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At least 253 records · Page 14Linked to original sources
USGS2003

Aquifer tests and simulation of ground-water flow in Triassic sedimentary rocks near Colmar, Bucks and Montgomery Counties, Pennsylvania

This report presents the results of a study by the U.S. Geological Survey in cooperation with the U.S. Environmental Protection Agency to evaluate ground-water flow in Triassic sedimentary rocks near Colmar, in Bucks and Montgomery Counties, Pa. The study was conducted to help the U.S. Environmental Protection Agency evaluate remediation alternatives at the North Penn Area 5 Superfund Site near Colmar, where ground water has been contaminated by volatile organic solvents (primarily trichloroethene). The investigation focused on determining the (1) drawdown caused by separately pumping North PennWater Authority wells NP–21 and NP–87, (2) probable paths of groundwater movement under present-day (2000) conditions (with NP–21 discontinued), and (3) areas contributing recharge to wells if pumping from wells NP-21 or NP–87 were restarted and new recovery wells were installed. Drawdown was calculated from water levels measured in observation wells during aquifer tests of NP–21 and NP–87. The direction of ground-water flow was estimated by use of a three-dimensional ground-water-flow model. Aquifer tests were conducted by pumping NP–21 for about 7 days at 257 gallons per minute in June 2000 and NP–87 for 3 days at 402 gallons per minute in May 2002. Drawdown was measured in 45 observation wells during the NP–21 test and 35 observation wells during the NP–87 test. Drawdown in observation wells ranged from 0 to 6.8 feet at the end of the NP–21 test and 0.5 to 12 feet at the end of the NP–87 test. The aquifer tests showed that ground-water levels declined mostly in observation wells that were completed in the geologic units penetrated by the pumped wells. Because the geologic units dip about 27 degrees to the northwest, shallow wells up dip to the southeast of the pumped well showed a good hydraulic connection to the geologic units stressed by pumping. Most observation wells down dip from the pumping well penetrated units higher in the stratigraphic section that were not well connected to the units stressed by pumping. The best hydraulic connection to the pumped wells was indicated by large drawdown in observation wells that penetrate the water-bearing unit encountered below 400 feet below land surface in wells NP–21 and NP–87. The hydraulic connection between wells NP–21 (or NP–87) and observation wells in the southern area of ground-water contamination near the BAE Systems facility is good because the observation wells probably penetrate this water-bearing unit. A 3-dimensional, finite-difference, groundwater- flow model was used to simulate flow paths and areas contributing recharge to wells for current (2000) conditions of pumping in the Colmar area and for hypothetical situations of pumping suggested by the U.S. Environmental Protection Agency that might be used for remediation. Simulations indicate that under current conditions, ground water in the northern area of contamination near the former Stabilus facility moves to the northwest and discharges mostly to West Branch Neshaminy Creek; in the southern area of contamination near BAE Systems facility, ground water probably moves west and discharges to a tributary of West Branch Neshaminy Creek near well NP–21. Model simulations indicate that if NP–21 or NP–87 are pumped at 400 gallons per minute, groundwater recharge is likely captured from the southern area of contamination, but ground-water recharge from the northern area of contamination is less likely to be captured by the pumping. Simulations also indicate that pumping of a new recovery well near BAE Systems facility at 8 gallons per minute and two new recovery wells near the former Stabilus facility at a total of about 30 gallons per minute probably would capture most of the ground-water recharge in the areas where contamination is greatest.

Water-Resources Investigations Report↗
USGS2003

Case study for delineating a contributing area to a well in a fractured siliciclastic-bedrock aquifer near Lansdale, Pennsylvania

A supply well used by the North Penn Water Authority near Lansdale, Pa., was selected as a case study for delineating a contributing area in a fractured siliciclastic-bedrock aquifer. The study emphasized the importance of refining the understanding of factors that control ground-water movement to the well by conducting (1) geophysical logging and flow measurements, (2) ground-water level monitoring, (3) aquifer testing, and (4) geochemical sampling. This approach could be applicable for other wells in siliciclastic-bedrock terranes, especially those of Triassic age in southeastern Pennsylvania. The principal methods for refining the understanding of hydrology at supply well MG-1125 were aquifer testing, water-level measurements, and geophysical logging. Results of two constant-discharge aquifer tests helped estimate the transmissivity of water-producing units and evaluate the anisotropy caused by dipping beds. Results from slug tests provided estimates of transmissivity that were used to evaluate the results from the constant-discharge aquifer tests. Slug tests also showed the wide distribution of transmissivity, indicating that ground-water velocities must vary considerably in the well field. Water-level monitoring in observation wells allowed maps of the potentiometric surface near the well field to be drawn. The measurements also showed that the hydraulic gradient can change abruptly in response to pumping from nearby supply wells. Water levels measured at a broader regional scale in an earlier study also provided a useful view of the potentiometric surface for purposes of delineating the contributing area. Geophysical logging and measurements of flow within wells showed that about 60 percent of water from supply well MG-1125 probably is contributed from relatively shallow water-producing fractures from 60 to 125 feet below land surface, but measurable amounts of water are contributed by fractures to a depth of 311 feet below land surface. Chemical samples supported the evidence that shallow fractures probably contribute significant amounts of water to well MG-1125. The large contribution of water from shallow fractures indicates that the area providing part of the recharge to the well is not far removed from the wellhead. Preliminary delineations of the contributing area and the 100-day time-of travel area were computed from a water budget and time-of-travel equation. These delineations provided insight into the size (but not the shape) of the contributing areas. Three other approaches were used and results compared: (1) uniform-flow equation, (2) hydrogeologic mapping, and (3) numerical modeling. The uniform-flow equation predicted a contributing area that seemed unrealistic—extending far across the ground-water divide into an adjacent watershed. Hydrogeologic mapping, if used with the potentiometric surface and constrained by the water budget, produced contributing area that was similar to that from numerical modeling. Numerical modeling allowed the incorporation of anisotropy caused by dipping water-producing units, differing transmissivity values of geologic units, and ground-water withdrawals from nearby supply wells. The numerical modeling showed that groundwater withdrawals from nearby supply wells affected the contributing area to supply well MG-1125 but had less effect on the 100-day time-of-travel area.

Water-Resources Investigations Report↗
USGS2005

Characterization of surface-water quality in the S-Line Canal and potential geochemical reactions from storage of surface water in the Basalt aquifer near Fallon, Nevada

The Fallon basalt aquifer serves as the sole source of municipal water supply for the Lahontan Valley in west-central Nevada. Principal users include the City of Fallon, Naval Air Station Fallon, and the Fallon Paiute-Shoshone Tribe. Pumpage from the aquifer increased from about 1,700 acre-feet per year in the early 1970's to more than 3,000 acre-feet per year in the late 1990's, and has been accompanied by declines in water levels and changes in water quality. Storage of surface water in the basalt may mitigate the effects of pumpage, but may cause undesirable changes in water chemistry. In May 2001, the U.S. Geological Survey began a study, in cooperation with the Fallon Paiute-Shoshone Tribe, to characterize the surface-water quality of the S-Line Canal, a likely source of water for augmenting recharge. Because arsenic concentrations in ground water of the basalt aquifer exceed drinking water standards, the potential for arsenic release to artificial recharge was explored by using geochemical modeling. Model results suggest that arsenic release may increase concentrations to levels that could limit the use of artificial recharge. Field-based experiments are needed to evaluate the underlying model assumptions.

Scientific Investigations Report↗
USGS1996

Evaluation of agricultural best-management practices in the Conestoga River headwaters, Pennsylvania: Effects of nutrient management on water quality in the Little Conestoga Creek headwaters, 1983-89

Water quality in the headwaters of the Little Conestoga Creek, Lancaster County, Pa., was investigated from April 1986 through September 1989 to determine possible effects of agricultural nutrient management on water quality. Nutrient management, an agricultural Best-Management Practice, was promoted in the 5.8-square-mile watershed by the U.S. Department of Agriculture Rural Clean Water Program. Nonpoint-source- agricultural contamination was evident in surface water and ground water in the watershed; the greatest contamination was in areas underlain by carbonate rock and with intensive row-crop and animal production. Initial implementation of nutrient management covered about 30 percent of applicable land and was concentrated in the Nutrient-Management Subbasin. By 1989, nutrient management covered about 45 percent of the entire Small Watershed, about 85 percent of the Nutrient- Management Subbasin, and less than 10 percent of the Nonnutrient-Management Subbasin. The number of farms implementing nutrient management increased from 14 in 1986 to 25 by 1989. Nutrient applications to cropland in the Nutrient- Management Subbasin decreased by an average of 35 percent after implementation. Comparison of base- flow surface-water quality from before and after implementation suggests that nutrient management was effective in slowing or reversing increases in concentrations of dissolved nitrate plus nitrite in the Nutrient-Management Subbasin. Although not statistically significant, the Mann-Whitney step-trend coefficient for the Nutrient-Management Subbasin was 0.8 milligram per liter, whereas trend coefficients for the Nonnutrient-Management Subbasin and the Small Watershed were 0.4 and 1.4 milligrams per liter, respectively, for the period of study. Analysis of covariance comparison of concurrent concentrations from the two sub- basins showed a significant decrease in concen- trations from the Nutrient-Management Subbasin compared to the Nonnutrient-Management Subbasin. The small, positive effect of nutrient management on base-flow water quality should be interpreted with caution. Lack of statistical significance for most tests, short-term variation in climate and agricultural activities, unknown ground-water flow rates, and insufficient agricultural-activity data for farms outside of the Nutrient-Management Subbasin were potential problems. A regression model relating nutrient applications to concen- trations of dissolved nitrate plus nitrite showed no significant explanatory relation.

Pennsylvania↗
USGS1999

Water Budget of East Maui, Hawaii

Ground-water recharge is estimated from six monthly water budgets calculated using long-term average rainfall and streamflow data, estimated pan-evaporation and fog-drip data, and soil characteristics. The water-budget components are defined seasonally, through the use of monthly data, and spatially by broad climatic and geohydrologic areas, through the use of a geographic information system model. The long-term average water budget for east Maui was estimated for natural land-use conditions. The average rainfall, fog-drip, runoff, evapotranspiration, and ground-water recharge volumes for the east Maui study area are 2,246 Mgal/d, 323 Mgal/d, 771 Mgal/d, 735 Mgal/d, and 1,064 Mgal/d, respectively.

Water-Resources Investigations Report↗
USGS1996

Summary of the San Juan structural basin regional aquifer-system analysis, New Mexico, Colorado, Arizona, and Utah

Ground-water resources are the only source of water in most of the San Juan structural basin and are mainly used for municipal, industrial, domestic, and stock purposes. Industrial use increased dramatically during the late 1970's and early 1980's because of increased exploration and development of uranium and coal resources. The San Juan structural basin is a northwest-trending, asymmetric structural depression at the eastern edge of the Colorado Plateau. The basin contains as much as 14,000 feet of sedimentary rocks overlying a Precambrian basement complex. The sedimentary rocks dip basinward from the basin margins toward the troughlike structural center, or deepest part of the basin. Rocks of Triassic age were selected as the lower boundary for the study. The basin is well defined by structural boundaries in many places with structural relief of as much as 20,000 feet reported. Faulting is prevalent in parts of the basin with displacement of several thousand feet along major faults. The regional aquifers in the basin generally are coincident with the geologic units that have been mapped. Data on the hydrologic properties of the regional aquifers are minimal. Most data were collected on those aquifers associated with uranium and coal resource production. These data are summarized in table format in the report. The regional flow system throughout most of the basin has been affected by the production of oil or gas and subsequent disposal of produced brine. To date more than 26,000 oil- or gas- test holes have been drilled in the basin, the majority penetrating no deeper than the bottom of the Cretaceous rocks. The general water chemistry of the regional aquifers is based on available data. The depositional environments are the major factor controlling the quality of water in the units. The dominant ions are generally sodium, bicarbonate, and sulfate. A detailed geochemical study of three sandstone aquifers--Morrison, Dakota, and Gallup--was undertaken in the northwestern part of the study area. Results of this study indicate that water chemistry changed in individual wells over short periods of time, not expected in a regional flow system. The chemistry of the water is affected by mixing of recharge, ion filtrate, or very dilute ancient water, and by leakage of saline water. The entire system of ground-water flow and its controlling factors has been defined as the conceptual model. A steady-state, three-dimensional ground-water flow model was constructed to simulate modern predevelopment flow in the post-Jurassic rocks of the regional flow system. In the ground-water flow model, 14 geologic units or combinations of geologic units were considered to be regional aquifers, and 5 geologic units or combinations of geologic units were considered to be regional confining units. The model simulated flow in 12 layers (hydrostratigraphic units) and used harmonic-mean vertical leakance to indirectly simulate aquifer connection across 3 other hydrostratigraphic confining units in addition to coupling the 12 units.

Water-Resources Investigations Report↗
USGS1996

Geology, hydrogeology, and potential of intrinsic bioremediation at the National Park Service Dockside II site and adjacent areas, Charleston, South Carolina, 1993-94

A long history of industrial and commercial use of the National Park Service property and adjacent properties located in downtown Charleston, South Carolina, has caused extensive contamination of the shallow subsurface soils and water-table aquifer. The National Park Service property is located adjacent to a former manufactured-gas plant site, which is the major source of the contamination. Contamination of this shallow water-table aquifer is of concern because shallow ground water discharges to the Cooper River and contains contaminants, which may affect adjacent wildlife or human populations. The geology of the National Park Service property above the Ashley Formation of the Cooper Group consists of two Quaternary lithostratigraphic marine units, the Wando Formation and Holocene deposits, overlain by artificial fill. The Wando Formation overlies the Ashley Formation, a sandy calcareous clay, and consists of soft, organic clay overlain by gray sand. The Holocene deposits are composed of clayey to silty sand and soft organic-rich clay. The artificial fill, which was placed at the site to create dry land where salt marsh existed previously, is composed of sand, silt, and various scrap materials. The shallow hydrogeology of the National Park Service property overlying the Ashley Formation can be subdivided into two sandy aquifers separated by a leaky, black, organic-rich clay. The unconfined upper surficial aquifer is primarily artificial fill. The lower surficial aquifer consists of the Wando sand unit and is confined by the leaky organic-rich clay. Aquifer tests performed on the wells screened in these aquifers resulted in hydraulic conductivities from 0.1 to 10 feet per day for the upper surficial aquifer, and 16 feet per day for the lower surficial aquifer. Vertical hydraulic gradients at the site are typically low. A downward gradient from the upper surficial aquifer to the lower surficial aquifer occurs throughout most of the year. A brick-lined storm-water-drainage archway located in the study area is a conduit for the overflow of seawater into the surficial aquifer during exceptionally high tides. The efficiency of intrinsic bioremediation to reduce contaminant migration in the upper surficial aquifer at the National Park Service site was assessed to determine if, and at what concentrations, contaminants are being transported to the Cooper River. This assessment required incorporating hydrologic, geochemical, microbiologic, and demographic information into a predictive solute-transport model to determine rates of contaminant transport to the Cooper River. The transport of toluene and naphthalene was modeled as a surrogate for the transport of aromatic and other hydrocarbon compounds at the study area. Laboratory estimates of the adsorption coefficients for sediments of the upper surficial aquifer suggest preferential adsorption of naphthalene over toluene. The adsorption coefficient of naphthalene is at least two orders of magnitude greater than that determined for toluene. Laboratory microbial-biodegradation experiments indicate that microorganisms present in the shallow aquifer have the potential to degrade toluene under anaerobic and aerobic conditions, and naphthalene primarily under aerobic conditions. Rates of microbial biodegradation are similar for both compounds under aerobic conditions. Flow-model calibration to the January 1994 water-table surface of the upper surficial aquifer was achieved by specifying appropriate hydrogeologic boundary conditions and using hydraulic conductivity values determined in the field. The brick-lined storm-water drainage archway located in the study area was modeled to account for ground-water discharge through this drain. An exploratory modeling approach was used to evaluate the range of possible solutions that approximate the transport of contaminants to the observed distributions. Approximate toluene solute-transport conditions for January 1994 were estimated using velocity dist

South Carolina↗
USGS2002

Preliminary report on geophysical data in Yavapai County, Arizona

Recently acquired geophysical data provide information on the geologic framework and its effect of groundwater flow and on stream/aquifer interaction in Yavapai County, Arizona. High-resolution aeromagnetic data reflect diverse rock types at and below the topographic surface and have permitted a preliminary interpretation of faults and underlying rock types (in particular, volcanic) that will provide new insights on the geologic framework, critical input to future hydrologic investigations. Aeromagnetic data map the western end of the Bear Wallow Canyon fault into the sedimentary fill of Verde Valley. Regional gravity data indicate potentially significant accumulations of low-density basin fill in Big Chino, Verde, and Williamson Valleys. Electrical and seismic data were also collected and help evaluate the approximate depth and extent of recent alluvium overlying Tertiary and Paleozoic sediments. These data will be used to ascertain the potential contribution of shallow ground-water subflow that cannot be measured by gages or flow meters and whether stream flow in losing reaches is moving as subflow or is being lost to the subsurface. The geophysical data will help produce a more robust groundwater flow model of the region.

Arizona↗
USGS1983

Hydrologic conditions in the Wheatland Flats area, Platte County, Wyoming

The area includes about 260 square miles in central Platte County that consists of Wheatland Flats and a border region. Wheatland Flats is an area of about 100 square miles that is bounded by Chugwater Creek on the east, the Laramie River on the north, and Sybille Creek on the west. The southern boundary is approximately the southernmost limit of alluvial terrace deposits. Surface water diverted from the Laramie River along with ground water from wells is used to irrigate about 57,000 acres most of which are on and adjacent to Wheatland Flats. More than 200 wells are used for irrigation, industrial, and municipal supplies. The wells are completed in an upper aquifer consisting primarily of shallow alluvial deposits of Quaternary age and a lower aquifer, the Arikaree Formation of early Miocene age. Net water-level decline after approximately 20 years (1958-60 to 1979) generally is less than 10 feet in each aquifer , although declines of as much as 13 feet have occurred in the Airkaree Formation at specific locations. A digital model was used to simulate hydrologic conditions in the Wheatland Flats area. The model indicated that ground-water discharge to streams decreased by 10 percent from 1971 to 1978. Stream-discharge measurements are not available to verify the loss. However, it is reasonable to assume, on the basis of hydraulic-head decline in the aquifers, that there has been some ground-water contribution to the stream. (USGS)

Water-Resources Investigations Report↗
USGS2005

Classification of hydrogeologic areas and hydrogeologic flow systems in the basin and range physiographic province, southwestern United States

The hydrogeology of the Basin and Range Physiographic Province in parts of Arizona, California, New Mexico, Utah, and most of Nevada was classified at basin and larger scales to facilitate information transfer and to provide a synthesis of results from many previous hydrologic investigations. A conceptual model for the spatial hierarchy of the hydrogeology was developed for the Basin and Range Physiographic Province and consists, in order of increasing spatial scale, of hydrogeologic components, hydrogeologic areas, hydrogeologic flow systems, and hydrogeologic regions. This hierarchy formed a framework for hydrogeologic classification. Hydrogeologic areas consist of coincident ground-water and surface-water basins and were delineated on the basis of existing sets of basin boundaries that were used in past investigations by State and Federal government agencies. Within the study area, 344 hydrogeologic areas were identified and delineated. This set of basins not only provides a framework for the classification developed in this report, but also has value for regional and subregional purposes of inventory, study, analysis, and planning throughout the Basin and Range Physiographic Province. The fact that nearly all of the province is delineated by the hydrogeologic areas makes this set well suited to support regional-scale investigations. Hydrogeologic areas are conceptualized as a control volume consisting of three hydrogeologic components: the soils and streams, basin fill, and consolidated rocks. The soils and streams hydrogeologic component consists of all surface-water bodies and soils extending to the bottom of the plant root zone. The basin-fill hydrogeologic component consists of unconsolidated and semiconsolidated sediment deposited in the structural basin. The consolidated-rocks hydrogeologic component consists of the crystalline and sedimentary rocks that form the mountain blocks and basement rock of the structural basin. Hydrogeologic areas were classified into 19 groups through a cluster analysis of 8 characteristics of each area's hydrologic system. Six characteristics represented the inflows and outflows of water through the soils and streams, basin fill, and consolidated rocks, and can be used to determine the hydrogeologic area's position in a hydrogeologic flow system. Source-, link-, and sink-type hydrogeologic areas have outflow but not inflow, inflow and outflow, and inflow but not outflow, respectively, through one or more of the three hydrogeologic components. Isolated hydrogeologic areas have no inflow or outflow through any of the three hydrogeologic components. The remaining two characteristics are indexes that represent natural recharge and discharge processes and anthropogenic recharge and discharge processes occurring in the hydrogeologic area. Of the 19 groups of hydrogeologic areas, 1 consisted of predominantly isolated-type hydrogeologic areas, 7 consisted of source-type hydrogeologic areas, 9 consisted of link-type hydrogeologic areas, and 2 consisted of sink-type hydrogeologic areas. Groups comprising the source-, link-, and sink-type hydrogeologic areas can be distinguished between each other on the basis of the hydrogeologic component(s) through which interbasin flow occurs, as well as typical values for the two indexes. Conceptual models of the hydrologic systems of a representative hydrogeologic area for each group were developed to help distinguish groups and to synthesize the variation in hydrogeologic systems in the Basin and Range Physiographic Province. Hydrogeologic flow systems consist of either a single isolated hydrogeologic area or a series of multiple hydrogeologic areas that are hydraulically connected through interbasin flows. A total of 54 hydrogeologic flow systems were identified and classified into 9 groups. One group consisted of single isolated hydrogeologic areas. The remaining eight groups consisted of multiple hydrogeologic areas and were distinguished o

Professional Paper↗
USGS1978

Preliminary hydrologic budget of the sand-and-gravel aquifer under unstressed conditions: with a section on water-quality monitoring, Pensacola, Florida

The sand-and-gravel aquifer is the only freshwater aquifer in southern Escambia County, Fla. Problems related to the development of the aquifer include sustained yield, contamination, and saltwater intrusion. A digital model was applied to the sand-and-gravel aquifer in central and southern Escambia County treating the aquifer 's 'main producing zone ' as a discrete, leaky, confined aquifer. Under conditions of no pumping, most values for the final-head matrix agreed with assumed values within 4 feet in the area of principal interest. Discharge per unit land area was 1.04 cubic feet per second per square mile, in close agreement with the base runoff streams maintained by the aquifer. Total natural aquifer discharge within the area of principal interest determined by the model was 159 million gallons per day. The applicability of the present non-unique calibration for predicting the effects of pumping is questionable; a multilayered model may be required. Effluent infiltrating from holding lagoons for spray irrigation at the Scenic Hills Sewage Plant may have affected the quality of local perched ground water in the sand-and-gravel aquifer. Observation wells drilled near areas of heavy pumping around Bayou Chico indicated no saltwater intrusion. (Woodard-USGS)

Florida↗
USGS2002

Three-dimensional measurements of flow in uncased wells completed in basalt, Mountain Home Air Force Base, Idaho, March 2000

Several ground-water monitoring wells on the Mountain Home Air Force Base in southwestern Idaho were constructed in February 2000 to replace existing monitoring wells that became ineffective as a result of declining water levels. Upon completion of the replacement wells, borehole geophysical logs were collected, including natural gamma radiation, electromagnetic induction, caliper, fluid temperature, and resistivity. A prototype borehole acoustic doppler velocimeter (B-ADV) was used to make experimental three-dimensional measurements of lateral and vertical flow in two of the replacement wells, MW11–2 and MW3–2, each 450 feet deep, to better understand ground-water flow in the basalt underlying this area. Measurements indicated two independent flow zones in each well: unit B, from about 380 to about 415 feet below land surface, and unit C, from about 415 to about 430 feet below land surface. In each well, direction of flow in unit B was north-northwest toward Canyon Creek and, in unit C, south-southwest toward the Snake River. Measurements also indicated downward intraborehole flow in both wells. Unit B appeared to represent a local-scale flow regime; unit C appeared to represent a regional flow regime. This information suggests the existence of a complex three-dimensional hydrogeologic setting that cannot be discriminated easily on conventional waterlevel maps. Although data from only two wells are insufficient to construct a conceptual model of the ground-water flow regime, these experimental results demonstrate the capability of the B-ADV to obtain detailed flow measurements that, combined with data from other types of geophysical logs, discrete measurements of hydraulic head, and water chemistry, would aid in future studies and management of the ground-water resources, including contaminant transport and remediation.

Idaho↗
USGS1979

Effects of pumping on ground-water levels near Taylorsville, Bartholomew County, Indiana

A two-dimensional digital flow model was used to estimate the effects of continuous pumping of a public-supply well field on the ground-water levels near Taylorsville, Indiana. Results of the modeling showed that the water levels would decline from less than 1 to about 4.5 feet within the study area and a maximum of 1 to 2 feet in Taylorsville in response to a pumping rate of 700 gallons per minute. Model results also show that the ground-water system would reach steady state in approximately 5 years after pumping begins. Corrections applied to water-level declines indicated by the model, to account for the effects of partial penetration of the aquifer by wells, showed that these effects, although substantial in the pumping wells, are negligible 200 feet from the wells.

Indiana↗
USGS1984

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

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

Water-Resources Investigations Report↗
USGS2005

Effects of alternative instream-flow criteria and water-supply demands on ground-water development options in the Big River Area, Rhode Island

Transient numerical ground-water-flow simulation and optimization techniques were used to evaluate potential effects of instream-flow criteria and water-supply demands on ground-water development options and resultant streamflow depletions in the Big River Area, Rhode Island. The 35.7 square-mile (mi2) study area includes three river basins, the Big River Basin (30.9 mi2), the Carr River Basin (which drains to the Big River Basin and is 7.33 mi2 in area), the Mishnock River Basin (3.32 mi2), and a small area that drains directly to the Flat River Reservoir. The overall objective of the simulations was to determine the amount of ground water that could be withdrawn from the three basins when constrained by streamflow requirements at four locations in the study area and by maximum rates of withdrawal at 13 existing and hypothetical well sites. The instream-flow requirement for the outlet of each basin and the outfall of Lake Mishnock were the primary variables that limited the amount of ground water that could be withdrawn. A requirement to meet seasonal ground-water-demand patterns also limits the amount of ground water that could be withdrawn by up to about 50 percent of the total withdrawals without the demand-pattern constraint. Minimum water-supply demands from a public water supplier in the Mishnock River Basin, however, did not have a substantial effect on withdrawals in the Big River Basin. Hypothetical dry-period instream-flow requirements and the effects of artificial recharge also affected the amount of ground water that could be withdrawn. Results of simulations indicate that annual average ground-water withdrawal rates that range up to 16 million gallons per day (Mgal/d) can be withdrawn from the study area under simulated average hydrologic conditions depending on instream-flow criteria and water-supply demand patterns. Annual average withdrawals of 10 to 12 Mgal/d are possible for proposed demands of 3.4 Mgal/d in the Mishnock Basin, and for a constant annual instream-flow criterion of 0.5 cubic foot per second per square mile (ft3/s/mi2) at the four streamflow-constraint locations. An average withdrawal rate of 10 Mgal/d can meet estimates of future (2020) water-supply needs of surrounding communities in Rhode Island. This withdrawal rate represents about 13 percent of the average 2002 daily withdrawal from the Scituate Reservoir (76 Mgal/d), the State?s largest water supply. Average annual withdrawal rates of 6 to 7 Mgal/d are possible for more stringent instream-flow criteria that might be used during dry-period hydrologic conditions. Two example scenarios of dry-period instream-flow constraints were evaluated: first, a minimum instream flow of 0.1 cubic foot per second at any of the four constraint locations; and second, a minimum instream flow of 10 percent of the minimum monthly streamflow estimate for each streamflow-constraint location during the period 1961?2000. The State of Rhode Island is currently (2004) considering methods for establishing instream-flow criteria for streams within the State. Twelve alternative annual, seasonal, or monthly instream-flow criteria that have been or are being considered for application in southeastern New England were used as hypothetical constraints on maximum ground-water-withdrawal rates in management-model calculations. Maximum ground-water-withdrawal rates ranged from 5 to 16 Mgal/d under five alternative annual instream-flow criteria. Maximum ground-water-withdrawal rates ranged from 0 to 13.6 Mgal/d under seven alternative seasonal or monthly instream-flow criteria. The effect of ground-water withdrawals on seasonal variations in monthly average streamflows under each criterion also were compared. Evaluation of management-model results indicates that a single annual instream-flowcriterion may be sufficient to preserve seasonal variations in monthly average streamflows and meet water-supply demands in the Big River Area, because withdrawals from wells in the Big

Scientific Investigations Report↗
USGS1976

Preliminary digital model of ground-water flow in the Madison Group, Powder River Basin and adjacent areas, Wyoming, Montana, South Dakota, North Dakota, and Nebraska

A digital simulation model was used to analyze regional ground-water flow in the Madison Group aquifer in the Powder River Basin in Montana and Wyoming and adjacent areas. Most recharge to the aquifer originates in or near the outcrop areas of the Madison in the Bighorn Mountains and Black Hills, and most discharge occurs through springs and wells. Flow through the aquifer in the modeled areas was approximately 200 cubic feet per second. The aquifer can probably sustain increased ground-water withdrawals of up to several tens of cubic feet per second, but these withdrawals probably would significantly lower the potentiometric surface in the Madison aquifer in a large part of the basin. (Woodard-USGS)

Water-Resources Investigations Report↗
USGS2007

A Deep Percolation Model for Estimating Ground-Water Recharge: Documentation of Modules for the Modular Modeling System of the U.S. Geological Survey

A daily water-budget model for estimating ground-water recharge, the Deep Percolation Model, was modularized for inclusion into the U.S. Geological Survey's Modular Modeling System. The model was modularized in order to facilitate estimation of ground-water recharge under a large range in climatic, landscape, and land-use and land-cover conditions. The model can be applied to areas as large as regions or as small as a field plot. An overview of the Modular Modeling System and the Deep Percolation Model is presented. Data requirements, parameters, and variables for the model are described. The modules that compose the Deep Percolation Model are documented.

Scientific Investigations Report↗
USGS2013

Hydraulic and Geomorphic Assessment of the Merced River and Historic Bridges in Eastern Yosemite Valley, Yosemite National Park, California: Sacramento, California

The Merced River in the popular and picturesque eastern-most part of Yosemite Valley in Yosemite National Park, California, USA, has been extensively altered since the park was first conceived in 1864. Historical human trampling of streambanks has been suggested as the cause of substantial increases in stream width, and the construction of undersized stone bridges in the 1920s has been suggested as the major factor leading to an increase in overbank flooding due to deposition of bars and islands between the bridges. In response, the National Park Service at Yosemite National Park (YNP) requested a study of the hydraulic and geomorphic conditions affecting the most-heavily influenced part of the river, a 2.4-km reach in eastern Yosemite Valley extending from above the Tenaya Creek and Merced River confluence to below Housekeeping Bridge. As part of the study, present-day conditions were compared to historical conditions and several possible planning scenarios were investigated, including the removal of an elevated road berm and the removal of three undersized historic stone bridges identified by YNP as potential problems: Sugar Pine, Ahwahnee and Stoneman Bridges. This Open-File Report will be superseded at a later date by a Scientific Investigations Report. A two-dimensional hydrodynamic model, the USGS FaSTMECH (Flow and Sediment Transport with Morphological Evolution of Channels) model, within the USGS International River Interface Cooperative (iRIC) model framework, was used to compare the scenarios over a range of discharges with annual exceedance probabilities of 50-, 20-, 10-, and 5- percent. A variety of topographic and hydraulic data sources were used to create the input conditions to the hydrodynamic model, including aerial LiDAR (Light Detection And Ranging), ground-based LiDAR, total station survey data, and grain size data from pebble counts. A digitized version of a historical topographic map created by the USGS in 1919, combined with estimates of grain size, was used to simulate historical conditions, and the planning scenarios were developed by altering the present-day topography. Roughness was estimated independently of measured water-surface elevations by using the mapped grain-size data and the Keulegan relation of grain size to drag coefficient. The FaSTMECH hydrodynamic model was evaluated against measured water levels by using a 130.9 m 3 s -1 flow (approximately a 33-percent annual exceedance probability flood) with 36 water-surface elevations measured by YNP personnel on June 8, 2010. This evaluation run had a root mean square error of 0.21 m between the simulated- and observed water-surface elevations (less than 10 percent of depth), though the observed water-surface elevations had relatively high variation due to the strong diurnal stage changes over the course of the 4.4-hour collection period, during which discharge varied by about 15 percent. There are presently no velocity data with which to test the model. A geomorphic assessment was performed that consisted of an estimate of the magnitude and frequency of bedload and suspended-sediment transport at “Tenaya Bar”, an important gravel-cobble bar located near the upstream end of the study site that determines the amount of flow across the floodplain at the Sugar Pine – Ahwahnee bend. An analysis of select repeat cross-sections collected by YNP since the late 1980s was done to investigate changes in channel cross-sectional area near the Tenaya Bar site. The results of the FaSTMECH models indicate that the maximum velocities in the present-day channel within the study reach are associated with Stoneman and Sugar Pine Bridges, at close to 3.0 m s -1 for the 5-percent annual exceedance probability flood. The modeled maximum velocities at Ahwahnee Bridge are comparatively low, at between 1.5 and 2.0 m s -1 , most likely due to the bridge's orientation parallel to down-valley floodplain flows. The results of the FaSTMECH models for the bridge removal scenarios indicate a reduction in average velocity at the bridge sites for the range of flows by approximately 23-38 percent (Sugar Pine Bridge), 32-42 percent (Ahwahnee Bridge), and 33-39 percent (Stoneman Bridge), though a side channel of concern to YNP management did not appear to be substantially affected by the removal scenarios. In comparison to the historical data, the FaSTMECH results suggest that flows for present-day conditions do not inundate the floodplain until between the 50- and 20-percent annual exceedance probability flood, whereas historically, a large portion of the floodplain was inundated during the 50-percent annual exceedance probability flood. Modeled maximum velocities in the present-day channel commonly exceed 2.0 m s -1 , whereas with the historical scenario, modeled maximum in-channel velocities rarely exceeded 2.0 m s -1 . The geomorphic analysis of the magnitude-frequency of bedload and suspended-sediment transport suggests that at the important Tenaya Bar site, the majority of bed sediment is mobile during most snowmelt-dominated floods. In contrast to sediment transport capacity, the analysis of repeat cross-sections suggests that bedload sediment supply into the eastern Yosemite Valley may be quite different between rain-on-snow floods and snowmelt-dominated floods, potentially with most sediment supply occurring during rain-on-snow floods, such as the 1997 flood. In contrast, the magnitude-frequency analysis of bedload and suspended-sediment transport suggests that long-term bedload sediment transport is likely dominated by snowmelt floods, and suspended-sediment transport is relatively low compared to bedload transport. Obtaining measured velocity data throughout the study reach would aid in model calibration, and thus would improve confidence in model results. Improved confidence in the model velocity results would allow additional substantial analyses of reach-scale effects of the planning scenarios and would enable the development of geomorphic models to evaluate the long-term geomorphic responses of the site. In addition, the collection of watershed sediment-supply data, about which little is presently known, would give planners helpful tools to plan restoration scenarios for this nationally important river.

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