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At least 145 records · Page 8Linked to original sources
USGS1966

Sedimentation and chemical quality of surface water in the Heart River drainage basin, North Dakota

The Heart River drainage basin of southwestern North Dakota comprises an area of 3,365 square miles and lies within the Missouri Plateau of the Great Plains province. Streamflow of the Heart River and its tributaries during 1949-58 was directly proportional to .the drainage area. After the construction of Heart Butte Dam in 1949 and Dickinson Dam in 1950, the mean annual streamflow near Mandan was decreased an estimated 10 percent by irrigation, evaporation from the two reservoirs, and municipal use. Processes that contribute sediment to the Heart River are mass wasting, advancement of valley heads, and sheet, lateral stream, and gully erosion. In general, glacial deposits, terraces, and bars of Quaternary age are sources of sand and larger sediment, and the rocks of Tertiary age are sources of clay, silt. and sand. The average annual suspended-sediment discharges near Mandan were estimated to be 1,300,000 tons for 1945-49 and 710,000 tons for 1970-58. The percentage composition of ions in water of the Heart River, based on average concentrations in equivalents per million for selected ranges of streamflow, changes with flow and from station to station. During extremely low flows the water contains a large percentage of sodium and about equal percentages of bicarbonate and .sulfate, and during extremely high flows the water contains a large percentage of calcium plus magnesium and bicarbonate. The concentrations, in parts per million, of most of the ions vary inversely with flow. The water in the reservoirs--Edward Arthur Patterson Lake and Lake Tschida--during normal or above-normal runoff is of suitable quality for public use. Generally, because of medium or high salinity hazards, the successful long-term use of Heart River water for irrigation will depend on a moderate amount of leaching, adequate drainage, ,and the growing of crops that have moderate or good salt tolerance.

Water Supply Paper↗
USGS1960

Geology and ground water in the Platte-Republican Rivers watershed and the Little Blue River basin above Angus, Nebraska, with a section on chemical quality of the ground water

This report describes an area of about 7,300 square miles in south-central Nebraska. Approximately one-fourth of the area, largely at its east end, consists of an undissected southeastward-sloping upland plain and is almost wholly irrigable; the remainder is in various stages of dissection and only parts of it are suitable for irrigation. Although some of the deeper lying bedrock formations are potential sources of water supply, they are not likely to be tapped in the near future because abundant supplies are available at shallower depth from semiconsolidated and unconsolidated deposits. The Ogallala formation of Tertiary (Pliocene) age consists of gravel, sand, silt, and volcanic ash, some layers of which are partly cemented. It was deposited by eastward-flowing streams, which formed a constructional plain above a surface into which the streams had previously eroded broad valleys. In turn, valleys were cut into the surface of the Ogallala before the overlying deposits of gravel, sand, silt, and clay of Quaternary (Pleistocene) age were laid down, also forming a constructional plain. During Recent time, streams have dissected the older deposits and have deposited thin alluvium in their valleys; also, several parts of the area have become mantled by wind-deposited sand. Because during Tertiary and Quaternary time the area repeatedly was the site of deposition and erosion, the thickness of all the stratigraphic units differs markedly from place to place. In general, however, the Ogallala formation thins eastward and in the central and eastern parts of the area is overlain by the eastward-thickening deposits of Pleistocene age. The maximum thickness of the Ogallala formation is about 500 feet, and the maximum thickness of the Pleistocene deposits is a little more than 300 feet. Each thins to a featheredge and is completely absent in parts of the area. The water-bearing part of the combined Tertiary and Pleistocene deposits is considered to be a single zone of saturation because the ground water, as it percolates southeastward beneath the area, moves out of the Tertiary and into the Quaternary deposits without apparent hindrance. The water that enters the area as underflow from the west is augmented within the area by water that infiltrates from the land surface. The principal sources of irrigating water are precipitation, seepage from canals and reservoirs, and applied irrigation water. Except for the water withdrawn through wells or discharged by natural processes where valleys have been cut into the zone of saturation, ground water leaves the area as underflow into the Platte River valley on the north, the Blue River drainage basin on the east, or the Republican River valley on the south. Part of the water used for irrigation and watering livestock and all the water used in rural and urban homes, in public buildings, and for industrial purposes is obtained from wells, To date (1952) there is no indication that the supply of ground water is being depleted faster than it is being replenished; instead, studies indicate that greater quantities can be withdrawn without causing an excessive decline of the water table. An increase of ground-water withdrawals to a sustainable maximum, however, will be possible only if the points of withdrawal are scattered fairly uniformly. It is estimated that annual withdrawals per township should not exceed 2,100 acre-feet where infiltrating precipitation is the only source of recharge, or 3,000 acre-feet where other sources of recharge are significant. Although perennial withdrawals of this amount could be sustained indefinitely, they would cause some lowering of the water table and eventually a decrease in the amount of water discharged from the area by natural means. The ground water is of the calcium bicarbonate type. In much of the area it is hard or very hard, and in places it contains excessive amounts of iron. In all other respects the water is chemically suitable for domesti

Nebraska↗
USGS2012

Fish population and habitat analysis in Buck Creek, Washington, prior to recolonization by anadromous salmonids after the removal of Condit Dam

We assessed the physical and biotic conditions in the part of Buck Creek, Washington, potentially accessible to anadromous fishes. This creek is a major tributary to the White Salmon River upstream of Condit Dam, which was breached in October 2011. Habitat and fish populations were characterized in four stream reaches. Reach breaks were based on stream gradient, water withdrawals, and fish barriers. Buck Creek generally was confined, with a single straight channel and low sinuosity. Boulders and cobble were the dominant stream substrate, with limited gravel available for spawning. Large-cobble riffles were 83 percent of the available fish habitat. Pools, comprising 15 percent of the surface area, mostly were formed by bedrock with little instream cover and low complexity. Instream wood averaged 6—10 pieces per 100 meters, 80 percent of which was less than 50 centimeters in diameter. Water temperature in Buck Creek rarely exceeded 16 degrees Celsius and did so for only 1 day at river kilometer (rkm) 3 and 11 days at rkm 0.2 in late July and early August 2009. The maximum temperature recorded was 17.2 degrees Celsius at rkm 0.2 on August 2, 2009. Minimum summer discharge in Buck Creek was 3.3 cubic feet per second downstream of an irrigation diversion (rkm 3.1) and 7.7 cubic feet per second at its confluence with the White Salmon River. Rainbow trout ( Oncorhynchus mykiss ) was the dominant fish species in all reaches. The abundance of age-1 or older rainbow trout was similar between reaches. However, in 2009 and 2010, the greatest abundance of age-0 rainbow trout (8 fish per meter) was in the most downstream reach. These analyses in Buck Creek are important for understanding the factors that may limit fish abundance and productivity, and they will help identify and prioritize potential restoration actions. The data collected constitute baseline information of pre-dam removal conditions that will allow assessment of changes in fish populations now that Condit Dam has been removed and anadromous fish have an opportunity to recolonize Buck Creek.

Washington↗
USGS1982

Availability and quality of water from the Dakota aquifer, northwest Iowa

The Dakota aquifer in northwest Iowa consists of sandstones in the Dakota Formation. It underlies most of the study area and is the most extensive source of ground water in the area. Individual sandstone beds are from less than 10 to more than 150 feet thick. The cumulative thickness of sandstone is more than 200 feet throughout much of the area. The aquifer is confined by overlying Cretaceous limestone and shale, Quaternary glacial deposits and loess. The underlying confining material is shale of the Dakota Formation, undifferentiated Paleozoic age rocks, or Precambrian crystalline rock. Water flows through the aquifer from the north-central part of the study area to the east, south and southwest. Recharge is dominantly by infiltration from the land surface through the confining materials. Discharge is to underlying Paleozoic aquifers and to the alluvium and glacial outwash deposits along the Missouri and Big Sioux Rivers in the southwest part of the area. Flow components toward bedrock valleys may reflect discharge to Quaternary sand and gravel deposits in these valleys. Pumping tests conducted in the study area indicate a narrow range of hydraulic conductivities of the Dakota aquifer, from 37 to 50 feet per day. Consequently, an average hydraulic conductivity of 40 feet per day was used to estimate the potential yield to wells completed in the aquifer. Yields of more than 250 gallons per minute can be expected throughout much of the study area and more than 1000 gallons per minute could be produced in some areas. The quality of water from the Dakota is a calcium, magnesium, sulfate type. It is generally suitable for irrigation purposes, based on comparisons of sodium adsorption ratios and electrical conductivities. In some areas the aquifer has water with high salinity hazard that may restrict its use to irrigation of only well drained types of soil. The concentration of radium226 and other radionuclides exceed recommended limits at several sites. The quality of water pumped from the aquifer may be altered by induced leakage from the underlying aquifers in Paleozoic age rocks if withdrawals reverse the pattern of natural flow from the Dakota into the Paleozoic aquifers. Evidence for such a reversal exists in the area around the city of LeMars.

Iowa↗
USGS2000

Rapid recharge of parts of the high plains aquifer indicated by a reconnaissance study in Oklahoma, 1999

The High Plains aquifer underlies about 174,000 square miles in parts of eight states, including about 7,100 square miles in northwestern Oklahoma (fig. 1). This aquifer consists of the saturated part of the Ogallala Formation and saturated materials of Quaternary Age that are hydraulically connected to the Ogallala. The High Plains aquifer in northwestern Oklahoma is the primary source of water to an important agricultural region. Most water is withdrawn from the aquifer for irrigating wheat and other grain crops, with the remainder used for livestock (primarily cattle and swine), municipal, and domestic needs. Historically, water from precipitation was thought to take hundreds or thousands of years to reach the water table because the depth of the water table is greater than 100 feet over most of the aquifer and the low-permeability beds in the Ogallala would impede downward flow. It also was thought that land uses would take a similar period of time to affect water quality in the aquifer.

Oklahoma↗
USGS1977

Selected water-level records for western Oklahoma, 1950-1975

A systematic program to collect water-level records in Oklahoma began in 1937. The objectives of this program are (1) to provide long-term records of water-level fluctuations in representative wells, (2) to facilitate the prediction of water-level trends and indicate future availability of ground-water supplies, and (3) to provide information for use in basic research. Water-level data in table 1 are from wells that are measured annually, prior to the irrigation season to achieve the most natural representation of the static water level. Figure 1 shows the counties and number of wells therein, where data were obtained for this report. The stratigraphic nomenclature and age determinations used in this report are those accepted by the Oklahoma Geological Survey and do not necessarily agree with those at the U.S. Geological Survey. Records of water levels in Oklahoma are collected through a cooperative program by the U.S. Geological Survey and the Oklahoma Water Resources Board. The records are tabulated and published by the U.S. Geological Survey on an annual basis.

Open-File Report↗
USGS1965

Water resources of the Humboldt River Valley near Winnemucca, Nevada

This report, resulting from studies made by the U.S. Geological Survey as part of the interagency Humboldt River Research Project, describes the qualitative and quantitative relations among the components of the hydrologic system in the Winnemucca Reach of the Humboldt River valley. The area studied includes the segment of the Humboldt River valley between the Comus and Rose Creek gaging stations. It is almost entirely in Humboldt County in north-central Nevada, and is about 200 miles downstream from the headwaters of the Humboldt River. Agriculture is the major economic activity in the area. Inasmuch as the valley lowlands receive an average of about 8 inches of precipitation per year and because the rate of evaporation from free-water surfaces is about six times the average annual precipitation, all crops in the area (largely forage crops) are irrigated. About 85 percent of the cultivated land is irrigated with Humboldt River water; the remainder is irrigated from about 20 irrigation wells. The consolidated rocks of the uplifted fault-block mountains are largely barriers to the movement of ground water and form ground-water and surface-water divides. Unconsolidated deposits of late Tertiary and Quaternary age underlie the valley lowlands to a maximum depth of about 5,000 feet. These deposits are in hydraulic continuity with the Humboldt River and store and transmit most of the economically recoverable ground water. Included in the valley fill is a highly permeable sand and gravel deposit having a maximum thickness of about 90-100 feet; it underlies the flood plain and bordering terraces throughout most of the project area. This deposit is almost completely saturated and contains about 500,000 acre-feet of ground water in storage. The Humboldt River is the source of 90-95 percent of the surface-water inflow to the area. In water years 1949-62 the average annual streamflow at the Comus gaging station at the upstream margin of the area was 172,100 acre-feet; outflow at the Rose Creek gaging station averaged about 155,400 acre-feet. Accordingly, the measured loss of Humboldt River streamflow averaged nearly 17,000 acre-feet per year. Most of this water was transpired by phreatophytes and crops, evaporated from free-water surfaces, and evaporated from bare soil. Inasmuch as practically no tributary streamflow normally discharges into the river in the Winnemucca reach and because pumpage is virtually negligible during the nonirrigation season, gains and losses of streamflow during most of the year reflect the close interrelation of the Humboldt River and the groundwater reservoir. An estimated average of about 14,000 acre-feet per year of ground-water underflow moves toward the Humboldt River from tributary areas. Much of this water discharges into the Humboldt River; hovever, some evaporates or is transpired before reaching the river. More than 65 percent of the average annual flow of the river horn-ally occurs in April, May, and June owing to the spring runoff. The stage of the river generally rises rapidly during these months causing water to move from the river to the ground-water reservoir. Furthermore, the period of high streamflow normally coincides with the irrigation season, and much of the excess irrigation water diverted from the river percolates downward to the zone of saturation. The net measured loss of streamflow in April-June, which averaged about 24,000 acre-feet in water years 1949-62, was about 7,000 acre-feet more than the average annual loss. The estimated net average annual increase of ground water in storage during these months in this period was on the order of 10,000 acre-feet. Following the spring runoff and the irrigation season, normally in July, some of the ground water stored in the flood-plain deposits during the spring runoff begins to discharge into the river. In addition, ground-water inflow from tributary areas again begins to discharge into the river. Experiments utilizin

Water Supply Paper↗
USGS2016

Groundwater quality, age, and susceptibility and vulnerability to nitrate contamination with linkages to land use and groundwater flow, Upper Black Squirrel Creek Basin, Colorado, 2013

The Upper Black Squirrel Creek Basin is located about 25 kilometers east of Colorado Springs, Colorado. The primary aquifer is a productive section of unconsolidated deposits that overlies bedrock units of the Denver Basin and is a critical resource for local water needs, including irrigation, domestic, and commercial use. The primary aquifer also serves an important regional role by the export of water to nearby communities in the Colorado Springs area. Changes in land use and development over the last decade, which includes substantial growth of subdivisions in the Upper Black Squirrel Creek Basin, have led to uncertainty regarding the potential effects to water quality throughout the basin. In response, the U.S. Geological Survey, in cooperation with Cherokee Metropolitan District, El Paso County, Meridian Service Metropolitan District, Mountain View Electric Association, Upper Black Squirrel Creek Groundwater Management District, Woodmen Hills Metropolitan District, Colorado State Land Board, and Colorado Water Conservation Board, and the stakeholders represented in the Groundwater Quality Study Committee of El Paso County conducted an assessment of groundwater quality and groundwater age with an emphasis on characterizing nitrate in the groundwater. Groundwater-quality samples were collected from 50 randomly selected wells between May and June 2013. The samples were analyzed for major ions, nutrients, dissolved gases, tritium ( 3 H), chlorofluorocarbons (CFC-11, CFC-12, and CFC-113), and fuel products (such as benzene, toluene, ethylbenzene, and xylenes). None of the groundwater samples exceeded the U.S. Environmental Protection Agency (EPA) National Primary Drinking Water Regulations for primary maximum contaminant levels (MCL) for major ions. Secondary maximum contaminant levels, which are not health concerns and affect mainly taste, color, or odor of the water, were observed in rare instances for pH (2 samples), chloride (1 sample), iron (3 samples), and manganese (8 samples). The secondary maximum contaminant level for total dissolved solids was also exceeded for two samples. Nitrate (nitrite plus nitrate as nitrogen in groundwater) was elevated above the estimated background concentration of natural recharge waters of 1 milligram per liter (mg/L) in 44 of the 50 wells sampled and showed a median concentration of 5.4 mg/L. Nitrate concentrations were above the MCL of 10 mg/L in 5 of the 50 wells sampled and above half of the EPA MCL (5 mg/L) in 27 of the 50 wells sampled, which included samples above the MCL. Dissolved-oxygen concentrations exceeded 0.5 mg/L in 95 percent of reported values (40 of 42 samples) and exceeded 2.0 mg/L in 90 percent of reported values (38 of 42 samples). The oxidized conditions observed in most areas indicate that nitrate from fertilizers and animal or human waste was geochemically stable and could persist in the groundwater for decades or perhaps longer. A historical analysis of median nitrate concentrations over nearly three decades showed an increase in nitrate of approximately 1 mg/L from 4.3 to 5.4 mg/L, although the increase was not determined to be significantly different using nonparametric statistical methods. Major-ion data indicate that groundwater representative of the primary aquifer was classified as calcium-sodium bicarbonate type water. Other water samples from wells located mainly along the periphery of the primary aquifer had cation-anion compositions consistent with distinct water sources, including groundwater contributions from the underlying bedrock aquifers. The areas with differentiable water sources were located mainly where alluvial deposits were thin and geologic contacts to the underlying bedrock aquifers were relatively shallow. Nitrate concentrations in the groundwater were evaluated for relations to land use. An agricultural region was defined using a sequence of land satellite imagery. Groundwater flow directions interpreted from median water-table elevations measured from 2000 to 2013 were used in conjunction with cropland locations to define the agricultural region boundaries by encompassing potential pathways of nitrate transport in the groundwater from nitrogen-based fertilizers. A statistically significant higher median nitrate concentration was observed for areas inside the agricultural region (6.7 mg/L) compared to areas outside the agricultural region (2.3 mg/L), although median concentrations in both areas were below the MCL (10 mg/L). Median nitrate concentration was also significantly greater in land parcels with septic use (4.9 mg/L) compared to nonseptic parcels (1.7 mg/L). In general, agriculture or septic use was identified as the primary source of nitrate, depending on location, while commercial, county, grazing, and residential land uses were generally secondary sources of nitrate. Apparent groundwater ages were estimated from chlorofluorocarbons (CFC-11, CFC-12, and CFC-113) and tritium ( 3 H) data using models that assumed piston flow and binary mixing (dilution of a young component with old, tracer-free water). The mean and median groundwater ages were about 30 years and the standard deviation was 6 years, indicating that most groundwater in the primary aquifer was “young” water that had recharged to the aquifer over the last few decades (post-1950s). The median fraction of young water was about 71 percent, and the standard deviation was 29 percent. The remaining water predated the 1950s, which may have originated from deeper geologic formations or may represent slow moving groundwater within the primary aquifer. Some of the oldest groundwater ages (older than 30 years) were observed in the upper reaches of the aquifer to the northwest where the primary aquifer is thin and intersects bedrock, supporting the hypothesis of geochemically distinct groundwater entering the primary aquifer from below. Groundwater that had reached the central part of the aquifer from upgradient areas of the basin was variable in age because of differences in flow paths and travel velocities. The groundwater age analysis showed that current (2013) land-use practices could affect water quality over decades to come, and that responses to remedial actions could be slow, especially for constituents, such as nitrate, that are stable under oxidized conditions. Fuel products (including acetone, benzene, diisopropyl ether, ethylbenzene, methyl acetate, methyl tertiary butyl ether (MTBE), methyl tert-pentyl ether, m- + p-xylene, o-xylene, tert-amyl alcohol, tert-butyl alcohol, tert-butyl ethyl ether, and toluene) were analyzed in groundwater from 49 of the 50 wells. Water from seven sites had detections for fuel compounds; all concentrations were below MCL. The results provided assurance of water quality and a valuable baseline to evaluate future trends of fuel constituents as the region is further developed. Probability maps were developed from logistic regression models to examine the likelihood that nitrate concentrations in groundwater exceeded specified levels. Susceptibility analysis examined relations between mid-level (5.0 mg/L) nitrate concentrations and climatic, hydrologic, and geologic variables; the significant variables were identified as depth to groundwater, soil organic matter, and soil water storage to 25-centimeter (cm) depth. The vulnerability assessments included natural factors driving susceptibility but also human factors related to land use and septic use. Vulnerability to low-level (2.5 mg/L) nitrate was related to depth to groundwater, septic zoning, and soil organic matter. The results highlighted that septic zoning affected low-level nitrate concentrations. Vulnerability to mid-level (5.0 mg/L) nitrate was examined using all 50 samples and also with two data outliers removed, which showed relatively high nitrate concentrations but also anomalous water chemistry or were located beyond the primary study area. Vulnerability to mid-level (5.0 mg/L) nitrate using all 50 samples was related to depth to groundwater, land use, septic use within a 500-meter (m) radius, soil water storage to a 25-cm depth, soil organic matter, and whether a location was within the agricultural region. The mid-level (5.0 mg/L) vulnerability model using 48 samples (two outliers removed) produced the best overall fit and was related to the same variables as when using all samples except septic use. The results for mid-level vulnerability provided additional support that septic use was associated with low levels of nitrate in the groundwater. Soil properties and land use were identified as the main drivers of moderate nitrate concentrations. Probabilities of exceeding low-level nitrate concentrations were high in most areas with the lowest probabilities usually to the northwest along thin geologic deposits in the upper part of the basin. The results of this investigation offer the foundational information needed for developing best management practices to mitigate nitrate contamination, basic concepts on water quality to aid public education, and information to guide regulatory measures if policy makers determine this is warranted. Science-based decision making will require continued monitoring and analysis of water quality in the future.

Colorado↗
USGS1964

Ground water in folded Cretaceous sandstone of the Bhachau area, Kutch, India, with reference to the Kandla Port water supply

This report is based on an investigation of the availability of ground-water supplies in the Bhachau area for the nearby Kandla Port and township development undertaken by the Government of India. This seaport lies on an estuary of the Gulf of Kutch in western India and in the eastern part of the State of Kutch. The fieldwork on the investigation was carried on from November 1952 through April 1953 with continuing hydrologic observations through 1954-55. The fieldwork included: geologic mapping and delimitation of the principal aquifers of the region; preparation of water-table maps; a detailed inventory of existing wells and springs; observations of significant water table fluctuations; preparation of isobicarb, isochlor and isosulf maps to show the areal distribution of ground-water salinity. The Bhachau area includes about 116 square miles in eastern Kutch and lies in a belt of semiarid low-latitude steppes. The mean annual rainfall is about 15 inches, most of which falls from late June to late September during the southwest monsoon. The area includes a central sandy upland ranging from about 100 to 250 feet above sea level ; a northern lowland of between about 50 to 125 feet altitude that slopes north to the Great Rann of Kutch; a belt of low buttes and discontinuous ridges ranging from about 200 to 275 feet above sea level; and southern lowland which slopes in a southerly to southeasterly direction from an altitude of about 125 feet to 25 feet or less near the Gulf of Kutch. The principal streams are Kageshwar Vokra and Kara Vokra which drain north to the Great Rann and Kotwala Vokra and Dalwala Vokra which drain south toward the Gulf of Kutch. The rocks of the Bhachau area include nonmarine and marine sediments of Mesozoic, Tertiary, and Quaternary age and volcanic rocks of late Mesozoic to early Tertiary age. The oldest rocks in the area are medium- to coarse-grained white to buff current-bedded friable sandstone with occasional partings of white silty shale of the Upper Bhuj series that has been assigned to the Early Cretaceous. The soft friable sandstone of the Upper Bhuj series constitutes the most productive ground-water reservoir in the Bhachau area. At present (1955) there are nine irrigated tracts for which water is obtained from dug wells less than 90 feet deep in the Upper Bhuj. These wells are worked by bullocks and 'motes' (leather bags) at withdrawal rates ranging from about 6,000 to 24,000imperial gallons per day; however, many existing individual wells if equipped with mechanical pumps are capable of yielding 100,000 gallons per day. The Deccan trap of Late Cretaceous to Eocene age occurs in a sequence of basaltic lava flows in the Bhachau area, but trap dikes, sills and plugs that are common in other parts of Kutch have not been observed in the area. Laterite of probable Eocene age is extensive at the top of the Deccan trap, and in places where the lava flows are thin the parent rock has been almost completely lateritized. The Deccan lava flows or the laterite, where the trap is absent, rest disconformably on the Upper Bhuj. No wells have been observed in the Deccan trap of the Bhachau area, but it is possible that locally small supplies of good water may be obtained from these rocks. The Tertiary sediments, which are assigned to the Manchhar series of Pliocene age, generally rest on the laterite or the Deccan trap ; but where both are absent, the Manchhar rests directly on the Upper Bhuj. The Manchhar series includes massive reddish-brown gypseous clay shales, laminated gray siltstones, some limestone, mottled sandstone, and laterite trap gravel. Only meager supplies of brackish water are obtained from wells in these sediments. Along the channels of Kotwala, Dalwala, Kageshwar, and Kara Vokras are narrow bands of unconsolidated coarse sand with fine gravel of Quaternary age. No wells were observed in these deposits, but it is possible that locally they may contain small supplies of bracki

Water Supply Paper↗
USGS1984

Availability and quality of water from the Dakota aquifer, northwest Iowa

The Dakota aquifer in northwest Iowa consists of sandstones in the Dakota Formation. It underlies most of the study area and is the most extensive source of ground water in the area. Individual sandstone beds are from less than 10 to more than 150 feet thick. The cumulative thickness of sandstone is more than 200 feet throughout much of the area. The aquifer is confined by overlying Cretaceous limestone and shale, Quaternary glacial deposits and loess. The underlying confining material is shale of the Dakota Formation, undifferentiated Paleozoic age rocks, or Precambrian crystalline rock. Water flows through the aquifer from the northcentral part of the study area to the east, south and southwest. Recharge is dominantly by infiltration from the land surface through the confining materials. Discharge is to underlying Paleozoic aquifers and to the alluvium and glacial outwash deposits along the Missouri and Big Sioux Rivers in the southwest part of the area. Flow components toward bedrock valleys may reflect discharge to Quaternary sand and gravel deposits in these valleys. Pumping tests conducted in the study area indicate a narrow" range of hydraulic conductivities of the Dakota aquifer, from 37 to 50 feet per day. Consequently, an average hydraulic conductivity of 40 feet per day was used to estimate the potential yield to wells completed in the aquifer. Yields of more than 250 gallons per minute can be expected throughout much of the study area and more than 1,000 gallons per minute could be produced in some areas. The quality of water from the Dakota is a calcium, magnesium, sulfate type. It is generally suitable for irrigation purposes, based on comparisons of sodium adsorption ratios and electrical conductivities. In some areas the aquifer has water with high salinity hazard that may restrict its use to irrigation of only well-drained types of soil. The concentration of radium-226 and other radionuclides exceeds recommended limits at several sites. The quality of water pumped from the aquifer may be altered by induced leakage from the underlying aquifers in Paleozoic age rocks if withdrawals reverse the pattern of natural flow from the Dakota into the Paleozoic aquifers. Evidence for such a reversal exists in the area around the city of LeMars.

Iowa↗
USGS2010

Status and understanding of groundwater quality in the central-eastside San Joaquin Basin, 2006: California GAMA Priority Basin Project

Groundwater quality in the approximately 1,695-square-mile Central Eastside San Joaquin Basin (Central Eastside) study unit was investigated as part of the Priority Basin Project (PBP) of the Groundwater Ambient Monitoring and Assessment (GAMA) Program. The GAMA PBP was developed in response to the California Groundwater Quality Monitoring Act of 2001, and is being conducted by the California State Water Resources Control Board in collaboration with the U.S. Geological Survey and the Lawrence Livermore National Laboratory. The GAMA Central Eastside study unit was designed to provide a spatially unbiased assessment of untreated-groundwater quality, as well as a statistically consistent basis for comparing water quality throughout California. During March through June 2006, samples were collected from 78 wells in Stanislaus and Merced Counties, 58 of which were selected using a spatially distributed, randomized grid-based method to provide statistical representation of the study unit (grid wells), and 20 of which were sampled to evaluate changes in water chemistry along groundwater-flow paths (understanding wells). Water-quality data from the California Department of Public Health (CDPH) database also were used for the assessment. An assessment of the current status of the groundwater quality included collecting samples from wells for analysis of anthropogenic constituents such as volatile organic compounds (VOCs) and pesticides, as well as naturally occurring constituents such as major ions and trace elements. The assessment of status is intended to characterize the quality of untreated-groundwater resources within the primary aquifer system, not the treated drinking water delivered to consumers by water purveyors. The primary aquifer system (hereinafter, primary aquifer) is defined as that part of the aquifer corresponding to the perforation interval of wells listed in the CDPH database for the Central Eastside study unit. The quality of groundwater in shallower or deeper water-bearing zones may differ from that in the primary aquifer; shallower groundwater may be more vulnerable to surficial contamination. The primary aquifer is represented by the grid wells, of which 90 percent had depths to the tops of their perforations of about 80 to 330 feet and depths to bottom of about 100 to 670 feet. Relative-concentrations (sample concentration divided by benchmark concentration) were used as the primary metric for assessing the status of water quality for those constituents that have Federal and (or) California human health or aesthetic benchmarks. A relative-concentration greater than (>) 1.0 indicates a concentration above a benchmark, and less than or equal to (≤) 1.0 indicates a concentration equal to or below a benchmark. For organic and special interest constituents, relative-concentrations were classified as high (>1.0), moderate (≤1.0 and >0.1), or low (≤0.1). For inorganic constituents, relative-concentrations were classified as high (>1.0), moderate (≤1.0 and >0.5), or low (≤0.5). The threshold between low and moderate classifications was lower for organic and special interest constituents than for inorganic constituents because organic constituents generally are less prevalent and have smaller relative-concentrations than inorganic constituents. Grid-based and spatially-weighted approaches, the latter incorporating data from all CDPH wells, were used to evaluate the proportion of the primary aquifer (aquifer-scale proportions) with high, moderate, or low relative-concentrations. For individual constituents or classes of constituents, the aquifer-scale high proportion is the percentage of the area of the study unit having high relative-concentrations within the depth-zones of the primary aquifer. Aquifer-scale moderate and low proportions are defined similarly. Spatially-weighted aquifer-scale high proportions nearly always fell within the 90-percent confidence interval of grid-based aquifer-scale high proportions, indicating that the grid-based approach yielded statistically equivalent results to the spatially-weighted approach incorporating CDPH data. The status assessment for inorganic constituents showed that inorganic constituents (one or more) were high, relative to human-health benchmarks, in 18.0 percent of the primary aquifer, moderate in 44.0 percent, and low in 38.0 percent. Of inorganic constituents with human-health benchmarks, arsenic, vanadium, and nitrate were detected at high relative-concentrations in 15.6 percent, 3.6 percent, and 2.1 percent, respectively, of the primary aquifer. Of inorganic constituents with secondary maximum contaminant levels (SMCL), manganese, iron, and TDS were detected at high relative-concentrations in 4.5 percent, 2.2 percent, and 1.7 percent, respectively, of the primary aquifer. The status assessment for organic constituents showed that organic constituents (one or more) were high, relative to human-health benchmarks, in a smaller proportion of the primary aquifer (1.2 percent) than inorganic constituents (18.0 percent). Organic constituents had moderate relative-concentrations in 14.3 percent, and had low relative-concentrations or were not detected in 84.5 percent, of the primary aquifer. The proportion of the primary aquifer with high relative-concentrations of organic constituents reflected high proportions of the discontinued soil fumigant 1,2-dibromo-3-chlororopane (DBCP; 1.0 percent) and the solvent tetrachloroethene (PCE; 0.2 percent). Most of the organic and special interest constituents detected in groundwater in the Central Eastside study unit have human-health benchmarks. Of the 205 organic and special interest constituents analyzed for, 36 constituents were detected. Of these constituents, 32 were detected only at low relative-concentrations. Four constituents, chloroform, carbon tetrachloride, DBCP, and perchlorate, were detected at moderate relative-concentrations in grid wells. Nine organic and special-interest constituents were detected frequently (detected in greater than 10 percent of samples): the trihalomethanes chloroform, bromoform, bromodichloromethane, and dibromochloromethane; the solvent PCE; the herbicides atrazine, simazine, and metolachlor, and special-interest constituent perchlorate. An assessment of understanding of the groundwater quality included sampling of understanding wells, some of which were perforated in shallower or deeper portions of the aquifer system than the primary aquifer, and analysis of correlations of groundwater quality with land use, depth, age classification, and other potential explanatory factors. The understanding assessment indicated that the concentrations of many constituents were related to depth and groundwater age. However, concentrations of individual constituents or constituent classes also were sometimes related to geochemical conditions, lateral position in the flow system, or land use. High and moderate relative-concentrations of uranium, nitrate, and total dissolved solids (TDS) were detected in some wells where the tops of perforations are within the upper 200 feet of the aquifer system. In wells with the depth to the top of perforations below this depth, concentrations were low. A similar pattern occurred for the sum of herbicide concentrations. These vertical water-chemistry patterns are consistent with the hydrogeologic setting, in which return flows from agricultural and urban land use are the major source of recharge, and withdrawals for irrigation and urban supply are the major source of discharge, resulting in substantial vertical components of groundwater flow. The decrease in concentrations of many constituents with depth reflects in part that groundwater gets older with depth. Tritium, helium-isotopes, and carbon-14 data were used to classify the predominant age of groundwater samples into three categories: modern (water that has entered the aquifer in the last 50 years), pre-modern (water that entered the aquifer more than 50 years, up to tens of thousands of years, ago), and mixed (mixtures of waters with modern and pre-modern ages). Uranium, nitrate, and herbicide concentrations were significantly higher in groundwater having modern- and mixed-ages than pre-modern ages, indicating that these constituents may be affected by anthropogenic activities in the last 50 years. Other patterns in the distribution of nitrate, uranium, and TDS are evident. Isotopic and geochemical data are consistent with partial denitrification of nitrate in some reducing groundwaters in the western and deeper parts of the flow system. Uranium and TDS concentrations increase from east to west across the valley, along the direction of regional lateral groundwater flow. High and moderate relative-concentrations of arsenic can be attributed to reductive dissolution of manganese or iron oxides, or to desorption by high pH waters. Arsenic concentrations also increased with increasing depth and groundwater age. High to moderate relative-concentrations of vanadium primarily are related to high pH under oxic conditions. The frequency of detections of DBCP was greater in areas with orchard-vineyard land use >40 percent and at depths <200 feet. THMs and solvents were correlated positively with percent urban land use. Herbicide concentrations were correlated negatively with percent natural land use. Perchlorate concentrations were significantly greater in waters having modern and mixed ages than waters having pre-modern ages and were significantly and positively correlated with two land uses—percent orchard/vineyard land use and percent urban land use.

California↗
USGS1976

Changes in the water supply in the Upper Republican Natural Resources District, Southwest Nebraska, from 1952-75

Use of ground water for irrigation has increased rapidly in the Upper Republican Natural Resources District in southwestern Nebraska in recent years. The principal aquifer being developed is composed of saturated sand and gravel of the Ogallala Formation of Tertiary age. Water-level declines of as much as 16 feet (4.9 metres) have occurred. Base flow of major streams draining the aquifer was reduced by as much as 19 percent between 1967 and 1975. Recoverable ground water in storage was reduced by about 1 percent. Net withdrawal of ground water in 1975 was about 250,000 acre-feet (308 million cubic metres), compared with an estimated recharge from precipitation of 176,000 acre-feet (217 million cubic metres). Water levels and streamflow will continue to decline if ground-water withdrawals continue at or greater than the 1975 rate.

Nebraska↗
USGS1909

Geology and water resources of the northern portion of the Black Hills and adjoining regions in South Dakota and Wyoming

This paper, which supplements the report on the geology and water resources of the southern half of the Black Hills, published in 1901, is the result of studies made at intervals during the years 1899 to 1907. It relates to an area of about 7,500 square miles, situated about half in South Dakota and half in the northeast corner of Wyoming (Pl. II), and covering the northern half of the Black Hills uplift and a wide area of adjacent plains. The report describes the geology of the sedimentary rocks - their stratigraphy, structure, and history - and discusses their mineral resources, including underground water, coal, gypsum, etc. It also contains information respecting surface waters available for irrigation and stock raising, timber, climate, and the history of the topographic development of the region. The crystalline rocks of the central portion of the Black Hills area and the various igneous rocks of later age are shown on some of the accompanying maps but without differentiation, as the study of their geology was not within the scope of the investigation; neither are their mineral resources considered here, for these are treated in other publications. In the field work I have been assisted mainly by Prof. C. C. O'Harra, of the School of Mines at Rapid, who has mapped the geology of large areas about Aladdin, the Devils Tower, Belle Fourche, and Rapid. Dr. W. S. Tangier Smith has mapped portions of the Bear Lodge and Nigger Hill uplifts, and Mr. C. A. Fisher has assisted in portions of the work. The geology of the region from Sturgis to a point beyond Spearfish Canyon was mapped by Prof. T. A. Jaggar, jr., with the assistance of Mr. J. M. Boutwell, in 1898 and 1899. It is desirable to repeat here the statement made in my previous report that all who study the geology of the Black Hills must feel impressed by the remarkably clear general conceptions of the geologic relations of this region afforded by the survey made by Mr. Henry Newton over a quarter of a century ago. In one short season, with many unfavorable conditions for traveling, he determined most of the broader features and recorded many of the essential details. His posthumous report, edited by Mr. G. K. Gilbert, will always remain a standard work on Black Hills geology. Later studies have added greatly to our knowledge of the details of the stratigraphy and structure, the distribution of the rocks and minerals, and the age of the beds, and have afforded means for a more complete elucidation of the geologic history, especially the physiographic development of the Black Hills region.

South Dakota, Wyoming↗
USGS1988

Geologic and geohydrologic reconnaissance of Staten Island, New York

The public water supply for about 350,000 people on Staten Island (Richmond County)--a mainly suburban 60-sq mi borough of the City of New York is provided by the City from reservoirs in upstate New York. Since 1962, many individuals and businesses have used groundwater for supplemental supply as a result of the City 's ban on the use of public supply water for irrigation, swimming pools, and automobile washing during protracted droughts that depleted the reservoirs. Hundreds of wells were installed on the island during droughts of 1962-66 and 1983-85. Bedrock of Late Proterozoic to Jurassic age and unconsolidated deposits of the Upper Cretaceous and late Pleistocene age contain groundwater that is generally suitable for the city prohibited purposes. The groundwater of the island receives sufficient recharge to meet the current demands and could sustain considerably greater withdrawals. (USGS)

New York↗
USGS1998

Hydrogeology, water quality, and geochemistry of the Rush Springs aquifer, western Oklahoma

The Rush Springs aquifer, in western Oklahoma, is equivalent to the Permian-age Rush Springs Formation. It is composed of very fine-grained to fine-grained sandstone that is massive to highly cross-bedded and is underlain by less-permeable Marlow Formation. Reported irrigation well yields exceed 1,000 gallons per minute; yields reported on 89 drillers' logs ranged from 11 to 850 gallons per minute. Transmissivities range from 670 to 1,870 feet squared per day. Specific yields for core samples range from 0.13 to 0.34. Estimates of hydraulic conductivities at one site ranged from 1.05 to 5.62 feet per day. The Rush Springs aquifer is recharged by infiltration of precipitation, ranging from 0.2 to more than 2 inches per year. Discharge is primarily to streams and rivers where the Rush Springs aquifer crops. Estimated total withdrawal was 54.7 million gallons per day in 1990. Over 42 million gallons per day, or 77.8 percent of water withdrawn, was used for irrigation of crops. Thirty-five of the 64 wells sampled produced nitrate concentration that equaled or exceeded drinking water standards. Sulfate concentration also exceeds the drinking water standards in some areas. Two major water types occur in the aquifer, a calcium-magnesium bicarbonate type and a calcium sulfate type. Dissolved solids concentrations in water samples from the aquifer ranged from 52 to 1,840 milligrams per liter. The chemical composition of ground water in the Rush Springs aquifer is the result of chemical reactions between the recharge waters and minerals in the overlying soils and rocks in the Rush Springs and Marlow Formations. Saturation indices of minerals were calculated for 64 water-quality analyses using the geochemical computer model WATEQF. Mass transfer rates were calculated using the mass-balance model NETPATH.

Water-Resources Investigations Report↗
USGS1982

Reconnaissance of the quality of surface water in the San Rafael River basin, Utah

The water-quality reconnaissance of the San Rafael River basin, Utah, encompassed an area of about 2,300 square miles (5,960 square kilometers). Data were obtained by the U.S. Geological Survey one or more times at 116 sites from June 1977 to September 1978. At 19 other sites visited during the same period, the streams were dry. Precipitation and stream discharge were significantly less than normal during 1977 and ranged from less than to more than normal during 1978. Exposed rocks in the San Rafael River basin range in age from Permian to Holocene. The Carmel Formation of Jurassic age and various members of the Mancos Shale of Cretaceous age are major contributors of dissolved solids to streams in the basin. There are eight major reservoirs having a total usable capacity of 115, 000 acre-feet (142 cubic hectometers); seven are mainly for irrigation supply; one, having a usable capacity of 30,530 acre-feet (38 cubic hectometers), is for power plant water supply. From about April to November, major diversions from Huntington, Cottonwood, and Ferron Creeks nearly deplete the flow downstream; during such periods, downstream flow in these streams and in the San Rafael River is mainly irrigation-return flow and some ground-water seepage. The water at the points of major diversion on Huntington, Cottonwood, and Ferron Creeks is of excellent quality for irrigation; salinity hazard is low to medium, and sodium hazard is low. Dissolved-solids concentrations are less than 500 milligrams per liter. The water at the mouths of Huntington, Cottonwood, and Ferron Creeks has markedly larger dissolved-solids concentrations than does the water upstream from major diversions. The changes in the chemical quality occur in stream reaches that cross a belt of land 10 to 15 miles (16 to 24 kilometers) wide where the Mancos Shale is widely exposed. This also is the area where nearly all the intensive irrigation in the San Rafael River basin is practiced. There are no perennial tributaries to the San Rafael River downstream from Ferron Creek. Except during infrequent short periods of runoff from cloudbursts or snowmelt, the flow in the San Rafael River is composed of the flow that reaches the mouths of Huntington, Cottonwood, and Ferron Creeks. The quality of water in the mainstem of the San Rafael River is largely determined by the major consumptive use of water for irrigation in upstream areas and by the poor quality of irrigation-return flow. During the data-collection periods for this study, dissolved-solids concentrations in the San Rafael River were more than 2,000 milligrams per liter except during snowmelt runoff in June 1978 and during a major flood in August 1977. The concentrations of trace elements, with the exception of strontium, were relatively small; strontium concentrations exceeded 1,500 micrograms per liter at seven sites. Most of the suspended-sediment discharge of the San Rafael River probably occurs during a few days each year and results mainly from cloudburst runoff.

Utah↗
USGS2011

Hydrogeologic and geochemical characterization of groundwater resources in Rush Valley, Tooele County, Utah

The water resources of Rush Valley were assessed during 2008–2010 with an emphasis on refining the understanding of the groundwater-flow system and updating the groundwater budget. Surface-water resources within Rush Valley are limited and are generally used for agriculture. Groundwater is the principal water source for most other uses including supplementing irrigation. Most groundwater withdrawal in Rush Valley is from the unconsolidated basin-fill aquifer where conditions are generally unconfined near the mountain front and confined at lower altitudes near the valley center. Productive aquifers also occur in fractured bedrock along the valley margins and beneath the basin-fill deposits in some areas. Drillers’ logs and geophysical gravity data were compiled and used to delineate seven hydrogeologic units important to basin-wide groundwater movement. The principal basin-fill aquifer includes the unconsolidated Quaternary-age alluvial and lacustrine deposits of (1) the upper basin-fill aquifer unit (UBFAU) and the consolidated and semiconsolidated Tertiary-age lacustrine and alluvial deposits of (2) the lower basin-fill aquifer unit (LBFAU). Bedrock hydrogeologic units include (3) the Tertiary-age volcanic unit (VU), (4) the Pennsylvanian- to Permian-age upper carbonate aquifer unit (UCAU), (5) the upper Mississippian- to lower Pennsylvanian-age upper siliciclastic confining unit (USCU), (6) the Middle Cambrian- to Mississippian-age lower carbonate aquifer unit (LCAU), and (7) the Precambrian- to Lower Cambrian-age noncarbonate confining unit (NCCU). Most productive bedrock wells in the Rush Valley groundwater basin are in the UCAU. Average annual recharge to the Rush Valley groundwater basin is estimated to be about 39,000 acre-feet. Nearly all recharge occurs as direct infiltration of snowmelt and rainfall within the mountains with smaller amounts occurring as infiltration of streamflow and unconsumed irrigation water at or near the mountain front. Groundwater generally flows from the higher altitude recharge areas toward two distinct valley-bottom discharge areas: one in the vicinity of Rush Lake in northern Rush Valley and the other located west and north of Vernon. Average annual discharge from the Rush Valley groundwater basin is estimated to be about 43,000 acre-feet. Most discharge occurs as evapotranspiration in the valley lowlands, as discharge to springs and streams, and as withdrawal from wells. Subsurface discharge outflow to Tooele and Cedar Valleys makes up only a small fraction of natural discharge. Groundwater samples were collected from 25 sites (24 wells and one spring) for geochemical analysis. Dissolved-solids concentrations in water from these sites ranged from 181 to 1,590 milligrams per liter. Samples from seven wells contained arsenic concentrations that exceed the Environmental Protection Agency Maximum Contaminant Level of 10 micrograms per liter. The highest arsenic levels are found north of Vernon and in southeastern Rush Valley. Stable-isotope ratios of oxygen and deuterium, along with dissolved-gas recharge temperatures, indicate that nearly all modern groundwater is meteoric and derived from the infiltration of high altitude precipitation in the mountains. These data are consistent with recharge estimates made using a Basin Characterization Model of net infiltration that shows nearly all recharge occurring as infiltration of precipitation and snowmelt within the mountains surrounding Rush Valley. Tritium concentrations between 0.4 and 10 tritium units indicate the presence of modern (less than 60 years old) groundwater at 7 of the 25 sample sites. Apparent 3 H/ 3 He ages, calculated for six of these sites, range from 3 to 35 years. Adjusted minimum radiocarbon ages of premodern water samples range from about 1,600 to 42,000 years with samples from 11 of 13 sites being more than 11,000 years. These data help to identify areas where modern groundwater is circulating through the hydrologic system on time scales of decades or less and indicate that large parts of the principal basin-fill and the bedrock aquifers are much less active and receive little to no modern recharge.

Utah↗
USGS2008

Simulation of Ground-Water Flow and Effects of Ground-Water Irrigation on Base Flow in the Elkhorn and Loup River Basins, Nebraska

Irrigated agriculture is vital to the livelihood of communities in the Elkhorn and Loup River Basins in Nebraska, and ground water is used to irrigate most of the cropland. Concerns about the sustainability of ground-water and surface-water resources have prompted State and regional agencies to evaluate the cumulative effects of ground-water irrigation in this area. To facilitate understanding of the effects of ground-water irrigation, a numerical computer model was developed to simulate ground-water flow and assess the effects of ground-water irrigation (including ground-water withdrawals, hereinafter referred to as pumpage, and enhanced recharge) on stream base flow. The study area covers approximately 30,800 square miles, and includes the Elkhorn River Basin upstream from Norfolk, Nebraska, and the Loup River Basin upstream from Columbus, Nebraska. The water-table aquifer consists of Quaternary-age sands and gravels and Tertiary-age silts, sands, and gravels. The simulation was constructed using one layer with 2-mile by 2-mile cell size. Simulations were constructed to represent the ground-water system before 1940 and from 1940 through 2005, and to simulate hypothetical conditions from 2006 through 2045 or 2055. The first simulation represents steady-state conditions of the system before anthropogenic effects, and then simulates the effects of early surface-water development activities and recharge of water leaking from canals during 1895 to 1940. The first simulation ends at 1940 because before that time, very little pumpage for irrigation occurred, but after that time it became increasingly commonplace. The pre-1940 simulation was calibrated against measured water levels and estimated long-term base flow, and the 1940 through 2005 simulation was calibrated against measured water-level changes and estimated long-term base flow. The calibrated 1940 through 2005 simulation was used as the basis for analyzing hypothetical scenarios to evaluate the effects of ground-water irrigation on stream base flow for 1940 through 2005 and for 2006 through 2045. Simulated base flows were compared for scenarios that alternately did or did not include a representation of the effects of ground-water irrigation. The difference between simulated base flows for the two scenarios represents the predicted effects of ground-water irrigation on base flow. Comparison of base flows between simulations with ground-water irrigation and no ground-water irrigation indicated that ground-water irrigation has cumulatively reduced streamflows from 1940 through 2005 by 888,000 acre-feet in the Elkhorn River Basin and by 2,273,000 acre-feet in the Loup River Basin. Generally, predicted cumulative effects of ground-water irrigation on base flow were 5 to 10 times larger from 2006 through 2045 than from 1940 through 2005, and were 7,678,000 acre-feet for the Elkhorn River Basin and 14,784,000 acre-feet for the Loup River Basin. The calibrated simulation also was used to estimate base-flow depletion as a percentage of pumping volumes for a 50-year future time period, because base-flow depletion percentages are used to guide the placement of management boundaries in Nebraska. Mapped results of the base-flow depletion analysis conducted for most of the interior of the study area indicated that pumpage of one additional theoretical well simulated for a future 50-year period generally would result in more than 80 percent depletion when it was located close to the stream, except in areas where depletion was partly offset by reduced ground-water discharge to evapotranspiration in wetland areas. In many areas, depletion for the 50-year future period composed greater than 10 percent of the pumped water volume for theoretical wells placed less than 7 or 8 miles from the stream, though considerable variations existed because of the heterogeneity of the natural system represented in the simulation. For a few streams, predicted future simulated base flows dec

Scientific Investigations Report↗