Search USGS⌕ Search

SEARCH · Search USGS

Results for “Water Hydrological Data”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 919 records · Page 51Linked to original sources

Investigations and research in Nevada by the Water Resources Division, U.S. Geological Survey, 1982

The Water Resources Division, U.S. Geological Survey, is charged with (1) maintaining a hydrologic network in Nevada that provides information on the status of the State 's water resources and (2) engaging in technical water-resources investigations that have a high degree of transferability. To meet these broad objectives, 26 projects were active during fiscal year 1982, in cooperation with 36 Federal, State, and local agencies. Total funds were $3,319,455, of which State and local cooperative funding amounted to $741,500 and Federal funding (comprised of Geological Survey Federal and cooperative program plus funds from six other Federal agencies) amounted to $2,577,955 for the fiscal year. Projects other than continuing programs for collection of hydrologic data included the following topics of study: geothermal resources, areal ground-water resources and ground-water modeling, waste disposal , paleohydrology, acid mine drainage, the unsaturated zone, stream and reservoir sedimentation, river-quality modeling, flood hazards, and remote sensing in hydrology. In total, 26 reports and symposium abstracts were published or in press during fiscal year 1982. (USGS)

Open-File Report↗

Antibiotic, pharmaceutical, and wastewater-compound data for Michigan, 1998-2005

Beginning in the late 1990's, the U.S. Geological Survey began to develop analytical methods to detect, at concentrations less than 1 microgram per liter (ug/L), emerging water contaminants such as pharmaceuticals, personal-care chemicals, and a variety of other chemicals associated with various human and animal sources. During 1998-2005, the U.S. Geological Survey analyzed the following Michigan water samples: 41 samples for antibiotic compounds, 28 samples for pharmaceutical compounds, 46 unfiltered samples for wastewater compounds (dissolved and suspended compounds), and 113 filtered samples for wastewater compounds (dissolved constituents only). The purpose of this report is to summarize the status of emerging contaminants in Michigan waters based on data from several different project-specific sample-collection efforts in Michigan during an 8-year period. During the course of the 8-year sampling effort, antibiotics were determined at 20 surface-water sites and 2 groundwater sites, pharmaceuticals were determined at 11 surface-water sites, wastewater compounds in unfiltered water were determined at 31 surface-water sites, and wastewater compounds in filtered water were determined at 40 surface-water and 4 groundwater sites. Some sites were visited only once, but others were visited multiple times. A variety of quality-assurance samples also were collected. This report describes the analytical methods used, describes the variations in analytical methods and reporting levels during the 8-year period, and summarizes all data using current (2009) reporting criteria. Very few chemicals were detected at concentrations greater than current laboratory reporting levels, which currently vary from a low of 0.005 ug/L for some antibiotics to 5 ug/L for some wastewater compounds. Nevertheless, 10 of 51 chemicals in the antibiotics analysis, 9 of 14 chemicals in the pharmaceuticals analysis, 34 of 67 chemicals in the unfiltered-wastewater analysis, and 56 of 62 chemicals in the filtered-wastewater analysis were detected. Antibiotics were detected at 7 of 20 tested surface-water sites, but none were detected in 2 groundwater samples. Pharmaceuticals were detected at 7 of 11 surface-water sites. Wastewater compounds were detected at 25 of 31 sites for which unfiltered water samples were analyzed and at least once at all 40 surface-water sites and all 4 groundwater sites for which filtered water samples were analyzed. Overall, the chemicals detected most frequently in Michigan waters were similar to those reported frequently in other studies nationwide. Patterns of chemical detections were site specific and appear to be related to local sources, overall land use, and hydrologic conditions at the time of sampling. Field-blank results provide important information for the design of future sampling programs in Michigan and demonstrate the need for careful field-study design. Field-replicate results indicated substantial confidence regarding the presence or absence of the many chemicals tested. Overall, data reported herein indicate that a wide array of antibiotic, pharmaceutical, and organic wastewater compounds occur in Michigan waters. Patterns of occurrence, with respect to hydrologic, land use, and source variables, generally appear to be similar for Michigan as for other sampled waters across the United States. The data reported herein can serve as a basis for future studies in Michigan.

Michigan↗

Laboratory evaluation of the pressure water level data logger manufactured by Infinities USA, Inc.: results of pressure and temperature tests

The Pressure Water Level Data Logger manufactured by Infinities USA, Inc., was evaluated by the U.S. Geological Survey (USGS) Hydrologic Instrumentation Facility for conformance with the manufacturer’s stated accuracy specifications for measuring pressure throughout the device’s operating temperature range and with the USGS accuracy requirements for water-level measurements. The Pressure Water Level Data Logger (Infinities Logger) is a submersible, sealed, water-level sensing device with an operating pressure range of 0 to 11.5 feet of water over a temperature range of −18 to 49 degrees Celsius. For the pressure range tested, the manufacturer’s accuracy specification of 0.1 percent of full scale pressure equals an accuracy of ±0.138 inch of water. Three Infinities Loggers were evaluated, and the testing procedures followed and results obtained are described in this report. On the basis of the test results, the device is poorly compensated for temperature. For the three Infinities Loggers, the mean pressure differences varied from –4.04 to 5.32 inches of water and were not within the manufacturer’s accuracy specification for pressure measurements made within the temperature-compensated range. The device did not meet the manufacturer’s stated accuracy specifications for pressure within its temperature-compensated operating range of –18 to 49 degrees Celsius or the USGS accuracy requirements of no more than 0.12 inch of water (0.01 foot of water) or 0.10 percent of reading, whichever is larger. The USGS accuracy requirements are routinely examined and reported when instruments are evaluated at the Hydrologic Instrumentation Facility. The estimated combined measurement uncertainty for the pressure cycling test was ±0.139 inch of water, and for temperature, the cycling test was ±0.127 inch of water for the three Infinities Loggers.

Open-File Report↗

Selected hydrologic data for Spokane Valley, Spokane, Washington 1977-78

This report presents the ground-water data collected from March 1977 to May 1978 in the Spokane Valley, Spokane, Washington, for the purpose of developing a computer simulation of flow and mass transport in the Spokane aquifer. Data collected include an inventory of wells and springs, water-level data, and chemical analyses of water from selected wells and springs. (Kosco-USGS)

Open-File Report↗

Simulation of the impacts of projected climate change on groundwater resources in the urban, semiarid Yucaipa Valley watershed, southern California using an integrated hydrologic model

Managing water resources in semiarid watersheds is challenging due to limited supply and uncertain future climate conditions. This paper examines the impact of future climate changes on an urban watershed in southern California using an integrated hydrologic model. GSFLOW modeling software is used to simulate the nonlinear relationships between climate trends and precipitation partitioning into ET, runoff, and subsurface storage. Four global circulation models (GCMs), each with two greenhouse-gas scenarios, RCP45 and RCP85 are used to project future climate conditions. GCMs include the CanESM2, CNRM-CM5, HadGEM2-ES, and MIROC5 models. The model's simulated hydrologic conditions are compared with historical data to assess changes in water budgets and groundwater supply. Results indicate decreased groundwater storage in most scenarios due to increased natural evapotranspiration, vegetation consumptive use, and streamflow out of the watershed. Only scenarios with substantially increased future precipitation show increased groundwater storage. The study also highlights increased future aridity despite the rise in precipitation and large precipitation events forecast by GCMs, which increase the risk of urban floods and decrease stream leakage and water available to vegetation.

California↗

Importance of hydrologic data for interpreting wetland maps and assessing wetland loss and mitigation

The US Geological Survey collects and disseminates, in written and digital formats, groundwater and surface-water information related to the tidal and nontidal wetlands of the United States. This information includes quantity, quality, and availability of groundwater and surface water; groundwater and surface-water interactions (recharge-discharge); groundwater flow; and the basic surface-water characteristics of streams, rivers, lakes, and wetlands. Water resources information in digital format can be used in geographic information systems (GISs) for many purposes related to wetlands. US Geological Survey wetland-related activities include collection of information important for assessing and mitigating coastal wetland loss and modification, hydrologic data collection and interpretation, GIS activities, identification of national trends in water quality and quantity, and process-oriented wetland research. -Author

Biological Report - US Fish & Wildlife Service↗

Summary of Hydrologic Data for the Tuscarawas River Basin, Ohio, with an Annotated Bibliography

The Tuscarawas River Basin drains approximately 2,600 square miles in eastern Ohio and is home to 600,000 residents that rely on the water resources of the basin. This report summarizes the hydrologic conditions in the basin, describes over 400 publications related to the many factors that affect the groundwater and surface-water resources, and presents new water-quality information and a new water-level map designed to provide decisionmakers with information to assist in future data-collection efforts and land-use decisions. The Tuscarawas River is 130 miles long, and the drainage basin includes four major tributary basins and seven man-made reservoirs designed primarily for flood control. The basin lies within two physiographic provinces-the Glaciated Appalachian Plateaus to the north and the unglaciated Allegheny Plateaus to the south. Topography, soil types, surficial geology, and the overall hydrology of the basin were strongly affected by glaciation, which covered the northern one-third of the basin over 10,000 years ago. Within the glaciated region, unconsolidated glacial deposits, which are predominantly clay-rich till, overlie gently sloping Pennsylvanian-age sandstone, limestone, coal, and shale bedrock. Stream valleys throughout the basin are filled with sands and gravels derived from glacial outwash and alluvial processes. The southern two-thirds of the basin is characterized by similar bedrock units; however, till is absent and topographic relief is greater. The primary aquifers are sand- and gravel-filled valleys and sandstone bedrock. These sands and gravels are part of a complex system of aquifers that may exceed 400 feet in thickness and fill glacially incised valleys. Sand and gravel aquifers in this basin are capable of supporting sustained well yields exceeding 1,000 gallons per minute. Underlying sandstones within 300 feet of the surface also provide substantial quantities of water, with typical well yields of up to 100 gallons per minute. Although hydraulic connection between the sandstone bedrock and the sands and gravels in valleys is likely, it has not been assessed in the Tuscarawas River Basin. In 2001, the major land uses in the basin were approximately 40 percent forested, 39 percent agricultural, and 17 percent urban/residential. Between 1992 and 2001, forested land use decreased by 2 percent with correspondingly small increases in agricultural and urban land uses, but from 1980 to 2005, the 13-county area that encompasses the basin experienced a 7.1-percent increase in population. Higher population density and percentages of urban land use were typical of the northern, headwaters parts of the basin in and around the cities of Akron, Canton, and New Philadelphia; the southern area was rural. The basin receives approximately 38 inches of precipitation per year that exits the basin through evapotranspiration, streamflow, and groundwater withdrawals. Recharge to groundwater is estimated to range from 6 to 10 inches per year across the basin. In 2000, approximately 89 percent of the 116 million gallons per day of water used in the basin came from groundwater sources, whereas 11 percent came from surface-water sources. To examine directions of groundwater flow in the basin, a new dataset of water-level contours was developed by the Ohio Department of Natural Resources. The contours were compiled on a map that shows that groundwater flows from the uplands towards the valleys and that the water-level surface mimics surface topography; however, there are areas where data were too sparse to adequately map the water-level surface. Additionally, little is known about deep groundwater that may be flowing into the basin from outside the basin and groundwater interactions with surface-water bodies. Many previous reports as well as new data collected as part of this study show that water quality in the streams and aquifers in the Tuscarawas River Basin has been degraded by urban, suburban, and rural

Scientific Investigations Report↗

Compilation of hydrologic data, Pin Oak Creek, Trinity River basin, Texas, 1968

The U.S. Soil Conservation Service is actively engaged in the installation of flood and soil erosion reducing measures in Texas under the authority of "The Flood Control Act of 19 36 and 1944" and "Watershed Protection and Flood Prevention Act" (Public Law 566), as amended. In June 1968, the Soil Conservation Service estimated approximately 3,500 structures to be physically and economically feasible for installation in Texas. As of September 30, 1968, 1,271 of these structures had been built. This watershed-development program will have varying but important effects on the surface- and ground-water resources of river basins, especially where a large number of the floodwater-retarding structures are built. Basic hydrologic data are needed to appraise the effects of structures on water yield and mode of occurrence of runoff. Hydrologic investigations of these small watersheds were begun by the U.S. Geological Survey in 1951 and are now being made in 11 areas (fig. 1). These studies are being made in cooperation with the Texas Water Development Board, the Soil Conservation Service, the San Antonio River Authority, the city of Dallas, and the Tarrant ounty Water Control and Improvement District No. 1. The 11 study areas were chosen to sample watersheds having different rainfall, topography, geology, and soils. In four of the study areas (Mukewater, North, Little Elm, and Pin Oak Creeks), streamflow and rainfall records were collected prior to construction of the floodwater-retarding structures, thus affording the opportunity for analyses of the conditions "before and after" development. Structures have now been built in three of these study areas. A summary of the development of the floodwater-retarding structures on each study area as of September 30, 1968, is shown in table 1.

Texas↗

Tracing nitrogen sources and cycling in catchments

This chapter focuses on the uses of isotopes to understand water chemistry.I Isotopic compositions generally cannot be interpreted successfully in the absence of other chemical and hydrologic data. The chapter focusses on uses of isotopes in tracing sources and cycling of nitrogen in the water-component of forested catchment, and on dissolved nitrate in shallow waters, nutrient uptake studies in agricultural areas, large-scale tracer experiments, groundwater contamination studies, food-web investigations, and uses of compound-specific stable isotope techniques. Shallow waters moving along a flowpath through a relatively uniform material and reacting with minerals probably do not achieve equilibrium but gradually approach some steady-state composition. The chapter also discusses the use of isotopic techniques to assess impacts of changes in land-management practices and land use on water quality. The analysis of individual molecular components for isotopic composition has much potential as a method for tracing the source, biogeochemistry, and degradation of organic liquids and gases because different materials have characteristic isotope spectrums or biomarkers.

Book chapter↗

Records of wells, water levels, and chemical quality of water in the lower Santiam River basin, middle Willamette Valley, Oregon

Basic water data on the lower Santiam River basin is preliminary to a comprehensive hydrologic study of this productive and intensely irrigated area where expanding population and industry increases the demand for water . Highest yielding wells are in shallow alluvial aquifers near the main streams; yields range from several hundred to more than a thousand gpm. Wells in lacustrine and older alluvial aquifers that underlie low, flat terraces have yields from a few tens to a few hundred gpm. Wells in the Salem Hills and in the Cascade Range foothills yield moderate to small quantities of water and tap a variety of geologic units. Tabulated material includes records of representative wells , drillers' logs, and chemical and spectrographic analyses of the ground water .

Oregon↗

Hydrologic reconnaissance of the Blue Creek Valley area, Box Elder County, Utah

This report is the tenth in a series of reports prepared by the U. S. Geological Survey in cooperation with the Utah Department of Natural Resources, Division of Water Rights, that describe the water resources of selected areas in northwestern Utah. The purpose of this report is to present available hydrologic data for the Blue Creek Valley area and to provide a quantitative evaluation of the potential water-resources development of the area.

Utah↗

Water resources program of the U.S. Geological Survey related to agriculture in Louisiana

Surveillance activities of the U.S. Geological Survey Louisiana District include long-term, hydrologic-data-collection sites that serve a current-purpose, management function and (or) that furnish a data base for interpretative studies. The proposed program for 1982 includes a network of 69 surface-water data sites (continuous gaging stations), 250 flood-data sites (crest-stage stations), 679 ground-water wells (water-level observation and water-quality monitor wells), and 138 water-quality sites. The geographic distribution of the data sites is shown in the report. Interpretive studies have objectives that are oriented toward a particular geographic area , to a particular set of hydrologic phenomena, or to obtain information for use in solving specific problems. Current studies of interest to agriculture include the following: (1) Flood hydraulics and hydrology, (2) Low-flow or base-flow of streams in Louisiana, (3) Hydrologic studies in southwestern Louisiana, (4) Hydrologic impacts of surface mining in northern Louisiana, (5) Sparta aquifer study, and (6) Limnology of freshwater lakes. A network of partial record sites is also maintained to monitor specific flows. Peak stages (crest stage) are only recorded at sites where flood information is of interest. At other sites, only the low-flow or base-flow recession is obtained for use in determining relations between ground water and surface water, to assess water supply, and for effluent studies. (USGS)

Open-File Report↗

Regional Water-Resources Studies in Nevada

Introduction: Water-resources information for the State of Nevada should be readily accessible to community planners and the general public in a user-friendly web environment and should be actively managed and maintained with accurate historic and current hydrologic data. The USGS, in cooperation with State of Nevada and local government agencies, has established a data framework that provides critical hydrologic information to meet the challenges of water resources planning for Nevada.

Fact Sheet↗

Selected ground-water data for Yucca Mountain region, southern Nevada and eastern California, January 2000-December 2002

The U.S. Geological Survey, in support of the U.S. Department of Energy, Yucca Mountain Project, collects, compiles, and summarizes hydrologic data in the Yucca Mountain region. The data are collected to allow assessments of ground-water resources during activities to determine the potential suitability or development of Yucca Mountain for storing high-level nuclear waste. Data on ground-water levels at 35 wells and a fissure (Devils Hole), ground-water discharge at 5 springs and a flowing well, and total reported ground-water withdrawals within Crater Flat, Jackass Flats, Mercury Valley, and the Amargosa Desert are tabulated from January 2000 through December 2002. Historical data on water levels, discharges, and withdrawals are graphically presented to indicate variations through time. A statistical summary of ground-water levels at seven wells in Jackass Flats is presented for 1992-2002 to indicate potential effects of ground-water withdrawals associated with U.S. Department of Energy activities near Yucca Mountain. The statistical summary includes the annual number of measurements, maximum, minimum, and median water-level altitudes, and average deviation of measured water-level altitudes compared to selected baseline periods. Baseline periods varied for 1985-93. At six of the seven wells in Jackass Flats, the median water levels for 2002 were slightly higher (0.3-2.4 feet) than for their respective baseline periods. At the remaining well, data for 2002 was not summarized statistically but median water-level altitude in 2001 was 0.7 foot higher than that in its baseline period.

California, Nevada↗

Water-resources activities in New England, fiscal year 1993

The U.S. Geological Survey has 82 active or complete-except-report projects of hydrologic investigations ongoing within the New England Program Area. Of this total, 23 are data projects. Data projects contain statistics and data on the conditions of surface water, ground water, water quality and (or) water use for the study area. There currently are six data projects in Connecticut, five in Maine, four in Massachusetts, four in Rhode Island, and four in New Hampshire and Vermont. The remaining 59 of these projects are interpretive projects. Interpretive projects include research, aerial appraisal, and other hydrologic studies and include projects as diverse as (1) determining the direction of ground-water flow at a toxic site, (2) predicting the effect of acid rain on water quality of a reservoir, and (3) estimating yields of aquifers on Cape Cod. Of the interpretive projects, 26 are in Massachusetts, 17 in Connecticut, 17 are in New Hampshire and Vermont, 6 are in Maine, and 3 in Rhode Island. The report is compiled from project descriptions for fiscal year 1993. It briefly describes the water-resources activities and projects that were active in each District of the USGS, Water Resources Division, New England Program Area of September 30, 1993. Cooperator or funding source, problem statements, objectives, approaches, progress, and plans for next year are described for each project. The project area is located on a map of the appropriate State(s). The report contains a bibliography, by District and by author, of reports completed since 1977.

Open-File Report↗

Variability of differences between two approaches for determining ground-water discharge and pumpage, including effects of time trends, Lower Arkansas River Basin, southeastern Colorado, 1998-2002

In the mid-1990s, the Colorado Division of Water Resources (CDWR) adopted rules governing measurement of tributary ground-water pumpage for the Arkansas River Basin. The rules allowed ground-water pumpage to be determined using one of two approaches?power conversion coefficient (PCC) or totalizing flowmeters (TFM). In addition, the rules allowed a PCC to be applied to the electrical power usage up to 4 years in the future to estimate ground-water pumpage. As a result of concerns about potential errors in applying the PCC approach forward in time, a study was done by the U.S. Geological Survey, in cooperation with CDWR and Colorado Water Conservation Board, to evaluate the variability in differences in pumpage between the two approaches, including the effects of time trends. This report compared measured ground-water pumpage using TFMs to computed ground-water pumpage using PCCs by developing statistical models of relations between explanatory variables, such as site, time, and pumping water level, and dependent variables, which are based on discharge, PCC, and pumpage. When differences in pumpage (diffP) were computed using PCC measurements and power consumption for the same year (1998-2002), the median diffP, depending on the year, ranged from +0.1 to -2.9 percent; the median diffP for the entire period was -1.5 percent. However, when diffP was computed using PCC measurements applied to the next year's power consumption, the median diffP was -0.3 percent; and when PCC measurements were applied 2, 3, or 4 years into the future, median diffPs were +1.8 percent for a 2-year forward lag and +5.3 percent for a 4-year forward lag, indicating that pumpage computed with the PCC approach, as generally applied under the ground-water pumpage measurement rules by CDWR, tended to overestimate pumpage as compared to pumpage using TFMs when PCC measurement was applied to future years of measured power consumption. Analyses were done to better understand the causes of the time trend; an estimate of the overall trend with time (uncorrected for pumping water-level changes) yielded a trend of about 2.2 percent per lag year for diffP. A separate analysis that incorporated a surface-water diversion term in the statistical model rendered the time-trend term insignificant, indicating that the time trend in the models served as a surrogate for other variables, some of which reflect underlying hydrologic conditions. A more precise explanation of the potential causes of the time trend was not obtained with the available data. However, the model results with the surface-water diversion term indicate that much of the trend of 2.2 percent per lag year in diffP resulted from applying a PCC to estimate pumpage under hydrologic conditions different from those under which the PCC was measured. Although there is no evidence to conclude that the upward time trend determined in the data for this 5-year period would hold in the future, historical static ground-water levels in the study area generally have exhibited small variations over multidecadal time scales. Therefore, the approximately 2 percent per lag year trend determined in these data is expected to be a reasonable guideline for estimating potential errors in the PCC approach resulting from temporally varying hydrologic conditions between time of PCC measurement and pumpage estimation. Comparisons also were made between total, or aggregated, pumpage for a network of wells as computed by the PCC approach and the TFM approach. For 100 wells and a lag of 4 years between PCC measurement and pumpage estimation, there was a 95-percent probability that the difference between total network pumpage measured by the PCC approach and that measured using a TFM would be between 5.2 and 14.4 percent. These estimates were based on a bias of 2.2 percent per lag year estimated for the period 1998-2002 during which hydrologic conditions were known to have changed. Using the same assumptions, the estimated d

Scientific Investigations Report↗

Soil-water dynamics and unsaturated storage during snowmelt following wildfire

Many forested watersheds with a substantial fraction of precipitation delivered as snow have the potential for landscape disturbance by wildfire. Little is known about the immediate effects of wildfire on snowmelt and near-surface hydrologic responses, including soil-water storage. Montane systems at the rain-snow transition have soil-water dynamics that are further complicated during the snowmelt period by strong aspect controls on snowmelt and soil thawing. Here we present data from field measurements of snow hydrology and subsurface hydrologic and temperature responses during the first winter and spring after the September 2010 Fourmile Canyon Fire in Colorado, USA. Our observations of soil-water content and soil temperature show sharp contrasts in hydrologic and thermal conditions between north- and south-facing slopes. South-facing burned soils were ∼1–2 °C warmer on average than north-facing burned soils and ∼1.5 °C warmer than south-facing unburned soils, which affected soil thawing during the snowmelt period. Soil-water dynamics also differed by aspect: in response to soil thawing, soil-water content increased approximately one month earlier on south-facing burned slopes than on north-facing burned slopes. While aspect and wildfire affect soil-water dynamics during snowmelt, soil-water storage at the end of the snowmelt period reached the value at field capacity for each plot, suggesting that post-snowmelt unsaturated storage was not substantially influenced by aspect in wildfire-affected areas. Our data and analysis indicate that the amount of snowmelt-driven groundwater recharge may be larger in wildfire-impacted areas, especially on south-facing slopes, because of earlier soil thaw and longer durations of soil-water contents above field capacity in those areas.

Hydrology and Earth System Sciences↗

Digital model of the Bates Creek alluvial aquifer near Casper, Wyoming

A digital model was used to simulate ground-water flow within the Bates Creek alluvial aquifer, southwest of Casper, Wyoming. Hydrologic data collected during 1977 and 1978 were used to develop the flow model under steady-state and transient conditions. Three scenarios for operating the stream-aquifer system were evaluated with the digital model. The scenarios represent no ground-water pumping, pumping by all existing wells , and pumping by all existing and proposed wells. The model simulations used average values of stream discharge, ground-water pumpage and water use as input parameters. A decrease in the quantitity of ground-water discharge to Bates Creek is predicted to occur through 1988 as a result of pumping. The magnitude and timing of the predicted decrease in ground-water discharge may differ from actual ground-water discharge if hydrologic conditions through 1988 vary significantly from the averaged input values used in the simulations. (USGS)

Water-Resources Investigations Report↗