulic equations for saturated flow, the model deploys an improved least squares gradient reconstruction technique to evaluate the gradient at the control volume face, derived from the application of the finite volume formulation and using a cell-centred structured quadrilateral grid. The model has

D. Loudyi; R. A. Falconer; B. Lin

2007-01-01

356

The numerical simulation of groundwater flow in the vadose zone continues to be a challenge for many problems of practical interest. Under commonly used constitutive relations, the governing equations can be highly nonlinear and produce sharp fronts in the solution variables for problems such as wetting phase infiltration into an initially dry medium. For a number of multiphase flow problems,

M. W. Farthing; H. Li; C. T. Miller; C. E. Kees

2003-01-01

357

Mixed Finite Elements for Accurate Particle Tracking in Saturated Groundwater Flow.

National Technical Information Service (NTIS)

Saturated groundwater flow can often be described by the law of mass conservation and Darcy's law, i.e. by a potential flow problem. An accurate approximation of the specific discharge can be determined by the mixed finite element method. In this article ...

E. F. Kaasschieter

1994-01-01

358

The theory of regional groundwater flow is critical for understanding many geologic processes. It is known that heterogeneity and anisotropy in hydraulic conductivity caused by varying lithology and faults affect the pattern of nested flow systems in complex basin. In addition, depth-decaying hydraulic conductivity, a widely observed phenomenon in the earth's crust, cannot be neglected in studies related to regional

X. Jiang; L. Wan; X. Wang; S. Ge; G. Cao; F. Hu

2010-01-01

359

GROUNDWATER FLOW MODEL CALIBRATION USING WATER LEVEL MEASUREMENTS AT SHORT INTERVALS

Groundwater flow models are usually calibrated with respect to water level measurements collected at intervals of several months or even years. Measurements of these kinds are not sensitive to sudden or short stress conditions, such as impact from stormwater drainage flow or flas...

360

Quantification of groundwater flow dynamics and of the interactions among groundwater, surface water, and riparian vegetation, represent key components in the development of a balanced restoration plan for functional riparian ecosystems. A groundwater model was developed using MODFLOW 2000 to support of riparian restoration along the Colorado River Delta (Mexico: Baja California, Sonora). The Colorado River is widely recognized as

T. Maddock; E. Feirstein; K. J. Baird; H. Ajami

2007-01-01

361

Previous efforts to simulate regional groundwater flow in the Texas Gulf Coast aquifer did not include explicit representation of streams and their interaction with groundwater, but instead used a model- calibrated effective recharge value. However, historical data indicates a considerable amount of surface water\\/groundwater interaction throughout the Central Gulf Coast (CGC) region. Using the MODFLOW STR package, streams were incorporated

Gilbert Barth

362

MODFLOW-2005 : the U.S. Geological Survey modular ground-water model--the ground-water flow process

This report presents MODFLOW-2005, which is a new version of the finite-difference ground-water model commonly called MODFLOW. Ground-water flow is simulated using a block-centered finite-difference approach. Layers can be simulated as confined or unconfined. Flow associated with external stresses, such as wells, areal recharge, evapotranspiration, drains, and rivers, also can be simulated. The report includes detailed explanations of physical and mathematical concepts on which the model is based, an explanation of how those concepts are incorporated in the modular structure of the computer program, instructions for using the model, and details of the computer code. The modular structure consists of a MAIN Program and a series of highly independent subroutines. The subroutines are grouped into 'packages.' Each package deals with a specific feature of the hydrologic system that is to be simulated, such as flow from rivers or flow into drains, or with a specific method of solving the set of simultaneous equations resulting from the finite-difference method. Several solution methods are incorporated, including the Preconditioned Conjugate-Gradient method. The division of the program into packages permits the user to examine specific hydrologic features of the model independently. This also facilitates 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 also are designed to permit maximum flexibility. The program is designed to allow other capabilities, such as transport and optimization, to be incorporated, but this report is limited to describing the ground-water flow capability. The program is written in Fortran 90 and will run without modification on most computers that have a Fortran 90 compiler.

Harbaugh, Arlen W.

2005-01-01

363

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

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.

Buxton, Herbert, T.; Modica, Edward

1992-01-01

364

Modelling water flow and seasonal soil moisture dynamics in an alluvial groundwater-fed wetland

Complex interactions occur in riparian wetlands between groundwater, surface water and climatic conditions. Knowledge of the hydrology of these systems is necessary to understand their functioning and their value and models are a useful and probably essential tool to capture their hydrological complexity. In this study, a 2D-model describing saturated-unsaturated water flow is applied to a transect through a groundwater-fed

I. Joris; J. Feyen

2003-01-01

365

A three-dimensional modular model (MODFLOW) was used to simulate groundwater flow in the Azul River basin, Buenos Aires Province,\\u000a Argentina, in order to assess the correctness of the conceptual model of the hydrogeological system. Simulated heads satisfactorily\\u000a match observed heads in the regional water-table aquifer. Model results indicate that: (1) groundwater recharge is not uniform\\u000a throughout the region but is

Marcelo R. Varni; Eduardo J. Usunoff

1999-01-01

366

A three dimensional steady-state finite difference groundwater flow model is used to quantify the groundwater fluxes and analyze\\u000a the subsurface hydrodynamics in the Akaki catchment by giving particular emphasis to the well field that supplies water to\\u000a the city of Addis Ababa. The area is characterized by Tertiary volcanics covered with thick residual and alluvial soils. The\\u000a model is calibrated

Tenalem Ayenew; Molla Demlie; Stefan Wohnlich

2008-01-01

367

A ROOT ZONE MODELLING APPROACH TO ESTIMATING GROUNDWATER RECHARGE FROM IRRIGATED AREAS

Technology Transfer Automated Retrieval System (TEKTRAN)

In irrigated semi-arid and arid regions, accurate knowledge of groundwater recharge is important for the sustainable management of scarce water resources. The Campo de Cartagena area of southeast Spain is a semi-arid region where irrigation return flow accounts for a substantial portion of recharge....

368

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.

Bohling, G. C.; Butler, Jr. , J. J.

2001-01-01

369

Increase in thermal groundwater due to a flowing well near the Songshan hot spring in Beijing, China

NASA Astrophysics Data System (ADS)

The Songshan hot spring occurs in granite in Yanqing County in northwestern Beijing, China. TDS of the hot water ranges from 459 to 475 mg/L and pH varies between 8.6 and 9.13. The water is of Na SO4 type. Isotopic analyses indicate that the hot spring is meteoric in origin and receives recharge from precipitation in the northern and northwestern granite mountain with elevation of about 1,600 1,800 m. The depth of circulation of the thermal groundwater is estimated to be 2,240 m below the spring’s threshold and the temperature of the geothermal reservoir, 76°C. The residence time of the thermal groundwater is estimated to be about 52 years. A flowing well near the spring has chemical compositions and formation conditions similar to the spring. The discharge of the flowing well is approximately eighteen times larger than that of the spring and the residence time of the former (about 15.4 years) is about three times smaller than that of the latter. Although the well and spring are close to each other, the well’s larger flow rates, indicated residence time and high hydraulic head suggest that the well taps a separate, but genetically similar flow system.

Xun, Zhou; Juan, Li; Haiyan, Zhou; Bin, Fang; Lan, Yu; Shijun, Li

2008-02-01

370

NASA Astrophysics Data System (ADS)

The Martian cryosphere is defined as that region of the crust where the temperature remains continuously below the freezing point of water. Previous estimates of its present thickness have ranged from ˜2.3-4.7 km at the equator to ˜6.5-12.5 km at the poles. Here we revisit these calculations, review some of the assumptions on which they were based, and investigate the effects of several parameters, not previously considered, on the cryosphere’s thermal evolution and extent. These include astronomically driven climate change, the temperature-dependent thermal properties of an ice-rich crust, the potential presence of gas hydrate and perchlorate-saturated groundwater, and consideration of recent lower estimates of present-day global heat flow (which suggest a mean value roughly half that previously thought, effectively doubling the potential thickness of frozen ground). The implications of these findings for the continued survival of subpermafrost groundwater and its potential detection by the MARSIS radar sounder onboard Mars Express are then discussed. Although our estimates of the maximum potential thickness of the cryosphere have significantly increased, consideration of the likely range and spatial variability of crustal heat flow and thermal properties, in combination with the potential presence of potent freezing point depressing salts, may result in substantial local variations in cryosphere thickness. The locations that appear best suited for the detection of groundwater are those that combine low latitude (minimizing the thickness of frozen ground) and low elevation (minimizing the depth to a water table in hydrostatic equilibrium). Preliminary results from a MARSIS investigation of one such area are discussed.

Clifford, Stephen M.; Lasue, Jeremie; Heggy, Essam; Boisson, Joséphine; McGovern, Patrick; Max, Michael D.

2010-07-01

371

NASA Astrophysics Data System (ADS)

When running a groundwater flow model, a recurrent and seemingly subsidiary question arises at the starting step of computations: what value of acceleration parameter do we need to optimize the numerical solver? A method is proposed to provide a practical estimate of the optimal acceleration parameter via a geostatistical analysis of the spatial variability of the logarithm of the transmissivity field Y. The background of the approach is illustrated on the successive over-relaxation method (SOR) used, either as a stand-alone solver, or as a symmetric preconditioner (SSOR) to the gradient conjugate method, or as a smoother in multigrid methods. It shows that this optimum acceleration factor is a function of the standard deviation and the correlation length of Y. This provides an easy-to-use heuristic procedure to estimate the acceleration factors, which could even be incorporated in the software package. A case study illustrates the steps needed to perform this estimation.

Benali, Abdelmajid

2013-01-01

372

EVALUATION OF GROUNDWATER FLOW PATTERNS AROUND A DUAL-SCREENED GROUNDWATER CIRCULATION WELL

Dual-screened groundwater circulation wells (GCWs) can be used to remove contaminant mass and to mix reagents in situ. GCWs are so named because they force water in a circular pattern between injection and extraction screens. The radial extent, flux and direction of the effective...

373

Complexity in the validation of ground-water travel time in fractured flow and transport systems

Ground-water travel time is a widely used concept in site assessment for radioactive waste disposal. While ground-water travel time was originally conceived to provide a simple performance measure for evaluating repository sites, its definition in many flow and transport environments is ambiguous. The US Department of Energy siting guidelines (10 CFR 960) define ground-water travel time as the time required for a unit volume of water to travel between two locations, calculated by dividing travel-path length by the quotient of average ground-water flux and effective porosity. Defining a meaningful effective porosity in a fractured porous material is a significant problem. Although the Waste Isolation Pilot Plant (WIPP) is not subject to specific requirements for ground-water travel time, travel times have been computed under a variety of model assumptions. Recently completed model analyses for WIPP illustrate the difficulties in applying a ground-water travel-time performance measure to flow and transport in fractured, fully saturated flow systems. 12 refs., 4 figs.

Davies, P.B; Hunter, R.L. (Sandia National Labs., Albuquerque, NM (USA)); Pickens, J.F. (INTERA, Inc., Austin, TX (USA))

1991-02-01

374

Groundwater flow model for the General Separations Area, Savannah River Site

The Savannah River Site (SRS) is a Department of Energy (DOE) facility located near Aiken, South Carolina. Assessment of groundwater flow rates and directions, potential contaminant transport times, and concentration of potential contaminants is required to determine current and future environmental effects resulting from releases by these facilities. Proposed closure actions and/or remedial alternatives also need to be evaluated. Numerical groundwater flow and solute transport models are a means of assessing the environmental effects on the groundwater system. They provide a logical method of integrating all available data into a consistent framework for quantitative analysis. The results of groundwater models can be used directly for input to management decisions and design/construct issues or can provide input into risk assessment models for site evaluations. GeoTrans, Inc. was contracted by the Environmental Restoration Department of WSRC to develop a groundwater model of the entire General Separations Area (GSA). Of particular interest is the area surrounding the Mixed Waste Management Facility (MWMF) as shown in Figure 1.2. The model developed in this phase of the study will be used to assess groundwater flow issues for the entire GSA. The second phase of the study will address contaminant transport issues specific to the area surrounding the MWMF.

Not Available

1992-05-15

375

Existing data on base-flow and groundwater nitrate loads were compiled and analyzed to assess the significance of groundwater discharge as a source of the nitrate load to nontidal streams of the Chesapeake Bay watershed. These estimates were then related to hydrogeomorphic settings based on lithology and physiographic province to provide insight on the areal distribution of ground-water discharge. Base-flow nitrate load accounted for 26 to about 100 percent of total-flow nitrate load, with a median value of 56 percent, and it accounted for 17 to 80 percent of total-flow total-nitrogen load, with a median value of 48 percent. Hydrograph separations were conducted on continuous streamflow records from 276 gaging stations within the watershed. The values for base flow thus calculated were considered an estimate of ground-water discharge. The ratio of base flow to total flow provided an estimate of the relative importance of ground-water discharge within a basin. Base-flow nitrate loads, total-flow nitrate loads, and total-flow total-nitrogen loads were previously computed from water-quality and discharge measurements by use of a regression model. Base-flow nitrate loads were available from 78 stations, total-flow nitrate loads were available from 86 stations, and total-flow total-nitrogen loads were available for 48 stations. The percentage of base-flow nitrate load to total-flow nitrate load could be computed for 57 stations, whereas the percentage of base-flow nitrate load to totalflow total-nitrogen load could be computed for 36 stations. These loads were divided by the basin area to obtain yields, which were used to compare the nitrate discharge from basins of different sizes. The results indicate that ground-water discharge is a significant source of water and nitrate to the total streamflow and nitrate load. Base flow accounted for 16 to 92 percent of total streamflow at the 276 sampling sites, with a median value of 54 percent. It is estimated that of the 50 billion gallons of water that reaches the Chesapeake Bay each day, nearly 27 billion gallons is base flow. Generalized lithology (siliciclastic, carbonate, crystalline, and unconsolidated) was combined with physiographic province (the Appalachian Plateau, the Valley and Ridge, the Blue Ridge, the Piedmont, including the Mesozoic Lowland section, and the Coastal Plain) to delineate 11 hydrogeomorphic regions. Areal variation of base flow and base-flow nitrate yield were assessed by means of nonparametric, one-way analysis of variance on basins grouped by the dominant hydrogeomorphic region and by correlation analysis of base flow or base-flow nitrate yield with the percentage of land area of a given hydrogeomorphic region within a basin. Base flow appeared to have a significant relation to the hydrogeomorphic regions. The highest percentages of base flow were found in areas underlain by carbonate rock, crystalline rock with relatively low relief, and unconsolidated sediments. Lower percentages were found in areas underlain by siliclastic rocks and crystalline rocks with relatively high relief. The relation between base-flow nitrate yield and hydrogeomorphic region is less clear. Although there is a relation between low nitrate yields and areas underlain by highrelief siliciclastic rocks, and a relation between high yields and carbonate rocks, much of this relation can be explained by the strong association between the hydrogeomorphic units and land use. In addition, most basins are mixtures of several hydrogeomorphic regions, so the nitrate yield from a basin depends on a large number of complex interacting factors. These unclear results indicate that the sample of available data used here may not be adequate to fully assess the relation between base-flow nitrate yield and the hydrogeomorphic setting of the basin. The results appear to show, however, that ground-water discharge is an important component of the total nontidal streamflow, and that ground

Bachman, L. Joseph; Lindsey, Bruce D.; Brakebill, John W.; Powars, David S.

1998-01-01

376

Velocity estimation using optic flow and radar

NASA Astrophysics Data System (ADS)

This paper presents the development of a static estimator for obtaining state information from optic flow and radar measurements. It is shown that estimates of translational and rotational speed can be extracted using a least squares inversion. The approach is demonstrated in a simulated three dimensional urban environment on an autonomous quadrotor micro-air-vehicle (MAV). The resulting methodology has the advantages of computation speed and simplicity, both of which are imperative for implementation on MAVs due to stringent size, weight, and power requirements.

Gerardi, Steven A.; Humbert, J. Sean; Pierce, Leland E.; Sarabandi, Kamal

2011-05-01

377

Groundwater samples were collected in two different types of aquifers (i.e., Carrizo sand aquifer, Texas and Upper Floridan\\u000a carbonate aquifer, west-central Florida) to study the concentration, speciation, and fractionation of rare earth elements\\u000a (REE) along the groundwater flow path in each system. Major solutes and dissolved organic carbon (DOC) were also measured\\u000a in these groundwaters. In the Carrizo aquifer, groundwaters

Jianwu Tang; Karen H. Johannesson

378

Groundwater flow and velocity in a 500 ka pre-Illinoian till, eastern Iowa

NASA Astrophysics Data System (ADS)

Few hydrology studies have investigated glacial till older than Illinoian time (> 300,000 BP) despite these older tills overlying a large portion of North America. An 8- and 6-well monitoring well nest installed into a 31 m thick pre-Illinoian till sequence near Cedar Rapids, Iowa was characterized using traditional hydrologic methods and chemical tracers. The aquitard system consists of about 9 m of fine-grained oxidized pre-Illinoian till overlying 22 m of unoxidized till and Devonian dolomite bedrock. Hydraulic conductivity ranged from 10-7 m/s in oxidized till and 10-10 m/s in unoxidized till. Hydraulic head relations indicated downward groundwater flow through the till profile with hydraulic gradients steepest near the unoxidized till/bedrock interface. Tritium and nitrate concentrations indicated recent (< 50 years old) recharge to a depth of 9-12 m below land surface. 18O and 2H results ranged between -6.2 to -7.9% and -38.0 to -50.9%, respectively, and plotted near the local Meteoric Water Line. A 1 per mil shift toward less negative 18O values with depth may suggest a climate change signal contained in the till water but more data are needed to verify this trend. Vertical groundwater velocity through the unoxidized till was estimated to range from 0.4 to 5.7 cm/year. The thickness of unoxidized pre-Illinoian till in Linn County was estimated from available records and contoured against vertical travel times to evaluate the effectiveness of pre-Illinoian till in preventing nitrate migration to underlying bedrock aquifers.

Schilling, K. E.; Tassier-Surine, S.

2006-09-01

379

Groundwater flow and velocity in a 500 ka pre-Illinoian till, eastern Iowa

Few hydrology studies have investigated glacial till older than Illinoian time (> 300,000 BP) despite these older tills overlying a large portion of North America. An 8- and 6-well monitoring well nest installed into a 31 m thick pre-Illinoian till sequence near Cedar Rapids, Iowa was characterized using traditional hydrologic methods and chemical tracers. The aquitard system consists of about 9 m of fine-grained oxidized pre-Illinoian till overlying 22 m of unoxidized till and Devonian dolomite bedrock. Hydraulic conductivity ranged from 10-7 m/s in oxidized till and 10-10 m/s in unoxidized till. Hydraulic head relations indicated downward groundwater flow through the till profile with hydraulic gradients steepest near the unoxidized till/bedrock interface. Tritium and nitrate concentrations indicated recent (< 50 years old) recharge to a depth of 9-12 m below land surface. 18O and 2H results ranged between -6.2 to -7.9% and -38.0 to -50.9%, respectively, and plotted near the local Meteoric Water Line. A 1 per mil shift toward less negative 18O values with depth may suggest a climate change signal contained in the till water but more data are needed to verify this trend. Vertical groundwater velocity through the unoxidized till was estimated to range from 0.4 to 5.7 cm/year. The thickness of unoxidized pre-Illinoian till in Linn County was estimated from available records and contoured against vertical travel times to evaluate the effectiveness of pre-Illinoian till in preventing nitrate migration to underlying bedrock aquifers. ?? Springer-Verlag 2006.

Schilling, K. E.; Tassier-Surine, S.

2006-01-01

380

NASA Astrophysics Data System (ADS)

Nitrate in drinking water causes health problems, and causes eutrophication. Miyakonojo basin is a well- known agricultural area in Southern Kyushu, Japan and highly depends on groundwater resources for everyday use. The detailed three dimensional groundwater flow system study has been done in the basin to understand the three dimensional distribution of Nitrate-Nitrogen in the aquifer. Field water sampling was conducted between Sep. 2006 and July 2007. The result suggests that the tributary river water mainly recharges to the shallow groundwater in the eastern part of the basin. On the other hand, the summer precipitation recharges the shallow groundwater which flows from upland down toward the river in the western part of the basin. This means that the shallow groundwater flow system is primarily affected by the surface geomorphology, which is completely different between eastern and western parts of the studied basin. For nitrate concentration, the shallow groundwater shows gradual increasing tendency along the flow line in the eastern part of the basin, while the nitrate concentration decreases and the reduction product increases along the flow in the western part. Especially in the western part of the basin, the major land use are the intensive cattle farming and dry farm land using artificial fertilizer, both are the potential sources of the nitrate for the local shallow groundwater. Also geomorphologic upland of the western part of the basin works as the recharge area of the shallow groundwater, and high concentration of nitrate is supplied at these areas. To understand this site-specific nitrate reduction process in the western basin, it is important to understand the nitrate origin and nitrogen process including denitrifcation process. For this, a multi-Isotope approach of dN and dO to tracing the sources of nitrate is applied in the study area with the relation of groundwater flow system. The field sampling was done in July 2007 and Sep. 2008 to analyze inorganic water chemistry, dD and d18O stable isotopes in water andd15N and d18O in Nitrate. We intend to report this result and related discussion at the meeting.

Mikami, K.; Shimada, J.; Tashiro, S.

2008-12-01

381

Low flow drainage from a river system, in the absence of precipitation or snowmelt, derives directly from the water stored\\u000a in the upstream aquifers in the basin; therefore, observations of the trends of the annual lowest flows can serve to deduce\\u000a quantitative estimates of the evolution of the basin-scale groundwater storage over the period of the streamflow record. Application\\u000a of

Wilfried Brutsaert

2010-01-01

382

The influence of human activities on the flow system and contamination of groundwater were investigated in Seoul City, South Korea, one of the largest Asian cities, using a combination of isotopes (deltaD, T, delta15N, delta18O, delta34S, and 87Sr/86Sr). Eighteen representative groundwater and river water samples, which were collected over a wide area of the city, were compared with previously reported data. The distribution of stable isotopes (deltaD and delta18O) with groundwater potential data shows that recharged groundwater from either the surrounding mountainous area as well as the Han River and other surface streams discharged towards the northern-central part of the city, where a subway tunnel pumping station is located. It is suggested from T values (3.3 to 5.8 T.U.) that groundwater was recharged in the last 30 to 40 years. The delta34S and delta15N of SO4(2-) and NO3- data were efficiently used as indicators of contamination by human activities. These isotopes clarified that the contribution of anthropogenic contaminants i.e., industrial and household effluents, waste landfills, and fertilizers, are responsible for the enrichment by SO4(2-) (>30 ppm as SO4(2-)) and NO3- (>20 ppm as NO3-) of groundwater. The 87Sr/86Sr values of groundwater vary (0.71326 to 0.75058) in accordance with the host rocks of different origins. Mineral elements such as Ca are also suggested to be derived naturally from rocks. The groundwater under Seoul City is greatly affected by transportation of pollutants along the groundwater flow controlled by subway tunnel pumping, contributing to the degradation of water quality in urbanized areas. PMID:18495214

Hosono, Takahiro; Ikawa, Reo; Shimada, Jun; Nakano, Takanori; Saito, Mitsuyo; Onodera, Shin-ichi; Lee, Kang-Kun; Taniguchi, Makoto

2008-05-20

383

STATISTICAL ESTIMATION AND VISUALIZATION OF GROUND-WATER CONTAMINATION DATA

This work presents methods of visualizing and animating statistical estimates of ground water and/or soil contamination over a region from observations of the contaminant for that region. The primary statistical methods used to produce the regional estimates are nonparametric re...

384

Seasonal Variability and Simulation of Groundwater Flow in a Prairie Wetland

NASA Astrophysics Data System (ADS)

Wetlands in regional discharge areas of the Red River Valley of eastern North Dakota provide runoff, flood protection and wildlife habitat. Two years of groundwater and soil water monitoring were used to characterize the hydrology of a 500 ha wetland 24 km north-west of Grand Forks. The objective was to describe, monitor and model important water budget processes. From November through March 1990 and 1991, the water-table dropped as water flowed towards frost in the vadose zone. Where saturated soils occurred near the surface, the water-table rose quickly in the spring. A later, larger rise occurred where the water-table and capillary fringe were deeper. During the summer, precipitation was rapidly depleted by evapotranspiration (ET). The low hydraulic conductivity of the clayey lacustrine sediments (0.1-2 m/yr) combined with a small horizontal hydraulic gradient results in minimal lateral and maximum vertical flow. The US Geological Survey MODFLOW code was used to simulate vertical saturated flow. By including actual ET (estimated from potential evaporation) and using the recharge option to represent vadose flow, the model provided good correspondence between observed and simulated hydrographs. These results suggest that a shallow vertical flow of ground and soil water dominates the hydrological budget. Simulation of unusually dry conditions, such as those experienced during the 1930s, indicates that water levels in the wetland would reach a steady-state about 0.3 m lower than normal within two to three years. Less winter vadose storage would decrease the water-level rise in spring and early summer, but would have a minimal impact on the overall yearly water budget.

Gerla, Philip J.; Matheney, Ronald K.

1996-07-01