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1

Estimation of Groundwater Flow Parameters Using Least Squares  

E-print Network

Estimation of Groundwater Flow Parameters Using Least Squares K.R. Bailey \\Lambda , B state flow parameters in a groundwater model. We test the approach on numerically generated data algorithm is implemented in parallel using PVM. 1 Introduction The successful modeling of groundwater flow

2

3PE: A Tool for Estimating Groundwater Flow Vectors  

EPA Science Inventory

Evaluation of hydraulic gradients and the associated groundwater flow rates and directions is a fundamental aspect of hydrogeologic characterization. Many methods, ranging in complexity from simple three-point solution techniques to complex numerical models of groundwater flow, ...

3

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

NASA Astrophysics Data System (ADS)

Estimation of groundwater recharge is extremely important for proper management of groundwater systems. Many different approaches exist for estimating recharge. The main purpose of this paper is to apply a water balance concept with two methods to estimate the groundwater recharge in the Ching-Shui watershed, Taiwan. First, a soil moisture budget method is established to estimate the infiltration, runoff, evapotranspiration, and groundwater recharge in the watershed, where the moisture content of the soil is tracked through time. Both soil-water properties of the unsaturated zone and climatic conditions must be fully considered. Second the base-flow model uses the base-flow separation from the total streamflow discharge to obtain a measure of groundwater recharge so that groundwater evapotranspiration is negligible. In contrast to the soil moisture budget method, base-flow estimation does not require complex hydrogeologic modeling and detailed knowledge of soil characteristics. In a previous study, we suggested that high base-flow is caused by rainstorm events. Using model analysis, depths of recharge estimated by stable-base-flow analysis are adopted to obtain more reasonable groundwater recharge values. The results indicate that assessment of the average annual recharge obtained with a soil moisture budget and the base-flow are very close; the ratio of the two methods is about 95.3%.

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

2008-06-01

4

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

Microsoft Academic Search

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

Using groundwater temperature data to constrain parameter estimation in a groundwater flow model of a wetland system  

USGS Publications Warehouse

Parameter estimation is a powerful way to calibrate models. While head data alone are often insufficient to estimate unique parameters due to model nonuniqueness, flow-and-heat-transport modeling can constrain estimation and allow simultaneous estimation of boundary fluxes and hydraulic conductivity. In this work, synthetic and field models that did not converge when head data were used did converge when head and temperature were used. Furthermore, frequency domain analyses of head and temperature data allowed selection of appropriate modeling timescales. Inflows in the Wilton, Wisconsin, wetlands could be estimated over periods such as a growing season and over periods of a few days when heads were nearly steady and groundwater temperature varied during the day. While this methodology is computationally more demanding than traditional head calibration, the results gained are unobtainable using the traditional approach. These results suggest that temperature can efficiently supplement head data in systems where accurate flux calibration targets are unavailable.

Bravo, H.R.; Jiang, F.; Hunt, R.J.

2002-01-01

6

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

Microsoft Academic Search

Quantitative evaluation of management strategies for long-term supply of safe groundwater for drinking from the Bengal Basin\\u000a aquifer (India and Bangladesh) requires estimation of the large-scale hydrogeologic properties that control flow. The Basin\\u000a consists of a stratified, heterogeneous sequence of sediments with aquitards that may separate aquifers locally, but evidence\\u000a does not support existence of regional confining units. Considered at

Holly A. Michael; Clifford I. Voss

2009-01-01

7

Estimated Ground-Water Withdrawals from the Death Valley Regional Flow System, Nevada and California, 1913-98  

USGS Publications Warehouse

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

8

Relative efficiency of four parameter-estimation methods in steady-state and transient ground-water flow models  

USGS Publications Warehouse

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

9

Hydraulic-property estimates for use with a transient ground-water flow model of the Death Valley regional ground-water flow system, Nevada and California  

SciTech Connect

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

10

Hydraulic-property estimates for use with a transient ground-water flow model of the Death Valley regional ground-water flow system, Nevada and California  

USGS Publications Warehouse

The Death Valley regional ground-water flow system encompasses an area of about 43,500 square kilometers in southeastern California and southern Nevada, between latitudes 35? and 38?15' north and longitudes 115? and 117?45' west. 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.

Belcher, Wayne R.; Elliott, Peggy E.; Geldon, Arthur L.

2001-01-01

11

Groundwater Flow Model  

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.

Alex Manda

12

Estimation of groundwater consumption by phreatophytes using diurnal water table fluctuations: A saturated-unsaturated flow assessment  

USGS Publications Warehouse

Groundwater consumption by phreatophytes is a difficult-to-measure but important component of the water budget in many arid and semiarid environments. Over the past 70 years the consumptive use of groundwater by phreatophytes has been estimated using a method that analyzes diurnal trends in hydrographs from wells that are screened across the water table (White, 1932). The reliability of estimates obtained with this approach has never been rigorously evaluated using saturated-unsaturated flow simulation. We present such an evaluation for common flow geometries and a range of hydraulic properties. Results indicate that the major source of error in the White method is the uncertainty in the estimate of specific yield. Evapotranspirative consumption of groundwater will often be significantly overpredicted with the White method if the effects of drainage time and the depth to the water table on specific yield are ignored. We utilize the concept of readily available specific yield as the basis for estimation of the specific yield value appropriate for use with the White method. Guidelines are defined for estimating readily available specific yield based on sediment texture. Use of these guidelines with the White method should enable the evapotranspirative consumption of groundwater to be more accurately quantified. Copyright 2005 by the American Geophysical Union.

Loheide, S.P., II; Butler, J.J., Jr.; Gorelick, S.M.

2005-01-01

13

Death Valley regional groundwater flow model calibration using optimal parameter estimation methods and geoscientific information systems  

USGS Publications Warehouse

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

14

Ground-water discharge determined from estimates of evapotranspiration, Death Valley regional flow system, Nevada and California  

USGS Publications Warehouse

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

15

Scarce data in hydrology and hydrogeology: Estimation and modelling of groundwater recharge for a numerical groundwater flow model in a semi-arid to arid catchment  

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

16

Estimation of groundwater use for a groundwater-flow model of the Lake Michigan Basin and adjacent areas, 1864-2005  

USGS Publications Warehouse

The U.S. Geological Survey, at the request of Congress, is assessing the availability and use of the Nation's water resources to help characterize how much water is available now, how water availability is changing, and how much water can be expected to be available in the future. The Great Lakes Basin Pilot project of the U.S. Geological Survey national assessment of water availability and use focused on the Great Lakes Basin and included detailed studies of the processes governing water availability in the Great Lakes Basin. One of these studies included the development of a groundwater-flow model of the Lake Michigan Basin. This report describes the compilation and estimation of the groundwater withdrawals in those areas in Wisconsin, Michigan, Indiana, and Illinois that were needed for the Lake Michigan Basin study groundwater-flow model. These data were aggregated for 12 model time intervals spanning 1864 to 2005 and were summarized by model area, model subregion, category of water use, aquifer system, aquifer type, and hydrogeologic unit model layer. The types and availability of information on groundwater withdrawals vary considerably among states because water-use programs often differ in the types of data collected and in the methods and frequency of data collection. As a consequence, the methods used to estimate and verify the data also vary. Additionally, because of the different sources of data and different terminologies applied for the purposes of this report, the water-use data published in this report may differ from water-use data presented in other reports. These data represent only a partial estimate of groundwater use in each state because estimates were compiled only for areas in Wisconsin, Michigan, Indiana, and Illinois within the Lake Michigan Basin model area. Groundwater-withdrawal data were compiled for both nearfield and farfield model areas in Wisconsin and Illinois, whereas these data were compiled primarily for the nearfield model area in Michigan and Indiana. Overall water use for the selected areas in Wisconsin, Michigan, Indiana, and Illinois was less during early time intervals than during more recent intervals, with large increases beginning around the 1960s. Total estimated groundwater withdrawals for model input range from 18.01 million gallons per day (Mgal/d) for interval 1 (1864-1900) to 1,280.25 Mgal/d for interval 12 (2001-5). Withdrawals for the public-supply category make up the majority of the withdrawals in each of the four states. In Wisconsin and Michigan, the second largest withdrawals are for the irrigation category; in Indiana and Illinois, industrial withdrawals account for the second largest withdrawal amounts. The smallest withdrawals are for miscellaneous uses in Wisconsin and irrigation uses in Indiana and Illinois. Estimated groundwater withdrawals in the Southern Lower Peninsula of Michigan, Northeastern Illinois, and the farfield model area are generally larger than in the other model subregions. Withdrawals in Michigan and Indiana are predominantly from the Quaternary aquifer system, whereas withdrawals in Illinois are predominantly from the Cambrian-Ordovician aquifer systems. Withdrawals in Wisconsin are about equal from the Quaternary and Cambrian-Ordovician aquifer systems. Estimated groundwater withdrawals in Michigan and Indiana are predominantly from the unconfined unconsolidated aquifer type. Withdrawals in Illinois are largely from the deep confined bedrock aquifer type, although they decreased considerably in more recent time intervals. Wisconsin withdrawals are about equal from unconfined unconsolidated and deep confined bedrock aquifer types. Groundwater-withdrawal estimates in Wisconsin were compiled for the 47 easternmost counties within the boundary of the Lake Michigan Basin model, of which 32 counties, though not entirely contained, are at least partly within the Lake Michigan Basin. Overall, 6,457 withdrawal locations were estima

Buchwald, Cheryl A.; Luukkonen, Carol L.; Rachol, Cynthia M.

2010-01-01

17

Global scale groundwater flow model  

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

18

A Basin-Averaged Water Balance Approach to Estimate Catchment-Scale Groundwater Flow in a Semi-arid Mountainous Catchment  

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

19

Ground-water system, estimation of aquifer hydraulic properties, and effects of pumping on ground-water flow in Triassic sedimentary rocks in and near Lansdale, Pennsylvania  

USGS Publications Warehouse

Ground water in Triassic-age sedimentary fractured-rock aquifers in the area of Lansdale, Pa., is used as drinking water and for industrial supply. In 1979, ground water in the Lansdale area was found to be contaminated with trichloroethylene, tetrachloroethylene, and other man-made organic compounds, and in 1989, the area was placed on the U.S. Environmental Protection Agency's (USEPA) National Priority List as the North Penn Area 6 site. To assist the USEPA in the hydrogeological assessment of the site, the U.S. Geological Survey began a study in 1995 to describe the ground-water system and to determine the effects of changes in the well pumping patterns on the direction of ground-water flow in the Lansdale area. This determination is based on hydrologic and geophysical data collected from 1995-98 and on results of the simulation of the regional ground-water-flow system by use of a numerical model.Correlation of natural-gamma logs indicate that the sedimentary rock beds strike generally northeast and dip at angles less than 30 degrees to the northwest. The ground-water system is confined or semi-confined, even at shallow depths; depth to bedrock commonly is less than 20 feet (6 meters); and depth to water commonly is about 15 to 60 feet (5 to 18 meters) below land surface. Single-well, aquifer-interval-isolation (packer) tests indicate that vertical permeability of the sedimentary rocks is low. Multiple-well aquifer tests indicate that the system is heterogeneous and that flow appears primarily in discrete zones parallel to bedding. Preferred horizontal flow along strike was not observed in the aquifer tests for wells open to the pumped interval. Water levels in wells that are open to the pumped interval, as projected along the dipping stratigraphy, are drawn down more than water levels in wells that do not intersect the pumped interval. A regional potentiometric map based on measured water levels indicates that ground water flows from Lansdale towards discharge areas in three drainages, the Wissahickon, Towamencin, and Neshaminy Creeks.Ground-water flow was simulated for different pumping patterns representing past and current conditions. The three-dimensional numerical flow model (MODFLOW) was automatically calibrated by use of a parameter estimation program (MODFLOWP). Steady-state conditions were assumed for the calibration period of 1996. Model calibration indicates that estimated recharge is 8.2 inches (208 millimeters) and the regional anisotropy ratio for the sedimentary-rock aquifer is about 11 to 1, with permeability greatest along strike. The regional anisotropy is caused by up- and down-dip termination of high-permeability bed-oriented features, which were not explicitly simulated in the regional-scale model. The calibrated flow model was used to compare flow directions and capture zones in Lansdale for conditions corresponding to relatively high pumping rates in 1994 and to lower pumping rates in 1997. Comparison of the 1994 and 1997 simulations indicates that wells pumped at the lower 1997 rates captured less ground water from known sites of contamination than wells pumped at the 1994 rates. Ground-water flow rates away from Lansdale increased as pumpage decreased in 1997.A preliminary evaluation of the relation between ground-water chemistry and conditions favorable for the degradation of chlorinated solvents was based on measurements of dissolved-oxygen concentration and other chemical constituents in water samples from 92 wells. About 18 percent of the samples contained less than or equal to 5 milligrams per liter dissolved oxygen, a concentration that indicates reducing conditions favorable for degradation of chlorinated solvents.

Senior, Lisa A.; Goode, Daniel J.

1999-01-01

20

U.S. Geological Survey groundwater toolbox, a graphical and mapping interface for analysis of hydrologic data (version 1.0): user guide for estimation of base flow, runoff, and groundwater recharge from streamflow data  

USGS Publications Warehouse

This report is a user guide for the streamflow-hydrograph analysis methods provided with version 1.0 of the U.S. Geological Survey (USGS) Groundwater Toolbox computer program. These include six hydrograph-separation methods to determine the groundwater-discharge (base-flow) and surface-runoff components of streamflow—the Base-Flow Index (BFI; Standard and Modified), HYSEP (Fixed Interval, Sliding Interval, and Local Minimum), and PART methods—and the RORA recession-curve displacement method and associated RECESS program to estimate groundwater recharge from streamflow data. The Groundwater Toolbox is a customized interface built on the nonproprietary, open source MapWindow geographic information system software. The program provides graphing, mapping, and analysis capabilities in a Microsoft Windows computing environment. In addition to the four hydrograph-analysis methods, the Groundwater Toolbox allows for the retrieval of hydrologic time-series data (streamflow, groundwater levels, and precipitation) from the USGS National Water Information System, downloading of a suite of preprocessed geographic information system coverages and meteorological data from the National Oceanic and Atmospheric Administration National Climatic Data Center, and analysis of data with several preprocessing and postprocessing utilities. With its data retrieval and analysis tools, the Groundwater Toolbox provides methods to estimate many of the components of the water budget for a hydrologic basin, including precipitation; streamflow; base flow; runoff; groundwater recharge; and total, groundwater, and near-surface evapotranspiration.

Barlow, Paul M.; Cunningham, William L.; Zhai, Tong; Gray, Mark

2015-01-01

21

Coupled Modeling of Self Potential and Groundwater Flow to Estimate Permeability Structure of the Elkhorn Fault, South Park, Colorado  

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

22

Groundwater-flow parameter estimation and quality modeling of the Equus Beds aquifer in Kansas, U.S.A.  

USGS Publications Warehouse

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 of Wichita, Kansas. In this paper, an attempt is made to predict where and how fast the brine plume will move in this area, and what the average chloride concentrations in different parts of the aquifer are. In order to make such predictions, it was necessary to get a calibrated model of the groundwater-flow velocity field. Multiple regression analysis is used for parameter estimation of the steady-state groundwater-flow equation applied in the most critical area of the Equus Beds aquifer. Results of such an analysis produced a correlation coefficient of 0.992 between calculated and observed values of hydraulic head. A chloride transport modeling effort is then carried out despite some serious data deficiencies, the significance of which are evaluated through sensitivity analysis. Thus, starting with the quasi steady-state conditions of the early 1940's, it was possible to match the present chloride distribution satisfactorily. Chloride concentration predictions made for the year 2000 indicate that the quality of the Wichita well-field waters will not generally deteriorate from their present condition by that time. ?? 1984.

Sophocleous, M.A.

1984-01-01

23

Ground-water pumpage and artificial recharge estimates for calendar year 2000 and average annual natural recharge and interbasin flow by hydrographic area, Nevada  

USGS Publications Warehouse

Nevada's reliance on ground-water resources has increased because of increased development and surface-water resources being fully appropriated. The need to accurately quantify Nevada's water resources and water use is more critical than ever to meet future demands. Estimated ground-water pumpage, artificial and natural recharge, and interbasin flow can be used to help evaluate stresses on aquifer systems. In this report, estimates of ground-water pumpage and artificial recharge during calendar year 2000 were made using data from a variety of sources, such as reported estimates and estimates made using Landsat satellite imagery. Average annual natural recharge and interbasin flow were compiled from published reports. An estimated 1,427,100 acre-feet of ground water was pumped in Nevada during calendar year 2000. This total was calculated by summing six categories of ground-water pumpage, based on water use. Total artificial recharge during 2000 was about 145,970 acre-feet. At least one estimate of natural recharge was available for 209 of the 232 hydrographic areas (HAs). Natural recharge for the 209 HAs ranges from 1,793,420 to 2,583,150 acre-feet. Estimates of interbasin flow were available for 151 HAs. The categories and their percentage of the total ground-water pumpage are irrigation and stock watering (47 percent), mining (26 percent), water systems (14 percent), geothermal production (8 percent), self-supplied domestic (4 percent), and miscellaneous (less than 1 percent). Pumpage in the top 10 HAs accounted for about 49 percent of the total ground-water pumpage. The most ground-water pumpage in an HA was due to mining in Pumpernickel Valley (HA 65), Boulder Flat (HA 61), and Lower Reese River Valley (HA 59). Pumpage by water systems in Las Vegas Valley (HA 212) and Truckee Meadows (HA 87) were the fourth and fifth highest pumpage in 2000, respectively. Irrigation and stock watering pumpage accounted for most ground-water withdrawals in the HAs with the sixth through ninth highest pumpage. Geothermal production accounted for most pumpage in the Carson Desert (HA 101). Reinjection of ground water pumped for geothermal energy production accounted for about 64 percent (93,310 acre-feet) of the total artificial recharge. The only artificial recharge by water systems was in Las Vegas Valley, where 29,790 acre-feet of water from the Colorado River was injected into the aquifer system. Artificial recharge by mining totaled 22,870 acre-feet. Net ground-water flow was estimated only for the 143 HAs with available estimates of both natural recharge and interbasin flow. Of the 143 estimates, 58 have negative net ground-water flow, indicating that ground-water storage could be depleted if pumpage continues at the same rate. The State has designated HAs where permitted ground-water rights approach or exceed the estimated average annual recharge. Ten HAs were identified that are not designated and have a net ground-water flow between -1,000 to -35,000 acre-feet. Due to uncertainties in recharge, the water budgets for these HAs may need refining to determine if ground-water storage is being depleted.

Lopes, Thomas J.; Evetts, David M.

2004-01-01

24

Ground-water and surface-water flow and estimated water budget for Lake Seminole, southwestern Georgia and northwestern Florida  

USGS Publications Warehouse

Lake Seminole is a 37,600-acre impoundment formed at the confluence of the Flint and Chattahoochee Rivers along the Georgia?Florida State line. Outflow from Lake Seminole through Jim Woodruff Lock and Dam provides headwater to the Apalachicola River, which is a major supply of freshwater, nutrients, and detritus to ecosystems downstream. These rivers,together with their tributaries, are hydraulically connected to karst limestone units that constitute most of the Upper Floridan aquifer and to a chemically weathered residuum of undifferentiated overburden. The ground-water flow system near Lake Seminole consists of the Upper Floridan aquifer and undifferentiated overburden. The aquifer is confined below by low-permeability sediments of the Lisbon Formation and, generally, is semiconfined above by undifferentiated overburden. Ground-water flow within the Upper Floridan aquifer is unconfined or semiconfined and discharges at discrete points by springflow or diffuse leakage into streams and other surface-water bodies. The high degree of connectivity between the Upper Floridan aquifer and surface-water bodies is limited to the upper Eocene Ocala Limestone and younger units that are in contact with streams in the Lake Seminole area. The impoundment of Lake Seminole inundated natural stream channels and other low-lying areas near streams and raised the water-level altitude of the Upper Floridan aquifer near the lake to nearly that of the lake, about 77 feet. Surface-water inflow from the Chattahoochee and Flint Rivers and Spring Creek and outflow to the Apalachicola River through Jim Woodruff Lock and Dam dominate the water budget for Lake Seminole. About 81 percent of the total water-budget inflow consists of surface water; about 18 percent is ground water, and the remaining 1 percent is lake precipitation. Similarly, lake outflow consists of about 89 percent surface water, as flow to the Apalachicola River through Jim Woodruff Lock and Dam, about 4 percent ground water, and about 2 percent lake evaporation. Measurement error and uncertainty in flux calculations cause a flow imbalance of about 4 percent between inflow and outflow water-budget components. Most of this error can be attributed to errors in estimating ground-water discharge from the lake, which was calculated using a ground-water model calibrated to October 1986 conditions for the entire Apalachicola?Chattahoochee?Flint River Basin and not just the area around Lake Seminole. Evaporation rates were determined using the preferred, but mathematically complex, energy budget and five empirical equations: Priestley-Taylor, Penman, DeBruin-Keijman, Papadakis, and the Priestley-Taylor used by the Georgia Automated Environmental Monitoring Network. Empirical equations require a significant amount of data but are relatively easy to calculate and compare well to long-term average annual (April 2000?March 2001) pan evaporation, which is 65 inches. Calculated annual lake evaporation, for the study period, using the energy-budget method was 67.2 inches, which overestimated long-term average annual pan evaporation by 2.2 inches. The empirical equations did not compare well with the energy-budget method during the 18-month study period, with average differences in computed evaporation using each equation ranging from 8 to 26 percent. The empirical equations also compared poorly with long-term average annual pan evaporation, with average differences in evaporation ranging from 3 to 23 percent. Energy budget and long-term average annual pan evaporation estimates did compare well, with only a 3-percent difference between estimates. Monthly evaporation estimates using all methods ranged from 0.7 to 9.5 inches and were lowest during December 2000 and highest during May 2000. Although the energy budget is generally the preferred method, the dominance of surface water in the Lake Seminole water budget makes the method inaccurate and difficult to use, because surface water makes up m

Dalton, Melinda S.; Aulenbach, Brent T.; Torak, Lynn J.

2004-01-01

25

Gradual Variation Analysis for Groundwater Flow  

E-print Network

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 the aquifer has a recharging boundary. The practical way of calculation is to use numerical methods to solve these equations. The most popular system is called MODFLOW, which was developed by USGS. MODFLOW is based on the finite-difference method in rectangular Cartesian coordinates. MODFLOW can be viewed as a "quasi 3D" simulation since it only deals with the vertical average (no z-direction derivative). Flow calculations between the 2D horizontal layers use the concept of leakage. In this project, we have established a mathematical model based on gradually varied functions for groundwater data volume reconstruction. T...

Chen, Li

2010-01-01

26

Monitoring probe for groundwater flow  

DOEpatents

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

27

Monitoring probe for groundwater flow  

DOEpatents

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

28

Challenges to estimate surface- and groundwater flow in arid regions: the Dead Sea catchment.  

PubMed

The overall aim of the this study, which was conducted within the framework of the multilateral IWRM project SUMAR, was to expand the scientific basement to quantify surface- and groundwater fluxes towards the hypersaline Dead Sea. The flux significance for the arid vicinity around the Dead Sea is decisive not only for a sustainable management in terms of water availability for future generations but also for the resilience of the unique ecosystems along its coast. Coping with different challenges interdisciplinary methods like (i) hydrogeochemical fingerprinting, (ii) satellite and airborne-based thermal remote sensing, (iii) direct measurement with gauging station in ephemeral wadis and a first multilateral gauging station at the river Jordan, (iv) hydro-bio-geochemical approach at submarine and shore springs along the Dead Sea and (v) hydro(geo)logical modelling contributed to the overall aim. As primary results, we deduce that the following: (i) Within the drainage basins of the Dead Sea, the total mean annual precipitation amounts to 300 mm a(?1) west and to 179 mm a(?1) east of the lake, respectively. (ii) The total mean annual runoff volumes from side wadis (except the Jordan River) entering the Dead Sea is approximately 58–66 × 10(6) m(3) a(?1) (western wadis: 7–15 × 10(6) m(3) a(?1); eastern wadis: 51 × 10(6) m(3) a(?1)). (iii) The modelled groundwater discharge from the upper Cretaceous aquifers in both flanks of the Dead Sea towards the lake amounts to 177 × 10(6) m(3) a(?1). (iv) An unexpected abundance of life in submarine springs exists, which in turn explains microbial moderated geo-bio-chemical processes in the Dead Sea sediments, affecting the highly variable chemical composition of on- and offshore spring waters.The results of this work show a promising enhancement of describing and modelling the Dead Sea basin as a whole. PMID:24767316

Siebert, Christian; Rödiger, Tino; Mallast, Ulf; Gräbe, Agnes; Guttman, Joseph; Laronne, Jonathan B; Storz-Peretz, Yael; Greenman, Anat; Salameh, Elias; Al-Raggad, Marwan; Vachtman, Dina; Ben Zvi, Arie; Ionescu, Danny; Brenner, Asher; Merz, Ralf; Geyer, Stefan

2014-07-01

29

Groundwater flow modeling of two-levels perched karstic leaking aquifers as a tool for estimating recharge and hydraulic parameters  

NASA Astrophysics Data System (ADS)

SummaryPerched springs in nature emerge from aquifers laying on aquitards within the unsaturated zone, some of which emerge one above the other. A finite element model was introduced, using the FEFLOW code, for simulating the groundwater flow regime in each of these aquifers, for quantifying the fraction of rain that recharges the aquifers, and for estimating the hydrogeological parameters of the aquifers and aquitards. Many of the perched springs in Israel are found in the Judea Group aquifer, a stratified carbonate rock unit, characterised by a well-developed karst system. The Batir and Jamia springs exemplifies such a system, where Batir is the upper spring discharging at the contact between Aminadav and Moza Formations, and Jamia is the lower one, discharging at the contact between Kesalon and Sorek Formations. The 25-year-long measured spring's hydrographs were used to calibrate the spring's coefficients, the hydraulic conductivities of the different layers, the karst features and the yearly amount of rain recharging the spring.

Peleg, Nadav; Gvirtzman, Haim

2010-06-01

30

Death valley regional ground-water flow model calibration using optimal parameter estimation methods and geoscientific information systems  

USGS Publications Warehouse

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

31

A numerical modelling and neural network approach to estimate the impact of groundwater abstractions on river flows  

NASA Astrophysics Data System (ADS)

SummaryEvaluation of the impacts of groundwater abstractions on surface water systems is a necessary task in integrated water resources management. A range of hydrological, hydrogeological, and geomorphological factors influence the complex processes of interaction between groundwater and rivers. This paper presents an approach which uses numerical modeling of generic river-aquifer systems to represent the interaction processes, and neural networks to capture the impacts of the different controlling factors. The generic models describe hydrogeological settings representing most river-aquifer systems in England and Wales: high diffusivity (e.g. Chalk) and low diffusivity (e.g. Triassic Sandstone) aquifers with flow to rivers mediated by alluvial gravels; the same aquifers where they are in direct connection with the river; and shallow alluvial aquifers which are disconnected from regional aquifers. Numerical model simulations using the SHETRAN integrated catchment modeling system provided outputs including time-series and spatial variations in river flow depletion, and spatially distributed groundwater levels. Artificial neural network models were trained using input parameters describing the controlling factors and the outputs from the numerical model simulations, providing an efficient tool for representing the impacts of groundwater abstractions across a wide range of conditions. There are very few field data sets of accurately quantified river flow depletion as a result of groundwater abstraction under controlled conditions. One such data set from an experimental study carried out in 1967 on the Winterbourne stream in the Lambourne catchment over a Chalk aquifer was used successfully to test the modeling tool. This modeling approach provides a general methodology for rapid simulations of complex hydrogeological systems which preserves the physical consistency between multiple and diverse model outputs.

Parkin, G.; Birkinshaw, S. J.; Younger, P. L.; Rao, Z.; Kirk, S.

2007-06-01

32

Effects of wetlands creation on groundwater flow  

USGS Publications Warehouse

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

33

Estimates of tracer-based piston-flow ages of groundwater from selected sites-National Water-Quality Assessment Program, 1992-2005  

USGS Publications Warehouse

This report documents selected age data interpreted from measured concentrations of environmental tracers in groundwater from 1,399 National Water-Quality Assessment (NAWQA) Program groundwater sites across the United States. The tracers of interest were chlorofluorocarbons (CFCs), sulfur hexafluoride (SF6), and tritium/helium-3 (3H/3He). Tracer data compiled for this analysis primarily were from wells representing two types of NAWQA groundwater studies - Land-Use Studies (shallow wells, usually monitoring wells, in recharge areas under dominant land-use settings) and Major-Aquifer Studies (wells, usually domestic supply wells, in principal aquifers and representing the shallow, used resource). Reference wells (wells representing groundwater minimally impacted by anthropogenic activities) associated with Land-Use Studies also were included. Tracer samples were collected between 1992 and 2005, although two networks sampled from 2006 to 2007 were included because of network-specific needs. Tracer data from other NAWQA Program components (Flow System Studies, which are assessments of processes and trends along groundwater flow paths, and various topical studies) were not compiled herein. Tracer data from NAWQA Land-Use Studies and Major-Aquifer Studies that previously had been interpreted and published are compiled herein (as piston-flow ages), but have not been reinterpreted. Tracer data that previously had not been interpreted and published are evaluated using documented methods and compiled with aqueous concentrations, equivalent atmospheric concentrations (for CFCs and SF6), estimates of tracer-based piston-flow ages, and selected ancillary data, such as redox indicators, well construction, and major dissolved gases (N2, O2, Ar, CH4, and CO2). Tracer-based piston-flow ages documented in this report are simplistic representations of the tracer data. Tracer-based piston-flow ages are a convenient means of conceptualizing groundwater age. However, the piston-flow model is based on the potentially limiting assumptions that tracer transport is advective and that no mixing occurs. Additional uncertainties can arise from tracer degradation, sorption, contamination, or fractionation; terrigenic (natural) sources of tracers; spatially variable atmospheric tracer concentrations; and incomplete understanding of mechanisms of recharge or of the conditions under which atmospheric tracers were partitioned to recharge. The effects of some of these uncertainties are considered herein. For example, degradation, contamination, or fractionation often can be identified or inferred. However, detailed analysis of the effects of such uncertainties on the tracer-based piston-flow ages is constrained by sparse data and an absence of complementary lines of evidence, such as detailed solute transport simulations. Thus, the tracer-based piston-flow ages compiled in this report represent only an initial interpretation of the tracer data.

Hinkle, Stephen R.; Shapiro, Stephanie D.; Plummer, L. Niel; Busenberg, Eurybiades; Widman, Peggy K.; Casile, Gerolamo C.; Wayland, Julian E.

2011-01-01

34

Groundwater Flow in the Ganges Delta  

E-print Network

Groundwater Flow in the Ganges Delta Basu et al. (1) reported that 2 1011 m3 /year of groundwater groundwater than in Ganges-Brahmaputra river water. The flow could also have impli- cations for the origin and fate of other groundwater constituents in the Ganges delta that could be flushed by such rapid regional

Entekhabi, Dara

35

A tidal creek water budget: Estimation of groundwater discharge and overland flow using hydrologic modeling in the Southern Everglades  

NASA Astrophysics Data System (ADS)

Taylor Slough is one of the natural freshwater contributors to Florida Bay through a network of microtidal creeks crossing the Everglades Mangrove Ecotone Region (EMER). The EMER ecological function is critical since it mediates freshwater and nutrient inputs and controls the water quality in Eastern Florida Bay. Furthermore, this region is vulnerable to changing hydrodynamics and nutrient loadings as a result of upstream freshwater management practices proposed by the Comprehensive Everglades Restoration Program (CERP), currently the largest wetland restoration project in the USA. Despite the hydrological importance of Taylor Slough in the water budget of Florida Bay, there are no fine scale (˜1 km 2) hydrodynamic models of this system that can be utilized as a tool to evaluate potential changes in water flow, salinity, and water quality. Taylor River is one of the major creeks draining Taylor Slough freshwater into Florida Bay. We performed a water budget analysis for the Taylor River area, based on long-term hydrologic data (1999-2007) and supplemented by hydrodynamic modeling using a MIKE FLOOD (DHI, http://dhigroup.com/) model to evaluate groundwater and overland water discharges. The seasonal hydrologic characteristics are very distinctive (average Taylor River wet vs. dry season outflow was 6 to 1 during 1999-2006) with a pronounced interannual variability of flow. The water budget shows a net dominance of through flow in the tidal mixing zone, while local precipitation and evapotranspiration play only a secondary role, at least in the wet season. During the dry season, the tidal flood reaches the upstream boundary of the study area during approximately 80 days per year on average. The groundwater field measurements indicate a mostly upwards-oriented leakage, which possibly equals the evapotranspiration term. The model results suggest a high importance of groundwater contribution to the water salinity in the EMER. The model performance is satisfactory during the dry season where surface flow in the area is confined to the Taylor River channel. The model also provided guidance on the importance of capturing the overland flow component, which enters the area as sheet flow during the rainy season. Overall, the modeling approach is suitable to reach better understanding of the water budget in the mangrove region. However, more detailed field data is needed to ascertain model predictions by further calibrating overland flow parameters.

Michot, Béatrice; Meselhe, Ehab A.; Rivera-Monroy, Victor H.; Coronado-Molina, Carlos; Twilley, Robert R.

2011-07-01

36

Groundwater flow into Lake Michigan from Wisconsin  

USGS Publications Warehouse

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

37

Geothermal properties and groundwater flow estimated with a three-dimensional geological model in a late Pleistocene terrace area, central Japan  

NASA Astrophysics Data System (ADS)

1. Introduction The ground source heat pump (GSHP) is a highly efficient and renewable energy technology for space heating and cooling, with benefits that include energy conservation and reductions in greenhouse gas emissions. One result of the huge Tohoku-oki earthquake and tsunami and the subsequent nuclear disasters is that GSHPs are receiving more attention from the media and they are being introduced by some local governments. Heat generated by underground GSHP installation, however, can pollute the geothermal environment or change groundwater flow patterns . In this study, we estimated possible effects from the use of GSHPs in the Tokyo area with a three-dimensional (3D) geological model. 2. Geological model The Tokyo Metropolitan Area is surrounded by the Late Pleistocene terraces called the Musashino uplands. The terrace surfaces are densely populated residential areas. One of these surfaces, the Shimosueyohi surface, formed along the Tama River during the last deglacial period. The CRE-NUCHS-1 core (Funabiki et al., 2011) was obtained from this surface, and the lithology, heat transfer coefficients, and chemical characteristics of the sediments were analyzed. In this study, we used borehole log data from a 5 km2 area surrounding the CRE-NUCHS-1 core site to create a 3D geological model. In this area, the Pleistocene Kazusa Group is overlain by terrace gravels and a volcanic ash layer called the Kanto Loam. The terrace gravels occur mainly beneath the Kanda, Kitazawa, and Karasuyama rivers , which flow parallel to the Tama River, whereas away from the rivers , the Kanto Loam directly overlies the Kazusa Group sediments. 3. Geothermal disturbance and groundwater flow Using the geological model, we calculated the heat transfer coefficients and groundwater flow velocities in the sediments. Within the thick terrace gravels, which are at relatively shallow depth (8-20 m), heat transfer coefficients were high and groundwater flow was relatively fast. The amount of disturbance of the geothermal environment and groundwater flow caused by the use of GSHPs, therefore, would depend on the thickness of these gravels. Reference Funabiki, A., Nagoya, K., Kaneki, A., Uemura, K., Kurihara, M., Obara, H., Goto, A., Chiba, T., Naya, T., Ueki, T., and Takemura, T. (2011) Sedimentary facies and physical properties of the sediment core CRE-NUCHS-1 in Setagaya district, Tokyo, central Japan. Abstracts, The 118th Annual Meeting of theGeological Society of Japan. Acknowledgement This work was supported by the Core Research for Evolutional Science and Technology (CREST) program of the Japan Science and Technology Agency (JST).

Funabiki, A.; Takemura, T.; Hamamoto, S.; Komatsu, T.

2012-12-01

38

Groundwater flow across spatial scales: importance for climate modeling  

NASA Astrophysics Data System (ADS)

Current regional and global climate models generally do not represent groundwater flow between grid cells as a component of the water budget. We estimate the magnitude of between-cell groundwater flow as a function of grid cell size by aggregating results from a numerical model of equilibrium groundwater flow run and validated globally. We find that over a broad range of cell sizes spanning that of state-of-the-art regional and global climate models, mean between-cell groundwater flow magnitudes scale with the reciprocal of grid cell length. We also derive this scaling a priori from a simple statistical model of a flow network. We offer operational definitions of ‘significant’ groundwater flow contributions to the grid cell water budget in both relative and absolute terms (between-cell flow magnitude exceeding 10% of local recharge or 10 mm y-1, respectively). Groundwater flow is a significant part of the water budget, as measured by a combined test requiring both relative and absolute significance, over 42% of the land area at 0.1° grid cell size (typical of regional and mesoscale models), decreasing to 1.5% at 1° (typical of global models). Based on these findings, we suggest that between-cell groundwater flow should be represented in regional and mesoscale climate models to ensure realistic water budgets, but will have small effects on water exchanges in current global models. As well, parameterization of subgrid moisture heterogeneity should include the effects of within-cell groundwater flow.

Krakauer, Nir Y.; Li, Haibin; Fan, Ying

2014-03-01

39

Regionally compartmented groundwater flow on Mars  

Microsoft Academic Search

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

40

GROUNDWATER FLOW MODELS C. P. Kumar  

E-print Network

GROUNDWATER FLOW MODELS C. P. Kumar Scientist `E1' National Institute of Hydrology Roorkee ­ 247667 (Uttaranchal) 1.0 INTRODUCTION The use of groundwater models is prevalent in the field of environmental science, groundwater models are being applied to predict the transport of contaminants for risk evaluation. In general

Kumar, C.P.

41

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.

42

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

USGS Publications Warehouse

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

: Belcher, Wayne R., (Edited By); Sweetkind, Donald S.

2010-01-01

43

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.

C.J. Hemker

44

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

USGS Publications Warehouse

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

: Belcher, Wayne R., (Edited By)

2004-01-01

45

New analytical solution for sizing vertical borehole ground heat exchangers in environments with significant groundwater flow: Parameter estimation from thermal response test data  

Microsoft Academic Search

Accurate prediction of transient subsurface heat transfer is important in sizing ground heat exchangers in ground coupled heat pump systems. This article examines three analytical solutions for the heat transfer characteristics around closed-loop borehole heat exchangers in significant groundwater flow. The first solution is the so-called moving line source solution, the second is based on the groundwater g-function, and the

Andrew Chiasson; Amanda O’Connell

2011-01-01

46

Influence of perched groundwater on base flow  

USGS Publications Warehouse

Analysis with a three-dimensional variably saturated groundwater flow model provides a basic understanding of the interplay between streams and perched groundwater. A simplified, layered model of heterogeneity was used to explore these relationships. Base flow contribution from perched groundwater was evaluated with regard to varying hydrogeologic conditions, including the size and location of the fine-sediment unit and the hydraulic conductivity of the fine-sediment unit and surrounding coarser sediment. Simulated base flow was sustained by perched groundwater with a maximum monthly discharge in excess of 15 L/s (0.6 feet3/s) over the length of the 2000-m stream reach. Generally, the rate of perched-groundwater discharge to the stream was proportional to the hydraulic conductivity of sediment surrounding the stream, whereas the duration of discharge was proportional to the hydraulic conductivity of the fine-sediment unit. Other aspects of the perched aquifer affected base flow, such as the depth of stream penetration and the size of the fine-sediment unit. Greater stream penetration decreased the maximum base flow contribution but increased the duration of contribution. Perched groundwater provided water for riparian vegetation at the demand rate but reduced the duration of perched-groundwater discharge nearly 75%. Copyright 2008 by the American Geophysical Union.

Niswonger, R.G.; Fogg, G.E.

2008-01-01

47

Using groundwater levels to estimate recharge  

USGS Publications Warehouse

Accurate estimation of groundwater recharge is extremely important for proper management of groundwater systems. Many different approaches exist for estimating recharge. This paper presents a review of methods that are based on groundwater-level data. The water-table fluctuation method may be the most widely used technique for estimating recharge; it requires knowledge of specific yield and changes in water levels over time. Advantages of this approach include its simplicity and an insensitivity to the mechanism by which water moves through the unsaturated zone. Uncertainty in estimates generated by this method relate to the limited accuracy with which specific yield can be determined and to the extent to which assumptions inherent in the method are valid. Other methods that use water levels (mostly based on the Darcy equation) are also described. The theory underlying the methods is explained. Examples from the literature are used to illustrate applications of the different methods.

Healy, R.W.; Cook, P.G.

2002-01-01

48

Groundwater recharge rate and zone structure estimation using PSOLVER algorithm.  

PubMed

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

2014-01-01

49

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

SciTech Connect

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

50

Post processing of zone budgets to generate improved groundwater influx estimates associated with longwall mining.  

PubMed

Impacts of underground longwall mining on groundwater systems are commonly assessed using numerical groundwater flow models that are capable of forecasting changes to strata pore pressures and rates of groundwater seepage over the mine life. Groundwater ingress to a mining operation is typically estimated using zone budgets to isolate relevant parts of a model that represent specific mining areas, and to aggregate flows at nominated times within specific model stress periods. These rates can be easily misinterpreted if simplistic averaging of daily flow budgets is adopted. Such misinterpretation has significant implications for design of underground dewatering systems for a new mine site or it may lead to model calibration errors where measured mine water seepage rates are used as a primary calibration constraint. Improved estimates of groundwater ingress can be made by generating a cumulative flow history from zone budget data, then differentiating the cumulative flow history using a low order polynomial convolved through the data set. PMID:23895016

Mackie, C D

2014-01-01

51

Regionally compartmented groundwater flow on Mars  

NASA Astrophysics Data System (ADS)

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 assumed, but the validity of this assumption has not been tested. Chaotic terrains, thought to have formed owing to the disruption of a cryosphere under high aquifer pore pressures, provide the basis for such a test. Specifically, we use groundwater models to predict regions of cryosphere disruption due to recharge-driven pore pressure increases, and we compare these regions to observed Martian chaotic terrains. Our results suggest that a globally connected aquifer cannot give rise to cryosphere disruption at the two locations where large chaotic terrains are observed (the circum-Chryse region and the eastern Hellas Planitia). Conversely, modeled cryosphere disruption occurs in locations such as Amazonis Planitia and west Hellas Planitia where no supporting evidence is present, suggesting again that groundwater flow was likely regionally compartmented. Furthermore, the consistent occurrence of modeled breakouts in the Valles Marineris canyon system suggests that large-scale fractures there likely discharged most of the groundwater required for circum-Chryse outflow channel formation, with only minor contributions from chaotic terrains. The fractures are close to a likely source of recharge over Tharsis, and their low elevations lead to high pore pressures even if groundwater flow is regionally compartmented.

Harrison, Keith P.; Grimm, Robert E.

2009-04-01

52

Estimating exposure to groundwater contaminants in karst areas  

NASA Astrophysics Data System (ADS)

Large multidisciplinary projects investigate health effects and environmental impacts of contamination. Such multidisciplinary projects challenge groundwater hydrologist because they demand estimations of human or environmental exposure to groundwater contaminants. But especially in karst regions, groundwater quality is subject to rapid changes resulting from highly dynamic flow systems with rapid groundwater recharge and contaminant transport in karst conduits. There is a strong need for tools that allow the quantification of the risk of contaminant exposure via the karst groundwater and its temporal variation depending on rainfall events and overall hydrological conditions. A fact that makes the assessment of contaminant exposure even more difficult is that many contaminants behave differently in the subsurface than the groundwater, because they do not dissolve and exist as a separate phase. Important examples are particulate contaminants, such as bacteria, and non-aqueous phase liquids (NAPLs), such as many organic compounds. Both are ubiquitous in the environment and have large potential for health impacts. It is known from bacterial contamination of karst springs that such contamination is strongly related to flow conditions. Bacteria, which are present at the land surface, in the soil, rock matrix or the conduit system, are immobile during base flow conditions. During storm events however, they become mobilized and are rapidly transported through the conduit flow system from sources to areas of potential exposure. As a result, bacteria concentrations that most times are low at a spring can show a high peak during storm flow. Conceptual models exist that suggest that the transport of NAPLs in karst aquifers is, just like bacterial contamination, related to flow conditions. Light NAPLs that reach the saturated zone float and accumulate on the water table; and dense NAPLs sink downward in the aquifer until they are trapped in pores, fractures and conduits where they remain stationary under base flow conditions. During storm flows, however, they can be dragged downstream or flushed as suspensions and emulsions. As a result, storm flow can send previously immobilized NAPLs to exposure zones in toxic pulses. An approach is presented to estimate the risk of contaminant exposure by bacteria and NAPLs via the groundwater under variable hydrological conditions (Butscher et al. 2011). The approach uses an indicator that is expressed as the Dynamic Vulnerability Index (DVI). This index is defined as the ratio of conduit to matrix flow contributions to spring discharge, and is calculated based on a numerical model simulating karst groundwater flow. The approach is illustrated at a test site in Switzerland, where calculated DVI was compared to the occurrence of fecal indicators during five storm flow events. Key words: karst hydrogeology; groundwater contamination; fecal indicators; NAPLs; numerical modeling References: Butscher, C. Auckenthaler, A., Scheidler, S., Huggenberger, P. (2011). Validation of a Numerical Indicator of Microbial Contamination for Karst Springs. Ground Water 49 (1), 66-76.

Butscher, C.

2012-12-01

53

GROUNDWATER FLOW IN LOW-PERMEABILITY ENVIRONMENTS.  

USGS Publications Warehouse

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

54

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

PubMed

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

2011-02-01

55

Geospatial database of estimates of groundwater discharge to streams in the Upper Colorado River Basin  

USGS Publications Warehouse

The U.S. Geological Survey, as part of the Department of the Interior’s WaterSMART (Sustain and Manage America’s Resources for Tomorrow) initiative, compiled published estimates of groundwater discharge to streams in the Upper Colorado River Basin as a geospatial database. For the purpose of this report, groundwater discharge to streams is the baseflow portion of streamflow that includes contributions of groundwater from various flow paths. Reported estimates of groundwater discharge were assigned as attributes to stream reaches derived from the high-resolution National Hydrography Dataset. A total of 235 estimates of groundwater discharge to streams were compiled and included in the dataset. Feature class attributes of the geospatial database include groundwater discharge (acre-feet per year), method of estimation, citation abbreviation, defined reach, and 8-digit hydrologic unit code(s). Baseflow index (BFI) estimates of groundwater discharge were calculated using an existing streamflow characteristics dataset and were included as an attribute in the geospatial database. A comparison of the BFI estimates to the compiled estimates of groundwater discharge found that the BFI estimates were greater than the reported groundwater discharge estimates.

Garcia, Adriana; Masbruch, Melissa D.; Susong, David D.

2014-01-01

56

Estimates of tracer-based piston-flow ages of groundwater from selected sites: National Water-Quality Assessment Program, 2006-2010  

USGS Publications Warehouse

Piston-flow age dates were interpreted from measured concentrations of environmental tracers from 812 National Water-Quality Assessment (NAWQA) Program groundwater sites from 27 Study Units across the United States. The tracers of interest include chlorofluorocarbons (CFCs), sulfur hexafluoride (SF6), and tritium/helium-3 (3H/3He). Tracer data compiled for this analysis were collected from 2006 to 2010 from groundwater wells in NAWQA studies, including: * Land-Use Studies (LUS, shallow wells, usually monitoring wells, located in recharge areas under dominant land-use settings), * Major-Aquifer Studies (MAS, wells, usually domestic supply wells, located in principal aquifers and representing the shallow drinking water supply), * Flow System Studies (FSS, networks of clustered wells located along a flowpath extending from a recharge zone to a discharge zone, preferably a shallow stream) associated with Land-Use Studies, and * Reference wells (wells representing groundwater minimally impacted by anthropogenic activities) also associated with Land-Use Studies. Tracer data were evaluated using documented methods and are presented as aqueous concentrations, equivalent atmospheric concentrations (for CFCs and SF6), and tracer-based piston-flow ages. Selected ancillary data, such as redox data, well-construction data, and major dissolved-gas (N2, O2, Ar, CH4, and CO2) data, also are presented. Recharge temperature was inferred using climate data (approximated by mean annual air temperature plus 1°C [MAAT +1°C]) as well as major dissolved-gas data (N2-Ar-based) where available. The N2-Ar-based temperatures showed significantly more variation than the climate-based data, as well as the effects of denitrification and degassing resulting from reducing conditions. The N2-Ar-based temperatures were colder than the climate-based temperatures in networks where recharge was limited to the winter months when evapotranspiration was reduced. The tracer-based piston-flow ages compiled in this report are provided as a consistent means of reporting the tracer data. The tracer-based piston-flow ages may provide an initial interpretation of age in cases in which mixing is minimal and may aid in developing a basic conceptualization of groundwater age in an aquifer. These interpretations are based on the assumption that tracer transport is by advection only and that no mixing occurs. In addition, it is assumed that other uncertainties are minimized, including tracer degradation, sorption, contamination, or fractionation, and that terrigenic (natural) sources of tracers, and spatially variable atmospheric tracer concentrations are constrained.

Shapiro, Stephanie D.; Plummer, L. Niel; Busenberg, Eurybiades; Widman, Peggy K.; Casile, Gerolamo C.; Wayland, Julian E.; Runkle, Donna L.

2012-01-01

57

Intuitive visualization of transient groundwater flow  

NASA Astrophysics Data System (ADS)

Understanding and interpreting flow problems is an existing challenge in scientific visualization. In particular, the graphical presentation of transient flow data can be a significant problem. This contribution introduces an intuitive method to animate transient 3D groundwater flow on planar and curved 2D surfaces in a very illustrative way. The main aim of this approach is to support the presentation of simulation results in front of audiences for whom groundwater modeling is outside their area of expertise, that is, non-experts. Particularly, data sets with a highly irregular mesh or point distribution can be visualized descriptively. The flow field is easily rendered in a comprehensible way using animated pathlets with a novel, time-dependent seeding strategy which is described in more detail in this contribution. A hydrological example is used to present the capabilities and especially the intuitive character of our visualization method.

Seidel, T.; König, C.; Schäfer, M.; Ostermann, I.; Biedert, T.; Hietel, D.

2014-06-01

58

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

USGS Publications Warehouse

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

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

2004-01-01

59

Nonlinear groundwater flow during a slug test in fractured rock  

NASA Astrophysics Data System (ADS)

A series of slug tests with various initial head displacements was carried out to investigate the influence of nonlinear groundwater flow on a slug test in fractured rock. To identify the nonlinear flow regime during a slug test, a representative Reynolds number (Re) was calculated using the slug test results and the fractures identified from geophysical logging and core logs. The Forchheimer equation and cubic law were used to determine the critical Re where nonlinear flow arose in the test zone. Our results showed that nonlinear flow arose when the initial displacement was over 1.0 m. Then, the degree of nonlinearity increased and the estimated hydraulic conductivity from the test results decreased with increasing initial displacement. The study also suggested that the Forchheimer and cubic law can be used to estimate the hydraulic conductivity in a linear flow regime using data from the slug tests in a nonlinear flow regime.

Ji, Sung-Hoon; Koh, Yong-Kwon

2015-01-01

60

An Efficient Probabilistic Finite Element Method for Stochastic Groundwater Flow  

E-print Network

An Efficient Probabilistic Finite Element Method for Stochastic Groundwater Flow Harald Osnes Hans of groundwater flow and transport from mathematical models involves considerable uncertainty due to the presence of computer power. Numerical methods for stochastic groundwater flow fall basically into two categories; Monte

Osnes, Harald

61

Ground-water flow directions and estimation of aquifer hydraulic properties in the lower Great Miami River Buried Valley aquifer system, Hamilton Area, Ohio  

USGS Publications Warehouse

The Great Miami River Buried Valley Aquifer System is one of the most productive sources of potable water in the Midwest, yielding as much as 3,000 gallons per minute to wells. Many water-supply wells tapping this aquifer system are purposely placed near rivers to take advantage of induced infiltration from the rivers. The City of Hamilton's North Well Field consists of 10 wells near the Great Miami River, all completed in the lower Great Miami River Buried Valley Aquifer System. A well-drilling program and a multiple-well aquifer test were done to investigate ground-water flow directions and to estimate aquifer hydraulic properties in the lower part of the Great Miami River Buried Valley Aquifer System. Descriptions of lithology from 10 well borings indicate varying amounts and thickness of clay or till, and therefore, varying levels of potential aquifer confinement. Borings also indicate that the aquifer properties can change dramatically over relatively short distances. Grain-size analyses indicate an average bulk hydraulic conductivity value of aquifer materials of 240 feet per day; the geometric mean of hydraulic conductivity values of aquifer material was 89 feet per day. Median grain sizes of aquifer material and clay units were 1.3 millimeters and 0.1 millimeters, respectively. Water levels in the Hamilton North Well Field are affected by stream stage in the Great Miami River and barometric pressure. Bank storage in response to stream stage is evident. Results from a multiple-well aquifer test at the well field indicate, as do the lithologic descriptions, that the aquifer is semiconfined in some areas and unconfined in others. Transmissivity and storage coefficient of the semiconfined part of the aquifer were 50,000 feet squared per day and 5x10-4, respectively. The average hydraulic conductivity (450 feet per day) based on the aquifer test is reasonable for glacial outwash but is higher than calculated from grain-size analyses, implying a scale effect. Although the part of the lower Great Miami River Buried Valley Aquifer System where the Hamilton North Well Field is located is semiconfined, unconfined, or locally confined and not directly connected to the Great Miami River, the discontinuity of the clay/till layers beneath the river indicates that other, deeper parts of the aquifer system may be directly connected to the Great Miami River.

Sheets, Rodney A.; Bossenbroek, Karen E.

2005-01-01

62

Multiphase groundwater flow near cooling plutons  

USGS Publications Warehouse

We investigate groundwater flow near cooling plutons with a computer program that can model multiphase flow, temperatures up to 1200??C, thermal pressurization, and temperature-dependent rock properties. A series of experiments examines the effects of host-rock permeability, size and depth of pluton emplacement, single versus multiple intrusions, the influence of a caprock, and the impact of topographically driven groundwater flow. We also reproduce and evaluate some of the pioneering numerical experiments on flow around plutons. Host-rock permeability is the principal factor influencing fluid circulation and heat transfer in hydrothermal systems. The hottest and most steam-rich systems develop where permeability is of the order of 10-15 m2. Temperatures and life spans of systems decrease with increasing permeability. Conduction-dominated systems, in which permeabilities are ???10-16m2, persist longer but exhibit relatively modest increases in near-surface temperatures relative to ambient conditions. Pluton size, emplacement depth, and initial thermal conditions have less influence on hydrothermal circulation patterns but affect the extent of boiling and duration of hydrothermal systems. Topographically driven groundwater flow can significantly alter hydrothermal circulation; however, a low-permeability caprock effectively decouples the topographically and density-driven systems and stabilizes the mixing interface between them thereby defining a likely ore-forming environment.

Hayba, D.O.; Ingebritsen, S.E.

1997-01-01

63

CONTINUOUSTIME FINITE ELEMENT ANALYSIS OF MULTIPHASE FLOW IN GROUNDWATER HYDROLOGY  

E-print Network

CONTINUOUS­TIME FINITE ELEMENT ANALYSIS OF MULTIPHASE FLOW IN GROUNDWATER HYDROLOGY Zhangxin Chen­water system in groundwater hydrology is given. The system is written in a fractional flow formulation, i for an air­water system in groundwater hydrology, ff = a; w [1], [11], [26]: @(OEae ff s ff ) @t +r \\Delta

64

Simulation analysis of the ground-water flow system in the Portland Basin, Oregon and Washington  

USGS Publications Warehouse

This report presents results derived from a numerical model of the ground-water flow system in the Portland Basin, Oregon and Washington, that was used to test and refine the conceptual understanding of the flow system, estimate the effects of past and future human-caused changes to ground-water recharge and discharge on ground-water levels and streamflow, and determine priorities for ground-water monitoring and data collection that would facilitate improvements in the utility and accuracy of the model.

Morgan, David S.; McFarland, William D.

1996-01-01

65

Pajarito Plateau Groundwater Flow and Transport Modeling Process-Level and Systems Models of Groundwater Flow and  

E-print Network

Pajarito Plateau Groundwater Flow and Transport Modeling 1 Process-Level and Systems Models of Groundwater Flow and Transport Beneath the Pajarito Plateau: Migration of High Explosives from Technical Area Groundwater Modeling Project Systems Model Vadose Zone Model Regional Aquifer Model #12;Pajarito Plateau

Lu, Zhiming

66

Regional groundwater flow in hard rocks.  

PubMed

The territory of continental Portugal has a geologic history marked by the Hercynian orogeny, and to the north of this country the Hercynian large-scale tectonic structures are typically represented by long and deep NW-SE trending ductile shear zones and NNE-SSW trending fragile faults. These structures are elements of mineral and thermal water circuits that discharge as springs in more than one hundred locations. The purpose of this study is to investigate if these structures are also used by shallower non-mineral groundwater, integrated in a large-scale regional flow system. Using an original combination of water balance and recession flow models, it was possible to calculate catchment turnover times based solely on groundwater discharge rates and recession flow parameters. These times were then used to classify a group of 46 watersheds as closed or open basins, and among the later class to identify source and sink basins, based on innovative interpretations of relationships between turnover time and catchment area. By definition, source basins transfer groundwater to sink basins and altogether form a regional flow system. Using a Geographic Information System, it could be demonstrated the spatial association of open basins to the Hercynian ductile and fragile tectonic structures and hence to classify the basins as discharge cells of a regional flow system. Most of the studied watersheds are sub-basins of the Douro River basin, one of the largest regional catchments in the Iberian Peninsula, being located in its mouth area. Because the largest part of open basins is sink, which by definition tends to dominate in the mouth area of regional catchments, it is proposed as an extension of the studied area conceptual boundaries towards the Douro River basin headwaters, where the corresponding sources could be searched for. PMID:25460951

Pacheco, Fernando A L

2015-02-15

67

Use of Chemical and Isotopic Tracers for Estimating Ground-Water Recharge, Flow Paths, and Residence Times in the Middle San Pedro Basin, Southeast Arizona  

NASA Astrophysics Data System (ADS)

Ground water is often the primary source of water for rapidly growing populations in the semi-arid southwestern United States. In addition, ground-water discharge to streams sustains wildlife in riparian areas. Improved understanding of the sources of ground water, recharge areas, flow paths, and water quality of basin aquifer systems is needed to assess water availability and develop effective water management policies. This study analyzes variations of major ion (Ca, Na, K, Mg, Sr, Fe, Si, Zn, F, Cl, Br, NO3, SO4) and isotope (18O, 2H, 3H, 34S, 13C, 14C) chemistry of ground water, surface waters and precipitation with in conjunction with hydrogeologic data (e.g. hydraulic head, subsurface structure, and stratigraphy) to infer recharge areas, mixing of water sources, and residence times of ground water within the middle San Pedro watershed in southeastern Arizona. The San Pedro basin is bound by crystalline and carbonate rocks of the Whetstone and Rincon Mountains on the west and by crystalline rocks of the Dragoon Mountains to the east. Differences in mineral assemblages of these mountain blocks impart distinct chemical signatures in ground waters through mineral weathering. Potentially, these differences in water chemistry can serve as chemical tracers for identifying ground-water flow paths and mixing relations. Ground-water chemistry variations suggest compartmentalization of waters into an upper and lower alluvial aquifer system comprised of permeable sands and gravels ranging in depth from ten to over one thousand feet in the basin center; the units are separated by confining units of silt and clay in the basin center. Variations include higher fluoride (up to 8 ppm) near the Dragoon Mountains, higher chloride (up to 54 ppm) near the Whetstone Mountains, and higher sulfate (up to 750 ppm) concentrations in both upper and lower sands and gravels owing to interaction with thick Permian or Neocene evaporites. Chloride is generally lower (less than 8 ppm) in the lower unit of the aquifer due to limited evaporation. The presence of high nitrates (up to 32 ppm) in the upper sands and gravels indicate modern recharge to this unit. ä18O values ranging from -6.8 to -8.9 suggest that recharge to upper unit originates mostly from summer monsoon precipitation especially along certain reaches of the San Pedro River. Oxygen isotope values between -7.2 and -11.8 indicate that recharge to lower units originates from a mixture of summer and winter precipitation and high elevation recharge. Low percent modern carbon values (8.0 to 37.8 PMC) within lower units indicate recharge within the past ~14,000 years. Detectable tritium (1.0-6.8 TU) near bounding mountain blocks and shallow units near the river indicate recharge within the past sixty years. These parameters yield a complex snapshot of groundwater variability and indicate modern recharge is occurring within high elevation areas and along stretches of the river. The lower unit's geochemical signature suggests it may be hydrologically isolated from modern recharge.

Adkins, C. B.; McIntosh, J.; Eastoe, C.; Dickinson, J.

2008-12-01

68

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

USGS Publications Warehouse

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 surfacewater 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.

Winter, T.C.

1999-01-01

69

Simulation of groundwater flow within observation boreholes for confined aquifers  

NASA Astrophysics Data System (ADS)

SummaryObservation wells around a pumping well are the primary means of monitoring the change of hydraulic head in an aquifer. Pipe flow in open observation boreholes will affect the measurement of hydraulic head in the observation wells and alter the flow patterns around the wells, but the influences of non-Darcian pipe flow in observation wells on the accuracy of hydraulic head measurements are not fully recognized. This paper presents a coupled seepage-pipe flow theory which integrates the aquifer and well as a continuous medium for assessing the influences. The objective of this study is to examine the pipe-flow effects in observation wells of varied diameters under several pumping scenarios including different penetration lengths of the pumping well. A numerical model based on the Galerkin finite element method and the finite difference method was developed for the study. Numerical simulations were conducted for a homogeneous and isotropic confined aquifer in which a pumping well penetrated a different thickness of the aquifer and a number of full penetrating observation wells were placed to obtain drawdowns. The simulation results indicated that vertical pipe flow within the observation wells was significant and the flow was non-linear. The pipe flow resulted in a conduit effect that disturbed the distribution of the hydraulic head within the observation wells. After comparing with the results of the Hantush (1961) integral by using the case study, which neglected the wellbore effect on the groundwater flow system, the authors found that the Hantush integral may be only conditionally applicable for estimating the drawdown within the observation wells when well diameter is greater than 0.20 m and radial distance is greater than the thickness of the aquifer. Our study suggests that use of hydraulic heads from observation wells for the evaluation of groundwater flow systems must be cautious before the pipe-flow effect can be assumed to be negligible.

Hu, Litang; Chen, Chongxi; Chen, Xunhong

2011-02-01

70

Simulation of salt migrations in density dependent groundwater flow  

E-print Network

Simulation of salt migrations in density dependent groundwater flow E.S. van Baaren Master's Thesis for the salt migration in the groundwater underneath the polders near the coast. The problem description of this thesis is to investigate the possibilities of modelling salt migrations in density dependent groundwater

Vuik, Kees

71

Ground-water flow and solute transport at a municipal landfill site on Long Island, New York; Part 2, Simulation of ground-water flow  

USGS Publications Warehouse

Data on the hydrogeology of a 26-sq-mi area surrounding the Brookhaven landfill site in central Suffolk County were collected as part of a hydrologic investigation of solute transport from the site. These data were used to develop a steady-state groundwater flow model of the upper glacial (water table) aquifer in the area. The model accounts for the leakage through confining units underlying the aquifer, seepage to streams, recharge from precipitation, and pumpage and redistribution of water. Refined estimates of aquifer and confining-unit properties were obtained through model calibrations. Water table altitudes generated by the calibrated model were used to determine groundwater velocities and probable flow paths in the vicinity of the site under long-term average hydrologic conditions. Groundwater velocities and probable flow paths in the study area were calculated from simulated water table altitudes generated by the calibrated flow model. Groundwater at the center of the site flows southeastward at a velocity of 1.1 ft/d. The report is the second in a three part series describing the hydrologic conditions and groundwater quality, groundwater flow, and solute transport in the vicinity of the Brookhaven landfill. (USGS)

Wexler, E.J.; Maus, P.E.

1988-01-01

72

Application of chlorofluorocarbons (CFCs) to estimate the groundwater age at a headwater wetland in Ichikawa City, Chiba Prefecture, Japan  

NASA Astrophysics Data System (ADS)

To delineate the groundwater flow system in a basin, the groundwater age was estimated by analyzing chlorofluorocarbons (CFC-11, CFC-12 and CFC-113) in a typical headwater wetland in Ichikawa, Japan. Feasibility of groundwater dating by CFCs was assessed comprehensively based on the concentrations of NO3 -, SO4 2-, Fe2+ and dissolved CH4 in the groundwater, because the CFCs would be degraded under the reduction condition available in a wetland. It was found that the CFC-11 apparent age was much older than that estimated by other CFC species. It showed that CFC-12 and CFC-113 were suitable tracers for groundwater dating because of their stability in the wetland environment. Furthermore, the mixture of groundwater with different age was discussed by CFC-12 and CFC-113 based on the binary mixing model and piston-flow model. As a result, the apparent age of groundwater in the study area is in the range of 38-48 years.

Han, Zhiwei; Tang, Changyuan; Piao, Jingqiu; Li, Xing; Cao, Yingjie; Matsumaru, Touma; Zhang, Chipeng

2014-09-01

73

Assessment of interbasin groundwater flows between catchments using a semi-distributed water balance model  

NASA Astrophysics Data System (ADS)

In hydrological modeling it is often assumed that the aquifers boundaries are formed by the geographical demarcation of the catchment. However, this assumption is rarely met, given the existence of groundwater flows going beyond the catchment limits. The assessment of interbasin groundwater flows is crucial when managing water resources in areas where baseflows are mainly formed by groundwater, especially when catchments are managed separately. Aiming at estimating the volume and direction of the main groundwater flows, this work presents a new methodological approach for hydrological modeling. This approach employs a semi-distributed water balance model created with lumped models. This model is formulated in such a way that a part of the groundwater discharge of a specific catchment can become baseflows in other catchments, which helps characterize interbasin groundwater flows. This methodology is applied in the headwater of the Segura River Basin (southeast of Spain), where groundwater plays an important role in surface hydrology. The catchments are modeled with a high goodness of fit, and the main interbasin groundwater flows between them is evaluated, proving its importance in the characterization of hydrological modeling.

Pellicer-Martínez, Francisco; Martínez-Paz, José Miguel

2014-11-01

74

A correction on coastal heads for groundwater flow models.  

PubMed

We introduce a simple correction to coastal heads for constant-density groundwater flow models that contain a coastal boundary, based on previous analytical solutions for interface flow. The results demonstrate that accurate discharge to the sea in confined aquifers can be obtained by direct application of Darcy's law (for constant-density flow) if the coastal heads are corrected to ((??+?1)/?)hs ?-?B/2?, in which hs is the mean sea level above the aquifer base, B is the aquifer thickness, and ? is the density factor. For unconfined aquifers, the coastal head should be assigned the value hs1+?/?. The accuracy of using these corrections is demonstrated by consistency between constant-density Darcy's solution and variable-density flow numerical simulations. The errors introduced by adopting two previous approaches (i.e., no correction and using the equivalent fresh water head at the middle position of the aquifer to represent the hydraulic head at the coastal boundary) are evaluated. Sensitivity analysis shows that errors in discharge to the sea could be larger than 100% for typical coastal aquifer parameter ranges. The location of observation wells relative to the toe is a key factor controlling the estimation error, as it determines the relative aquifer length of constant-density flow relative to variable-density flow. The coastal head correction method introduced in this study facilitates the rapid and accurate estimation of the fresh water flux from a given hydraulic head measurement and allows for an improved representation of the coastal boundary condition in regional constant-density groundwater flow models. PMID:24571623

Lu, Chunhui; Werner, Adrian D; Simmons, Craig T; Luo, Jian

2015-01-01

75

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

PubMed

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

2013-01-01

76

Estimated Water Flows in 2005: United States  

SciTech Connect

Flow charts depicting water use in the United States have been constructed from publicly available data and estimates of water use patterns. Approximately 410,500 million gallons per day of water are managed throughout the United States for use in farming, power production, residential, commercial, and industrial applications. Water is obtained from four major resource classes: fresh surface-water, saline (ocean) surface-water, fresh groundwater and saline (brackish) groundwater. Water that is not consumed or evaporated during its use is returned to surface bodies of water. The flow patterns are represented in a compact 'visual atlas' of 52 state-level (all 50 states in addition to Puerto Rico and the Virgin Islands) and one national water flow chart representing a comprehensive systems view of national water resources, use, and disposition.

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

2011-03-16

77

Groundwater flow system under a rapidly urbanizing coastal city as determined by hydrogeochemistry  

NASA Astrophysics Data System (ADS)

In the Jakarta area (Indonesia), excessive groundwater pumping due to the rapidly increasing population has caused groundwater-related problems such as brackish water contamination in coastal areas and land subsidence. In this study, we adopted multiple hydrogeochemical techniques to demonstrate the groundwater flow system in the Jakarta area. Although almost all groundwater existing in the Jakarta basin is recharged at similar elevations, the water quality and residence time demonstrates a clear difference between the shallow and deep aquifers. Due to the rapid decrease in the groundwater potential in urban areas, we found that the seawater intrusion and the shallow and deep groundwaters are mixing, a conclusion confirmed by major ions, Br -:Cl - ratios, and chlorofluorocarbon (CFC)-12 analysis. Spring water and groundwater samples collected from the southern mountainside area show younger age characteristics with high concentrations of 14C and Ca-HCO 3 type water chemistry. We estimated the residence times of these groundwaters within 45 years under piston flow conditions by tritium analysis. Also, these groundwater ages can be limited to 20-30 years with piston flow evaluated by CFCs. Moreover, due to the magnitude of the CFC-12 concentration, we can use a pseudo age indicator in this field study, because we found a positive correlation between the major type of water chemistry and the CFC-12 concentration.

Kagabu, Makoto; Shimada, Jun; Delinom, Robert; Tsujimura, Maki; Taniguchi, Makoto

2011-01-01

78

Use of a ground-water flow model with particle tracking to evaluate ground-water vulnerability, Clark County, Washington  

USGS Publications Warehouse

A ground-water flow model was used in conjunction with a particle-tracking program to demonstrate a method of evaluating ground-water vulnerability. The study area encompassed the part of the Portland Basin located in Clark County, Washington. A new computer program was developed that interfaces the particle-tracking program with a geographic information system (GIS). The GIS was used to display and analyze the particle-tracking results and to evaluate ground-water vulnerability by identifying recharge areas and their characteristics, determining the downgradient impact of land use at recharge areas, and estimating the age of ground water. The report presents a description of the methods used and the results of the evaluation of ground-water vulnerability.

Snyder, Daniel T.; Wilkinson, James M.; Orzol, Leonard L.

1998-01-01

79

Effect of Fractures on Groundwater Flow Patterns  

NSDL National Science Digital Library

The goal of this exercise is to have students gain an understanding of how fractures affect groundwater flow patterns. In order for them to complete the activity, they need some background on characteristic fracture patterns in different rock types. This background could be provided in a variety of ways depending on geographic location and outcrop availability. If outcrops of crystalline and sedimentary sequences are available, you could take students in the field and have them observe (and perhaps sketch) the differing fracture patterns. If geology (and or weather) preclude this option, the students could observe fracture patterns from slides of outcrops (see slides in accompanying PowerPoint Presentation). The classroom portion of the exercise uses a simple 2D numerical model (TopoDrive, available from USGS) to simulate flow in three aquifers: 1) homogeneous isotropic, 2) fractured crystalline, and 3) fractured sedimentary sequences. The task is to observe how the fracture patterns alter the flow patterns as compared to the homogeneous, isotropic simulation. The activity gives students practice in integrating geologic data into numerical models, describing flow patterns, and using computer technology. The activity also integrates knowledge from structural geology with hydrogeology.

Maureen Muldoon

80

Using 14C and 3H to understand groundwater flow and recharge in an aquifer window  

NASA Astrophysics Data System (ADS)

Knowledge of groundwater residence times and recharge locations is vital to the sustainable management of groundwater resources. Here we investigate groundwater residence times and patterns of recharge in the Gellibrand Valley, southeast Australia, where outcropping aquifer sediments of the Eastern View Formation form an "aquifer window" that may receive diffuse recharge from rainfall and recharge from the Gellibrand River. To determine recharge patterns and groundwater flow paths, environmental isotopes (3H, 14C, ?13C, ?18O, ?2H) are used in conjunction with groundwater geochemistry and continuous monitoring of groundwater elevation and electrical conductivity. The water table fluctuates by 0.9 to 3.7 m annually, implying recharge rates of 90 and 372 mm yr-1. However, residence times of shallow (11 to 29 m) groundwater determined by 14C are between 100 and 10 000 years, 3H activities are negligible in most of the groundwater, and groundwater electrical conductivity remains constant over the period of study. Deeper groundwater with older 14C ages has lower ?18O values than younger, shallower groundwater, which is consistent with it being derived from greater altitudes. The combined geochemistry data indicate that local recharge from precipitation within the valley occurs through the aquifer window, however much of the groundwater in the Gellibrand Valley predominantly originates from the regional recharge zone, the Barongarook High. The Gellibrand Valley is a regional discharge zone with upward head gradients that limits local recharge to the upper 10 m of the aquifer. Additionally, the groundwater head gradients adjacent to the Gellibrand River are generally upwards, implying that it does not recharge the surrounding groundwater and has limited bank storage. 14C ages and Cl concentrations are well correlated and Cl concentrations may be used to provide a first-order estimate of groundwater residence times. Progressively lower chloride concentrations from 10 000 years BP to the present day are interpreted to indicate an increase in recharge rates on the Barongarook High.

Atkinson, A. P.; Cartwright, I.; Gilfedder, B. S.; Cendón, D. I.; Unland, N. P.; Hofmann, H.

2014-12-01

81

Groundwater balance estimation in karst by using a conceptual rainfall-runoff model  

NASA Astrophysics Data System (ADS)

SummaryA conceptual rainfall-runoff model is proposed for the estimation of groundwater balance components including the influences of time-variant catchment boundaries and intercatchment groundwater flows. Karst underground is considered as a lumped system that contains: (1) soil cover, (2) epikarst zone and (3) vadose and phreatic zones. The soil cover receives an average rainfall in catchment as the input into the system. The epikarst zone is composed of a production store and a routing store. The production store contributes to the loss of water in process of evapotranspiration. The routing store contributes to the retention of percolated water and the lateral distribution of groundwater recharge between internal runoff and diffuse infiltration. The vadose and phreatic zones accumulate groundwater in fissures, fractures and vertical shafts, and produce the vadose seepage, vadose flow and shaft flow components of the karst spring discharge. The parameter estimation and calculation procedure assemble the moisture balance and the groundwater-balance approaches. The rainfall-runoff model is divided in two sub-models. The sub-model based on the moisture balance of soil cover and epikarst production store calculates effective rainfalls. The sub-model based on the groundwater balance of vadose and phreatic zone calculates groundwater recharges. The difference between the effective rainfalls and the groundwater recharges represents the contribution of epikarst zone and non-conservative and time-variant components to the groundwater balance. The proposed methodology is applied to the Jadro Spring located near the city of Split in Croatia. The calculated groundwater balance shows that the Jadro Spring aquifer contains a significant storage capacity in the vadose and phreatic zones. During the year, the aquifer may accumulate up to 140 millions m 3. The variability of calculated catchment area is explained with the time-variant catchment boundary dependent on groundwater levels and the intercatchment groundwater flows from neighboring catchments. The average catchment area of 396 km 2 is estimated by using the average monthly effective rainfalls and the average monthly groundwater recharges.

Juki?, Damir; Deni?-Juki?, Vesna

2009-07-01

82

Groundwater flow in heterogeneous composite C. L. Winter and Daniel M. Tartakovsky  

E-print Network

Groundwater flow in heterogeneous composite aquifers C. L. Winter and Daniel M. Tartakovsky Hydrology: Stochastic processes; 1829 Hydrology: Groundwater hydrology; 1832 Hydrology: Groundwater, upscaled, decomposition 1. Introduction [2] It has become common to quantify uncertainty in groundwater

Tartakovsky, Daniel M.

83

Rapid, cost-effective estimation of groundwater age based on hydrochemistry  

NASA Astrophysics Data System (ADS)

In order to manage and protect groundwater resources, the complex and diverse recharge, mixing and flow processes occurring in groundwater systems need to be better understood. Groundwater age information can give valuable information on groundwater flow, recharge sources, and aquifer volumes. However current groundwater dating techniques, for example tracers such as tritium or CFCs, or hydrological models, have limitations and method specific application ranges and uncertainties. Due to this, ambiguous age interpretation is a problem. New technique(s) are essential to overcome limitations and complement existing methods. The aim of this study is to advance the use of hydrochemistry for groundwater dating. To date, hydrochemistry has only been applied sparsely to support groundwater age determination, despite its wide availability from national groundwater monitoring programs. This is due to the lack of any established distinct relationships between hydrochemistry and groundwater age. Establishing these is complex, since hydrochemistry is influenced by complex interrelationships of aquifer specific processes. Therefore underlying processes, such as mineral weathering and redox reactions, and diverse reactions, such as quartz dissolution, are not directly interpretable from hydrochemistry data. Additionally reaction kinetics (of e.g. quartz dissolution) are often aquifer specific, and field data are sparse; furthermore data gained in laboratory environments are difficult to relate back to field situations as comparative studies have found lab and field measurements can differ by orders of magnitude. We wish to establish relationships between hydrochemistry and groundwater age, to allow hydrochemical data to better inform groundwater dating through two separate approaches. Firstly relationships between groundwater age (determined by state of the art dating techniques) and single hydrochemistry parameters, such as silica concentration, can be established in a given aquifer. This relation can then be used in the same or similar aquifer to infer groundwater age from given hydrochemistry. Secondly specific reaction rates of underlying reactions, such as quartz dissolution, can be determined and used to determine specific and ';generic' reaction rates for field environments. We postulate this may in future lead to groundwater dating directly from specific hydrochemistry data in any given aquifer by using ';generic' kinetics. To illustrate these two approaches, regularly measured hydrochemistry data and estimates of groundwater age inferred from tritium, SF6 and CFC-12 within the Lower Hutt Groundwater Zone, a gravel aquifer in Wellington, New Zealand, are used. Correlations of hydrochemistry parameters and groundwater age are presented. Hierarchical Cluster and Factor Analysis are used to investigate major processes which caused the given hydrochemistry. Inverse modelling is used to identify specific underlying reactions, such as weathering of quartz. Reaction kinetics are investigated and results presented.

Beyer, M.; Morgenstern, U.; Jackson, B. M.; Daughney, C.

2013-12-01

84

Groundwater  

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.

85

Groundwater dating for understanding nitrogen in groundwater systems - Time lag, fate, and detailed flow path ways  

NASA Astrophysics Data System (ADS)

Nitrate contamination of groundwater is a problem world-wide. Nitrate from land use activities can leach out of the root zone of the crop into the deeper part of the unsaturated zone and ultimately contaminate the underlying groundwater resources. Nitrate travels with the groundwater and then discharges into surface water causing eutrophication of surface water bodies. To understand the source, fate, and future nitrogen loads to ground and surface water bodies, detailed knowledge of the groundwater flow dynamics is essential. Groundwater sampled at monitoring wells or discharges may not yet be in equilibrium with current land use intensity due to the time lag between leaching out of the root zone and arrival at the sampling location. Anoxic groundwater zones can act as nitrate sinks through microbial denitrification. However, the effect of denitrification on overall nitrate fluxes depends on the fraction of the groundwater flowing through such zones. We will show results from volcanic aquifers in the central North Island of New Zealand where age tracers clearly indicate that the groundwater discharges into large sensitive lakes like Lake Taupo and Lake Rotorua are not yet fully realising current land use intensity. The majority of the water discharging into these lakes is decades and up to over hundred years old. Therefore, increases in dairy farming over the last decades are not yet reflected in these old water discharges, but over time these increased nitrate inputs will eventually work their way through the large groundwater systems and increasing N loads to the lakes are to be expected. Anoxic zones are present in some of these aquifers, indicating some denitrification potential, however, age tracer results from nested piezo wells show young groundwater in oxic zones indicating active flow in these zones, while anoxic zones tend to have older water indicating poorer hydraulic conductivity in these zones. Consequently, to evaluate the effect of denitrification on nitrate fluxes it is insufficient to consider only the spatial distribution of oxic and anoxic zones; the flow through these zones needs to be quantified. If the majority of groundwater passes through the oxic zones rather the anoxic zones, insignificant N attenuation must be expected. Our results indicate about an order of magnitude lower vertical flow velocity and flux through anoxic zones compared to oxic zones. The age distribution of the groundwater allows identification of groundwater flow path ways, which in the Lake Taupo catchment is characterised by high piston flow, indicating groundwater flow between widely connected impermeable layers, probably paleosol layers. Groundwater dating has become an important tool for management of nitrate contamination.

Morgenstern, Uwe; Hadfield, John; Stenger, Roland

2014-05-01

86

Groundwater-flow and land-subsidence model of Antelope Valley, California  

USGS Publications Warehouse

The groundwater-flow model of the basin was discretized horizontally into a grid of 130 rows and 118 columns of square cells 1 kilometer (0.621 mile) on a side, and vertically into four layers representing the upper (two layers), middle (one layer), and lower (one layer) aquifers. Faults that were thought to act as horizontal-flow barriers were simulated in the model. The model was calibrated to simulate steady-state conditions, represented by 1915 water levels and transient-state conditions during 1915–95, by using water-level and subsidence data. Initial estimates of the aquifer-system properties and stresses were obtained from a previously published numerical model of the Antelope Valley groundwater basin; estimates also were obtained from recently collected hydrologic data and from results of simulations of groundwater-flow and land-subsidence models of the Edwards Air Force Base area. Some of these initial estimates were modified during

Siade, Adam J.; Nishikawa, Tracy; Rewis, Diane L.; Martin, Peter; Phillips, Steven P.

2014-01-01

87

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

88

Groundwater  

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.

89

Groundwater flow and groundwater-stream interaction in fractured and dipping sedimentary rocks  

E-print Network

Groundwater flow and groundwater-stream interaction in fractured and dipping sedimentary rocks is influenced by topography, but in fractured and dipping sedimentary rocks, it is also influenced by structure sedimentary rocks: Insights from numerical models, Water Resour. Res., 43, W01409, doi:10.1029/2006WR004864. 1

Toran, Laura

90

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

USGS Publications Warehouse

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

91

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

NASA Astrophysics Data System (ADS)

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

Spanoudaki, Katerina; Kampanis, Nikolaos A.

2014-05-01

92

Regional Groundwater Flow in the Louisville Aquifer.  

PubMed

The unconfined alluvial aquifer at Louisville, Kentucky, is an important source of water for domestic and industrial uses. It has been the object of several modeling studies in the past, particularly via the application of classical analytical solutions, and numerical solutions (finite differences and finite elements). A new modeling procedure of the Louisville aquifer is presented based on a modification of Adomian's Decomposition Method (ADM) to handle irregularly shaped boundaries. The new approach offers the simplicity, stability, and spatial continuity of analytical solutions, in addition to the ability to handle irregular boundaries typical of numerical solutions. It reduces to the application of a simple set of algebraic equations to various segments of the aquifer. The calculated head contours appear in reasonably agreement with those of previous studies, as well as with those from measured head values from the U.S. Geological Survey field measurement program. A statistical comparison of the error standard deviation is within the same range as that reported in previous studies that used complex numerical solutions. The present methodology could be easily implemented in other aquifers when preliminary results are needed, or when scarce hydrogeologic information is available. Advantages include a simple approach for preliminary groundwater modeling; an analytic description of hydraulic heads, gradients, fluxes, and flow rates; state variables are described continuously over the spatial domain; complications from stability and numerical roundoff are minimized; there is no need for a numerical grid or the handling of large sparse matrices; there is no need to use specialized groundwater software, because all calculations may be done with standard mathematics or spreadsheet programs. Nonlinearity, the effect of higher order terms, and transient simulations could be included if desired. PMID:25070643

Tiaif, Syafrin; Serrano, Sergio E

2014-07-28

93

Analytical studies on transient groundwater flow induced by land reclamation  

E-print Network

Analytical studies on transient groundwater flow induced by land reclamation Litang Hu,1 Jiu Jimmy materials into the sea. Land reclamation may have a significant effect on groundwater regimes, especially when the reclamation is at large scale. Analytical studies on the impact of land reclamation on steady

Jiao, Jiu Jimmy

94

Estimating Ground-Water Recharge from Stream Hydrographs  

Microsoft Academic Search

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

95

New method to estimate variability in groundwater volumes  

NASA Astrophysics Data System (ADS)

As the warming climate and increasing population put stress on the world's water supply, it has become increasingly important to have a global understanding of how groundwater volumes vary from season to season and from year to year. Current global hydrological models do not include lateral groundwater flow, which plays a significant role in providing water to plants and in recharging lakes, rivers, and streams.

Wendel, JoAnna

2014-04-01

96

GROUNDWATER FLOW AND TRANSPORT MODELING Application to Submarine Groundwater Discharge, Coastal Wetland Hydrology, and Deep Well Injection  

E-print Network

GROUNDWATER FLOW AND TRANSPORT MODELING Application to Submarine Groundwater Discharge, Coastal, but is also lost to surface water drainage and potential submarine groundwater discharge. There are also to deal with issues such as submarine groundwater discharge and coastal wetland hydrology. SEAWAT also has

Sukop, Mike

97

Characterizing three-dimensional groundwater flow and transport  

E-print Network

indirect formulations. Examples in characterizing groundwater flow include: use of a Galerkin method (Frind and Finder 1973), an algebraic approach (Sagar et al. 1975), the minimization of a quadratic objective function with a penalty function (Navarro...

Hollenshead, Jeromy Todd

1995-01-01

98

Update to the Ground-Water Withdrawals Database for the Death Valley REgional Ground-Water Flow System, Nevada and California, 1913-2003  

SciTech Connect

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

99

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

100

Stable isotope and groundwater flow dynamics of agricultural irrigation recharge into groundwater resources of the Central Valley, California  

SciTech Connect

Intensive agricultural irrigation and overdraft of groundwater in the Central Valley of California profoundly affect the regional quality and availability of shallow groundwater resources. In the natural state, the {delta}{sup 18}O values of groundwater were relatively homogeneous (mostly -7.0 {+-} 0.5{per_thousand}), reflecting local meteoric recharge that slowly (1-3m/yr) flowed toward the valley axis. Today, on the west side of the valley, the isotope distribution is dominated by high {sup 18}O enclosures formed by recharge of evaporated irrigation waters, while the east side has bands of low {sup 18}O groundwater indicating induced recharge from rivers draining the Sierra Nevada mountains. Changes in {delta}{sup 18}O values caused by the agricultural recharge strongly correlate with elevated nitrate concentrations (5 to >100 mg/L) that form pervasive, non-point source pollutants. Small, west-side cities dependent solely on groundwater resources have experienced increases of >1.0 mg/L per year of nitrate for 10-30 years. The resultant high nitrates threaten the economical use of the groundwater for domestic purposes, and have forced some well shut-downs. Furthermore, since >80% of modern recharge is now derived from agricultural irrigation, and because modern recharge rates are {approximately}10 times those of the natural state, agricultural land retirement by urbanization will severely curtail the current safe-yields and promote overdraft pumping. Such overdrafting has occurred in the Sacramento metropolitan area for {approximately}40 years, creating cones of depression {approximately}25m deep. Today, groundwater withdrawal in Sacramento is approximately matched by infiltration of low {sup 18}O water (-11.0{per_thousand}) away from the Sacramento and American Rivers, which is estimated to occur at 100-300m/year from the sharp {sup 18}O gradients in our groundwater isotope map.

Davisson, M.L.; Criss, R.E.

1995-01-01

101

A fuzzy logic model for estimation of groundwater recharge  

Microsoft Academic Search

Water budget models are commonly accepted methods for estimating the groundwater recharge. Some of the inputs to these models such as soil-moisture deficit, actual evapotranspiration, direct runoff etc, are difficult to measure. The space dynamic nature of these parameters makes their quantification even more difficult. The error in estimation increases significantly during extreme events. In addition, it has been found

A. K. Awasthi; O. P. Dubey; S. Sharma

2005-01-01

102

Regional groundwater flow modelling of Upper Chaj Doab of Indus Basin, Pakistan using finite element model (Feflow) and geoinformatics  

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

103

Quantitative dye-tracing of karst ground-water flow  

USGS Publications Warehouse

Analysis of the results of repeat quantitative dye traces between a sinkhole and a spring used for public water supply were used to describe predictive relations between discharge, mean travel time, apparent ground-water flow velocity and solute transport characteristics. Normalized peak concentration, mean travel time, and standard deviation of travel times were used to produce a dimensionless, composite type curve that was used to produce a dimensionless, composite type curve that was used to simulate solute transport characteristics for selected discharges. Using this curve and previously developed statistical relations, a water manager can estimate the arrival time, peak concentration, and persistence of a soluble contaminant at a supply spring or well based on discharge and the quantity of spilled contaminant.

Smoot, James; Mull, Donald; Liebermann, Timothy

1989-01-01

104

Estimation of evapotranspiration using diurnal groundwater level fluctuations: Comparison of different approaches with groundwater lysimeter data  

NASA Astrophysics Data System (ADS)

In wetlands or riparian areas, water withdrawal by plants with access to groundwater or the capillary fringe often causes diurnal groundwater fluctuations. Various approaches use the characteristics of these fluctuations for estimation of daily groundwater evapotranspiration rates. The objective of this paper was to review the available methods, compare them with measured evapotranspiration and assess their recharge assumptions. For this purpose, we employed data of 85 rain-free days of a weighable groundwater lysimeter situated at a grassland site in the Spreewald wetland in north-east Germany. Measurements of hourly recharge and daily evapotranspiration rates were used to assess the different approaches. Our results showed that a maximum of 50% of the day to day variance of the daily evapotranspiration rates could be explained by the approaches based on groundwater fluctuations. Simple and more complex methods performed similarly. For some of the approaches, there were indications that erroneous assumptions compensated each other (e.g., when overestimated recharge counteracted underestimated storage change). We found that the usage of longer time spans resulted in improved estimates of the daily recharge rates and that the estimates were further enhanced by including two night averages. When derived from fitting estimates of recharge or evapotranspiration with according measurements the specific yield, needed to convert changes in water level to water volumes, differed considerably among the methods (from 0.022 to 0.064). Thus, the specific yield can be seen as "correction factor" that compensates for inadequate process descriptions.

Fahle, Marcus; Dietrich, Ottfried

2014-01-01

105

Simulation of Groundwater Flow around a Waste Landfill Site  

NASA Astrophysics Data System (ADS)

Waste landfill sites in Japan are constructed in mountainous regions because the Japanese population is concentrated in limited flat areas. Consequently, waste landfill locations necessarily correspond with water resources areas. Therefore, we need to evaluate previously the influences of contaminants leached from waste landfill sites when it is newly constructed. For this purpose, it is important to predict the groundwater movement accurately because the contaminants are diffused and advected in groundwater. In this study, we simulated the groundwater flow around a waste landfill site using MODFLOW which was a software package.The groundwater levels around a waste landfill site have been measured to verify the accuracy of simulation results. The target area, which was 750m*450m, was modeled by a GIS tool which was contained in GMS (Groundwater Modeling System). The cell size for finite difference was 15m*15m. The model parameters were adjusted, comparing the simulated groundwater levels with the measured ones. The results were as follows: The variations of groundwater levels were predicted reasonably using the relationship between the measured groundwater levels and rainfalls. The groundwater levels in the upper area were simulated within appropriate ranges and the variations of simulated groundwater levels showed the same tendency as those of the measured ones. On the other hand, the simulated water levels in the lower area were overestimated and over the soil surface. In the future study, we need to simulate the groundwater considering that the topography and layers of the site is very complicated, compared with the previous works used in the MODFLOW.

Moroizumi, T.; Ikemoto, M.; Suito, H.; Ono, Y.

2006-12-01

106

Subsurface thermal environment and groundwater flow around Tokyo Bay, Japan  

Microsoft Academic Search

Previous studies and borehole temperature measurements suggest that subsurface temperature distribution on the west side of\\u000a Tokyo Bay (from Tokyo to Yokohama) is higher than that of the east side (Chiba side). To understand the groundwater flow and\\u000a other factors which may contribute to the subsurface temperature discrepancy such as geological setting in the study area,\\u000a groundwater temperature profiles were

Vuthy Monyrath; Yasuo Sakura; Akinobu Miyakoshi; Takeshi Hayashi

2010-01-01

107

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

USGS Publications Warehouse

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

Smith, Barry S.

2001-01-01

108

A Guide for Using the Transient Ground-Water Flow Model of the Death Valley Regional Ground-Water Flow System, Nevada and California  

SciTech Connect

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

109

A guide for using the transient ground-water flow model of the Death Valley regional ground-water flow system, Nevada and California  

USGS Publications Warehouse

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.

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

2006-01-01

110

Groundwater Flow Dynamic Simulations of a Buried Valley Aquifer Calibrated with Field and Remotely Sensed Data  

NASA Astrophysics Data System (ADS)

Buried valleys are a common occurrence in the North American prairie landscape. They are often characterized as high yield sources of groundwater in regions where low yield shale and tills dominate the hydrogeological setting. Firstly, 3D conceptual and geological models have been generated and used as a basis for creating a 3D finite element groundwater flow model. Field data, including piezometric readings, base flow measurements, and soil moisture probe data were collected between 2011 and 2013 and are used for calibrating the flow model. Secondly, the study aims to improve the spatial discretization of recharge estimates and include these refined values in the flow model. A temporal series of C-band Radar data and several land surface models were compared with the soil moisture probe data from the Spiritwood buried valley aquifer. The radar backscatter was used to develop moisture estimates at the regional scale. These estimates were then input into the HELP multi-parameter recharge model with the aim of assisting in estimates of a spatial discretization for groundwater recharge. Preliminary groundwater simulation results, with uniform recharge, show good agreement with piezometer readings and measured base flow readings. The temporal series of C-band radar backscatter, moisture probe data, and land surface models show corresponding variations between October, 2011 and October, 2012. The high resolution and regional extent of the radar data has a high potential to help develop a better understanding of recharge patterns in buried valley settings. Integrating a temporal series of high-resolution data into conceptual and numerical model development will refine our mapping, understanding and assessment of buried valley aquifers. Future work will include incorporating the spatially variable recharge estimates into the 3D finite element flow model. Additionally, various interpretations of the geological model will be tested to determine the extent, if any, that a geophysical dataset (airborne electromagnetic AEM or seismic) can help yield a more realistic flow pattern in buried valley aquifers.

Calderhead, A. I.; Hinton, M. J.; Logan, C. E.; Sharpe, D.; Russel, H. A.; Oldenborger, G. A.; Pugin, A.; Rivera, A.; Castellazzi, P.; Martel, R.

2013-12-01

111

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

Microsoft Academic Search

A finite-element model of the ground-water flow system in the vicinity of Yucca Mountain at the Nevada Test Site was developed using parameter-estimation techniques. The model simulated steady-state ground-water flow occurring in tuffaceous, volcanic, and carbonate rocks, and alluvial aquifers. Hydraulic gradients in the modeled area range from 0.00001 for carbonate aquifers to 0.19 for barriers in tuffaceous rocks. Three

J. B. Czarnecki; R. K. Waddell

1984-01-01

112

Headers will be added later Deriving groundwater estimates in Australia  

E-print Network

and Climate Experiment space gravity mission detects changes in mass by sensing perturbations of the EarthHeaders will be added later 1 Deriving groundwater estimates in Australia from GRACE observations P. Tregoning 1 and S.C. McClusky 1 1 Research School of Earth Sciences, The Australian National University

Tregoning, Paul

113

Estimating seepage flux from ephemeral stream channels using surface water and groundwater level data  

NASA Astrophysics Data System (ADS)

flux from ephemeral streams can be an important component of the water balance in arid and semiarid regions. An emerging technique for quantifying this flux involves the measurement and simulation of a flood wave as it moves along an initially dry channel. This study investigates the usefulness of including surface water and groundwater data to improve model calibration when using this technique. We trialed this approach using a controlled flow event along a 1387 m reach of artificial stream channel. Observations were then simulated using a numerical model that combines the diffusion-wave approximation of the Saint-Vénant equations for streamflow routing, with Philip's infiltration equation and the groundwater flow equation. Model estimates of seepage flux for the upstream segments of the study reach, where streambed hydraulic conductivities were approximately 101 m d-1, were on the order of 10-4 m3 d-1 m-2. In the downstream segments, streambed hydraulic conductivities were generally much lower but highly variable (˜10-3 to 10-7 m d-1). A Latin Hypercube Monte Carlo sensitivity analysis showed that the flood front timing, surface water stage, groundwater heads, and the predicted streamflow seepage were most influenced by specific yield. Furthermore, inclusion of groundwater data resulted in a higher estimate of total seepage estimates than if the flood front timing were used alone.

Noorduijn, Saskia L.; Shanafield, Margaret; Trigg, Mark A.; Harrington, Glenn A.; Cook, Peter G.; Peeters, L.

2014-02-01

114

Simulation of ground-water flow and areas contributing ground water to production wells, Cadillac, Michigan  

USGS Publications Warehouse

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

115

Incorporation of prior information on parameters into nonlinear regression groundwater flow models. l. Theory.  

USGS Publications Warehouse

Prior information on the parameters of a groundwater flow model can be used to improve parameter estimates obtained from nonlinear regression solution of a modeling problem. Two scales of prior information can be available: 1) prior information having known reliability (that is, bias and random error structure), and 2) prior information consisting of best available estimates of unknown reliability. It is shown that if both scales of prior information are available, then a combined regression analysis may be made. -from Author

Cooley, R.L.

1982-01-01

116

Multivariate analyses and end-member mixing to characterize karst groundwater flow  

NASA Astrophysics Data System (ADS)

End-member mixing (EMM) is a simple modeling approach that is used to estimate the mixing proportions of different waters contributing to sampled sites. This approach has advantages for karst aquifers and groundwater in caves because no assumptions need to be made regarding the presence, locations, or dimensions of conduits. Principal component analysis (PCA) applied to hydrochemical data is useful for assessing hydrochemical data to be used in EMM and for determining appropriate constraints on the EMM model. The combination of these two methods has been used to a limited extent to characterize groundwater flow and has excellent potential for further development and application, but aspects of this approach are unresolved. Previous similar approaches typically have assumed that the extreme-value samples identified by PCA represent end members. The approach we present is different from previous work in that (1) end members were not assumed to have been sampled but rather were estimated and constrained by prior knowledge; (2) end-member mixing was quantified in relation to hydrogeologic domains, which focuses model results on major hydrologic processes; (3) a method to select an appropriate number of end members using a series of cluster analyses is presented; and (4) conservative tracers were weighted preferentially in model calibration, which distributed model errors of optimized values, or residuals, more appropriately than otherwise would be the case. The latter item also provides an estimate of the relative influence of geochemical evolution along flow paths in comparison to mixing. This method was applied to groundwater in Wind Cave and an associated karst aquifer in the Black Hills of South Dakota, USA. The EMM model was used to test a hypothesis that five different end-member waters are mixed in the groundwater system comprising five hydrogeologic domains. The model estimated that Wind Cave received most of its groundwater inflow from local surface recharge with an additional 33% from an upgradient aquifer. Artesian springs in the vicinity of Wind Cave primarily received water from regional groundwater flow.

Long, A. J.; Valder, J. F.

2011-12-01

117

Intercomparison of Groundwater Flow Monitoring Technologies at Site OU 1, Former Fort Ord, California  

SciTech Connect

This report presents an intercomparison of three groundwater flow monitoring technologies at a trichloroethylene (TCE) groundwater plume at Operational Unit 1 (OU 1) adjacent to the former Fritzsche Army Airfield at the former Fort Ord Army Base, located on Monterey Bay in northern Monterey County, California. Soil and groundwater at this site became contaminated by fuels and solvents that were burned on a portion of OU 1 called the Fire Drill Area (FDA) as part of firefighter training from 1962 and 1985. Cont Contamination is believed to be restricted to the unconfined A-aquifer, where water is reached at a depth of approximately 60 to 80 feet below the ground surface; the aquifer is from 15 to 20 feet in thickness, and is bounded below by a dense clay layer, the Salinas Valley Aquitard. Soil excavation and bioremediation were initiated at the site of fire training activities in the late 1980s. Since that time a pump-and-treat operation has been operated close to the original area of contamination, and this system has been largely successful at reducing groundwater contamination in this source area. However, a trichloroethylene (TCE) groundwater plume extends approximately 3000 ft (900 m) to the northwest away from the FDA. In this report, we have augmented flow monitoring equipment permanently installed in an earlier project (Oldenburg et al., 2002) with two additional flow monitoring devices that could be deployed in existing monitoring wells, in an effort to better understand their performance in a nearly ideal, homogeneous sand aquifer, that we expected would exhibit laminar groundwater flow owing to the site's relatively simple hydrogeology. The three flow monitoring tools were the Hydrotechnics{reg_sign} In In-Situ Permeable Flow Sensor (ISPFS), the RAS Integrated Subsurface Evaluation Hydrophysical Logging tool (HPL), and the Lawrence Livermore National Laboratory Scanning Colloidal Borescope Flow Meter (SCBFM). All three devices produce groundwater flow velocity measurements, and the ISPFS and SCBFM systems also gene generate flow direction rate estimates. The ISPFS probes are permanently installed and are non-retrievable, but produce long-term records with essentially no operator intervention or maintenance. The HPL and SCBFM systems are lightweight, portable logging devices that employ recording of electrical conductivity changes in wells purged with deionized water (HPL), or imaging of colloidal particles traversing the borehole (SCBFM) as the physical basis for estimating the velocity of groundwater flow through monitoring wells. All three devices gave estimates of groundwater velocity that were in reasonable agreement. However, although the ISPFS produced groundwater azimuth data that correlated well with conventional conductivity and gradient analyses of the groundwater flow field, the SCBFM direction data were in poor agreement. Further research into the reasons for this lack of correlation would seem to be warranted, given the ease of deployment of this tool in existing conventional monitoring wells, and its good agreement with the velocity estimates of the other technologies examined.

Daley, P F; Jantos, J; Pedler, W H; Mandell, W A

2005-09-20

118

Controls on groundwater flow in a semiarid folded and faulted intermountain basin  

NASA Astrophysics Data System (ADS)

major processes controlling groundwater flow in intermountain basins are poorly understood, particularly in basins underlain by folded and faulted bedrock and under regionally realistic hydrogeologic heterogeneity. To explore the role of hydrogeologic heterogeneity and poorly constrained mountain hydrologic conditions on regional groundwater flow in contracted intermountain basins, a series of 3-D numerical groundwater flow models were developed using the South Park basin, Colorado, USA as a proxy. The models were used to identify the relative importance of different recharge processes to major aquifers, to estimate typical groundwater circulation depths, and to explore hydrogeologic communication between mountain and valley hydrogeologic landscapes. Modeling results show that mountain landscapes develop topographically controlled and predominantly local-scale to intermediate-scale flow systems. Permeability heterogeneity of the fold and fault belt and decreased topographic roughness led to permeability controlled flow systems in the valley. The structural position of major aquifers in the valley fold and fault belt was found to control the relative importance of different recharge mechanisms. Alternative mountain recharge model scenarios showed that higher mountain recharge rates led to higher mountain water table elevations and increasingly prominent local flow systems, primarily resulting in increased seepage within the mountain landscape and nonlinear increases in mountain block recharge to the valley. Valley aquifers were found to be relatively insensitive to changing mountain water tables, particularly in structurally isolated aquifers inside the fold and fault belt.

Ball, Lyndsay B.; Caine, Jonathan Saul; Ge, Shemin

2014-08-01

119

Complex groundwater flow systems as traveling agent models  

PubMed Central

Analyzing field data from pumping tests, we show that as with many other natural phenomena, groundwater flow exhibits complex dynamics described by 1/f power spectrum. This result is theoretically studied within an agent perspective. Using a traveling agent model, we prove that this statistical behavior emerges when the medium is complex. Some heuristic reasoning is provided to justify both spatial and dynamic complexity, as the result of the superposition of an infinite number of stochastic processes. Even more, we show that this implies that non-Kolmogorovian probability is needed for its study, and provide a set of new partial differential equations for groundwater flow. PMID:25337455

Padilla, Pablo; Escolero, Oscar; González, Tomas; Morales-Casique, Eric; Osorio-Olvera, Luis

2014-01-01

120

Assessing the groundwater fortunes of aquifers in the White Volta Basin, Ghana: An application of numerical groundwater flow modeling and isotopic studies  

NASA Astrophysics Data System (ADS)

Effective development and informed management of groundwater resources represent a critical opportunity for improved rural water supply in Ghana and enhanced livelihoods particularly in the northern part of the White Volta Basin, a region already prone to a myriad of water-related infirmities. If adequately developed, the resource will form a sufficient buffer against the effects of climate change/variability and foster food security and sustainable livelihoods among the largely peasant communities in the region. This research presents the results of a preliminary assessment of the hydrogeological conditions and recharge regimes of the aquifers in the Northern parts of the White Volta Basin, Ghana. Results of estimates of groundwater recharge through the conventional isotopic and mass balance techniques are presented. Details of the groundwater flow pattern and preliminary delineation of local and regional groundwater recharge areas are presented from initial simulations of the hydrogeological system with a robust groundwater flow simulation code, MODFLOW, in the Groundwater Modeling System, GMS, version 7.1. The stream flow and evapotranspiration components of the program were activated to incorporate surface flow processes, so that the resulting model represents the conditions of the entire hydrological system. The results of this study form a platform for detailed numerical assessment of the conditions of the aquifers in the area under transient conditions of fluctuating rainfall patterns in the face of climate change/variability.

Oteng, F. M.; Yidana, S. M.; Alo, C. A.

2012-12-01

121

Automatic Time Stepping with Global Error Control for Groundwater Flow Models  

SciTech Connect

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

122

Estimation of submarine groundwater discharge and associated nutrient fluxes in Tolo Harbour, Hong Kong  

E-print Network

Estimation of submarine groundwater discharge and associated nutrient fluxes in Tolo Harbour, Hong 2012 Keywords: Submarine groundwater discharge Nutrients Radium isotope Groundwater Estuary Tolo of algal blooms and red tides. An attempt was made to first quantify the submarine groundwater discharge

Jiao, Jiu Jimmy

123

Application of Integral Pumping Tests to estimate the influence of losing streams on groundwater quality  

NASA Astrophysics Data System (ADS)

Urban streams receive effluents of wastewater treatment plants and untreated wastewater during combined sewer overflow events. In the case of losing streams substances, which originate from wastewater, can reach the groundwater and deteriorate its quality. The estimation of mass flow rates Mex from losing streams to the groundwater is important to support groundwater management strategies, but is a challenging task. Variable inflow of wastewater with time-dependent concentrations of wastewater constituents causes a variable water composition in urban streams. Heterogeneities in the structure of the streambed and the connected aquifer lead, in combination with this variable water composition, to heterogeneous concentration patterns of wastewater constituents in the vicinity of urban streams. Groundwater investigation methods based on conventional point sampling may yield unreliable results under these conditions. Integral Pumping Tests (IPT) can overcome the problem of heterogeneous concentrations in an aquifer by increasing the sampled volume. Long-time pumping (several days) and simultaneous sampling yields reliable average concentrations Cav and mass flow rates Mcp for virtual control planes perpendicular to the natural flow direction. We applied the IPT method in order to estimate Mex of a stream section in Leipzig (Germany). The investigated stream is strongly influenced by combined sewer overflow events. Four pumping wells were installed up- and downstream of the stream section and operated for a period of five days. The study was focused on four inorganic (potassium, chloride, nitrate and sulfate) and two organic (caffeine and technical-nonylphenol) wastewater constituents with different transport properties. The obtained concentration-time series were used in combination with a numerical flow model to estimate Mcp of the respective wells. The difference of the Mcp's between up- and downstream wells yields Mex of wastewater constituents that increase downstream of the stream. In order to confirm the obtained Mcp's concentrations of additional measurements in the investigated stream were compared with the concentrations in the groundwater up- and downstream of the stream section. The results revealed increased Mcp's downstream of the stream section for chloride, potassium and nitrate, whereas Mcp of sulfate was decreased. Micropollutants caffeine and technical-nonylphenol showed decreased Mcp's downstream of the stream section in 75 % of the cases. Values of Mex could only be given for chloride, potassium, nitrate and caffeine. The comparison of concentrations in the stream with those in the groundwater points to the streambed as a zone where mass accumulation and degradation processes occur. The obtained results imply that the applied method can provide reliable data about the influence of losing streams on groundwater quality.

Leschik, S.; Musolff, A.; Reinstorf, F.; Strauch, G.; Schirmer, M.

2009-05-01

124

Verification of a Conceptual Model of Groundwater flow in a Poorly Productive Metasedimentary Bedrock Aquifer  

NASA Astrophysics Data System (ADS)

Poorly Productive Aquifers (PPA) underlie approximately two-thirds of the landmass of Ireland yet the behaviour of groundwater in these bedrock types remains poorly understood. Existing (unverified) conceptual models represent most groundwater as travelling through the uppermost metres of the bedrock and at the base of overlying unconsolidated deposits (transition zone), with a subordinate fraction flowing through the shallower bedrock (to 24m BGS) and the deeper rock (to 76m BGS). However, the hydrogeological properties of these units remain largely uninvestigated and thus any conceptual model of groundwater flow requires verification before application to meet the requirements of EU Water Framework Directive legislation. This study aimed to investigate and refine the current conceptual model of groundwater flow within a poorly productive shallow greenschist-grade metasedimentary (Dalradian) bedrock aquifer in the Gortinlieve Catchment, Co. Donegal. The final model will act as a basis for simulating groundwater flow in the uppermost 50 metres of bedrock in the area. A programme of field-based characterisation involved outcrop measurements of fracture length, aperture, orientation and density. High resolution acoustic televiewer and caliper geophysical logs provided details of fracture frequency, orientation, and aperture at depth in six monitoring wells within the catchment, while differential temperature and differential conductivity logs permitted identification of hydraulically active fractures. Constant rate pumping tests conducted on all monitoring wells established the hydrogeological properties at different depths in the aquifer along a transect stretching from the catchment divide to the discharge zone (stream). A flow balance for the catchment provided an estimate of the groundwater contribution to stream flow. Preliminary results identified two prominent conjugate fracture sets in outcropping, which were also encountered in the boreholes thus providing potential hydraulic connections between the transition zone, shallow and deep bedrock. Results from the resistivity logs indicate that the fractured bedrock aquifer is strongly heterogeneous. Analysis of pumping test, differential temperature and differential conductivity data demonstrated several of the fracture planes to be hydraulically active and facilitating the flow of groundwater. Average values of hydraulic conductivity obtained from pumping test analysis for the transition, shallow and deep bedrock are 1.83, 0.01 and 0.01 m/d respectively, suggesting that 85% of groundwater flow occurs within the heavily weathered transition zone and that the shallow and deep bedrock transmit a significantly lower proportion of the total groundwater flow per unit thickness. Pumping test and hydraulic gradient data also demonstrate the rate of groundwater flow increases with increasing saturated thickness. Overall, flow balance results suggest that only 20-30% of groundwater flow within the catchment contributes to flow in the nearby stream and the main component forms part of the deeper regional flow system. These preliminary findings provide an important basis for refining existing conceptual models of PPA.

Nitsche, Janka; Flynn, Raymond

2010-05-01

125

The in situ permeable flow sensor: A device for measuring groundwater flow velocity  

SciTech Connect

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 velocity vector in unconsolidated, saturated, porous media. The velocity measured is an average value characteristic of an approximately 1 cubic meter volume of the subsurface. During a test at the Savannah River Site in South Carolina, two flow sensors were deployed in a confined aquifer in close proximity to a well which was screened over the entire vertical extent of the aquifer and the well was pumped at four different pumping rates. In this situation horizontal flow which is radially directed toward the pumping well is expected. The flow sensors measured horizontal flow which was directed toward the pumping well, within the uncertainty in the measurements. The observed magnitude of the horizontal component of the flow velocity increased linearly with pumping rate, as predicted by theoretical considerations. The measured horizontal component of the flow velocity differed from the predicted flow velocity, which was calculated with the assumptions that the hydraulic properties of the aquifer were radially homogeneous and isotropic, by less than a factor of two. Drawdown data obtained from other wells near the pumping well during the pump test indicate that the hydraulic properties of the aquifer are probably not radially homogeneous but the effect of the inhomogeneity on the flow velocity field around the pumping well was not modeled because the degree and distribution of the inhomogeneity are unknown. Grain size analysis of core samples from wells in the area were used to estimate the vertical distribution of hydraulic conductivity.

Ballard, S.; Barker, G.T. [Sandia National Labs., Albuquerque, NM (United States); Nichols, R.L. [Savannah River Technology Center, Aiken, SC (United States)

1994-03-01

126

MODELLING GROUNDWATER FLOW ON THE REGIONAL SCALE IN THE UPPER DANUBE CATCHMENT (GERMANY)  

E-print Network

MODELLING GROUNDWATER FLOW ON THE REGIONAL SCALE IN THE UPPER DANUBE CATCHMENT (GERMANY) Roland.barthel@iws.uni-stuttgart.de Abstract. A groundwater flow model for the Upper Danube catchment (A=77,000km2 at gauge Passau, Germany coupled models. Modelling of groundwater flow, using coupled deterministic and hydrological approaches

Cirpka, Olaf Arie

127

Using Multiple Natural Tracers to Investigate Groundwater Recharge and Flow in Mountains  

NASA Astrophysics Data System (ADS)

Because mountain precipitation provides the majority of groundwater recharge in the western USA, an understanding of groundwater recharge and flow in mountain ranges is needed to make informed resource-management decisions. Natural tracers are excellent tools for studying these systems, but a single tracer can only provide limited information. As a result, using multiple tracers is ideal - by using several tracers, several aspects of mountain groundwater systems can be examined. For instance, groundwater stable-isotope measurements (?D and ?18O) can reveal the elevation at which the water fell as precipitation, but not the elevation at which the water was recharged. However, concentrations of dissolved gases in groundwater can be used to determine actual recharge elevations. Major-ion chemistry can provide insight into the geologic units through which the water has moved, and may also provide a qualitative indication of residence time; radioisotopes can yield more precise estimates of groundwater age. Other information is helpful for interpreting natural tracer data, including the local and regional geology, the area's climate, and the locations where groundwater recharge ('disappearing' streams) or discharge (springs and seeps) occur. A study utilizing these tools was conducted in the Chiricahua Mountains (Arizona, USA). Stable-isotope data show that precipitation from near the crest of the range is responsible for the majority of the groundwater recharge. Dissolved-gas data indicate that, while most of this recharge takes place near the crest of the range; some waters recharge in a high-permeability zone near the base of the range. Based on our observations of the range's hydraulics, the majority of this low-elevation recharge appears to be 're-recharge'---water that recharged at higher elevations, flowed underground, discharged, flowed downslope overland, then re-recharged. Major-ion chemistry data show that both volcanic (tuff and rhyolite) and sedimentary (primarily carbonates) units are conduits for groundwater flow in the range, depending on location. Dissolved-gas data demonstrate that the extent of the high-elevation recharge zone is nearly identical to the area of the range that develops snowpack. If snowpack development is a needed condition for recharge in other ranges of the western USA, groundwater recharge could be seriously impacted if current predictions for global-warming-induced changes in precipitation in the western USA (decreased percentage of precipitation falling as snow, and higher snowlines) are accurate.

Earman, S.; Phillips, F. M.

2005-12-01

128

Arsenic and Antimony in Groundwater Flow Systems: A Comparative Study  

Microsoft Academic Search

Arsenic (As) and antimony (Sb) concentrations and speciation were determined along flow paths in three groundwater flow systems,\\u000a the Carrizo Sand aquifer in southeastern Texas, the Upper Floridan aquifer in south-central Florida, and the Aquia aquifer\\u000a of coastal Maryland, and subsequently compared and contrasted. Previously reported hydrogeochemical parameters for all three\\u000a aquifer were used to demonstrate how changes in oxidation–reduction

Stephanie S. Willis; Shama E. Haque; Karen H. Johannesson

129

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

PubMed

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

2012-01-01

130

Estimation of shallow ground-water recharge in the Great Lakes basin  

USGS Publications Warehouse

This report presents the results of the first known integrated study of long-term average ground-water recharge to shallow aquifers (generally less than 100 feet deep) in the United States and Canada for the Great Lakes, upper St. Lawrence, and Ottawa River Basins. The approach used was consistent throughout the study area and allows direct comparison of recharge rates in disparate parts of the study area. Estimates of recharge are based on base-flow estimates for streams throughout the Great Lakes Basin and the assumption that base flow in a given stream is equal to the amount of shallow ground-water recharge to the surrounding watershed, minus losses to evapotranspiration. Base-flow estimates were developed throughout the study area using a single model based on an empirical relation between measured base-flow characteristics at streamflow-gaging stations and the surficial-geologic materials, which consist of bedrock, coarse-textured deposits, fine-textured deposits, till, and organic matter, in the surrounding surface-water watershed. Model calibration was performed using base-flow index (BFI) estimates for 959 stations in the U.S. and Canada using a combined 28,784 years of daily streamflow record determined using the hydrograph-separation software program PART. Results are presented for watersheds represented by 8-digit hydrologic unit code (HUC, U.S.) and tertiary (Canada) watersheds. Recharge values were lowest (1.6-4.0 inches/year) in the eastern Lower Peninsula of Michigan; southwest of Green Bay, Wisconsin; in northwestern Ohio; and immediately south of the St. Lawrence River northeast of Lake Ontario. Recharge values were highest (12-16.8 inches/year) in snow shadow areas east and southeast of each Great Lake. Further studies of deep aquifer recharge and the temporal variability of recharge would be needed to gain a more complete understanding of ground-water recharge in the Great Lakes Basin.

Neff, B.P.; Piggott, A.R.; Sheets, R.A.

2006-01-01

131

A method to estimate groundwater depletion from confining layers  

USGS Publications Warehouse

Although depletion of storage in low-permeability confining layers is the source of much of the groundwater produced from many confined aquifer systems, it is all too frequently overlooked or ignored. This makes effective management of groundwater resources difficult by masking how much water has been derived from storage and, in some cases, the total amount of water that has been extracted from an aquifer system. Analyzing confining layer storage is viewed as troublesome because of the additional computational burden and because the hydraulic properties of confining layers are poorly known. In this paper we propose a simplified method for computing estimates of confining layer depletion, as well as procedures for approximating confining layer hydraulic conductivity (K) and specific storage (Ss) using geologic information. The latter makes the technique useful in developing countries and other settings where minimal data are available or when scoping calculations are needed. As such, our approach may be helpful for estimating the global transfer of groundwater to surface water. A test of the method on a synthetic system suggests that the computational errors will generally be small. Larger errors will probably result from inaccuracy in confining layer property estimates, but these may be no greater than errors in more sophisticated analyses. The technique is demonstrated by application to two aquifer systems: the Dakota artesian aquifer system in South Dakota and the coastal plain aquifer system in Virginia. In both cases, depletion from confining layers was substantially larger than depletion from the aquifers.

Konikow, L.F.; Neuzil, C.E.

2007-01-01

132

Use of a ground-water flow model with particle tracking to evaluate ground-water vulnerability, Clark County, Washington  

USGS Publications Warehouse

A ground-water flow model was used in conjunction with particle tracking to evaluate ground-water vulnerability in Clark County, Washington. Using the particle-tracking program, particles were placed in every cell of the flow model (about 60,000 particles) and tracked backwards in time and space upgradient along flow paths to their recharge points. A new computer program was developed that interfaces the results from a particle-tracking program with a geographic information system (GIS). The GIS was used to display and analyze the particle-tracking results. Ground-water vulnerability was evaluated by selecting parts of the ground-water flow system and combining the results with ancillary information stored in the GIS to determine recharge areas, characteristics of recharge areas, downgradient impact of land use at recharge areas, and age of ground water. Maps of the recharge areas for each hydrogeologic unit illustrate the presence of local, intermediate, or regional ground-water flow systems and emphasize the three-dimensional nature of the ground-water flow system in Clark County. Maps of the recharge points for each hydrogeologic unit were overlaid with maps depicting aquifer sensitivity as determined by DRASTIC (a measure of the pollution potential of ground water, based on the intrinsic characteristics of the near-surface unsaturated and saturated zones) and recharge from on-site waste-disposal systems. A large number of recharge areas were identified, particularly in southern Clark County, that have a high aquifer sensitivity, coincide with areas of recharge from on-site waste-disposal systems, or both. Using the GIS, the characteristics of the recharge areas were related to the downgradient parts of the ground-water system that will eventually receive flow that has recharged through these areas. The aquifer sensitivity, as indicated by DRASTIC, of the recharge areas for downgradient parts of the flow system was mapped for each hydrogeologic unit. A number of public-supply wells in Clark County may be receiving a component of water that recharged in areas that are more conducive to contaminant entry. The aquifer sensitivity maps illustrate a critical deficiency in the DRASTIC methodology: the failure to account for the dynamics of the ground-water flow system. DRASTIC indices calculated for a particular location thus do not necessarily reflect the conditions of the ground-water resources at the recharge areas to that particular location. Each hydrogeologic unit was also mapped to highlight those areas that will eventually receive flow from recharge areas with on-site waste-disposal systems. Most public-supply wells in southern Clark County may eventually receive a component of water that was recharged from on-site waste-disposal systems.Traveltimes from particle tracking were used to estimate the minimum and maximum age of ground water within each model-grid cell. Chlorofluorocarbon (CFC)-age dating of ground water from 51 wells was used to calibrate effective porosity values used for the particle- tracking program by comparison of ground-water ages determined through the use of the CFC-age dating with those calculated by the particle- tracking program. There was a 76 percent agreement in predicting the presence of modern water in the 51 wells as determined using CFCs and calculated by the particle-tracking program. Maps showing the age of ground water were prepared for all the hydrogeologic units. Areas with the youngest ground-water ages are expected to be at greatest risk for contamination from anthropogenic sources. Comparison of these maps with maps of public- supply wells in Clark County indicates that most of these wells may withdraw ground water that is, in part, less than 100 years old, and in many instances less than 10 years old. Results of the analysis showed that a single particle-tracking analysis simulating advective transport can be used to evaluate ground-water vulnerability for any part of a ground-wate

Snyder, D.T.; Wilkinson, J.M.; Orzol, L.L.

1996-01-01

133

Validation Analysis of the Shoal Groundwater Flow and Transport Model  

SciTech Connect

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

134

Estimated ground-water discharge by evapotranspiration, Ash Meadows Area, Nye County, Nevada, 1994  

SciTech Connect

Ground water discharges from the regional ground-water flow system that underlies the eastern part of the Nevada Test Site through numerous springs and seeps in the Ash Meadows National Wildlife Refuge in southern Nevada. The total spring discharge was estimated to be about 17,000 acre-feet per year by earlier studies. Previous studies estimated that about 10,500 acre-feet of this discharge was lost to evapotranspiration. The present study was undertaken to develop a more rigorous approach to estimating ground-water discharge in the Ash Meadows area. Part of the study involves detailed field investigation of evapotranspiration. Data collection began in early 1994. The results of the first year of study provide a basis for making preliminary estimates of ground-water discharge by evapotranspiration. An estimated 13,100 acre-feet of ground water was evapotranspired from about 6,800 acres of marsh and salt-grass. Additional 3,500 acre-feet may have been transpired from the open water and from about 1,460 acres of other areas of Ash Meadows in which field studies have not yet been made.

Nichols, W.D.; Laczniak, R.J.; DeMeo, G.A.; Rapp, T.R.

1997-05-01

135

Bias in groundwater samples caused by wellbore flow  

USGS Publications Warehouse

Proper design of physical installations and sampling procedures for groundwater monitoring networks is critical for the detection and analysis of possible contaminants. Monitoring networks associated with known contaminant sources sometimes include an array of monitoring wells with long well screens. The purpose of this paper is: (a) to report the results of a numerical experiment indicating that significant borehole flow can occur within long well screens installed in homogeneous aquifers with very small head differences in the aquifer (less than 0.01 feet between the top and bottom of the screen); (b) to demonstrate that contaminant monitoring wells with long screens may completely fail to fulfill their purpose in many groundwater environments.

Reilly, Thomas E.; Franke, O. Lehn; Bennett, Gordon D.

1989-01-01

136

Groundwater availability as constrained by hydrogeology and environmental flows.  

PubMed

Groundwater pumping from aquifers in hydraulic connection with nearby streams has the potential to cause adverse impacts by decreasing flows to levels below those necessary to maintain aquatic ecosystems. The recent passage of the Great Lakes-St. Lawrence River Basin Water Resources?Compact has brought attention to this issue in the Great Lakes region. In particular, the legislation requires the Great Lakes states to enact measures for limiting water withdrawals that can cause adverse ecosystem impacts. This study explores how both hydrogeologic and environmental flow limitations may constrain groundwater availability in the Great Lakes Basin. A methodology for calculating maximum allowable pumping rates is presented. Groundwater availability across the basin may be constrained by a combination of hydrogeologic yield and environmental flow limitations varying over both local and regional scales. The results are sensitive to factors such as pumping time, regional and local hydrogeology, streambed conductance, and streamflow depletion limits. Understanding how these restrictions constrain groundwater usage and which hydrogeologic characteristics and spatial variables have the most influence on potential streamflow depletions has important water resources policy and management implications. PMID:23582026

Watson, Katelyn A; Mayer, Alex S; Reeves, Howard W

2014-01-01

137

Estimation of methane concentrations and loads in groundwater discharge to Sugar Run, Lycoming County, Pennsylvania  

USGS Publications Warehouse

A stream-sampling study was conducted to estimate methane concentrations and loads in groundwater discharge to a small stream in an active shale-gas development area of northeastern Pennsylvania. Grab samples collected from 15 streams in Bradford, Lycoming, Susquehanna, and Tioga Counties, Pa., during a reconnaissance survey in May and June 2013 contained dissolved methane concentrations ranging from less than the minimum reporting limit (1.0) to 68.5 micrograms per liter (µg/L). The stream-reach mass-balance method of estimating concentrations and loads of methane in groundwater discharge was applied to a 4-kilometer (km) reach of Sugar Run in Lycoming County, one of the four streams with methane concentrations greater than or equal to 5 µg/L. Three synoptic surveys of stream discharge and methane concentrations were conducted during base-flow periods in May, June, and November 2013. Stream discharge at the lower end of the reach was about 0.10, 0.04, and 0.02 cubic meters per second, respectively, and peak stream methane concentrations were about 20, 67, and 29 µg/L. In order to refine estimated amounts of groundwater discharge and locations where groundwater with methane discharges to the stream, the lower part of the study reach was targeted more precisely during the successive studies, with approximate spacing between stream sampling sites of 800 meters (m), 400 m, and 200 m, in May, June, and November, respectively. Samples collected from shallow piezometers and a seep near the location of the peak methane concentration measured in streamwater had groundwater methane concentrations of 2,300 to 4,600 µg/L. These field data, combined with one-dimensional stream-methane transport modeling, indicate groundwater methane loads of 1.8 ±0.8, 0.7 ±0.3, and 0.7 ±0.2 kilograms per day, respectively, discharging to Sugar Run. Estimated groundwater methane concentrations, based on the transport modeling, ranged from 100 to 3,200 µg/L. Although total methane load and the uncertainty in calculated loads both decreased with lower streamflow conditions and finer-resolution sampling in June and November, the higher loads during May could indicate seasonal variability in base flow. This is consistent with flowmeter measurements indicating that there was less inflow occurring at lower streamflow conditions during June and November.

Heilweil, Victor M.; Risser, Dennis W.; Conger, Randall W.; Grieve, Paul L.; Hynek, Scott A.

2014-01-01

138

Development of a numerical model to simulate groundwater flow in the shallow aquifer system of Assateague Island, Maryland and Virginia  

USGS Publications Warehouse

A three-dimensional groundwater-flow model was developed for Assateague Island in eastern Maryland and Virginia to simulate both groundwater flow and solute (salt) transport to evaluate the groundwater system response to sea-level rise. The model was constructed using geologic and spatial information to represent the island geometry, boundaries, and physical properties and was calibrated using an inverse modeling parameter-estimation technique. An initial transient solute-transport simulation was used to establish the freshwater-saltwater boundary for a final calibrated steady-state model of groundwater flow. This model was developed as part of an ongoing investigation by the U.S. Geological Survey Climate and Land Use Change Research and Development Program to improve capabilities for predicting potential climate-change effects and provide the necessary tools for adaptation and mitigation of potentially adverse impacts.

Masterson, John P.; Fienen, Michael N.; Gesch, Dean B.; Carlson, Carl S.

2013-01-01

139

Groundwater occurrence and flow pattern in the Eaugu coal-mine area, Anambra State, Nigeria  

Microsoft Academic Search

The distribution of major geological units, static water level data, water chemistry data, and observations of surface features influenced by groundwater seepage were used to ascertain the nature of groundwater occurrence and flow pattern in the Enugu coal field, Nigeria. Considerations of the geological units, the static groundwater levels and groundwater seepages in the mines indicate that the coal sequence

G. LNWANKWOR

140

Modeling Groundwater Flow using both Neumann and Dirichlet Boundary Conditions  

NASA Astrophysics Data System (ADS)

In groundwater flow models it is customary to use the recharge rate, obtained from measured precipitation minus run off and evapotranspiration, as the top boundary condition (a Neumann boundary condition). However, as has been emphasized by Tóth (1962; 2009), the topography of the water table offers a better boundary condition (a Dirichlet boundary condition), because it leads to the delineation of flow systems and stagnation zones. However, in practical modeling studies the recharge rates obtained when using the Dirichlet boundary condition may turn out to be unrealistically small or large. To remediate this we have developed an unconventional modeling procedure that is based on both the Neumann and the Dirichlet boundary condition on the phreatic surface. Such a model does not only calculate the heads and fluxes, but also an update of the initially perceived hydraulic conductivities, in such a way that the initially perceived conductivity model is preserved as much as possible. For given grid block conductivities, numerical groundwater models (e.g. MODFLOW) are linear in the heads. However, for given heads the numerical models are not linear in the grid block conductivities. Mohammed et al. (2009) have developed a MODFLOW-compatible numerical model that is linear in the stream functions for given grid block conductivities, while it is also linear in the grid block resistivities (inverse of conductivities) if the heads are given. Unconventional modeling is based on this bi-linearity. Assume we specify a reasonable perception of the hydraulic conductivities and determine the numerical solution with Neumann boundary conditions. The resulting fluxes are then substituted into the stream function model, together with Dirichlet boundary conditions, and the grid block resistivities can then be determined by a standard routine for solving systems of linear algebraic equations. The thus calibrated grid block conductivities do not deviate much from the initially perceived conductivity model and honor all the Dirichlet and Neumann boundary data. This so called Constrained Back Projection (CBP) has been developed by Mohammed et al. (2009) and exemplified for synthetic problems. The method is well suited to determine conductivities in ten to hundreds of zones, but solving the algebraic system for thousands to millions of grid block conductivities becomes problematic. A related idea has already been proposed in the 1980s by Wexler (Wexler et al., 1985; Yorkey and Webster, 1987; Kohn and Vogelius, 1987; Wexler, 1988; Kohn and McKenney, 1990) in the context of electric impedance tomography for geophysical and medical imaging. El-Rawy et al. (2010, 2011) has developed and validated this so-called Double Constraint Method (DCM) in the context of hydrogeology and groundwater flow, with applications to two case studies in Belgium. DCM can handle MODFLOW models with thousands to millions of grid block conductivities, but is not very suitable for zonation and is, therefore, complementary to CBP. Application of DCM under a number of different hydrogeological conditions makes the estimate of the hydraulic conductivities more accurate by using a Kalman Filter.

Zijl, Wouter; El-Rawy, Mustafa; Batelaan, Okke

2013-04-01

141

Multivariate analyses with end-member mixing to characterize groundwater flow: Wind Cave and associated aquifers  

NASA Astrophysics Data System (ADS)

SummaryPrincipal component analysis (PCA) applied to hydrochemical data has been used with end-member mixing to characterize groundwater flow to a limited extent, but aspects of this approach are unresolved. Previous similar approaches typically have assumed that the extreme-value samples identified by PCA represent end members. The method presented herein is different from previous work in that (1) end members were not assumed to have been sampled but rather were estimated and constrained by prior knowledge; (2) end-member mixing was quantified in relation to hydrogeologic domains, which focuses model results on major hydrologic processes; (3) a method to select an appropriate number of end members using a series of cluster analyses is presented; and (4) 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 influence of geochemical evolution along flow paths in comparison to mixing. This method was applied to groundwater in Wind Cave and the associated karst aquifer in the Black Hills of South Dakota, USA. The end-member mixing model was used to test a hypothesis that five different end-member waters are mixed in the groundwater system comprising five hydrogeologic domains. The model estimated that Wind Cave received most of its groundwater inflow from local surface recharge with an additional 33% from an upgradient aquifer. Artesian springs in the vicinity of Wind Cave primarily received water from regional groundwater flow.

Long, Andrew J.; Valder, Joshua F.

2011-10-01

142

Regional scale impact of tidal forcing on groundwater flow in unconfined coastal aquifers  

NASA Astrophysics Data System (ADS)

This paper considers the impact of tidal forcing on regional groundwater flow in an unconfined coastal aquifer. Numerical models are used to quantify this impact for a wide range of hydrogeological conditions. Both a shallow and a deep aquifer are investigated with regard to three dimensionless parameter groups that determine the groundwater flow to a large extent. Analytical expressions are presented that allow for a quick estimate of the regional scale effect of tidal forcing under the same conditions as used in the numerical models. Quantitatively, the results in this paper are complementary to previous studies by taking into account variable density groundwater flow, dispersive salt transport and a seepage face in the intertidal area. Qualitatively, the results are in line with previous investigations. The time-averaged hydraulic head at the high tide mark increases upon a decrease of each of the three considered dimensionless parameter groups: R (including the ratio of the hydraulic conductivity and the precipitation excess), ? (the slope of the intertidal area) and AL (the ratio of the width of the fresh water lens and the tidal amplitude). The relative change of the location and the hydraulic head of the groundwater divide, which together characterize regional groundwater flow, increase as ? and AL decrease, but decrease as R decreases. The difference between the analytical solutions and numerical results is small. Therefore, the presented analytical solutions can be used to estimate the bias that is introduced in a numerical model if tidal forcing is neglected. The results should be used with caution in case of significant wave forcing, as this was not considered.

Pauw, P. S.; Oude Essink, G. H. P.; Leijnse, A.; Vandenbohede, A.; Groen, J.; van der Zee, S. E. A. T. M.

2014-09-01

143

Partitioning a regional groundwater flow system into shallow local and deep regional flow compartments  

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

144

1 INTRODUCTION The modular finitedifference groundwater flow  

E-print Network

1 INTRODUCTION The modular finite­difference ground­water flow model (MODFLOW) developed by the U­dimensional ground­water systems (McDonald & Harbaugh, 1988, Harbaugh & McDonald, 1996). MOC3D is a solute is optimal for advection­ dominated systems, which are typical of many field problems involving ground­water

Russell, Thomas F.

145

Groundwater flow and salt transport in a subterranean estuary2 driven by intensified wave conditions3  

E-print Network

1 Groundwater flow and salt transport in a subterranean estuary2 driven by intensified wave, Western University, London, Canada.6 Email: crobinson@eng.uwo.ca7 b National Centre for Groundwater A numerical study, based on a density-dependent variably saturated groundwater flow model,26 was conducted

Candea, George

146

Groundwater flow to the coastal ocean Ann E. Mulligan and Matthew A. Charette  

E-print Network

1 Groundwater flow to the coastal ocean Ann E. Mulligan and Matthew A. Charette Introduction Water estuaries are well known. Only recently has significant attention turned toward the role of groundwater inputs to the ocean. Historically, such inputs were considered insignificant because groundwater flow

147

MODOPTIM: A general optimization program for ground-water flow model calibration and ground-water management with MODFLOW  

USGS Publications Warehouse

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

148

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.

Tim Callahan

149

2007 Estimated International Energy Flows  

SciTech Connect

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

150

Ensemble smoother assimilation of hydraulic head and return flow data to estimate hydraulic conductivity distribution  

E-print Network

Ensemble smoother assimilation of hydraulic head and return flow data to estimate hydraulic and data measurements, an ensemble smoother (ES) to provide enhanced estimates of aquifer hydraulic conductivity (K) through assimilation of hydraulic head (H) and groundwater return flow volume (RFV

Bau, Domenico A.

151

Groundwater flow and radionuclide decay-chain transport modelling around a proposed uranium tailings pond in India  

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

152

Parameter Estimation for Groundwater Models under Uncertain Irrigation Data.  

PubMed

The success of modeling groundwater is strongly influenced by the accuracy of the model parameters that are used to characterize the subsurface system. However, the presence of uncertainty and possibly bias in groundwater model source/sink terms may lead to biased estimates of model parameters and model predictions when the standard regression-based inverse modeling techniques are used. This study first quantifies the levels of bias in groundwater model parameters and predictions due to the presence of errors in irrigation data. Then, a new inverse modeling technique called input uncertainty weighted least-squares (IUWLS) is presented for unbiased estimation of the parameters when pumping and other source/sink data are uncertain. The approach uses the concept of generalized least-squares method with the weight of the objective function depending on the level of pumping uncertainty and iteratively adjusted during the parameter optimization process. We have conducted both analytical and numerical experiments, using irrigation pumping data from the Republican River Basin in Nebraska, to evaluate the performance of ordinary least-squares (OLS) and IUWLS calibration methods under different levels of uncertainty of irrigation data and calibration conditions. The result from the OLS method shows the presence of statistically significant (p?estimated parameters and model predictions that persist despite calibrating the models to different calibration data and sample sizes. However, by directly accounting for the irrigation pumping uncertainties during the calibration procedures, the proposed IUWLS is able to minimize the bias effectively without adding significant computational burden to the calibration processes. PMID:25040235

Demissie, Yonas; Valocchi, Albert; Cai, Ximing; Brozovic, Nicholas; Senay, Gabriel; Gebremichael, Mekonnen

2014-07-12

153

Sensitivity Analysis and Uncertainty in Groundwater Flow  

NASA Astrophysics Data System (ADS)

Sensitivity analysis and uncertainty quantification have long been considered complementary. In systems with spatially varying parameters, the Fréchet derivative provides a local measure of system sensitivity. We show how the spectral decomposition of the Fréchet operator leads naturally to a hierarchical ordering of local variations to which the the model output is most sensitive and use these to form families of physically meaningful reduced order models that can be used in uncertainty propagation as well as parameter estimation

Nunes, Vitor; Werner, Hans

2014-05-01

154

Striking effect of time variation in the estimation of groundwater age in the Wairarapa valley  

NASA Astrophysics Data System (ADS)

The Wairarapa Valley exhibits complex interactions between its rivers and shallow aquifers. With agriculture being an essential part of the region the risk of contamination and depletion of groundwater exists. In order to assist with water resource management in the region, we can do predictions with the help of numerical models. Among these predictions, the evaluation of groundwater age is critical for decision making. This project builds on work done by Greater Wellington Regional Council and will focus on the Wairarapa Valley. The aim of this study is to evaluate the age of the groundwater in the Wairarapa region. Investigations have already been done thanks to hydrochemistry. However radiometric age can be misleading in the sense that it does not consider the mixing process in the motion of groundwater particules. Therefore another approach can be considered .This latter is physic based by considering the age as a property that we transport through two main processes: advection at a macroscopic scale and diffusion at a microscopic scale. The determination of the distribution age by this approach has already been done for the Lake Rotorua but in the steady state case (cf Daughney). The unique contribution of the present study is to estimate the changes in groundwater age distribution through time within the region. Indeed transient simulations are needed to explicitly account for seasonally variable rainfall and pumping wells. This affects the simulated flow solution and then the simulated age solution. In order to solve numerically the transport of age distribution we have chosen to use the Time Marching Laplace Transform Galerkin technique which has been developed in a research code by Fabien Cornaton. The obtained results depict that temporal variations in groundwater age are present and have important implication for resource management

Petrus, Karine; Toews, Michael; Daughney, Christopher; Cornaton, Fabien

2014-05-01

155

Estimation of groundwater recharge in a major sand and gravel aquifer in Ireland using multiple approaches  

NASA Astrophysics Data System (ADS)

Groundwater recharge was investigated in the most extensive sand and gravel aquifer (area of approximately 200 km2) in the Republic of Ireland as part of a wider study seeking to derive recharge estimates using aquifer vulnerability mapping. The proportion of effective rainfall (total rainfall minus actual evapotranspiration) that leads to recharge is known as the recharge coefficient. The recharge investigation involved a variety of approaches, including soil moisture budgeting, well hydrograph analysis, numerical modelling and a catchment water balance. The adoption of multiple techniques provided insights on recharge and also on aquifer properties. Comparison of two soil moisture budgeting approaches (FAO Penman-Monteith with Penman-Grindley) showed how variations in the effective rainfall values from these methods influence groundwater levels simulated in a numerical groundwater model. The catchment water balance estimated the recharge coefficient to be between 81 and 85%, which is considered a reasonable range for this aquifer, where overland flow is rarely observed. The well hydrograph analysis, using a previous estimate of specific yield (0.13), gave recharge coefficients in the range of 40-80%, considered low for this aquifer: a revised specific yield of 0.19 resulted in a more reasonable range of recharge coefficients of between 70 and 100%.

Misstear, B. D. R.; Brown, L.; Johnston, P. M.

2009-05-01

156

Mechanism and rate of denitrification in an agricultural watershed: Electron and mass balance along groundwater flow paths  

USGS Publications Warehouse

The rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer. Intensive agricultural activity in this area has resulted in nitrate concentrations in groundwater often exceeding drinking water standards. Both the extent and rate of denitrification varied depending on the groundwater flow path. While little or no denitrification occurred in much of the upland portions of the aquifer, a gradual redox gradient is observed as aerobic upland groundwater moves deeper in the aquifer. In contrast, a sharp shallow redox gradient is observed adjacent to a third-order stream as aerobic groundwater enters reduced sediments. An essentially complete loss of nitrate concurrent with increases in excess N2 provide evidence that denitrification occurs as groundwater enters this zone. Electron and mass balance calculations suggest that iron sulfide (e.g., pyrite) oxidation is the primary source of electrons for denitrification. Denitrification rate estimates were based on mass balance calculations using nitrate and excess N2 coupled with groundwater travel times. Travel times were determined using a groundwater flow model and were constrained by chlorofluorocarbon-based age dates. Denitrification rates were found to vary considerably between the two areas where denitrification occurs. Denitrification rates in the deep, upland portions of the aquifer were found to range from < 0.01 to 0.14 mM of N per year; rates at the redoxcline along the shallow flow path range from 1.0 to 2.7 mM of N per year. Potential denitrification rates in groundwater adjacent to the stream may be much faster, with rates up to 140 mM per year based on an in situ experiment conducted in this zone.The rate and mechanism of nitrate removal along and between groundwater flow paths were investigated using a series of well nests screened in an unconfined sand and gravel aquifer. Intensive agricultural activity in this area has resulted in nitrate concentrations in groundwater often exceeding drinking water standards. Both the extent and rate of denitrification varied depending on the groundwater flow path. While little or no denitrification occurred in much of the upland portions of the aquifer, a gradual redox gradient is observed as aerobic upland groundwater moves deeper in the aquifer. In contrast, a sharp shallow redox gradient is observed adjacent to a third-order stream as aerobic groundwater enters reduced sediments. An essentially complete loss of nitrate concurrent with increases in excess N2 provide evidence that denitrification occurs as groundwater enters this zone. Electron and mass balance calculations suggest that iron sulfide (e.g., pyrite) oxidation is the primary source of electrons for denitrification. Denitrification rate estimates were based on mass balance calculations using nitrate and excess N2 coupled with groundwater travel times. Travel times were determined using a groundwater flow model and were constrained by chlorofluorocarbon-based age dates. Denitrification rates were found to vary considerably between the two areas where denitrification occurs. Denitrification rates in the deep, upland portions of the aquifer were found to range from <0.01 to 0.14 mM of N per year; rates at the redoxcline along the shallow flow path range from 1.0 to 2.7 mM of N per year. Potential denitrification rates in groundwater adjacent to the stream may be much faster, with rates up to 140 mM per year based on an in situ experiment conducted in this zone.

Tesoriero, A.J.; Liebscher, H.; Cox, S.E.

2000-01-01

157

Comparison of groundwater flow model results and isotopic data in the Leon valley, Mexico  

NASA Astrophysics Data System (ADS)

The study area is located in the State of Guanajuato, Northwest of the city of Mexico. Leon Valley has covered with groundwater its demand of water, estimated in 20.6 cubic meters per second. The constant increase of population and economic activities in the region have a constant growth in water needs. Related extraction rate has produced an average decrease of approximately 1.0 m per year over the past two decades. This suggests that the present management of the groundwater should be checked. Management of groundwater in the study area involves the possibility of producing environmental impacts by extraction. This vital resource under stress becomes necessary studying its hydrogeological functioning to achieve scientific management of groundwater in the Valley. This research was based on the analysis and integration of existing information and the field generated by the authors. Outstanding concepts were: i) the geological structure of the area, ii) hydraulic parameters and iii) composition of deuterium-delta and delta-oxygen - 18. This information has been fully analyzed by applying a groundwater flow model (MODFLOW) and a particle tracking model (FLOWPATH): the results were similar to interpretations in terms of travel time and paths derived from isotopic data.

Hernandez-Garcia, G.

2013-12-01

158

Geochemical and Isotopic Interpretations of Groundwater Flow in the Oasis Valley Flow System, Southern Nevada  

SciTech Connect

This report summarizes the findings of a geochemical investigation of the Pahute Mesa-Oasis Valley groundwater flow system in southwestern Nevada. It is intended to provide geochemical data and interpretations in support of flow and contaminant transport modeling for the Western and Central Pahute Mesa Corrective Action Units.

J.M. Thomas; F.C. Benedict, Jr.; T.P. Rose; R.L. Hershey; J.B. Paces; Z.E. Peterman; I.M. Farnham; K.H. Johannesson; A.K. Singh; K.J. Stetzenbach; G.B. Hudson; J.M. Kenneally; G.F. Eaton; D.K. Smith

2003-01-08

159

A geostatistical framework for incorporating transport information in estimating the distribution of a groundwater  

E-print Network

of a groundwater contaminant plume Shahar Shlomi1 and Anna M. Michalak1 Received 25 April 2006; revised 1 September 2006; accepted 13 October 2006; published 8 March 2007. [1] The goal of groundwater contaminant plume transport information in estimating the spatial distribution of groundwater contaminant plumes. The methods

Michalak, Anna M.

160

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

161

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

USGS Publications Warehouse

The extensive and highly managed surface-water system in southeastern Florida constructed during the 20th Century has allowed for the westward expansion of urban and agricultural activities in Miami-Dade County. In urban areas of the county, the surface-water system is used to (1) control urban flooding, (2) supply recharge to production well fields, and (3) control seawater intrusion. Previous studies in Miami-Dade County have determined that on a local scale, leakage from canals adjacent to well fields can supply a large percentage (46 to 78 percent) of the total groundwater pumpage from production well fields. Canals in the urban areas also receive seepage from the Biscayne aquifer that is derived from a combination of local rainfall and groundwater flow from Water Conservation Area 3 and Everglades National Park, which are west of urban areas of Miami-Dade County. To evaluate the effects of groundwater pumpage on canal leakage and regional groundwater flow, the U.S. Geological Survey (USGS) developed and calibrated a coupled surface-water/groundwater model of the urban areas of Miami-Dade County, Florida. The model was calibrated by using observation data collected from January 1997 through December 2004. The model calibration was verified using observation data collected from January 2005 through December 2010. A 1-year warmup period (January 1996 through December 1996) was added prior to the start of the calibration period to reduce the effects of inaccurate initial conditions on model calibration. The model is designed to simulate surface-water stage and discharge in the managed canal system and dynamic canal leakage to the Biscayne aquifer as well as seepage to the canal from the aquifer. The model was developed using USGS MODFLOW–NWT with the Surface-Water Routing (SWR1) Process to simulate surface-water stage, surface-water discharge, and surface-water/groundwater interaction and the Seawater Intrusion (SWI2) Package to simulate seawater intrusion, respectively. Automated parameter estimation software (PEST) and highly parameterized inversion techniques were used to calibrate the model to observed surface-water stage, surface-water discharge, net surface-water subbasin discharge, and groundwater level data from 1997 through 2004 by modifying hydraulic conductivity, specific storage coefficients, specific yield, evapotranspiration parameters, canal roughness coefficients (Manning’s n values), and canal leakance coefficients. Tikhonov regularization was used to produce parameter distributions that provide an acceptable fit between model outputs and observation data, while simultaneously minimizing deviations from preferred values based on field measurements and expert knowledge. Analytical and simulated water budgets for the period from 1996 through 2010 indicate that most of the water discharging through the salinity control structures is derived from within the urban parts of the study area and that, on average, the canals are draining the Biscayne aquifer. Simulated groundwater discharge from the urban areas to the coast is approximately 7 percent of the total surface-water inflow to Biscayne Bay and is consistent with previous estimates of fresh groundwater discharge to Biscayne Bay. Simulated groundwater budgets indicate that groundwater pumpage in some surface-water basins ranges from 13 to 27 percent of the sum of local sources of groundwater inflow. The largest percentage of groundwater pumpage to local sources of groundwater inflow occurs in the basins that have the highest pumping rates (C–2 and C–100 Basins). The ratio of groundwater pumpage to simulated local sources of groundwater inflow is less than values calculated in previous local-scale studies. The position of the freshwater-seawater interface at the base of the Biscayne aquifer did not change notably during the simulation period (1996–2010), consistent with the similar positions of the interface in 1984, 1995, and 2011 under similar hydrologic and groundwater pumping conditions. Landward movement of the freshwater-seawater interface

Hughes, Joseph D.; White, Jeremy T.

2014-01-01

162

Numerical modeling of groundwater flow in the coastal aquifer system of Taranto (southern Italy)  

NASA Astrophysics Data System (ADS)

The Mediterranean region is characterized by a strong development of coastal areas with a high concentration of water-demanding human activities, resulting in weakly controlled withdrawals of groundwater which accentuate the saltwater intrusion phenomenon. The worsening of groundwater quality is a huge problem especially for those regions, like Salento (southern Italy), where a karst aquifer system represents the most important water resource because of the deficiency of a well developed superficial water supply. In this frame, the first 2D numerical model describing the groundwater flow in the karst aquifer of Salento peninsula was developed by Giudici et al. [1] at the regional scale and then improved by De Filippis et al. [2]. In particular, the estimate of the saturated thickness of the deep aquifer highlighted that the Taranto area is particularly sensitive to the phenomenon of seawater intrusion, both for the specific hydrostratigraphic configuration and for the presence of highly water-demanding industrial activities. These remarks motivate a research project which is part of the research program RITMARE (The Italian Research for the Sea), within which a subprogram is specifically dedicated to the problem of the protection and preservation of groundwater quality in Italian coastal aquifers and in particular, among the others, in the Taranto area. In this context, the CINFAI operative unit aims at providing a contribution to the characterization of groundwater in the study area. The specific objectives are: a. the reconstruction of the groundwater dynamic (i.e., the preliminary identification of a conceptual model for the aquifer system and the subsequent modeling of groundwater flow in a multilayered system which is very complex from the hydrostratigraphical point of view); b. the characterization of groundwater outflows through submarine and subaerial springs and the water exchanges with the shallow coastal water bodies (e.g. Mar Piccolo) and the off-shore sea; c. the modeling of seawater intrusion in the coastal aquifer system. The first objective is achieved through the analysis of hydrostratigraphic reconstructions obtained from different data sets: well logs, published geological field maps, studies for the characterization of contaminated sites. The hydrostratigraphic setup is merged with maps of land use, hydraulic head maps, data on water extraction and source discharge, in order to identify the conceptual model. For the numerical simulations, the computer code YAGMod, which was originally developed to perform 3D groundwater flow simulation with a simplified treatment of unsaturated/saturated conditions and the effects of strong aquifer exploitation (i.e., high well pumping rates), is extended to the case of a variable density flow. The results will be compared with those obtained with other modeling software (e.g., Tough2). [1] Giudici M., Margiotta S., Mazzone F., Negri S., Vassena C., 2012. Modelling Hydrostratigraphy and groundwater flow of a fractured and karst aquifer in a Mediterranean basin (Salento peninsula, southeastern Italy), Environmental Earth Sciences. doi: 10.1007/s12665-012-1631-1 [2] De Filippis G., Giudici M., Margiotta S., Mazzone F., Negri S., Vassena C., 2013. Numerical modeling of the groundwater flow in the fractured and karst aquifer of the Salento peninsula (Southern Italy), Acque Sotterranee, 2:17-28. doi: 10.7343/AS-016-013-0040

De Filippis, Giovanna; Giudici, Mauro; Negri, Sergio; Margiotta, Stefano; Cattaneo, Laura; Vassena, Chiara

2014-05-01

163

Estimates of riparian evapotranspiration using diurnal monitoring of groundwater regime in desert environments  

NASA Astrophysics Data System (ADS)

Shallow groundwater is mainly discharged by phreatophytes in many riparian ecosystems of arid and semiarid environment, while estimation of groundwater evapotranspiration in these regions still remains a challenge for regional water resources assessment. In this study, a simple relationship between the average standard deviation of diurnal groundwater level fluctuations and the daily evapotranspiration over relatively short periods (days or weeks) was developed for estimating groundwater consumption by phreatophytes in arid/semi-arid areas. Our approach allows estimating groundwater evapotranspiration using stable statistical characteristics of diurnal groundwater fluctuation, and it is useful for analyzing large amounts of data obtained from digital groundwater level monitoring sensors. The developed methodology was applied to two phreatophyte-dominated riparian areas (Populus euphratica and Tamarix ramosissima) in a typical Gobi desert region of northwest China to demonstrate the usefulness of the technique.

Wang, P.; Pozdniakov, S. P.; Grinevsky, S.; Yu, J.

2013-12-01

164

Ground-water flow in Melton Valley, Oak Ridge reservation, Roane County, Tennessee; preliminary model analysis  

USGS Publications Warehouse

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

165

Unsaturated-zone fast-path flow calculations for Yucca Mountain groundwater travel time analyses (GWTT-94)  

SciTech Connect

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

166

Estimating evapotranspiration in different rain-fed peatlands from groundwater level changes  

NASA Astrophysics Data System (ADS)

Biogeochemical processes in peatlands are strongly controlled by the hydrological conditions of these environments. One of the key parameters controlling the water balance is the evapotranspiration, which can be calculated e.g. by the FAO crop reference evapotranspiration or the Penman-Monteith equation as a function of atmospheric conditions and plant specific parameters. These parameters are well investigated for agricultural crops and forests but poorly for most peatland vegetation types. Direct measurement of the evapotranspiration is possible with weighing lysimeters or the eddy-covariance technique, but expensive and time consuming. In many peatlands and riparian areas groundwater table changes are characterized by diurnal fluctuations (daytime decline, night-time recovery) caused by the evapotranspiration and groundwater recharge. White introduced 1932 a method to calculate the evapotranspiration from these diurnal fluctuations. In contrast to traditional evapotranspiration models only a small number of variables need to be measured (groundwater level changes, possibly precipitation) or calculated (specific yield). Over the last decades, several studies and modifications of the White method have been published. Several authors showed the applicability of the method for riparian areas and fens, but this relies on the assumption of a constant recharge over the whole day. As there is no groundwater inflow at rain-fed peatlands, recovery during night-time can only result from redistribution in the soil profile or from lateral flow processes within the peatland. Thus, approaches to calculate evapotranspiration from diurnal groundwater fluctuations used to date need to be adapted. Based on 50 hydrographs measured in 6 rain-fed peatlands in Germany characterized by different soil properties, land use and vegetation, we systematically analyzed diurnal patterns of the groundwater levels. These patterns were spatially and temporally very variable. At some sites, the groundwater level continuously declined during rain-free periods with different slopes during the night and the day, resulting in a step-like shape of the hydrograph. Other sites showed a continuous decline at daytime followed by weakly increasing or constant groundwater levels at night. Based on this analysis, we developed a modification of the White-method for estimating the evapotranspiration of rain-fed peatlands. The approach will be validated with eddy-covariance data from one site.

Dettmann, Ullrich; Maurer, Eike; Bechtold, Michel; Brümmer, Christian; Tiemeyer, Bärbel

2014-05-01

167

Estimating pumping time and ground-water withdrawals using energy- consumption data  

USGS Publications Warehouse

Evaluation of the hydrology of an aquifer requires knowledge about the volume of groundwater in storage and also about the volume of groundwater withdrawals. Totalizer flow meters may be installed at pumping plants to measure withdrawals; however, it generally is impractical to equip all pumping plants in an area with meters. A viable alternative is the use of rate-time methods. Rate-time methods may be used at individual pumping plants to decrease the data collection necessary for determining withdrawals. At sites where pumping-time measurement devices are not installed, pumping time may be determined on the basis of energy consumption and power demand. At pumping plants where energy consumption is metered, data acquired by reading of meters is used to estimate pumping time. Care needs to be taken to read these meters correctly. At pumping plants powered by electricity, the calculations need to be modified if transformers are present. At pumping plants powered by natural gas, the effects of the pressure-correction factor need to be included in the calculations. At pumping plants powered by gasoline, diesel oil, or liquid petroleum gas, the geometry of storage tanks needs to be analyzed as part of the calculations. The relation between power demand and pumping rate at a pumping plant can be described through the use of the power-consumption coefficient. Where equipment and hydrologic conditions are stable, this coefficient can be applied to total energy consumption at a site to estimate total groundwater withdrawals. Random sampling of power consumption coefficients can be used to estimate area-wide groundwater withdrawal. (USGS)

Hurr, R.T.; Litke, D.W.

1989-01-01

168

Evaluation of ground-water flow and hydrologic budget for Lake Five-O, a seepage lake in northwestern Florida  

USGS Publications Warehouse

Temporal and spatial distributions of ground-water inflow to, and leakage from Lake Five-O, a softwater, seepage lake in northwestern Florida, were evaluated using hydrologic data and simulation models of the shallow ground-water system adjacent to the lake. The simulation models indicate that ground-water inflow to the lake and leakage from the lake to the ground-water system are the dominant components in the total inflow (precipitation plus ground-water inflow) and total outflow (evaporation plus leakage) budgets of Lake Five-O. Simlulated ground-water inflow and leakage were approximately 4 and 5 times larger than precipitation inputs and evaporative losses, respectively, during calendar years 1989-90. Exchanges of water between Lake Five-O and the ground-water system were consistently larger than atmospheric-lake exchanges. A consistent pattern of shallow ground-water inflow and deep leakage was also evident throughout the study period. The mean time of travel from ground-water that discharges at Lake Five-O (time from recharge at the water table to discharge at the lake) was estimated to be within a range of 3 to 6 years. Flow-path evaluations indicated that the intermediate confining unit probably has a negligible influence on the geochemistry of ground-water inflow to Lake Five-O. The hydrologic budgets and flow-path evaluations provide critical information for developing geochemical budgets for Lake Five-O and for improving the understanding of the relative importance of various processes that regulate the acid-neutralizing capacity of softwater seepage lakes in Florida.

Grubbs, J.W.

1995-01-01

169

Estimation of Relative Recharge Sequence to Groundwater with Minimum Entropy Deconvolution  

NASA Astrophysics Data System (ADS)

Groundwater is widely used as natural resources for the drink, spa, etc., and a supplement to the official and/or natural water supply. In these cases, the establishment of water balance model can provide a safe and effective usage of resources. To establish the appropriate water balance model and the design of water usage, recharge rate must be estimated with an allowed accuracy. For these purposes, many methods were suggested to estimate recharge rate. One of most popular methods in recent years is measuring groundwater age with environmental tracer(Solomon et. al., 1993; Leduc et. al., 1997; Bromley et. al., 1997; Williams, 1997; Ayalon et. al. 1998). Using the distributed environmental tracer, the vertical profile of groundwater age can be composed, and recharge rate can be estimated with the composed profile. Water budget analysis can be the other one of available method(Bradbury and Rushton, 1998; Finch, 1998; Bekesi and McConchie, 1999). However, to explain the expansion of contaminant with temporal variation of unsaturated flow, sequential estimation of recharge must be needed. Unfortunately, it is a very hard work to find out some studies on sequential approaches to estimate the recharge rate to groundwater. Even predictive deconvolution technique was rarely. In general, minimum phase condition, preposition of classical predictive deconvolution, can hardly be satisfied in nature. On the contrary, the input signal in natural system can be considered as a random signal. To avoid the strong restriction of minimum phase condition, Wiggins(1978) proposed minimum entropy deconvolution(MED) with varimax norm. However, solution process with varimax norm is non-linear. For the linearization of MED problem, Carbrelli suggested another criterion, D norm(1984). In this study, MED with D norm was applied to the estimation of the sequence of relative recharge rate, and the applicability of MED to evaluation of recharge sequence was investigated. To check out the applicability of MED to the estimation of relative recharge sequence, synthesized data set and two real data set were applied. To compare the estimated results with source wavelets, cross-correaltion coefficient was adopted. Cross-correaltion in synthesized cases are over 0.9, and in real case with rainfall sequence is 0.73~0.8. The cross correlations in both of two cases indicate that results from MED are the appropriate estimations of recharge sequences.

Kim, T.; Lee, K.

2002-12-01

170

Processing, Analysis, and General Evaluation of Well-Driller Logs for Estimating Hydrogeologic Parameters of the Glacial Sediments in a Ground-Water Flow Model of the Lake Michigan Basin  

USGS Publications Warehouse

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

171

Groundwater.  

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

172

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

USGS Publications Warehouse

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

173

Estimation of in situ groundwater chemistry using geochemical modeling: A test case for saline type groundwater in argillaceous rock  

NASA Astrophysics Data System (ADS)

Saline type groundwaters data in the Mobara area (a marine based argillaceous rock) located in the well-known “South Kanto gas field” in Japan were investigated by JNC as part of a natural analogue study. Most groundwaters in the field were extracted from deep gas wells ( e. g., 400-2000 m below the surface), and the all data reported previously were sampled at the wellhead, where physico-chemical parameters ( e. g., temperature, pH, Eh etc.) were also measured. In such cases, particular attention should be paid to whether the measured and/or analyzed results are consistent with the chemical and physical conditions in the in situ geological formation because air contamination, the temperature and pressure changes during sampling can affect the groundwater chemistry. The present study shows a test case to estimate the in situ groundwater chemistry in argillaceous rock of the Mobara area using geochemical model calculations. Results from thermodynamic interpretation of groundwater chemistry using the measured pH and Eh of groundwater sampled at wellhead ( e. g., pH = 7.86, Eh = -50 mV) indicate that the groundwaters are supersaturated with respect to calcite ( e. g., the saturation index; SI is 1.14). Calcite is known to equilibrate relatively quickly with aqueous solutions at low temperatures and this mineral is present in the Otadai formation, however. Therefore the values greater than 0 for SI of calcite may be due to errors in the pH measurement. Also the measured Eh is relatively oxidizing value which may be inconsistent with the in situ geochemical conditions ( e. g., pyrite and siderite coexist, CH 4(g) dominates in the groundwaters). Thus such Eh value may be disturbed by contact of the samples with atmospheric oxygen and other effects like degassing. Errors in the pH measurement might be caused by degassing during sampling of groundwaters. As a test case to estimate the groundwater considering such degassing effect, we first assume that the in situ groundwaters are saturated with respect to calcite. A back-titration geochemical model is then used to simulate the addition of CO 2(g). Regarding the redox conditions of groundwater, we also assume that pyrite-siderite equilibrium controls the Eh of Mobara groundwaters considering the mineralogy identified in the Otadai formation. The assumed equilibrium between pyrite and siderite implies a fixed value of PS at a given temperature and pH. A back-titration of trace levels H 2S(g) is also applied to estimate the possible effect of the in situ Eh and pH of groundwaters. The calculated result shows that pH is about 6.7 and Eh is about -190 mV, respectively. The estimated pH value for the in situ groundwater is about 1 unit lower than the measured pH value at the surface and the in situ redox potential is significantly lower than Eh value measured in surface sample. Based on a preliminary assessment of mineral-water equilibria using the mineral stability relations in the CaO-MgO-Al 2O 3-SiO 2-H 2O system, the estimated in situ groundwater composition is more consistent with the mineralogy of the Otadai formation than the measured groundwater composition. However, further consideration ( e. g., detail mineralogical investigation, reliable and consistent thermodynamic data with site mineralogy) would be needed to check the reliability of estimation technique. JNC (Japan Nuclear Cycle Development Institute) was merged in October 2005 with the Japan Atomic Energy Research Institute (JAERI) to form the Japan Atomic Energy Agency (JAEA).

Sasamoto, Hiroshi; Yui, Mikazu; Arthur, Randolph C.

174

Groundwater, springs, and stream flow generation in an alpine meadow of a tropical glacierized catchment  

NASA Astrophysics Data System (ADS)

Melting tropical glaciers supply approximately half of dry season stream discharge in glacierized valleys of the Cordillera Blanca, Peru. The remainder of streamflow originates as groundwater stored in alpine meadows, moraines and talus slopes. A better understanding of the dynamics of alpine groundwater, including sources and contributions to streamflow, is important for making accurate estimates of glacial inputs to the hydrologic budget, and for our ability to make predictions about future water resources as glaciers retreat. Our field study, conducted during the dry season in the Llanganuco valley, focused on a 0.5-km2 alpine meadow complex at 4400 m elevation, which includes talus slopes, terminal moraines, and a debris fan. Two glacial lakes and springs throughout the complex feed a network of stream channels that flow across the meadow (~2 km total length). We combined tracer measurements of stream and spring discharge and groundwater-surface water exchange with synoptic sampling of water isotopic and geochemical composition, in order to characterize and quantify contributions to streamflow from different geomorphic features. Surface water inputs to the stream channels totaled 58 l/s, while the stream gained an additional 57 l/s from groundwater inputs. Water chemistry is primarily controlled by flowpath type (surface/subsurface) and length, as well as bedrock lithology, while stable water isotopic composition appears to be controlled by water source (glacial lake, meadow or deep groundwater). Stream water chemistry is most similar to meadow groundwater springs, but isotopic composition suggests that the majority of stream water, which issues from springs at the meadow/fan interface, is from the same glacial source as the up-gradient lake. Groundwater sampled from piezometers in confined meadow aquifers is unique in both chemistry and isotopic composition, but does not contribute a large percentage of stream water exiting this small meadow, as quantified by discharge measurements and isotopic mixing. However, we expect that as streams flow down through extensive meadows and wetlands in many Cordillera Blanca valleys, meadow groundwater is a more significant contributor to streamflow. Results from this small, high meadow in Llanganuco will be compared to a larger and lower-elevation meadow system in the Quilcayhuanca valley.

Gordon, R.; Lautz, L. K.; McKenzie, J. M.; Mark, B. G.; Chavez, D.

2013-12-01

175

Impacts of glacially recharged groundwater flow systems on talik evolution  

NASA Astrophysics Data System (ADS)

Most currently permafrost-covered landscapes underwent fundamental shifts in the hydrogeological and the thermal regime as a result of deglaciation after the Last Glacial Maximum (LGM). The transient effects of heat and fluid flow associated with retreating ice sheets are important to consider for the present-day hydrogeology of these regions. In this paper, we use numerical models to evaluate the evolution of taliks underneath proglacial lakes during deglaciation. In our models, the hydrological and thermal boundary conditions at the lake site are constraint by the hydrogeological impacts of ice sheet dynamics since the LGM. During the LGM, the ground surface was insulated from air temperatures, and as a result, there was no permafrost underneath the wet-based ice. Subsequently, ice sheet retreat led to an exposure of a proglacial area to subzero air temperatures and the formation of permafrost. Where proglacial lakes form, discharge of deeper groundwater becomes focused. In this scenario, subpermafrost groundwater flow is driven by a combination of direct subglacial recharge and elevated hydraulic heads preserved in that part of the aquifer. Advective heat flow can delay or prevent through taliks from freezing as function of aquifer properties. The presence and evolution of through taliks in thick permafrost can create complex and transient hydrogeological phenomena.

Scheidegger, J. M.; Bense, V. F.

2014-04-01

176

Characterization of the subregional ground-water flow system of a potential site for a high-level nuclear waste repository  

Microsoft Academic Search

A study was performed to characterize the subregional ground-water flow system that includes Yucca Mountain, Nevada, the potential site of a high-level nuclear-waste repository. The study consisted of three parts: (1) The development of a finite-element parameter-estimation model of ground-water flow, from which sensitivity analyses of model variables were performed; (2) the characterization of the geohydrology and evapotranspiration at Franklin

Czarnecki

1988-01-01

177

Description of the ground-water flow system in the Portland Basin, Oregon and Washington  

USGS Publications Warehouse

An increasing dependence on ground-water resources in the Portland Basin has made it necessary for State and local governments to evaluate the capability of the ground-water system to meet present and future demands for water. This report describes the regional ground-water system and provides a conceptualization of the aquifer system. Aquifer geometry, recharge, ground-water flow directions, ground-water/surface water relations, water use, and water-level changes with time are presented.

McFarland, William D.; Morgan, David S.

1996-01-01

178

Hyporheic transport and biogeochemical reactions in pool-riffle systems under varying ambient groundwater flow conditions  

NASA Astrophysics Data System (ADS)

the interface between stream water, groundwater, and the hyporheic zone (HZ), important biogeochemical processes that play a crucial role in fluvial ecology occur. Solutes that infiltrate into the HZ can react with each other and possibly also with upwelling solutes from the groundwater. In this study, we systematically evaluate how variations of gaining and losing conditions, stream discharge, and pool-riffle morphology affect aerobic respiration (AR) and denitrification (DN) in the HZ. For this purpose, a computational fluid dynamics model of stream water flow is coupled to a reactive transport model. Scenarios of variations of the solute concentration in the upwelling groundwater were conducted. Our results show that solute influx, residence time, and the size of reactive zones strongly depend on presence, magnitude, and direction of ambient groundwater flow. High magnitudes of ambient groundwater flow lower AR efficiency by up to 4 times and DN by up to 3 orders of magnitude, compared to neutral conditions. The influence of stream discharge and morphology on the efficiency of AR and DN are minor, in comparison to that of ambient groundwater flow. Different scenarios of O2 and NO3 concentrations in the upwelling groundwater reveal that DN efficiency of the HZ is highest under low upwelling magnitudes accompanied with low concentrations of O2 and NO3. Our results demonstrate how ambient groundwater flow influences solute transport, AR, and DN in the HZ. Neglecting groundwater flow in stream-groundwater interactions would lead to a significant overestimation of the efficiency of biogeochemical reactions in fluvial systems.

Trauth, Nico; Schmidt, Christian; Vieweg, Michael; Maier, Uli; Fleckenstein, Jan H.

2014-05-01

179

A deuterium-calibrated, discrete-state compartment model of regional groundwater flow, Nevada Test Site and vicinity  

SciTech Connect

A discrete--state compartment (DSC) model was developed, using the conservative tracer deuterium, to simulate the regional groundwater flow for a portion of southern Nevada, including the Nevada Test Site. The model simulates flow rates, discharge rates, and flow directions, as well as mean ages of the groundwater. The results obtained by this model were found to be similar to those of other studies and available hydrogeologic information. The deep regional groundwater was observed to consistently be more depleted in deuterium than the local vertical recharge waters. However, the deep system is consistently more enriched in deuterium than the underflow water from higher latitudes, which was used as input for the model. The total groundwater flow through the modeled area was estimated to be 58.9 {times} 10{sup 6} m{sup 3}/yr. Approximately 40 percent of this ground water originates as underflow from the higher latitudes, while the remaining 60 percent is from local vertical recharge. The Spring Mountains and the Fortymile Canyon/Wash--Stockade Wash area were determined to be sources of major vertical recharge with 9.6 {times} 10{sup 6} m{sup 3}/yr, and 7.6 {times} 10{sup 6} m{sup 3}/yr of recharge, respectively. The simulated ages of the groundwater were found to vary considerably, however, the ages do not correlate with position along the simulated flow path. The mean and median ages of the groundwater at Fortymile Canyon/Wash were simulated to be 6,700 and 1,400 years, respectively, while the ages of the groundwater at Yucca Flat were 26,300 and 21,600 years, respectively.

Sadler, W.R. [Nevada Univ., Reno, NV (United States). Water Resources Center; Campana, M.E. [New Mexico Univ., Albuquerque, NM (United States). Dept. of Geology; Jacobson, R.L.; Ingraham, N.L. [Nevada Univ., Las Vegas, NV (United States). Water Resources Center

1992-03-01

180

Groundwater flow, velocity, and age in a thick, fine-grained till unit in southeastern Wisconsin  

USGS Publications Warehouse

Piezometer nests were installed at study sites in each of five north-south-trending end moraines of the late Pleistocene Oak Creek Formation in southeastern Wisconsin. The formation is composed primarily of a fine-grained glacial diamicton (till) and laterally continuous and discontinuous, coarse-grained lake and meltwater stream sediment. It overlies the Silurian dolomite aquifer, which is a source of drinking water to rural areas. The average vertical linear velocity and age of ground water in the Oak Creek Formation were estimated by three methods: Darcy's Law, environmental isotopes including 3H, ??2H, ??18O, and 14C (dissolved inorganic carbon), and solute transport modeling of 18O. The F-1 and Metro sites in the Tinley moraine showed excellent agreement among the three estimates of vertical velocity and showed the lowest velocity values (0.3-0.5 cm year-1 downward), which suggests that diffusion controls vertical mass transport at these sites. Although the extrapolated maximum age of ground water is 35 000 years, ground water below 75 m at these sites is probably not older than 15 000 years, which is the maximum age of the formation. Estimates of velocity showed less agreement at study sites in the Lake Border moraine system to the east and ranged from about 0.2 to 20.7 cm year-1; maximum groundwater age could range from 213 to 6000 years. Higher and more variable velocities, perhaps owing to thinner and more heterogeneous sediment in these areas, suggest that diffusion may not dominate vertical mass transport. Heterogeneity and fractures may also promote the development of groundwater flow systems dominated by lateral flow. Because of the uncertainty about the nature of groundwater flow, velocity, and age in the formation east of the Tinley moraine, future waste-disposal activity in southeastern Wisconsin should be confined to the thickest parts of the Tinley moraine near the present F-1 and Metro sites. ?? 1992.

Simpkins, W.W.; Bradbury, K.R.

1992-01-01

181

Simulation of recharge for the Death Valley regional groundwater flow system using an integrated hydrologic model  

NASA Astrophysics Data System (ADS)

A proof-of-concept study was conducted using the integrated hydrologic model, GSFLOW, to simulate spatially and temporally distributed recharge for the Death Valley regional groundwater flow system (DVRFS). GSFLOW is an integrated groundwater - surface water flow model that combines two modeling applications: the Precipitation-Runoff-Modeling-System (PRMS) and MODFLOW. Previous methods used to estimate recharge for the DVRFS include empirical models based on precipitation, applications of the chloride mass-balance method, and applications of a precipitation-runoff model, INFIL, which used a daily time step to simulate recharge as net infiltration through the root zone. The GSFLOW model offers several potential advantages compared to the previous methods including (1) the ability to simulate complex flow through a thick unsaturated zone (UZ), allowing for the dampening and time delay of recharge relative to the infiltration signal at the top of the UZ and also allowing for the redistribution of flow within the UZ, as enabled by the MODFLOW-NWT and UZF capabilities, (2) the simulation of rejected recharge in response to the dynamics of groundwater discharge and low permeability zones in the UZ, (3) a more explicit representation of streamflow and recharge processes in the mostly ephemeral stream channels that characterize the DVRFS, and (4) the ability to simulate complex flow paths for runoff occurring as both overland flow and shallow subsurface flow (interflow) in the soil zone using a network of cascades connecting hydrologic response units (HRUs). Simulations were done using a daily time step for water years 1980-2010. Preliminary estimates of recharge using GSFLOW indicate that the distribution of recharge is highly variable both spatially and temporally due to variability in precipitation, snowmelt, evapotranspiration, runoff, and the permeability of bedrock and alluvium underlying the root zone. Results averaged over the areas of subbasins were similar to results obtained from previous studies. However, estimates of recharge on the local scale of the HRUs indicate significant (greater than 100 percent) differences at some locations compared to results obtained using INFIL due to differences in (1) the geometry and scale of HRUs, (2) the layout of the cascading flow network and the location of stream channels, (3) the representation of the physical characteristics of the root zone, and (4) model processes controlling the simulation of evapotranspiration and the movement of water through the root zone.

Hevesi, J. A.; Regan, R. S.; Hill, M. C.; Heywood, C.; Kohn, M. S.

2012-12-01

182

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

SciTech Connect

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

183

Submarine groundwater discharge to a small estuary estimated from radon and salinity measurements and a box model  

USGS Publications Warehouse

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

184

WIRADA Science Symposium Proceedings, Melbourne, Australia, 15 August 2011 Deriving groundwater estimates in Australia from Gravity Recovery and  

E-print Network

groundwater estimates in Australia from Gravity Recovery and Climate Experiment (GRACE) observations Deriving groundwater estimates in Australia from Gravity Recovery and Climate Experiment (GRACE) observations The Gravity Recovery and Climate Experiment (GRACE) space gravity mission detects changes ",-./''-48

Tregoning, Paul

185

Comparison of ground-water flow model particle-tracking results and isotopic data in the Mojave River ground-water basin, southern California, USA  

Microsoft Academic Search

Flow-path and time-of-travel results for the Mojave River ground-water basin, southern California, calculated using the ground-water flow model modflow and particle-tracking model modpath were similar to flow path and time-of-travel interpretations derived from delta-deuterium and carbon-14 data. Model and isotopic data both show short flow paths and young ground-water ages throughout the floodplain aquifer along most the Mojave River. Longer

J. A. Izbicki; C. L. Stamos; T. Nishikawa; P. Martin

2004-01-01

186

Regional ground-water flow modeling of the Glacial Lake Agassiz Peatlands, Minnesota  

Microsoft Academic Search

Three-dimensional ground-water modeling experiments were done to test the hypothesis that regional ground-water flow is an important component of the water budget in the Glacial Lake Agassiz Peatlands of northern Minnesota. Previous data collected from the Glacial Lake Agassiz Peatlands suggest that regional ground-water flow discharges to these peatlands, maintaining saturation, controlling the peat pore-water chemistry, and driving ecological change.

A. S. Reeve; J. Warzocha; P. H. Glaser; D. I. Siegel

2001-01-01

187

Groundwater flow dynamics and arsenic source characterization in an aquifer system of West Bengal, India  

NASA Astrophysics Data System (ADS)

groundwater flow modeling, reverse particle tracking, and environmental tracers are used to locate the source of geogenic As affecting an aquifer in West Bengal. The aquifer is hosted by point-bar sands deposited in a meandering fluvial environment. Wells tapping the aquifer exhibit As concentrations up to 531 ?g/L. High-As groundwaters are recharged in ponds marking an abandoned river channel. The source of As is traced to the underlying fine-grained channel-fill sediments. Arsenic release within these sediments is accompanied by a concomitant release of Br and DOC indicating that these species may be decay products of natural organobromines codeposited along with As. Mass transfer of As to the dissolved phase and its flushing from source sediments are described using a simplified reactive solute transport model. Based on this model, a characteristic reaction time for mass transfer is estimated at 6.7 years. Average groundwater residence times in the source are estimated to have declined from 16.6 to 6.6 years with the advent of intensive irrigation pumping. The ratio of residence and reaction times, a Damköhler number, has declined correspondingly from 2.49 to 0.99, indicating a shift from transport to reaction rate limited As mobilization. Greater insight into the As problem in SE Asia may be achieved by shifting the focus of field investigations from aquifers to potential contamination sources in aquitards.

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

2014-06-01

188

A conceptual hydrogeologic model for the hydrogeologic framework, geochemistry, and groundwater-flow system of the Edwards-Trinity and related aquifers in the Pecos County region, Texas  

USGS Publications Warehouse

The Edwards-Trinity aquifer is a vital groundwater resource for agricultural, industrial, and municipal uses in the Trans-Pecos region of west Texas. A conceptual model of the hydrogeologic framework, geochemistry, and groundwater-flow system in the 4,700 square-mile study area was developed by the U.S. Geological Survey (USGS) in cooperation with the Middle Pecos Groundwater Conservation District, Pecos County, City of Fort Stockton, Brewster County, and Pecos County Water Control and Improvement District No. 1. The model was developed to gain a better understanding of the groundwater system and to establish a scientific foundation for resource-management decisions. Data and information were collected or obtained from various sources to develop the model. Lithologic information obtained from well reports and geophysical data were used to describe the hydrostratigraphy and structural features of the groundwater system, and aquifer-test data were used to estimate aquifer hydraulic properties. Groundwater-quality data were used to evaluate groundwater-flow paths, water and rock interaction, aquifer interaction, and the mixing of water from different sources. Groundwater-level data also were used to evaluate aquifer interaction as well as to develop a potentiometric-surface map, delineate regional groundwater divides, and describe regional groundwater-flow paths. Several previous studies have been done to compile or collect physical and chemical data, describe the hydrogeologic processes, and develop conceptual and numerical groundwater-flow models of the Edwards-Trinity aquifer in the Trans-Pecos region. Documented methods were used to compile and collect groundwater, surface-water, geochemical, geophysical, and geologic information that subsequently were used to develop this conceptual model.

Thomas, Jonathan V.; Stanton, Gregory P.; Bumgarner, Johnathan R.; Pearson, Daniel K.; Teeple, Andrew P.; Houston, Natalie A.; Payne, Jason D.; Musgrove, MaryLynn

2013-01-01

189

Ground-water flow in the Coastal Plain aquifers of South Carolina.  

USGS Publications Warehouse

The Coastal Plain aquifers are recharged primarily by precipitation in their outcrop areas. Groundwater flows from these areas of recharge, through the aquifers, and discharges to upper Costal Plain rivers, overlying aquifers as upward leakage, and wells. Ground-water flow in the Floridan aquifer system and the Tertiary sand aquifer prior to development is generally perpendicular to the coast.-from Authors

Aucott, W.R.; Speiran, G.K.

1985-01-01

190

A quantitative model of ground-water flow during formation of tabular sandstone uranium deposits  

Microsoft Academic Search

Tabular sandstone uranium deposits constitute the largest uranium resource type in the United States. A major point of contention has been the nature and direction of the groundwater flow. This paper presents a quantitative simulation of regional ground-water flow during uranium deposition in the Westwater Canyon Member and Jackpile Sandstone Member of the Upper Jurassic Morrison Formation in the San

Sanford

2009-01-01

191

Impact of horizontal groundwater flow and localized deforestation on the development of shallow  

E-print Network

Impact of horizontal groundwater flow and localized deforestation on the development of shallow that develop in the shallow subsurface as a result of localized deforestation in combination with shallow horizontal groundwater flow. Model results show how a patch-wise pattern of deforestation at the surface

Bense, Victor

192

Characterizing groundwater flow and heat transport in fractured rock using fiber-optic distributed temperature sensing  

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

193

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

USGS Publications Warehouse

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

194

Groundwater flow and hydrochemistry in mountain areas affected by DSGSDs  

NASA Astrophysics Data System (ADS)

Large slope instabilities such as DSGSD and rockslides locally affect the groundwater flow at the slope scale. These phenomena present morphostructures (scarps, counterscarps and trenches) parallel to the slope direction that control the surface water runoff, directing it transversal to the slope dip and favouring its percolation within the slope through the more conductive materials aligned with the trench . This also affects the slope hydrochemistry, locally controlling the solute transport and circulation. The upper Valtellina (Central European Alps, Northern Italy) is characterize by a high density of DSGSD phenomena, with 29 DSGSDs within an area of about 900 km2 (Crosta et al, 2013). The study area ranges from 1150 to 3500 m in altitude, and shows a clear glacial imprint, which significantly influenced the geomorphology and water distribution in the study area. In order to characterize the groundwater flow and the hydrochemistry of the area, we collected historical data analysis (4070 samples from springs, wells, lakes, rivers and public fountains), and we performed four seasonal campaigns, from summer 2012 to spring 2013, to complete a hydrologic year. During these campaigns, we measured the spring discharge, and we collected samples for chemical (anions and cations) and isotopic (tritium, deuterium and O18) analyses in more almost 40 selected spring located throughout the study area. These springs were selected because representative of main spring clusters, with a particular attention to problems related to the presence of Arsenic in high concentration. In this study, we analyze the effect of DSGSD phenomena on the aquifers of upper Valtellina through the quantitative analysis of hydro-chemical and isotopic data. We show how these phenomena affect the ground water flow also in relation to the presence of geological structures that are associated and locally reactivated by DSGSDs.

Crosta, Giovanni B.; Frattini, Paolo; Pena Reyes, Fredy; Riva, Federico

2014-05-01

195

Evaluation of Parameter Uncertainty Reduction in Groundwater Flow Modeling Using Multiple Environmental Tracers  

NASA Astrophysics Data System (ADS)

Calibration of groundwater flow models for the purpose of evaluating flow and aquifer heterogeneity typically uses observations of hydraulic head in wells and appropriate boundary conditions. Environmental tracers have a wide variety of decay rates and input signals in recharge, resulting in a potentially broad source of additional information to constrain flow rates and heterogeneity. A numerical study was conducted to evaluate the reduction in uncertainty during model calibration using observations of various environmental tracers and combinations of tracers. A synthetic data set was constructed by simulating steady groundwater flow and transient tracer transport in a high-resolution, 2-D aquifer with heterogeneous permeability and porosity using the PFLOTRAN software code. Data on pressure and tracer concentration were extracted at well locations and then used as observations for automated calibration of a flow and transport model using the pilot point method and the PEST code. Optimization runs were performed to estimate parameter values of permeability at 30 pilot points in the model domain for cases using 42 observations of: 1) pressure, 2) pressure and CFC11 concentrations, 3) pressure and Ar-39 concentrations, and 4) pressure, CFC11, Ar-39, tritium, and He-3 concentrations. Results show significantly lower uncertainty, as indicated by the 95% linear confidence intervals, in permeability values at the pilot points for cases including observations of environmental tracer concentrations. The average linear uncertainty range for permeability at the pilot points using pressure observations alone is 4.6 orders of magnitude, using pressure and CFC11 concentrations is 1.6 orders of magnitude, using pressure and Ar-39 concentrations is 0.9 order of magnitude, and using pressure, CFC11, Ar-39, tritium, and He-3 concentrations is 1.0 order of magnitude. Data on Ar-39 concentrations result in the greatest parameter uncertainty reduction because its half-life of 269 years is similar to the range of transport times (hundreds to thousands of years) in the heterogeneous synthetic aquifer domain. The slightly higher uncertainty range for the case using all of the environmental tracers simultaneously is probably due to structural errors in the model introduced by the pilot point regularization scheme. It is concluded that maximum information and uncertainty reduction for constraining a groundwater flow model is obtained using an environmental tracer whose half-life is well matched to the range of transport times through the groundwater flow system. Sandia is a multiprogram 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.

Arnold, B. W.; Gardner, P.

2013-12-01

196

Regional heat flow variations in the northern Michigan and Lake Superior region determined using the silica heat flow estimator  

USGS Publications Warehouse

Conventional heat flow data are sparse for northern Michigan. The groundwater silica heat flow estimator expands the database sufficiently to allow regional variations in heat flow to be examined. Heat flow shows a pattern of alternating highs and lows trending ESE across the Upper Peninsula and Lake Superior. The informal names given to these features, their characteristic heat flow and inferred causes are listed: {A table is presented} The results suggest that, for the study area, regional variations in heat flow cannot be interpreted solely in terms of regional variations of the heat generation rate of basement rocks. ?? 1987.

Vugrinovich, R.

1987-01-01

197

Ground-Water Flow Model of the Sierra Vista Subwatershed and Sonoran Portions of the Upper San Pedro Basin, Southeastern Arizona, United States, and Northern Sonora, Mexico  

USGS Publications Warehouse

A numerical ground-water model was developed to simulate seasonal and long-term variations in ground-water flow in the Sierra Vista subwatershed, Arizona, United States, and Sonora, Mexico, portions of the Upper San Pedro Basin. This model includes the simulation of details of the groundwater flow system that were not simulated by previous models, such as ground-water flow in the sedimentary rocks that surround and underlie the alluvial basin deposits, withdrawals for dewatering purposes at the Tombstone mine, discharge to springs in the Huachuca Mountains, thick low-permeability intervals of silt and clay that separate the ground-water flow system into deep-confined and shallow-unconfined systems, ephemeral-channel recharge, and seasonal variations in ground-water discharge by wells and evapotranspiration. Steady-state and transient conditions during 1902-2003 were simulated by using a five-layer numerical ground- water flow model representing multiple hydrogeologic units. Hydraulic properties of model layers, streamflow, and evapotranspiration rates were estimated as part of the calibration process by using observed water levels, vertical hydraulic gradients, streamflow, and estimated evapotranspiration rates as constraints. Simulations approximate observed water-level trends throughout most of the model area and streamflow trends at the Charleston streamflow-gaging station on the San Pedro River. Differences in observed and simulated water levels, streamflow, and evapotranspiration could be reduced through simulation of climate-related variations in recharge rates and recharge from flood-flow infiltration.

Pool, D.R.; Dickinson, Jesse E.

2007-01-01

198

Regional groundwater flow and tritium transport modeling and risk assessment of the underground test area, Nevada Test Site, Nevada  

SciTech Connect

The groundwater flow system of the Nevada Test Site and surrounding region was evaluated to estimate the highest potential current and near-term risk to the public and the environment from groundwater contamination downgradient of the underground nuclear testing areas. The highest, or greatest, potential risk is estimated by assuming that several unusually rapid transport pathways as well as public and environmental exposures all occur simultaneously. These conservative assumptions may cause risks to be significantly overestimated. However, such a deliberate, conservative approach ensures that public health and environmental risks are not underestimated and allows prioritization of future work to minimize potential risks. Historical underground nuclear testing activities, particularly detonations near or below the water table, have contaminated groundwater near testing locations with radioactive and nonradioactive constituents. Tritium was selected as the contaminant of primary concern for this phase of the project because it is abundant, highly mobile, and represents the most significant contributor to the potential radiation dose to humans for the short term. It was also assumed that the predicted risk to human health and the environment from tritium exposure would reasonably represent the risk from other, less mobile radionuclides within the same time frame. Other contaminants will be investigated at a later date. Existing and newly collected hydrogeologic data were compiled for a large area of southern Nevada and California, encompassing the Nevada Test Site regional groundwater flow system. These data were used to develop numerical groundwater flow and tritium transport models for use in the prediction of tritium concentrations at hypothetical human and ecological receptor locations for a 200-year time frame. A numerical, steady-state regional groundwater flow model was developed to serve as the basis for the prediction of the movement of tritium from the underground testing areas on a regional scale. The groundwater flow model was used in conjunction with a particle-tracking code to define the pathlines followed by groundwater particles originating from 415 points associated with 253 nuclear test locations. Three of the most rapid pathlines were selected for transport simulations. These pathlines are associated with three nuclear test locations, each representing one of the three largest testing areas. These testing locations are: BOURBON on Yucca Flat, HOUSTON on Central Pahute Mesa, and TYBO on Western Pahute Mesa. One-dimensional stochastic tritium transport simulations were performed for the three pathlines using the Monte Carlo method with Latin hypercube sampling. For the BOURBON and TYBO pathlines, sources of tritium from other tests located along the same pathline were included in the simulations. Sensitivity analyses were also performed on the transport model to evaluate the uncertainties associated with the geologic model, the rates of groundwater flow, the tritium source, and the transport parameters. Tritium concentration predictions were found to be mostly sensitive to the regional geology in controlling the horizontal and vertical position of transport pathways. The simulated concentrations are also sensitive to matrix diffusion, an important mechanism governing the migration of tritium in fractured carbonate and volcanic rocks. Source term concentration uncertainty is most important near the test locations and decreases in importance as the travel distance increases. The uncertainty on groundwater flow rates is as important as that on matrix diffusion at downgradient locations. The risk assessment was performed to provide conservative and bounding estimates of the potential risks to human health and the environment from tritium in groundwater. Risk models were designed by coupling scenario-specific tritium intake with tritium dose models and cancer and genetic risk estimates using the Monte Carlo method. Estimated radiation doses received by individuals from chronic exposure to tritium, and the corre

None

1997-10-01

199

Identification of potential groundwater flow paths using geological and geophysical data  

SciTech Connect

This project represents the first phase in the development of a methodology for generating three-dimensional equiprobable maps of hydraulic conductivity for the Nevada Test Site (NTS). In this study, potential groundwater flow paths were investigated for subsurface tuffs at Yucca Flat by studying how these units are connected. The virtual absence of site-specific hydraulic conductivity data dictates that as a first step a surrogate attribute (geophysical logs) be utilized. In this first phase, the connectivity patterns of densely welded ash-flow tuffs were studied because these tuffs are the most likely to form zones of high hydraulic conductivity. Densely welded tuffs were identified based on the response shown on resistivity logs and this information was transformed into binary indicator values. The spatial correlation of the indicator data was estimated through geostatistical methods. Equiprobable three-dimensional maps of the distribution of the densely-welded and nonwelded tuffs (i.e., subsurface heterogeneity) were then produced using a multiple indicator simulation formalism. The simulations demonstrate that resistivity logs are effective as soft data for indicating densely welded tuffs. The simulated welded tuffs reproduce the stratigraphic relationships of the welded tuffs observed in hydrogeologic cross sections, while incorporating the heterogeneity and anisotropy that is expected in this subsurface setting. Three-dimensional connectivity of the densely welded tuffs suggests potential groundwater flow paths with lengths easily over 1 km. The next phase of this investigation should incorporate other geophysical logs (e.g., gamma-gamma logs) and then calibrate the resulting soft data maps with available hard hydraulic conductivity data. The soft data maps can then augment the hard data to produce the final maps of the spatial distribution of hydraulic conductivity that can be used as input for numerical solution of groundwater flow and transport.

Pohlmann, K.; Andricevic, R.

1994-09-01

200

Assessing the Impact of Climate Change on Groundwater Resources Using Groundwater Flow Models  

Microsoft Academic Search

\\u000a Climate change is a potential stressor of groundwater resources and its effects on the availability of groundwater need to\\u000a be understood and determined. The impacts of climate change on groundwater systems are conceptually known, however in the\\u000a context of climate change impact assessment there has been little research conducted on groundwater compared to surface water\\u000a resources. One of the tools

Alper Elçi

201

Numerical Simulation on the Continuous Operation of an Aquifer Thermal Energy Storage System Under Regional Groundwater Flow  

Microsoft Academic Search

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

202

Groundwater flow near the Shoal Site, Sand Springs Range, Nevada: Impact of density-driven flow  

SciTech Connect

The nature of flow from a highland recharge area in a mountain range in north-central Nevada to discharge areas on either side of the range is evaluated to refine a conceptual model of contaminant transport from an underground nuclear test conducted beneath the range. The test, known as the Shoal event, was conducted in 1963 in granitic rocks of the Sand Springs Range. Sparse hydraulic head measurements from the early 1960s suggest flow from the shot location to the east to Fairview Valley, while hydrochemistry supports flow to salt pans in Fourmile Flat to the west. Chemical and isotopic data collected from water samples and during well-logging arc best explained by a reflux brine system on the west side of the Sand Springs Range, rather than a typical local flow system where all flow occurs from recharge areas in the highlands to a central discharge area in a playa. Instead, dense saline water from the playa is apparently being driven toward the range by density contrasts. The data collected between the range and Fourmile Flat suggest the groundwater is a mixture of younger, fresher recharge water with older brine. Chemical contrasts between groundwater in the east and west valleys reflect the absence of re-flux water in Fairview Valley because the regional discharge area is distant and thus there is no accumulation of salts. The refluxing hydraulic system probably developed after the end of the last pluvial period and differences between the location of the groundwater divide based on hydraulic and chemical indicators could reflect movement of the divide as the groundwater system adjusts to the new reflux condition.

Chapman, J.; Mihevc, T.; McKay, A.

1994-09-01

203

Estimation of groundwater recharge to chalk and sandstone aquifers using simple soil models  

Microsoft Academic Search

On the assumption that the water draining below the root zone is potentially available for groundwater recharge, two current UK methods for estimating annual groundwater recharge have been compared with a new soil model using data from four sites under permanent grass in the UK: two sites representative of the Chalk aquifer at Bridgest Farm (Hampshire) and Fleam Dyke (Cambridgeshire),

R. Ragab; J. Finch; R. Harding

1997-01-01

204

Estimation of groundwater evaporation and salt flux from Owens Lake, California, USA  

E-print Network

Estimation of groundwater evaporation and salt flux from Owens Lake, California, USA S.W. Tylera Received 23 April 1996; revised 20 December 1996; accepted 6 January 1997 Abstract Groundwater evaporation largest sources of airborne dust in the USA, yet the evaporation and salt flux have not been fully

Katul, Gabriel

205

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

206

Incorporation of prior information on parameters into nonlinear regression groundwater flow models: 2. Applications  

NASA Astrophysics Data System (ADS)

This paper investigates factors influencing the degree of improvement in estimates of parameters of a nonlinear regression groundwater flow model by incorporating prior information of unknown reliability. Consideration of expected behavior of the regression solutions and results of a hypothetical modeling problem lead to several general conclusions. First, if the parameters are properly scaled, linearized expressions for the mean square error (MSE) in parameter estimates of a nonlinear model will often behave very nearly as if the model were linear. Second, by using prior information, the MSE in properly scaled parameters can be reduced greatly over the MSE of ordinary least squares estimates of parameters. Third, plots of estimated MSE and the estimated standard deviation of MSE versus an auxiliary parameter (the ridge parameter) specifying the degree of influence of the prior information on regression results can help determine the potential for improvement of parameter estimates. Fourth, proposed criteria can be used to make appropriate choices for the ridge parameter and another parameter expressing degree of overall bias in the prior information. Results of a case study of Truckee Meadows, Reno-Sparks area, Washoe County, Nevada, conform closely to the results of the hypothetical problem. In the Truckee Meadows case, incorporation of prior information did not greatly change the parameter estimates from those obtained by ordinary least squares. However, the analysis showed that both sets of estimates are more reliable than suggested by the standard errors from ordinary least squares.

Cooley, Richard L.

1983-06-01

207

A simple method for estimating basin-scale groundwater discharge by vegetation in the basin and range province of Arizona using remote sensing information and geographic information systems  

USGS Publications Warehouse

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

208

Estimates of ground-water discharge as determined from measurements of evapotranspiration, Ash Meadows area, Nye County, Nevada  

USGS Publications Warehouse

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

209

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

210

RAFT: A simulator for ReActive Flow and Transport of groundwater contaminants  

SciTech Connect

This report documents the use of the simulator RAFT for the ReActive flow and Transport of groundwater contaminants. RAFT can be used as a predictive tool in the design and analysis of laboratory and field experiments or it can be used for the estimation of model/process parameters from experiments. RAFT simulates the reactive transport of groundwater contaminants in one, two-, or three-dimensions and it can model user specified source/link configurations and arbitrary injection strategies. A suite of solvers for transport, reactions and regression are employed so that a combination of numerical methods best suited for a problem can be chosen. User specified coupled equilibrium and kinetic reaction systems can be incorporated into RAFT. RAFT is integrated with a symbolic computational language MAPLE, to automate code generation for arbitrary reaction systems. RAFT is expected to be used as a simulator for engineering design for field experiments in groundwater remediation including bioremediation, reactive barriers and redox manipulation. As an integrated tool with both the predictive ability and the ability to analyze experimental data, RAFT can help in the development of remediation technologies, from laboratory to field.

Chilakapati, A.

1995-07-01

211

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.

212

Estimating residents' willingness to pay for groundwater protection in the Vietnamese Mekong Delta  

NASA Astrophysics Data System (ADS)

Groundwater in the Vietnamese Mekong Delta is facing the pollution and it needs to be protected. Searching literature reviews on economic valuation techniques, the contingent valuation method (CVM) has been popularly applied to estimate the economic value of water protection. This approach is based on a hypothetical scenario in which respondents are requested through questionnaires to reveal their maximum willingness to pay (WTP) for the water protection project. The study used the approach of CVM to analyze the households' motivations and their WTP for the program of groundwater protection in the Mekong Delta. The study performed that the residents in the delta were willing to pay approximately 141,730 VND (US6.74) per household a year. Groundwater could be an inferior good with the negative income effect found in the demanding for clean groundwater. Respondent's gender and groundwater-related health risk consideration were factors sensitively affecting the probability of demanding for groundwater protection.

Vo, Danh Thanh; Huynh, Khai Viet

2014-11-01

213

Estimating Urban-Induced Groundwater Recharge Through Coupled Hydrologic Modeling in Ballona Creek Watershed, Los Angeles, CA  

NASA Astrophysics Data System (ADS)

The current research focuses on the modeling and prediction of urban-induced groundwater recharge in highly developed, semi-arid regions. The groundwater component of the hydrologic cycle goes through significant changes during urbanization and has historically been understudied. The changes brought on by urbanization not only include physical alterations (increased surface imperviousness, channelized flow, increased sub-surface infrastructure etc.) but also changes to the water cycle due to human interactions (increased use of imported water, variable landscape irrigation, industrial water use, etc.). We undertake our initial analysis in Ballona Creek watershed, which contains highly urbanized and diverse portions of the cities of Santa Monica and Los Angeles, California along with more natural land surfaces in the northern portions of the watershed in the Santa Monica Mountains. The primary focus of this research is the development of a fully distributed and coupled surface-groundwater model of the Ballona Creek watershed. We use the three-dimensional finite-difference surface and groundwater flow model, ParFlow, fully-coupled to a land surface model, CLM, at a 30-meter by 30-meter resolution forced by observed meteorological data from 2000 to 2010. Previous work in Ballona includes a detailed historical water budget analysis from the early 1900s to the present. This extensive in situ data set will be used to estimate model parameters as well as provide upper and lower boundaries for groundwater recharge values across the system. Preliminary results focus on annual and seasonal (wet/dry periods) surface and groundwater fluxes, including the influence of natural spring flow and dry weather runoff in the watershed. Los Angeles and the surrounding metropolitan area rely on some of the most extensive and oldest centralized water redistribution projects in the United States where water is transported hundreds of kilometers to support agricultural and urban activities in the Los Angeles area. Increasingly, local governments and water districts are committed to increased reliance on local water sources within the southern California coastal areas including local groundwater, rainwater capture, conservation measures, and recycled water sources. Our ultimate goal is to use the validated model to evaluate the influence of altered landscapes and future climate in developing sustainable groundwater supplies across the southern California region.

Reyes, B.; Hogue, T. S.

2012-12-01

214

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

USGS Publications Warehouse

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. Copyright. Published in 2011 by the American Geophysical Union.

Ganju, Neil K.

2011-01-01

215

Optical Flow Estimation Using Diffusion Distances  

Microsoft Academic Search

In this paper we apply the diffusion framework to dense optical flow estimation. Local image information is represented by matrices of gradients between paired locations. Diffusion distances are modelled as sums of eigenvectors weighted by their eigenvalues extracted following the eigen decomposion of these matrices. Local optical flow is estimated by correlating diffusion distances characterizing features from different frames. A

Szymon Wartak; Adrian G. Bors

2010-01-01

216

Ground-water levels in water year 1987 and estimated ground-water pumpage in water years 1986-87, Carson Valley, Douglas County, Nevada  

USGS Publications Warehouse

Groundwater levels were measured at 58 wells during water year 1987 and a summary of estimated pumpage is given for water years 1986 and 1987 in Carson Valley, Douglas County, Nevada. The data were collected to provide a record of groundwater changes over the long-term and pumpage estimates that can be incorporated into an existing groundwater model. The estimated total pumpage in water year 1986 was 10,200 acre-ft and in water year 1987 was 13,400 acre-ft. Groundwater levels exhibited seasonal fluctuations but remained relatively stable over the reporting period throughout most of the valley. (USGS)

Berger, D.L.

1990-01-01

217

Impact of Groundwater Flow and Energy Load on Multiple Borehole Heat Exchangers.  

PubMed

The effect of array configuration, that is, number, layout, and spacing, on the performance of multiple borehole heat exchangers (BHEs) is generally known under the assumption of fully conductive transport. The effect of groundwater flow on BHE performance is also well established, but most commonly for single BHEs. In multiple-BHE systems the effect of groundwater advection can be more complicated due to the induced thermal interference between the boreholes. To ascertain the influence of groundwater flow and borehole arrangement, this study investigates single- and multi-BHE systems of various configurations. Moreover, the influence of energy load balance is also examined. The results from corresponding cases with and without groundwater flow as well as balanced and unbalanced energy loads are cross-compared. The groundwater flux value, 10(-7) m/s, is chosen based on the findings of previous studies on groundwater flow interaction with BHEs and thermal response tests. It is observed that multi-BHE systems with balanced loads are less sensitive to array configuration attributes and groundwater flow, in the long-term. Conversely, multi-BHE systems with unbalanced loads are influenced by borehole array configuration as well as groundwater flow; these effects become more pronounced with time, unlike when the load is balanced. Groundwater flow has more influence on stabilizing loop temperatures, compared to array characteristics. Although borehole thermal energy storage (BTES) systems have a balanced energy load function, preliminary investigation on their efficiency shows a negative impact by groundwater which is due to their dependency on high temperature gradients between the boreholes and surroundings. PMID:25227154

Emad Dehkordi, S; Schincariol, Robert A; Olofsson, Bo

2014-09-16

218

Applications of remote sensing, GIS, and groundwater flow modeling in evaluating groundwater resources: Two case studies; East Nile Delta, Egypt and Gold Valley, California, USA  

NASA Astrophysics Data System (ADS)

Quaternary aquifer, East Nile Delta, Egypt. Due to the progressive increase in the development of desert land in Egypt, the demand for efficient water resources management and accurate land cover change information is increasing. In this study, we introduce a methodology to map and monitor land cover change patterns related to agricultural development and urban expansion in the desert fringes of the Eastern Nile Delta region. Using a hybrid classification approach, we employ multitemporal Landsat TM/ETM+ images from 1984, 1990, and 2003 to produce three land cover/land use maps. Post-classification comparison of these maps was used to obtain "from-to" statistics and change detection maps. The change detection results show that agricultural development increased 14% through the study period. Land reclamation during 1990-2003 exceeded that during 1984-1990 by a factor of two, reflecting a systematic national plan for desert reclamation that went into effect. We find that the increase in urbanization (by ˜21,300 hectares) during 1990-2003 was predominantly due to encroachment into traditionally cultivated land at the fringes of urban centers. Our results accurately quantify the land cover changes and delineate their spatial patterns, demonstrating the utility of Landsat data in analyzing landscape dynamics over time. Such information is critical for making efficient and sustainable policies for resource management. A three dimensional GIS-based groundwater flow model was developed to delineate a safe future framework for groundwater development in the Quaternary aquifer north Ismaelia Canal, East Nile Delta where a progressive rise in head associated with agricultural development is reported. The calibrated transient model was used to predict the future head distribution after 20 years assuming the same landuse. Results of this run showed that the groundwater head continued to increase with maximum increase up to 2.0 m in the unconfined part of the aquifer which jeopardizes a considerable area of the agricultural land with soil salinity and water logging. Therefore, three strategies, each with three scenarios, extending between 2004 and 2024 were designed to involve different pumping stress and infiltration rates from irrigation return to control the rising water level and estimate the production potential of the aquifer during drought. Gold Valley, Death Valley, California, USA. This study evaluates the hydrogeology of Gold Valley as a typical example of intermountain basins of Death Valley area and develops a GIS-based model that reasonably estimates the precipitation infiltration rates from altitude and slope data of the catchment area. Water balance calculations of the hydrological parameters in Gold Valley, provided by Inyo County, California, indicated that the majority of recharge takes place at high altitude (>1100 m) during winter with a negligible effect of evaporation on the stable isotopic composition of groundwater. Furthermore, water balance calculations in Gold Valley were utilized in identifying the coefficients of a GIS-based model that subsequently was refined to the best fit with the calculations of the water budget. A resistivity survey conducted in Gold Valley showed that groundwater is collected in upstream compartmentalized reservoirs and suggests that groundwater flow mostly takes place through the fracture zone of the bedrock. This pattern explains the relationship between precipitational infiltration in the Gold Valley catchment area and the attachment spring flow in Willow Creek. The estimated water budget in Gold Valley and the geoelectric profiles provided from this study can be investigated into the Death Valley Regional Groundwater Flow model (DVRGWF). In addition, the GIS-based model can be efficiently applied in other intermountain basins in Death Valley or other areas of arid environment of the Western U.S. to estimate the local precipitational infiltration. Accurate estimates of flux, well defined flow systems, and locations of recharge/discharge in mountain ranges provide e

Abdelaziz Ali Ismael, Abdulaziz Mohamed

219

Application of nonlinear-regression methods to a ground-water flow model of the Albuquerque Basin, New Mexico  

USGS Publications Warehouse

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

220

A comparison of groundwater recharge estimation methods in the Williston and Powder River structural basins in the Northern Great Plains  

E-print Network

A comparison of groundwater recharge estimation methods in the Williston and Powder River-water-balance (SWB) model to estimate groundwater recharge in the Williston and Powder River structural basins and CMB methods were applied to local areas with available groundwater-level and chloride data. The SWB

Torgersen, Christian

221

Ground-water levels in water years 1984-86 and estimated ground-water pumpage in water years 1984-85, Carson Valley, Douglas County, Nevada  

USGS Publications Warehouse

Tabulations of groundwater level measurements made during the water years 1984-86 and summaries of estimated pumpage for water years 1984 and 1985 in Carson valley, Douglas County, Nevada, are included in this report. The data are being collected to provide a record of long-term groundwater changes and pumpage estimates that can be incorporated in a groundwater model change at a later date. (USGS)

Berger, D.L.

1987-01-01

222

Descriptions and characterizations of water-level data and groundwater flow for the Brewster Boulevard and Castle Hayne Aquifer Systems and the Tarawa Terrace Aquifer  

USGS Publications Warehouse

This supplement of Chapter A (Supplement 3) summarizes results of analyses of groundwater-level data and describes corresponding elements of groundwater flow such as vertical hydraulic gradients useful for groundwater-flow model calibration. Field data as well as theoretical concepts indicate that potentiometric surfaces within the study area are shown to resemble to a large degree a subdued replica of surface topography. Consequently, precipitation that infiltrates to the water table flows laterally from highland to lowland areas and eventually discharges to streams such as Northeast and Wallace Creeks and New River. Vertically downward hydraulic gradients occur in highland areas resulting in the transfer of groundwater from shallow relatively unconfined aquifers to underlying confined or semi-confined aquifers. Conversely, in the vicinity of large streams such as Wallace and Frenchs Creeks, diffuse upward leakage occurs from underlying confined or semi-confined aquifers. Point water-level data indicating water-table altitudes, water-table altitudes estimated using a regression equation, and estimates of stream levels determined from a digital elevation model (DEM) and topographic maps were used to estimate a predevelopment water-table surface in the study area. Approximate flow lines along hydraulic gradients are shown on a predevelopment potentiometric surface map and extend from highland areas where potentiometric levels are greatest toward streams such as Wallace Creek and Northeast Creek. The distribution of potentiometric levels and corresponding groundwater-flow directions conform closely to related descriptions of the conceptual model.

Faye, Robert E.; Jones, L. Elliott; Suárez-Soto, René J.

2013-01-01

223

Groundwater flow in a relatively old oceanic volcanic island: the Betancuria area, Fuerteventura Island, Canary Islands, Spain.  

PubMed

The island of Fuerteventura is the oldest of the Canary Islands' volcanic archipelago. It is constituted by volcanic submarine and subaerial activity and intrusive Miocene events, with some residual later volcanism and Quaternary volcanic deposits that have favored groundwater recharge. The climate is arid, with an average rainfall that barely attains 60 mm/year in the coast and up to 200 mm/year in the highlands. The aquifer recharge is small but significant; it is brackish due to large airborne atmospheric salinity, between 7 and 15 gm(-2)year(-1) of chloride deposition, and high evapo-concentration in the soil. The average recharge is estimated to be less than about 5 mm/year at low altitude and up to 10 mm/year in the highlands, and up to 20 mm/year associated to recent lava fields. Hydrochemical and water isotopic studies, supported by water table data and well and borehole descriptions, contribute a preliminary conceptual model of groundwater flow and water origin in the Betancuria area, the central area of the island. In general, water from springs and shallow wells tends to be naturally brackish and of recent origin. Deep saline groundwater is found and is explained as remnants of very old marine water trapped in isolated features in the very low permeability intrusive rocks. Preliminary radiocarbon dating indicates that this deep groundwater has an apparent age of less than 5000 years BP but it is the result of mixing recent water recharge with very old deep groundwater. Most of the groundwater flow occurs through the old raised volcanic shield of submarine and subaerial formations and later Miocene subaerial basalts. Groundwater transit time through the unsaturated zone is of a few decades, which allows the consideration of long-term quasi-steady state recharge. Transit times are up to a few centuries through the saturated old volcanics and up to several millennia in the intrusive formations, where isolated pockets of very old water may exist. PMID:25108255

Herrera, Christian; Custodio, Emilio

2014-10-15

224

The effect of fault relayand clay smearing on groundwater flow patterns in the Lower Rhine  

E-print Network

The effect of fault relayand clay smearing on groundwater flow patterns in the Lower Rhine,Vrije Universiteit Amsterdam, Amsterdam, The Netherlands ABSTRACT Faults strongly impact groundwater £ow in the unconsolidated sediments of the Lower Rhine Embayment. Hydraulic head maps show that many individual faults form

Bense, Victor

225

Verification of a Conceptual Model of Groundwater flow in a Poorly Productive Metasedimentary Bedrock Aquifer  

Microsoft Academic Search

Poorly Productive Aquifers (PPA) underlie approximately two-thirds of the landmass of Ireland yet the behaviour of groundwater in these bedrock types remains poorly understood. Existing (unverified) conceptual models represent most groundwater as travelling through the uppermost metres of the bedrock and at the base of overlying unconsolidated deposits (transition zone), with a subordinate fraction flowing through the shallower bedrock (to

Janka Nitsche; Raymond Flynn

2010-01-01

226

Preliminary assessment of the impacts of deep foundations and land reclamation on groundwater flow  

E-print Network

Preliminary assessment of the impacts of deep foundations and land reclamation on groundwater flow are increasing. Land reclamation from the sea and high-rise buildings are common approaches to satis- fying in a groundwater system due to land reclamation and con- struction of building foundations in a coastal area

Jiao, Jiu Jimmy

227

Age-distribution estimation for karst groundwater: Issues of parameterization and complexity in inverse modeling by convolution  

NASA Astrophysics Data System (ADS)

SummaryConvolution modeling is useful for investigating the temporal distribution of groundwater age based on environmental tracers. The framework of a quasi-transient convolution model that is applicable to two-domain flow in karst aquifers is presented. The model was designed to provide an acceptable level of statistical confidence in parameter estimates when only chlorofluorocarbon (CFC) and tritium ( 3H) data are available. We show how inverse modeling and uncertainty assessment can be used to constrain model parameterization to a level warranted by available data while allowing major aspects of the flow system to be examined. As an example, the model was applied to water from a pumped well open to the Madison aquifer in central USA with input functions of CFC-11, CFC-12, CFC-113, and 3H, and was calibrated to several samples collected during a 16-year period. A bimodal age distribution was modeled to represent quick and slow flow less than 50 years old. The effects of pumping and hydraulic head on the relative volumetric fractions of these domains were found to be influential factors for transient flow. Quick flow and slow flow were estimated to be distributed mainly within the age ranges of 0-2 and 26-41 years, respectively. The fraction of long-term flow (>50 years) was estimated but was not dateable. The different tracers had different degrees of influence on parameter estimation and uncertainty assessments, where 3H was the most critical, and CFC-113 was least influential.

Long, Andrew J.; Putnam, Larry D.

2009-10-01

228

Age-distribution estimation for karst groundwater: Issues of parameterization and complexity in inverse modeling by convolution  

USGS Publications Warehouse

Convolution modeling is useful for investigating the temporal distribution of groundwater age based on environmental tracers. The framework of a quasi-transient convolution model that is applicable to two-domain flow in karst aquifers is presented. The model was designed to provide an acceptable level of statistical confidence in parameter estimates when only chlorofluorocarbon (CFC) and tritium (3H) data are available. We show how inverse modeling and uncertainty assessment can be used to constrain model parameterization to a level warranted by available data while allowing major aspects of the flow system to be examined. As an example, the model was applied to water from a pumped well open to the Madison aquifer in central USA with input functions of CFC-11, CFC-12, CFC-113, and 3H, and was calibrated to several samples collected during a 16-year period. A bimodal age distribution was modeled to represent quick and slow flow less than 50 years old. The effects of pumping and hydraulic head on the relative volumetric fractions of these domains were found to be influential factors for transient flow. Quick flow and slow flow were estimated to be distributed mainly within the age ranges of 0-2 and 26-41 years, respectively. The fraction of long-term flow (>50 years) was estimated but was not dateable. The different tracers had different degrees of influence on parameter estimation and uncertainty assessments, where 3H was the most critical, and CFC-113 was least influential.

Long, A.J.; Putnam, L.D.

2009-01-01

229

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

SciTech Connect

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

230

Hydrogeology and simulation of ground-water flow at Arnold Air Force Base, Coffee and Franklin counties, Tennessee  

USGS Publications Warehouse

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

231

Simulation of ground-water flow in the Mississippi River Valley alluvial aquifer in eastern Arkansas  

USGS Publications Warehouse

The U.S Geological Survey has developed and calibrated a digital model of the flow system in the alluvial aquifer as part of a multiagency Eastern Arkansas Region Comprehensive Study being conducted by the U. S. Army Corps of Engineers. Other cooperating agencies include the U.S. Soil Conservation Service, the Arkansas Soil and Water Conservation Commission, and the University of Arkansas. The study was prompted by the growing concern about significant water level declines in the Mississippi River Valley alluvial aquifer north of the Arkansas River in eastern Arkansas. The declines are a result of large groundwater withdrawals, mainly for irrigation. After calibration, the flow model was used to simulate the effects of projected groundwater pumpage through the year 2050, based on estimates made by the U.S. Soil Conservation Service for pumpage scenarios with and without water conservation measures. Simulations of projected pumpage indicated that by the year 2050 water level declines would reduce the saturated thickness of the aquifer to less than 20 ft in large areas of eastern Arkansas. More than 26% of the active cells in the scenario without conservation had saturated thicknesses of 20 ft or less and mroe than 16% in the scenario with conservation. The principal areas where the saturated thickness is expected to reach these critical levels are in the Grand Prairie region and in two areas on the east and west sides of Crowleys Ridge. (USGS)

Mahon, G.L.; Ludwig, A.H.

1990-01-01

232

Simulation of the ground-water flow system at Naval Submarine Base Bangor and vicinity, Kitsap County, Washington  

USGS Publications Warehouse

An evaluation of the interaction between ground-water flow on Naval Submarine Base Bangor and the regional-flow system shows that for selected alternatives of future ground-water pumping on and near the base, the risk is low that significant concentrations of on-base ground-water contamination will reach off-base public-supply wells and hypothetical wells southwest of the base. The risk is low even if worst-case conditions are considered ? no containment and remediation of on-base contamination. The evaluation also shows that future saltwater encroachment of aquifers below sea level may be possible, but this determination has considerable uncertainty associated with it. The potential effects on the ground-water flow system resulting from four hypothetical ground-water pumping alternatives were considered, including no change in 1995 pumping rates, doubling the rates, and 2020 rates estimated from population projections with two different pumping distributions. All but a continuation of 1995 pumping rates demonstrate the possibility of future saltwater encroachment in the Sea-level aquifer on Naval Submarine Base Bangor. The amount of time it would take for encroachment to occur is unknown. For all pumping alternatives, future saltwater encroachment in the Sea-level aquifer also may be possible along Puget Sound east and southeast of the base. Future saltwater encroachment in the Deep aquifer also may be possible throughout large parts of the study area. Projections of saltwater encroachment are least certain outside the boundaries of Naval Submarine Base Bangor. The potential effects of the ground-water pumping alternatives were evaluated by simulating the ground-water flow system with a three-dimensional uniform-density ground-water flow model. The model was calibrated by trial-and-error by minimizing differences between simulated and measured or estimated variables. These included water levels from prior to January 17, 1977 (termed 'predevelopment'), water-level drawdowns since predevelopment until April 15, 1995, ground-water discharge to streams in water year 1995, and residence times of ground water in different parts of the flow system that were estimated in a separate but related study. Large amounts of ground water were pumped from 1977 through 1980 from the Sea-level aquifer on Naval Submarine Base Bangor to enable the construction of an off-shore drydock. Records of the flow-system responses to the applied stresses were used to help calibrate the model. Errors in the calibrated model were significant. The poor agreement between simulated and measured values could be improved by making many local changes to hydraulic parameters but these changes were not supported by other data. Model errors may have resulted in errors in the simulated effects of ground-water pumping alternatives.

Heeswijk, Marijke van; Smith, Daniel T.

2002-01-01

233

Estimation of groundwater evaportranspiration using diurnal water table fluctuations in the Mu Us Desert, northern China  

NASA Astrophysics Data System (ADS)

Groundwater evapotranspiration (ETg) is a significant component of water balance analysis in desert areas. Estimation of ETg using diurnal water table fluctuations, i.e. the White method, is considered simple and straightforward, but it was seldom applied in desert areas. In this study, long-term and high-resolution groundwater level data were used to estimate ETg rate at two sites covered by typical desert plants Salix psammophila and Artemisia ordosica, respectively, in the Mu Us Desert in northern China. The specific yield (Sy) was derived from a drainage experiment in laboratory. The results showed that the water demand of S. psammophila could result in a weak but identifiable diurnal fluctuation of water table that was 2.35 m below the land surface, reasonable estimates of ETg could be derived from the White method, and the level of the ETg corresponded with the plant growth stages. However, the water table data from the area covered by A. ordosica did not show diurnal fluctuation during the growing season. The White method is good for the desert areas where groundwater use by other processes is negligible, and evapotranspiration is the main process for groundwater consumption. In addition, the information about diurnal water table fluctuations is useful for identification of groundwater-dependence of vegetation. A. ordosica is groundwater-independent, whereas S. psammophila is groundwater-dependent.

Cheng, Dong-hui; Li, Ying; Chen, Xunhong; Wang, Wen-ke; Hou, Guang-cai; Wang, Cun-liang

2013-05-01

234

Groundwater-flow modeling in the Yucatan karstic aquifer, Mexico  

NASA Astrophysics Data System (ADS)

The current conceptual model of the unconfined karstic aquifer in the Yucatan Peninsula, Mexico, is that a fresh-water lens floats above denser saline water that penetrates more than 40 km inland. The transmissivity of the aquifer is very high so the hydraulic gradient is very low, ranging from 7-10 mm/km through most of the northern part of the peninsula. The computer modeling program AQUIFER was used to investigate the regional groundwater flow in the aquifer. The karstified zone was modeled using the assumption that it acts hydraulically similar to a granular, porous medium. As part of the calibration, the following hypotheses were tested: (1) karstic features play an important role in the groundwater-flow system; (2) a ring or belt of sinkholes in the area is a manifestation of a zone of high transmissivity that facilitates the channeling of groundwater toward the Gulf of Mexico; and (3) the geologic features in the southern part of Yucatan influence the groundwater-flow system. The model shows that the Sierrita de Ticul fault, in the southwestern part of the study area, acts as a flow barrier and head values decline toward the northeast. The modeling also shows that the regional flow-system dynamics have not been altered despite the large number of pumping wells because the volume of water pumped is small compared with the volume of recharge, and the well-developed karst system of the region has a very high hydraulic conductivity. Résumé. Le modèle conceptuel classique de l'aquifère karstique libre de la péninsule du Yucatan (Mexique) consiste en une lentille d'eau douce flottant sur une eau salée plus dense qui pénètre à plus de 40 km à l'intérieur des terres. La transmissivité de l'aquifère est très élevée, en sorte que le gradient hydraulique est très faible, compris entre 7 et 10 mm/km dans la plus grande partie du nord de la péninsule. Le modèle AQUIFER a été utilisé pour explorer les écoulements souterrains régionaux dans cet aquifère. La zone karstifiée a été modélisée en posant l'hypothèse qu'il fonctionne hydrauliquement comme un milieu poreux granulaire. Au cours de la calibration, les hypothèses suivantes ont été testées: (1) les phénomènes karstiques jouent un rôle important dans le système aquifère, (2) un anneau ou une ceinture de dépressions dans la région est la manifestation d'une zone à forte transmissivité qui permet l'écoulement en conduits de l'eau souterraine en direction du Golfe du Mexique, et (3) la situation géologique dans la partie sud du Yucatan détermine les écoulements souterrains. Le modèle montre que la faille de la Sierrita de Ticul, dans la partie sud-ouest de la région étudiée, joue le rôle de barrière et que les valeurs de la piézométrie décroissent en direction du nord-est. La modélisation montre également que la dynamique du système aquifère à l'échelle régionale n'a pas été modifiée malgré le grand nombre de puits de pompage, parce que le volume pompé est faible en comparaison du volume de recharge; en outre, le réseau karstique très bien développé dans cette région possède une très forte conductivité hydraulique. Resumen. El modelo conceptual actual del acuífero cárstico no confinado de la Península de Yucatán (México) es el de un lentejón de agua dulce flotando sobre agua salada, más densa, la cual penetra más de 40 kilómetros tierra adentro. Debido a la alta conductividad hidráulica del acuífero, existe un gradiente hidráulico muy bajo cuyo rango está entre 7 y 10 milímetros por kilómetro en la porción norte de la península. Se utilizó el código AQUIFER para investigar el sistema de flujo de las aguas subterráneas a escala regional en el acuífero. La zona carstificada se modeló suponiendo que actúa hidráulicamente como un medio poroso granular. Como parte de la calibración, se probaron las siguientes hipótesis: (1) las características cársticas desempeñan un papel importante en el sistema de flujo de agua subterránea (2) un anillo o cinturón de sumideros en el área e

González-Herrera, Roger; Sánchez-y-Pinto, Ismael; Gamboa-Vargas, José

2002-09-01

235

The combined use of MODFLOW and precipitation-runoff modeling to simulate groundwater flow in a diffuse-pollution prone watershed.  

PubMed

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

236

Freshwater flow into a coastal embayment: Groundwater and surface water inputs  

SciTech Connect

Freshwater discharge to a shallow coastal embayment was measured with two upland hydrologic and three embayment physical methods for 2 yr. Parallel measurements from the five methods ranged from 3,900 ({plus_minus}630) to 9,400 ({plus_minus}3,400) m{sup 3} d{sup {minus}1}, and four of the methods showed close agreement and averaged 4,800 ({plus_minus}670) m{sup 3} d{sup {minus}1}. The most precise estimate of discharge was from a chloride balance, while the best understanding of the rate and pattern of groundwater flow was from a Darcian streamtube approach. Groundwater dominated the freshwater budget, accounting for >95% of the total annual input, and was partitioned almost equally between direct seepage to embayment waters and seepage to a stream with final discharge via surface flow. Freshwater inputs decreased rapidly toward the mouth of the estuary and >80% entered into the upper half. The lack of fixed watershed boundaries resulted in large errors in both the location and area of the topographically defined watershed when compared to a watershed defined by water-table mapping. Seasonal variations were found in both the boundaries of the watershed (8%) and in groundwater discharge (6-fold) in response to changing water-table gradients due to recharge. Hydrologic alterations of the upland through the import of water and the increased recharge from impermeable surfaces led to an apparent increase in the total freshwater discharge to the embayment of nearly 50% over {open_quotes}natural{close_quotes}levels. 48 refs., 9 figs., 7 tabs.

Millham, N.P. [Boston Univ., MA (United States); Howes, B.L. [Woods Hole Oceanographic Inst., MA (United States)

1994-12-01

237

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

USGS Publications Warehouse

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

238

AN INTEGRATED VIEW OF GROUNDWATER FLOW CHARACTERIZATION AND MODELING IN FRACTURED GEOLOGIC MEDIA  

EPA Science Inventory

The particular attributes of fractured geologic media pertaining to groundwater flow characterization and modeling are presented. These cover the issues of fracture network and hydraulic control of fracture geometry parameters, major and minor fractures, heterogeneity, anisotrop...

239

Geohydrology, simulation of ground-water flow, and ground-water quality at two landfills, Marion County, Indiana  

USGS Publications Warehouse

Geologic, hydrologic, and water-quality data were collected at the Julietta and Tibbs-Banta landfills in Marion County. Both landfills were closed in the mid 1970's, and sewage sludge mixed with dirt was spread on the landfills in the mid 1980 's as part of a revegetation project. The landfills are constructed in unconsolidated glacial sediments that consist of sand, gravel, silt, and clay. The maximum thickness of the sediments it 180 ft at Julietta and 100 ft at Tibbs-Banta. Both landfills are underlain by sand and gravel aquifers and are adjacent to gaining streams. Groundwater flows toward and into the streams at each study area. Two sand and gravel aquifers were mapped at Julietta and four were mapped at Tibbs-Banta. The aquifers are separated in places by discontinuous clay layers. Groundwater-flow models, calibrated to simulate steady-state low-flow conditions, indicate that about 19,000 gal of water/day flow through the refuse at Julietta and about 42,000 gal/day flow through the refuse at Tibbs-Banta. Concentrations of dissolved inorganic substances in groundwater samples indicate that leachate from both landfills is reaching the shallow aquifers. The effect of the leachate on deep aquifers is minimal because of the predominance of horizontal groundwater flow and discharge to the streams. Increases in almost all dissolved constituents were observed in shallow wells that are screened beneath and downgradient from the landfills. Bromide, dissolved solids, and ammonia were useful in delineating the plume of leachate at both landfills. (USGS)

Duwelius, R.F.; Greeman, T.K.

1989-01-01

240

Conceptual evaluation of regional ground-water flow in the carbonate-rock province of the Great Basin, Nevada, Utah, and adjacent states  

USGS Publications Warehouse

The regional groundwater flow system in the carbonate rocks of Nevada and Utah is conceptualized as shallow systems superimposed on deeper systems, which transmit water primarily through carbonate rocks. A computer model was used to simulate the two systems. The regional model includes simplifying assumptions that are probably valid for parts of the province; however, the validity of each assumption is unknown for the province as a whole. Therefore, simulation results do not perfectly replicate actual groundwater flow; instead they provide a conceptual evaluation of regional groundwater flow. The model was calibrated by adjusting transmissivity and vertical leakance until simulated water levels and simulated discharge generally agreed with known water levels, mapped areas of discharge, and estimates of discharge. Simulated flow is about 1.5 million acre-ft/yr. Most groundwater flow is simulated in the upper model layer where about 45 shallow flow regions were identified. In the lower layer, 17 deep-flow subregions were identified and grouped into 5 large regions on the basis of water-flow patterns. Simulated flow in this layer is about 28 percent of the total inflow and about half is discharged as springflow. Interbasin flow to several large springs is through thick, continuous, permeable carbonate rocks; elsewhere deep consolidated rocks are not highly transmissive, suggesting that carbonate rocks are not highly permeable everywhere or are not present everywhere. (USGS)

Prudic, D.E.; Harrill, J.R.; Burbey, T.J.

1993-01-01

241

Coupling Ensemble Kalman filter and groundwater flow moment equations for real time data assimilation  

NASA Astrophysics Data System (ADS)

We consider data assimilation through ensemble Kalman filter (EnKF) in the context of groundwater flow through complex geologic media. EnKF enables one to efficiently assimilate diverse data types to characterize earth system models. The approach allows real-time Bayesian updating of system states and parameters as new data are collected. Modeling hydraulic conductivity as a correlated random field conditioned on measured conductivity and/or hydraulic head values renders the corresponding (conditional) groundwater flow equations stochastic. Solving these equations and coupling them with EnKF is typically performed within a numerical Monte Carlo (MC) simulation framework. We circumvent the need for MC through a direct solution of approximate nonlocal (integrodifferential) moment equations (MEs) that govern the space-time evolution of conditional ensemble means (statistical expectations) and covariances of hydraulic heads and fluxes. Embedding the solution of MEs in EnKF provides sequential updates of conductivity and head estimates throughout the space-time domain of interest. This is well suited for cases where real-time measurements can be used immediately to obtain a constantly up-to-date estimate of the aquifer parameters and avoids the need of assimilating all the available data in batch, where the process has to be repeated for all (previous and recent) data when new measurements become available. The methodology is illustrated through a hypothetical two-dimensional example in which a well pumps water from a randomly heterogeneous aquifer of finite extent. We analyze different scenarios, investigating the impact on the parameters estimates of (a) the number of head measurements assimilated, (b) the error variance associated with log conductivity measurements and (c) the initial hydraulic head field. We demonstrate the computational feasibility and accuracy of our methodology and show that hydraulic conductivity estimates are more sensitive to early than to later head values and improve with increasing assimilation frequency at early time. Increasing the variance of log hydraulic conductivity measurement errors by one order of magnitude brought about only a minor deterioration in the quality of corresponding parameter estimates. We test the influence of variogram model and parameters adopted to obtain the initial distributions of log hydraulic conductivity (Y ) mean and covariance on the resulting estimates of (a) hydraulic conductivity and (b) head. Our results show that assuming initial variogram sill and integral scale values different from the true ones has (in general) no adverse effect on the final estimate of Y . In contrast, adopting an incorrect variogram model caused the quality of the parameter estimates to deteriorate during the assimilation of head measurements.

Panzeri, Marco; Riva, Monica; Guadagnini, Alberto; Neuman, Shlomo P.

2013-04-01

242

Effects of turbulence on hydraulic heads and parameter sensitivities in preferential groundwater flow layers  

USGS Publications Warehouse

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 flow components were spatially extensive in preferential groundwater flow layers, with horizontal hydraulic conductivities of about 5,000,000 m d-1, mean void diameters equal to about 3.5 cm, groundwater temperature equal to about 25??C, and critical Reynolds numbers less than or equal to 400. Turbulence either increased or decreased simulated heads from their laminar elevations. Specifically, head differences from laminar elevations ranged from about -18 to +27 cm and were explained by the magnitude of net flow to the finite difference model cell. Turbulence also affected the sensitivities of model parameters. Specifically, the composite-scaled sensitivities of horizontal hydraulic conductivities decreased by as much as 70% when turbulence was essentially removed. These hydraulic head and sensitivity differences due to turbulent groundwater flow highlight potential errors in models based on the equivalent porous media assumption, which assumes laminar flow in uniformly distributed void spaces. Copyright 2008 by the American Geophysical Union.

Shoemaker, W.B.; Cunningham, K.J.; Kuniansky, E.L.; Dixon, J.

2008-01-01

243

Analytic Element Modeling of Ground-Water Flow and High Performance Computing  

Microsoft Academic Search

Several advances in the analytic element method have been made to enhance its performance and facilitate three- dimensional ground-water flow modeling in a regional aquifer setting. First, a new public domain modular code (ModAEM) has been developed for modeling ground-water flow on a regional scale by use of the AEM method. The code can be compiled as Fortran 90 for

H. M. Haitjema; V. A. Kelson; K. H. Luther

244

Regional groundwater-flow model of the Redwall-Muav, Coconino, and alluvial basin aquifer systems of northern and central Arizona  

USGS Publications Warehouse

A numerical flow model (MODFLOW) of the groundwater flow system in the primary aquifers in northern Arizona was developed to simulate interactions between the aquifers, perennial streams, and springs for predevelopment and transient conditions during 1910 through 2005. Simulated aquifers include the Redwall-Muav, Coconino, and basin-fill aquifers. Perennial stream reaches and springs that derive base flow from the aquifers were simulated, including the Colorado River, Little Colorado River, Salt River, Verde River, and perennial reaches of tributary streams. Simulated major springs include Blue Spring, Del Rio Springs, Havasu Springs, Verde River headwater springs, several springs that discharge adjacent to major Verde River tributaries, and many springs that discharge to the Colorado River. Estimates of aquifer hydraulic properties and groundwater budgets were developed from published reports and groundwater-flow models. Spatial extents of aquifers and confining units were developed from geologic data, geophysical models, a groundwater-flow model for the Prescott Active Management Area, drill logs, geologic logs, and geophysical logs. Spatial and temporal distributions of natural recharge were developed by using a water-balance model that estimates recharge from direct infiltration. Additional natural recharge from ephemeral channel infiltration was simulated in alluvial basins. Recharge at wastewater treatment facilities and incidental recharge at agricultural fields and golf courses were also simulated. Estimates of predevelopment rates of groundwater discharge to streams, springs, and evapotranspiration by phreatophytes were derived from previous reports and on the basis of streamflow records at gages. Annual estimates of groundwater withdrawals for agriculture, municipal, industrial, and domestic uses were developed from several sources, including reported withdrawals for nonexempt wells, estimated crop requirements for agricultural wells, and estimated per capita water use for exempt wells. Accuracy of the simulated groundwater-flow system was evaluated by using observational control from water levels in wells, estimates of base flow from streamflow records, and estimates of spring discharge. Major results from the simulations include the importance of variations in recharge rates throughout the study area and recharge along ephemeral and losing stream reaches in alluvial basins. Insights about the groundwater-flow systems in individual basins include the hydrologic influence of geologic structures in some areas and that stream-aquifer interactions along the lower part of the Little Colorado River are an effective control on water level distributions throughout the Little Colorado River Plateau basin. Better information on several aspects of the groundwater flow system are needed to reduce uncertainty of the simulated system. Many areas lack documentation of the response of the groundwater system to changes in withdrawals and recharge. Data needed to define groundwater flow between vertically adjacent water-bearing units is lacking in many areas. Distributions of recharge along losing stream reaches are poorly defined. Extents of aquifers and alluvial lithologies are poorly defined in parts of the Big Chino and Verde Valley sub-basins. Aquifer storage properties are poorly defined throughout most of the study area. Little data exist to define the hydrologic importance of geologic structures such as faults and fractures. Discharge of regional groundwater flow to the Verde River is difficult to identify in the Verde Valley sub-basin because of unknown contributions from deep percolation of excess surface water irrigation.

Pool, D.R.; Blasch, Kyle W.; Callegary, James B.; Leake, Stanley A.; Graser, Leslie F.

2011-01-01

245

Linking Climate, Hydrology and Groundwater in High-Resolution Transient Groundwater Flow Models: a Case Study For a Climate Change Impacts Assessment in Grand Forks, BC  

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

246

Rapid exchange effects on isotope ratios in groundwater systems: 2. Flow investigation using Sr isotope ratios  

NASA Astrophysics Data System (ADS)

Sr isotope ratios were measured in groundwater, whole rock digestions, and cation exchange extracts from a clay-rich groundwater system at Ernest O. Lawrence Berkeley National Laboratory and were used to constrain flow velocities and search for preferential flow paths. In the Orinda formation siltstone, 87Sr/86Sr increases strongly over tens of meters along presumed flow paths, indicating slow groundwater flow. Dissolved Sr is close to isotopic equilibrium with the exchangeable Sr in the clays, and the observed 87Sr/86Sr increase is interpreted as a cation exchange front moving slowly through the unit combined with dissolution of minerals with relatively high 87Sr/86Sr ratios. The data are inverted using a one-dimensional transport-dissolution-exchange model; the results indicate long-term average flow velocities of less than 0.2 m/yr which are consistent with 14C measurements. The data suggest a lack of strong preferential flow paths through this unit.

Johnson, Thomas M.; Depaolo, Donald J.

1997-01-01

247

Using MODFLOW drains to simulate groundwater flow in a karst environment  

SciTech Connect

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

248

Using Pre-Modeled Scenarios to Estimate Groundwater VOC Concentrations Resulting from Vadose Zone Sources  

SciTech Connect

Soil vapor extraction (SVE) is a prevalent remediation approach for volatile contaminants in the vadose zone. To support selection of an appropriate endpoint for the SVE remedy, an evaluation is needed to determine whether vadose zone contamination has been diminished sufficiently to protect groundwater. When vapor-phase transport is an important component of the overall contaminant fate and transport from a vadose zone source, the contaminant concentration expected in groundwater is controlled by a limited set of parameters, including specific site dimensions, vadose zone properties, and source characteristics. An approach was developed for estimating the contaminant concentration in groundwater resulting from a contaminant source in the vadose zone based on pre-modeling contaminant transport for a matrix of parameter value combinations covering a range of potential site conditions. An interpolation and scaling process are then applied to estimate groundwater impact for site-specific conditions.

Oostrom, Martinus; Truex, Michael J.; Rice, Amy K.; Johnson, Christian D.; Carroll, Kenneth C.; Becker, Dave; Simon, Michelle A.

2014-04-28

249

Using 14C and 3H to understand groundwater flow and recharge in an aquifer window  

NASA Astrophysics Data System (ADS)

Knowledge of groundwater residence times and recharge locations are vital to the sustainable management of groundwater resources. Here we investigate groundwater residence times and patterns of recharge in the Gellibrand Valley, southeast Australia, where outcropping aquifer sediments of the Eastern View Formation form an "aquifer window" that may receive diffuse recharge and recharge from the Gellibrand River. To determine recharge patterns and groundwater flowpaths, environmental isotopes (3H, 14C, ?13C, ?18O, ?2H) are used in conjunction with groundwater geochemistry and continuous monitoring of groundwater elevation and electrical conductivity. Despite the water table fluctuating by 0.9-3.7 m annually producing estimated recharge rates of 90 and 372 mm yr-1, residence times of shallow (11-29 m) groundwater determined by 14C ages are between 100 and 10 000 years. 3H activities are negligible in most of the groundwater and groundwater electrical conductivity in individual areas remains constant over the period of study. Although diffuse local recharge is evident, the depth to which it penetrates is limited to the upper 10 m of the aquifer. Rather, groundwater in the Gellibrand Valley predominantly originates from the regional recharge zone, the Barongarook High, and acts as a regional discharge zone where upward head gradients are maintained annually, limiting local recharge. Additionally, the Gellibrand River does not recharge the surrounding groundwater and has limited bank storage. 14C ages and Cl concentrations are well correlated and Cl concentrations may be used to provide a first-order estimate of groundwater residence times. Progressively lower chloride concentrations from 10 000 years BP to the present day are interpreted to indicate an increase in recharge rates on the Barongarook High.

Atkinson, A. P.; Cartwright, I.; Gilfedder, B. S.; Cendón, D. I.; Unland, N. P.; Hofmann, H.

2014-06-01

250

Density-Thermal-Driven Groundwater Flow and Brine Transport Near Salt Domes  

NASA Astrophysics Data System (ADS)

A major environmental and economic concern in many parts of the world is progressive salinization of groundwater system. Therefore, understanding the sources and flow patterns of encroachment of saline or brine water into freshwater aquifers is necessary for groundwater resources management. Flow patterns near salt domes in deep formation is of interest in this study because of complexity of different driving forces from salt concentration, thermal, and fluid pressure gradients. Because of rock formation and relative high temperature in the vicinity of salt domes, fluid salinity is much higher than seawater and density variation in the brine waters exceeds 20% with respect to fresh water. Groundwater flow, salt transport and heat transport equations are strongly coupled. Moreover, it is necessary to include the dispersive flux of total fluid mass in the flow equation. In this study, a two-dimensional density-thermal-driven groundwater flow induced by salt mass fraction gradient and temperature gradient near a hypothetical salt dome is considered. A fully implicit finite difference method has been developed to solve three coupled governing equations. The classical Elder problems and the Henry problem were used as benchmarks to verify the numerical code for solving the coupled flow and heat equations and the coupled flow and transport equations. Then, the numerical model is applied to a hypothetical salt dome problem to simulate upward density-thermal-driven groundwater flow and brine transport.

Jamshidzadeh, Z.; Tsai, F. T.; Mirbagheri, S.; Ghasemzadeh, H.

2012-12-01

251

Groundwater-recharge estimation in the Ordos Plateau, China: comparison of methods  

Microsoft Academic Search

Groundwater recharge is a key factor in water-balance studies, especially in (semi-)arid areas. In this study, multiple methods\\u000a were used to estimate groundwater recharge in the Ordos Plateau (China), including reference to water-table fluctuation, Darcy’s\\u000a law and the water budget. The mean annual recharge rates found were: water-table-fluctuation method (46–109 mm\\/yr); saturated-zone\\u000a Darcian method (17–54 mm\\/yr); and water-budget method (21–109 mm\\/yr). Generally, groundwater-recharge

Lihe Yin; Guangcheng Hu; Jinting Huang; Dongguang Wen; Jiaqiu Dong; Xiaoyong Wang; Hongbo Li

252

Estimating low flow characteristics in ungauged catchments  

Microsoft Academic Search

This paper describes the development and derivation of a methodology for estimating low flow characteristics and yield in small ungauged rural catchments. The methodology has been applied to 184 catchments located in New South Wales and Victoria, in south-eastern Australia. A systems approach was adopted in which multivariate techniques were used to develop relationships between low flow parameters and climatic

Rory J. Nathan; Tom A. McMahon

1992-01-01

253

Optical flow estimation using Fourier Mellin Transform  

Microsoft Academic Search

In this paper, we propose a novel method of computing the optical flow using the Fourier Mellin Transform (FMT). Each image in a sequence is divided into a regular grid of patches and the optical flow is estimated by calculating the phase correlation of each pair of co-sited patches using the FMT. By applying the FMT in calculating the phase

Huy Tho Ho; Roland Goecke

2008-01-01

254

Guiding optical flow estimation using superpixels  

Microsoft Academic Search

In this paper, we show how the segmentation of an image into superpixels may be used as preprocessing paradigm to improve the accuracy of the optical flow estimation in an image sequence. Superpixels play the role of accurate support masks for the integration of the optical flow equation. We employ a variation of a recently proposed opticalflow algorithm relying on

Theodosios Gkamas; Christophoros Nikou

2011-01-01

255

Estimating evapotranspiration from terrestrial groundwater-dependent ecosystems using Landsat images  

Microsoft Academic Search

Understanding and mitigating against the impact of groundwater extraction on groundwater-dependent ecosystems (GDE) requires information of evapotranspiration (ET) of these ecosystems. In this pilot study, we tested two remote-sensing methods, Surface Energy Balance Algorithms for Land (SEBAL) and Vegetation Index\\/Temperature Trapezoid (VITT), for ET estimation from terrestrial GDEs. Multi-temporal Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM + )

Xihua Yang; Peter L. Smith; Tao Yu; Hailiang Gao

2011-01-01

256

Ground-water flow in the Gulf Coast aquifer systems, south-central United States  

USGS Publications Warehouse

The Gulf Coast regional aquifer systems constitute one of the largest, most complicated, and most interdependent aquifer systems in the United States. Ground-water flow in a 230,000-square-mile area of the south-central United States was modeled for the effect of withdrawing freshwater at the rate of nearly 10 billion gallons per day in 1985 from regional aquifers in the Mississippi Embayment, the Texas coastal uplands, and the coastal lowlands aquifer systems. The 1985 rate of pumping was three times the average rate of recharge to the aquifers before development. The report also estimates the effects of even greater withdrawal rates in the aquifer systems. About two-thirds of the water in the aquifers is saline to brine, which complicates the modeling. Land subsidence due to water withdrawal also was modeled.

Williamson, A.K.; Grubb, H.F.

2001-01-01

257

Estimating spatially-variable rate constants of denitrification in irrigated agricultural groundwater systems using an Ensemble Smoother  

NASA Astrophysics Data System (ADS)

SummaryGroundwater contaminant transport models are being used increasingly to simulate the fate and transport of reactive solutes, particularly nitrate, within aquifer systems. These models, however, often are hindered by lack of information regarding parameters, such as kinetic decay rates, that govern the subsistence of the solute within the groundwater. In an overall effort to provide accurate estimates of spatially-variable parameters in numerical reactive transport modeling we employ a data assimilation scheme, the Ensemble Smoother (ES), which yields improved estimates of spatially-variable denitrification rates within an irrigated agricultural river-aquifer system using measurements of (i) nitrate concentration in the groundwater and (ii) mass of nitrate entering the river from the aquifer via groundwater flows. Based on the Kalman Filter methodology, in which distributed uncertain model results are corrected by assimilating measurement data from a reference system, the ES incorporates uncertain parameter values, associated model results, and measurement data into an update algorithm to provide an updated, corrected model state that approaches the reference system state. As an important step in eventually employing the methodology to real-world systems, this study evaluates the parameter estimation scheme for a synthetic aquifer system approaching hydrologic (heterogeneous hydraulic conductivity, cropping patterns, irrigation recharge, canal seepage) and chemical (denitrification, leaching concentrations) complexities expected in aquifers influenced by agricultural practices. Sensitivity analyses are conducted to investigate the influence of (i) the number of measurement data assimilated and (ii) the error assigned to the measurement data. Results indicate that the spatial distribution of denitrification rates can be estimated to a satisfying degree, and when implemented in additional model runs produce (i) simulated values that coincide favorably with measurement values from the reference state, and (ii) spatial distribution of nitrate concentration comparable to that of the reference state.

Bailey, Ryan T.; Baù, Domenico A.; Gates, Timothy K.

2012-10-01

258

Geohydrology of the Central Oahu, Hawaii, Ground-Water Flow System and Numerical Simulation of the Effects of Additional Pumping  

USGS Publications Warehouse

A two-dimensional, finite-difference, ground-water flow model was developed for the central Oahu flow system, which is the largest and most productive ground-water flow system on the island. The model is based on the computer code SHARP which simulates both freshwater and saltwater flow. The ground-water model was developed using average pumping and recharge conditions during the 1950's, which was considered to be a steady-state period. For 1950's conditions, model results indicate that 62 percent (90.1 million gallons per day) of the discharge from the Schofield ground-water area flows southward and the remaining 38 percent (55.2 million gallons per day) of the discharge from Schofield flows northward. Although the contribution of recharge from infiltration of rainfall and irrigation water directly on top of the southern and northern Schofield ground-water dams was included in the model, the distribution of natural discharge from the Schofield ground-water area was estimated exclusive of the recharge on top of the dams. The model was used to investigate the long-term effects of pumping under future land-use conditions. Future recharge was conservatively estimated by assuming no recharge associated with agricultural activities. Future pumpage used in the model was based on the 1995-allocated rates. Model results indicate that the long-term effect of pumping at the 1995-allocated rates will be a reduction of water levels from present (1995) conditions in all ground-water areas of the central Oahu flow system. In the Schofield ground-water area, model results indicate that water levels could decline about 30 feet from the 1995 water-level altitude of about 275 feet. In the remaining ground-water areas of the central Oahu flow system, water levels may decline from less than 1 foot to as much as 12 feet relative to 1995 water levels. Model results indicate that the bottoms of several existing deep wells in northern and southern Oahu extend below the model-calculated freshwater-saltwater interface location for the future recharge and pumping conditions. Model results indicate that an additional 10 million gallons per day (beyond the 1995-allocated rates) of freshwater can potentially be developed from northern Oahu. Various distributions of pumping can be used to obtain the additional 10 million gallons per day of water. The quality of the water pumped will be dependent on site-specific factors and cannot be predicted on the basis of model results. If the additional 10 million gallons per day pumpage is restricted to the Kawailoa and Waialua areas, model results indicate that a regional drawdown (relative to the water-level distribution associated with the 1995-allocated pumping rates) of less than 0.6 foot can be maintained in these two areas. The additional pumping, however, would cause salinity increases in water pumped by existing deep wells. In addition, increases in salinity may occur at other wells in areas where the model indicates no significant problem with upconing.

Oki, Delwyn S.

1998-01-01

259

Use of tritium and helium to define groundwater flow conditions in Everglades National Park  

NASA Astrophysics Data System (ADS)

The concentrations of tritium (3H) and helium isotopes (3He and 4He) were used as tracers of groundwater flow in the surficial aquifer system (SAS) beneath Everglades National Park (ENP), south Florida. From ages determined by 3H/3He dating techniques, groundwater within the upper 28 m originated within the last 30 years. Below 28 m, waters originated prior to 30 years before present with evidence of mixing at the interface. Interannual variation of the 3H/3He ages within the upper 28 m was significant throughout the 3 year investigation, corresponding with varying hydrologic conditions. In the region of Taylor Slough Bridge, younger groundwater was consistently detected below older groundwater in the Biscayne Aquifer, suggesting preferential flow to the lower part of the aquifer. An increase in 4He with depth in the SAS indicated that radiogenic 4He produced in the underlying Hawthorn Group migrates into the SAS by diffusion. Higher ?4He values in brackish groundwaters compared to fresh waters from similar depths suggested a possible enhanced vertical transport of 4He in the seawater mixing zone. Groundwater salinity measurements indicated the presence of a wide (6-28 km) seawater mixing zone. Comparison of groundwater levels with surface water levels in this zone indicated the potential for brackish groundwater discharge to the overlying Everglades surface water.

Price, René M.; Top, Zafer; Happell, James D.; Swart, Peter K.

2003-09-01

260

Analysis of the Shallow Groundwater Flow System at Fire Island National Seashore, Suffolk County, New York  

USGS Publications Warehouse

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

261

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

USGS Publications Warehouse

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, Kenneth L.

1986-01-01

262

Ramification of Channel Networks Incised by Groundwater Flow  

NASA Astrophysics Data System (ADS)

The geometry of channel networks has been a source of fascination since at least Leonardo da Vinci's time. Yet a comprehensive understanding of ramification---the mechanism of branching by which a stream network acquires its geometric complexity---remains elusive. To investigate the mechanisms of ramification and network growth, we consider channel growth driven by groundwater flow as a model system, analogous to a medical scientist's laboratory rat. We test our theoretical predictions through analysis of a particularly compelling example found on the Florida Panhandle north of Bristol. As our ultimate goal is to understand ramification and growth dynamics of the entire network, we build a computational model based on the following growth hypothesis: Channels grow in the direction that captures the maximum water flux. When there are two such directions, tips bifurcate. The direction of growth can be determined from the expansion of the ground water field around each tip, where each coefficient in this expansion has a physical interpretation. The first coefficient in the expansion determines the ground water discharge, leading to a straight growth of the channel. The second term describes the asymmetry in the water field leading to a bending of the stream in the direction of maximal water flux. The ratio between the first and the third coefficient determines a critical distance rc over which the tip feels inhomogeneities in the ground water table. This initiates then the splitting of the tip. In order to test our growth hypothesis and to determine rc, we grow the Florida network backward. At each time step we calculate the solution of the ground water field and determine the appropriate expansion coefficients around each tip. Comparing this simulation result to the predicted values provides us with a stringent measure for rc and the significance of our growth hypothesis.

Yi, R. S.; Seybold, H. F.; Petroff, A. P.; Devauchelle, O.; Rothman, D.

2011-12-01

263

Investigating groundwater flow between Edwards and Trinity aquifers in central Texas.  

PubMed

Understanding the nature of communication between aquifers can be challenging when using traditional physical and geochemical groundwater sampling approaches. This study uses two multiport wells completed within Edwards and Trinity aquifers in central Texas to determine the degree of groundwater inter-flow between adjacent aquifers. Potentiometric surfaces, hydraulic conductivities, and groundwater major ion concentrations and Sr isotope values were measured from multiple zones within three hydrostratigraphic units (Edwards and Upper and Middle Trinity aquifers). Physical and geochemical data from the multiport wells were combined with historical measurements of groundwater levels and geochemical compositions from the region to characterize groundwater flow and identify controls on the geochemical compositions of the Edwards and Trinity aquifers. Our results suggest that vertical groundwater flow between Edwards and Middle Trinity aquifers is likely limited by low permeability, evaporite-rich units within the Upper and Middle Trinity. Potentiometric surface levels in both aquifers vary with changes in wet vs. dry conditions, indicating that recharge to both aquifers occurs through distinct recharge areas. Geochemical compositions in the Edwards, Upper, and Middle Trinity aquifers are distinct and likely reflect groundwater interaction with different lithologies (e.g., carbonates, evaporites, and siliceous sediments) as opposed to mixing of groundwater between the aquifers. These results have implications for the management of these aquifers as they indicate that, under current conditions, pumping of either aquifer will likely not induce vertical cross-formational flow between the aquifers. Inter-flow between the Trinity and the Edwards aquifers, however, should be reevaluated as pumping patterns and hydrogeologic conditions change. PMID:24033308

Wong, C I; Kromann, J S; Hunt, B B; Smith, B A; Banner, J L

2014-01-01

264

Relation of tectonic structure to groundwater flow in the Beypazari region, NW Anatolia, Turkey  

NASA Astrophysics Data System (ADS)

The Beypazari region in NW Anatolia (Turkey) is characterized by high water demand and stress on available water resources. Tectonic structures control the groundwater flow, hydraulic head and well yield in the study area, which is located in the central part of the Beypazari Neogen basin. The impact of major tectonic structures on groundwater flow in the Cakiloba-Karadoruk aquifer is described. This aquifer is of sedimentary composition and underwent tectonic deformation, post-Miocene, forming northeast-striking asymmetric synclines, anticlines, monoclines, high-angle reverse faults and N-S striking tensional faults. Some of these structures affect groundwater flow by separating the aquifer system into sub-compartments, each having unique recharge, boundary and flow conditions. The groundwater system is compartmentalized into three sub-systems under the impacts of the Zaviye and Kanliceviz faults: (1) Arisekisi, (2) Elmabeli and (3) Southern sub-systems. The southern part of the Arisekisi sub-system and the Southern sub-system are characterized by a syncline and the aquifer is confined in the central part of the syncline. The Elmabeli sub-system has unconfined conditions. Consequently, the effects of tectonic structures are shown to be important for selecting well locations, evaluating groundwater use, groundwater management, and contaminant control in the study area, and also in other tectonic regions.

Apaydin, Ahmet

2010-09-01

265

Integrated Water Flow Model (IWFM), A Tool For Numerically Simulating Linked Groundwater, Surface Water And Land-Surface Hydrologic Processes  

Microsoft Academic Search

The Integrated Water Flow Model (IWFM) is a comprehensive input-driven application for simulating groundwater flow, surface water flow and land-surface hydrologic processes, and interactions between these processes, developed by the California Department of Water Resources (DWR). IWFM couples a 3-D finite element groundwater flow process and 1-D land surface, lake, stream flow and vertical unsaturated-zone flow processes which are solved

E. C. Dogrul; C. F. Brush; T. N. Kadir

2006-01-01

266

Microsphere estimates of blood flow: Methodological considerations  

SciTech Connect

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

267

Mapping of road-salt-contaminated groundwater discharge and estimation of chloride load to a small stream in southern New Hampshire, USA  

USGS Publications Warehouse

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

268

Groundwater flows in weathered crystalline rocks: Impact of piezometric variations and depth-dependent fracture connectivity  

NASA Astrophysics Data System (ADS)

Groundwater in shallow weathered and fractured crystalline rock aquifers is often the only perennial water resource, especially in semi-arid region such as Southern India. Understanding groundwater flows in such a context is of prime importance for sustainable aquifer management. Here, we describe a detailed study of fracture properties and relate the hydraulic connectivity of fractures to groundwater flows at local and watershed scales. Investigations were carried out at a dedicated Experimental Hydrogeological Park in Andhra Pradesh (Southern India) where a large network of observation boreholes has been set up. Twenty-height boreholes have been drilled in a small area of about 18,000 m2 in which borehole loggings and hydraulic tests were carried out to locate the main flowing fractured zones and investigate fractures connectivity. Several hydraulic tests (nineteen slug tests and three pumping tests) performed under two water level conditions revealed contrasting behavior. Under high water level conditions, the interface including the bottom of the saprolite and the first flowing fractured zone in the upper part of the granite controls groundwater flows at the watershed-scale. Under low water level conditions, the aquifer is characterized by lateral compartmentalization due to a decrease in the number of flowing fractures with depth. Depending on the water level conditions, the aquifer shifts from a watershed flow system to independent local flow systems. A conceptual groundwater flow model, which includes depth-dependent fracture connectivity, is proposed to illustrate this contrasting hydrological behavior. Implications for watershed hydrology, groundwater chemistry and aquifer vulnerability are also discussed.

Guihéneuf, N.; Boisson, A.; Bour, O.; Dewandel, B.; Perrin, J.; Dausse, A.; Viossanges, M.; Chandra, S.; Ahmed, S.; Maréchal, J. C.

2014-04-01

269

Estimation of selenium concentration in shallow groundwater in alluvial fan area in Tsukui, Central Japan.  

PubMed

Total selenium (Se) and water-soluble Se in soil, and Se in a shallow groundwater were hydrogeochemically researched in an alluvial fan area in Tsukui, Central Japan. The water-soluble Se was estimated at average level of 2.6 +/- 1.2 microg Se kg(-1) dry soil (+/- SD, n = 25), showing less than 1% of the total Se (349-508 microg Se kg(-1) dry soil) in soil. The monthly Se concentration in groundwater was average 2.2 microg,L(-1), ranging 1.6-2.4 microg,L(-1) during 2001-2003. The Se in groundwater significantly decreased with increasing groundwater level after rainfall. This result indicated that Se-bearing water percolated with relatively low Se concentration through the soil layer. According to our prediction model of linear regression curve on the observation data, Se concentration in the groundwater was estimated to be increasing with the very low rate of 4.35 x 10(-3) microg Se L(-1),yr(-1). The hydrogeochemical research and the result of the prediction model showed that any explosive increase of Se will hardly occur in this groundwater without an anthropogenic Se contamination. PMID:16897511

Ham, Young-Sik; Tamiya, Sayaka; Choi, I-Song

2007-02-01

270

Parameter estimation techniques and uncertainty in ground water flow model predictions  

SciTech Connect

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

271

Hydrogeological and Groundwater Flow Model for C, K, L, and P Reactor Areas, Savannah River Site, Aiken, South Carolina  

SciTech Connect

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

272

Climate change and groundwater ecohydrology: Simulating subsurface flow and discharge zones in Covey Hill, Quebec, Canada  

NASA Astrophysics Data System (ADS)

Nearly 2 billion people use groundwater and in Canada it is the potable water supply for about 30% of the population. Groundwater is also used in industrial and agricultural applications, and contributes to important hydrological habitats for various species. Limited research has been conducted to determine the potential impacts of climate change on groundwater. Local studies are crucial to better understand how, for example, increased duration and frequency of storms or drought periods may affect groundwater dependent ecosystems in order to anticipate and mitigate the impacts. Thus, the aim of this research is to explore the effects of climate change on a groundwater-surface water interacting system that supports a fragile ecosystem. This research is used to inform ecological conservation measures. The research site is the 17500 ha Covey Hill Natural Laboratory, which is located on the Quebec, Canada and New York State, USA border in the Chateauguay River watershed. At various locations within the Natural Laboratory there is continuous monitoring of groundwater levels and river flows. Covey Hill is an important recharge zone for the regional aquifer and provides habitat for endangered salamanders in discharge zones. Two hydrogeological models were constructed to represent flow at the site. First, a three-dimensional, finite difference model was developed using MODFLOW software to simulate overall groundwater flow at the research site. Second, a smaller-scale, discrete fracture, transient, three-dimensional, finite difference, integrated model was developed using HydroGeoSphere software to represent in better detail flow from bedrock springs that occur at mid-slope and provide the habitat for endangered salamanders. The models were used to: 1) observe groundwater flow under current climate conditions; 2) quantify water dynamics in response to climate change using 10 scenarios from the Canadian Regional Climate Model (for 1971-2000 and 2041-2070 time periods); and 3) simulate past hydrogeological conditions (100 years). Results show, for example, that future predicted changes in recharge may impact flow to groundwater springs and seeps inhabited by the endangered salamanders. For example, in the 2041-2070 period, some springs are predicted to flow more days per year, but the periods of flow are shifted, which could be critical for the salamander populations. Changes in recharge also induce variations in flow between the headwater peatland and the surrounding bedrock aquifer. Using the results from this study and ecological modeling that was conducted simultaneously by collaborators, measures to mitigate the impacts of climate change on the hydrology and ecology of Covey Hill were made to local water managers and conservationists. This study highlights the importance of conducting ecohydrological and climate change-based studies at various scales and using numerous scenarios to help capture uncertainty of future flows.

Levison, J.; Larocque, M.; Ouellet, M.; van Waterschoot, L.

2013-12-01

273

Krypton-81, Helium-4 and Carbon-14 based estimation of groundwater ages in the Guarani Aquifer System: implications for the He-4 geochronometer  

NASA Astrophysics Data System (ADS)

Characterization of aquifer systems remains a challenge, particularly for large aquifers with limited hydrogeological information. Groundwater age is an important parameter that integrates aquifer recharge and flow dynamics and provides the ability to reliably constrain groundwater models. We have used multiple isotope tracers (C-14, He-4, and Kr-81) to estimate the age of groundwater along a 400-km transect in the north-eastern part of the Guarani Aquifer System (GAS) in Brazil. Carbon-14 measurements were made with an AMS, He-4 by mass-spectrometry, and Kr-81 by atom trap trace analysis (ATTA). Groundwater samples were collected along a groundwater flow path that runs from the outcrop area in the east to the deep confined section in the west, where the aquifer is up to about 1000 m deep. Present groundwater recharge occurs in the outcrop areas, as indicated by the presence of tritium and modern 14C. Carbon-14 activities reach values below detection limit at relatively short distances (a few km) from the outcrop. Abundance of 81Kr (half-life 229 Ka), in samples free of C-14, decreases from 0.81±0.11 (expressed as (81Kr/Kr)sample/(81Kr/Kr)air) in the east to 0.18±0.03 in the western-most sample (estimated age = 566±60 ka). Measured 4He-excess is far above that expected from in-situ production rates in sandstone aquifers and overestimates the age by several orders of magnitude. We used 81Kr ages to calibrate the 4He geochronometer which indicates a basal flux of about 2.8 x10-11 cm3STP He/cm2/a. This flux is lower than most estimates of basal flux in previous studies and will allow a wider use of 4He for groundwater dating and aquifer characterization.

Aggarwal, P. K.; Chang, H. K.; Gastmans, D.; Sturchio, N. C.; Araguas, L.; Matsumoto, T.; Lu, Z.; Jiang, W.; Yokochi, R.; Mueller, P.

2012-12-01

274

Estimated natural ground-water recharge, discharge, and budget for the Dixie Valley area, west-central Nevada  

USGS Publications Warehouse

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

275

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

USGS Publications Warehouse

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

276

Groundwater availability and flow processes in the Williston and Powder River basins in the Northern Great Plains  

E-print Network

Groundwater availability and flow processes in the Williston and Powder River basins Center, Cheyenne, WY 4 Office of Groundwater, Denver, CO 5 Oklahoma Water Science Center, Oklahoma City in Montana and Wyoming, provides an opportunity to study the water-energy nexus within a groundwater context

Torgersen, Christian

277

Deep groundwater flow as the main pathway for chemical outputs in a small headwater watershed (Mule Hole, South India)  

E-print Network

Deep groundwater flow as the main pathway for chemical outputs in a small headwater watershed (Mule of a groundwater baseflow located into the active zone of the crystalline aquifer, below the weir. These findings indicate that groundwater contributes to a large part of chemical outputs at the catchment scale

Paris-Sud XI, Université de

278

Impact of Groundwater Flow on Thermal Energy Storage and Borehole Thermal Interference  

NASA Astrophysics Data System (ADS)

Borehole heat exchanger (BHE) systems are drawing increasing attention and popularity due to their potential energy efficiency and environmental sustainability, as well as their worldwide applicability. Consequently the concern for sustainable designs and proper implementation is rising too. Furthermore an improperly planned and executed system can be economically unjustifiable. To address these issues related design software and to some extent regulatory guidelines have been developed. Thermal input load function and interaction with the subsurface significantly affect thermal performance and sustainability of geothermal heat pump (GHP) systems. Of particular interest is the interaction of such systems with groundwater flow and its impacts. However the related guidelines and the design software do not seem to properly address this growing concern. Typically regulations do not distinguish between high and no groundwater flow conditions, nor do they specify a groundwater velocity threshold at which it becomes important. A further limitation is that most BHE design software used by industry assume a closed box approach discounting the heat transport in/out by the groundwater flow. To efficiently model grids of multiple BHEs, FEFLOW® 6 and the integrated BHE solution is used. Single and multiple borehole grids with U-tube heat exchanger are modeled and compared here. All boreholes are assigned equal heat extraction and flow rates; loop temperatures are then calculated over the system lifetime to compare the thermal efficiency and evaluate the thermal interference between boreholes. For the purpose of assessing the effect of groundwater flow on thermal storage as well as interference, multiple heat loads (balanced and unbalanced) are simulated. Groundwater velocity and borehole spacing are also varied to identify possible thresholds for each case. The study confirms the significance of groundwater flow in certain conditions. The results can be applied to improve the regulatory guidelines and design methods in regards with hydrogeological aspect of thermal and economical sustainability.

Emad Dehkordi, S.; Schincariol, Robert A.

2013-04-01

279

Quantification of surface water and groundwater flows to open and closedbasin lakes in a headwaters watershed  

E-print Network

flows is commonly a lake management goal [Gibson and Edwards, 2002] and influent water can deliverClick Here for Full Article Quantification of surface water and groundwater flows to open, but they are typically only effective in lakes with long water residence times. We developed a descriptive time series

280

GROUNDWATER FLOW MODEL CALIBRATION USING WATER LEVEL MEASUREMENTS AT SHORT INTERVALS  

EPA Science Inventory

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...

281

Engineering Geology 52 (1999) 231250 Mathematical modelling of groundwater flow at Sellafield, UK  

E-print Network

Engineering Geology 52 (1999) 231­250 Mathematical modelling of groundwater flow at Sellafield, UK Chris McKeown 1, *, R. Stuart Haszeldine 2, Gary D. Couples 1 Geology and Applied Geology, University and geologically complex models, topographically driven flow dominated the regional hydrogeology. Fluids trended

Haszeldine, Stuart

282

Flow path-composition relationships for groundwater entering an acidic lake  

SciTech Connect

The relationship of groundwater flow paths to the acid/base status and composition of groundwater was examined by directly monitoring groundwater inputs to an acidic Adirondack, New York, lake (Dart's Lake). Groundwater inputs near the shoreline of the lake were acidic throughout the year ( pH <5 and alkalinity <0 [mu]eq L[sup [minus]1]) and reflected the influence of shallow soil horizons. Groundwater transported within the deep surficial deposits and through sediments farther from shore was characterized by higher alkalinity and higher pH values and was enriched in nitrate (>40 [mu]eq L[sup [minus]1]). Elevated concentrations of basic cations and alkalinity as well as lower concentrations of organic anions and sulfate were characteristic of deep ground water entering the lake at the study site. Spatial variability of groundwater chemistry was found to be substantial over a relatively short distance (<6 m) from the lake shoreline and indicates that input, to the lake of components dissolved in groundwater are highly flow path dependent.

Schafran, G.C. (Old Dominion Univ., Norfolk, VA (United States)); Driscoll, C.T. (Syracuse Univ., NY (United States))

1993-01-01

283

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

EPA Science Inventory

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...

284

Effects of Daily Precipitation and Evapotranspiration Patterns on Flow and VOC Transport to Groundwater along a Watershed Flow Path  

USGS Publications Warehouse

MTBE and other volatile organic compounds (VOCs) are widely observed in shallow groundwater in the United States, especially in urban areas. Previous studies suggest that the atmosphere and/or nonpoint surficial sources could be responsible for some of those VOCs, especially in areas where there is net recharge to groundwater. However, in semiarid locations where annual potential evapotranspiration can exceed annual precipitation, VOC detections in groundwater can be frequent. VOC transport to groundwater under net discharge conditions has not previously been examined. A numerical model is used here to demonstrate that daily precipitation and evapotranspiration (ET) patterns can have a significant effect on recharge to groundwater, water table elevations, and VOC transport. Ten-year precipitation/ET scenarios from six sites in the United States are examined using both actual daily observed values and "average" pulsed precipitation. MTBE and tetrachloroethylene transport, including gas-phase diffusion, are considered. The effects of the precipitation/ET scenarios on net recharge and groundwater flow are significant and complicated, especially under low-precipitation conditions when pulsed precipitation can significantly underestimate transport to groundwater. In addition to precipitation and evapotranspiration effects, location of VOC entry into the subsurface within the watershed is important for transport in groundwater. This is caused by groundwater hydraulics at the watershed scale as well as variations in ET within the watershed. The model results indicate that it is important to consider both daily precipitation/ET patterns and location within the watershed in order to interpret VOC occurrence in groundwater, especially in low-precipitation settings.

Johnson, R.L.; Thoms, R.B.; Zogorski, J.S.

2003-01-01

285

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

SciTech Connect

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

286

Application of isotopes to estimate water ages in variable time scales in surface and groundwaters  

NASA Astrophysics Data System (ADS)

Water-Isotopes (2H, 3H, 18O) are ideal tracers not only to determine the origin of waters in precipitation, surface water (river + lakes) as well as in groundwater close to the surface and in deep groundwater but also the mean residence time (MRT) in many applied projects as drinking water supply, hydroelectric power plants, road tunnels etc. . Their application has a long history, but must be always evaluated by a feasible hydrogeological concept and/or other isotope and geochemical tracers. In Alpine areas the retention of precipitation in form of snow and ice in the winter half year is indicated by the lowest 18O-values. The snow melt of the highest part of the recharge area is marked by the lowest 18O-values in the river water, but may not coincide with the maximum flow. Time-series of precipitation station in the mountain and on river station indicate the arrival of the peak snow-melt water in the river and in Low-land areas 4-7 month later. Tritium series indicate that MRTs of several Austrian rivers are in the range of 4 - 6 years. The seasonal input variation of in 18O in precipitation and/or river waters can be used to calculate by lumped parameter models MRT of groundwater at a certain well and compare it with lysimeter measurements and transient model simulations. The MRT of the dispersion model is in good agreement with the estimated time calculated by the numerical transport model and the vertical lysimeter measurements. The MRT of spring water was studied by several methods (3H/3He, SF6 and 85Kr) and a long time series of 3H-measurements. The gas tracers are in good agreement in the range of 6-10 year whereas the 3H-series model (dispersion model) indicate ages in the range of 18-23 years. The hydrogeological concept indicate that the precipitation infiltrates in a mountainous karst area, but the transfer into the porous aquifer in the Vienna Basin occurs either through rivers draining away in the basin or through the lateral transport from the karst area to the porous aquifer. This transfer leads to an equilibration with the atmosphere causing the age difference.

Kralik, Martin

2014-05-01

287

Fitting a groundwater contaminant transport model by L1 and L2 parameter estimators  

NASA Astrophysics Data System (ADS)

This paper presents a study on the use of linear and nonlinear L1-norm parameter estimators to fit an analytical groundwater contaminant transport model with nonuniform contaminant source distributions. The model solution is obtained as a superposition of an analytical solution developed by Cleary (Cleary, R.W., Analytical Models for Groundwater Pollution and Hydrology, 208 Long Island Groundwater Pollution Study, draft report, vol. 3, Princeton University, NJ, 1978). Comparisons with the commonly used linear and nonlinear L2-norm estimators are conducted. The posterior statistical inference theory by Nyquist (Nyquist, H., Commun. Statist.-Theor. Meth., 1983, 12, 2511-24) and Gonin and Money (Gonin, G. & Money, A.H., Commun. Statist.-Theor. Meth., 1985, 14, 827-40) is used to provide the posterior covariance matrix and the probability distribution for the unknown parameter vector. As the conclusion, it is suggested that in view of the nature of groundwater contaminant transport modeling, L1-norm estimators may be preferred as robust alternatives to L2-norm estimators in solving parameter estimation problems.

Xiang, Yanyong; Thomson, N. R.; Sykes, J. F.

288

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

NASA Astrophysics Data System (ADS)

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 to the intrusion drives a flow that extends well beyond the heated region. The forcing parameter for pressurization and flow is ? ?T, where ? is a thermal expansion coefficient reflecting the overall expansion of water heated through the temperature difference ?T between the initial ambient and intrusive values. Pore pressure increases due to heating are greatest when the intrusion is emplaced rapidly and where the intrusive contact is impervious to groundwater contained in stiff, impermeable rocks with high thermal diffusivities and porosities. The maximum velocity of water flowing in pores decays with the inverse square root of time and is insensitive to hydraulic properties of the host rocks. Pressures are lessened and flow directions are reversed with the onset of hydrothermal convection. This occurs at times ranging from hours to weeks after onset of intrusion. As magma rises into near-surface rocks, steam can be generated. Solutions indicate that pressure increases and velocities are sensitive to the overall amount of expansion rather than the behavior of the water-steam transition. Both the overall thermal expansion coefficient ? and the temperature difference ?T are greater in shallow (<1 km) environments than in deep (˜5 km) ones. Thus, for rocks with similar transport properties, pressure increases due to heating are greatest in shallow environments. Although solutions can be applied to rocks with a wide variety of properties, pressure increases are calculated for compliant quartz-rich sedimentary rocks with a porosities between 1 and 20% and permeabilities between 1 darcy and 1 ?darcy, subject to temperature increases of 500 and 1000 K at depths ranging from 0.1 to 5 km in a region of hydrostatic pressures and normal geothermal gradient. Such rocks, with porosities greater than 5%, permeabilities less than a 0.1 mdarcy, and drained hydrostatic compressibilities of 10-4/MPa, undergo pressure increases greater than 10 MPa (100 bars)for conditions typical of water table depths of 2.5 km and heating to 500 K above ambient. Similar rocks, but with permeabilities less than 1 mdarcy, undergo pressure increases of 10 MPa for conditions typical of 1 km water table depth. Rocks commonly considered to be good aquifers undergo pressure increases of less than 1 MPa, primarily because of their high permeability. Although these estimates neglect the effects of fracturing and brecciation that may accompany such pressure increases, calculations indicate that pressure increases due to heating of cool groundwater can lead to failure of host rocks by a phreatic mechanism.

Delaney, Paul T.

1982-09-01

289

Coupling of groundwater, river flow and rainfall in an upland floodplain  

NASA Astrophysics Data System (ADS)

Upland floodplains provide an important function in regulating river flows and controlling the coupling of hillslope runoff with rivers. To investigate the responses of floodplain groundwater to river flows and rainfall events, a small floodplain in an upland area of the River Tweed catchment, Scotland, was characterised using geophysics, 3D geological mapping and hydrogeological testing; and monitoring undertaken from September 2011 to February 2013 of: groundwater levels in five pairs of piezometers; river stage and flow at the upstream and downstream limits of the study site; soil moisture on the adjacent hillslope; and meteorological parameters. Periodical groundwater chemistry and residence data were also collected. The floodplain aquifer is permeable throughout but partially stratified, comprising dominantly alluvial and glaciofluvial sandy gravels between 8 and 15m interspersed with thin, intermittent layers of low permeability silts, clays and peats. Overlying the gravel aquifer is a partial thin cover of low permeability alluvial silts, and it is underlain dominantly by low permeability glaciolacustrine silts and clays. High permeability solifluction deposits mantle much of the adjacent hillslope and provide a rapid connection to the floodplain aquifer. The unusually wet year of 2012 provides a good example of how a temperate upland floodplain responds to consistently high rainfall. Statistical analysis and graphical interpretation of groundwater level, rainfall, soil moisture and river stage demonstrates that: 1) dominant groundwater flow within the floodplain is in the same direction as the river, from up-valley to down-valley; 2) soil moisture in the hillslope is strongly correlated with local rainfall, but groundwater across much of the floodplain is more strongly influenced by river stage; except 3) groundwater near the edge of floodplain, which responds more slowly to local rainfall and river stage changes ; and 4) subsurface flow from the hillslope to the floodplain occurs during high rainfall events. A detailed investigation of three flood events, when the river rose above bank level and flooded adjacent fields and groundwater became artesian in parts of the floodplain, suggests that antecedent moisture conditions can partly explain the differences in groundwater response during different flood events, where high intensity or long duration rainfall can cause saturated soil conditions, reducing soil water storage capacity and hence promoting flood conditions. A conceptual model based on field data of groundwater flow after storm events during antecedent unsaturated and saturated soil conditions is presented.

Archer, Nicole; Dochartaigh, Brighid Ó.; MacDonald, Alan; Bonell, Mike; Black, Andrew; Coles, Neil

2014-05-01

290

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

USGS Publications Warehouse

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

291

Flow path oscillations in transient ground-water simulations of large peatland systems  

USGS Publications Warehouse

Transient numerical simulations of the Glacial Lake Agassiz Peatland near the Red Lakes in Northern Minnesota were constructed to evaluate observed reversals in vertical ground-water flow. Seasonal weather changes were introduced to a ground-water flow model by varying evapotranspiration and recharge over time. Vertical hydraulic reversals, driven by changes in recharge and evapotranspiration were produced in the simulated peat layer. These simulations indicate that the high specific storage associated with the peat is an important control on hydraulic reversals. Seasonally driven vertical flow is on the order of centimeters in the deep peat, suggesting that seasonal vertical advective fluxes are not significant and that ground-water flow into the deep peat likely occurs on decadal or longer time scales. Particles tracked within the ground-water flow model oscillate over time, suggesting that seasonal flow reversals will enhance vertical mixing in the peat column. The amplitude of flow path oscillations increased with increasing peat storativity, with amplitudes of about 5 cm occurring when peat specific storativity was set to about 0.05 m-1. ?? 2005 Elsevier B.V. All rights reserved.

Reeve, A.S.; Evensen, R.; Glaser, P.H.; Siegel, D.I.; Rosenberry, D.

2006-01-01

292

Performance evaluation of a dual-flow recharge filter for improving groundwater quality.  

PubMed

A dual-flow multimedia stormwater filter integrated with a groundwater recharge system was developed and tested for hydraulic efficiency and pollutant removal efficiency. The influent stormwater first flows horizontally through the circular layers of planted grass and biofibers. Subsequently, the flow direction changes to a vertical direction so that water moves through layers of pebbles and sand and finally gets recharged to the deep aquifers. The media in the sequence of vegetative medium:biofiber to pebble:sand were filled in nine proportions and tested for the best performing combination. Three grass species, viz., Typha (Typha angustifolia), Vetiver (Chrysopogon zizanioides), and St. Augustine grass (Stenotaphrum secundatum), were tested as the best performing vegetative medium. The adsorption behavior of Coconut (Cocos nucifera) fiber, which was filled in the middle layer, was determined by a series of column and batch studies.The dual-flow filter showed an increasing trend in hydraulic efficiency with an increase in flowrate. The chemical removal efficiency of the recharge dual-flow filter was found to be very high in case of K+ (81.6%) and Na+ (77.55%). The pH normalizing efficiency and electrical conductivity reduction efficiency were also recorded as high. The average removal percentage of Ca2+ was moderate, while that of Mg2+ was very low. The filter proportions of 1:1 to 1:2 (plant:fiber to pebble:sand) showed a superior performance compared to all other proportions. Based on the estimated annual costs and returns, all the financial viability criteria (internal rate of return, net present value, and benefit-cost ratio) were found to be favorable and affordable to farmers in terms of investing in the developed filtration system. PMID:25112029

Samuel, Manoj P; Senthilvel, S; Mathew, Abraham C

2014-07-01

293

Phase II Groundwater Flow Model of Corrective Action Unit 98: Frenchman Flat, Nevada Test Site, Nye County, Nevada, Rev. No.: 0  

SciTech Connect

The Phase II Frenchman Flat groundwater flow model is a key element in the ''Federal Facility Agreement and Consent Order'' (FFACO) (1996) corrective action strategy for the Underground Test Area (UGTA) Frenchman Flat corrective action unit (CAU). The objective of this integrated process is to provide an estimate of the vertical and horizontal extent of contaminant migration for each CAU to predict contaminant boundaries. A contaminant boundary is the model-predicted perimeter that defines the extent of radionuclide-contaminated groundwater from underground testing above background conditions exceeding the ''Safe Drinking Water Act'' (SDWA) standards. The contaminant boundary will be composed of both a perimeter boundary and a lower hydrostratigraphic unit (HSU) boundary. The computer model will predict the location of this boundary within 1,000 years and must do so at a 95 percent level of confidence. Additional results showing contaminant concentrations and the location of the contaminant boundary at selected times will also be presented. These times may include the verification period, the end of the five-year proof-of-concept period, as well as other times that are of specific interest. This report documents the development and implementation of the groundwater flow model for the Frenchman Flat CAU. Specific objectives of the Phase II Frenchman Flat flow model are to: (1) Incorporate pertinent information and lessons learned from the Phase I Frenchman Flat CAU models. (2) Develop a three-dimensional (3-D), mathematical flow model that incorporates the important physical features of the flow system and honors CAU-specific data and information. (3) Simulate the steady-state groundwater flow system to determine the direction and magnitude of groundwater fluxes based on calibration to Frenchman Flat hydrogeologic data. (4) Quantify the uncertainty in the direction and magnitude of groundwater flow due to uncertainty in parameter values and alternative component conceptual models (e.g., geology, boundary flux, and recharge).

John McCord

2006-05-01

294

Estimating annual groundwater recharge coefficient for karst aquifers of the southern Apennines (Italy)  

NASA Astrophysics Data System (ADS)

To assess the mean annual groundwater recharge of the karst aquifers in the southern Apennines (Italy), the estimation of the mean annual groundwater recharge coefficient (AGRC) was conducted by means of an integrated approach based on hydrogeological, hydrological, geomorphological, land use and soil cover analyses. Starting from the hydrological budget equation, the coefficient was conceived as the ratio between the net groundwater outflow and the precipitation minus actual evapotranspiration (P - ETR) for a karst aquifer. A large part of the southern Apennines, which is covered by a meteorological network containing 40 principal karst aquifers, was studied. Using precipitation and air temperature time series gathered through monitoring stations operating in the period 1926-2012, the mean annual P - ETR was estimated, and its distribution was modelled at a regional scale by considering the orographic barrier and rain shadow effects of the Apennine chain, as well as the altitudinal control. Four sample karst aquifers with available long spring discharge time series were identified for estimating the AGRC. The resulting values were correlated with other parameters that control groundwater recharge, such as the extension of outcropping karst rocks, morphological settings, land use and covering soil type. A multiple linear regression between the AGRC, lithology and the summit plateau and endorheic areas was found. This empirical model was used to assess the AGRC and mean annual groundwater recharge in other regional karst aquifers. The coefficient was calculated as ranging between 50 and 79%, thus being comparable with other similar estimations carried out for karst aquifers of European and Mediterranean countries. The mean annual groundwater recharge for karst aquifers of the southern Apennines was assessed by these characterizations and validated by a comparison with available groundwater outflow measurements. These results represent a deeper understanding of an aspect of groundwater hydrology in karst aquifers which is fundamental for the formulation of appropriate management models of groundwater resources at a regional scale, also taking into account mitigation strategies for climate change impacts. Finally, the proposed hydrological characterizations are also supposed to be useful for the assessment of mean annual runoff over carbonate mountains, which is another important topic concerning water management in the southern Apennines.

Allocca, V.; Manna, F.; De Vita, P.

2014-02-01

295

Estimating groundwater recharge on a temperate humid to semiarid volcanic island (Jeju, Korea) from water table fluctuations, Cl mass balance, apparent CFC-12 ages and 3H renewal  

NASA Astrophysics Data System (ADS)

Groundwater table fluctuations, Chloride mass balance, apparent groundwater Chlorofluorocarbon (CFC-12) ages and tritium (3H) renewal rates were used to assess recharge on Jeju Island (Korea), where groundwater is the main source of potable water. Given the limitations of various techniques and the respective data, the methods yield highly variable results of 10 to 1,991 mm/yr, with an average of 780 mm/yr that represents about 40% of the average annual rainfall over the island. The magnitude of recharge has not changed significantly over the past 50 years as indicated by an overall agreement of estimates for recent inter-seasonal recharge from the water table fluctuation method, and the long term average values from the geochemical techniques and the detailed water budget. Heterogeneity of recharge at the catchment scale is caused by spatially and temporally variable rainfall and evapotranspiration as well as the wide range in effective porosity and specific yield values of the aquifer lithologies. A Piston Flow model with negligible dispersion and diffusion fits 3H values for most groundwater samples. This implies that the mafic to intermediate volcanics exhibit fracture-hosted groundwater flow and that rapid recharge may be occurring in zones of interconnected porosity that represent a fraction of the total porosity. Calculated recharge rates that are generally highest (>1,000 mm/yr) in southern and eastern catchments and decrease with altitude indicate a strong control of topography and rainfall. However, since high recharge may occur across broad areas, attempts to protect groundwater from surface contamination require management of the landscape as a whole, not just the uplands. Increased recharge in western catchments (i.e., Hallim and Hangyeong) has not lowered groundwater nitrate contents due to the low effective porosities of the aquifers, where older nitrate-rich water is trapped in massive lava blocks within the unsaturated zone and is slowly mixed with groundwater as the water table rises.

Hagedorn, K. B.; El-Kadi, A. I.; Mair, A.; Whittier, R.

2010-12-01

296

Challenging the distributed temperature sensing technique for estimating groundwater discharge to streams through controlled artificial point source experiment  

NASA Astrophysics Data System (ADS)

Spatially confined groundwater discharge can contribute significantly to stream discharge. Distributed fibre optic temperature sensing (DTS) of stream water has been successfully used to localize- and quantify groundwater discharge from this type "point sources" (PS) in small first-order streams. During periods when stream and groundwater temperatures differ PS appear as abrupt step in longitudinal stream water temperature distribution. Based on stream temperature observation up- and downstream of a point source and estimated or measured groundwater temperature the proportion of groundwater inflow to stream discharge can be quantified using simple mixing models. However so far this method has not been quantitatively verified, nor has a detailed uncertainty analysis of the method been conducted. The relative accuracy of this method is expected to decrease nonlinear with decreasing proportions of lateral inflow. Furthermore it depends on the temperature differences (?T) between groundwater and surface water and on the accuracy of temperature measurement itself. The latter could be affected by different sources of errors. For example it has been shown that a direct impact of solar radiation on fibre optic cables can lead to errors in temperature measurements in small streams due to low water depth. Considerable uncertainty might also be related to the determination of groundwater temperature through direct measurements or derived from the DTS signal. In order to directly validate the method and asses it's uncertainty we performed a set of artificial point source experiments with controlled lateral inflow rates to a natural stream. The experiments were carried out at the Vollnkirchener Bach, a small head water stream in Hessen, Germany in November and December 2011 during a low flow period. A DTS system was installed along a 1.2 km sub reach of the stream. Stream discharge was measured using a gauging flume installed directly upstream of the artificial PS. Lateral inflow was simulated using a pumping system connected to a 2 m3 water tank. Pumping rates were controlled using a magnetic inductive flowmeter and kept constant for a time period of 30 minutes to 1.5 hours depending on the simulated inflow rate. Different temperatures of lateral inflow were adjusted by heating the water in the tank (for summer experiments a cooling by ice cubes could be realized). With this setup, different proportions of lateral inflow to stream flow ranging from 2 to 20%, could be simulated for different ?T's (2-7° C) between stream- and inflowing water. Results indicate that the estimation of groundwater discharge through DTS is working properly, but that the method is very sensitive to the determination of the PS groundwater temperature. The span of adjusted ?T and inflow rates of the artificial system are currently used to perform a thorough uncertainty analysis of the DTS method and to derive thresholds for detection limits.

Lauer, F.; Frede, H.-G.; Breuer, L.

2012-04-01

297

INCORPORATION OF GROUNDWATER FLOW INTO NUMERICAL MODELS AND DESIGN MODELS  

E-print Network

-coupled, ground-source heat pumps, groundwater, heat pump, heat exchanger, heat transfer, numerical models-loop ground-coupled heat exchangers. Green and Perry (1961) demonstrated that the value of effective thermal-loop systems assume that heat transfer within geologic formations occurs by conduction only. In the absence

298

A quantitative model of ground-water flow during formation of tabular sandstone uranium deposits  

USGS Publications Warehouse

Presents a quantitative simulation of regional groundwater flow during uranium deposition in the Westwater Canyon Member and Jackpile Sandstone Member of the Upper Jurassic Morrison Formation in the San Juan basin. Topographic slope, shoreline position, and density contrasts in the lake and pore fluids controlled the directions of flow and recharge-discharge areas. The most important results for uranium ore deposit formation are that regional groundwater discharged throughout the basin, regional discharge was concentrated along the shore line or playa margin, flow was dominantly gravity driven, and compaction dewatering was negligible. A strong association is found between the tabular sandstone uranium deposits and major inferred zones of mixed local and regional groundwater discharge. -from Author

Sanford, R.F.

1994-01-01

299

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

USGS Publications Warehouse

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

Swain, Eric D.; Wexler, Eliezer J.

1996-01-01

300

Two-dimensional DNAPL migration affected by groundwater flow in unconfined aquifer.  

PubMed

The dense non-aqueous phase liquid (DNAPL) migration process was experimentally investigated in a laboratory-scale tank (150 cm width, 82.5 cm height, and 15 cm depth) to assess a site characterization on DNAPL contamination below a groundwater table. The heterogeneous ground of the tank model consisted of Toyoura sand (hydraulic conductivity, k = 1.5 x 10(-2) cm/s for void ratio, e = 0.62) and silica #7 sand (k = 2.3 x 10(-3) cm/s for e = 0.72). A series of experiments was carried out with or without lateral groundwater flow. Hydrofluoroether was used as a representative DNAPL. The main results obtained in this study are as follows: (1) the DNAPL plume does not invade into the less permeable soil layer with higher displacement pressure head; (2) the DNAPL plume migrates faster with lateral groundwater flow than without it; (3) lateral groundwater flow does not affect lateral DNAPL migration; rather, it promotes downward migration; and (4) pore DNAPL pressure without groundwater flow is higher than that with it. The above experimental results were compared with numerical analysis. The fundamental behaviors of DNAPL source migration observed experimentally are expected to be useful for assessing the characteristics of two-dimensional DNAPL migration in an aquifer. PMID:15177722

Kamon, Masashi; Endo, Kazuto; Kawabata, Junichi; Inui, Toru; Katsumi, Takeshi

2004-07-01

301

Estimating annual effective infiltration coefficient and groundwater recharge for karst aquifers of the southern Apennines  

NASA Astrophysics Data System (ADS)

To assess the mean annual groundwater recharge of the karst aquifers in southern Apennines (Italy), the estimation of the mean annual effective infiltration coefficient (AEIC) was conducted by means of an integrated approach based on hydrogeological, hydrological, geomorphological, land use and soil cover analyses. We studied a large part of the southern Apennines that is covered by a meteorological network and containing 40 principal karst aquifers. Using precipitation and air temperature time series gathered through monitoring stations operating in the period 1926-2012, the annual effective precipitation (AEP) was estimated, and its distribution was modelled, by considering the orographic barrier and rain shadow effects of the Apennines chain, as well as the altitudinal control. Four sample karst aquifers with available long spring discharge time series were identified for estimating the AEIC by means of the hydrological budget equation. The resulting AEIC values were correlated with other parameters that control groundwater recharge, such as the extension of outcropping karst-rock, morphological settings, land use and covering soil type. A simple correlation relationship between AEIC, lithology and the summit flat and endorheic areas was found. This empirical model has been used to estimate AEIC and mean annual groundwater recharge in other regional karst aquifers. The estimated AEIC values ranged between 48% and 78%, thus matching intervals estimated for other karst aquifers in European and Mediterranean countries. These results represent a deeper understanding of an aspect of groundwater hydrology in karst aquifers which is fundamental for the formulation of appropriate management models of groundwater resources, also taking into account mitigation strategies for climate change impacts. Finally, the proposed hydrological characterisations are also perceived as useful for the assessment of mean annual runoff over carbonate mountains, which is another important topic concerning water management in the southern Apennines.

Allocca, V.; Manna, F.; De Vita, P.

2013-08-01

302

Analysis of multicomopnent groundwater flow in karst aquifer by CFC, tritium, tracer test and modelling, case study at Skaistkalnes vicinity, Latvia  

NASA Astrophysics Data System (ADS)

Groundwater in karst environments tends to have difficulties to distinguish multiple flows if several sources of water are present. Skaistkalne vicinity faces with such situation where old groundwater, fresh groundwater and inflow from river Iecava occurs. Attempts were made to distinguish groundwater residence time of multiple components of water applying CFC and tritium dating techniques supplied by tracer test and numerical model of study area. Study area covers territory between two rivers Iecava and Memele with water level difference of 7 meters and horizontal distance of 2.2 kilometres between both. Study area consists of karst affected Devonian gypsum and carbonaceous rocks covered by Quaternary low to high permeable deposits. Confined groundwater at depth of 10-25 meters where analysed by CFC's and tritium. At this depth groundwater exhibits anoxic reducing environment that has caused degradation of CFC's at similar degree in all samples. Taking it into account, mean residence time based on CFC piston flow model is 22 - 42 years and 28 - 34 years based on binary mixing model. Tritium results show signs of incensement of groundwater residence time towards discharge area. CFC combined with tritium proved increased vertical velocity in middle part between the rivers likely caused by hydrogeological window in Quaternary deposits created by karst processes. Numerical model (Delina et al. 2012) was applied and calculations yielded groundwater flow velocity rate at 0.3 - 1 m/day in area between the rivers. Investigation of CFC data resulted in possible groundwater flow rate of at a minimum of 0.2 m/day although it's not applicable to all sampled wells due to specific hydrogeological conditions. Tracer test was made between the rivers in order to distinguish main water flow paths and flow velocity. Results showed that very high permeable conduits connect rivers and karst lakes with velocity rates of 800 - 1300 m/day. Complex investigation leads to conclude that three different sources of groundwater occur characterized by different flow velocity, recharge age and chemical composition. Although CFC's has been degraded, it is possible to use the results to distinguish groundwater different components and even to estimate groundwater flow velocity because of near located recharge and discharge areas. Tritium results doesn't show considerable variations along flow path with 6 TU in average confirming conclusions based on CFC's. Tracer test approve very high groundwater velocity zones in study area that supposedly doesn't mix with groundwater in matrix. References Delina A., Babre A., Popovs K., Sennikovs J., Grinberga B. 2012. Effects of karst processes on surface water and groundwater hydrology at Skaistkalne vicinity, Latvia. - Hydrology Research, 43(4), IWA Publishing, pp. 445-459, doi:10.2166/nh.2012.123. This study is supported by ERAF project Nr. 1013/00542DP/2.1.1.1.0/13/APIA/VIAA/007

Bikshe, Janis; Babre, Alise; Delina, Aija; Popovs, Konrads

2014-05-01

303

COMMUNITY-RANDOMIZED INTERVENTION TRIAL WITH UV DISINFECTION FOR ESTIMATING THE RISK OF PEDIATRIC ILLNESS FROM MUNICIPAL GROUNDWATER CONSUMPTION  

EPA Science Inventory

The goal of this study is to estimate the risk of childhood febrile and gastrointestinal illnesses associated with drinking municipal water from a groundwater source. The risk estimate will be partitioned into two separate components— illness attributable to contaminated...

304

Recharge Estimation in the Liverpool Plains (NSW) for input Groundwater Models  

Microsoft Academic Search

Abstract Dryland salinity, caused by rising watertables, is a potential major land degradation issue on the Liverpool Plains, in northern NSW. This study aims to provide recharge estimates for the modelling of the Tertiary\\/Quaternary alluvial groundwater system, believed to be the origin of the surface salinisation problem in the Liverpool Plains. In particular, it aims to indicate the relativity of

L. Zhang; M. Stauffacher; G. R. Walker; P. Dyce

1997-01-01

305

ESTIMATION OF GROUNDWATER POLLUTION POTENTIAL BY PESTICIDES IN MID-ATLANTIC COASTAL PLAIN WATERSHEDS  

EPA Science Inventory

A simple GIS-based transport model to estimate the potential for groundwater pollution by pesticides has been developed within the ArcView GIS environment. The pesticide leaching analytical model, which is based on one-dimensional advective-dispersive-reactive (ADR) transport, ha...

306

STATISTICAL ESTIMATION AND VISUALIZATION OF GROUND-WATER CONTAMINATION DATA  

EPA Science Inventory

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...

307

Simulation of groundwater flow at the LBNL site using TOUGH2  

SciTech Connect

In the late 1980s, groundwater contamination was detected at the site of the Lawrence Berkeley National Laboratory (LBNL). A detailed investigation was conducted to locate the source and the extent of the contamination. Interim corrective measures were initiated where appropriate and required, typically directed towards removing the source of contamination, excavating contaminated soil, and limiting further spreading of contaminants. As the first step for predicting the fate of remaining contaminants, a three-dimensional transient groundwater flow model was developed for the complex hydrogeological situation. This flow model captured strong variations in thickness, slope, and hydrogeological properties of geologic units, representative of a mountainous groundwater system with accentuated morphology. The flow model accounts for strong seasonal fluctuations in the groundwater table. Other significant factors are local recharge from leaking underground storm drains and significant water re charge from steep hills located upstream. The strong heterogeneous rock properties were calibrated using the inverse simulator ITOUGH2. For validation purposes, the model was calibrated for a time period from 1994 to 1996, and then applied to a period from 1996 to 1998. Comparison of simulated and measured water levels demonstrated that the model accurately represents the complex flow situation, including the significant seasonal fluctuations in water table and flow rate. Paths of particles originating from contaminant plumes in the simulated transient flow fields were obtained to represent advective transport.

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

2003-05-12

308

Influence of Permafrost Distribution on Regional Groundwater Flow in the Yukon Flats Basin, Alaska  

NASA Astrophysics Data System (ADS)

Degradation of permafrost in interior Alaska is expected to have significant impacts on the routing of water above and below the land surface. This study attempts to elucidate modes of regional groundwater flow for various patterns of permafrost to assess the hydrologic control of permafrost presence and to evaluate potential hydrologic consequences of permafrost degradation. The Yukon Flats Basin, a large (118,340 sq km) sub-basin within the Yukon River Basin in Alaska, provides the basis for this regional groundwater flow modeling investigation. Model simulations that represent an assumed permafrost thaw sequence via diminishing permafrost spatial coverage and volume exhibit the following trends: 1) increased groundwater discharge to rivers, consistent with historical trends in baseflow observations in the Yukon River Basin, 2) increased potential for overall recharge and overall groundwater flow, 3) increased extent of groundwater discharge in the flats, and 4) decreased ratio of supra-permafrost to sub-permafrost groundwater in river baseflow. Such trends have implications for the chemical composition and residence time of riverine exports, the status of lakes and wetlands influenced by groundwater, seasonal river ice thickness, and seasonal stream temperatures. Model results identify the classically-defined transition from continuous to discontinuous permafrost coverage at 90% to be within a relatively narrow range of the permafrost distribution spectrum that is particularly vulnerable to hydrologic change. Major hydrologic changes are predicted near this transition with relatively minor changes in permafrost distribution. For example, the model-predicted proportion of stream baseflow derived from lateral flow in the supra-permafrost zone decreases from 52% to 17% as permafrost coverage decreases from 95% and 89%, respectively. Presently, the Yukon Flats Basin is coarsely mapped as spanning the critical transition between continuous and discontinuous permafrost, thus underscoring the need for improved characterization of permafrost and other hydrogeologic information in the study area via geophysical techniques, remote sensing, and ground truthed observations.

Walvoord, M. A.; Voss, C. I.; Wellman, T. P.

2011-12-01

309

Monitoring of flow field based on stable isotope geochemical characteristics in deep groundwater.  

PubMed

The water circulation in deep aquifers controls not only chemical composition of the groundwater, but also stable isotope composition. In order to analyze the flow field in the process of the deep groundwater circulation in different aquifers, specimens belonging to the fourth aquifer in the Quaternary (the fourth aquifer for short), the coal and sandstone cranny aquifer in the Permian, and Carboniferous (the coal catena aquifer for short), the Taiyuan group limestone aquifer in the Carboniferous (the Taiyuan limestone aquifer for short), and the limestone aquifer in the Ordovician (the Ordovician limestone aquifer for short) were gained from the top down in Renlou colliery and local Linhuan coalmine district, northern Anhui, China, in the study. ?D, ?(18)O, and the content of tall dissolve solids (TDS for short) of these specimens were tested. The experimental results had revealed that the groundwater in the fourth aquifer and the Taiyuan limestone aquifer takes on (18)O excursion and the coal catena aquifer takes on D excursion in Linhuan coalmine district, while excursion characteristic in the Ordovician limestone aquifer is not evident in the coalmine district. By analysis, ?(18)O and the content of TDS are in negative relationship in the groundwater of the fourth aquifer and the Taiyuan limestone aquifer in Linhuan coalmine district, yet ?D and the content of TDS are in positive relationship in the coal catena aquifer. Mining greatly influences the fourth aquifer and the coal catena aquifer so the groundwater in the fourth aquifer flows from northwest and southeast to mining areas and the groundwater in the coal catena aquifer flows from around to mining areas. However, mining does not influence the Taiyuan limestone aquifer evidently so the groundwater flows from east to west still. PMID:20963482

Chen, Lu-wang; Gui, He-rong; Yin, Xiao-xi

2011-08-01

310

ANALYSIS AND REDUCTION OF LANDSAT DATA FOR USE IN A HIGH PLAINS GROUND-WATER FLOW MODEL.  

USGS Publications Warehouse

Data obtained from 59 Landsat scenes were used to estimate the areal extent of irrigated agriculture over the High Plains region of the United States for a ground-water flow model. This model provides information on current trends in the amount and distribution of water used for irrigation. The analysis and reduction process required that each Landsat scene be ratioed, interpreted, and aggregated. Data reduction by aggregation was an efficient technique for handling the volume of data analyzed. This process bypassed problems inherent in geometrically correcting and mosaicking the data at pixel resolution and combined the individual Landsat classification into one comprehensive data set.

Thelin, Gail; Gaydas, Leonard; Donovan, Walter; Mladinich, Carol

1984-01-01

311

Influence of groundwater extraction on river flows and the surrounding ecosystem  

NASA Astrophysics Data System (ADS)

Influence of groundwater extraction on river flows and the surrounding ecosystem. Change of hydro-geological conditions and the conditions of environment connected with them? One of the most adverse consequences of the large centralised operation of underground waters coastal (riverine) water fences. Such situation is predicted on the Permilovsky deposit reconnoitered for water supply of Arkhangelsk. The projected water fence was planned in a valley of the river of Vajmugi on its left coast. The predesigns spent on hydrogeodynamic of model of a deposit, show that as a result of operation of underground waters the damage to a drain of the river Vajmuga approximately equal ?????? of a water fence that leads to a considerable shallowing of the river, especially during its periods ????????????, up to a drain total disappearance on a water fence site is formed. On the average, on territories of a deposit expenses of the river concerning natural state can be reduced more than to 50 %. Reduction of a river drain will lead to considerable negative consequences in environment, including: - changes in surface runoff, reduced groundwater levels, inhibit vegetation and changes in plant communities, draining wetlands, changing soil moisture conditions, a decrease of spring runoff, damage to forestry; - earth's surface subsidence, damage to streets and roads, buildings, structures and communications, drainage wells, the development of karst processes and suffosion; - the formation of deep depressions, capturing several zones of water exchange, which could lead to mixing of water of different chemical composition and mineralization of the runoff into surface water bodies, increase the nitrogen content in groundwater; - discontinuity separating the layers and the increased vulnerability of groundwater and surface water, the action of man-made agents. The aim of this study was a preliminary study of alternative schemes of exploitation of underground water deposits, in which damage to river flow, essentially inevitable, will be minimized. The alternative scheme provides reduction of productivity of the basic water fence during the periods critical aquaticity. During these periods, for preservation of volume of water giving, the additional (compensatory) water fence is entered into operation. Settlement remoteness compensatory water fence is defined by a condition that for rather short-term period (in low flow) water fence works, its hydrodynamic influence did not reach the river and basic water fence. At the same time, during the periods high aquaticity when compensatory water fence does not work, stocks ??????????? horizon on the area of its depression should be restored completely. For use of this scheme it is necessary to define the periods of an inadmissible damage to a drain during which reduction discharge of the basic water fence both use compensatory water fence, and operational loading basic water fence and compensatory water fence during the periods of their teamwork is required. Is minimum admissible expense for the given territory should be defined after the special ecological analysis. For tentative estimations 2 variants are considered: 1) in the river of Vajmuga, in a water fence alignment, the expense not below 25 % from minimum low-flow natural size all-the-year-round should remain; 2) on a water fence site in the river the expense not below 25 % from mid-annual size should remain. For both variants the periods of reduction of productivity of the basic water fence are proved and introductions in operation of the compensatory water fence. Have been calculated values of reduction of productivity of the basic water fence, its new discharge and as discharge of the compensatory water fence. It is received that discharge of the basic water fence should be reduced to 35 and 37 % for the first and second settlement variants accordingly. The quantity of knots

Belova, Anna

2010-05-01

312

The in situ permeable flow sensor: A ground-water flow velocity meter  

SciTech Connect

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 ground-water flow velocity vector in unconsolidated, saturated, porous media. The velocity measured is an average value characteristic of an approximately 1 cubic meter volume of the subsurface. The sensors are permanently buried in direct contact with the formation at the point where the velocity measurement is to be made. While this deployment strategy means that the approximately $2,500 instruments are not recovered, borehole effects which can negatively influence the quality of the measurement are avoided. The sensors can be connected to a data acquisition system which can be monitored remotely, via modem and telephone connection, for extended periods of time. The technology is able to measure flow velocities in the range of 5 {times} 10{sup {minus}6} to 1 {times} 10{sup {minus}3} cm/s, depending on the thermal properties of the medium in which it is buried.

Ballard, S. [Sandia National Labs., Albuquerque, NM (United States). Geophysics Dept.

1996-03-01

313

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

NASA Astrophysics Data System (ADS)

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

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

2013-12-01

314

Stochastic ground-water flow analysis FY-81 status report. Assessment of effectiveness of geologic isolation systems  

SciTech Connect

Research was conducted at Pacific Northwest Laboratory to develop a research computational package for the stochastic analysis of ground-water flow. Both unsteady and steady-state analysis were examined, and a steady-state research code was developed for the study of stochastic processes. This report describes the theoretical development of both unsteady and steady analyses, and presents the preliminary studies undertaken to verify and exercise the encoded algorithm. The stochastic analysis of ground-water flow is a promising new method which can supply more comprehensive analyses of the ground-water environment. The work reported herein provided experience in the methodology while producing a research-oriented stochastic analysis capability. Single-layer aquifers of horizontal extent were selected for this effort. Kriging has been employed to describe the uncertainty in field data. The resulting stochastic parameters enter the problem physics through boundary conditions and Darcy's equation. The mean and variance of the piezometric head are estimated by the stochastic analysis.

Kincaid, C.T.; Vail, L.W.; Devary, J.L.

1983-07-01

315

Coupled modelling of groundwater flow and hydrochemistry in the Sellafield area  

SciTech Connect

UK Nirex Limited (Nirex) is investigating a site at Sellafield in Cumbria to assess its suitability as a host formation for a deep disposal facility for solid low and intermediate level radioactive waste. As part of the evaluation process, extensive characterization work has been performed. This characterization has included the acquisition of various types of information and data from the area around the site, and the use of this information in developing an understanding of the groundwater flow regime at Sellafield. Modelling the groundwater flow processes at the site is an important input to assessing the performance of the site as a host for a radioactive waste repository.

Littleboy, A.K. [United Kingdom Nirex Limited, Oxon (United Kingdom); Metcalfe, R.; Noy, D.J. [British Geological Survey Limited, Nottingham (United Kingdom)

1996-12-01

316

A theory for modeling ground-water flow in heterogeneous media  

USGS Publications Warehouse

Construction of a ground-water model for a field area is not a straightforward process. Data are virtually never complete or detailed enough to allow substitution into the model equations and direct computation of the results of interest. Formal model calibration through optimization, statistical, and geostatistical methods is being applied to an increasing extent to deal with this problem and provide for quantitative evaluation and uncertainty analysis of the model. However, these approaches are hampered by two pervasive problems: 1) nonlinearity of the solution of the model equations with respect to some of the model (or hydrogeologic) input variables (termed in this report system characteristics) and 2) detailed and generally unknown spatial variability (heterogeneity) of some of the system characteristics such as log hydraulic conductivity, specific storage, recharge and discharge, and boundary conditions. A theory is developed in this report to address these problems. The theory allows construction and analysis of a ground-water model of flow (and, by extension, transport) in heterogeneous media using a small number of lumped or smoothed system characteristics (termed parameters). The theory fully addresses both nonlinearity and heterogeneity in such a way that the parameters are not assumed to be effective values. The ground-water flow system is assumed to be adequately characterized by a set of spatially and temporally distributed discrete values, ?, of the system characteristics. This set contains both small-scale variability that cannot be described in a model and large-scale variability that can. The spatial and temporal variability in ? are accounted for by imagining ? to be generated by a stochastic process wherein ? is normally distributed, although normality is not essential. Because ? has too large a dimension to be estimated using the data normally available, for modeling purposes ? is replaced by a smoothed or lumped approximation y?. (where y is a spatial and temporal interpolation matrix). Set y?. has the same form as the expected value of ?, y 'line' ? , where 'line' ? is the set of drift parameters of the stochastic process; ?. is a best-fit vector to ?. A model function f(?), such as a computed hydraulic head or flux, is assumed to accurately represent an actual field quantity, but the same function written using y?., f(y?.), contains error from lumping or smoothing of ? using y?.. Thus, the replacement of ? by y?. yields nonzero mean model errors of the form E(f(?)-f(y?.)) throughout the model and covariances between model errors at points throughout the model. These nonzero means and covariances are evaluated through third and fifth-order accuracy, respectively, using Taylor series expansions. They can have a significant effect on construction and interpretation of a model that is calibrated by estimating ?.. Vector ?.. is estimated as 'hat' ? using weighted nonlinear least squares techniques to fit a set of model functions f(y'hat' ?) to a. corresponding set of observations of f(?), Y. These observations are assumed to be corrupted by zero-mean, normally distributed observation errors, although, as for ?, normality is not essential. An analytical approximation of the nonlinear least squares solution is obtained using Taylor series expansions and perturbation techniques that assume model and observation errors to be small. This solution is used to evaluate biases and other results to second-order accuracy in the errors. The correct weight matrix to use in the analysis is shown to be the inverse of the second-moment matrix E(Y-f(y?.))(Y-f(y?.))', but the weight matrix is assumed to be arbitrary in most developments. The best diagonal approximation is the inverse of the matrix of diagonal elements of E(Y-f(y?.))(Y-f(y?.))', and a method of estimating this diagonal matrix when it is unknown is developed using a special objective function to compute 'hat' ?. When considered to be an estimate of f

Cooley, Richard L.

2004-01-01

317

A comparative analysis of groundwater recharge estimates from three major methods: An analysis of subsurface recharge in the Nabogo sub-catchment of the White Volta Basin, Northern Ghana  

NASA Astrophysics Data System (ADS)

Groundwater recharge in the Nabogo sub-catchment of the White Volta Basin is assessed using three main methods: the water table fluctuations method, baseflow recession method, and chloride mass balance approach. The objective is to quantify the relative proportions of direct vertical infiltration and percolation of rainwater in the area and subsurface flows in determining the total groundwater recharge in the basin. Groundwater resources development for commercial irrigation activities is an essential aspect of the livelihoods of communities living within the catchments of the Volta Basin. A comprehensive assessment of the recharge component of groundwater budgets in the basin is critical towards determining optimal abstraction rates in order to ensure resource sustainability and ecological integrity. This will form the basis for quantifying abstraction rates that are permissible to support large scale irrigation activities in the basin. The presence and thickness of the clay layer in the unsaturated zone serves to limit vertical infiltration of rainwater, and thus reduce vertical groundwater recharge in the area. In this study, the chloride mass balance technique, supported by the analysis of stable isotope signatures, has been used to estimate the vertical groundwater recharge and its spatial pattern of distribution in the area. The water table fluctuations technique and base flow recession method are then used to estimate total groundwater recharge in the basin. It is then possible to quantify the relative contributions of subsurface flows in the groundwater recharge in the basin. Temporal variations in groundwater recharge in the area are examined from time series of estimates from the baseflow recession technique. The results will assist in assessing the short term impacts of rainfall variability on groundwater budgets in the area.

Fynn, O. F.; Yidana, S. M.; Alo, C. A.; Mensah, F. O.

2013-12-01

318

Linking ground-water age and chemistry data along flow paths: Implications for trends and transformations of nitrate and pesticides  

NASA Astrophysics Data System (ADS)

Tracer-based ground-water ages, along with the concentrations of pesticides, nitrogen species, and other redox-active constituents, were used to evaluate the trends and transformations of agricultural chemicals along flow paths in diverse hydrogeologic settings. A range of conditions affecting the transformation of nitrate and pesticides (e.g., thickness of unsaturated zone, redox conditions) was examined at study sites in Georgia, North Carolina, Wisconsin, and California. Deethylatrazine (DEA), a transformation product of atrazine, was typically present at concentrations higher than those of atrazine at study sites with thick unsaturated zones but not at sites with thin unsaturated zones. Furthermore, the fraction of atrazine plus DEA that was present as DEA did not increase as a function of ground-water age. These findings suggest that atrazine degradation occurs primarily in the unsaturated zone with little or no degradation in the saturated zone. Similar observations were also made for metolachlor and alachlor. The fraction of the initial nitrate concentration found as excess N 2 (N 2 derived from denitrification) increased with ground-water age only at the North Carolina site, where oxic conditions were generally limited to the top 5 m of saturated thickness. Historical trends in fluxes to ground water were evaluated by relating the times of recharge of ground-water samples, estimated using chlorofluorocarbon concentrations, with concentrations of the parent compound at the time of recharge, estimated by summing the molar concentrations of the parent compound and its transformation products in the age-dated sample. Using this approach, nitrate concentrations were estimated to have increased markedly from 1960 to the present at all study sites. Trends in concentrations of atrazine, metolachlor, alachlor, and their degradates were related to the timing of introduction and use of these compounds. Degradates, and to a lesser extent parent compounds, were detected in ground water dating back to the time these compounds were introduced.

Tesoriero, Anthony J.; Saad, David A.; Burow, Karen R.; Frick, Elizabeth A.; Puckett, Larry J.; Barbash, Jack E.

2007-10-01

319

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

USGS Publications Warehouse

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

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

1984-01-01

320

"A space-time ensemble Kalman filter for state and parameter estimation of groundwater transport models"  

NASA Astrophysics Data System (ADS)

Herrera (1998) proposed a method for the optimal design of groundwater quality monitoring networks that involves space and time in a combined form. The method was applied later by Herrera et al (2001) and by Herrera and Pinder (2005). To get the estimates of the contaminant concentration being analyzed, this method uses a space-time ensemble Kalman filter, based on a stochastic flow and transport model. When the method is applied, it is important that the characteristics of the stochastic model be congruent with field data, but, in general, it is laborious to manually achieve a good match between them. For this reason, the main objective of this work is to extend the space-time ensemble Kalman filter proposed by Herrera, to estimate the hydraulic conductivity, together with hydraulic head and contaminant concentration, and its application in a synthetic example. The method has three steps: 1) Given the mean and the semivariogram of the natural logarithm of hydraulic conductivity (ln K), random realizations of this parameter are obtained through two alternatives: Gaussian simulation (SGSim) and Latin Hypercube Sampling method (LHC). 2) The stochastic model is used to produce hydraulic head (h) and contaminant (C) realizations, for each one of the conductivity realizations. With these realization the mean of ln K, h and C are obtained, for h and C, the mean is calculated in space and time, and also the cross covariance matrix h-ln K-C in space and time. The covariance matrix is obtained averaging products of the ln K, h and C realizations on the estimation points and times, and the positions and times with data of the analyzed variables. The estimation points are the positions at which estimates of ln K, h or C are gathered. In an analogous way, the estimation times are those at which estimates of any of the three variables are gathered. 3) Finally the ln K, h and C estimate are obtained using the space-time ensemble Kalman filter. The realization mean for each one of the variables is used as the prior space-time estimate for the Kalman filter, and the space-time cross-covariance matrix of h-ln K-C as the prior estimate-error covariance-matrix. The synthetic example has a modeling area of 700 x 700 square meters; a triangular mesh model with 702 nodes and 1306 elements is used. A pumping well located in the central part of the study area is considered. For the contaminant transport model, a contaminant source area is present in the western part of the study area. The estimation points for hydraulic conductivity, hydraulic head and contaminant concentrations are located on a submesh of the model mesh (same location for h, ln K and c), composed by 48 nodes spread throughout the study area, with an approximately separation of 90 meters between nodes. The results analysis was done through the mean error, root mean square error, initial and final estimation maps of h, ln K and C at each time, and the initial and final variance maps of h, ln K and C. To obtain model convergence, 3000 realizations of ln K were required using SGSim, and only 1000 with LHC. The results show that for both alternatives, the Kalman filter estimates for h, ln K and C using h and C data, have errors which magnitudes decrease as data is added. HERRERA, G. S.(1998), Cost Effective Groundwater Quality Sampling Network Design. Ph. D. thesis, University of Vermont, Burlington, Vermont, 172 pp. HERRERA G., GUARNACCIA J., PINDER G. Y SIMUTA R.(2001),"Diseño de redes de monitoreo de la calidad del agua subterránea eficientes", Proceedings of the 2001 International Symposium on Environmental Hydraulics, Arizona, U.S.A. HERRERA G. S. and PINDER G.F. (2005), Space-time optimization of groundwater quality sampling networks Water Resour. Res., Vol. 41, No. 12, W12407, 10.1029/2004WR003626.

Briseño, Jessica; Herrera, Graciela S.

2010-05-01

321

A Proposed Non-Intrusion Method for Estimating the Specific Yield for a Regional Groundwater System  

NASA Astrophysics Data System (ADS)

In Taiwan, groundwater resources play an important role in the management of regional water supply. However, because the lack of proper management over the last several decades, over-pumping of groundwater occurred, which resulted in serious land subsidence in the coastal areas. To properly manage the coastal aquifers, an accurately estimation of the specific yield (Sy) for the aquifer is needed. The traditional pumping test is costly. In this paper, we present a cost-saving, non-intrusive, geophysical method for estimating Sy. The method is based on gravity measurements and uses theories derived from geophysics. Because gravity variation is a function of the mass variation of materials, the gravity measurements correlate with the mass variation of the shallow groundwater in the neighborhood of the measurements. Comparing the groundwater level variations and gravity measurements between the droughts and flooding seasons, Sy can be interpreted. The proposed method combines MODFLOW with a numerical integration procedure that calculates the gravity variations. Heterogeneous parameters (Sy) can be assigned to MODFLOW cells. An inverse procedure is then applied to interpret and identify the Sy value around the gravity station. The proposed methodology is applied to the Choshui alluvial fan, one of the most important groundwater basins in Taiwan. Three gravity measurement stations, 'GS01', 'GS02' and 'GS03', were established. The location of GS01 is in the neighborhood of a groundwater observation well where pumping test data are available. The Sy value estimated from the gravitation measurements collected from GS01 compares favorably with that obtained from the traditional pumping test. The comparison verifies the correctness and accuracy of the proposed method. We then use the gravity measurements collected from GS02 and GS03 to estimate the Sy values in the areas where there exist no pumping test data. Using the estimated values obtained from gravity measurements, the spatial distribution of the values of specific yield for the aquifer can be further refined. The proposed method is a cost-saving and accuracy alternative for the estimation of specific yield in a regional groundwater system.

Chen, Y.; Cheng, C.; Chang, L.; Hwang, C.; Tsai, J.; Yeh, W.

2013-12-01

322

A comparison of uncertainty analysis methods using a groundwater flow model  

SciTech Connect

This report evaluates three uncertainty analysis methods that are proposed for use in performances assessment activities within the OCRWM and Nuclear Regulatory Commission (NRC) communities. The three methods are Monte Carlo simulation with unconstrained sampling, Monte Carlo simulation with Latin Hypercube sampling, and first-order analysis. Monte Carlo simulation with unconstrained sampling is a generally accepted uncertainty analysis method, but it has the disadvantage of being costly and time consuming. Latin Hypercube sampling was proposed to make Monte Carlo simulation more efficient. However, although it was originally formulated for independent variables, which is a major drawback in performance assessment modeling, Latin Hypercube can be used to generate correlated samples. The first-order method is efficient to implement because it is based on the first-order Taylor series expansion; however, there is concern that it does not adequately describe the variability for complex models. These three uncertainty analysis methods were evaluated using a calibrated groundwater flow model of a unconfined aquifer in southern Arizona. The two simulation methods produced similar results, although the Latin Hypercube method tends to produce samples whose estimates of statistical parameters are closer to the desired parameters. The mean travel times for the first-order method does not agree with those of the simulations. In additions, the first-order method produces estimates of variance in travel times that are more variable than those produced by the simulation methods, resulting in nonconservative tolerance intervals. 13 refs., 33 figs.

Doctor, P.G.; Jacobson, E.A.; Buchanan, J.A.

1988-06-01

323

Slope instability in complex 3D topography promoted by convergent 3D groundwater flow  

NASA Astrophysics Data System (ADS)

Slope instability in complex topography is generally controlled by the interaction between gravitationally induced stresses, 3D strengths, and 3D pore-fluid pressure fields produced by flowing groundwater. As an example of this complexity, coastal bluffs sculpted by landsliding commonly exhibit a progression of undulating headlands and re-entrants. In this landscape, stresses differ between headlands and re-entrants and 3D groundwater flow varies from vertical rainfall infiltration to lateral groundwater flow on lower permeability layers with subsequent discharge at the curved bluff faces. In plan view, groundwater flow converges in the re-entrant regions. To investigate relative slope instability induced by undulating topography, we couple the USGS 3D limit-equilibrium slope-stability model, SCOOPS, with the USGS 3D groundwater flow model, MODFLOW. By rapidly analyzing the stability of millions of potential failures, the SCOOPS model can determine relative slope stability throughout the 3D domain underlying a digital elevation model (DEM), and it can utilize both fully 3D distributions of pore-water pressure and material strength. The two models are linked by first computing a groundwater-flow field in MODFLOW, and then computing stability in SCOOPS using the pore-pressure field derived from groundwater flow. Using these two models, our analyses of 60m high coastal bluffs in Seattle, Washington showed augmented instability in topographic re-entrants given recharge from a rainy season. Here, increased recharge led to elevated perched water tables with enhanced effects in the re-entrants owing to convergence of groundwater flow. Stability in these areas was reduced about 80% compared to equivalent dry conditions. To further isolate these effects, we examined groundwater flow and stability in hypothetical landscapes composed of uniform and equally spaced, oscillating headlands and re-entrants with differing amplitudes. The landscapes had a constant slope for both headlands and re-entrants to minimize slope effects on stability. Despite these equal slopes, our analyses, given dry conditions, illustrated that the headlands can be 5-7% less stable than the re-entrants, owing to the geometry of the 3D failure mass with the lowest stability. We then simulated groundwater flow in these landscapes; flow was caused by recharge perching on a horizontal low permeability layer with discharge at the bluff faces. By systematically varying recharge, hydraulic conductivity of the material, and conductance at the bluffs, we created different 3D pore-pressure fields. Recharge rates and hydraulic conductivities controlled the height of the water table, whereas bluff conductance influenced the gradient of the water table near the bluff face. Given elevated water tables with steep gradients, bluffs in the re-entrants became unstable where flow converged. Thus, with progressively stronger effects from water flow, overall instability evolved from relatively unstable headlands to more uniform stability to relatively unstable re-entrants. Larger re-entrants led to more 3D flow convergence and greater localized instability. One- or two-dimensional models cannot fully characterize slope instability in complex topography.

Reid, M. E.; Brien, D. L.

2012-12-01

324

MODFLOW-2000, the U.S. Geological Survey Modular Ground-Water Model -Documentation of the Hydrogeologic-Unit Flow (HUF) Package  

USGS Publications Warehouse

This report documents the Hydrogeologic-Unit Flow (HUF) Package for the groundwater modeling computer program MODFLOW-2000. The HUF Package is an alternative internal flow package that allows the vertical geometry of the system hydrogeology to be defined explicitly within the model using hydrogeologic units that can be different than the definition of the model layers. The HUF Package works with all the processes of MODFLOW-2000. For the Ground-Water Flow Process, the HUF Package calculates effective hydraulic properties for the model layers based on the hydraulic properties of the hydrogeologic units, which are defined by the user using parameters. The hydraulic properties are used to calculate the conductance coefficients and other terms needed to solve the ground-water flow equation. The sensitivity of the model to the parameters defined within the HUF Package input file can be calculated using the Sensitivity Process, using observations defined with the Observation Process. Optimal values of the parameters can be estimated by using the Parameter-Estimation Process. The HUF Package is nearly identical to the Layer-Property Flow (LPF) Package, the major difference being the definition of the vertical geometry of the system hydrogeology. Use of the HUF Package is illustrated in two test cases, which also serve to verify the performance of the package by showing that the Parameter-Estimation Process produces the true parameter values when exact observations are used.

Anderman, E.R.; Hill, M.C.

2000-01-01

325

Ground-water levels and flow near the industrial excess landfill, Uniontown, Ohio  

USGS Publications Warehouse

Under an interagency contractual agreement with the Agency for Toxic Substances and Disease Registration, the U.S. Geological Survey evaluated geologic and hydrogeologic data available for the Industrial Excess Landfill (IEL) site in Uniontown, Ohio. During previous studies, ground-water contaminations was detected in observation wells installed at the site and in residential wells near the site. Water levels recorded on drillers' logs from 279 wells were used to characterize the regional ground-water flow system in the area of the IEL site. On the basis of the gross lithologic differences between the unconsolidated glacial-drift material and the indurated bedrock, and the inferred differences in their hydraulic properties, the flow system in the area of the IEL site was divided into two regional aquifers: a shallow, unconfined glacial-drift aquifer and a deeper, semiconfined bedrock aquifer. About 33 percent of the drillers' logs were from wells completed in the glacial-drift aquifer, whereas 67 percent were from wells completed in the bedrock aquifer. A composite potentiometric-surface map of the glacial drift aquifer shows that the IEL site appears to straddle a prominent ground-water ridge that trends northeast-southwest. Ground water flows radially away from this ridge, primarily to the northwest and to the southeast; as a result flow in the glacial-drift aquifer as the IEL site moves in a radial pattern away from the site in all directions. A composite, regional potentiometric-surface map of the bedrock aquifer shows a similar shows a similar elongated ground-water ridge trending northeast-southwest across the north-western corner of the IEL site; however, it does not appear that the IEL site straddles the ground-water ridge in the bedrock potentiometric surface. As a consequence of the radial-type of flow pattern in the glacial-drift aquifer at the IEL site, the direction of potential off-site movement of a contaminant at the IEL site, This radial type of flow pattern may explain the nonuniform distribution of some of the contaminants detected in observation wells and residential wells, particularly if specific contaminants were not disposed of uniformly across the site. Available data also indicate a downward flow component within the glacial-drift aquifer, as manifested by a reduction of hydraulic heads with increasing depth of wells near the site. Such downward flow is consistent with the presence of the ground-water ridge, which would serve as a local recharge area within the regional flow system. Consequently, contaminants present at the site will flow both laterally within the local flow patterns and vertically downward within the flow system.

Bair, E.S.; Norris, S.E.

1989-01-01

326

COMPARISON OF METHODS FOR ESTIMATING GROUND-WATER PUMPAGE FOR IRRIGATION.  

USGS Publications Warehouse

Ground-water pumpage for irrigation was measured at 32 sites on the eastern Snake River Plain in southern Idaho during 1983. Pumpage at these sites also was estimated by three commonly used methods, and pumpage estimates were compared to measured values to determine the accuracy of each estimate. Statistical comparisons of estimated and metered pumpage using an F-test showed that only estimates made using the instantaneous discharge method were not significantly different ( alpha equals 0. 01) from metered values. Pumpage estimates made using the power consumption method reflect variability in pumping efficiency among sites. Pumpage estimates made using the crop-consumptive use method reflect variability in water-management practices. Pumpage estimates made using the instantaneous discharge method reflect variability in discharges at each site during the irrigation season.

Frenzel, Steven A.

1985-01-01

327

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

USGS Publications Warehouse

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

Carleton, Glen B.; Gordon, Alison D.

2007-01-01

328

Regional ground-water flow and geochemistry in the Midwest Basins and Arches aquifer system in parts of Indiana, Ohio, Michigan and Illinois  

USGS Publications Warehouse

This report synthesizes information on the regional ground-water flow and geochemistry in the Midwestern Basins and Arches aquifer system in parts of Indiana, Ohio, Michigan, and Illinois. Aquifers that compose this water-table aquifer system include glacial aquifers and an underlying, areally extensive carbonate-rock aquifer. Water within the aquifers is most commonly a Ca-Mg-HCO3 type or a Ca-Mg-SO4 type. In general, the distribution of hydrochemical facies within the aquifer system is controlled by the mineralogy of the aquifer material, rather than by a chemical evolution of water along general directions of regional ground-water flow.Some ground-water flow systems within the aquifer system provide base flow to streams in response to ground-water recharge events. Other (often deeper) ground-water flow systems respond minimally to variations in ground-water recharge from precipitation and provide a fairly constant supply of water to streams. Streamflow hydrographs and base-flow duration curves were used to estimate such components of base flow in selected streams for long-term steady-state conditions in the aquifer system. Mean sustained ground-water discharge (discharge from fairly stable ground-water flow systems) ranges from 3 to 50 percent of mean ground-water discharge (discharge from all ground-water flow systems) to the selected stream reaches. These percentages indicate that 50 to 97 percent of base flow in the streams within the study area can be attributed to transient ground-water flow systems, which typically have a major component of local-scale flow. Because ground-water flow across the external boundaries of the aquifer system is minimal, such percentages indicate that most ground-water flow in the aquifer system is associated with seasonally transient local flow systems.Results of a ground-water flow model that was calibrated by use of regression methods and that simulates regional flow systems within the aquifer system (approximately 10 percent of total ground-water flow in the aquifer system) indicate that most water (99 percent) in simulated regional flow systems is from recharge at the water table. Most water (78 percent) discharges from simulated regional flow systems to the principal streams. Less than 3 percent of water in simulated regional flow systems discharges to the Ohio River, Lake Erie, or downdip areas in the Illinois (structural) Basin. Simulations also indicate that most of the Midwestern Basins and Arches aquifer system is characterized by alternating regional recharge and discharge areas at intervals of less than every 10 miles along the dominant regional trends of the potentiometric surfaces in the aquifers. Such alternating regional recharge and discharge areas result in the absence of long flow paths from the very highest regional potentiometric levels to the very lowest regional potentiometric levels. The presence of tritiated ground water (less than 50 years old) across most of the aquifer system also indicates that the aquifer system receives recharge across most of the study area.The northeastern part of the aquifer system near Lake Erie differs from the rest of the system with respect to regional ground-water flow and chemistry. Specifically, part of the northeastern part of the aquifer system can be characterized as a broad area (tens of miles) of weak regional discharge (less than 0.5 inch per year). Results of the regional ground-water flow model indicate that regional flow systems have a limited ability to carry ground water away from this area; thus precipitation is prevented from recharging the regional flow systems in this part of the aquifer system. Some ground water recharged during Pleistocene glaciation was found in this area. Sulfide concentrations and sulfur isotope data, which indicate that extensive sulfate reduction has occurred in the aquifer system within this area, confirm that only minimal recharge of this part of the aquifer system has taken place over a long

Eberts, Sandra M.; George, Lori L.

2000-01-01

329

Groundwater flow systems in the great Aletsch glacier region (Valais, Switzerland)  

NASA Astrophysics Data System (ADS)

Groundwater flow systems in Alpine areas are often complex and challenging to investigate due to special topographic and climatic conditions governing groundwater recharge and bedrock flow. Studies seeking to characterize high-alpine groundwater systems remain rare, but are of high interest, e.g. for water supply, hydropower systems, traffic tunnels or rock slope deformation and landslide hazards. The goal of this study is to better understand the current and past groundwater flow systems of the UNESCO World Heritage mountain ridge separating the great Aletsch glacier and the Rhone valley, considering climatic and glacier fluctuations during the Lateglacial and Holocene periods. This ridge is crossed by a hydropower bypass drift (Riederhornstollen) and is composed of fractured crystalline rocks overlain by various types of landslides and glacial deposits. Surface hydrology observations (fracture properties, groundwater seepage, spring lines and physico-chemical parameters) and hydropower drift inflow measurements contributed to the characterization of bedrock hydraulic conductivities and preferential groundwater pathways. Basic conceptual hydrogeological models were tested with observed drift inflows and the occurrence of springs using free-surface, variably saturated, vertical 2D groundwater flow models (using the code SEEP/W from GeoStudio 2007). Already simple two-layer models, representing profile sections orthogonal to the mountain ridge, provided useful results. Simulations show that differences in the occurrence of springs on each side of the mountain ridge are likely caused by the occurrence of glacial till (generating perched groundwater), the deep-seated sagging landslide mass, faults and asymmetric ridge topography, which together force the main groundwater flow direction to be oriented towards the Rhone valley, even from beyond the mountain ridge. Surprisingly, the most important springs (those with high discharge rates) are located at high elevations above the terraces of Riederalp and Bettmeralp in or near steeply dipping fault zones striking parallel to the ridge, suggesting locally a near-surface groundwater table. Drying up of several of these springs (at lateral distances up to 4 km) after construction of the Riederhornstollen, as well as associated large tunnel water inflows, demonstrates large scale hydraulic connections along strike of these fault zones. The catchment areas of these springs have to be located close to the ridge crest, above the terraces of Riederalp and Bettmeralp, and extend over many kilometers. This fault system thus drains significant portions of the high-altitude recharge and induces a complex 3D groundwater flow field of the Aletsch area. Variations in glacial ice extent due to different climatic conditions during the Lateglacial and Holocene periods were studied by varying the boundary condition of the great Aletsch glacier. Results have to be interpreted with care, as the glacier pressure boundary conditions were modelled like a lake. Detailed investigations of these boundary conditions have been initialized by glacier drillings equipped with melt water pressure sensors. With the simplified boundary conditions applied to the glacier bed, elevated ice surfaces during the Little Ice Age stage only slightly influence the flow field and total hydraulic head conditions on the NW side of the ridge. On the other hand, the Egesen stadial causes a fundamental change of the groundwater devide with all flow lines, even from below the Aletsch glacier, oriented towards the Rhone valley.

Alpiger, Andrea; Loew, Simon

2014-05-01

330

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

NASA Astrophysics Data System (ADS)

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

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

2014-09-01

331

Shallow Ground-Water Flux Beneath a Restored Wetland Using Two-Dimensional Simulation of Ground-Water Flow and Heat Transport  

NASA Astrophysics Data System (ADS)

Water flowing through the Sacramento-San Joaquin River Delta supplies drinking water to more than 20 million people in California. Delta water contains elevated concentrations of dissolved organic carbon (DOC) from drainage through the delta peat soils, forming trihalomethanes when the water is chlorinated for drinking. Land subsidence caused by oxidation of the peat soils has led to increased pumping of drainage water from delta islands to maintain arable land. An agricultural field on Twitchell Island was flooded in 1997 to evaluate continuous flooding as a technique to mitigate subsidence. The effects of shallow flooding on DOC loads to the drain water must be determined to evaluate the feasibility of this technique. In this study, heat is used as a nonconservative tracer to determine shallow ground-water flux and calculate DOC loads to an adjacent drainage ditch. Temperature profiles and water levels were measured in 12 wells installed beneath the pond, in the pond, and in an adjacent drainage ditch from May 2000 to June 2001. The range in seasonal temperatures decreased with depth, but seasonal temperature variation was evident in wells screened as deep as 10 to 12 feet below land surface. A constant temperature of 17 degrees C was measured in wells 25 feet beneath the pond. Ground-water flux beneath the pond was quantified in a two-dimensional simulation of water and heat exchange using the SUTRA flow and transport model. The effective vertical hydraulic conductivity of the peat soils underlying the pond was estimated through model calibration. Calibrated hydraulic conductivity is higher (1E-5 m/sec) than estimates from slug tests (2E-6 m/sec). Modeled pond seepage is similar to that estimated from a water budget, although the total seepage determined from the water budget is within the range of error of the instrumentation. Overall, model results indicate that recharge from the pond flows along shallow flow paths and that travel times through the peat to the drainage ditch may be on the order of decades.

Burow, K. R.; Gamble, J. M.; Fujii, R.; Constantz, J.

2001-12-01

332

Guidelines for model calibration and application to flow simulation in the Death Valley regional groundwater system  

USGS Publications Warehouse

Fourteen guidelines are described which are intended to produce calibrated groundwater models likely to represent the associated real systems more accurately than typically used methods. The 14 guidelines are discussed in the context of the calibration of a regional groundwater flow model of the Death Valley region in the southwestern United States. This groundwater flow system contains two sites of national significance from which the subsurface transport of contaminants could be or is of concern: Yucca Mountain, which is the potential site of the United States high-level nuclear-waste disposal; and the Nevada Test Site, which contains a number of underground nuclear-testing locations. This application of the guidelines demonstrates how they may be used for model calibration and evaluation, and also to direct further model development and data collection.Fourteen guidelines are described which are intended to produce calibrated groundwater models likely to represent the associated real systems more accurately than typically used methods. The 14 guidelines are discussed in the context of the calibration of a regional groundwater flow model of the Death Valley region in the southwestern United States. This groundwater flow system contains two sites of national significance from which the subsurface transport of contaminants could be or is of concern: Yucca Mountain, which is the potential site of the Unit