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1

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

2

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

3

Estimating groundwater recharge through unsaturated flow modelling: Sensitivity to boundary conditions and vertical discretization  

NASA Astrophysics Data System (ADS)

SummaryUnsaturated flow modelling is increasingly being used to estimate potential groundwater recharge. A review of previous studies found that unit-gradient and fixed water table lower boundary conditions have been applied to models of both constant and variable vertical grid spacing (discretization). In order to provide a general guidance, this work studies the effect of both discretization and boundary conditions on simulation times and estimated fluxes at the water table, using one-dimensional models of 2, 4, 6, and 12 m comprised of sand, sandy loam, loamy sand, and loam. The study uses climatological data from the Boreal Plain of northern Alberta, Canada. Because of the long-term average water deficit and the thick unconsolidated glacial deposits, unsaturated flow is expected to be vertical, both downward and upward, and inter-annual changes in water storage will be important. Long-term simulations (1919-2007) that comprised both wet and dry cycles, reveal that when a variable vertical discretization at both the top and bottom of the columns (varying from 0.1 to 10 cm) is utilized, a balance between simulation accuracy and running time can be achieved. It is also found that whenever the unsaturated flow modelling approach is used to estimate potential groundwater recharge, a fixed-head lower boundary condition should be selected because it also allows upward flux from the water table during dry periods, a situation that prevails on both sub-humid and semi-arid areas, where accurate groundwater recharge estimates are needed the most. However, it should be kept in mind that the use of a fixed water table is a simple representation of the regional water table, which in reality interacts with the regional groundwater flow and surface water bodies (e.g., lakes and wetlands).

Carrera-Hernández, J. J.; Smerdon, B. D.; Mendoza, C. A.

2012-07-01

4

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

USGS Publications Warehouse

Quantitative evaluation of management strategies for long-term supply of safe groundwater for drinking from the Bengal Basin aquifer (India and Bangladesh) requires estimation of the large-scale hydrogeologic properties that control flow. The Basin consists of a stratified, heterogeneous sequence of sediments with aquitards that may separate aquifers locally, but evidence does not support existence of regional confining units. Considered at a large scale, the Basin may be aptly described as a single aquifer with higher horizontal than vertical hydraulic conductivity. Though data are sparse, estimation of regional-scale aquifer properties is possible from three existing data types: hydraulic heads, 14C concentrations, and driller logs. Estimation is carried out with inverse groundwater modeling using measured heads, by model calibration using estimated water ages based on 14C, and by statistical analysis of driller logs. Similar estimates of hydraulic conductivities result from all three data types; a resulting typical value of vertical anisotropy (ratio of horizontal to vertical conductivity) is 104. The vertical anisotropy estimate is supported by simulation of flow through geostatistical fields consistent with driller log data. The high estimated value of vertical anisotropy in hydraulic conductivity indicates that even disconnected aquitards, if numerous, can strongly control the equivalent hydraulic parameters of an aquifer system. ?? US Government 2009.

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

2009-01-01

5

An analytical solution to transient groundwater flow and its application to recharge estimation  

NASA Astrophysics Data System (ADS)

An analytical solution to transient groundwater flow along a cross section of an unconfined aquifer was presented and applied to recharge estimation. The solutions for both the hydraulic head (h) and specific discharge (q) were derived under the Dupuit assumption and linearization with a specific initial water-table condition and verified with numerical simulations. The solution for h provides a theoretical water-table recession curve and that for q quantifies the time-dependent lateral discharge for any location along the cross section. The theoretical results allow accurate calculations of the water-table decline and lateral drainage and are applied to the recharge estimation with groundwater levels or water-table fluctuations.

Zhang, Y.

2009-12-01

6

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

Microsoft Academic Search

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

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

2008-01-01

7

Groundwater dating by estimation of groundwater flow velocity and dissolved 4He accumulation rate calibrated by 36Cl in the Great Artesian Basin, Australia  

NASA Astrophysics Data System (ADS)

We tested two methods for dating groundwaters that cannot be reliably measured by 36Cl dating alone, one based on groundwater flow velocity plus distance along a flow path and the other based on 4He accumulation rates calibrated with 36Cl dates. We sampled groundwaters along six inferred regional groundwater flow paths in the Great Artesian Basin (GAB) of Australia. We selected three groundwater paths where the decrease in 36Cl was largely controlled by cosmogenic 36Cl radioactive decay without a significant increase in chloride concentration. The extrapolated groundwater velocities were 0.133 ± 0.018 m/y to 0.433 ± 0.140 m/y. The estimated residence time of 1.06 × 10 6 y at the discharge area around Lake Eyre was comparable to the estimate of (1-2.2) × 10 6 y in previous studies. On the other hand, our estimated 4He accumulation rates for the selected three groundwater flow paths (1.85 ± 0.31 × 10 - 11 to 1.51 ± 0.63 × 10 - 10 ccSTP/cm 3•y) were approximately 2-15 times lower than previously reported rates for the central GAB. Our estimated rate of 1.51 × 10 - 10 ccSTP/cm 3•y - 1 in the western GAB is compatible with previous estimates based on 81Kr ages. The groundwater residence time estimated from the 4He accumulation rate was approximately 7 × 10 5 y near the discharge area at Lake Eyre. Finally, both estimations were mutually compatible with a 30% error.

Mahara, Y.; Habermehl, M. A.; Hasegawa, T.; Nakata, K.; Ransley, T. R.; Hatano, T.; Mizuochi, Y.; Kobayashi, H.; Ninomiya, A.; Senior, B. R.; Yasuda, H.; Ohta, T.

2009-09-01

8

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

Microsoft Academic Search

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.

M. T. Moreo; K. J. Halford; R. J. LaCamera

2003-01-01

9

Estimates of consumptive use and ground-water return flow using water budgets in Palo Verde Valley, California  

USGS Publications Warehouse

Palo Verde Valley, California, is an agricultural area in the flood plain of the Colorado River where irrigation water is diverted from the river and groundwater is discharged to a network of drainage ditches and (or) the river. Consumptive use by vegetation and groundwater return flow were calculated using water budgets. Consumptive use by vegetation was 484,000 acre-ft in 1981, 453,600 acre-ft in 1982, 364,400 acre-ft in 1983, and 374,300 acre-ft in 1984. The consumptive-use estimates are most sensitive to two measured components of the water budget, the diversion at Palo Verde Dam and the discharge from drainage ditches to the river. Groundwater return flow was 31,700 acre-ft in 1981, 24,000 acre-ft in 1982, 2,500 acre-ft in 1983, and 7 ,900 acre-ft in 1984. The return-flow estimates are most sensitive to discharge from drainage ditches; various irrigation requirements and crop areas, particularly alfalfa; the diversion at Palo Verde Dam; and the estimate of consumptive use. During increasing flows in the river, the estimate of groundwater return flow is sensitive also to change in groundwater storage. Change in groundwater storage was estimated to be -5,700 acre-ft in 1981, -12,600 acre-ft in 1982, 5,200 acre-ft in 1983, and 11 ,600 acre-ft in 1984. Changes in storage can be a significant component in the water budget used to estimate groundwater return flow but is negligible in the water budget used to estimate consumptive use. Change in storage was 1 to 3% of annual consumptive use. Change in storage for the area drained by the river ranged from 7 to 96% of annual groundwater return flow during the 4 years studied. Consumptive use calculated as diversions minus return flows was consistently lower than consumptive use calculated in a water budget. Water-budget estimates of consumptive use account for variations in precipitation, tributary inflow, river stage, and groundwater storage. The calculations for diversions minus return flows do not account for these components, which can be large enough to affect the estimates of consumptive use. (Author 's abstract)

Owen-Joyce, Sandra J.; Kimsey, Steven L.

1987-01-01

10

Linking soil moisture balance and source-responsive preferential flow models for estimating groundwater recharge  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

11

Groundwater dating by estimation of groundwater flow velocity and dissolved 4He accumulation rate calibrated by 36Cl in the Great Artesian Basin, Australia  

Microsoft Academic Search

We tested two methods for dating groundwaters that cannot be reliably measured by 36Cl dating alone, one based on groundwater flow velocity plus distance along a flow path and the other based on 4He accumulation rates calibrated with 36Cl dates. We sampled groundwaters along six inferred regional groundwater flow paths in the Great Artesian Basin (GAB) of Australia. We selected

Y. Mahara; M. A. Habermehl; T. Hasegawa; K. Nakata; T. R. Ransley; T. Hatano; Y. Mizuochi; H. Kobayashi; A. Ninomiya; B. R. Senior; H. Yasuda; T. Ohta

2009-01-01

12

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

SciTech Connect

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.

M.T. Moreo; K.J. Halford; R.J. LaCamera; and R.J. Laczniak

2003-09-30

13

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

14

Estimates of ground-water recharge, base flow, and stream reach gains and losses in the Willamette River basin, Oregon  

USGS Publications Warehouse

Precipitation-runoff models, base-flow-separation techniques, and stream gain-loss measurements were used to study recharge and ground-water surface-water interaction as part of a study of the ground-water resources of the Willamette River Basin. The study was a cooperative effort between the U.S. Geological Survey and the State of Oregon Water Resources Department. Precipitation-runoff models were used to estimate the water budget of 216 subbasins in the Willamette River Basin. The models were also used to compute long-term average recharge and base flow. Recharge and base-flow estimates will be used as input to a regional ground-water flow model, within the same study. Recharge and base-flow estimates were made using daily streamflow records. Recharge estimates were made at 16 streamflow-gaging-station locations and were compared to recharge estimates from the precipitation-runoff models. Base-flow separation methods were used to identify the base-flow component of streamflow at 52 currently operated and discontinued streamflow-gaging-station locations. Stream gain-loss measurements were made on the Middle Fork Willamette, Willamette, South Yamhill, Pudding, and South Santiam Rivers, and were used to identify and quantify gaining and losing stream reaches both spatially and temporally. These measurements provide further understanding of ground-water/surface-water interactions.

Lee, Karl K.; Risley, John C.

2002-01-01

15

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.

Manda, Alex

16

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

17

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

18

Systematic Parameter Estimation of a Density-Dependent Groundwater-Flow and Solute-Transport Model  

NASA Astrophysics Data System (ADS)

A SEAWAT-based, flow and transport model of seawater-intrusion was developed for the Santa Barbara groundwater basin in southern California that utilizes dual-domain porosity. Model calibration can be difficult when simulating flow and transport in large-scale hydrologic systems with extensive heterogeneity. To facilitate calibration, the hydrogeologic properties in this model are based on the fraction of coarse and fine-grained sediment interpolated from drillers' logs. This approach prevents over-parameterization by assigning one set of parameters to coarse material and another set to fine material. Estimated parameters include boundary conditions (such as areal recharge and surface-water seepage), hydraulic conductivities, dispersivities, and mass-transfer rate. As a result, the model has 44 parameters that were estimated by using the parameter-estimation software PEST, which uses the Gauss-Marquardt-Levenberg algorithm, along with various features such as singular value decomposition to improve calibration efficiency. The model is calibrated by using 36 years of observed water-level and chloride-concentration measurements, as well as first-order changes in head and concentration. Prior information on hydraulic properties is also provided to PEST as additional observations. The calibration objective is to minimize the squared sum of weighted residuals. In addition, observation sensitivities are investigated to effectively calibrate the model. An iterative parameter-estimation procedure is used to dynamically calibrate steady state and transient simulation models. The resulting head and concentration states from the steady-state-model provide the initial conditions for the transient model. The transient calibration provides updated parameter values for the next steady-state simulation. This process repeats until a reasonable fit is obtained. Preliminary results from the systematic calibration process indicate that tuning PEST by using a set of synthesized observations generated from model output reduces execution times significantly. Parameter sensitivity analyses indicate that both simulated heads and chloride concentrations are sensitive to the ocean boundary conductance parameter. Conversely, simulated heads are sensitive to some parameters, such as specific fault conductances, but chloride concentrations are insensitive to the same parameters. Heads are specifically found to be insensitive to mobile domain texture but sensitive to hydraulic conductivity and specific storage. The chloride concentrations are insensitive to some hydraulic conductivity and fault parameters but sensitive to mass transfer rate and longitudinal dispersivity. Future work includes investigating the effects of parameter and texture characterization uncertainties on seawater intrusion simulations.

Stanko, Z.; Nishikawa, T.; Traum, J. A.

2013-12-01

19

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

20

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

21

U-234/U-238 ratio: Qualitative estimate of groundwater flow in Rocky Flats monitoring wells  

SciTech Connect

Groundwater movement through various pathways is the primary mechanism for the transport of radionuclides and trace elements in a water/rock interaction. About three dozen wells, installed in the Rocky Flats Plant (RFP) Solar Evaporation Ponds (SEP) area, are monitored quarterly to evaluate the extent of any lateral and downgradient migration of contaminants from the Solar Evaporation Ponds: 207-A; 207-B North, 207-B Center, and 207-B South; and 207-C. The Solar Ponds are the main source for the various contaminants: radionuclides (U-238, U-234, Pu-239, 240 and Am-241); anions; and trace metals to groundwaters. The U-238 concentrations in Rocky Flats groundwaters vary from <0.2 to 69 pCi/I (IpCi = 3 ug). However, the activity U-234/U-238 ratios are low and range mostly 1.2 to 2.7. The low activity ratios can be interpreted to suggest that the groundwaters are moving slow (estimate of about a few ft/year based on hydrologic parameters [1]. Uranium is probably present in the +6 state, predominantly as a uranyl carbonate complexes UO{sub 2}(CO{sub 3}){sub 2}{sup 2{minus}}, because of the predominant bicarbonate medium.

Laul, J.C.

1994-02-01

22

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

23

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

24

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

25

Method for estimating ground-water return flow to the Colorado River in the Palo Verde-Cibola area, California and Arizona  

Microsoft Academic Search

Ground-water return flow to the Colorado River was estimated as the residual in water budgets for the areas that drain in the subsurface to the river in Palo Verde and Cibola Valleys, California and Arizona. Two ground-water drainage areas in each valley were delineated using average annual water-table altitudes in the shallow alluvial aquifer that underlies Palo Verde and Cibola

Owen-Joyce

1984-01-01

26

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

27

Groundwater hydrology--coastal flow  

USGS Publications Warehouse

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

Sanford, Ward E.

2010-01-01

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

Evaluation of geohydrologic framework, recharge estimates and ground-water flow of the Joshua Tree area, San Bernardino County, California  

USGS Publications Warehouse

Ground water historically has been the sole source of water supply for the community of Joshua Tree in the Joshua Tree ground-water subbasin of the Morongo ground-water basin in the southern Mojave Desert. The Joshua Basin Water District (JBWD) supplies water to the community from the underlying Joshua Tree ground-water subbasin. The JBWD is concerned with the long-term sustainability of the underlying aquifer. To help meet future demands, the JBWD plans to construct production wells in the adjacent Copper Mountain ground-water subbasin. As growth continues in the desert, there may be a need to import water to supplement the available ground-water resources. In order to manage the ground-water resources and to identify future mitigating measures, a thorough understanding of the ground-water system is needed. The purpose of this study was threefold: (1) improve the understanding of the geohydrologic framework of the Joshua Tree and Copper Mountain ground-water subbasins, (2) determine the distribution and quantity of recharge using field and numerical techniques, and (3) develop a ground-water flow model that can be used to help manage the water resources of the region. The geohydrologic framework was refined by collecting and interpreting water-level and water-quality data, geologic and electric logs, and gravity data. The water-bearing deposits in the Joshua Tree and Copper Mountain ground-water subbasins are Quarternary alluvial deposits and Tertiary sedimentary and volcanic deposits. The Quarternary alluvial deposits were divided into two aquifers (referred to as the 'upper' and the 'middle' alluvial aquifers), which are about 600 feet (ft) thick, and the Tertiary sedimentary and volcanic deposits were assigned to a single aquifer (referred to as the 'lower' aquifer), which is as thick as 1,500 ft. The ground-water quality of the Joshua Tree and Copper Mountain ground-water subbasins was defined by collecting 53 ground-water samples from 15 wells (10 in the Joshua Tree ground-water subbasin and 5 in the Copper Mountain ground-water subbasin) between 1980 and 2002 and analyzing the samples for major ions, nutrients, and selected trace elements. Selected samples also were analyzed for oxygen-18, deuterium, tritium, and carbon-14. The water-quality data indicated that dissolved solids and nitrate concentrations were below regulatory limits for potable water; however, fluoride concentrations in the lower aquifer exceeded regulatory limits. Arsenic concentrations and chromium concentrations were generally below regulatory limits; however, arsenic concentrations measured in water from wells perforated in the lower aquifer exceeded regulatory limits. The carbon-14 activities ranged from 2 to 72 percent modern carbon and are consistent with uncorrected ground-water ages (time since recharge) of about 32,300 to 2,700 years before present. The oxygen-18 and deuterium composition of water sampled from the upper aquifer is similar to the volume-weighted composition of present-day winter precipitation indicating that winter precipitation was the predominant source of ground-water recharge. Field studies, conducted during water years 2001 through 2003 to determine the distribution and quantity of recharge, included installation of instrumented boreholes in selected washes and at a nearby control site. Core material and cuttings from the boreholes were analyzed for physical, chemical, and hydraulic properties. Instruments installed in the boreholes were monitored to measure changes in matric potential and temperature. Borehole data were supplemented with temperature data collected from access tubes installed at additional sites along study washes. Streambed hydraulic properties and the response of instruments to infiltration were measured using infiltrometers. Physical and geochemical data collected away from the stream channels show that direct infiltration of precipitation to depths below the root zone and subsequent gro

Nishikawa, Tracy; Izbicki, John A.; Hevesi, Joseph A.; Stamos, Christina L.; Martin, Peter

2005-01-01

30

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

31

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

32

ESTIMATING FLOW AND FLUX OF GROUND-WATER DISCHARGE USING WATER TEMPERATURE AND VELOCITY. (R827961)  

EPA Science Inventory

The nature of ground water discharge to a stream has important implications for nearby ground water flow, especially with respect to contaminant transport and well-head protection. Measurements of ground water discharge were accomplished in this study using (1) differences bet...

33

Estimates of consumptive use and ground-water return flow using water budgets in Parker Valley, Arizona and California, 1981-84  

USGS Publications Warehouse

Annual water budgets were used to estimate consumptive use by vegetation and groundwater return flow in Parker Valley, Arizona and California. Consumptive use by vegetation was estimated to be 482,800 acre-ft in 1981, 432,000 acre-ft in 1982, 413,500 acre-ft in 1983, and 420,900 acre-ft in 1984 on the Arizona side of the Colorado River, and 45,400 acre-ft in 1984 on the California side of the river. Groundwater return flow from the area north of Tyson Wash in Arizona was estimated to be 0 acre-ft in 1981, 1983, and 1984 and 1,900 acre-ft in 1982. Water budget estimates of consumptive use by vegetation were compared to estimates of evapotranspiration. Estimates of evapotranspiration were from 1% less to 9% higher than estimates of consumptive use by vegetation in the area north of Tyson Wash. The percentage differences in the two estimates were within the measurement errors of the two major measured components in the water budget regardless of differences in year-to-year conditions. Estimates of consumptive use of Colorado River water calculated as measured diversions minus return flows were consistently lower than estimates of consumptive use by vegetation. Estimates of consumptive use of Colorado River water were from 18 to 37% lower than estimates of consumptive use by vegetation variations in tributary inflow, river stage, and induced seepage from the river to replace groundwater transpired by phreatophytes are not accounted for in the calculation. (USGS)

Owen-Joyce, Sandra J.

1988-01-01

34

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

35

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

36

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

37

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

38

Real-time groundwater flow modeling with the Ensemble Kalman Filter: Joint estimation of states and parameters and the filter inbreeding problem  

Microsoft Academic Search

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

H. J. Hendricks Franssen; W. Kinzelbach

2008-01-01

39

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

40

Estimation of groundwater velocities from Yucca Flat to the Amargosa Desert using geochemistry and environmental isotopes  

Microsoft Academic Search

Geochemical and isotopic data from groundwater sampling locations can be used to estimate groundwater flow velocities for independent comparison to velocities calculated by other methods. The objective of this study was to calculate groundwater flow velocities using geochemistry and environmental isotopes from the southern end of Yucca Flat to the Amargosa Desert, considering mixing of different groundwater inputs from sources

Ronald L. Hershey; Steve Y. Acheampong

1997-01-01

41

Real-time groundwater flow modeling with the Ensemble Kalman Filter: Joint estimation of states and parameters and the filter inbreeding problem  

NASA Astrophysics Data System (ADS)

Real-time groundwater flow modeling with filter methods is interesting for dynamical groundwater flow systems, for which measurement data in real-time are available. The Ensemble Kalman Filter (EnKF) approach is used here to update states together with parameters by adopting an augmented state vector approach. The performance of EnKF is investigated in a synthetic study with a two-dimensional transient groundwater flow model where (1) only the recharge rate is spatiotemporally variable, (2) only transmissivity is spatially variable with ?lnT2 = 1.0 or (3) with ?lnT2 = 2.7, and (4) both recharge rate and transmissivity are uncertain (a combination of (1) and (3)). The performance of EnKF for simultaneous state and parameter estimation in saturated groundwater flow problems is investigated in dependence of the number of stochastic realizations, the updating frequency and updating intensity of log-transmissivity, the amount of measurements in space and time, and the method (iterative versus noniterative EnKF), among others. Satisfactory results were also obtained if both transmissivity and recharge rate were uncertain. However, it was found that filter inbreeding is much more severe if hydraulic heads and transmissivities are jointly updated than if only hydraulic heads are updated. The filter inbreeding problem was investigated in more detail and could be strongly reduced with help of a damping parameter, which limits the intensity of the perturbation of the log-transmissivity field. An additional reduction of filter inbreeding could be achieved by combining two measures: (1) inflating the elements of the predicted state covariance matrix on the basis of a comparison between the model uncertainty and the observed errors at the measurement points and (2) starting the flow simulations with a very large number of realizations and then sampling the desired number of realizations after one simulation time step by minimizing the differences between the local cpdfs (and bivariate cpdfs) of hydraulic head for the large ensemble and the corresponding cpdfs for the reduced ensemble. The two measures, which cause very limited CPU costs, allowed making 100 stochastic realizations for the reproduction of the states as efficient as 200-500 untreated stochastic realizations.

Hendricks Franssen, H. J.; Kinzelbach, W.

2008-09-01

42

Comparison of methods for estimating ground-water recharge and base flow at a small watershed underlain by fractured bedrock in the Eastern United States  

USGS Publications Warehouse

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

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

2005-01-01

43

Estimates of consumptive use and ground-water return flow and the effect of rising and sustained high river stage on the method of estimation in Cibola Valley, Arizona and California, 1983 and 1984  

USGS Publications Warehouse

In Cibola Valley, Arizona, water is pumped from the Colorado River to irrigate crops and to maintain wildlife habitat. Unused water percolates to the water table and, as groundwater, moves downgradient into areas of phreatophytes, into a drainage ditch, out of the flood plain, and back to the river. In 1983 and 1984, groundwater return flow was negligible because in most of Cibola Valley the river lost water to the aquifer. Evapotranspiration was used as an approximation for consumptive use by vegetation. Evapotranspiration was calculated as the sum of the products of the area of vegetation types and water-use rate by vegetation type. Evapotranspiration was estimated to be 70,100 acre-ft in 1983 and 62,600 acre-ft in 1984. These estimates may be in error because of the effect of sustained inundation on the rate of water use by phreatophytes. The effects cannot be quantified and therefore adjustments to rates calculated for dry-surface conditions could not be made. The method of estimating consumptive use of water by vegetation and groundwater return flow is affected by changing conditions during years of rising and sustained high river stage caused by flood-control releases at Parker Dam. Most of the bank storage that will return to the river when the high river stage subsides did not originate as irrigation water. High river stage caused some areas to be flooded directly or raised groundwater levels above the land surface. No crops could be grown in flooded fields. The decreased depth to water and inundation with fresh water resulted in new phreatophyte growth in some areas. In some areas that were flooded, many phreatophytes died. Changes in the inundated and flooded areas throughout the years made it difficult to estimate the evaporation losses from the increased water surface. (USGS)

Owen-Joyce, Sandra J.

1990-01-01

44

Flow and storage in groundwater systems.  

PubMed

The dynamic nature of groundwater is not readily apparent, except where discharge is focused at springs or where recharge enters sinkholes. Yet groundwater flow and storage are continually changing in response to human and climatic stresses. Wise development of groundwater resources requires a more complete understanding of these changes in flow and storage and of their effects on the terrestrial environment and on numerous surface-water features and their biota. PMID:12065826

Alley, William M; Healy, Richard W; LaBaugh, James W; Reilly, Thomas E

2002-06-14

45

Groundwater Flow in Low-Permeability Environments  

Microsoft Academic Search

Certain geologic media are known to have small permeability; subsurface environments composed of these media and lacking well developed secondary permeability have groundwater flow sytems 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 pertroleum and ores, and probably has a role

C. E. Neuzil

1986-01-01

46

Groundwater flow in layered aquifer systems  

NSDL National Science Digital Library

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

Hemker, C. J.; Microfem

47

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

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

2010-01-01

48

Estimating the Submarine Groundwater Discharge Flux of Rare Earth Elements to the Indian River Lagoon, Fl, USA, Using the 1-D Vertical - Flow Equation  

NASA Astrophysics Data System (ADS)

Understanding the sources and sinks of trace elements like the rare earth elements (REE) in the oceans has important implications for quantifying their global geochemical cycles, their application as paleoceanographic tracers, and in discerning the geochemical reactions that mobilize, sequester, and fractionate REEs in the environment. This understanding is critical for neodymium (Nd) because radiogenic Nd isotopes are commonly used in paleoceanographic studies over glacial-interglacial to million year time scales. The submarine groundwater discharge (SGD) flux of each REE for the Indian River Lagoon, Fl, USA, was calculated using a modified form of the 1-dimensional vertical-flow equation that accounts for diffusion, advection, and non-local mass transfer processes. The SGD REE flux is comprised of two sources: a near shore, heavy REE (HREE) enriched advective source chiefly composed of terrestrial SGD, and a light REE (LREE) and middle REE (MREE) enriched source that originates from reductive dissolution of Fe (III) oxides/hydroxides in the subterranean estuary. This SGD flux mixture of REE sources is subsequently transported by groundwater seepage and bioirrigation to the overlying lagoon water column. The total SGD flux of REEs reveals that the subterranean estuary of the Indian River Lagoon is a source for LREE and MREEs, and a sink for the HREEs, to the local coastal ocean. The calculated SGD flux of Nd presented in this study is estimated at 7.69×1.02 mmol/day, which is roughly equivalent to the effective local river flux to the Indian River Lagoon. Although our re-evaluated SGD flux of Nd to the Indian River Lagoon is lower than estimates in our previous work, it nonetheless represents a substantial input to the coastal ocean.

Chevis, D. A.; Johannesson, K. H.; Burdige, D.; Cable, J. E.; Martin, J. B.

2013-12-01

49

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

edited by Belcher, Wayne R.

2004-01-01

50

Simultaneous identification of unknown groundwater pollution sources and estimation of aquifer parameters  

Microsoft Academic Search

Pollution source identification is a common problem encountered frequently. In absence of prior information about flow and transport parameters, the performance of source identification models depends on the accuracy in estimation of these parameters. A methodology is developed for simultaneous pollution source identification and parameter estimation in groundwater systems. The groundwater flow and transport simulator is linked to the nonlinear

Bithin Datta; Dibakar Chakrabarty; Anirban Dhar

2009-01-01

51

Using remote sensing and GIS techniques to estimate discharge and recharge fluxes for the Death Valley regional groundwater flow system, USA  

Microsoft Academic Search

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

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

1996-01-01

52

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

53

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

2014-05-01

54

Heat as a Tracer for Estimating Ground-water Recharge  

NASA Astrophysics Data System (ADS)

Temperature profiles above the water table may be analyzed to estimate ground-water recharge (or discharge). Depending on depth, sediment temperature profiles are established by meteorological conditions and/or the geothermal gradient, and modified by the direction and rate of ground-water fluxes through the sediments. For shallow water tables (less than 30 m), the combined effects of meteorological boundary conditions and ground-water fluxes generally determine sediment temperature profiles, while for deeper water tables, the combined effects of the geothermal gradient and ground-water fluxes determine vertical temperature profiles. Three approaches are presented to demonstrate the manner in which recharge rates may be estimated by matching predicted temperatures with measured temperatures above the water table. For the case of a shallow water table beneath a streambed, a variably saturated heat and water (liquid-only) transport simulation code, VS2DH, was used with an optimization procedure to inversely fit simulated temperatures to measured temperatures for several Southwestern stream channels. In some cases, temperature-based estimates of vertical flux were compared to surface-water measurements of streamflow loss. For the case of a deep water table, two different approaches were examined. An analytical solution with limitations on stratigraphic complexity was compared to measured temperature profiles beneath Yucca Flat, NV. A simulation code, TOUGH2, was used to match simulated to measured temperatures profiles beneath washes near Beatty, NV. Hypothetical results using the analytical solution generated a linear vertical temperature gradient for no-flow conditions, a concave upward gradient for groundwater recharge, and a concave downward gradient for groundwater discharge. TOUGH2 simulation results were capable of matching the complex temperature profiles in the deep, highly layered unsaturated material underlying the wash sites. Best-fit analytical and simulation temperature profiles yielded estimates of ground-water recharge for the Yucca Flat and wash sites, which reflected their dissimilar hydrological settings.

Constantz, J. E.; Tyler, S. W.; Kwicklis, E.

2001-12-01

55

The Use of Atmospheric Contaminants to Estimate the Minimum Age of Environmental Releases Impacting Groundwater  

Microsoft Academic Search

Numerous age-dating techniques are available to estimate the time frame of contaminant releases impacting groundwater. One method, historically used in the hydrology field to assess recharge ages and rates of groundwater flow, can be applied to estimating the age of contaminant releases. Chlorofluorocarbons (CFCs) and tritium are anthropogenic substances present in the atmosphere over the past half century. These atmospheric

Gil Oudijk

2005-01-01

56

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

57

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

2014-07-01

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

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

USGS Publications Warehouse

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

Maurer, D. K.

1988-01-01

60

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

EPA Science Inventory

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

61

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

EPA Science Inventory

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

62

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

63

Effects of Radiogenic Heat on Groundwater Flow.  

National Technical Information Service (NTIS)

The effects of radiogenic heat released by a nuclear waste repository on the groundwater flow in the neighboring rock mass is reviewed. The report presents an overview of the hydrogeologic properties of crystalline rocks in the Canadian Shield and also de...

R. J. Beddoes H. Y. Tammemagi

1986-01-01

64

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

65

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

66

Hydrodynamic modelling for groundwater flow through permeable reactive barriers  

Microsoft Academic Search

Hydrodynamic modelling for analysis of groundwater flow through permeable reactive barriers (PRBs) is addressed in this paper. Permeable reactive barriers constitute an emerging technology for in situ remediation of groundwater contamination and have many advantages over the traditional ex situ treatment methods. The transport domains during groundwater flow through PRBs often may involve free-flow or non-porous sections. To model the

Diganta Bhusan Das

2002-01-01

67

Detecting influential observations in nonlinear regression modeling of groundwater flow  

USGS Publications Warehouse

Nonlinear regression is used to estimate optimal parameter values in models of groundwater flow to ensure that differences between predicted and observed heads and flows do not result from nonoptimal parameter values. Parameter estimates can be affected, however, by observations that disproportionately influence the regression, such as outliers that exert undue leverage on the objective function. Certain statistics developed for linear regression can be used to detect influential observations in nonlinear regression if the models are approximately linear. This paper discusses the application of Cook's D, which measures the effect of omitting a single observation on a set of estimated parameter values, and the statistical parameter DFBETAS, which quantifies the influence of an observation on each parameter. The influence statistics were used to (1) identify the influential observations in the calibration of a three-dimensional, groundwater flow model of a fractured-rock aquifer through nonlinear regression, and (2) quantify the effect of omitting influential observations on the set of estimated parameter values. Comparison of the spatial distribution of Cook's D with plots of model sensitivity shows that influential observations correspond to areas where the model heads are most sensitive to certain parameters, and where predicted groundwater flow rates are largest. Five of the six discharge observations were identified as influential, indicating that reliable measurements of groundwater flow rates are valuable data in model calibration. DFBETAS are computed and examined for an alternative model of the aquifer system to identify a parameterization error in the model design that resulted in overestimation of the effect of anisotropy on horizontal hydraulic conductivity.

Yager, R. M.

1998-01-01

68

Estimating Flow in Streams  

NSDL National Science Digital Library

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

Porter, Dana O.

2008-10-14

69

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

70

Inherited drainage - paleochannels and preferential groundwater flow  

NASA Astrophysics Data System (ADS)

It is suggested that in a localized remnant of Kalahari sand at Dufuya, central Zimbabwe, groundwater flows in an integrated pattern inherited from the paleochannel network of the underlying gneiss. Contact springs occur at discrete localities along the Kalahari sand/gneiss boundary and are associated with spring sapping and land surface subsidence. Subsidence is presumed to be due to preferential solute removal by leaching and dissolution as a result of concentration of groundwater flow within the buried paleochannel network and the location of the springs is presumed to occur where the paleochannel network intersects the Kalahari sand/gneiss boundary. Over time the surficial Kalahari sand is preferentially removed along these buried drainage lines by spring sapping and headwards erosion, exposing the gneiss. Multi-electrode direct current resistivity profiling and radar have been used to map the sub-surface, revealing the topography of the basement and nature of the Kalahari cover. Coincidence of gneiss basement depressions with the spring sites, leached sands and subsidence zones suggests inheritance of the gneiss fluvial paleochannel network pattern by the present day groundwater flow. Washed sand and gravel intersected in shallow boreholes in these areas provides further evidentiary support for the concept of inherited drainage.

Owen, Richard; Dahlin, T.

2010-06-01

71

Numerical simulation of groundwater flow on MPPs  

SciTech Connect

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

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

1994-03-01

72

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

73

Groundwater Flow in the Edwards Aquifer: Comparison of Groundwater Modeling and Dye Trace Results  

Microsoft Academic Search

The Edwards Aquifer of central Texas is a karst aquifer developed in faulted and fractured Cretaceous-age limestones and dolomites. Numerous groundwater models have been developed for the three segments of the Edwards Aquifer since completion of the first major flow model in 1979. Groundwater models have helped refine our understanding of the relationships among flowpaths, recharge, groundwater pumping, and springflow.

Brian A. Smith; Brian B. Hunt; Geary M. Schindel

74

Storm-driven groundwater flow in a salt marsh  

Microsoft Academic Search

Storms can cause significant groundwater flow in coastal settings, but prior studies of the effects of storms on groundwater flow and transport have largely focused on very large storms and used salinity as a tracer. We have little information about the effects of smaller storms on coastal flow and how storm-induced variability affects key tidal wetlands like salt marshes, which

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

2011-01-01

75

Conceptual and mathematical modeling of the Hanford groundwater flow regime  

Microsoft Academic Search

Disposal of radioactive wastes to surface disposal sites at the Hanford Atomic Reservation has resulted in some radioactive and chemical contamination of the underlying groundwater flow systems. In support of the Hanford groundwater management effort a preliminary conceptual model of the groundwater system has been formulated as a first step in understanding possible contaminant movement. The mathematical modeling capabilities needed

R. C. Arnett; R. A. Deju; R. W. Nelson; C. R. Cole; R. E. Gephart

1976-01-01

76

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

77

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

78

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

2013-12-01

79

Shallow groundwater in the Matanuska-Susitna Valley, Alaska—Conceptualization and simulation of flow  

USGS Publications Warehouse

The Matanuska-Susitna Valley is in the Upper Cook Inlet Basin and is currently undergoing rapid population growth outside of municipal water and sewer service areas. In response to concerns about the effects of increasing water use on future groundwater availability, a study was initiated between the Alaska Department of Natural Resources and the U.S. Geological Survey. The goals of the study were (1) to compile existing data and collect new data to support hydrogeologic conceptualization of the study area, and (2) to develop a groundwater flow model to simulate flow dynamics important at the regional scale. The purpose of the groundwater flow model is to provide a scientific framework for analysis of regional-scale groundwater availability. To address the first study goal, subsurface lithologic data were compiled into a database and were used to construct a regional hydrogeologic framework model describing the extent and thickness of hydrogeologic units in the Matanuska-Susitna Valley. The hydrogeologic framework model synthesizes existing maps of surficial geology and conceptual geochronologies developed in the study area with the distribution of lithologies encountered in hundreds of boreholes. The geologic modeling package Geological Surveying and Investigation in Three Dimensions (GSI3D) was used to construct the hydrogeologic framework model. In addition to characterizing the hydrogeologic framework, major groundwater-budget components were quantified using several different techniques. A land-surface model known as the Deep Percolation Model was used to estimate in-place groundwater recharge across the study area. This model incorporates data on topography, soils, vegetation, and climate. Model-simulated surface runoff was consistent with observed streamflow at U.S. Geological Survey streamgages. Groundwater withdrawals were estimated on the basis of records from major water suppliers during 2004-2010. Fluxes between groundwater and surface water were estimated during field investigations on several small streams. Regional groundwater flow patterns were characterized by synthesizing previous water-table maps with a synoptic water-level measurement conducted during 2009. Time-series water-level data were collected at groundwater and lake monitoring stations over the study period (2009–present). Comparison of historical groundwater-level records with time-series groundwater-level data collected during this study showed similar patterns in groundwater-level fluctuation in response to precipitation. Groundwater-age data collected during previous studies show that water moves quickly through the groundwater system, suggesting that the system responds quickly to changes in climate forcing. Similarly, the groundwater system quickly returns to long-term average conditions following variability due to seasonal or interannual changes in precipitation. These analyses indicate that the groundwater system is in a state of dynamic equilibrium, characterized by water-level fluctuation about a constant average state, with no long-term trends in aquifer-system storage. To address the second study goal, a steady-state groundwater flow model was developed to simulate regional groundwater flow patterns. The groundwater flow model was bounded by physically meaningful hydrologic features, and appropriate internal model boundaries were specified on the basis of conceptualization of the groundwater system resulting in a three-layer model. Calibration data included 173 water?level measurements and 18 measurements of streamflow gains and losses along small streams. Comparison of simulated and observed heads and flows showed that the model accurately simulates important regional characteristics of the groundwater flow system. This model is therefore appropriate for studying regional-scale groundwater availability. Mismatch between model-simulated and observed hydrologic quantities is likely because of the coarse grid size of the model and seasonal transient effects. Next steps towards model refinement include the development of a transi

Kikuchi, Colin P.

2013-01-01

80

Hydraulics Analysis for Groundwater Flow Through Permeable Reactive Barriers  

Microsoft Academic Search

Groundwater flow modelling is an important tool in simulating and predicting hydraulic behaviour of groundwater transporting\\u000a in the domain consisted of groundwater flow zone (aquifer) and permeable reactive barriers (PRBs). The aquifer regime is modelled\\u000a using the Darcy equation, whereas PRBs are simulated by the Brinkman equation. By combining the above equations, the present\\u000a paper is devoted to analyse the

Shejiang Liu; Xingang Li; Hongxing Wang

81

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.

Muldoon, Maureen

82

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

USGS Publications Warehouse

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.

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

2013-01-01

83

A ground-water flow Mathematica tool package  

SciTech Connect

Mathematica, a symbolic computer mathematics program, is used to construct a tool package for ground-water flow and contaminant transport simulations. High level, mnemonic functions are designed that allow users to plot type curves, to animate ground-water flow fields, to perform parameter determination, and to visualize the movement of contaminant cloud.

Cheng, A.H.D.; Sidauruk, P. [Univ. of Delaware, Newark, DE (United States). Dept. of Civil Engineering

1996-01-01

84

CONCEPTUAL FRAMEWORK FOR REGRESSION MODELING OF GROUND-WATER FLOW.  

USGS Publications Warehouse

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

Cooley, Richard, L.

1985-01-01

85

Simulation of groundwater flow and effects of groundwater irrigation on stream base flow in the Elkhorn and Loup River Basins, Nebraska, 1895-2055-Phase Two  

USGS Publications Warehouse

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

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

2010-01-01

86

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

87

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

88

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.

89

A full-Bayesian approach to the groundwater inverse problem for steady state flow  

Microsoft Academic Search

A full-Bayesian approach to the estimation of transmissivity from hydraulic head and transmissivity measurements is developed for two-dimensional steady state groundwater flow. The approach combines both Bayesian and maximum entropy viewpoints of probability. In the first phase, log transmissivity measurements are incorporated into Bayes' theorem, and the prior probability density function is updated, yielding posterior estimates of the mean value

Allan D. Woodbury; Tadeusz J. Ulrych

2000-01-01

90

Equally likely inverse solutions to a groundwater flow problem including pattern information from remote sensing images  

Microsoft Academic Search

Groundwater flow modeling for large areas in arid and semiarid regions, like the Chobe region in Botswana, suffers from a severe lack of data. This study addresses the usefulness of remote sensing (RS) images to constrain the recharge rate estimates for a region. The estimates derived from METEOSAT and NOAA advanced very high resolution radar (AVHRR) images are correlated with

H. J. Hendricks Franssen; P. Brunner; P. Makobo; W. Kinzelbach

2008-01-01

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

Simulation of ground-water flow and land subsidence in the Antelope Valley ground-water basin, California  

USGS Publications Warehouse

Antelope Valley, California, is a topographically closed basin in the western part of the Mojave Desert, about 50 miles northeast of Los Angeles. The Antelope Valley ground-water basin is about 940 square miles and is separated from the northern part of Antelope Valley by faults and low-lying hills. Prior to 1972, ground water provided more than 90 percent of the total water supply in the valley; since 1972, it has provided between 50 and 90 percent. Most ground-water pumping in the valley occurs in the Antelope Valley ground-water basin, which includes the rapidly growing cities of Lancaster and Palmdale. Ground-water-level declines of more than 200 feet in some parts of the ground-water basin have resulted in an increase in pumping lifts, reduced well efficiency, and land subsidence of more than 6 feet in some areas. Future urban growth and limits on the supply of imported water may continue to increase reliance on ground water. To better understand the ground-water flow system and to develop a tool to aid in effectively managing the water resources, a numerical model of ground-water flow and land subsidence in the Antelope Valley ground-water basin was developed using old and new geohydrologic information. The ground-water flow system consists of three aquifers: the upper, middle, and lower aquifers. The aquifers, which were identified on the basis of the hydrologic properties, age, and depth of the unconsolidated deposits, consist of gravel, sand, silt, and clay alluvial deposits and clay and silty clay lacustrine deposits. Prior to ground-water development in the valley, recharge was primarily the infiltration of runoff from the surrounding mountains. Ground water flowed from the recharge areas to discharge areas around the playas where it discharged either from the aquifer system as evapotranspiration or from springs. Partial barriers to horizontal ground-water flow, such as faults, have been identified in the ground-water basin. Water-level declines owing to ground-water development have eliminated the natural sources of discharge, and pumping for agricultural and urban uses have become the primary source of discharge from the ground-water system. Infiltration of return flows from agricultural irrigation has become an important source of recharge to the aquifer system. The ground-water flow model of the basin was discretized horizontally into a grid of 43 rows and 60 columns of square cells 1 mile on a side, and vertically into three layers representing the upper, middle, and lower 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 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 ground-water basin; estimates also were obtained from recently collected hydrologic data and from results of simulations of ground-water flow and land subsidence models of the Edwards Air Force Base area. Some of these initial estimates were modified during model calibration. Ground-water pumpage for agriculture was estimated on the basis of irrigated crop acreage and crop consumptive-use data. Pumpage for public supply, which is metered, was compiled and entered into a database used for this study. Estimated annual pumpage peaked at 395,000 acre-feet (acre-ft) in 1952 and then declined because of declining agricultural production. Recharge from irrigation-return flows was estimated to be 30 percent of agricultural pumpage; the irrigation-return flows were simulated as recharge to the regional water table 10 years following application at land surface. The annual quantity of natural recharge initially was based on estimates from previous studies. During model calibration, natural recharge was reduced from the initial

Leighton, David A.; Phillips, Steven P.

2003-01-01

93

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

94

Estimating ground-water recharge from streamflow records  

Microsoft Academic Search

The purpose of this paper is to estimate ground-water recharge based on the investigation of the balance between ground-water recharge and discharge from streamflow hydrographs. Two methods of hydrograph analysis are employed in a case study of Cho-Shui River basin, Taiwan. The first is the recession-curve-displacement method, which assumes the linearity of the master recession curve while the profile of

Wei-Ping Chen; Cheng-Haw Lee

2003-01-01

95

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

96

Groundwater flow and solute movement to drain laterals, western San Joaquin Valley, California: 1. Geochemical assessment  

USGS Publications Warehouse

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

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

1991-01-01

97

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

98

Geochemical and isotopic investigations on groundwater residence time and flow in the Independence Basin, Mexico  

NASA Astrophysics Data System (ADS)

The Independence Basin in the semi-arid Guanajuato state of central Mexico is facing serious groundwater resources deficiency due to an increasing demand linked to a rapid population growth and agricultural development. This problem is aggravated by an inadequate evaluation of groundwater resources in the region. Geochemistry and isotopic tracers were used in order to investigate the groundwater flow system and estimate the groundwater residence time. The groundwater is characterized by low salinity with some exceptions associated to a contribution of more saline groundwater from deep formations. The predominant reactions are CO 2 gas dissolution, carbonate dissolution, albite weathering, kaolinite and chalcedony precipitation. Six principal hydrochemical zones were recognized, which provided information on plausible recharge sources and groundwater chemical evolution. The 14C concentration varies between 19 and 94 pmc. The high 14C values indicating recent recharge are observed at the basin margins and a trend to lower 14C values is observed along the modern groundwater flow paths. The groundwater residence time according to radiocarbon estimations ranges between recent and ˜11 ka. The residence time distribution matches the regional important discharge zones west in the basin center (from Dolores Hidalgo and southwest from Doctor Mora). Hydrochemical tracers are in general agreement with the predeveloped and current hydraulic-head configuration, however, show some inconsistencies with the predeveloped head in the downgradient areas, which means that the impact by gradually increasing groundwater extraction during the last decades is reflected on radiocarbon age distribution. Geochemical evidences imply that the recharge input from the northern basin area is insignificant.

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

2006-06-01

99

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

100

Unbounded, Exact Solution for 3-D Topography Driven Groundwater Flow  

NASA Astrophysics Data System (ADS)

An exact analytical solution is presented for saturated groundwater flow to provide improved understanding of the renewal rate of deep and shallow groundwater and the long-term management of groundwater resources. The solution is derived under the assumptions that the hydraulic potential of the groundwater surface follows the topography and imposes a steady boundary condition for driving the groundwater flow. This assumption is justified in most areas of humid climate. The solution is applicable on a wide range of spatial scales and accounts for decaying permeability with depth, stratified aquifers as well as anisotropy. The flow problem is solved by representing the topography with a three-dimensional spectral scaling solution based on harmonic functions that are independent in x- and y-directions. In most areas the Fourier-series, representing the topography, give a nearly perfect image of the ground surface elevation. The topography is found to be fractal and this imposes a fractal nature of the groundwater flow that is altered by the additional geometrical scales. The groundwater flow solution, based on the Fourier-spectrum, depends on the decay with depth and anisotropy in hydraulic conductivity and stratifications due to quaternary deposits, layered sediments etc. Prior analytical solutions are limited to either two-dimensional flows or harmonic functions uniform in the x- and y- directions, hence making them unable to predict three-dimensional subsurface flows beneath a realistic landscape. However, the most important advantage of this new method is the ability to analyse the impact of different geometrical scales on the groundwater flow. Analyses indicate that in a homogeneous subsurface, shallow groundwater flows would be approximately equally controlled by all scales of topography. Although shorter topographical wavelengths control the surface water flux, their impact decreases faster with depth in relation to longer wavelengths. This induces an increasing importance of large-scale topography with depth. However, the hydraulic conductivity tends to decay with depth and this counteracts the effect of the large-scale topography on the groundwater flow more effectively than the smaller landscape scales. For the depth-dependent hydraulic conductivity applicable to the Fennoscandian bedrock, we find a depth-limitation of the flow cells that tends to reduce the importance of the larger wavelengths on the fluxes at all depths.

Marklund, L.; Wörman, A.

2007-12-01

101

GIS and SBF for estimating groundwater recharge of a mountainous basin in the Wu River watershed, Taiwan  

NASA Astrophysics Data System (ADS)

The temporal and spatial distributions of precipitation are extremely uneven; so, careful management of water resources in Taiwan is crucial. The long-term overexploitation of groundwater resources poses a challenge to water resource management in Taiwan. However, assessing groundwater resources in mountainous basins is challenging due to limited information. In this study, a geographic information system (GIS) and stable base-flow (SBF) techniques were used to assess the characteristics of groundwater recharge considering the Wu River watershed in central Taiwan as a study area. First, a GIS approach was used to integrate five contributing factors: lithology, land cover/land use, lineaments, drainage, and slope. The weights of factors contributing to the groundwater recharge were obtained from aerial photos, geological maps, a land use database, and field verification. Second, the SBF was used to estimate the groundwater recharge in a mountainous basin scale. The concept of the SBF technique was to separate the base-flow from the total streamflow discharge in order to obtain a measure of groundwater recharge. The SBF technique has the advantage of integrating groundwater recharge across an entire basin without complex hydro-geologic modelling and detailed knowledge of the soil characteristics. In this study, our approach for estimating recharge provides not only an estimate of how much water becomes groundwater, but also explains the characteristics of a potential groundwater recharge zone.

Yeh, Hsin-Fu; Lin, Hung-I.; Lee, Shing-Tsz; Chang, Min-Hsiang; Hsu, Kuo-Chin; Lee, Cheng-Haw

2014-05-01

102

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

103

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

104

Computer programs for describing the recession of ground-water discharge and for estimating mean ground-water recharge and discharge from streamflow records-update  

USGS Publications Warehouse

The computer programs included in this report can be used to develop a mathematical expression for recession of ground-water discharge and estimate mean ground-water recharge and discharge. The programs are intended for analysis of the daily streamflow record of a basin where one can reasonably assume that all, or nearly all, ground water discharges to the stream except for that which is lost to riparian evapotranspiration, and where regulation and diversion of flow can be considered to be negligible. The program RECESS determines the master reces-sion curve of streamflow recession during times when all flow can be considered to be ground-water discharge and when the profile of the ground-water-head distribution is nearly stable. The method uses a repetitive interactive procedure for selecting several periods of continuous recession, and it allows for nonlinearity in the relation between time and the logarithm of flow. The program RORA uses the recession-curve displacement method to estimate the recharge for each peak in the streamflow record. The method is based on the change in the total potential ground-water discharge that is caused by an event. Program RORA is applied to a long period of record to obtain an estimate of the mean rate of ground-water recharge. The program PART uses streamflow partitioning to estimate a daily record of base flow under the streamflow record. The method designates base flow to be equal to streamflow on days that fit a requirement of antecedent recession, linearly interpolates base flow for other days, and is applied to a long period of record to obtain an estimate of the mean rate of ground-water discharge. The results of programs RORA and PART correlate well with each other and compare reasonably with results of the corresponding manual method.

Rutledge, A. T.

1998-01-01

105

Estimation of groundwater velocities from Yucca Flat to the Amargosa Desert using geochemistry and environmental isotopes  

SciTech Connect

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

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

1997-06-01

106

Glaciation and regional groundwater flow in the Fennoscandian shield  

USGS Publications Warehouse

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

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

2012-01-01

107

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

USGS Publications Warehouse

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. -from Author

Cooley, R. L.

1983-01-01

108

Nonstationary spectral methods to delineate stochastic well capture zones in mildly nonstationary groundwater flow systems  

Microsoft Academic Search

This study presents an approximate spectral method (ASM) to delineate well capture zones in mildly nonstationary groundwater systems. Taking advantages of spectral theories in solving unmodeled small-scale variability in hydraulic conductivity (K), the proposed spectral method can efficiently estimate flow uncertainties. Such velocity uncertainties associated with the particle backward tracking algorithm and the concept of direct propagation of uncertainties of

Chuen-Fa Ni; Chi-Ping Lin; Yi-Ru Huang

2010-01-01

109

Estimates of vertical hydraulic conductivity and regional ground-water flow rates in rocks of Jurassic and Cretaceous age, San Juan Basin, New Mexico and Colorado  

USGS Publications Warehouse

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

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

1982-01-01

110

Estimation of Groundwater Recharge at Pahute Mesa using the Chloride Mass-Balance Method  

SciTech Connect

Groundwater recharge on Pahute Mesa was estimated using the chloride mass-balance (CMB) method. This method relies on the conservative properties of chloride to trace its movement from the atmosphere as dry- and wet-deposition through the soil zone and ultimately to the saturated zone. Typically, the CMB method assumes no mixing of groundwater with different chloride concentrations; however, because groundwater is thought to flow into Pahute Mesa from valleys north of Pahute Mesa, groundwater flow rates (i.e., underflow) and chloride concentrations from Kawich Valley and Gold Flat were carefully considered. Precipitation was measured with bulk and tipping-bucket precipitation gauges installed for this study at six sites on Pahute Mesa. These data, along with historical precipitation amounts from gauges on Pahute Mesa and estimates from the PRISM model, were evaluated to estimate mean annual precipitation. Chloride deposition from the atmosphere was estimated by analyzing quarterly samples of wet- and dry-deposition for chloride in the bulk gauges and evaluating chloride wet-deposition amounts measured at other locations by the National Atmospheric Deposition Program. Mean chloride concentrations in groundwater were estimated using data from the UGTA Geochemistry Database, data from other reports, and data from samples collected from emplacement boreholes for this study. Calculations were conducted assuming both no underflow and underflow from Kawich Valley and Gold Flat. Model results estimate recharge to be 30 mm/yr with a standard deviation of 18 mm/yr on Pahute Mesa, for elevations >1800 m amsl. These estimates assume Pahute Mesa recharge mixes completely with underflow from Kawich Valley and Gold Flat. The model assumes that precipitation, chloride concentration in bulk deposition, underflow and its chloride concentration, have been constant over the length of time of recharge.

Cooper, Clay A [DRI] [DRI; Hershey, Ronald L [DRI] [DRI; Healey, John M [DRI] [DRI; Lyles, Brad F [DRI] [DRI

2013-07-01

111

Hydrogeology, simulated ground-water flow, and ground-water quality at two landfills in Bristol, Vermont  

USGS Publications Warehouse

A study was done to describe the hydrogeology of unconsolidated deposits, simulated ground-water flow, and ground-water quality at two landfills in Bristol, Vermont. The study area is characterized by a glacial delta greater than 200 feet thick on the west flank of the Green Mountains. An upper unconfined, coarse-grained glacial aquifer and a lower fine-grained glacial aquifer are separated throughout most of the study area by a sand, silt, and clay confining unit. A two-layer ground-water flow model was designed and calibrated to estimate ground-water-flow paths form the aquifers beneath the landfills. Large upward head gradients of 0.03 to 0.30 foot per foot are the result of ground water leaking from the underlying bedrock aquifer, which caused ground-water flow to concentrate in the upper aquifer. Most simulated ground-water-flow paths in the lower glacial aquifer beneath the landfills crossed into the upper aquifer. Simulated ground- water-flow paths in the upper aquifer, beneath the landfills, remained in the upper aquifer. Ground water characterized as landfill leachate, or influenced by landfill leachate, has a median specific conductance of 700 microseimens per centimeter at 25 degrees Celsius. Landfill leachate contained mean concentrations 1.5 to 10 times the background concentrations of common constituents and metals, including calcium, potassium, sodium, chloride, iron, magnesium, and manganese. Trace metals detected in the leachate included copper, nickel, zinc, cobalt, lead, and arsenic. Ten volatile organic compounds were found at four observation wells associated with one landfill and three volatile organic compounds were found at two observation wells associated with the record landfill. No one volatile organic compound was consistently found and detections were generally at or near detection limits.

Mack, T. J.

1995-01-01

112

Groundwater flow through anisotropic fault zones in multiaquifer systems  

Microsoft Academic Search

Vertical faults through the shallow crust are commonly believed to act as either barriers to horizontal groundwater flow normal to the fault, conduits to horizontal flow tangential to the fault, or a combination of both. In addition, enhanced vertical permeability has been identified as a common feature. We investigate the effects of vertical anisotropy of a fault zone on the

E. I. Anderson; M. Bakker

2008-01-01

113

Conceptual model and numerical simulation of the groundwater-flow system of Bainbridge Island, Washington  

USGS Publications Warehouse

Groundwater is the sole source of drinking water for the population of Bainbridge Island. Increased use of groundwater supplies on Bainbridge Island as the population has grown over time has created concern about the quantity of water available and whether saltwater intrusion will occur as groundwater usage increases. A groundwater-flow model was developed to aid in the understanding of the groundwater system and the effects of groundwater development alternatives on the water resources of Bainbridge Island. Bainbridge Island is underlain by unconsolidated deposits of glacial and nonglacial origin. The surficial geologic units and the deposits at depth were differentiated into aquifers and confining units on the basis of areal extent and general water-bearing characteristics. Eleven principal hydrogeologic units are recognized in the study area and form the basis of the groundwater-flow model. A transient variable-density groundwater-flow model of Bainbridge Island and the surrounding area was developed to simulate current (2008) groundwater conditions. The model was calibrated to water levels measured during 2007 and 2008 using parameter estimation (PEST) to minimize the weighted differences or residuals between simulated and measured hydraulic head. The calibrated model was used to make some general observations of the groundwater system in 2008. Total flow through the groundwater system was about 31,000 acre-ft/ yr. The recharge to the groundwater system was from precipitation and septic-system returns. Groundwater flow to Bainbridge Island accounted for about 1,000 acre-ft/ yr or slightly more than 5 percent of the recharge amounts. Groundwater discharge was predominately to streams, lakes, springs, and seepage faces (16,000 acre-ft/yr) and directly to marine waters (10,000 acre-ft/yr). Total groundwater withdrawals in 2008 were slightly more than 6 percent (2,000 acre-ft/yr) of the total flow. The calibrated model was used to simulate predevelopment conditions, during which no groundwater pumping or secondary recharge occurred and currently developed land was covered by conifer forests. Simulated water levels in the uppermost aquifer generally were slightly higher at the end of 2008 than under predevelopment conditions, likely due to increased recharge from septic returns and reduced evapotranspiration losses due to conversion of land cover from forests to current conditions. Simulated changes in water levels for the extensively used sea-level aquifer were variable, although areas with declines between zero and 10 feet were common and generally can be traced to withdrawals from public-supply drinking wells. Simulated water-level declines in the deep (Fletcher Bay) aquifer between predevelopment and 2008 conditions ranged from about 10 feet in the northeast to about 25 feet on the western edge of the Island. These declines are related to groundwater withdrawals for public-supply purposes. The calibrated model also was used to simulate the possible effects of increased groundwater pumping and changes to recharge due to changes in land use and climactic conditions between 2008 and 2035 under minimal, expected, and maximum impact conditions. Drawdowns generally were small for most of the Island (less than 10 ft) for the minimal and expected impact scenarios, and were larger for the maximum impact scenario. No saltwater intrusion was evident in any scenario by the year 2035. The direction of flow in the deep Fletcher Bay aquifer was simulated to reverse direction from its predevelopment west to east direction to an east to west direction under the maximum impact scenario.

Frans, Lonna M.; Bachmann, Matthew P.; Sumioka, Steve S.; Olsen, Theresa D.

2011-01-01

114

Noble gas loss may indicate groundwater flow across flow barriers in southern Nevada  

Microsoft Academic Search

Average calculated noble gas temperatures increase from 10 to 22 °C in groundwater from recharge to discharge areas in carbonate-rock aquifers of southern Nevada. Loss of noble gases from groundwater in these regional flow systems at flow barriers is the likely process that produces an increase in recharge noble gas temperatures. Emplacement of low permeability rock into high permeability aquifer

James M. Thomas; Bryant G. Hudson; Martin Stute; Jordan F. Clark

2003-01-01

115

SWB-A modified Thornthwaite-Mather Soil-Water-Balance code for estimating groundwater recharge  

USGS Publications Warehouse

A Soil-Water-Balance (SWB) computer code has been developed to calculate spatial and temporal variations in groundwater recharge. The SWB model calculates recharge by use of commonly available geographic information system (GIS) data layers in combination with tabular climatological data. The code is based on a modified Thornthwaite-Mather soil-water-balance approach, with components of the soil-water balance calculated at a daily timestep. Recharge calculations are made on a rectangular grid of computational elements that may be easily imported into a regional groundwater-flow model. Recharge estimates calculated by the code may be output as daily, monthly, or annual values.

Westenbroek, S. M.; Kelson, V. A.; Dripps, W. R.; Hunt, R. J.; Bradbury, K. R.

2010-01-01

116

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

117

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

118

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

119

Flow calculations for Yucca Mountain groundwater travel time (GWTT-95)  

SciTech Connect

In 1983, high-level radioactive waste repository performance requirements related to groundwater travel time were defined by NRC subsystem regulation 10 CFR 60.113. Although DOE is not presently attempting to demonstrate compliance with that regulation, understanding of the prevalence of fast paths in the groundwater flow system remains a critical element of any safety analyses for a potential repository system at Yucca Mountain, Nevada. Therefore, this analysis was performed to allow comparison of fast-path flow against the criteria set forth in the regulation. Models developed to describe the conditions for initiation, propagation, and sustainability of rapid groundwater movement in both the unsaturated and saturated zones will form part of the technical basis for total- system analyses to assess site viability and site licensability. One of the most significant findings is that the fastest travel times in both unsaturated and saturated zones are in the southern portion of the potential repository, so it is recommended that site characterization studies concentrate on this area. Results support the assumptions regarding the importance of an appropriate conceptual model of groundwater flow and the incorporation of heterogeneous material properties into the analyses. Groundwater travel times are sensitive to variation/uncertainty in hydrologic parameters and in infiltration flux at upper boundary of the problem domain. Simulated travel times are also sensitive to poorly constrained parameters of the interaction between flow in fractures and in the matrix.

Altman, S.J.; Arnold, B.W.; Barnard, R.W.; Barr, G.E.; Ho, C.K.; McKenna, S.A.; Eaton, R.R.

1996-09-01

120

Flow and patterns of nitrate pollution in groundwater: a case study of an agricultural area in Tsukuba City, Japan  

Microsoft Academic Search

A numerical simulation was applied to first characterize the groundwater flow and patterns of nitrate pollution of a small-agricultural\\u000a catchment in Tsukuba City, Japan, for a 10-year period. There was a good performance of the flow simulation. In contrast,\\u000a although the transport model calculated the evolution of the plume, it only provided estimates of solute concentrations. Groundwater\\u000a contamination increased exponentially

Adrian H. Gallardo; Walter Reyes-Borja; Norio Tase

2005-01-01

121

A Complementary Modeling Framework to Quantify and Reduce Groundwater Flow Model Uncertainty  

NASA Astrophysics Data System (ADS)

Although modern inverse techniques are powerful tools for parameter estimation, results of calibrated groundwater models are nevertheless subject to uncertainty since it is not possible to account for all the natural subsurface complexity. We present a complementary modeling framework in which error-correcting data-driven models are used to handle the bias and uncertainties arising mainly from ignored or misrepresented processes in the physically-based groundwater model. We use MODFLOW as the groundwater flow model and PEST for automatic calibration. The uncertainty of the combined MODFLOW and data-driven models is quantified using First Order Second Moment (FOSM) and bootstrap methods. For both methods, we consider the propagation of uncertainty due to the estimation variance of both the MODFLOW and data-driven models parameters. However, since the data-driven model uses the estimated MODFLOW heads as an input, its predictive variance also incorporates the effect of input data uncertainty. The prediction uncertainties are presented as approximate 95 percent confidence and prediction intervals or quantiles of the underlying distribution of prediction errors. The methods are applied to a case study of transient groundwater flow in the Spokane Valley aquifer that has been previously addressed using a calibrated MODFLOW model. The results are compared with those of more common uncertainty estimation techniques, such as Generalized Likelihood Uncertainty Estimation (GLUE) and Bayesian Model Averaging (BMA). We compare the performance and efficiency of the methods, and discuss some of the challenges related to their practical application.

Valocchi, A. J.; Demissie, Y. K.

2008-12-01

122

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

123

A Method to Evaluate Groundwater flow system under the Seabed  

NASA Astrophysics Data System (ADS)

A rapid increase of population in the world causes growth of water demands, and this may result worldwide water shortage in future. Especially, in the coastal area, water resource development becomes important because the half of the world population is concentrated in this area. Recently, countermeasures to mitigate climate change are discussed. Coastal area is one of the promising places for disposal of high-level nuclear waste or carbon dioxide capture and storage. Lots of development will be conducted in the coastal areas, however there are a lot of uncertainties remaining to understand the hydrogeological environment in there. It has been said that salt water / fresh water interface is formed in the place where meteoric fresh groundwater and salt groundwater from the ocean meet, and there is a large amount of groundwater discharge on the seafloor of the end of this interface so far. Recently, there is a lot of research about this submarine groundwater discharge because of the protection of the coastal ecosystem. In addition, there is a report that fresh water under the seabed was discovered on the continental shelf away from a present coastline by tens of kilometers in many parts of the world, because recently offshore drilling technology has been improving. Classical theory about formulation of salt water / fresh water interface could not explain completely, and consideration of longterm geochemical process (e.g., sea level fluctuations) is needed to understand this mechanism. Fresh (or brackish) groundwater under the seabed have been found on the investigation related to a seabed resources exploration in the field of coal mining, oceanic engineering works such as submarine tunnels, the atomic research, and the collection investigations of the basic data in the earth science field. A lot of fresh water under the seabed is confirmed on the offshore side from a present coastline as for these cases, and it is suggested that the end position of the salt water / fresh water interface (position of the submarine groundwater discharge) may appear on the seafloor. Moreover, neither the salinity concentration nor the groundwater age depends on depth. It is thought that it is because that the groundwater forms the complex flow situation through the change in a long-term groundwater flow system. The technology to understand the coastal groundwater flow consists of remote sensing, geographical features analysis, surface of the earth investigation, geophysical exploration, drilling survey, and indoor examination and the measurement. Integration of each technology is needed to interpret groundwater flow system because the one is to catch the local groundwater flow in the time series and another one is to catch the long-term and regional groundwater flow in the general situation. The purpose of this study is to review the previous research of coastal groundwater flow, and to integrate an applicable evaluation approach to understand this mechanism. In this presentation, the review of the research and case study using numerical simulation are introduced.

Kohara, N.; Marui, A.

2011-12-01

124

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

125

Groundwater flow along and across structural folding: an example from the Judean Desert, Israel  

Microsoft Academic Search

The considerable influence of the geological structure on groundwater flow regime is exhibited in the thick carbonate aquifer beneath the Judean Desert, Israel. Groundwater flow is diverted from the general steep hydraulic gradient, creating a subsurface ‘river-like’ meandering flow pattern. The structure of the extensive-folded anticlinorium forces groundwater flow through synclinal axes in the upper aquifer and in places it

Leehee Laronne Ben-Itzhak; Haim Gvirtzman

2005-01-01

126

Consistency of groundwater flow patterns in mountainous topography: Implications for valley bottom water replenishment and for defining groundwater flow boundaries  

NASA Astrophysics Data System (ADS)

Topographic influences on groundwater flow processes that contribute to baseflow and mountain block recharge (MBR) are conceptually investigated using three-dimensional numerical models of saturated groundwater flow. Model domains for conceptual and real topographies are developed as "mountain groundwatershed units" (MGUs) to represent regional-scale watershed systems. Results indicate regularity in groundwater flow patterns that reflect consistency of prominent topographic features, providing a basis for conceptualizing three-dimensional groundwater flow. Baseflow is generated mainly from recharge within the watershed area. MBR is produced primarily from recharge that is focused across triangular facets near the mountain front (˜73%-97% of total MBR), with additional contributions originating within the watershed (up to ˜27% of MBR). MBR contributions originating from recharge near the highest-elevation watershed boundaries are minimal but are greater for topography with less stream incision. With orographic influences, more MBR originates within the watershed. MBR rates are relatively consistent between models because of similarities in mountain front topography, while baseflow is variable. Gains and losses to systems via cross-watershed groundwater flux, generated because of topographic differences between adjacent watersheds, cause baseflow to vary by up to ˜10% but do not significantly influence MBR. In data-sparse regions such as mountains, a basic numerical modeling approach, using the MGU concept with topography data and mapped watershed boundaries, can be used to develop site-specific conceptual models to constrain water budgets, to delineate recharge areas, and to guide further investigation and data collection.

Welch, L. A.; Allen, D. M.

2012-05-01

127

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

128

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

129

Groundwater Flow in the Arthur Marble Aquifer, New Zealand  

Microsoft Academic Search

Arthur Marble underlies the Takaka Valley and outcrops in Karst Uplands to east and west of the valley in the South Island of New Zealand. It is the principal groundwater aquifer in the region and host to the remarkable Waikoropupu Springs near the coast. With average flow of 13,300 L\\/s, the karstic springs have many interesting features including unusual size

M. K. Stewart

2008-01-01

130

Groundwater Flow Model (GWFM) Development, Midnite Mine, Wellpinit, WA.  

National Technical Information Service (NTIS)

The ultimate purpose of this research effort was to develop a groundwater flow model (GWFM) for the Midnite Mine that can be utilized by the contractor preparing the Environment Impact Statement (EIS) and by other interested parties. The objectives of thi...

F. E. Kirschner

1996-01-01

131

Analytical studies on transient groundwater flow induced by land reclamation  

Microsoft Academic Search

In many coastal areas, land has been reclaimed by dumping fill 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-state ground water flow conditions were conducted previously, but transient analytical solutions are not yet available. Transient analytical

Litang Hu; Jiu Jimmy Jiao; Haipeng Guo

2008-01-01

132

Geohydrology, simulation of regional groundwater flow, and assessment of watermanagement strategies, Twentynine Palms area, California  

USGS Publications Warehouse

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

Li, Zhen; Martin, Peter

2011-01-01

133

Characterization and conceptualization of groundwater flow systems: Chapter 2  

USGS Publications Warehouse

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

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

2013-01-01

134

Reconstructing the groundwater flow in the Baltic Basin during the Last glaciation  

NASA Astrophysics Data System (ADS)

In last decades it has been discussed that most large ice sheets tend to reside on warm beds even in harsh clima tic conditions and subglacial melting occurs due to geothermal heat flow and deformation heat of the ice flow. However the subglacial groundwater recharge and flow conditions have been addressed in only few studies. The aim of this study is to establish the groundwater flow pattern in the Baltic Basin below the Scandinavian ice sheet during the Late Weichselian glaciation. The calculation results are compared to the known distribution of the groundwater body of the glacial origin found in Cambrian - Vendian (Cm-V) aquifer in the Northern Estonia which is believed to have originated as a result of subglacial meltwater infiltration during the reoccurring glaciations. Steady state regional groundwater flow model of the Baltic Basin was used to simulate the groundwater flow beneath the ice sheet with its geometry adjusted to reflect the subglacial topography. Ice thickness modelling data (Argus&Peltier, 2010) was used for the setup of the boundary conditions: the meltwater pressure at the ice bed was assumed equal to the overlying ice mass. The modelling results suggest two main recharge areas of the Cm-V aquifer system, and reversed groundwater flow that persisted for at least 14 thousand years. Model results show that the groundwater flow velocities in the Cm-V aquifer in the recharge area in N-Estonia beneath the ice sheet exceeded the present velocities by a factor of 10 on average. The calculated meltwater volume recharged into the Cm-V aquifer system during the Late Weichselian corresponds roughly to the estimated, however, considering the fact, that the study area has been glaciated at least 4 times this is an overestimation. The modeling results attest the hypothesis of light dO18 groundwater glacial origin in the Cm-V aquifer system, however the volumes, timing and processes involved in the meltwater intrusion are yet to be explored. This study was financed by the European Social fund Nr. 2009/0212/1DP/1.1.1.2.0/09/APIA/VIAA/060

Saks, T.; Sennikovs, J.; Timuhins, A.; Kalv?ns, A.

2012-04-01

135

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

136

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

137

Interbasin groundwater flow and groundwater interaction with surface water in a lowland rainforest, Costa Rica: A review  

Microsoft Academic Search

This paper reviews work related to interbasin groundwater flow (naturally occurring groundwater flow beneath watershed topographic divides) into lowland rainforest watersheds at La Selva Biological Station in Costa Rica. Chemical mixing calculations (based on dissolved chloride) have shown that up to half the water in some streams and up to 84% of the water in some riparian seeps and wells

David P. Genereux; Michael Jordan

2006-01-01

138

Ground-water age, flow, and quality near a landfill, and changes in ground-water conditions from 1976 to 1996 in the Swinomish Indian Reservation, northwestern Washington  

USGS Publications Warehouse

This report describes the results of two related studies: a study of ground-water age, flow, and quality near a landfill in the south-central part of the Swinomish Indian Reservation; and a study of changes in ground-water conditions for the entire reservation from 1976 to 1996. The Swinomish Indian Reservation is a 17-square-mile part of Fidalgo Island in northwestern Washington. The groundwater flow system in the reservation is probably independent of other flow systems in the area because it is almost completely surrounded by salt water. There has been increasing stress on the ground-water resources of the reservation because the population has almost tripled during the past 20 years, and 65 percent of the population obtain their domestic water supply from the local ground-water system. The Swinomish Tribe is concerned that increased pumping of ground water might have caused decreased ground-water discharge into streams, declines in ground-water levels, and seawater intrusion into the ground-water system. There is also concern that leachate from an inactive landfill containing mostly household and wood-processing wastes may be contaminating the ground water. The study area is underlain by unconsolidated glacial and interglacial deposits of Quaternary age that range from about 300 to 900 feet thick. Five hydrogeologic units have been defined in the unconsolidated deposits. From top to bottom, the hydrogeologic units are a till confining bed, an outwash aquifer, a clay confining bed, a sea-level aquifer, and an undifferentiated unit. The ground-water flow system of the reservation is similar to other island-type flow systems. Water enters the system through the water table as infiltration and percolation of precipitation (recharge), then the water flows downward and radially outward from the center of the island. At the outside edges of the system, ground water flows upward to discharge into the surrounding saltwater bodies. Average annual recharge is estimated to be about 3 inches, or 12 percent of the average annual precipitation. Ground water in the outwash aquifer near the landfill is estimated to be between 15 and 43 years old. Some deeper ground waters and ground water near the discharge areas close to the shoreline are older than 43 years. Analysis of water-quality data collected for this study and review of existing data indicate that material in the landfill has had no appreciable impact on the current quality of ground water outside of the landfill. The water quality of samples from seven wells near to and downgradient from the landfill appears to be similar to the ground-water quality throughout the entire study area. The high iron and manganese concentrations found in most of the samples from wells near the landfill are probably within the range of natural concentrations for the study area. Ground-water pumping during the past 20 years has not caused any large changes in ground-water discharge to streams, ground-water levels, or seawater intrusion into the ground-water system. Ground-water discharge into Snee-oosh Creek and Munks Creek had similar magnitudes in the summers of 1976 and 1996; flows in both creeks during those summers ranged from 0.07 t 0.15 cubic feet per second. Ground-water levels changed minimally between 1976 and 1996. The average water-level change for 20 wells with more than 10 years between measurements was -0.7 feet and the two largest waterlevel declines were 6 and 9 feet. No appreciable seawater intrusion was found in the ground water in 1996, and there was no significant increase in the extent of seawater intrusion from 1976 to 1996. Median chloride concentrations of water samples collected from wells were 22 milligrams per liter in 1976 and 18 milligrams per liter in 1996.

Thomas, B. E.; Cox, S. E.

1998-01-01

139

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

140

Improving Radium-based Estimates of Submarine Groundwater Discharge  

NASA Astrophysics Data System (ADS)

Groundwater discharge is vital for the exchange of solutes between salt marshes and estuaries, and radium isotopes are frequently used as tracers of groundwater flow paths and discharge in coastal systems. Considerable spatial and temporal variability in porewater radium activity has hindered the accuracy of this tracer. In porewater, radium activity is a complex function of production by parent isotopes in and grain size of the aquifer material, individual decay rates, porewater salinity, temperature, redox- and pH-dependent adsorption and desorption, sediment Fe- and Mn-oxide/hydroxide coatings, and groundwater transport (advection and dispersion). In order to resolve the primary factors controlling porewater radium activity in an intertidal salt marsh, where high salinity and reducing conditions prevail, and sediment oxide coatings vary from winter to summer, a field and modeling study was conducted at a salt marsh island within North Inlet Salt Marsh, Georgetown, South Carolina. This site was previously developed as part of a larger study to understand the links between salt marsh groundwater dynamics and acute marsh dieback. Porewater and surface water samples were collected from November 2009 - February 2011. Shallow sediment samples were collected in winter and summer 2010, and deeper sediments were split from cores collected during site development. Measurements of water temperature, salinity, mV, and pH were taken in the field, and radium isotopes were measured via delayed-coincidence counter or gamma spectrometry. Surface-bound sediment radium activity was determined by desorption experiments. Iron and manganese oxide coatings on surface sediments were isolated through a sequential leaching process, and the leachate analyzed via ICP-AES. Finally, a 3-D groundwater flow model was developed using SUTRA, a U.S.G.S. numerical model, which was modified to account for changes in total stress resulting from tidal loading of the marsh surface and for complex boundary conditions. Model calibration was performed using observed hydraulic data collected during the salt marsh dieback study, and initial model results suggest slow (0.1 cm/day), downward flow through the marsh mud and lateral flow in the confined, sand aquifer at depth with greater flow rates (2 cm/day) near the channel edges. Preliminary porewater radium activities were 0.4, 8.1, 3.0, and 6.6 dpm/L for 223Ra, 224Ra, 226Ra and 228Ra, respectively, with dilution resulting in lower surface water activities by an order of magnitude. Mean bulk radium activities in the surface sediments were 0.9 and 1.0 dpm/g and for the deeper sediments were 1.4 and 1.6 dpm/g for 226Ra and 228Ra, respectively. Paired t-tests between winter and summer surface sediment samples indicated no significant difference in bulk radium activity (P>>0.1). Statistical tests indicate significant seasonal differences in porewater salinity, temperature, and pH (P?0.001), but no significant seasonal differences in porewater radium activity (P>0.05). These preliminary results suggest groundwater transport and generation rates within the aquifer are the primary factors controlling porewater radium activity. Final radium results will be discussed in terms of the groundwater flow model.

Hughes, A. L.; Wilson, A. M.

2011-12-01

141

Application of HEC-RAS 4.0 temperature model to estimate groundwater contributions to Swan Creek, Ontario, Canada  

NASA Astrophysics Data System (ADS)

SummaryThe HEC-RAS 4.0 model has been expanded to include a water quality component which can simulate water temperatures and the movement of contaminants in rivers. Stream temperature is often considered a critical habitat parameter because it affects in stream chemical and biological processes. For streams where groundwater discharge is present, the thermal regime of the surface water system is influenced by the distribution and rate of groundwater discharge. Groundwater provides a source of thermally stable water that can mitigate the effects of diurnal variations and sustain refugia and spawning habitat. In the field, heterogeneous groundwater-surface water interactions can make it very difficult to estimate the amount of groundwater entering a stream. Reach-level stream gains can be highly uncertain when groundwater discharge represents a moderate to small percentage of the total stream flow. In this paper a small southern Ontario creek is modelled in HEC-RAS 4.0 to explore the temperature modelling capabilities of HEC-RAS 4.0. Specifically, the ability to use HEC-RAS 4.0 as a secondary means of estimating groundwater discharge during low-flow conditions is examined using measured stream temperature data.

Drake, Jennifer; Bradford, Andrea; Joy, Doug

2010-08-01

142

Seepage Flows-Groundwater Pollution Investigations.  

National Technical Information Service (NTIS)

Soil structure, ground water flows, and pollutant dispersal from field and laboratory tests were investigated. Soil structure characteristics at the Adelphia Experimental Station were evaluated through measurements in situ and field data analysis in the l...

E. L. Bourodimos T. J. Harlukowicz

1975-01-01

143

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

144

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

145

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

146

Analysis of ground-water flow along a regional flow path of the Midwestern Basins and Arches aquifer system in Ohio  

USGS Publications Warehouse

A cross-sectional analysis of ground-water flow in central-western and northwestern Ohio was done as part of the Midwestern Basins and Arches Regional Aquifer-System Analysis project. The Midwestern Basins and Arches aquifer system is composed of carbonate bedrock of Silurian and Devonian age and overlying glacial flow analysis of the Scioto and Blanchard rivers in the study area were used to describe patrems of ground-water flow, to evaluate stream-aquifer interaction, and to quantify recharge and discharge within the ground-water-flow system along a regional ground-water-flow path. The selected regional flow path begins at a regional topographic high in Logan County, Ohio, and ends in Sandusky Bay (Lake Erie), a regional topographic low. Recharge to the ground-water system along the selected regional flow path was estimated from hydrograph separation of streamflow and averaged 3.24 inches per year. Computer model simulations indicate that 84 percent of the water entering the ground-water system flows less than 5 miles from point of recharge to point of discharge and no deeper than the upper surficial aquifers. The distance and depth that ground water travels and traveltime from point of recharge to point of discharge is controlled largely by where ground water enters the flow system. Ground water entering the flow system in the vicinity of major surface- water divides generally travels further, deeper, and longer than ground water entering the flow system elsewhere along the regional flow path. Particle tracking simulations substantiate the concept that the 80-mile-long regional flow path is within a continuous ground-water basin. Estimated traveltimes for ground-water from the regional high to Sandusky Bay range from 22,000 to 40,700 years, given a range of porosities from 8 to 22 percent for the carbonate-rock aquifer.

Hanover, R. H.

1994-01-01

147

Impact of the Wisconsinian Glaciation on Canadian Continental Groundwater Flow  

NASA Astrophysics Data System (ADS)

During the last glacial period (75 kyr - 10 kyr), the Canadian landscape was almost entirely covered with ice. The Laurentide ice-sheet, the largest of the three North-American ice sheets, reached a thickness of about 4 km and the force exerted by its weight on the earth's crust was sufficient to cause a depression of the surface of about 1 km and an over-pressurization of porewater fluids. These dramatic conditions are suspected to have had a large impact on the groundwater flow system over the whole continent. Although an analysis of the evolution of groundwater flow systems during glacial periods is relevant to a number of problems, such as the long-term stability of high-level spent nuclear-fuel repositories located at depth, very few studies have been conducted to assess the impact of glaciation on deep-seated groundwater flow systems, particularly in a North-American context. A transient, three-dimensional groundwater flow model including the effect of the advective-dispersive redistribution of shield brines was constructed in order to capture the impact of the advance and retreat of the ice sheet over the Canadian landscape. The model is driven by a thermomechanical ice-sheet model of the last glacial cycle [Tarasov and Peltier, 2004] which provides the transient boundary conditions that includes the spatio-temporal distribution of the glacial ice, the elevation of the surface topography, meltwater rates, permafrost thicknesses, as well as temporal changes in sea level along the coastal margins. The evolving surface water drainage patterns and features such as proglacial lakes are also incorporated based on the hydrologic routing calculations performed by Tarasov and Peltier [2005]. The treatment of physical processes related to the influence of the ice sheet on the groundwater flow system such as hydromechanics, isostasy, subglacial melting and permafrost formation are also discussed. Simulation results show that hydraulic heads at depth below the ice sheet increase by several hundred meters and groundwater flow directions also change dramatically from what is observed today. Infiltration of subglacial meltwater also plays a key role in the increase of subsurface hydraulic heads as the meltwater is driven into the subsurface by the weight of the ice.

Lemieux, J.; Sudicky, E. A.; Peltier, W. R.; Tarasov, L.

2005-12-01

148

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

149

A simple daily soil water balance model for estimating the spatial and temporal distribution of groundwater recharge in temperate humid areas  

Microsoft Academic Search

Quantifying the spatial and temporal distribution of natural groundwater recharge is usually a prerequisite for effective groundwater modeling and management. As flow models become increasingly utilized for management decisions, there is an increased need for simple, practical methods to delineate recharge zones and quantify recharge rates. Existing models for estimating recharge distributions are data intensive, require extensive parameterization, and take

W. R. Dripps; K. R. Bradbury

2007-01-01

150

A root zone modelling approach to estimating groundwater recharge from irrigated areas  

NASA Astrophysics Data System (ADS)

SummaryIn irrigated semi-arid and arid regions, accurate knowledge of groundwater recharge is important for the sustainable management of scarce water resources. The Campo de Cartagena area of southeast Spain is a semi-arid region where irrigation return flow accounts for a substantial portion of recharge. In this study we estimated irrigation return flow using a root zone modelling approach in which irrigation, evapotranspiration, and soil moisture dynamics for specific crops and irrigation regimes were simulated with the HYDRUS-1D software package. The model was calibrated using field data collected in an experimental plot. Good agreement was achieved between the HYDRUS-1D simulations and field measurements made under melon and lettuce crops. The simulations indicated that water use by the crops was below potential levels despite regular irrigation. The fraction of applied water (irrigation plus precipitation) going to recharge ranged from 22% for a summer melon crop to 68% for a fall lettuce crop. In total, we estimate that irrigation of annual fruits and vegetables produces 26 hm 3 y -1 of groundwater recharge to the top unconfined aquifer. This estimate does not include important irrigated perennial crops in the region, such as artichoke and citrus. Overall, the results suggest a greater amount of irrigation return flow in the Campo de Cartagena region than was previously estimated.

Jiménez-Martínez, J.; Skaggs, T. H.; van Genuchten, M. Th.; Candela, L.

2009-03-01

151

Correlation between permeability and groundwater flow patterns in carbonate rocks  

NASA Astrophysics Data System (ADS)

Groundwater flow in carbonate rocks is controlled by many factors such as degree of fracture and pore development, weathering and diagenesis. Among these factors, fracture is main factor and can form main flow path. Also, flow patterns in carbonate area are decided by these factors. This study was performed to understand factors controlling permeability and flow patterns in carbonate area and to evaluate correlation between permeability and flow patterns. Data used in this study were collected from many literatures and these data were analyzed and evaluated using graphic and statistical analysis. In many carbonate areas, branching conduit patterns were dominant. Of these areas, permeability was relatively high in areas where moving distance of flow was short and hydraulic gradient was steep. This work was supported by the Energy Resources R&D program of the Korea Institute of Energy Technology Evaluation and Planning (KETEP) grant funded by the Korea government Ministry of Knowledge Economy (No. 2009201030001A).

Park, Y.; Lee, J.; Park, Y.; Keehm, Y.

2011-12-01

152

Basin wide Nitrate-Nitrogen pollution of groundwater, Miyakonojo, Japan, with the relation of the regional Groundwater flow system  

NASA Astrophysics Data System (ADS)

Miyakonojo basin is well-known agriculture area in Southern Kyushu, Japan and highly depends on groundwater resources for their everyday use. Local unconfined groundwater aquifer is widely polluted by Nitrate-Nitrogen originated from agriculture. It will become serious problem if this unconfined Nitrate pollution enlarges into the confined aquifer system which is used for local city water source. However, the detailed groundwater flow system between unconfined and confined aquifer system has not been cleared yet. The detailed three dimensional groundwater flow system study has been done by using existing wells in a basin to understand the three dimensional distribution pattern of Nitrate-Nitrogen in the aquifer. The field sampling for unconfined, intermediate and confined groundwater was done in July, 2005 and February, 2006 for about 200 wells to analyze inorganic water chemistry, hydrogen / oxygen stable isotopes and tritium. For the unconfined groundwater, there exists clear difference for the groundwater flow pattern between the eastern and western basin, which is mostly affected by the surface topography. The unconfined groundwater flowed into the confined aquifer at the eastern part of a basin, while in the western part of a basin the unconfined groundwater on a plateau flowed into the confined aquifer somehow, but most part of the unconfined groundwater has been discharge out to small river valleys between plateaus. While for the confined groundwater, the topographic effect has been disappeared and basin scale groundwater flow from the basin margin toward the basin center is dominated. In the unconfined aquifer, basin wide distribution of Nitrate-Nitrogen content has been recognized and it is relatively higher in the western basin where the cattle farming are dominated. While in the confined aquifer, there are some high Nitrate-Nitrogen spots but do not have regional trend. It is considered that some part of the basin has not distributed the welded tuff layers which exist between unconfined and confined aquifers and this may somehow influences the groundwater flow between unconfined and confined aquifers. Also the existing groundwater flow system based on the groundwater potential distribution clearly relates with the denitrification zone in the confined aquifer, where the Nitrate-Nitrogen reduction has been occurred in an aquifer by the organic products and showed the decreasing tendency along the flow line.

Mikami, K.; Shimada, J.; Zikuzono, Y.

2006-12-01

153

Kriging groundwater solute concentrations using flow coordinates and nonstationary covariance functions  

NASA Astrophysics Data System (ADS)

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

Rivest, M.; Marcotte, D.

2012-11-01

154

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

155

Heat flow and subsurface temperature as evidence for basin-scale ground-water flow, North Slope of Alaska  

USGS Publications Warehouse

Several high-resolution temperature logs were made in each of 21 drillholes and a total of 601 thermal conductivity measurements were made on drill cuttings and cores. Near-surface heat flow (??20%) is inversely correlated with elevation and ranges from a low of 27 mW/m2 in the foothills of the Brooks Range in the south, to a high of 90 mW/m2 near the north coast. Subsurface temperatures and thermal gradients estimated from corrected BHTs are similarly much higher on the coastal plain than in the foothills province to the south. Significant east-west variation in heat flow and subsurface temperature is also observed; higher heat flow and temperature coincide with higher basement topography. The observed thermal pattern is consistent with forced convection by a topographically driven ground-water flow system. Average ground-water (Darcy) velocity in the postulated flow system is estimated to be of the order of 0.1 m/yr; the effective basin-scale permeability is estimated to be of the order of 10-14 m2. -from Authors

Deming, D.; Sass, J. H.; Lachenbruch, A. H.; De Rito, R. F.

1992-01-01

156

Some Analytical Solutions for Groundwater Flow and Transport Equation  

Microsoft Academic Search

This paper presents the use of symmetry reduction method resulting in new exact solutions for the groundwater flow and transport equation. It is assumed that the radionuclides are transported by advection-diffusion in a single fracture and diffusion in the surrounding rock-matrix. The application of one-parameter group reduces the number of independent variables, and consequently the governing PDE of (1+2)-dimension reduces

Effat A. Saied; M. E. Khalifa

2002-01-01

157

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

158

Recharge and Lateral Groundwater Flow Boundary Conditions for the Saturated Zone Site-Scale Flow and Transport Model  

SciTech Connect

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

S. James

2004-10-06

159

Discriminant analysis for estimation of groundwater age from hydrochemistry and well construction: Application to New Zealand aquifers  

NASA Astrophysics Data System (ADS)

Determination of groundwater age is valuable for a variety of reasons covering the spectrum from fundamental scientific research to applied resource management. In New Zealand, tracer methods based on tritium, chlorofluorocarbons (CFCs) and sulfur hexafluoride (SF6) are effective for dating young groundwater because their input concentrations via recharge over the past several decades are accurately known. In this study, tritium, CFC and SF6 concentrations have been measured at over 100 groundwater monitoring sites included in the New Zealand National Groundwater Monitoring Programme, followed by interpretation of groundwater age distribution using the exponential-piston flow model. Interpreted mean residence times ranged from less than one year to more than 100 years, with the 25th, 50th (median) and 75th percentiles being approximately 10, 40 and 100 years, respectively. Classification functions derived from discriminant analysis and based on nine input variables (well depth, electrical conductivity and the concentrations of the ions Na, K, Ca, Mg, HCO3, Cl and SO4) allowed assignment of 71% of the sites to the correct of four age categories (mean residence time ten years or less, 11 to 40 years, 41 to 100 years, or more than 100 years). The discriminant analysis classification functions were more effective than regression methods for estimating groundwater age from hydrochemistry and well depth, and can thus be used to estimate the groundwater age category for any monitoring site in New Zealand.

Daughney, C.; Morgenstern, U.; van der Raaij, R.; Reeves, R.

2009-12-01

160

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

161

Regional stochastic estimation of the groundwater catchment for distributed hydrological modelling  

NASA Astrophysics Data System (ADS)

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

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

2012-04-01

162

Estimation of Groundwater Storage Variations based on Baseflow Recession Analysis  

NASA Astrophysics Data System (ADS)

One of the intrinsic assumptions of the widely used Brutsaert and Nieber (B-N) method for groundwater recession slope analysis is the existence of a general non-linear proportional relationship between (unconfined) aquifer storage and baseflow recession. The parameters in the B-N method estimated from baseflow recession slope curve analysis in principle can be linked to the parameters characterizing aquifer storage-discharge relations. However, this has seldom been tested due to the lack of observed data on groundwater storage. In this study, we test the hypothesis that baseflow recession behaviors depend on the adjacent shallow unconfined aquifer storage by using the daily measurements of water table depth from nine shallow wells in Illinois and the concurrent streamflow data at the nearest gauges. The purpose is to test how much information of groundwater storage variations can be obtained from baseflow recession analysis. The results indicate that baseflow fluctuations in general faithfully reflect the variations in nearby unconfined aquifer storage and a consistent estimation of specific yield can be derived from the data, whereby substantiate the linkage between aquifer storage-discharge relationship and the GW recession parameters. In addition, the following issues are identified for further studies: (1) The interference of recharge to (evaporation from) the underlying aquifers need to be clarified and removed when analyzing winter (summer) recession data; (2) for all the wells analyzed, a threshold depth exists below which baseflow cannot reflect aquifer storage decline usually caused by high evaporation in summer. Finally, the implications of this study to various critical issues in land surface hydrologic modeling are discussed.

Yeh, P. J.; He, X.; Oki, T.

2012-12-01

163

Data Intensive Simulation and Analysis of Groundwater Flow and Transport in the Los Alamos aquifer  

NASA Astrophysics Data System (ADS)

Characterization of the groundwater flow and transport in regional aquifer systems is a challenging task. In most practical cases, there is not sufficient hydrogeologic information that can be applied to evaluate aquifer properties. In addition, the development, execution and analyses of large-scale numerical models are computational demanding requiring advanced high-performance codes and state-of-the-art computational resources. We have developed a complex 3D regional groundwater flow model of the regional aquifer beneath the Los Alamos National Laboratory (LANL) site to provide a better understanding of hydrogeologic properties, recharge sources, groundwater travel times, migration pathways for potential contaminants, and potential contaminant concentrations at water supply wells. The 3D computational grid is generated using sophisticated grid generating software, LaGriT (http://lagrit.lanl.gov). LaGriT allows the use of unstructured meshing strategies, which capture the details of complex groundwater flow of the LANL site, including wellbore geometries and hydrostratigraphy. The numerical simulation is performed using the FEHM (Finite Element Heat and Mass transfer) (http://fehm.lanl.gov) codes. Long-term groundwater level monitoring at LANL started in the mid-1940s; the monitoring data is currently collected at more than 70 regional monitoring wells providing an extensive water-level observation data set. The water-level data represent over 62 years of recorded drawdowns and recovery caused by the spatially and temporally variable pumping at six municipal water-supply wells. The water-level data is applied in the 3D flow model to inversely estimate the aquifer parameters. The model calibration, uncertainty quantification, and sensitivity analyses are performed using the code MADS (Model Analyses and Decision Support; http://ees.lanl.gov/staff/monty/codes/mads). The research utilizes high performance computational resources (multiprocessor clusters) at LANL. In this study, we present the challenges of model development, lessons learned, and insights provided by the model into the LANL aquifer.

Mishra, P. K.; Harp, D.; Miller, T. A.; Vesselinov, V. V.

2011-12-01

164

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

165

Estimating submarine inputs of groundwater and nutrients to a coastal bay using radium isotopes  

Microsoft Academic Search

We have measured the concentrations of nutrients and radium isotopes (223Ra, 224Ra, and 226Ra) in surface seawater and coastal groundwater in Yeoja Bay (in the southern sea of Korea) to estimate submarine groundwater discharge (SGD) and associated nutrient fluxes. In general, the radium and nutrient concentrations in brackish groundwater were an order of magnitude higher than those in ambient bay

Dong-Woon Hwang; Guebuem Kim; Yong-Woo Lee; Han-Soeb Yang

2005-01-01

166

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

167

Groundwater Flow Model of Corrective Action Units 101 and 102: Central and Western Pahute Mesa, Nevada Test Site, Nye County, Nevada, Revision 0  

Microsoft Academic Search

The Pahute Mesa groundwater flow model supports the FFACO UGTA corrective action strategy objective of providing an estimate of the vertical and horizontal extent of contaminant migration for each CAU in order to predict contaminant boundaries. A contaminant boundary is the model-predicted perimeter that defines the extent of radionuclide-contaminated groundwater from underground nuclear testing above background conditions exceeding Safe Drinking

Greg Ruskauff

2006-01-01

168

Detection of deep groundwater flow in a sedimentary basin  

NASA Astrophysics Data System (ADS)

Although temperatures in the Earth’s upper crust are generally dominated by heat conduction they are often disturbed by advection of heat associated with groundwater flow. Aim of the investigation presented here is to develop a method to detect groundwater flow from precise subsurface temperature measurements, as well as to demonstrate their great sensitivity to flow. We propose here to detect advectively disturbed areas from calculated temperatures residuals, i.e. differences between temperatures measured in boreholes and those calculated in a three-dimensional conductive model based on the regional geology. The transient effect of paleoclimate is taken into account by subtracting its present signal from the measured data. If all processes are correctly taken into account, the calculated residuals represent the advective influence on the thermal field. We demonstrate the potential of the method based on data from the German part of the western Molasse Basin (North Alpine foreland basin). The results show that advective temperature anomalies can be detected this way. In order to explain the residuals calculated with respect to the conductive model results, it is necessary to simulate the hydraulic flow regime in a second step. For this purpose we are currently extending the model described above to a quantitative, fully coupled thermal simulation. The results of the conductive simulation are discussed in the light of our preliminarily results of the coupled simulations.

Rühaak, W.; Rath, V.; Clauser, C.

2003-04-01

169

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

170

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

171

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

NASA Astrophysics Data System (ADS)

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

Winter, Thomas C.

172

Hydrogeochemical indicators of groundwater flow systems in the Yangwu River alluvial fan, Xinzhou Basin, Shanxi, China.  

PubMed

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

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

2009-08-01

173

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

174

Development of a Sitewide Groundwater Flow and Radionuclide Transport Model at Idaho National Laboratory  

NASA Astrophysics Data System (ADS)

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

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

2007-12-01

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

Estimated ground-water availability in the Delaware River basin, 1997-2000  

USGS Publications Warehouse

Ground-water availability using a watershed-based approach was estimated for the 147 watersheds that make up the Delaware River Basin. This study, conducted by the U.S. Geological Survey in cooperation with the Delaware River Basin Commission (DRBC), supports the DRBC's Water Resources Plan for the Delaware River Basin. Different procedures were used to estimate ground-water availability for the region underlain by fractured rocks in the upper part of the basin and for surficial aquifers in the region underlain by unconsolidated sediments in the lower part of the basin. The methodology is similar to that used for the Delaware River Basin Commission's Ground-Water Protected Area in Pennsylvania. For all watersheds, ground-water availability was equated to average annual base flow. Ground-water availability for the 109 watersheds underlain by fractured rocks in Delaware, New Jersey, New York, and Pennsylvania was based on lithology and physiographic province. Lithology was generalized by grouping 183 geologic units into 14 categories on the basis of rock type and physiographic province. Twenty-three index streamflow-gaging stations were selected to represent the 14 categories. A base-flow-recurrence analysis was used to determine the average annual 2-, 5-, 10-, 25-, and 50-year-recurrence intervals for each index station. A GIS analysis used lithology and base flow at the index stations to determine the average annual base flow for the 109 watersheds. Average annual base flow for these watersheds ranged from 0.313 to 0.915 million gallons per day per square mile for the 2-year-recurrence interval to 0.150 to 0.505 million gallons per day per square mile for the 50-year-recurrence interval. Ground-water availability for watersheds underlain by unconsolidated surficial aquifers was based on predominant surficial geology and land use, which were determined from statistical tests to be the most significant controlling factors of base flow. Twenty-one index streamflow-gaging stations were selected to represent the 13 categories of predominant surficial geology and land use for the 38 Coastal Plain watersheds. A base-flow-recurrence analysis was used to determine the average annual 2-, 5-, 10-, 25-, and 50-year-recurrence intervals for each group of predominant surficial geology and land use. Average annual base flow for these watersheds ranged from 0.465 to 1.169 million gallons per day per square mile for the 2-year-recurrence interval to 0.178 to 0.670 million gallons per day per square mile for the 50-year-recurrence interval. Estimated 2-, 5-, 10-, 25-, and 50-year annual base-flow-recurrence interval values for each watershed in the Delaware River Basin are considered to be the quantity of ground water available for each watershed over a range of climatic conditions. The recurrence intervals are considered to be relative indicators of climatic difference; the 2-year-recurrence value represents wetter years, and the 50-year-recurrence value represents drier years. The remaining available ground water in each watershed was determined by subtracting current (1997-2000) ground-water withdrawals and consumptive domestic use and adding water recharged by agricultural irrigation and land application of treated-sewage effluent. Ground-water use ranged from 0 to 60.8 percent of available ground water for the 2-year-recurrence interval; it exceeded 25 percent in four watersheds and 50 percent in two watersheds. Ground-water use ranged from 0 to 75.9 percent of available ground water for the 5-year-recurrence interval; it exceeded 25 percent in five watersheds and 50 percent in three watersheds. Ground-water use ranged from 0 to 84.5 percent of available ground water for the 10-year-recurrence interval; it exceeded 25 percent in seven watersheds and 50 percent in four watersheds. Ground-water use ranged from 0 to 103 percent of available ground water for the 25-year-recurrence interval; it exceeded 25 percent in nine watersheds, 5

Sloto, Ronald A.; Buxton, Debra E.

2006-01-01

177

Inferring shallow groundwater flow in saprolite and fractured rock using environmental tracers  

USGS Publications Warehouse

The Ridge and Valley Province of eastern Tennessee is characterized by (1) substantial topographic relief, (2) folded and highly fractured rocks of various lithologies that have low primary permeability and porosity, and (3) a shallow residuum of medium permeability and high total porosity. Conceptual models of shallow groundwater flow and solute transport in this system have been developed but are difficult to evaluate using physical characterization or short-term tracer methods due to extreme spatial variability in hydraulic properties. In this paper we describe how chlorofluorocarbon 12, 3H, and 3He were used to infer groundwater flow and solute transport in saprolite and fractured rock near Oak Ridge, Tennessee. In the shallow residuum, fracture spacings are <0.05 m, suggesting that concentrations of these tracers in fractures and in the matrix have time to diffusionally equilibrate. The relatively smooth nature of tracer concentrations with depth in the residuum is consistent with this model and quantitatively suggests recharge fluxes of 0.2 to 0.4 m yr-. In contrast, groundwater flow within the unweathered rock appears to be controlled by fractures with spacings of the order of 2 to 5 m, and diffusional equilibration of fractures and matrix has not occurred. For this reason, vertical fluid fluxes in the unweathered rock cannot be estimated from the tracer data.

Cook, P. G.; Solomon, D. K.; Sanford, W. E.; Busenberg, E.; Plummer, L. N.; Poreda, R. J.

1996-01-01

178

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

179

NONLINEAR-REGRESSION GROUNDWATER FLOW MODELING OF A DEEP REGIONAL AQUIFER SYSTEM.  

USGS Publications Warehouse

A nonlinear regression groundwater flow model, based on a Galerkin finite-element discretization, was used to analyze steady state two-dimensional groundwater flow in the areally extensive Madison aquifer in a 75,000 mi**2 area of the Northern Great Plains. Regression parameters estimated include intrinsic permeabilities of the main aquifer and separate lineament zones, discharges from eight major springs surrounding the Black Hills, and specified heads on the model boundaries. Aquifer thickness and temperature variations were included as specified functions. The regression model was applied using sequential F testing so that the fewest number and simplest zonation of intrinsic permeabilities, combined with the simplest overall model, were evaluated initially; additional complexities (such as subdivisions of zones and variations in temperature and thickness) were added in stages to evaluate the subsequent degree of improvement in the model results. It was found that only the eight major springs, a single main aquifer intrinsic permeability, two separate lineament intrinsic permeabilities of much smaller values, and temperature variations are warranted by the observed data (hydraulic heads and prior information on some parameters) for inclusion in a model that attempts to explain significant controls on groundwater flow.

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

1986-01-01

180

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

USGS Publications Warehouse

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

Oki, Delwyn S.

1999-01-01

181

Modelling of the groundwater flow in Baltic Artesian Basin  

NASA Astrophysics Data System (ADS)

Baltic Artesian Basin (BAB) is a multi-layered complex hydrogeological system underlying about 480'000 km2 in the territory of Latvia, Lithuania, Estonia, Poland, Russia, Belarus and the Baltic Sea. The model of the geological structure contains 42 layers including aquifers and aquitards from Cambrian up to the Quaternary deposits. The finite element method was employed for the calculation of the steady state three-dimensional groundwater flow with free surface. The horizontal and vertical hydraulic conductivities of geological materials were assumed constant in each of the layers. The Precambrian basement forms the impermeable bottom of the model. The zero water exchange is assumed through the side boundaries of BAB. Simple hydrological model is applied on the surface. The level of the lakes, rivers and the sea is fixed as constant hydraulic head in corresponding mesh points. The infiltration is set as a flux boundary condition elsewhere. Instead of extensive coupling with hydrology model, a constant mean value of 70 mm/year was assumed as an infiltration flux for the whole BAB area and this value was adjusted during the automatic calibration process. Averaged long-term water extraction was applied at the water supply wells with large debits. In total 49 wells in Lithuania (total abstraction 45000 m3/day), 161 in Latvia (184000 m3/day) and 172 in Estonia (24000 m3/day) are considered. The model was calibrated on the statistically weighted (using both spatial and temporal weighting function) borehole water level measurements applying automatic parameter optimization method L-BFGS-B for hydraulic conductivities of each layer. The steady-stade calculations were performed for the situations corresponding to undisturbed situation (1950-ies), intensive groundwater use (1980-ies) and present state situation (after 2000). The distribution of piezometric heads and principal flows inside BAB was analyzed based on the model results. The results demonstrate that generally the flow is directed from southeast to northwest, but the more shallow aquifers show strong influence by local topography. There is an intensive transient flow in Cm aquifer system and this flow is separated from upper layers by thick aquitard O-S. About 25% of the aquifers volume is under free flowing artesian conditions. Acknowledgement The present work has been funded by the European Social Fund project "Establishment of interdisciplinary scientist group and modelling system for groundwater research" (Project No. 2009/0212/1DP/1.1.1.2.0/09/APIA/VIAA/060)

Virbulis, J.; Sennikovs, J.; Bethers, U.

2012-04-01

182

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

183

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

184

A new approach to a hydrochemical study of groundwater flow  

NASA Astrophysics Data System (ADS)

A statistical approach based on a multivariate correlation of various hydrochemical parameters has been developed for the interpretation of groundwater flow lines of the Vasilikon basin in the southern part of the central area of Euboea island in Greece. Water samples, mainly from wells but also from boreholes, were collected and analysed for 44 hydrochemical parameters, from which the conductivity, dissolved O 2, Ca, Mg, chloride, acid-consuming capacity, base-consuming capacity, Si, Fe and As were selected for the evaluation. After normalization of each parameter by z-transformation—to equalize the influence of parameters with small and large variations—a classification of the sampling stations was obtained by cluster analysis. By the use of the same z-transformed data the degree of similarity of element-concentration ( z-transformed) profiles between the central sampling points and the surrounding sampling points was investigated. The resulting radially distributed correlation vectors were reduced to the main axis of an ellipse, so that flow lines or trend of groundwater movements became visible. The results of this method were also compared with hydrogeological observations of the Vasilikon basin.

Ochsenkühn, K. M.; Kontoyannakos, J.; Ochsenkühn-Petropulu, M.

1997-07-01

185

Flow and geochemistry along shallow ground-water flowpaths in an agricultural area in southeastern Wisconsin  

USGS Publications Warehouse

Water-quality and geohydrologic data were collected from 19 monitor wells and a stream in an agricultural area in southeastern Wisconsin. These sites were located along a 2,700-ft transect from a local ground-water high to the stream. The transect is approximately parallel to the horizontal direction of ground-water flow at the water table. Most of the wells were installed in unconsolidated deposits at five locations along the transect and include an upgradient well nest, a midgradient well nest, a downgradient well nest, wells in the lowland area near the stream, and wells installed in the stream bottom. The data collected from this study site were used to describe the water quality and geohydrology of the area and to explain and model the variations in water chemistry along selected ground-water flowpaths. Water samples from most wells and the stream were analyzed for major ions, nutrients, pesticides, dissolved organic carbon, aluminum, tritium, CFCs, 15N, 18O, and dissolved gases. Measurements of temperature, pH, specific conductance, and dissolved oxygen were made in the field. Concentrations of all dissolved constituents were below Wisconsin ground-water quality enforcement standards. The concentrations of both nitrate and ammonium in precipitation concentrated by evapotranspiration are roughly equal to the concentrations of either in the shallow ground waters. The nitrogen and oxygen isotope data, however, indicate that soil ammonium, ammonium fertilizer, and animal waste are possible nitrate sources. Concentrated precipitation can also supply dissolved sulfate to the shallow ground waters and may be a principal source of pesticides to the ground water. However, some input of dissolved chloride to the ground water from mineral or anthropogenic sources is necessary. X-ray diffraction analyses of samples from 2 cores show the most abundant mineral to be dolomite, with subordinate quartz, microcline, and plagioclase, and minor amounts of mica, hornblende, and chlorite. Hydraulic conductivities determined from slug tests at selected wells range from 0.006 to 55 feet per day, with most values between 0.4 and 12 feet per day. A cross-sectional ground-water flow model, representing the water-table flow system, was developed for the site and was used to identify possible ground-water flowpaths for geochemical modeling. The model was calibrated against measured water levels and was most sensitive to variation in recharge and hydraulic conductivity. The calibrated model shows that downward flow from shallow to deeper wells within a nest may occur at the upgradient and midgradient well nests, but that flow from each well nest travels beneath downgradient nests to the stream. Pathline and travel-time analysis performed on the calibrated flow-model output yielded travel times that range from 5.8 to 59 years with a recharge of 4 inches per yr. Recharge dates based on tritium and CFC concentrations range from pre-1955 to 1986 and are consistent with flowpaths and travel times in the calibrated flow model. Changes in water quality along ground-water flowpaths were evaluated using the geochemical model PHREEQC. Geochemical mole balance models of shallow ground-water formation show that the principal reaction, by an order of magnitude, is dissolution of dolomite with CO2. Concentration factors in the mole-balance models range from 1 to 11, with most values between 5 and 10, which provides independent support for the concentration factor of 8 based on recharge estimates used in the flow model. Ground water recharging at mid- and downgradient wells is oxic and contains dissolved nitrate, whereas the ground water discharging to the stream is anoxic and contains dissolved ammonium. Redox environments were defined at each well on the basis of relative concentrations of various dissolved redox-active species. Chemically permissible flowpaths inferred from the observed sequence of redox environments at well sites are consisten

Saad, D. A.; Thorstenson, D. C.

1998-01-01

186

Heat transport by groundwater flow during the Baikal rift evolution  

NASA Astrophysics Data System (ADS)

A two-dimensional modelling study of sedimentation, fluid flow, and heat flow in the Baikal rift basin undergoing flank uplift and basin subsidence has been performed in order to understand the impact of these processes on the surface heat flow signal. Heat flow anomalies of different scales and magnitudes have been observed at the sediment surface of the lake Baikal basin, and the presence of a hydrothermal vent suggests that fluids play an important role in the regional distribution of heat flow. The BASIN-code applied for this study allows to simulate topographically and compaction-driven hydrodynamical fluid flow and coupled heat transfer. The flank uplift history provides the basis for a regional groundwater circulation towards the central basin area, with predicted Darcy velocities at present-day situation in the basement varying between 1 and 100 cm/year. Within the basin, the presence of aquifers and the pinch-out layering has a major control on the flow field, and compaction-driven flow velocities are strongly altered when combined with topography-driven flow. When velocities in the basement are larger than several centimeters per year, the regional fluid circulation is an effective mechanism of heat redistribution. Heat is brought from the flanks towards the basin area, with largest heat transported at a depth of 1-2 km at both sides. During the flank uplift, heat advection increases, with secondary variation related to the deposition of sedimentary layers. The heat flow is increased over the basin and reduced in the flanks, with a total heat output balance always positive. The extra heat output over the modelled transection is 2-10% of the initial heat output. The maximum computed heat fluxes are smaller than measured in the heat flow anomalies of the lake Baikal basin. Nevertheless, the model suggests that flow in the sedimentary basin combined with a topographically driven heat advection in the surrounding basement is a sufficient mechanism to account for the increased heat flow over the basin and the main features of the heat flow distribution.

Poort, Jeffrey; Polyansky, Oleg

2002-06-01

187

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

188

Spatial variability analysis of combining the water quality and groundwater flow model to plan groundwater and surface water management in the Pingtung plain  

NASA Astrophysics Data System (ADS)

As a result of rapid economic growth in the Pingtung Plain, the use of groundwater resources has changed dramatically. The groundwater is quite rich in the Pingtung plain and the most important water sources. During the several decades, a substantial amount of groundwater has been pumped for the drinking, irrigation and aquaculture water supplies. However, because the sustainable use concept of groundwater resources is lack, excessive pumping of groundwater causes the occurrence of serious land subsidence and sea water intrusion. Thus, the management and conservation of groundwater resources in the Pingtung plain are considerably critical. This study aims to assess the conjunct use effect of groundwater and surface water in the Pingtung plain on recharge by reducing the amount of groundwater extraction. The groundwater quality variability and groundwater flow models are combined to spatially analyze potential zones of groundwater used for multi-purpose in the Pingtung Plain. First, multivariate indicator kriging (MVIK) is used to analyze spatial variability of groundwater quality based on drinking, aquaculture and irrigation water quality standards, and probabilistically delineate suitable zones in the study area. Then, the groundwater flow model, Processing MODFLOW (PMWIN), is adopted to simulate groundwater flow. The groundwater flow model must be conducted by the calibration and verification processes, and the regional groundwater recovery is discussed when specified water rights are replaced by surface water in the Pingtung plain. Finally, the most suitable zones of reducing groundwater use are determined for multi-purpose according to combining groundwater quality and quantity. The study results can establish a sound and low-impact management plan of groundwater resources utilization for the multi-purpose groundwater use, and prevent decreasing ground water tables, and the occurrence of land subsidence and sea water intrusion in the Pingtung plain.

Chen, Ching-Fang; Chen, Jui-Sheng; Jang, Cheng-Shin

2014-05-01

189

Analysis of confidence in continental-scale groundwater recharge estimates for Africa using a distributed water balance model  

NASA Astrophysics Data System (ADS)

There is a growing need for improved access to reliable water in Africa as population and food production increases. Currently approximately 300 million people do not have access to a secure source of safe drinking water. To meet these current and future demands, groundwater will need to be increasingly abstracted; groundwater is more reliable than surface water sources due to its relatively long response time to meteorological stresses and therefore is likely to be a more secure water resource in a more variable climate. Recent studies also quantified the volumes of groundwater potentially available which suggest that, if exploited, groundwater could help to meet the demand for fresh water. However, there is still considerable uncertainty as to how these resources may respond in the future due to changes in groundwater recharge and abstraction. Understanding and quantifying groundwater recharge is vital as it forms a primary indicator of the sustainability of underlying groundwater resources. Computational hydrological models provide a means to do this, but the complexity of recharge processes in Africa mean that these simulations are often highly uncertain. This study aims to evaluate our confidence in simulating groundwater recharge over Africa based on a sensitivity analysis using a distributed hydrological model developed by the British Geological Survey, ZOODRM. The model includes land surface, canopy, river, soil and groundwater components. Each component is able to exchange water and as such, forms a distributed water balance of Africa. The components have been parameterised using available spatial datasets of African vegetation, land-use, soil and hydrogeology while the remaining parameters have been estimated by calibrating the model to available river flow data. Continental-scale gridded precipitation and potential evapotranspiration datasets, based on remotely sensed and ground observations, have been used to force the model. Following calibration, the sensitivity analysis has been undertaken in two stages. For the first stage, individual parameters are perturbed from each component of the model. For the second stage, different methods for calculating groundwater recharge are introduced. Both stages aim to investigate which aspects of the model most impact on groundwater recharge and consequently how confidently we can simulate the complex recharge processes that occur in Africa using large scale hydrological models. Preliminary results from the analysis indicate the parameters that control runoff generation from the land surface and the choice of groundwater recharge calculation method both have a significant impact on groundwater recharge simulations.

Mackay, Jonathan; Mansour, Majdi; Bonsor, Helen; Pachocka, Magdalena; Wang, Lei; MacDonald, Alan; Macdonald, David; Bloomfield, John

2014-05-01

190

Investigations of groundwater system and simulation of regional groundwater flow for North Penn Area 7 Superfund site, Montgomery County, Pennsylvania  

USGS Publications Warehouse

Groundwater in the vicinity of several industrial facilities in Upper Gwynedd Township and vicinity, Montgomery County, in southeast Pennsylvania has been shown to be contaminated with volatile organic compounds (VOCs), the most common of which is the solvent trichloroethylene (TCE). The 2-square-mile area was placed on the National Priorities List as the North Penn Area 7 Superfund site by the U.S. Environmental Protection Agency (USEPA) in 1989. The U.S. Geological Survey (USGS) conducted geophysical logging, aquifer testing, and water-level monitoring, and measured streamflows in and near North Penn Area 7 from fall 2000 through fall 2006 in a technical assistance study for the USEPA to develop an understanding of the hydrogeologic framework in the area as part of the USEPA Remedial Investigation. In addition, the USGS developed a groundwater-flow computer model based on the hydrogeologic framework to simulate regional groundwater flow and to estimate directions of groundwater flow and pathways of groundwater contaminants. The study area is underlain by Triassic- and Jurassic-age sandstones and shales of the Lockatong Formation and Brunswick Group in the Mesozoic Newark Basin. Regionally, these rocks strike northeast and dip to the northwest. The sequence of rocks form a fractured-sedimentary-rock aquifer that acts as a set of confined to partially confined layers of differing permeabilities. Depth to competent bedrock typically is less than 20 ft below land surface. The aquifer layers are recharged locally by precipitation and discharge locally to streams. The general configuration of the potentiometric surface in the aquifer is similar to topography, except in areas affected by pumping. The headwaters of Wissahickon Creek are nearby, and the stream flows southwest, parallel to strike, to bisect North Penn Area 7. Groundwater is pumped in the vicinity of North Penn Area 7 for industrial use, public supply, and residential supply. Results of field investigations by USGS at the site and results from other studies support, and are consistent with, a conceptual model of a layered leaky aquifer where the dip of the beds has a strong control on hydraulic connections in the groundwater system. Connections within and (or) parallel to bedding tend to be greater than across bedding. Transmissivities of aquifer intervals isolated by packers ranged over three orders of magnitude [from about 2.8 to 2,290 square feet per day (ft2/d) or 0.26 to 213 square meters per day (m2/d)], did not appear to differ much by mapped geologic unit, but showed some relation to depth being relatively smaller in the shallowest and deepest intervals (0 to 50 ft and more than 250 ft below land surface, respectively) compared to the intermediate depth intervals (50 to 250 ft below land surface) tested. Transmissivities estimated from multiple-observation well aquifer tests ranged from about 700 to 2,300 ft2/d (65 to 214 m2/d). Results of chemical analyses of water from isolated intervals or monitoring wells open to short sections of the aquifer show vertical differences in concentrations; chloride and silica concentrations generally were greater in shallow intervals than in deeper intervals. Chloride concentrations greater than 100 milligrams per liter (mg/L), combined with distinctive chloride/bromide ratios, indicate a different source of chloride in the western part of North Penn Area 7 than elsewhere in the site. Groundwater flow at a regional scale under steady-state conditions was simulated by use of a numerical model (MODFLOW-2000) for North Penn Area 7 with different layers representing saprolite/highly weathered rock near the surface and unweathered competent bedrock. The sedimentary formations that underlie the study area were modeled using dipping model layers for intermediate and deep zones of unweathered, fractured rock. Horizontal cell model size was 100 meters (m) by 100 meters (328 ft by 328 ft), and model layer thickness ranged from 6 m (19.7 ft) representing shallow weathered rock and saprolite up to 200 m (656 ft) representing deeper

Senior, Lisa A.; Goode, Daniel J.

2013-01-01

191

Hydrogeology and simulation of ground-water flow, Picatinny Arsenal and vicinity, Morris County, New Jersey  

USGS Publications Warehouse

Ground-water flow in glacial sediments and bedrock at Picatinny Arsenal, N.J., was simulated by use of a three-dimensional finite-difference ground- water-flow model. The modeled area includes a 4.3-square-mile area that extends from Picatinny Lake to the Rockaway River. Most of the study area is bounded by the natural hydrologic boundaries of the ground-water system. eophysical logs, lithologic logs, particle-size data, and core data from selected wells and surface geophysical data were analyzed to define the hydrogeologic framework. Hydrogeologic sections and thickness maps define six permeable and three low-permeability layers that are represented in the model as aquifers and confining units, respectively. Hydrologic data incorporated in the model include a rate of recharge from precipitation of 22 inches per year, estimated from long-term precipitation records and estimates of evapotranspiration. Additional recharge from infiltration along valleys was estimated from measured discharge of springs along the adjacent valley walls and from estimates of runoff from upland drainage that flows to the valley floor. Horizontal and vertical hydraulic conductivities of permeable and low-permeability layers were estimated from examination of aquifer-test data, gamma-ray logs, borehole cuttings, and previously published data. Horizontal hydraulic conductivities in glacial sediments range from 10 to 380 feet per day. Vertical hydraulic conductivities of the low-permeability layers range from 0.01 to 0.7 feet per day. The model was calibrated by simulating steady-state conditions during 1989-93 and by closely matching simulated and measured ground-water levels, vertical ground-water-head differences, and streamflow gain and loss. Simulated steady-state potentiometric- surface maps produced for the six permeable layers indicate that ground water in the unconfined material within Picatinny Arsenal flows predominantly toward the center of the valley, where it discharges to Green Pond Brook. Beneath the upper confining unit, ground water flows southwestward, down the valley. Between First Street and Farley Avenue, the upper confining unit pinches out near the valley walls, resulting in a major input of water to, and causing a local potentiometric high in, the underlying aquifer layers. Ground-water-flow directions southwest of the southern arsenal boundary are predominantly to the Rockaway River.

Voronin, L. M.; Rice, D. E.

1996-01-01

192

Stream and Pseudopotential Functions in Visualizing Groundwater Flow and Transport Processes  

NASA Astrophysics Data System (ADS)

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

Matanga, George B.

1996-04-01

193

The representative stream length for estimating surface water-groundwater exchange using Darcy’s Law  

NASA Astrophysics Data System (ADS)

Groundwater discharge to streams is spatially variable. We often estimate this flux based on an averaged measurement of hydraulic gradient and local estimate of hydraulic conductivity. It is important to understand how this estimated flux value relates to the flux into the stream. In this study we introduce the concept of representative stream length. The estimated flux value best represents the groundwater discharge over the representative stream length. We simulated groundwater discharge to a stream using synthetic stochastic hydraulic conductivity fields to investigate the impact of heterogeneity (variance and correlation length) on the estimated groundwater discharge and the representative stream length of this discharge. To obtain estimates of hydraulic conductivity between the stream and piezometer, the groundwater head response to a known change in stream stage was simulated and analyzed using a well-known analytical solution. The results of the theoretical investigation showed that the representative stream length of the groundwater discharge estimate was approximately equal to the distance of the piezometer from the stream, that is, groundwater discharge estimated using Darcy’s law from a piezometer 50 m from a stream will approximately represent the discharge occurring over a 50 m length of the stream. Furthermore, the results suggest that the variability in the estimated groundwater discharge significantly reduced when the distance of the piezometer from the stream increased. A field experiment was conducted using two controlled stream-stage change tests and found that results were consistent with the theoretical experiment. That is, as the distance of the piezometer from the stream increased, the variability in discharge estimates reduced. The implication of this finding is that future studies estimating groundwater discharge to streams applying Darcy’s law need to consider the representative stream length, as this will impact the spatial scale over which the discharge estimate can be applied.

Noorduijn, Saskia L.; Harrington, Glenn A.; Cook, Peter G.

2014-05-01

194

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

195

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

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

196

ESTIMATING RESIDENTIAL INDOOR AIR IMPACTS DUE TO GROUNDWATER CONTAMINATION  

Microsoft Academic Search

ABSTRACT Key words: chlorinated, decisions, groundwater, residential, risk The reliability of making,risk-based corrective action (RBCA) decisions using ASTM methods was evaluated. Indoor air quality (IAQ) testing results for 153 residential homes in 1998 at a site in Denver, Colo., were evaluated in this study. Decisions regarding groundwater remediation and indoor air mitigation in resi- dences located over a shallow groundwater,plume

D. w. Kurz

197

Estimating the dynamics of groundwater input into the coastal zone via continuous radon-222 measurements.  

PubMed

Submarine groundwater discharge (SGD) into the coastal zone has received increased attention in the last few years as it is now recognized that this process represents an important pathway for material transport. Assessing these material fluxes is difficult, as there is no simple means to gauge the water flux. To meet this challenge, we have explored the use of a continuous radon monitor to measure radon concentrations in coastal zone waters over time periods from hours to days. Changes in the radon inventories over time can be converted to fluxes after one makes allowances for tidal effects, losses to the atmosphere, and mixing with offshore waters. If one assumes that advective flow of radon-enriched groundwater (pore waters) represent the main input of 222Rn in the coastal zone, the calculated radon fluxes may be converted to water fluxes by dividing by the estimated or measured 222Rn pore water activity. We have also used short-lived radium isotopes (223Ra and 224Ra) to assess mixing between near-shore and offshore waters in the manner pioneered by. During an experiment in the coastal Gulf of Mexico, we showed that the mixing loss derived from the 223Ra gradient agreed very favorably to the estimated range based on the calculated radon fluxes. This allowed an independent constraint on the mixing loss of radon-an important parameter in the mass balance approach. Groundwater discharge was also estimated independently by the radium isotopic approach and was within a factor of two of that determined by the continuous radon measurements and an automated seepage meter deployed at the same site. PMID:12860087

Burnett, William C; Dulaiova, Henrieta

2003-01-01

198

Effects of Faults on Groundwater Flow for the Yucca Flat Basin, Nevada Test Site  

Microsoft Academic Search

The hydrostratigraphic model for the Yucca Flat basin on the Nevada Test Site contains over 100 faults which are thought to play a major role in the groundwater flow system. The effect of the faults will be incorporated into the conceptual groundwater flow model for Yucca Flat. Faults act as permeability structures depending on the nature of the fault core

W. Fryer; R. Dickerson

2008-01-01

199

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

200

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.

201

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

202

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

USGS Publications Warehouse

A two-dimensional, steady-state, areal ground-water flow model was developed for the island of Molokai, Hawaii, to enhance the understanding of (1) the conceptual framework of the ground-water flow system, (2) the distribution of aquifer hydraulic properties, and (3) the regional effects of ground-water withdrawals on water levels and coastal discharge. The model uses the finite-element code AQUIFEM-SALT, which simulates flow of fresh ground water in systems that may have a freshwater lens floating on denser underlying saltwater. Model results are in agreement with the general conceptual model of the flow system on Molokai, where ground water flows from the interior, high-recharge areas to the coast. The model-calculated ground-water divide separating flow to the northern and southern coasts lies to either the north or the south of the topographic divide but is generally not coincident with the topographic divide. On the basis of model results, the following horizontal hydraulic conductivities were estimated: (1) 1,000 feet per day for the dike-free volcanic rocks of East and West Molokai, (2) 100 feet per day for the marginal dike zone of the East Molokai Volcano, (3) 2 feet per day for the West Molokai dike complex, (4) 0.02 feet per day for the East Molokai dike complex, and (5) 500 feet per day for the Kalaupapa Volcanics. Three simulations to determine the effects of proposed ground-water withdrawals on water levels and coastal discharge, relative to model-calculated water levels and coastal discharge for 1992-96 withdrawal rates, show that the effects are widespread. For a withdrawal rate of 0.337 million gallons per day from a proposed well about 4 miles southeast of Kualapuu and 3 miles north of Kamiloloa, the model-calculated drawdown of 0.01 foot or more extends 4 miles southeast and 6 miles northwest from the well. For a withdrawal rate of 1.326 million gallons per day from the same well, the model-calculated drawdown of 0.01 foot or more extends 6 miles southeast and 9 miles northwest from the well. In a third scenario, the withdrawal rate from an existing well near Kualapuu was increased by 0.826 million gallons per day. The model-calculated drawdown of 0.01 foot or more extends 6 miles southeast and 8 miles northwest from the well. In all scenarios, coastal discharge is reduced by an amount equal to the additional withdrawal. Additional data needed to improve the understanding of the ground-water flow system on Molokai include: (1) a wider spatial distribution and longer temporal distribution of water-levels, (2) independent estimates of hydraulic conductivity, (3) improved recharge estimates, (4) information about the vertical distribution of salinity in ground water, (5) streamflow data at additional sites, and (6) improved information about the subsurface geology.

Oki, Delwyn S.

1997-01-01

203

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

204

Estimating recharge rate from groundwater age using a simplified analytical approach: Applicability and error estimation in heterogeneous porous media  

NASA Astrophysics Data System (ADS)

High-K lenses can induce complex groundwater age distributions.Quantifying recharge rate error requires a priori knowledge of heterogeneity.The average of multiple unbiased samples may provide a reasonable estimate.

Kozuskanich, John; Simmons, Craig T.; Cook, Peter G.

2014-04-01

205

Ground-water flow and quality near Canon City, Colorado  

USGS Publications Warehouse

Water in aquifers that underlie the Lincoln Park area near Canon City, Colorado, contains measurable concentrations of chemical constituents that are similar to those in raffinate (liquid waste) produced by a nearby uranium ore processing mill. The objective of this study was to expand the existing geohydrologic data base by collecting additional geohydrologic and water quality, in order to refine the description of the geohydrologic and geochemical systems in the study area. Geohydrologic data were collected from nine tests wells drilled in the area between the U.S. Soil Conservation Service dam and Lincoln Park. Lithologic and geophysical logs of these wells indicated that the section of Vermejo Formation penetrated consisted of interbedded sandstone and shale. The sandstone beds had a small porosity and small hydraulic conductivity. Groundwater flow from the U.S. Soil Conservation Service dam to Lincoln Park seemed to be along an alluvium-filled channel in the irregular and relatively undescribed topography of the Vermejo Formation subcrop. North of the De Weese Dye Ditch, the alluvium becomes saturated and groundwater generally flows to the northeast. Water samples from 28 sites were collected and analyzed for major ions and trace elements; selected water samples also were analyzed for stable isotopes; samples were collected from wells near the uranium ore processing mill, from privately owned wells in Lincoln Park, and from the test wells drilled in the intervening area. Results from the quality assurance samples indicate that cross-contamination between samples from different wells was avoided and that the data are reliable. Water in the alluvial aquifer underlying Lincoln Park is mainly a calcium bicarbonate type. Small variations in the composition of water in the alluvial aquifer appears to result from a reaction of water leaking from the De Weese Dye Ditch with alluvial material. Upward leakage from underlying aquifers does not seem to be significant in determining the chemical composition of water in the alluvial aquifer. (Author 's abstract)

Hearne, G. A.; Litke, D. W.

1987-01-01

206

A simple daily soil–water balance model for estimating the spatial and temporal distribution of groundwater recharge in temperate humid areas  

Microsoft Academic Search

Quantifying the spatial and temporal distribution of natural groundwater recharge is usually a prerequisite for effective\\u000a groundwater modeling and management. As flow models become increasingly utilized for management decisions, there is an increased\\u000a need for simple, practical methods to delineate recharge zones and quantify recharge rates. Existing models for estimating\\u000a recharge distributions are data intensive, require extensive parameterization, and take

W. R. Dripps; K. R. Bradbury

2007-01-01

207

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

208

Simulation of the shallow groundwater-flow system near the Hayward Airport, Sawyer County, Wisconsin  

USGS Publications Warehouse

There are concerns that removal and trimming of vegetation during expansion of the Hayward Airport in Sawyer County, Wisconsin, could appreciably change the character of a nearby cold-water stream and its adjacent environs. In cooperation with the Wisconsin Department of Transportation, a two-dimensional, steady-state groundwater-flow model of the shallow groundwater-flow system near the Hayward Airport was refined from a regional model of the area. The parameter-estimation code PEST was used to obtain a best fit of the model to additional field data collected in February 2007 as part of this study. The additional data were collected during an extended period of low runoff and consisted of water levels and streamflows near the Hayward Airport. Refinements to the regional model included one additional hydraulic-conductivity zone for the airport area, and three additional parameters for streambed resistance in a northern tributary to the Namekagon River and in the main stem of the Namekagon River. In the refined Hayward Airport area model, the calibrated hydraulic conductivity was 11.2 feet per day, which is within the 58.2 to 7.9 feet per day range reported for the regional glacial and sandstone aquifer, and is consistent with a silty soil texture for the area. The calibrated refined model had a best fit of 8.6 days for the streambed resistance of the Namekagon River and between 0.6 and 1.6 days for the northern tributary stream. The previously reported regional groundwater-recharge rate of 10.1 inches per year was adjusted during calibration of the refined model in order to match streamflows measured during the period of extended low runoff; this resulted in an optimal groundwater-recharge rate of 7.1 inches per year during this period. The refined model was then used to simulate the capture zone of the northern tributary to the Namekagon River.

Hunt, Randall J.; Juckem, Paul F.; Dunning, Charles P.

2010-01-01

209

Use of self-potential (SP) method to understand the regional groundwater flow system  

NASA Astrophysics Data System (ADS)

The self-potential method (SP method) is one of the geophysical explorations technique originally used to explore the mineral deposit for mining purposes. Recently, this technique has been applied to understand the geothermal fluid flow in and around the volcanic area. As there exists various factors to affect the surface SP measurement, it is rather difficult to find out the major cause of self-potential generation because their complexity of the generation mechanism. In this application, the behavior of groundwater flow is thought to be as a kind of noise. However, in case of non geothermal area, groundwater flow flux should create substantial self potential at the area which is less complex than geothermal area. The self-potential created by the groundwater flow is mainly caused by the streaming potential represented by the electrokinetic factors such as groundwater potential and the ground resistivity (Ishido and Mizutani,1981). As there exist little SP study to understand groundwater flow system, we have conducted the field SP measurement and its numerical model consideration in the clear groundwater flow existing area. A basin scale groundwater flow region including the mountainous ridge to the coastal area within one river-water catchment basin, which is geologically composed by the volcanic lava and tuff-breccia bedrock, was selected to apply the SP method_DThe study area is Shiranui town, Kumamoto, Kyusyu, Japan. In this area, following multi-hydrological studies have been conducted to understand the groundwater flow regime of the area: groundwater flow system study with observation boreholes and eivironmental isotopes, hydrometric observation for river discharge and precipitation for the regional water budget, micro-meteorological observation at different vegetation and altitude for the evapotranspiration measurement, submarine groundwater discharge investigation, geological borehole drilling, and 3D groundwater flow simulation, etc. The SP measurement results clearly show the regional groundwater flow characteristics revealed by the groundwater potential and environmental isotope study. Also the observed SP pattern could be reasonably explained by the result of preliminary self-potential numeric modeling with the potential data by the groundwater flow simulation for a simple mountain slope.

Satou, S.; Shimada, J.; Goto, T.

2005-12-01

210

Cash flow estimation practices in Mediterranean countries  

Microsoft Academic Search

Purpose – To examine, determine, investigate and compare the extent to which enterprises in Greece and Cyprus use the theoretical framework to evaluate investments which are the discouraging factors concerning the use of this framework with particular emphasis to investigate the type, size and percentage of total capital expenditures detailed cash flow estimates; cash flow estimation practices and forecasting errors

Ioannis T. Lazaridis

2006-01-01

211

Estimation of nutrient supply by groundwater in a tidal river, Seto Inland Sea region, Japan, using 222Rn  

NASA Astrophysics Data System (ADS)

Ground water discharge to the oceans is significant as nutrient supply (Slomp et al, 2004 etc). In coastal urban area, land fill has generally been conducted in offshore and tidal flat. Groundwater gradient is generally declined by these constructions of new lands, and submarine groundwater discharge tends to stop in coastal areas. On the other hand, groundwater would discharge to rivers in a terrestrial area. In the research, we aimed to estimate the nutrient supply by groundwater to the tidal river. The study area is located on the river mouth area of Asahi River in Seto Inland Sea watershed, western Japan. We collected water samples at one station of the river mouth area for the analysis of 222Rn, nutrient and inorganic elements at two hours interval from a low tide to the next low tide in a low and high flow period, respectively. In addition, groundwater near the river sampling station, bottom sea water in Seto Inland Sea, and river water at 4 points from the station to the 4km upstream area were collected. The hourly changes in 222Rn and nutrient concentrations at the river mouth station in low flow period of July 13, 2009 are shown in Figure 1. The low tides were at 9:00 and 21:00. The 222Rn concentration was lower at the high tide, and this value was almost same to the concentration at the point of 4km upstream. On the other hand, the 222Rn concentration was highest at the low tide, and it was twice of that at the high tide. The 222Rn of groundwater was one order higher than that of the river. These results suggested the groundwater discharges to the river at the low tide and it would stop at the high tide, respectively. In addition, comparative variations of dissolved nitrate and phosphorus were indicated that the nitrate was almost constant, however the phosphorus changed along with the 222Rn variation. This suggests that nitrate source was the river water from the upstream area, while phosphorus source was the groundwater. In the high flow period, the river discharge was one order larger than that in the low flow period. Therefore, 222Rn and phosphorus signals would became smaller than that in the low flow period.

Kato, Y.; Onodera, S.; Shimizu, Y.; Oyagi, H.; Saito, M.; Kitaoka, K.; Moriyama, Y.

2009-12-01

212

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

213

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

USGS Publications Warehouse

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

Luukkonen, Carol L.

2010-01-01

214

Fair bandwidth share using flow number estimation  

Microsoft Academic Search

We propose a novel active queue management mechanism, called flow number estimation (FNE), which is able to achieve network fair bandwidth share and tolerate burst traffic. FNE manages the length of a FIFO queue effectively and guarantees a reasonable queuing delay for every flow. The feature of traffic regulated by FNE is similar to that by the per-flow fair queuing

Jung-Shian Li; Ming-Shiann Leu

2002-01-01

215

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

216

Hydrogeology and Ground-Water Flow in the Opequon Creek Watershed area, Virginia and West Virginia  

USGS Publications Warehouse

Due to increasing population and economic development in the northern Shenandoah Valley of Virginia and West Virginia, water availability has become a primary concern for water-resource managers in the region. To address these issues, the U.S. Geological Survey (USGS), in cooperation with the West Virginia Department of Health and Human Services and the West Virginia Department of Environmental Protection, developed a numerical steady-state simulation of ground-water flow for the 1,013-square-kilometer Opequon Creek watershed area. The model was based on data aggregated for several recently completed and ongoing USGS hydrogeologic investigations conducted in Jefferson, Berkeley, and Morgan Counties in West Virginia and Clarke, Frederick, and Warren Counties in Virginia. A previous detailed hydrogeologic assessment of the watershed area of Hopewell Run (tributary to the Opequon Creek), which includes the USGS Leetown Science Center in Jefferson County, West Virginia, provided key understanding of ground-water flow processes in the aquifer. The ground-water flow model developed for the Opequon Creek watershed area is a steady-state, three-layer representation of ground-water flow in the region. The primary objective of the simulation was to develop water budgets for average and drought hydrologic conditions. The simulation results can provide water managers with preliminary estimates on which water-resource decisions may be based. Results of the ground-water flow simulation of the Opequon Creek watershed area indicate that hydrogeologic concepts developed for the Hopewell Run watershed area can be extrapolated to the larger watershed model. Sensitivity analyses conducted as part of the current modeling effort and geographic information system analyses of spring location and yield reveal that thrust and cross-strike faults and low-permeability bedding, which provide structural and lithologic controls, respectively, on ground-water flow, must be incorporated into the model to develop a realistic simulation of ground-water flow in the larger Opequon Creek watershed area. In the model, recharge for average hydrologic conditions was 689 m3/d/km2 (cubic meters per day per square kilometer) over the entire Opequon Creek watershed area. Mean and median measured base flows at the streamflow-gaging station on the Opequon Creek near Martinsburg, West Virginia, were 604,384 and 349,907 m3/d (cubic meters per day), respectively. The simulated base flow of 432,834 m3/d fell between the mean and median measured stream base flows for the station. Simulated base-flow yields for subwatersheds during average conditions ranged from 0 to 2,643 m3/d/km2, and the median for the entire Opequon Creek watershed area was 557 m3/d/km2. A drought was simulated by reducing model recharge by 40 percent, a rate that approximates the recharge during the prolonged 16-month drought that affected the region from November 1998 to February 2000. Mean and median measured streamflows for the Opequon Creek watershed area at the Martinsburg, West Virginia, streamflow-gaging station during the 1999 drought were 341,098 and 216,551 m3/d, respectively. The simulated drought base flow at the station of 252,356 m3/d is within the range of flows measured during the 1999 drought. Recharge was 413 m3/d/km2 over the entire watershed during the simulated drought, and was 388 m3/d/km2 at the gaging station. Simulated base-flow yields for drought conditions ranged from 0 to 1,865 m3/d/km2 and averaged 327 m3/d/km2 over the entire Opequon Creek watershed. Water budgets developed from the simulation results indicate a substantial component of direct ground-water discharge to the Potomac River. This phenomenon had long been suspected but had not been quantified. During average conditions, approximately 564,176 m3/d of base flow discharges to the Potomac River. An additional 124,379 m3/d of ground water is also estimated to discharge directly to the Potomac River and rep

Kozar, Mark D.; Weary, David J.

2009-01-01

217

Hydrogeology and ground-water flow at the Muddy Brook riparian zone, north-central Connecticut  

USGS Publications Warehouse

The hydrogeology and ground-water flow of Muddy Brook were investigated as part of a study to determine the effects of restoring agricultural riparian land to forest on water quality. Test-hole drilling, well installation, and slug-test analyses indicate that the part of Muddy Brook studied is underlain by thin stratified-drift deposits. These deposits are mostly less than 10 feet thick and have estimated horizontal hydraulic conductivities of 4 to 30 feet per day. Till deposits from 1 to 14 feet thick underlie the stratified-drift deposits and have estimated horizontal hydraulic conductivities of 0.1 and 4.3 feet per day. The water table in stratified drift is less than 10 feet below land surface during most of the year, and the horizontal hydraulic gradient varies seasonally and areally from 0.015 to 0.07 feet per foot. The horizontal hydraulic gradient in the till deposits is as great as 0.1 feet per foot. Vertical hydraulic gradients of as large as 0.4 feet per foot are present between the till and stratified drift and are predominantly upward from the till into the stratified drift but can reverse direction in response to recharge. Ground-water discharge to Muddy Brook comes mostly from the saturated stratified-drift deposits, and during April through September 1992, flowed at a rate of 0.015 to 0.027 cubic feet per second. Average ground-water velocity is about 1 feet per day in the stratified drift and about 0.2 foot per day through the till deposits. Discharge of ground water from the till can contribute as much as 0.006 cubic feet per second of water to the stratified drift.

Mullaney, J. R.

1995-01-01

218

Estimates of Ground-Water Recharge Based on Streamflow-Hydrograph Methods: Pennsylvania.  

National Technical Information Service (NTIS)

This study, completed by the U.S. Geological Survey (USGS) in cooperation with the Pennsylvania Department of Conservation and Natural Resources, Bureau of Topographic and Geologic Survey (T&GS), provides estimates of groundwater recharge for watersheds t...

D. W. Risser R. W. Conger J. E. Ulrich M. P. Asmussen

2005-01-01

219

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

220

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

221

Old Groundwater, Interbasin Groundwater Flow, Magmatic Solutes, and Hydrologic Fluxes of Carbon in a Lowland Costa Rican Rainforest  

NASA Astrophysics Data System (ADS)

Carbon (C), helium (He), and chloride (Cl) concentrations and isotopes were measured in groundwater and surface-water in a lowland Costa Rican rainforest at the foot of Volcan Barva (a 2900 m peak that is one of the largest in the Cordillera Central of Costa Rica). Results are consistent with the presence and mixing of two distinct groundwaters: (1) high-solute bedrock groundwater representing interbasin groundwater flow (IGF) into the rainforest watersheds, and (2) low-solute local groundwater recharged within the lowland rainforest watersheds. In bedrock groundwater, high ^13C (-4.89 o/oo), low 14C (7.98 pmC), high R/RA for He (6.88), and low 36Cl/Cl (17x10-15) suggest that elevated DIC, He, and Cl concentrations are derived from magmatic outgassing and/or weathering of volcanic rock beneath nearby Volcan Barva. In local groundwater, the magmatic signature is absent and data suggest atmospheric sources for He and Cl and a biogenic soil-gas CO2 source for DIC. 14C dating suggests the age of bedrock groundwater is 2700-4300 years (most likely at the lower end of the range). Local groundwater has 14C>100 pmC, indicating the presence of "bomb carbon" and thus ages less than ~50 years for these samples collected in 2006. Overall, the C, He, and Cl data are consistent with a prior conceptual hydrologic model developed with major ion and water-balance data from this tropical rainforest: (1) the large variation in solute concentrations can be explained by mixing of the two distinct groundwaters, (2) bedrock groundwater is much older than local water, (3) elevated solute concentrations in bedrock groundwater are derived from volcanic fluids and/or rock, and (4) local water has not had significant interaction with volcanic rock. Tracers with different behaviors and capabilities converge on the same hydrologic interpretation. Also, transport of magmatic CO2 into the lowland rainforest (as DIC in the IGF) seems to be significant relative to other large ecosystem-level carbon fluxes. Dissolved carbon export from the watersheds via streamflow is dominated by DIC (DOC accounts for

Genereux, D. P.; Webb, M.; Solomon, D. K.

2009-04-01

222

New dating method: Groundwater residence time estimated from the 4He accumulation rate calibrated by using cosmogenic and subsurface-produced 36Cl  

NASA Astrophysics Data System (ADS)

Groundwater contains dissolved He, and its concentration increases with the residence time of the groundwater. Thus, if the 4He accumulation rate is constant, the dissolved 4He concentration in ground-water is equivalent to the residence time. Since accumulation mechanisms are not easily separated in the field, we estimate the total He accumulation rate during the half-life of 36Cl (3.01 × 105 years). We estimated the 4He accumulation rate, calibrated using both cosmogenic and subsurface-produced 36Cl, in the Great Artesian Basin (GAB), Australia, and the subsurface-produced 36Cl increase at the Äspö Hard Rock Laboratory, Sweden. 4He accumulation rates range from (1.9±0.3) × 10-11 to (15±6) × 10-11 ccSTP·cm-3·y-1 in GAB and (1.8 ±0.7) × 10-8 ccSTP·cm-3·y-1 at Äspö. We confirmed a ground-water flow with a residence time of 0.7-1.06 Ma in GAB and stagnant groundwater with the long residence time of 4.5 Ma at Äspö. Therefore, the groundwater residence time can be deduced from the dissolved 4He concentration and the 4He accumulation rate calibrated by 36Cl, provided that 4He accumulation, groundwater flow, and other geo-environmental conditions have remained unchanged for the required amount of geological time.

Mahara, Y.; Ohta, T.; Kubota, T.; Miyakawa, K.; Hasegawa, T.; Habermehl, M. A.; Fifield, L. K.

2012-04-01

223

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

224

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

225

Identification of groundwater parameters at Columbus, Mississippi, using a 3D inverse flow and transport model  

USGS Publications Warehouse

An extensive amount of data including hydraulic heads, hydraulic conductivities and concentrations of several solutes from controlled injections have been collected during the MADE 1 and MADE 2 experiments at a heterogeneous site near Columbus, Mississippi. In this paper the use of three-dimensional inverse groundwater models including simultaneous estimation of flow and transport parameters is proposed to help identify the dominant characteristics at the site. Simulations show that using a hydraulic conductivity distribution obtained from 2187 borehole flowmeter tests directly in the model produces poor matches to the measured hydraulic heads and tritium concentrations. Alternatively, time averaged hydraulic head maps are used to define zones of constant hydraulic conductivity to be estimated. Preliminary simulations suggest that in the case of conservative transport many, but not all, of the major plume characteristics can be explained by large-scale heterogeneity in recharge and hydraulic conductivity.

Barlebo, H. C.; Rosbjerg, D.; Hill, M. C.

1996-01-01

226

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

227

Hanford groundwater modeling: a numerical comparison of Bayesian and Fisher parameter estimation techniques  

Microsoft Academic Search

This report is concerned with the performance of two promising techniques for estimating the parameters of groundwater models developed and applied by Rockwell Hanford Operations at the US Department of Energy Hanford site. The report begins with a fairly general formulation of the parameter estimation problem which helps to explain the capabilities and differences of the two estimation techniques (weighted

1980-01-01

228

Impact of Vertical Hydraulic Conductivity Variations on Flow and Solute Transport in Chalk Groundwater  

Microsoft Academic Search

Borehole measurements provide valuable information about how aquifer properties vary in the vertical dimension. Such vertical hydraulic conductivity variations are typically excluded from regional groundwater flow models, as their implications for prediction of sustainable yields are usually small. However, the prediction of groundwater quality trends and the impacts of land use planning decisions (e.g. impact of agrochemical applications, delineation of

A. H. Parker; L. J. West; N. E. Odling

2008-01-01

229

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

230

Structural control of groundwater flow regimes and groundwater chemistry along the lower reaches of the Zerka River, West Jordan, using remote sensing, GIS, and field methods  

NASA Astrophysics Data System (ADS)

A hydrogeological study was completed within a sub-catchment of the Zerka River drainage basin, in western Jordan. The system is characterized by anticlinal bending with an axis trending SSW-NNE and plunging a few degrees in the SSW direction. The anticlinal structure diverts groundwater flow towards the SSW while the strike-slipe faults cause the groundwater to diverge where the fault is perpendicular to the groundwater flow lines, and to converge where the fault is parallel to the groundwater flow lines. A direct relationship was found between the location of springs and the type of groundwater flow with regard to the amount of discharge wherein large spring discharges are located in zones of converging groundwater flow lines. In areas where faults are not abundant, the groundwater retention time in the aquifers is long and a zonation of the electrical conductivity was detected due to mineral dissolution. By controlling groundwater flow, the anticlinal setting produces three genetic groups of groundwater flow systems: (1) alkaline-earth alkaline water which is predominately a bicarbonate-type composition, (2) alkaline-earth alkaline water which is predominately bicarbonate-sulfate, and (3) alkaline-earth alkaline water with a high alkaline component.

Odeh, Taleb; Salameh, Elias; Schirmer, Mario; Strauch, Gerhard

2009-10-01

231

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

232

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

233

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

234

Estimation of emission from an LNAPL contaminated zone considering groundwater recharge  

NASA Astrophysics Data System (ADS)

The aim of this work was to develop an easy to handle semi-analytical method to estimate the temporal development of emission from a multi-component LNAPL pool considering groundwater recharge. The presented approach allows the estimation of the total mass flux out of an LNAPL pool into the gas and the water phase, the latter including the mass fluxes from groundwater recharge, advection through and diffusion out of the LNAPL zone. Therefore, the known set of constitutive relationships to determine fluid saturation profiles of 2- and 3-phase systems is extended in this work to account for dynamic conditions due to groundwater recharge. The methodology is applied to a kerosene pool at a former military airfield and it is found that the mass flux due to groundwater recharge dominates the aqueous mass flux from the kerosene contaminated zone. A sensitivity study using field parameters shows, that the apparent kerosene thicknesses observed in monitoring wells and the lithology control mass flux into the gas phase, whereas the mass flux into groundwater mainly depends on the groundwater recharge rate. For the kerosene found at the site, source emission into the soil gas is estimated to last longer than the emission into groundwater, the latter varying between less than 100 and 400 years.

Peter, A.; Miles, B.; Teutsch, G.

2008-07-01

235

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

236

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

237

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

238

Groundwater  

NSDL National Science Digital Library

This interactive Flash exercise explores groundwater and features models and animations for wet years and dry years as well as a diagram for groundwater terminology. This is a suitable overview or review for an introductory level course for high school or undergraduates.

Smoothstone; Mifflin, Houghton

239

Controls on groundwater flow in the Bengal Basin of India and Bangladesh: Regional modeling analysis  

USGS Publications Warehouse

Groundwater for domestic and irrigation purposes is produced primarily from shallow parts of the Bengal Basin aquifer system (India and Bangladesh), which contains high concentrations of dissolved arsenic (exceeding worldwide drinking water standards), though deeper groundwater is generally low in arsenic. An essential first step for determining sustainable management of the deep groundwater resource is identification of hydrogeologic controls on flow and quantification of basin-scale groundwater flow patterns. Results from groundwater modeling, in which the Bengal Basin aquifer system is represented as a single aquifer with higher horizontal than vertical hydraulic conductivity, indicate that this anisotropy is the primary hydrogeologic control on the natural flowpath lengths. Despite extremely low hydraulic gradients due to minimal topographic relief, anisotropy implies large-scale (tens to hundreds of kilometers) flow at depth. Other hydrogeologic factors, including lateral and vertical changes in hydraulic conductivity, have minor effects on overall flow patterns. However, because natural hydraulic gradients are low, the impact of pumping on groundwater flow is overwhelming; modeling indicates that pumping has substantially changed the shallow groundwater budget and flowpaths from predevelopment conditions. ?? Springer-Verlag 2009.

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

2009-01-01

240

Optical Flow Estimation: Advances and Comparisons  

Microsoft Academic Search

This contribution investigates local differential techniques for estimating optical flow and its derivatives based on the brightness change constraint. By using the tensor calculus representation we build the Taylor expansion of the gray-value derivatives as well as of the optical flow in a spatiotemporal neighborhood. Such a formulation simplifies a unifying framework for all existing local differential approaches and allows

Michael Otte; Hans-hellmut Nagel

1994-01-01

241

Towards optimal sampling for flow size estimation  

Microsoft Academic Search

The flow size distribution is a useful metric for traffic modeling and management. It is well known however that its estimation based on sampled data is problematic. Previous work has shown that flow sampling (FS) offers enormous statistical benefits over packet sam- pling, however it suffers from high resource requirements and is not currently used in routers. In this paper

Paul Tune; Darryl Veitch

2008-01-01

242

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

243

Ground-water conditions in Las Vegas Valley, Clark County, Nevada; Part II, Hydrogeology and simulation of ground-water flow  

USGS Publications Warehouse

Groundwater withdrawals in Las Vegas Valley, Nevada, primarily for municipal supplies, totaled more than 2.5 million acre-ft between 1912 and 1981, with a peak annual withdrawal rate of 88,000 acre-ft in 1968. Effects of heavy pumping are evident over large areas of the valley but are more pronounced near the major well fields. Secondary recharge from lawn irrigation and other sources is estimated to have totaled more than 340,000 acre-ft during 1972-81. Resulting rises in water-level in shallow, unconfined aquifers in the central and southeastern parts of the valley have caused: widespread water-logging of soils; increased groundwater discharge to Las Vegas Wash and its tributaries; and potential for degradation of water quality in deeper aquifers by accentuating downward vertical hydraulic potential in areas where shallow groundwater has high concentrations of dissolved solids and nitrate. A 3-dimensional groundwater flow model of the valley-fill aquifer system was constructed for use in evaluating possible groundwater management alternatives aimed at alleviating problems related to overdraft and water-logging while maximizing use of the groundwater resources. Natural recharge to the valley-fill aquifers is about 33,000 acre-ft/yr; in 1979, an estimated 44,000 acre-ft of secondary recharge infiltrated to the near-surface and developed-zone aquifers. Peak water use for lawn irrigation during summer results in rates of secondary recharge that may increase threefold from winter rates. Simulated rates of seepage to washes in the valley increased correspondingly from an average of 850 acre-ft/mo in winter to about 1,300 acre-ft/mo in the summer. Groundwater withdrawals by pumping totaled 620,000 acre-ft during 1972-81, and model results indicate that about 190,000 acre-ft of that total was derived from storage. Use of the model as a predictive tool was demonstrated by simulating the effects of using most municipal wells only during the peak-demand season of June 1 through September 20. Results of the 9-year simulation indicated that: (1) long-term rates of water-level decline near the municipal well field would be less than rates for 1972-81, but the magnitude of seasonal fluctuations would increase, and (2) total volume of water released from storage as a result of subsidence would be only 42,000 acre-feet per year, or about half the volume during 1972-81.

Morgan, D. S.; Dettinger, M. D.

1994-01-01

244

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...

245

Field identification of groundwater flow systems and hydraulic traps in drainage basins using a geophysical method  

NASA Astrophysics Data System (ADS)

flow systems and stagnant zones in drainage basins are critical to a series of geologic processes. Unfortunately, the difficulty of mapping flow system boundaries and no field example of detected stagnant zones restrict the application of the concept of nested flow systems. By assuming the variation in bulk resistivity of an aquifer with uniform porosity is mainly caused by groundwater salinity, the magnetotelluric technique is used to obtain the apparent resistivity of a profile across a groundwater-fed river in the Ordos Plateau, China. Based on the variations in apparent resistivity of the Cretaceous sandstone aquifer, the basin-bottom hydraulic trap below the river has been detected for the first time, and its size is found to be large enough for possible deposition of large ore bodies. The boundaries between local and regional flows have also been identified, which would be useful for groundwater exploration and calibration of large-scale groundwater models.

Jiang, Xiao-Wei; Wan, Li; Wang, Jun-Zhi; Yin, Bin-Xi; Fu, Wen-Xiang; Lin, Chang-Hong

2014-04-01

246

Flow paths and mixing properties of groundwater using hydrogeochemistry and environmental tracers in the southwestern area of Jeju volcanic island  

NASA Astrophysics Data System (ADS)

SummaryGroundwater from springs, test boreholes and domestic wells was investigated to assess the flow system of basaltic aquifers at base-flow conditions in the southwestern part of Jeju Island, South Korea. This study utilized hydrogeochemical parameters and environmental tracers of 18O, 2H, 3H and chlorofluorocarbons (CFCs), which showed that well-connected flow paths exist between coastal springs regardless of flow rates. In contrast, test boreholes near the coastal springs exhibited various flow paths. Nitrate concentrations were much higher than baseline values in mountainous groundwater while those decreased in coastal areas (<50 m asl) despite stronger anthropogenic land uses. Cl- was seemingly contributed from nitrate contamination sources and seawater sources were minimal due to low-permeability layers near sea level. The water-stable isotopes indicated little evaporation and were comparable to the local meteoric water line during the rainy season, which was confirmed by deuterium excess values, demonstrating that effective infiltration primarily occurs during the rainy season. From the effects of altitude on ?18O, the mean recharge altitudes for both mountainous and coastal springs were estimated as 300-400 m, which implies longer flow paths for the coastal springs. The relationship of CFC-12-CFC-113 and that of CFC-12-3H concordantly indicated that the groundwater consists mainly of binary mixtures composed of 15-25-year-old young water and old water with ages greater than 60 years. Lower nitrate levels in the coastal springs were well represented by the mixing models. Recharge altitudes for coastal springs increased up to 700 m, assuming that old water corresponds to high-altitude recharge, using the binary mixing model. Integration of hydrochemical and environmental tracer characteristics revealed that pahoehoe lava flows and hydrovolcanic tuffs play key roles in controlling the groundwater occurrence and quality.

Koh, Dong-Chan; Ha, Kyoochul; Lee, Kwang-Sik; Yoon, Yoon-Yeol; Ko, Kyung-Seok

2012-04-01

247

Three-dimensional model for multi-component reactive transport with variable density groundwater flow  

Microsoft Academic Search

PHWAT is a new model that couples a geochemical reaction model (PHREEQC-2) with a density-dependent groundwater flow and solute transport model (SEAWAT) using the split-operator approach. PHWAT was developed to simulate multi-component reactive transport in variable density groundwater flow. Fluid density in PHWAT depends not on only the concentration of a single species as in SEAWAT, but also the concentrations

X. Mao; D. A. Barry; C. D. Langevin

248

A modular three-dimensional finite-difference ground-water flow model  

Microsoft Academic Search

A computer program for simulating ground-water flow in three dimensions is presented. This report includes detailed explanations of physical and mathematical concepts on which the model is developed. Ground-water flow within the aquifer is simulated by using a block-centered finite-difference approach. The program is written in Fortran 77 and has a modular structure, which permits the addition of new packages

M. G. McDonald; A. W. Harbaugh

1988-01-01

249

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

Microsoft Academic Search

The Beypazari region in NW Anatolia (Turkey) is characterized by high water demand and stress on available water resources.\\u000a Tectonic structures control the groundwater flow, hydraulic head and well yield in the study area, which is located in the\\u000a central part of the Beypazari Neogen basin. The impact of major tectonic structures on groundwater flow in the Cakiloba-Karadoruk\\u000a aquifer is

Ahmet Apaydin

2010-01-01

250

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

251

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

SciTech Connect

Water levels recorded on drillers' logs from 279 wells were used to assess the regional groundwater flow system in the area of the Industrial Excess Landfill (IEL) site in Uniontown, Ohio. The flow system was divided into two regional aquifers: a shallow unconfined glacial-drift aquifer and a deeper, semiconfined bedrock aquifer. A composite potentiometric-surface map of the glacial-drift aquifer shows that the IEL site appears to straddle a prominent groundwater ridge that trends northeast-southwest. Groundwater flows radially away from this ridge, primarily to the northwest and to the southeast; as a result, flow in the glacial-drift aquifer at 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 elongated groundwater ridge trending northeast-southwest across the northwestern corner of the IEL site; however, the site does not appear to straddle the groundwater 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 any contaminant would, in large part, depend on the original location o the contaminant at the IEL site. Available data also indicate a downward flow component; consequently, contaminants present at the site could flow laterally within the local flow patterns and vertically downward within the flow systems. 8 refs., 6 figs.

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

1989-01-01

252

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

253

Linking soil moisture balance and source-responsive models to estimate diffuse and preferential components of groundwater recharge  

NASA Astrophysics Data System (ADS)

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

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

2013-03-01

254

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

255

Large-scale use of heat as a natural tracer of groundwater flow: Application to a Variscan terrane in Belgium  

NASA Astrophysics Data System (ADS)

Heat flow shifts between 20 and 60 mW/m² in the upper ˜2 km of the crust and 60 to 150 mW/m² at greater depth have been observed in the Soumagne, Havelange and Grand-Halleux deep wells, all located close to the Variscan thrust front in Belgium. A potential explanation for these anomalies might be provided by the existence of pervasive flow in the upper part of the crust, based on the concept of concave tectonics, and the flow through karstic pathways or major thrust faults. On the other hand, the paleoclimate is also known to disturb temperatures in the subsurface. To test the hypothesis that these processes are the cause of the observed anomalies, and to quantify the contributions of the different processes and flow paths, we performed large-scale 2-D coupled hydrothermal modelling of the current fluid and heat flow distribution. In order to account for the paleoclimate effect, we performed transient modelling, making use of paleotemperature data as boundary conditions. The results confirm that groundwater flow is the dominant cause of the observed heat flow shifts in the upper ˜2 km of the Variscan terrane. The estimated groundwater flow, both pervasive and along major conduits, is rivalled by the paleoclimatic influence only in the Grand-Halleux well. The currently observed cooling of the upper ~2 km, requires less than 0.5 Myr and is controlled by the present geomorphology.

Rogiers, Bart; Huysmans, Marijke; Vandenberghe, Noël; Verkeyn, Mieke

2014-05-01

256

MEAN VOLUME FLOW ESTIMATION IN PULSATILE FLOW CONDITIONS  

PubMed Central

To verify a previously reported three-dimensional (3D) ultrasound method for the measurement of time-average volumetric blood flow, experiments were performed under pulsatile flow conditions, including in vivo investigations, and results were compared with accepted, but invasive, “gold standard” techniques. Results showed that volume averaging results in the correct time-average volume flow without the need for cardiac gating. Unlike other currently employed methods, this method is independent of Doppler angle, flow profile and vessel geometry. A GE Logiq 9 ultrasound system (GE Medical Systems, Milwaukee, WI, USA) and a four-dimensional (4D) 10L and 4D 16L probe were used to acquire 3D Doppler measurements in the femoral and carotid arteries of four canines. Two invasive blood flow meters were used (electromagnetic for one canine and ultrasonic for three canines) as the gold standard techniques. Transcutaneous color flow measurements were taken to obtain 3D volume data sets encompassing the vessel. Constant depth planes were used to integrate color flow pixels encompassing the entire vessel cross-section. Power Doppler data were used to correct for partial volume effects. An artificial stenosis was induced to vary the ambient volume flow. Unrestricted, bidirectional flow was measured as high as 400 mL min?1. Several flow restrictions were imposed that decreased the measured volumetric flow rate to as low as 30 mL min?1. All flow rate estimates (n = 38) were plotted against results obtained via the gold standards. A general line fit resulted in y = 0.926 × ? 0.87 (r2 = 0.95), which corresponds to a 0.6% flow offset relative to the average flow rate of 142 mL min?1, as well as a 7.4% error in the linearity of our estimate. A secondary curve fit was performed that required the slope to be 1 and the intercept to be 0, which yielded an r2-value of 0.93. The percent-error distribution was computed and fitted to a Gaussian function, which yielded ? = ?7.04% and ? = 9.52%. Theoretical studies were conducted to estimate the expected error in our volume flow measurements as a function of number of samples (N) used for averaging pulsatile waveforms. Experiments showed the same 1?N dependence as theory. Direct comparisons of volume flow rate estimates using volumetric color Doppler and independent standards showed that our method has good accuracy under in vivo pulsatile blood flow conditions.

Richards, Michael S.; Kripfgans, Oliver D.; Rubin, Jonathan M.; Hall, Anne L.; Fowlkes, J. Brian

2009-01-01

257

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

258

Estimations of the past groundwater recharge rate from deep borehole temperature data  

Microsoft Academic Search

In order to estimate the past groundwater recharge rates from deep borehole temperature data, observed temperature–depth profiles are compared with the profiles calculated from heat conduction–convection equation under the condition of linear increase in surface temperature due to global warming and urbanization in Tokyo metropolitan area. The results show the increase in groundwater recharge rate from the 1890s to 1940s,

Makoto Taniguchi

2002-01-01

259

Quantifying uranium complexation by groundwater dissolved organic carbon using asymmetrical flow field-flow fractionation  

NASA Astrophysics Data System (ADS)

The long-term mobility of actinides in groundwaters is important for siting nuclear waste facilities and managing waste-rock piles at uranium mines. Dissolved organic carbon (DOC) may influence the mobility of uranium, but few field-based studies have been undertaken to examine this in typical groundwaters. In addition, few techniques are available to isolate DOC and directly quantify the metals complexed to it. Determination of U-organic matter association constants from analysis of field-collected samples compliments laboratory measurements, and these constants are needed for accurate transport calculations. The partitioning of U to DOC in a clay-rich aquitard was investigated in 10 groundwater samples collected between 2 and 30 m depths at one test site. A positive correlation was observed between the DOC (4-132 mg/L) and U concentrations (20-603 ?g/L). The association of U and DOC was examined directly using on-line coupling of Asymmetrical Flow Field-Flow Fractionation (AsFlFFF) with UV absorbance (UVA) and inductively coupled plasma-mass spectrometer (ICP-MS) detectors. This method has the advantages of utilizing very small sample volumes (20-50 ?L) as well as giving molecular weight information on U-organic matter complexes. AsFlFFF-UVA results showed that 47-98% of the DOC (4-136 mg C/L) was recovered in the AsFlFFF analysis, of which 25-64% occurred in the resolvable peak. This peak corresponded to a weight-average molecular weight of about 900-1400 Daltons (Da). In all cases, AsFlFFF-ICP-MS suggested that ? 2% of the U, likely present as U(VI), was complexed with the DOC. This result was in good agreement with the U speciation modeling performed on the sample taken from the 2.3 m depth, which predicted approximately 3% DOC-complexed U. This good agreement suggests that the AsFlFFF-ICP-MS method may be very useful for determining U-organic matter association in small volume samples. Because the pH (7.0-8.1) and carbonate concentrations of these waters are typical of many groundwaters, these data suggested that facilitated transport of U by DOC may be limited in its importance in many groundwater systems.

Ranville, James F.; Hendry, M. Jim; Reszat, Thorsten N.; Xie, Qianli; Honeyman, Bruce D.

2007-05-01

260

Numerical simulation of groundwater flow and particle tracking around the proposed Uranium mine site, Andhra Pradesh, India  

Microsoft Academic Search

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

Lakshmanan Elango

261

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

262

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

263

Estimating the Regional Flux of Nitrate and Agricultural Herbicide Compounds from Groundwater to Headwater Streams of the Northern Atlantic Coastal Plain, USA  

NASA Astrophysics Data System (ADS)

Agriculture is common in the Northern Atlantic Coastal Plain (NACP, including New Jersey through North Carolina), and groundwater discharge provides nitrogen (primarily in the form of nitrate) and herbicide compounds from agricultural sources along with the majority of flow to NACP streams. Poor water quality has contributed to ecological degradation of tidal streams and estuaries along much of the adjacent mid-Atlantic coast. Although statistical models have provided estimates of total instream nutrient flux in the Coastal Plain, the regional flux of nitrogen and herbicides during base flow is less well understood. We estimated the regional flux of nitrate and selected commonly used herbicide compounds from groundwater to non-tidal headwater streams of the NACP on the basis of late-winter or spring base-flow samples from 174 such streams. Sampled streams were selected using an unequal-probability random approach, and flux estimates are based on resulting population estimates rather than empirical models, which are commonly used for such estimates. Base-flow flux in the estimated 8,834 NACP non-tidal headwater streams are an estimated 21,200 kilograms per day of nitrate (as N) and 5.83, 0.565, and 20.7 kilograms per day of alachlor, atrazine, and metolachlor (including selected degradates), respectively. Base-flow flux of alachlor and metolachlor is dominated by degradates; flux of parent compounds is less than 3 percent of the total flux of parent plus degradates. Base-flow flux of nitrate and herbicides as a percentage of applications generally varies predictably with regional variations in hydrogeology. Abundant nonpoint (primarily agricultural) sources and hydrogeologic conditions, for example, contribute to particularly large base-flow flux from the Delmarva Peninsula to Chesapeake Bay. In the Delmarva Peninsula part of the Chesapeake Watershed, more than 10 percent of total nonpoint nitrogen applications is transported through groundwater to stream base flow, and base-flow nitrate flux represents 70 percent of total nitrogen flux in streams.

Ator, S.; Denver, J. M.

2011-12-01

264

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

265

Estimating profile soil moisture and groundwater variations using GRACE and Oklahoma Mesonet soil moisture data  

Microsoft Academic Search

In this study we estimate a time series of regional groundwater anomalies by combining terrestrial water storage estimates from the Gravity Recovery and Climate Experiment (GRACE) satellite mission with in situ soil moisture observations from the Oklahoma Mesonet. Using supplementary data from the Department of Energy's Atmospheric Radiation Measurement (DOE ARM) network, we develop an empirical scaling factor with which

Sean Swenson; James Famiglietti; Jeffrey Basara; John Wahr

2008-01-01

266

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

PubMed

Tolo Harbour, located in the northeastern part of Hong Kong's New Territories, China, has a high frequency of algal blooms and red tides. An attempt was made to first quantify the submarine groundwater discharge (SGD) into Tolo Harbour using (226)Ra, and then to estimate the nutrient fluxes into the Harbour by this pathway. The total SGD was estimated to be 8.28×10(6) m(3) d(-1), while the fresh submarine groundwater discharge (FSGD) was estimated to be 2.31×10(5) m(3) d(-1). This showed that a large amount of SGD was contributed by recirculated seawater rather than fresh groundwater in the Harbour. Using the SGD and groundwater nutrient information around Tolo Harbour, the nutrient loading through SGD was estimated to be 1.1×10(6) mold(-1) for DIN, 1.4×10(4) mold(-1) for PO(4)(3-)-P and 1.4×10(6) mold(-1) for SiO(2)-Si, which was much more significant than its counterpart through the river discharge. Despite uncertainties in the estimation, the nutrient loading to Tolo Harbour by SGD is clearly significant. Thus, the current efforts for management of red tides in Tolo Harbour have to be reviewed and control of groundwater contamination is obviously required. PMID:22819893

Lee, Chun Ming; Jiao, Jiu Jimmy; Luo, Xin; Moore, Willard S

2012-09-01

267

Preliminary model of regional Mesozoic groundwater flow and uranium deposition in the Colorado Plateau.  

USGS Publications Warehouse

Qualitative and numerical simulation of regional groundwater flow in the Colorado Plateau during Late Jurassic and Early Cretaceous time has led to a model of U deposition in areas of upwelling solutions. Palaeographic reconstruction shows that surface drainage and groundwater flow was generally to the NE and E. Groundwater flowing in these directions, principally through Triassic-Jurassic and Permian sandstones, encountered sediments of variable thickness due to buried uplifted or downdropped Precambrian blocks. The buried uplifted blocks caused upward movement of groundwater around them. These inferred zones of upwelling are closely associated with concentrations of Jurassic- and Cretaceous-age U deposits. The results are consistent with hypotheses of an upwelling brine mixing and reacting with descending meteoric water and causing U precipitation at the fluid interface. Whether the U came from above or below the interface is an unsolved problem.-A.P.

Sanford, R. F.

1982-01-01

268

Constraints on the Pattern of Hydraulic Properties, Groundwater Flow, and Transport at Upland-Estuary Margins  

NASA Astrophysics Data System (ADS)

The patterns of groundwater flux from uplands to adjacent water bodies in the coastal zone depend on both the spatial and temporal characteristics of coastal aquifer systems. In this study, we integrate hydrologic measurements and non-invasive environmental geophysics in an effort to constrain the groundwater flux from terrestrial uplands into adjacent tidal creeks and salt marshes near an island-estuary margin in the South Atlantic Bight. Aquifer testing and parameter estimation conducted at both the laboratory (grain size analyses and falling-head permeameter tests) and field (pumping tests and analyses of natural tidal pumping) scales provide independent constraints on hydraulic properties of the unconfined surficial aquifer systems at two focus sites. The analyses reveal a decrease in hydraulic conductivity of 3 to 4 orders of magnitude ( ~10-8 to ~10-4 m s-1) across the upland-estuary margin. The extent and variability of reduced permeability at the aquifer boundary may lead to localized areas of focused groundwater flux into the adjacent estuary and a variable distribution of subsurface salinity. Geophysical surveys (e.g., two-dimensional DC resistivity, terrain conductivity), borehole conductivity measurements, and geochemical analyses of groundwater samples confirm the existence of variable subsurface salinity regimes between the two different sites in the same tidal watershed. Based on the observed distribution of hydraulic properties and subsurface salinity near the island-estuary interface, we suggest that the combined effects of a low permeability clogging layer and tidal fluctuations may lead to a more diffuse region of freshwater discharge into the adjacent tidal creek-salt marsh complex. Using water level fluctuations monitored over a 32-day period, we calculate the frequency-dependent admittance between well levels and observed forcing functions. The results show that the aquifer acts as a low-pass filter for tidally forced perturbations and demonstrate the dispersive nature of these waves in the aquifer. Analyses of the phase lag and amplitude attenuation of tidal forcing in the aquifer systems imply that the nature of the aquifer boundary (e.g., amplitude and phase of tide, morphology of creek bank) largely controls the attenuation and lag characteristics of the propagating pressure wave in the aquifer. Results from these analyses suggest that the effective groundwater flow path in an equivalent homogeneous aquifer could extend up to 100 m into the marsh beyond the edge of the upland.

Schultz, G.; Ruppel, C.

2001-05-01

269

Linking soil moisture balance and source-responsive models to estimate diffuse and preferential components of groundwater recharge  

USGS Publications Warehouse

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

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

2012-01-01

270

Linking soil moisture balance and source-responsive models to estimate diffuse and preferential components of groundwater recharge  

NASA Astrophysics Data System (ADS)

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

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

2012-07-01

271

Factors Influencing Monitoring Strategies in a Catchment With Overland Flow and Groundwater Flow in an Unconfined Porous Aquifer Overlying a Fractured Bedrock Aquifer  

Microsoft Academic Search

Factors influencing strategies for monitoring contamination in a small catchment are examined. The watershed is modeled with overland flow on the surface and groundwater flow in an unconfined porous aquifer overlying a fractured bedrock aquifer. Surface-water flow and transport is two-dimensional both on the ground surface and in the stream channel, while groundwater flow and transport is represented with a

Y. Chen; L. Smith; R. Beckie

2006-01-01

272

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

273

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

274

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, Jr. , Kenneth, L.

1986-01-01

275

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

NASA Astrophysics Data System (ADS)

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

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

2013-04-01

276

Equally likely inverse solutions to a groundwater flow problem including pattern information from remote sensing images  

NASA Astrophysics Data System (ADS)

Groundwater flow modeling for large areas in arid and semiarid regions, like the Chobe region in Botswana, suffers from a severe lack of data. This study addresses the usefulness of remote sensing (RS) images to constrain the recharge rate estimates for a region. The estimates derived from METEOSAT and NOAA advanced very high resolution radar (AVHRR) images are correlated with recharge rate values estimated from chloride measurements and used jointly in the generation of multiple, equally likely recharge rate realizations with the colocated cosimulation algorithm. The colocated cosimulation algorithm is very suited to generate stochastic realizations of a parameter that includes information from a correlated covariable given on a regular, dense grid as in RS information. These equally likely recharge rate realizations, together with multiple equally likely transmissivity realizations, are conditioned by inversion to hydraulic head data and a digital elevation model. For the inverse conditioning an additional penalty term was added to the objective function, penalizing too large deviations of the recharge rate pattern from the RS image. As such, the recharge rate pattern observed with the RS images is still honored by the calibrated recharge rate realizations. It was observed that conditioning to the RS information reduces significantly the estimated ensemble variance of the recharge rates.

Hendricks Franssen, H. J.; Brunner, P.; Makobo, P.; Kinzelbach, W.

2008-01-01

277

Study of the flow incoherence introduced when using nested ground-water flow models for the SKI reference site.  

National Technical Information Service (NTIS)

Three new parameter variations have been made in the ground-water flow calculations for the SKI reference site in order to try to deduce the factors influencing the incoherence in flow between the local and the subregional models observed in an earlier st...

A. Boghammar B. Grundfelt H. Lindberg

1989-01-01

278

Simulation of ground-water flow in the Intermediate and Floridan aquifer systems in Peninsular Florida  

USGS Publications Warehouse

A numerical model of the intermediate and Floridan aquifer systems in peninsular Florida was used to (1) test and refine the conceptual understanding of the regional ground-water flow system; (2) develop a data base to support subregional ground-water flow modeling; and (3) evaluate effects of projected 2020 ground-water withdrawals on ground-water levels. The four-layer model was based on the computer code MODFLOW-96, developed by the U.S. Geological Survey. The top layer consists of specified-head cells simulating the surficial aquifer system as a source-sink layer. The second layer simulates the intermediate aquifer system in southwest Florida and the intermediate confining unit where it is present. The third and fourth layers simulate the Upper and Lower Floridan aquifers, respectively. Steady-state ground-water flow conditions were approximated for time-averaged hydrologic conditions from August 1993 through July 1994 (1993-94). This period was selected based on data from Upper Floridan a quifer wells equipped with continuous water-level recorders. The grid used for the ground-water flow model was uniform and composed of square 5,000-foot cells, with 210 columns and 300 rows.

Sepulveda, Nicasio

2002-01-01

279

Regional modeling of groundwater flow and arsenic transport in the Bengal Basin: challenges of scale and complexity (Invited)  

NASA Astrophysics Data System (ADS)

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

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

2009-12-01

280

Interbasin groundwater flow and groundwater interaction with surface water in a lowland rainforest, Costa Rica: A review  

NASA Astrophysics Data System (ADS)

This paper reviews work related to interbasin groundwater flow (naturally occurring groundwater flow beneath watershed topographic divides) into lowland rainforest watersheds at La Selva Biological Station in Costa Rica. Chemical mixing calculations (based on dissolved chloride) have shown that up to half the water in some streams and up to 84% of the water in some riparian seeps and wells is due to high-solute interbasin groundwater flow (IGF). The contribution is even greater for major ions; IGF accounts for well over 90% of the major ions at these sites. Proportions are highly variable both among watersheds and with elevation within the same watershed (there is greater influence of IGF at lower elevations). The large proportion of IGF found in water in some riparian wetlands suggests that IGF is largely responsible for maintaining these wetlands. ? 18O data support the conclusions from the major ion data. Annual water and major ion budgets for two adjacent watersheds, one affected by IGF and the other not, showed that IGF accounted for two-thirds of the water input and 92-99% of the major ion input (depending on the major ion in question) to the former watershed. The large (in some cases, dominating) influence of IGF on watershed surface water quantity and quality has important implications for stream ecology and watershed management in this lowland rainforest. Because of its high phosphorus content, IGF increases a variety of ecological variables (algal growth rates, leaf decay rate, fungal biomass, invertebrate biomass, microbial respiration rates on leaves) in streams at La Selva. The significant rates of IGF at La Selva also suggest the importance of regional (as opposed to small-scale local) water resource planning that links lowland watersheds with regional groundwater. IGF is a relatively unexplored and potentially critical factor in the conservation of lowland rainforest.

Genereux, David P.; Jordan, Michael

2006-04-01

281

Tidally driven groundwater flow and solute exchange in a marsh: Numerical simulations  

Microsoft Academic Search

Tidal fluctuations drive groundwater flow in salt marsh sediments. This flow could cause significant chemical exchange across the sediment-water interface and could affect marsh ecology. Numerical models of a generalized tidal creek and marsh were constructed to calculate flow patterns and solute exchange between the marsh and creek. The governing equation for saturated\\/unsaturated flow was modified to account for tide-related

Alicia Marie Wilson; Leonard Robert Gardner

2006-01-01

282

Application of boundary-fitted coordinate (BFC) transformations to groundwater flow and transport modeling  

SciTech Connect

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

Lee, K.K.

1992-01-01

283

Estimation of the percentage of annual groundwater recharge with bomb tritium using a cumulative mass balance method  

NASA Astrophysics Data System (ADS)

The bomb tritium (3H) distribution patterns in the aquifer beneath an abandoned landfill at the Canadian Forces Base (CFB) Borden, Ontario, and in a sandy aquifer at Whiteshell Nuclear Research Establishments (WNRE) Pinawa, Manitoba, all in Canada, were delineated in great detail. A sampling and monitoring network of multilevel samplers and bundle piezometers were used. The directions of groundwater flow were established, and the boundary between the tritiated and non-tritiated zones of the two aquifers were closely demarcated. Using a cumulative mass balance method, the3H input mass into the aquifers was compared with the3H mass in groundwater storage to estimate the percentages of annual groundwater recharge from 1953 to 1978. Two recharge calculations for the effective recharge zone and the total recharge area of the aquifers as established from the flownet analysis, and the distributions of dissolved geochemical constitutents showed that the effective recharge zone calculations gave higher values of 30.6 cm/yr for CFB Borden and 20.1 cm/yr for WNRE while the total recharge areas gave lower values of 19.1 and 10.1 cm/yr for the Borden and WNRE aquifers respectively. The two recharge values provide possible minimum and maximum recharge estimates for the two study areas.

Egboka, Boniface C. E.; Cherry, John A.; Farvolden, Robert N.

1982-03-01

284

Inverse Modeling of Groundwater Flow for a Fractured Confined Aquifer  

NASA Astrophysics Data System (ADS)

A two-dimensional inverse method is developed to simultaneously estimate steady-state hydraulic conductivities, state variables, and boundary conditions (BC) for a fractured confined aquifer. Computation experiments were performed with five fractured models where each model is driven by dominantly lateral flow (true BC) through both fractures (Kf) and matrix (Km). From each model, observation data including hydraulic heads and Darcy fluxes were sampled without imposing measurement errors. These data were provided to inversion to estimate Kf and the unknown model BC. For the first 4 models, the same sampling data density was used, while Kf/Km ratio is fixed at 10. The 1st model contains a single vertical fracture, and the error of the estimated Kf is almost 0. The 2nd model contains a single horizontal fracture, and the error of the estimated Kf is 4.6%. The 3rd model contains a vertical and a horizontal fracture, and the error is 5.3%. The 4th model is same as the third, except that the fracture volume is 25 times greater, and the error is 0.70%. In this model, the highest BC estimation error occurred at the domain corners, where the inversion extrapolation error is the greatest (reduction of this error will be investigated in the future with local grid refinement and increased data density). The 5th model contains a set of diagonal fractures, two of which run from the left bottom corner to the right top corner and the other one runs from the left top corner to the right bottom corner. For this model, under a given data density, increasing Kf/Km (10 to 1,000,000) was tested. Kf estimation is found not to be sensitive to this variability - the largest Kf error is only 5.27%. For the same model, at Kf/Km =10, local sensitivity analysis using 1 percent scaled sensitivity (1ss) suggests that observed heads at different locations are important for estimating different parameters. A global inverse sensitivity analysis was then performed by increasing the number of the observed heads from 10 to 250 (i.e., 20 random simulations for each sampling density), while using a single observed flux for inversion. Results suggest that Kf estimation error is significantly influenced by the density of the observed heads (Figure 1). With increasing heads, Kf accuracy increases while its estimation uncertainty decreases. In summary, inversion accuracy is not sensitive to fracture patterns or the magnitude of Kf/Km, but is sensitive to data density. Future work will explore the inverse analysis and its stability when increasing measurement errors are imposed on the observed data. Estimated Kf and its uncertainty under increasing data density for the 5th model. Mean error of Kf estimation is shown. At each data density, 20 inversions were performed using randomly sampled hydraulic heads and one flux measurement.

Zhang, Y.; Wang, D.

2013-12-01

285

Comparison of local- to regional-scale estimates of ground-water recharge in Minnesota, USA  

Microsoft Academic Search

Regional ground-water recharge estimates for Minnesota were compared to estimates made on the basis of four local- and basin-scale methods. Three local-scale methods (unsaturated-zone water balance, water-table fluctuations (WTF) using three approaches, and age dating of ground water) yielded point estimates of recharge that represent spatial scales from about 1 to about 1000 m2. A fourth method (RORA, a basin-scale

Geoffrey N. Delin; Richard W. Healy; David L. Lorenz; John R. Nimmo

2007-01-01

286

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

287

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

288

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...

289

A model of regional ground-water flow in secondary-permeability terrane ( Susquehanna River).  

USGS Publications Warehouse

The ground-water flow system in the Lower Susquehanna River Basin in Pennsylvania and Maryland can be considered as one complex unconfined aquifer in which secondary porosity and permeability are the dominant influences on the occurrence and flow of ground water. The degree of development of secondary porosity and permeability in the various lithologies of the lower basin determines the aquifer characteristics of each lithology. Based on qualitative evidence, the use of a porous-media model was assumed to be appropriate on a regional scale and a finite-difference ground-water flow model was constructed for the lower basin. -from Author

Gerhart, J. M.

1984-01-01

290

Numerical simulation of ground-water flow in La Crosse County, Wisconsin, and into nearby pools of the Mississippi River  

USGS Publications Warehouse

This report describes a two-dimensional regional screening model and two associated three-dimensional ground-water flow models that were developed to simulate the ground-water flow systems in La Crosse County, Wisconsin, and Pool 8 of the Mississippi River. Although the geographic extents of the three-dimensional models were slightly different, both were derived from the same geologic interpretation and regional screening model, and their calibrations were performed concurrently. The objectives of the La Crosse County (LCC) model were to assess the effects of recent (1990s) and potential future ground-water withdrawals and to provide a tool suitable to evaluate the effects of proposed water-management programs. The Pool 8 model objectives were to quantify the magnitude and distribution of ground-water flow into the Pool. The Wisconsin Geological and Natural History Survey and the U.S. Geological Survey developed the models cooperatively. The report describes: 1) the conceptual hydrogeologic model; 2) the methods used in simulating flow; 3) model calibration and sensitivity analysis; and 4) model results, such as simulation of predevelopment conditions and location and magnitude of ground-water discharge into Pool 8 of the Mississippi. Three aquifer units underlie the model area: 1) a shallow unconsolidated sand and gravel aquifer; 2) an upper bedrock aquifer, composed of Cambrian and Ordovician sandstone and dolomite; and 3) a lower bedrock aquifer composed of Cambrian sandstone of the Eau Claire Formation and the Mount Simon Formation. A shale layer that is part of the Eau Claire Formation forms a confining unit separating the upper and lower bedrock aquifers. This confining unit is absent in the Black River and parts of the La Crosse and Mississippi River valleys. Precambrian crystalline basement rock forms the lower base of the ground-water flow system. The U.S. Geological Survey ground-water flow model code, MODFLOW, was used to develop the La Crosse County (LCC) and Pool 8 ground-water flow models. Boundary conditions for the MODFLOW model were extracted from an analytic element screening model of the regional flow system surrounding La Crosse County. Model input was obtained from previously published and unpublished geologic and hydrologic data. Pumpages from municipal and high-capacity wells were also simulated. Model calibration included a comparison of modeled and field-measured water levels and field-measured base flows to simulated stream flows. At calibration, most measured water levels compared favorably to model-calculated water levels. Simulated streamflows at two targets were within 3 percent of estimated measured base flows. Mass balance results from the LCC and Pool 8 models indicated that 63 to 74 percent of ground water was from recharge and 19 to 26 percent was from surface-water sources. Ground-water flow out of the model was to rivers and streams (85 to 87 percent) and pumping wells (11 and 13 percent). The model demonstrates the effects of development on ground water in the study area. The maximum simulated water-level decline in the city of La Crosse metropolitan area is 9.3 feet. Simulated stream losses are similar to the amount of ground water pumped by wells. This indicates that ground water withdrawn by La Crosse County wells is water that under predevelopment conditions discharged to streams and lakes. The models provide estimates of the locations and amount of ground-water flow into Pool 8 and the southern portion of Pool 7 of the Mississippi River. Ground-water discharges into all areas of the pools, except along the eastern shore in the vicinity of the city of La Crosse and immediately downgradient from lock and dam 7 and 8. Ground-water flow into the pools is generally greatest around the perimeter with decreasing amounts away from the perimeter. An area of relatively high ground-water discharge extends out towards the center of Pool 7 from the upper reaches of the pool and may

Hunt, Randall J.; Saad, David A.; Chapel, Dawn M.

2003-01-01

291

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

292

Surface water seepage effects on shallow groundwater and Rio Grande flow in northern New Mexico  

Microsoft Academic Search

Timing, amount, and quality of upper Rio Grande flow may be importantly affected by irrigation water that seeps from canals and fields, percolates to shallow groundwater, and returns to the river along subsurface flow paths. In northern New Mexico, changing land use patterns point to potential future reductions in river water deliveries through traditional acequia irrigation canals. We assembled a

A. Fernald; A. Helmus; C. Ochoa; M. Ortiz; C. Brown

2006-01-01

293

Modeling of groundwater flow at Palmottu. A 2-dimensional approach using the SUTRA code.  

National Technical Information Service (NTIS)

The report presents the results of the modeling the groundwater flow at Palmottu analogue study site, which is a small U-Th mineralization near Nummi-Pusula in southern Finland. The objective of the study was to enhance existing knowledge of the flow cond...

P. Lampinen

1996-01-01

294

Regional scale groundwater flow systems and age distribution in basins with depth-decaying hydraulic conductivity  

Microsoft Academic Search

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

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

2010-01-01

295

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

National Technical Information Service (NTIS)

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

V. Taivassalo L. Koskinen K. Meling

1994-01-01

296

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...

297

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

298

Water balance-based estimation of groundwater recharge in the Lake Chad Basin  

NASA Astrophysics Data System (ADS)

Lake Chad Basin (LCB) has experienced drastic changes of land cover and poor water management practices during the last 50 years. The successive droughts in the 1970s and 1980s resulted in the shortage of surface water and groundwater resources. This problem of drought and shortage of water has a devastating implication on the natural resources of the Basin with great consequence on food security, poverty reduction and quality of life of the inhabitants in the LCB. Therefore, understanding the change of land use and its characteristics must be a first step to find how such changes disturb the water cycle especially the groundwater in the LCB. The abundance of groundwater is affected by the climate change through the interaction with surface water, such as lakes and rivers, and vertical recharge through an infiltration process. Quantifying the impact of climate change on the groundwater resource requires not only reliable forecasting of changes in the major climatic variables, but also accurate estimation of groundwater recharge. Spatial variations in the land use/land cover, soil texture, topographic slope, and meteorological conditions should be accounted for in the recharge estimation. In this study, we employed a spatially distributed water balance model WetSpass to simulate a long-term average change of groundwater recharge in the LCB of Africa. WetSpass is a water balance-based model to estimate seasonal average spatial distribution of surface runoff, evapotranspiration, and groundwater recharge. The model is especially suitable for studying the effect of land use/land cover change on the water regime in the LCB. The present study describes the concept of the model and its application to the development of recharge map of the LCB.

Babamaaji, R. A.; Lee, J.

2012-12-01

299

Estimating flow through an earthen dam  

NSDL National Science Digital Library

Students make measurements of dam dimensions and water levels above and below a small, accessible earthen dam. They assess the soil texture in the field. They follow up by developing a simple flow net and estimating seepage rate as part of a problem set. They discuss their assumptions and the likely sources and magnitude of error.

Savage, Kaye

300

Characterisation of recharge processes and groundwater flow mechanisms in weathered-fractured granites of Hyderabad (India) using isotopes  

Microsoft Academic Search

In order to address the problem of realistic assessment of groundwater potential and its sustainability, it is vital to study the recharge processes and mechanism of groundwater flow in fractured hard rocks, where inhomogeneties and discontinuities have a dominant role to play. Wide variations in chloride, ?18O and 14C concentrations of the studied groundwaters observed in space and time could

B. S. Sukhija; D. V. Reddy; P. Nagabhushanam; S. K. Bhattacharya; R. A. Jani; Devender Kumar

2006-01-01

301

Patterns and variability of groundwater flow and radium activity at the coast: A case study from Waquoit Bay, Massachusetts  

Microsoft Academic Search

Radium is widely used as a natural tracer of groundwater discharge to the ocean. To better understand how radium activities vary within the groundwater systems that contribute this discharge to coastal waters, we characterized the spatial patterns of porewater activities of the four radium isotopes in the context of the groundwater flow system of Waquoit Bay, Massachusetts. Radium activities were

Holly A. Michael; Matthew A. Charette; Charles F. Harvey

2011-01-01

302

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

303

Estimation of Blood Flow With Radioactive Tracers  

PubMed Central

The techniques of tracer dilution in the circulation, and of tracer uptake by and washout from an organ, may be described using expressions that are general and are not dependent on specific models such as exponentials. The expressions have been applied to the measurement of cardiac output using impulse and constant rate injection techniques. Further expressions have been given for estimating organ blood flow from inflow/outflow concentration-time curves, washout curves, and from the distribution of deposited tracer. Some problems with respect to the use of deposition techniques as they are ordinarily applied to the estimation of regional blood flow must be considered, particularly where there are capillary beds in series or where there is countercurrent diffusional shunting of diffusible tracers between inflow and outflow. This review deals with these various aspects of tracer theory as they relate to the measurement of blood flow.

Bassingthwaighte, James B.; Holloway, G. Allen

2010-01-01

304

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

USGS Publications Warehouse

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

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

2001-01-01

305

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

306

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

307

Geohydrology and simulation of ground-water flow in the aquifer system near Calvert City, Kentucky  

USGS Publications Warehouse

The U.S. Geological Survey, in cooperation with the Kentucky Natural Resources and Environmental Protection Cabinet, constructed a two-dimensional, steady-state ground-water-flow model to estimate hydraulic properties, contributing areas to discharge boundaries, and the average linear velocity at selected locations in an aquifer system near Calvert City, Ky. Nonlinear regression was used to estimate values of model parameters and the reliability of the parameter estimates. The regression minimizes the weighted difference between observed and calculated hydraulic heads and rates of flow. The calibrated model generally was better than alternative models considered, and although adding transmissive faults in the bedrock produced a slightly better model, fault transmissivity was not estimated reliably. The average transmissivity of the aquifer was 20,000 feet squared per day. Recharge to two outcrop areas, the McNairy Formation of Cretaceous age and the alluvium of Quaternary age, were 0.00269 feet per day (11.8 inches per year) and 0.000484 feet per day (2.1 inches per year), respectively. Contributing areas to wells at the Calvert City Water Company in 1992 did not include the Calvert City Industrial Complex. Since completing the fieldwork for this study in 1992, the Calvert City Water Company discontinued use of their wells and began withdrawing water from new wells that were located 4.5 miles east-southeast of the previous location; the contributing area moved farther from the industrial complex. The extent of the alluvium contributing water to wells was limited by the overlying lacustrine deposits. The average linear ground-water velocity at the industrial complex ranged from 0.90 feet per day to 4.47 feet per day with a mean of 1.98 feet per day.

Starn, J. J.; Arihood, L. D.; Rose, M. F.

1995-01-01

308

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

309

Hydrogeology and simulation of ground-water flow at the Gettysburg Elevator Plant Superfund Site, Adams County, Pennsylvania  

USGS Publications Warehouse

Ground water in Triassic-age sedimentary fractured-rock aquifers in the area of Gettysburg, Pa., is used as drinking water and for industrial and commercial supply. In 1983, ground water at the Gettysburg Elevator Plant was found by the Pennsylvania Department of Environmental Resources to be contaminated with trichloroethene, 1,1,1-trichloroethane, and other synthetic organic compounds. As part of the U.S. Environmental Protection Agency?s Comprehensive Environmental Response, Compensation, and Liability Act, 1980 process, a Remedial Investigation was completed in July 1991, a method of site remediation was issued in the Record of Decision dated June 1992, and a Final Design Report was completed in May 1997. In cooperation with the U.S. Environmental Protection Agency in the hydrogeologic assessment of the site remediation, the U.S. Geological Survey began a study in 1997 to determine the effects of the onsite and offsite extraction wells on ground-water flow and contaminant migration from the Gettysburg Elevator Plant. This determination is based on hydrologic and geophysical data collected from 1991 to 1998 and on results of numerical model simulations of the local ground-water flow-system. The Gettysburg Elevator Site is underlain by red, green, gray, and black shales of the Heidlersburg Member of the Gettysburg Formation. Correlation of natural-gamma logs indicates the sedimentary rock strike about N. 23 degrees E. and dip about 23 degrees NW. Depth to bedrock onsite commonly is about 6 feet but offsite may be as deep as 40 feet. The ground-water system consists of two zones?a thin, shallow zone composed of soil, clay, and highly weathered bedrock and a thicker, nonweathered or fractured bedrock zone. The shallow zone overlies the bedrock zone and truncates the dipping beds parallel to land surface. Diabase dikes are barriers to ground-water flow in the bedrock zone. The ground-water system is generally confined or semi-confined, even at shallow depths. Depth to water can range from flowing at land surface to more than 71 feet below land surface. Potentiometric maps based on measured water levels at the Gettysburg Elevator Plant indicate ground water flows from west to east, towards Rock Creek. Multiple-well aquifer tests indicate the system is heterogeneous and flow is primarily in dipping beds that contain discrete secondary openings separated by less permeable beds. Water levels in wells open to the pumped bed, as projected along the dipping stratigraphy, are drawn down more than water levels in wells not open to the pumped bed. Ground-water flow was simulated for steady-state conditions prior to pumping and long-term average pumping conditions. The three-dimensional numerical flow model (MODFLOW) was calibrated by use of a parameter estimation program (MODFLOWP). Steady-state conditions were assumed for the calibration period of 1996. An effective areal recharge rate of 7 inches was used in model calibration. The calibrated flow model was used to evaluate the effectiveness of the current onsite and offsite extraction well system. The simulation results generally indicate that the extraction system effectively captures much of the ground-water recharge at the Gettysburg Elevator Plant and, hence, contaminated ground-water migrating from the site. Some of the extraction wells pump at low rates and have very small contributing areas. Results indicate some areal recharge onsite will move to offsite extraction wells.

Low, Dennis J.; Goode, Daniel J.; Risser, Dennis W.

2000-01-01

310

Simulation of groundwater flow and hydrologic effects of groundwater withdrawals from the Kirkwood-Cohansey aquifer system in the Pinelands of southern New Jersey  

USGS Publications Warehouse

The Kirkwood-Cohansey aquifer system is an important source of present and future water supply in southern New Jersey. Because this unconfined aquifer system also supports sensitive wetland and aquatic habitats within the New Jersey Pinelands (Pinelands), water managers and policy makers need up-to-date information, data, and projections that show the effects of potential increases in groundwater withdrawals on these habitats. Finite-difference groundwater flow models (MODFLOW) were constructed for three drainage basins (McDonalds Branch Basin, 14.3 square kilometers (km2); Morses Mill Stream Basin, 21.63 km2; and Albertson Brook Basin, 52.27 km2) to estimate the effects of potential increases in groundwater withdrawals on water levels and the base-flow portion of streamflow, in wetland and aquatic habitats. Three models were constructed for each drainage basin: a transient model consisting of twenty-four 1-month stress periods (October 2004 through September 2006); a transient model to simulate the 5- to 10-day aquifer tests that were performed as part of the study; and a high-resolution, steady-state model used to assess long-term effects of increased groundwater withdrawals on water levels in wetlands and on base flow. All models were constructed with the same eight-layer structure. The smallest horizontal cell dimensions among the three model areas were 150 meters (m) for the 24-month transient models, 10 m for the steady-state models, and 3 m for the transient aquifer-test models. Boundary flows of particular interest to this study and represented separately are those for wetlands, streams, and evapotranspiration. The final variables calibrated from both transient models were then used in steady-state models to assess the long-term effects of increased groundwater withdrawals on water levels in wetlands and on base flow. Results of aquifer tests conducted in the three study areas illustrate the effects of withdrawals on water levels in wetlands and on base flow. Pumping stresses at aquifer-test sites resulted in measurable drawdown in each observation well installed for the tests. The magnitude of drawdown in shallow wetland observation wells at the end of pumping ranged from 5.5 to 16.7 centimeters (cm). The stresses induced by the respective tests reduced the flow of the smallest stream (McDonalds Branch) by 75 percent and slightly reduced flow in a side channel of Morses Mill Stream, but did not measurably affect the flow of Morses Mill Stream or Albertson Brook. Results of aquifer-test simulations were used to refine the estimates of hydraulic properties used in the models and to confirm the ability of the model to replicate observed hydrologic responses to pumping. Steady-state sensitivity simulation results for a variety of single well locations and depths were used to define overall “best-case” (smallest effect on wetland water levels and base flow) and “worst-case” (greatest effect on wetland water levels and base flow) groundwater withdrawal configurations. “Best-case” configurations are those for which the extent of the wetland areas within a 1-kilometer (km) radius of the withdrawal well is minimized, the well is located at least 100 m and as far from wetland boundaries as possible, and the withdrawal is from a deep well (50–90 m deep). “Worst-case” configurations are those for which the extent of wetlands within a 1-km radius of the withdrawal well is maximized, the well is located 100 m or less from a wetland boundary, and the withdrawal is from a relatively shallow well (30–67 m deep). “Best-” and “worst-case” simulations were applied by locating hypothetical wells across the study areas and assigning groundwater withdrawals so that the sum of the withdrawals for the basin is equal to 5, 10, 15, and 30 percent of overall recharge. The results were compared to the results of simulations of no groundwater withdrawals. Results for withdrawals of 5 percent of recharge show that the area of wetland water-level decline that exceeded 15 cm was as much as 1.5 percent of the total we

Charles, Emmanuel G.; Nicholson, Robert S.

2012-01-01

311

The fate of Nitrate under the natural groundwater flow system in a volcanic aquifer composed by pyroclastic flow  

NASA Astrophysics Data System (ADS)

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

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

2008-12-01

312

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

313

Estimation of streambed groundwater fluxes associated with coaster brook trout spawning habitat.  

PubMed

We hypothesized that the spatial distribution of groundwater inflows through river bottom sediments is a critical factor associated with the distribution of coaster brook trout (a life history variant of Salvelinus fontinalis) spawning redds. An 80-m reach of the Salmon Trout River, in the Huron Mountains of the upper peninsula of Michigan, was selected to test the hypothesis based on long-term documentation of coaster brook trout spawning at this site. A monitoring well system consisting of 22 wells was installed in the riverbed to measure surface and subsurface temperatures over a 13-month period. The array of monitoring wells was positioned to span areas where spawning has and has not been observed. Over 200,000 total temperature measurements were collected from five depths within each monitoring well. Temperatures in the substrate beneath the spawning area were generally less variable than river temperatures, whereas temperatures under the nonspawning area were generally more variable and closely tracked temporal variations in river temperatures. Temperature data were inverted to obtain subsurface groundwater velocities using a numerical approximation of the heat transfer equation. Approximately 45,000 estimates of groundwater velocities were obtained. Estimated groundwater velocities in the spawning area were primarily in the upward direction and were generally greater in magnitude than velocities in the nonspawning area. Both the temperature and velocity results confirm the hypothesis that spawning sites correspond to areas of significant groundwater flux into the river bed. PMID:21883191

Van Grinsven, Matthew; Mayer, Alex; Huckins, Casey

2012-01-01

314

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...

315

Seasonal changes in groundwater storage estimated by absolute ground gravity and MRS surveys in West Africa  

Microsoft Academic Search

Important and fast groundwater storage changes occur in tropical monsoon regions in response to seasonal rainfall and subsequent surface water redistribution. In West Africa, one main goal of the GHYRAF experiment (Gravity and Hydrology in Africa, 2008-2010) is to compare absolute gravimetric measurements with dense hydrological surveys to better estimate and model water storage changes at various time scales. Magnetic

G. Favreau; M. Boucher; B. Luck; J. Pfeffer; P. Genthon; J. Hinderer

2009-01-01

316

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

317

Annual drought flow and groundwater storage trends in the eastern half of the United States during the past two-third century  

Microsoft Academic Search

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

Wilfried Brutsaert

2010-01-01

318

Simulation of vertical compaction in models of regional ground-water flow  

USGS Publications Warehouse

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

Leake, S. A.

1991-01-01

319

Statistical Estimation and Visualization of Ground-Water Contamination Data.  

National Technical Information Service (NTIS)

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 estima...

R. K. Boeckenhauer D. D. Cox K. B. Ensor P. B. Bedient A. W. Holder

2000-01-01

320

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

321

Framework for Uncertainty Assessment - Hanford Site-Wide Groundwater Flow and Transport Modeling  

Microsoft Academic Search

Pacific Northwest National Laboratory is in the process of development and implementation of an uncertainty estimation methodology for use in future site assessments that addresses parameter uncertainty as well as uncertainties related to the groundwater conceptual model. The long-term goals of the effort are development and implementation of an uncertainty estimation methodology for use in future assessments and analyses being

M. P. Bergeron; C. R. Cole; C. J. Murray; P. D. Thorne; S. K. Wurstner

2002-01-01

322

Integrating address geocoding, land use regression, and spatiotemporal geostatistical estimation for groundwater tetrachloroethylene.  

PubMed

Geographic information systems (GIS) based techniques are cost-effective and efficient methods used by state agencies and epidemiology researchers for estimating concentration and exposure. However, budget limitations have made statewide assessments of contamination difficult, especially in groundwater media. Many studies have implemented address geocoding, land use regression, and geostatistics independently, but this is the first to examine the benefits of integrating these GIS techniques to address the need of statewide exposure assessments. A novel framework for concentration exposure is introduced that integrates address geocoding, land use regression (LUR), below detect data modeling, and Bayesian Maximum Entropy (BME). A LUR model was developed for tetrachloroethylene that accounts for point sources and flow direction. We then integrate the LUR model into the BME method as a mean trend while also modeling below detects data as a truncated Gaussian probability distribution function. We increase available PCE data 4.7 times from previously available databases through multistage geocoding. The LUR model shows significant influence of dry cleaners at short ranges. The integration of the LUR model as mean trend in BME results in a 7.5% decrease in cross validation mean square error compared to BME with a constant mean trend. PMID:22264162

Messier, Kyle P; Akita, Yasuyuki; Serre, Marc L

2012-03-01

323

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

324

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