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USGS2016

Delineation of the Pahute Mesa–Oasis Valley groundwater basin, Nevada

This report delineates the Pahute Mesa–Oasis Valley (PMOV) groundwater basin, where recharge occurs, moves downgradient, and discharges to Oasis Valley, Nevada. About 5,900 acre-feet of water discharges annually from Oasis Valley, an area of springs and seeps near the town of Beatty in southern Nevada. Radionuclides in groundwater beneath Pahute Mesa, an area of historical underground nuclear testing at the Nevada National Security Site, are believed to be migrating toward Oasis Valley. Delineating the boundary of the PMOV groundwater basin is necessary to adequately assess the potential for transport of radionuclides from Pahute Mesa to Oasis Valley. The PMOV contributing area is defined based on regional water-level contours, geologic controls, and knowledge of adjacent flow systems. The viability of this area as the contributing area to Oasis Valley and the absence of significant interbasin flow between the PMOV groundwater basin and adjacent basins are shown regionally and locally. Regional constraints on the location of the contributing area boundary and on the absence of interbasin groundwater flow are shown by balancing groundwater discharges in the PMOV groundwater basin and adjacent basins against available water from precipitation. Internal consistency for the delineated contributing area is shown by matching measured water levels, groundwater discharges, and transmissivities with simulated results from a single-layer, steady-state, groundwater-flow model. An alternative basin boundary extending farther north than the final boundary was rejected based on a poor chloride mass balance and a large imbalance in the northern area between preferred and simulated recharge.

California, Nevada↗

USGS2016

Streamflow and estimated loads of phosphorus and dissolved and suspended solids from selected tributaries to Lake Ontario, New York, water years 2012–14

This report presents results of the evaluation and interpretation of hydrologic and water-quality data collected as part of a cooperative program between the U.S. Geological Survey and the U.S. Environmental Protection Agency. Streamflow, phosphorus, and solids dissolved and suspended in stream water were the focus of monitoring by the U.S. Geological Survey at 10 sites on 9 selected tributaries to Lake Ontario during the period from October 2011 through September 2014. Streamflow yields (flow per unit area) were the highest from the Salmon River Basin due to sustained yields from the Tug Hill aquifer. The Eighteenmile Creek streamflow yields also were high as a result of sustained base flow contributions from a dam just upstream of the U.S. Geological Survey monitoring station at Burt. The lowest streamflow yields were measured in the Honeoye Creek Basin, which reflects a decrease in flow because of withdrawals from Canadice and Hemlock Lakes for the water supply of the City of Rochester. The Eighteenmile Creek and Oak Orchard Creek Basins had relatively high yields due in part to groundwater contributions from the Niagara Escarpment and seasonal releases from the New York State Barge Canal. Annual constituent yields (load per unit area) of suspended solids, phosphorus, orthophosphate, and dissolved solids were computed to assess the relative contributions and allow direct comparison of loads among the monitored basins. High yields of total suspended solids were attributed to agricultural land use in highly erodible soils at all sites. The Genesee River, Irondequoit Creek, and Honeoye Creek had the highest concentrations and largest mean yields of total suspended solids (165 short tons per square mile [t/mi 2 ], 184 t/mi 2 , and 89.7 t/mi 2 , respectively) of the study sites. Samples from Eighteenmile Creek, Oak Orchard Creek at Kenyonville, and Irondequoit Creek had the highest concentrations and largest mean yields of phosphorus (0.27 t/mi 2 , 0.26 t/mi 2 , and 0.20 t/mi 2 , respectively) and orthophosphate (0.17 t/mi 2 , 0.13 t/mi 2 , and 0.04 t/mi 2 , respectively) of the study sites. These results were attributed to a combination of sources, including discharges from wastewater treatment plants, diversions from the New York State Barge Canal, and manure and fertilizers applied to agricultural land. Yields of phosphorus also were high in the Genesee River Basin (0.17 t/mi 2 ) and were presumably associated with nutrient and sediment transport from agricultural land and from streambank erosion. The Salmon and Black Rivers, which drain a substantial amount of forested land and are influenced by large groundwater discharges, had the lowest concentrations and yields of phosphorus and orthophosphate of the study sites. Mean annual yields of dissolved solids were the highest in Irondequoit Creek due to a high percentage of urbanized area in the basin and in Oak Orchard Creek at Kenyonville and in Eighteenmile Creek due to groundwater contributions from the Niagara Escarpment. High yields of dissolved solids of 840 t/mi 2 , 829 t/mi 2 , and 715 t/mi 2 , respectively, from these basins can be attributed to seasonal chloride yields associated with use of road deicing salts. The Niagara Escarpment can produce large amounts of dissolved solids from the dissolution of minerals (a continual process reflected in base flow samples). Groundwater inflows in the Salmon River have very low concentrations of dissolved solids due to minimal bedrock interaction along the Tug Hill Plateau and discharge from the Tug Hill sand and gravel aquifer, which has minimal mineralization.

New York↗

USGS2020

Sediment and chemical contaminant loads in tributaries to the Anacostia River, Washington, District of Columbia, 2016–17

A study was conducted by the U.S. Geological Survey (USGS) in cooperation with the Washington, D.C., Department of Energy & Environment to estimate the loads of suspended-sediment-bound chemical compounds in five gaged tributaries and four ungaged tributaries of the Anacostia River (known locally as “Lower Anacostia River”) in Washington, D.C. Tributaries whose discharge is measured by the USGS are the Northeast and Northwest Branches of the Anacostia River, referred to in this report as “Northeast Branch” (NEB) and “Northwest Branch” (NWB), respectively; Watts Branch (WB); and Hickey Run (HR). A USGS streamflow-gaging station was established in 2016 on Beaverdam Creek (known locally as “Lower Beaverdam Creek” [LBDC]) to support this study. The ungaged streams studied include Nash Run; Pope Branch; an unnamed stream at Fort DuPont, referred to in this report as “Fort DuPont Creek”; and an unnamed stream at Fort Stanton, referred to in this report as “Fort Stanton Creek.” The gaged streams were sampled during four to five storms and two low-flow events during January, March, May, and July 2017. The ungaged streams were sampled during one storm and one low-flow event during July 2017. Storm sampling involved collecting large-volume (60- to 70-liter) composite samples, then removing sediment by filtration in the laboratory. Low-flow samples were obtained by filtering streamwater directly in the field. Continuously recording data sondes were deployed throughout the study to measure turbidity and other water-quality characteristics. During sampling, multiple discrete samples of streamwater were collected to determine suspended-sediment concentration (SSC) and particulate organic carbon (POC) concentration. Shortly after each storm, bed sediment was collected for chemical analysis. Sediment samples were analyzed for 209 polychlorinated biphenyl (PCB) congeners; 35 polyaromatic hydrocarbon (PAH) compounds, including 20 nonalkylated and 15 alkylated species; and 20 organochlorine pesticide (OP) compounds. Sediment from one storm was analyzed for 23 metals. Relations were developed among turbidity, discharge, and measured SSC by using multiple linear regression of log-transformed data. These relations were used to estimate SSC from continuous records of discharge and turbidity and were subsequently used to estimate sediment loads for the 2017 calendar year. USGS continuous records of turbidity in NEB, NWB, Watts Branch, and Hickey Run were available for 2013–17, which allowed sediment loads to be calculated for these years. Sediment loads for the ungaged streams were estimated by using loads measured in Watts Branch adjusted on the basis of stream-basin areas. Sediment loads for 2017 total 3.10×10 7 kilograms (kg), with 1.02×107 kg (33 percent of total) from the NEB, 1.55×10 7 kg (50 percent) from the NWB, 4.45×10 6 kg (14 percent) from LBDC, 5.62×10 5 kg (2 percent) from Watts Branch, and 2.82×10 5 kg (1 percent) from Hickey Run. Sediment yields were highest from NWB and LBDC (3.13×10 5 kilograms per year per square mile [kg/yr/mi 2 ] and 3.01 kg/yr/mi 2 , respectively). As a result of gaps in turbidity and discharge data, the load for LBDC reported here was calculated from measurements representing only 88 percent of the year (2017), and thus underestimates the actual load. All other gaged tributaries had datasets covering 100 percent of the year and are considered to fully represent actual loads. Estimated sediment loads for the ungaged streams during 2017 total 3.5×10 5 kg, with 1.2×10 5 kg from Nash Run, 6.2×10 4 kg from Pope Branch, 1.1×10 5 kg from Fort DuPont Creek, and 5.6×10 4 kg from Fort Stanton Creek. Concentrations of PCBs, PAHs, and chlorinated pesticides in streamwater are presented for stormflow and low-flow conditions. Average concentrations (in stormflow and low-flow samples) of total PCBs (sum of all congeners, including coelutions) are 5.9 micrograms per kilogram (µg/kg) for NEB, 6.6 µg/kg for NWB, 130 µg/kg for LBDC, 34 µg/kg for Watts Branch, and 69 µg/kg for Hickey Run. Average concentrations of total PAHs (tPAH) (total of nonalkylated and alkylated species) are 2,000 µg/kg for NEB, 3,300 µg/kg for NWB, 2,200 µg/kg for LBDC, 2,400 µg/kg for Watts Branch, and 18,000 µg/kg for Hickey Run. tPAH concentrations among the ungaged streams were highest in Nash Run (5,500 µg/kg); concentrations in the other ungaged streams were less than (<) 700 µg/kg. The general magnitude of tPCB and tPAH concentrations in streamwater samples was low-flow samples greater than (>) stormflow samples greater than or equal to (≥) bed-sediment samples. PCB congener profiles in the three types of samples were nearly identical in each stream and were similar in all streams except for LBDC, where the dominant PCBs shifted to the lighter di- through tetra- homologs. LBDC showed higher tPCB concentrations and a distinct congener profile from the other streams. The similarity in congener makeup supported that averaging PCB concentrations in stormflow and low-flow samples was appropriate for calculating chemical loads. Loads of tPCB, tPAH (total of alkylated and nonalkylated forms), and pesticides were estimated for each stream by multiplying average contaminant concentrations by the respective sediment loads. Total PCB loads for 2017 were estimated to be 820 grams (g) with 8 percent (60 g) from NEB, 12 percent (95 g) from NWB, 75 percent (590 g) from LBDC, 3 percent (25 g) from Watts Branch, and 2.5 percent (19 g) from Hickey Run. PCB toxicity totaled 3.8×10 −3 µg/kg, with the largest contribution (47 percent) derived from LBDC. Total PAH loads (sum of alkylated and nonalkylated forms) for 2017 were estimated to be 89,000 g, with 23 percent (20,000 g) from NEB, 59 percent (52,000 g) from NWB, 11 percent (9,800 g) from LBDC, 2 percent (1,400 g) from Watts Branch, and 6 percent (5,200 g) from Hickey Run. These results indicate that the largest contributor (75 percent) of PCBs to the Anacostia River is LBDC, although it contributes only 15 percent of the sediment and its basin area represents only 10 percent of the area of the Anacostia River watershed. The majority of the PAH load originates from NWB (59 percent of total) and NEB (22 percent). The ungaged tributaries contribute extremely small loads of PCBs and PAHs, totaling 8.1 g and 765 kg, respectively. More than 94 percent of the total load from the ungaged tributaries is derived from the Nash Run Basin. Various organochlorine pesticides were present in suspended and bed sediment from all gaged and ungaged tributaries; however, elevated detection levels associated with the analytical methods resulted in numerous unquantifiable concentrations in the suspended-sediment samples. Only the pesticide chlordane was found in measurable concentrations in all gaged tributaries. As a result, in this report, a combination of analytical data from suspended-sediment and bed-sediment samples was used to estimate the maximum pesticide loading for each tributary. Chlordane was the principal compound present in the gaged tributaries; the highest average concentration (average of stormflow and low-flow samples from each stream) was 62 µg/kg in sediment from Watts Branch. Chlordane loads for 2017 totaled 1,100 g, of which 7 percent (430 g) was from NEB, 28 percent (320 g) was from NWB, 28 percent (310 g) was from LBDC, 5 percent (56 g) was from Watts Branch, and 1 percent (11 g) was from Hickey Run. Chlordane was not present in suspended or bed sediment from any of the ungaged tributaries. Loads of the other pesticides were estimated by using the highest concentration measured in the combined suspended-sediment and bed-sediment data for each stream. Notable loads include dieldrin (860 g from NWB), methoxychlor (205 g from LBDC), endrin aldehyde (150 g from NWB), and 4,4-DDT (79 g from Watts Branch). Compared with pesticide loads from the gaged streams, those from the ungaged streams were minimal, with only the Pope Branch contribution exceeding 1 gram per year for 4,4-DDE (1.05 g) and 4,4’-DDT (1.3 g). The results of this study show that the dominant source of PCBs and chlordane is LBDC, despite its relatively small basin area. PAHs are ubiquitous throughout the study area, with the largest sources being NEB and NWB; this finding is a result of the large sediment load originating from these basins. The small, ungaged streams supply only minimal PCB and PAH loads, with Nash Run being the largest contributor.

District of Columbia↗

USGS2020

Spatially referenced models of streamflow and nitrogen, phosphorus, and suspended-sediment loads in streams of the northeastern United States

SPAtially Referenced Regression On Watershed attributes (SPARROW) models were developed to quantify and improve the understanding of the sources, fate, and transport of nitrogen, phosphorus, and suspended sediment in the northeastern United States. Excessive nutrients and suspended sediment from upland watersheds and tributary streams have contributed to ecological and economic degradation of northeastern surface waters. Recent efforts to reduce the flux of nutrients and suspended sediment in northeastern streams and to downstream estuaries have met with mixed results, and expected ecological improvements have been observed in some areas but not in others. Effective watershed management and restoration to improve surface-water quality are complicated by the multitude of nutrient sources in the Northeast and the multitude of natural and human landscape processes affecting the delivery of nutrients and suspended sediment from upland areas to and within surface waters. Individual models were constructed representing streamflow and the loads of total nitrogen, total phosphorus, and suspended sediment from watersheds draining to the Atlantic Ocean from southern Virginia through Maine. Northeastern streams contribute 303,000 metric tons (t) of nitrogen, 25,300 t of phosphorus, and 14,700,000 t of suspended sediment, annually (on average), to waters along the Atlantic Coast of North America. Although atmospheric deposition and natural mineral erosion contribute to nitrogen and phosphorus loads, respectively, in northeastern streams, most of the contributions are attributable to urban or agricultural sources. Within the Northeast, average yields of nutrients are therefore generally greater from densely populated or intensively cultivated areas of the mid-Atlantic region, the Hudson, Mohawk, and Connecticut River valleys, and the coastal areas of southern New England than in predominantly forested areas such as northern New England. Average upland sediment yields are similarly greater from agricultural areas than from urban or forested areas and are therefore generally greatest in areas yielding the greatest nutrients. Landscape conditions that are significant to nitrogen delivery from uplands to streams likely reflect the importance of groundwater transport in carbonate settings and of denitrification for removing nitrogen from uplands. Nitrogen losses to streams in agricultural areas are apparently mitigated by the use of cover crops but are exacerbated by the use of conservation tillage or no-till practices. The transport of phosphorus and suspended sediment from uplands to streams is greater in areas of more erodible soils but mitigated in agricultural areas with greater use of conservation tillage or no-till practices. Loads of nutrients and suspended sediment are significantly reduced within the stream network in impounded reaches, and nitrogen load is also significantly reduced in small flowing reaches.

Scientific Investigations Report↗

USGS2021

Analysis of Escherichia coli, total recoverable iron, and dissolved selenium concentrations, loading, and identifying data gaps for selected 303(d) listed streams, Grand Valley, western Colorado, 1980–2018

Tributaries to the Colorado River in the Grand Valley in western Colorado (segment COLCLC13b) have been placed on the State of Colorado 303(d) list as impaired for Escherichia coli (E. coli) , total recoverable iron, and dissolved selenium. The Colorado Department of Public Health and Environment Water Quality Control Division is required to develop total maximum daily loads for these constituents in these tributaries. The U.S. Geological Survey, in cooperation with the Grand Valley Drainage District and Colorado Water Conservation Board, conducted a study to (1) characterize concentrations, loads, and load reductions for E. coli , total recoverable iron, and dissolved selenium using existing data and (2) identify water-quality data gaps to inform future monitoring strategies. This study analyzed water-quality and streamflow data for 3 main-stem sites (2 sites along the Colorado River and 1 site along the Gunnison River) and 29 selected sites on tributaries to the Colorado River. Sample data were available at five sites along Adobe Creek and at six sites along Leach Creek, the two tributaries in the study area that are impaired for E. coli . All geometric mean E. coli concentrations at sites along Adobe Creek and Leach Creek exceeded the State recreational use standard of 126 colony forming units per 100 milliliters (CFU/100 mL). In Adobe Creek, E. coli concentrations in samples ranged from 45.7 to more than 2,420 CFU/100 mL (method upper reporting limit for undiluted samples), and geometric mean concentrations at sites ranged from 301 to 1,180 CFU/100 mL. The E. coli concentrations generally increased in the downstream direction in Adobe Creek; however, increases were not seen between all sites. The largest downstream increase in E. coli concentration was measured between the two most upstream sites. In Leach Creek, concentrations of E. coli in samples ranged from 25.9 to more than 2,420 CFU/100 mL, and geometric mean concentrations at sites ranged from 160 to 259 CFU/100 mL. The E. coli concentrations showed no consistent downgradient increase in Leach Creek. In fact, some of the highest E. coli concentrations were measured at the most upstream site, Leach Creek at Summer Hill Drive. Total recoverable iron concentrations and loads were evaluated at 15 tributary sites for samples collected from August 1993 to February 2018. Median total recoverable iron concentrations ranged from 211 to 4,670 micrograms per liter (µg/L). The chronic aquatic-life water-quality standard (1,000 µg/L) was exceeded in most irrigation season (April through October) samples but was rarely exceeded in nonirrigation season (November through March) samples. Concentrations were often an order of magnitude higher in samples collected during irrigation season than in samples collected during nonirrigation season. None of the sites had enough concurrent total recoverable iron and streamflow data to compute annual loads. As with E. coli , the lack of concurrent total recoverable iron and streamflow information represents a data gap, which needs to be addressed to compute annual loads. Dissolved selenium concentrations and loads were evaluated at 20 tributary sites using discrete water-quality data collected 1991–2018. Dissolved selenium concentrations were higher during nonirrigation season than during irrigation season at tributary sites. However, irrigation season dissolved selenium loads were generally higher than nonirrigation selenium loads, because streamflows were higher during irrigation season. Regression analysis was used to estimate daily dissolved selenium concentrations and loads at three main-stem sites for water years (WYs) 1980–2018 (Gunnison River near Grand Junction and Colorado River near Colorado-Utah State Line) and WYs 2002–18 (Colorado River near Cameo). A trend analysis of dissolved selenium concentrations and loads was completed for these sites from the same respective starting dates but ending in 2017. A continuing downward trend in dissolved selenium concentration was observed at all sites and across all seasonal designations of the analysis. The dissolved selenium concentration decreased by 0.12 µg/L from WY 2002 to 2017 at Colorado River near Cameo, representing an 18-percent decrease during the time period. The dissolved selenium concentration at Gunnison River near Grand Junction decreased by 4.2 µg/L from WY 1980 to 2017, representing a 56-percent decrease overall. During the same time period, dissolved selenium concentration at Colorado River near Colorado-Utah State Line decreased by 3.8 µg/L, representing a 56-percent decrease overall. A downward trend in dissolved selenium load was also observed at all sites and across all seasonal designations of the analysis. The relative contribution of dissolved selenium from the Grand Valley near Grand Junction was estimated by comparing loads at main-stem sites bracketing the study area. The two upstream sites, Colorado River near Cameo and Gunnison River near Grand Junction, contributed 60,300 cumulative pounds and 251,000 cumulative pounds, respectively, during WYs 2002–18. At the furthest downstream site, Colorado River near Colorado-Utah State Line, 490,000 cumulative pounds were estimated during the same time period, indicating that the region between Whitewater and State line contributed approximately 179,000 cumulative pounds or a mean annual load of 10,500 lb/yr. Grand Valley dissolved selenium contributions appear to be stable during WYs 2002–18.

Colorado↗

USGS2000

Suspended-sediment characteristics in the Housatonic River Basin, western Massachusetts and parts of eastern New York and northwestern Connecticut, 1994-96

Suspended-sediment concentrations, discharges, loads, and yields were determined for eight subbasins in the Housatonic River Basin in western Massachusetts, eastern New York, and northwestern Connecticut from April 1994 through March 1996. Suspended-sediment samples were collected at three continuous-record sediment stations and at four partial-record sediment stations. Suspended-sediment concentrations in samples collected during the period of study ranged from less than 0.5 to 3,400 milligrams per liter, and concurrent streamflows ranged from 0.03 to 126 cubic feet per second per square mile at the seven stations. Median suspended-sediment concentrations in samples collected at each station ranged from 7 to 61 milligrams per liter. Median streamflows during suspended-sediment sampling ranged from 1.86 to 5.88 cubic feet per second per square mile. Instantaneous suspended-sediment yields ranged from less than 0.005 to 185 tons per day per square mile, and medians ranged from 0.03 to 1.12 tons per day per square mile at the seven stations. Total suspended-sediment loads (mass) from April 1994 through March 1996 at the continuous-record sediment stations were 11,603 tons at Housatonic River near Great Barrington, 7,929 tons at Green River, and 54,347 tons at Housatonic River near Ashley Falls. Suspended-sediment load during January 1996 at the Green River station accounted for about 54 percent of the total suspended-sediment load for the Green River during the 2-year study. Suspended-sediment load on January 19 and 20, 1996, at the Green River station accounted for about 50 percent of the January 1996 suspended-sediment load, or about 27 percent of the total suspended-sediment load during the 2-year study. This large suspended-sediment transport was the result of rainfall and snowmelt on January 19 and 20, 1996--the equivalent of a 5- to 6-inch rain storm in the Green River subbasin. Total suspended-sediment loads during the 2-year study at the partial-record sediment stations were 3,052 tons at Williams River, 1,758 tons at Ironworks Brook, and 17,927 tons at Konkapot River. Suspended-sediment yields from April 1994 through March 1996 at the continuous-record sediment stations were 21 (tons/yr)/mi 2 at Housatonic River near Great Barrington, 78 (tons/yr)/mi 2 at Green River, and 58 (tons/yr)/mi 2 at Housatonic River near Ashley Falls. Suspended-sediment yields during the 2- year study at the partial-record sediment stations were 35 (tons/yr)/mi 2 at Williams River, 78 (tons/yr)/mi 2 at Ironworks Brook, and 147 (tons/yr)/mi 2 at Konkapot River. Suspended-sediment yields were estimated for two subbasins in the Housatonic River Basin--Schenob Brook at Sheffield, a partial-record sediment station, and the area adjacent to the Housatonic River between Great Barrington and Ashley Falls. The estimate of suspended-sediment yield at Schenob Brook at Sheffield of 82 (tons/yr)/mi 2 is comparable to the yield determined for the Green River and Ironworks Brook. The estimate of suspended-sediment yield for the area adjacent to the Housatonic River between Great Barrington and Ashley Falls was 395 (tons/yr)/mi 2 . This estimated suspended-sediment yield was 2.7 to 18.8 times greater than that estimated for any of the other subbasins. Several basin and land-use characteristics thought to affect suspended-sediment transport in the subbasins were compared to the suspended-sediment yields. The characteristics that seemed to affect suspended-sediment discharge were dams, which contributes to decreased yields; Hadley, Limerick, Linlithgo, Saco, and Winooski silt loam soils (high erodibility soils), which contributes to increased yields; stratified-drift deposits, which contributes to increased yields; and agricultural and open land, which contributes to increased yields. The effect of stratified-drift deposits on suspended-sediment discharge is thought to be greater when those deposits are of glaciolacustrine (generally clay, silt, and fine sand), rather than glaciofluvial (clay, silt, sand, gravel, and cobbles) origin. The silt loam soils, glaciolacustrine deposits, and agricultural and open land are interrelated, inasmuch as the silt loam soils generally are associated with glaciolacustrine deposits and agricultural activities.

Connecticut, Massachusetts, New York↗

USGS2001

Estimated recharge to the Madison and Minnelusa aquifers in the Black Hills area, South Dakota and Wyoming, water years 1931-98

The Madison and Minnelusa aquifers are two of the most important aquifers in the Black Hills area. Long-term estimates of recharge to the Madison and Minnelusa aquifers are important for managing the water resources in the Black Hills area. Thus, annual recharge from streamflow losses and infiltration of precipitation on outcrop areas is estimated for water years 1931-98. All estimates are for recharge that contributes to regional ground-water flow patterns and that occurs in outcrop areas connected to the regional flow system. Estimates exclude recharge to outcrop areas that are isolated from the regional flow system, which generally results in ground-water discharge to area streams. Streamflow recharge is calculated directly for 11 streams in the Black Hills area that have continuous-record gaging stations located upstream from loss zones, using available records of daily streamflow, against which estimated loss thresholds (from previous investigations) are applied. Daily streamflow records are extrapolated, when necessary, using correlations with long-term gages, to develop annual estimates of streamflow recharge for 1950-98. Streamflow recharge is estimated for a number of smaller basins using loss thresholds for miscellaneous-record sites. Annual recharge estimates are derived from synthetic records of daily streamflow for 1992-98, which are based on drainage-area ratios applied to continuous-record gaging stations. Recharge estimates are further extrapolated for 1950-91, based on the average percentage of streamflow recharge contributed by these basins during 1992-98, relative to overall streamflow recharge.Streamflow recharge also is estimated for small drainage areas with undetermined loss thresholds that are situated between larger basins with known thresholds. Estimates for 1992-98 are based on estimates of annual streamflow derived using drainage-area ratios, with assumed losses equal to 90 percent of annual streamflow. Recharge estimates also are extrapolated for 1950-91, based on the average percentage of streamflow recharge contributed by these basins.Precipitation recharge for 1931-98 is estimated using relations between precipitation and streamflow (or basin yield) for representative gaging stations. Basin yields are first normalized, relative to drainage area, by expressing in inches per unit of drainage area. Yields are further converted to yield efficiencies, by dividing by precipitation on contributing drainage areas. Relations between yield efficiency and precipitation are identified, which are developed for use in generically estimating annual yield for given areas, based on average yield efficiency and annual precipitation. The resulting annual yield is used as a surrogate for estimating annual recharge from infiltration of precipitation on outcrop areas of the Madison and Minnelusa aquifers. Annual yield (or recharge) efficiencies are estimated to range from about 2 percent to in excess of 30 percent, with corresponding average annual recharge estimates ranging from 0.4 inch in the southern Black Hills to about 8.7 inches in the northwestern Black Hills.Estimates of precipitation recharge for 1931-49 are used to estimate streamflow recharge for the same period, based on correlations between the two variables for 1989-98. Combined streamflow and precipitation recharge to both aquifers averaged about 344 ft3/s for 1931-98. Streamflow recharge averaged about 93 ft3/s, or 27 percent of combined recharge, and precipitation recharge averaged about 251 ft3/s, or 73 percent of combined recharge. Combined recharge ranged from 62 ft3/s in 1936 to 847 ft3/s in 1995. The lowest recharge amounts generally occurred during the 1930?s; however, a more prolonged period of low recharge occurred during 1947-61.For 1931-98, average precipitation recharge to the Madison aquifer is about 3.6 inches, compared with 2.6 inches for the Minnelusa aquifer. However, recharge volumes to these aquifers are nearly identical because th

Water-Resources Investigations Report↗

USGS2001

Water-quality assessment of the eastern Iowa basins– Nitrogen, phosphorus, suspended sediment, and organic carbon in surface water, 1996–98

Twelve sites on streams and rivers in the Eastern Iowa Basins study unit were sampled monthly and during selected storm events from March 1996 through September 1998 to assess the occurrence, distribution, and transport of nitrogen, phosphorus, suspended sediment, and organic carbon as part of the U.S. Geological Survey’s National Water-Quality Assessment Program. One site was dropped from monthly sampling after 1996. Dissolved nitrogen and phosphorus were detected in every water sample collected. Nitrate accounted for 92 percent of the total dissolved nitrogen. About 22 percent of the samples had nitrate concentrations that exceeded the U.S. Environmental Protection Agency’s maximum contaminant level of 10 milligrams per liter as nitrogen for drinking-water regulations. The median concentration of total dissolved nitrogen for surface water in the study unit was 7.2 milligrams per liter. The median total phosphorus concentration for the study unit was 0.22 milligram per liter. About 75 percent of the total phosphorus concentrations exceeded the U.S. Environmental Protection Agency recommended total phosphorus concentration of 0.10 milligram per liter or less to minimize algal growth. Median suspended sediment and dissolved organic-carbon concentrations for the study unit were 82 and 3.5 milligrams per liter, respectively. Median concentrations of nitrogen, phosphorus, and suspended sediment varied annually and seasonally. Nitrogen, phosphorus, and suspended-sediment concentrations increased each year of the study due to increased precipitation and runoff. Median concentrations of dissolved organic carbon were constant from 1996 to 1998. Nitrogen concentrations were typically higher in the spring after fertilizer application and runoff. During winter, nitrogen concentrations typically increased when there was little in-stream processing by biota. Nitrogen and phosphorus concentrations decreased in late summer when there was less runoff and in-stream processing of nitrogen and phosphorus was high. Dissolved organic carbon was highest in February and March when decaying vegetation and manure were transported during snowmelt. Suspendedsediment concentrations were highest in early summer (May–June) during runoff and lowest in January when there was ice cover with very little overland flow contributing to rivers and streams. Based on historical and study-unit data, eastern Iowa streams and rivers are impacted by both nonpoint and point-source pollution. Indicator sites that have homogeneous land use, and geology had samples with significantly higher concentrations of total dissolved nitrogen (median, 8.2 milligrams per liter) than did samples from integrator sites (median, 6.2 milligrams per liter) that were more heterogeneous in land use and geology. Samples from integrator sites typically had significantly higher total phosphorus and suspended-sediment concentrations than did samples from indicator sites. Typically, there was very little difference in median dissolved organic-carbon concentrations in samples from indicator and integrator sites. Concentrations of nitrogen and phosphorus varied across the study unit due to land use and physiography. Basins that are located in areas with a higher percentage of row-crop agriculture typically had samples with higher nitrogen concentrations. Basins that drain the Southern Iowa Drift Plain and the Des Moines Lobe typically had samples with higher total phosphorus and suspended-sediment concentrations. Total nitrogen loads increased each year from 1996 through 1998 in conjunction with increased concentrations and runoff. Total phosphorus loads in the Skunk River Basin decreased in 1997 due to less runoff and decreased sediment transport, but increased in 1998 due to higher runoff and increased sediment transport. Total nitrogen and total phosphorus loads varied seasonally. The highest loads typically occurred in early spring and summer after fertilizer application and runoff. Loads were lowest in January and September when there was typically very little runoff to transport nitrogen and phosphorus in the soil to the rivers and streams. Total nitrogen loads contributed to the Mississippi River from the Eastern Iowa Basins during 1996, 1997, and 1998 were 97,600, 120,000, and 234,000 metric tons, respectively. Total phosphorus loads contributed to the Mississippi River from the Eastern Iowa Basins during 1996, 1997, and 1998 were 6,860, 4,550, and 8,830 metric tons, respectively. Suspendedsediment loads contributed to the Mississippi River from the Eastern Iowa Basins during 1996, 1997, and 1998 were 7,480,000, 4,450,000, and 8,690,000 metric tons, respectively. The highest total nitrogen and total phosphorus yields typically occurred in samples from indicator sites. Sampling sites located in drainage basins with higher row-crop percentage typically had higher nitrogen and phosphorus yields. Sites that were located in the Des Moines Lobe and the Southern Iowa Drift Plain typically had higher phosphorus yields, probably due to physiographic features (for example, erodible soils, steeper slopes). Synoptic samples collected during low and high base flow had nitrogen, phosphorus, and organic-carbon concentrations that varied spatially and seasonally. Comparisons of water-quality data from six basic-fixed sampling sites and 19 other synoptic sites suggest that the water-quality data from basic-fixed sampling sites were representative of the entire study unit during periods of low and high base flow when most streamflow originates from ground water.

Iowa, Minnesota↗

USGS2003

Delineation of water sources for public-supply wells in three fractured-bedrock aquifer systems in Massachusetts

Fractured-bedrock aquifer systems in West Newbury, Maynard, and Paxton, Massachusetts, were studied to advance methods of data collection and analysis for delineating contributing areas to public-supply wells completed in fractured rock and for determining the effects of pumping on streams and wetlands. Contributing areas, as defined for this study, include all areas through which ground water flows from recharge areas to wells. In West Newbury, exploratory public-supply wells at two locations were completed in phyllite of the Eliot Formation. Aquifer testing indicated that subhorizontal and steeply dipping fractures that parallel two sets of foliation form elongated transmissive zones in the bedrock aquifer near the two well locations and also form a vertical hydraulic connection to surficial materials consisting of till at one location and marine clay at the other location. Recharge to bedrock is largely through a thin veneer of till over bedrock, but leakage through thick drumlin tills also recharges bedrock. Simulated contributing areas for the three supply wells pumped at a combined rate of 251 gallons per minute encompass about 1.3 square miles and extend to ground-water divides within most of a subbasin of the Artichoke River. Pumping likely would reduce streamflow in the Artichoke River subbasin by approximately the pumping rate. Pumping is likely to affect wetland areas underlain by till near the wells because of the vertical hydraulic connection to surficial materials. In Maynard, three exploratory public-supply wells were completed in coarse-grained schist of the Nashoba Formation. Aquifer testing indicated that a dense network of fractures in bedrock forms a laterally extensive transmissive zone in bedrock that is well connected vertically to surficial materials consisting of sandy till, lacustrine silts, sand and gravel, and wetland deposits. The simulated contributing area for the three supply wells pumped at a combined rate of 780 gallons per minute encompasses about 1.8 square miles of the Fort Pond Brook drainage area. Pumping likely would reduce streamflow in Fort Pond Brook by about the same amount as the pumping rate, and wetland-water levels within a 2,000-foot radius from the wells are likely to be lowered below the land surface by pumping. In Paxton, three existing supply wells are completed in granofels and schist of the Paxton and Littleton Formations. Aquifer testing demonstrated that a shallow bedrock well completed to a depth of 150 feet is closely connected hydraulically to overlying till. Two deep wells, however, receive much of their water from fractures at depths below 500 feet. Ground-water flow in bedrock appears to be mostly through parting fractures along a foliation set that dips gently (10 degrees) eastward. These parting fractures at depth are poorly connected vertically to shallow bedrock

Water-Resources Investigations Report↗

USGS2003

Evaluation of Streamflow Requirements for Habitat Protection by Comparison to Streamflow Characteristics at Index Streamflow-Gaging Stations in Southern New England

Streamflow characteristics and methods for determining streamflow requirements for habitat protection were investigated at 23 active index streamflow-gaging stations in southern New England. Fish communities sampled near index streamflow-gaging stations in Massachusetts have a high percentage of fish that require flowing-water habitats for some or all of their life cycle. The relatively unaltered flow condition at these sites was assumed to be one factor that has contributed to this condition. Monthly flow durations and low flow statistics were determined for the index streamflow-gaging stations for a 25- year period from 1976 to 2000. Annual hydrographs were prepared for each index station from median streamflows at the 50-percent monthly flow duration, normalized by drainage area. A median monthly flow of 1 ft 3 /s/mi 2 was used to split hydrographs into a high-flow period (November–May), and a low-flow period (June–October). The hydrographs were used to classify index stations into groups with similar median monthly flow durations. Index stations were divided into four regional groups, roughly paralleling the coast, to characterize streamflows for November to May; and into two groups, on the basis of base-flow index and percentage of sand and gravel in the contributing area, for June to October. For the June to October period, for index stations with a high base-flow index and contributing areas greater than 20 percent sand and gravel, median streamflows at the 50-percent monthly flow duration, normalized by drainage area, were 0.57, 0.49, and 0.46 ft 3 /s/mi 2 for July, August, and September, respectively. For index stations with a low base-flow index and contributing areas less than 20 percent sand and gravel, median streamflows at the 50-percent monthly flow duration, normalized by drainage area, were 0.34, 0.28, and 0.27 ft 3 /s/mi 2 for July, August, and September, respectively. Streamflow variability between wet and dry years can be characterized by use of the interquartile range of median streamflows at selected monthly flow durations. For example, the median Q50 discharge for August had an interquartile range of 0.30 to 0.87 ft 3 /s/mi 2 for the high-flow group and 0.16 to 0.47 ft 3 /s/mi 2 for the low-flow group. Streamflow requirements for habitat protection were determined for 23 index stations by use of three methods based on hydrologic records, the Range of Variability Approach, the Tennant method, and the New England Aquatic-Base-Flow method. Normalized flow management targets determined by the Range of Variability Approach for July, August, and September ranged between 0.21 and 0.84 ft 3 /s/mi 2 for the low monthly flow duration group, and 0.37 and 1.27 ft 3 /s/mi 2 for the high monthly flow duration group. Median streamflow requirements for habitat protection during summer for the 23 index streamflow-gaging stations determined by the Tennant method, normalized by drainage area, were 0.81, 0.61, and 0.21 ft 3 /s/mi 2 for the Tennant 40-, 30-, and 10-percent of the mean annual flow methods, representing good, fair, and poor stream habitat conditions in summer, according to Tennant. New England Aquatic-Base-Flow streamflow requirements for habitat protection during summer were determined from median of monthly mean flows for August for index streamflow-gaging stations having drainage areas greater than 50 mi 2 . For five index streamflow-gaging stations in the low median monthly flow group, the average median monthly mean streamflow for August, normalized by drainage area, was 0.48 ft 3 /s/mi 2 . Streamflow requirements for habitat protection were determined for riffle habitats near 10 index stations by use of two methods based on hydraulic ratings, the Wetted-Perimeter and R2Cross methods. Hydraulic parameters required by these methods were simulated by calibrated HEC-RAS models. Wetted-Perimeter streamflow requirements for habitat protection, normalized by drainage area, ranged between 0.13 and 0.58 ft 3 /s/mi 2 , and had a median value of 0.37 ft 3 /s/mi 2 . Streamflow requirements determined by the R2Cross 3-of-3 criteria method ranged between 0.39 and 2.1 ft 3 /s/mi 2 , and had a median of 0.84 ft 3 /s/mi 2 . Streamflow requirements determined by the R2Cross 2-of-3 criteria method, normalized by drainage area, ranged between 0.16 and 0.85 ft 3 /s/mi 2 and had a median of 0.36 ft 3 /s/mi 2 , respectively. Streamflow requirements determined by the different methods were evaluated by comparison to streamflow statistics from the index streamflow-gaging stations.

Water-Resources Investigations Report↗

USGS2001

Simulation of flow in the upper North Coast Limestone Aquifer, Manati-Vega Baja area, Puerto Rico

A two-dimensional computer ground-water model was constructed of the Manati-Vega Baja area to improve the understanding of the unconfined upper aquifer within the North Coast Province of Puerto Rico. The modeled area covers approximately 79 square miles within the municipios of Manati and Vega Baja and small portions of Vega Alta and Barceloneta. Steady-state two-dimensional ground-water simulations were correlated to conditions prior to construction of the Laguna Tortuguero outlet channel in 1940 and calibrated to the observed potentiometric surface in March 1995. At the regional scale, the unconfined Upper North Coast Limestone aquifer is a diffuse ground-water flow system through the Aguada and Aymamon limestone units. The calibrated model input parameters for aquifer recharge varied from 2 inches per year in coastal areas to 18 inches per year in the upland areas south of Manati and Vega Baja. The calibrated transmissivity values ranged from less than 500 feet squared per day in the upland areas near the southern boundary to 70,000 feet squared per day in the areas west of Vega Baja. Increased ground-water withdrawals from 1.0 cubic foot per second for 1940 conditions to 26.3 cubic feet per second in 1995, has reduced the natural ground-water discharge to springs and wetland areas, and induced additional recharge from the rivers. The most important regional drainage feature is Laguna Tortuguero, which is the major ground-water discharge body for the upper aquifer, and has a drainage area of approximately 17 square miles. The discharge to the sea from Laguna Tortuguero through the outlet channel has been measured on a bi-monthly basis since 1974. The outflow represents a combination of ground- and surface-water discharge over the drainage area. Hydrologic conditions, prior to construction of the Laguna Tortuguero outlet channel in 1943, can be considered natural conditions with minimal ground-water pumpage (1.0 cubic foot per second), and heads in the lagoon were 2.4 feet higher. The model was calibrated to March 1995 conditions during a dry period of minimal aquifer recharge and relatively constant water levels in the upper aquifer. For the steady-state 1995 model simulation, however, ground-water pumpage had been increased to 26.3 cubic foot per second, due to increased demand for public water supply, the heads at 0.9 feet, and the outflow to the sea at Laguna Tortuguero had been lowered considerably. Simulated ground-water inflow for 1940 hydrologic conditions included 35.9 cubic feet per second from areal recharge, contributions from streamflow along the southern boundary of 1.6 cubic feet per second, and streamflow infiltration to the upper aquifer of 4.2 cubic feet per second. Simulated ground-water outflow for 1940 hydrologic conditions are discharge to springs of 17.4 cubic feet per second, total ground-water withdrawals of 1.0 cubic feet per second, and aquifer contribution to streamflow or wetland areas of 23.4 cubic feet per second. Simulated ground-water inflow for hydrologic conditions of March 1995 include d contributions from streamflow along the southern boundary of 1.6 cubic feet per second, areal recharge of 35.9 cubic feet per second, and streamflow infiltration to the upper aquifer of 11 cubic feet per second. Simulated ground-water outflow for hydrologic conditions of March 1995 are ground-water withdrawals of 26.3 cubic feet per second, discharge from springs of 7.3 cubic feet per second, and aquifer contribution to streamflow or wetland areas of 14 .9 cubic feet per second. The overall ground-water budget increased from 41.8 cubic feet per second for 1940 conditions to 48.6 cubic feet per second for the hydrologic conditions of March 1995. The increase in ground-water budget is a direct result of increased ground-water withdrawals, which induced greater streamflow infiltration. Simulated ground-water flux to Laguna Tortuguero for 1940 conditions was 11 cubic feet per second, which drop

Water-Resources Investigations Report↗

USGS1989

Estimation of the recharge area of a pumped, stratified-drift aquifer in Connecticut by simulation modeling

Groundwater quality management plans in Connecticut require information about the size and shape of recharge areas that contribute flow to pumping centers in extensive, stratified-drift aquifers. Flow models of a hypothetical aquifer , and a stratified-drift aquifer in Farmington are used to evaluate how contributing areas change in response to variations in recharge and hydraulic conductivity. A series of simulations of a hypothetical aquifer model were made during which average annual recharge rates of 0, 15, 25, and 35 inches were combined with aquifer hydraulic conductivity values of 25, 75, and 225 ft/day. Under steady-state conditions, and a withdrawal rate of 1.2 million gal/day, the size of the contributing recharge area ranges from 0.16 to 0.75 sq mi as recharge from precipitation and average aquifer hydraulic conductivity range from highest to lowest values. Three simulations of the Farmington aquifer model were made: they assumed steady-state conditions, a withdrawal rate of 2.8 million gal/day, and combinations of recharge and aquifer hydraulic conductivity that represented highest, average and lowest rates. The size of the contributing recharge area, under these conditions, ranges from 0.89 to 1.94 sq mi. (USGS)

Water-Resources Investigations Report↗

USGS1989

Suspended sediment and sediment-source areas in the Fountain Creek drainage basin upstream from Widefield, southeastern Colorado

Suspended-sediment samples were collected from synoptic-sampling sites to determine suspended-sediment concentrations, loads, yields, and sediment-source areas in the Fountain Creek drainage basin upstream from Widefield, Colorado. Suspended-sediment yields ranged from 0.004 to 278 tons/sq mi/day. Twenty-four sites were sampled that represent urban and rural land use. The median suspended-sediment yield from urban drainage basins was 7.7 tons/sq mi/day and the median suspended-sediment yield from rural drainage basins was 0.46 ton/sq mi/day. Sediment-transport equations were derived for total suspended-sediment discharge and suspended-sand discharge at seven periodic-sampling sites. Annual suspended-sediment loads and yields were computed for the 1985 water year. Urbanization in the downstream parts of the Monument Creek drainage basin, the main tributary to Fountain Creek, affected sediment loads. The downstream 14% of the Monument Creek drainage basin contributed about 61% of the annual suspended-sediment load transported at the mouth of Monument Creek. About 73% of the annual suspended-sediment load for Fountain Creek at Colorado Springs was contributed by Monument Creek. Abandoned mill tailings along Fountain Creek contributed little to total suspended sediment load. Contributions of streambank erosion to basin sediment yields were not quantified. However, the measured rate of streambank erosion at a site on Fountain Creek has increased during a 37-year period. (USGS)

Water-Resources Investigations Report↗

USGS1995

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

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

Water-Resources Investigations Report↗

USGS1998

Analytical methods, numerical modeling, and monitoring strategies for evaluating the effects of ground-water withdrawals on unconfined aquifers in the New Jersey Coastal Plain

Analytical and numerical solutions of ground-water withdrawals in the unconfined part of the Kirkwood-Cohansey aquifer system of the Coastal Plain of New Jersey were evaluated for their usefulness in predicting the area of influence of a pumped well and in determining hydraulic characteristics of an aquifer. Additionally, simulations of ground-water withdrawal using a finite-difference model provided information on the ways in which prudent well-location strategies can disperse the local effects of withdrawal over a larger part of an aquifer system. The design of a monitoring network that is sensitive to the ground-water hydraulics of streams and wetlands of the Coastal Plain of New Jersey also was considered for its utility in providing hydrologic data necessary to establish the baseline hydrologic conditions near wetlands and streams and in signaling when ground-water levels are being adversely affected by withdrawals elsewhere in the system. The application of methods based on the Theis analytical solution to ground-water flow in unconfined aquifers can lead to erroneous estimates of the size of the area of influence generated by ground-water withdrawals. Analysis oftime-drawdown data from an unconfined aquifer system are best evaluated by means of the Neuman solution, which accounts for the effects of gravity drainage; however, the pumped well must be far enough from streams so that ground water is not drawn from nearby streams. Time-drawdown data from a test well in Winslow County, N.J., were analyzed by means of the Neuman solution. Results indicate that the aquifer has a relatively high vertical to horizontal anisotropy of 1:198, and a specific yield of 0.028, an indication that the area of influence of a pumped well at the test site would be relatively large. Results from a finite-difference ground-water-flow model of the northeastern part of the Mullica River Basin near Chesilhurst, N.J., show that the area influenced by a long-term withdrawal is best estimated from a steady state ground-water-flow analysis that includes the effects of average areal recharge. Withdrawal simulations indicate an order-of-magnitude difference between the size of the area of influence generated from a 3-day (72 hour) withdrawal and the size of the area produced under steady-state conditions. An aquifer characterized by a low specific yield will cause the area of influence to extend farther away from the pumped well. The contributing area of flow to the pumped well includes areas on the water table that would, under natural conditions, be incorporated into the contributing areas of flow to streams. Ground water that is drawn to a pumped well is diverted from nearby streams; the withdrawal decreases the size of the contributing areas of flow to streams by an amount equal to the contributing area of flow to the well. Withdrawals made from a well close to a stream divert ground water that would, under natural conditions, flow to the stream. The diverted ground water causes the area of influence of the well to be smaller than it would if the well were far from the stream. Water-table declines caused by withdrawals near streams are, to some degree, mitigated by ground-water diversion from streams. However, the withdrawals can significantly reduce ground-water seepage to nearby streams, especially along stream reaches and wetlands close to the well. Alternatively, these effects can be dispersed over a large part of the aquifer if wells are located on surface-water divides. Measurements of seasonal water-level fluctuations in the Mullica River Basin indicate that the greatest fluctuations in water levels are found in upland areas, where the average fluctuation is 3.4 feet. Fluctuations in hydraulic head in the wetland areas averages 1.3 feet. The bimodal average of ranges in water levels show that upland areas are more sensitive to recharge than lowland areas. The pattern of yearly mean water levels fluctuates irregularly about a long-term mean value. Abnormally low or high yearly average values that are brought on by periods of drought or excess recharge are short lived; over time, hydrologic conditions shift back to average levels under natural conditions. Wetland areas in the New Jersey Coastal Plain are characterized by ground-water seepage into wide, shallow depressions. Periods of inundation are longest in the deepest part of the depression, whereas inundation of areas near the fringes of wetlands due to ground-water seepage is only seasonal. The seepage face in the fringe areas expand and contract in response to seasonal variation in water-table elevation and in response to precipitation. Values of the aquifer storage coefficient and transmissivity can, in some cases, be determined by use of hydraulic head or streamflow recession analysis as an alternative to aquifer testing. The recession curves developed from hydro graphs of Middle Branch and McDonalds Branch in the New Jersey Coastal Plain indicate that the aquifer near McDonalds Branch has about 2.6 times the storage capacity of the aquifer adjacent to Middle Branch; this finding is consistent with the relatively small ranges of water-level changes measured in McDonalds Branch compared to those measured in Middle Branch.

New Jersey↗

USGS1998

Analysis of the streamflow-gaging station network in Ohio for effectiveness in providing regional streamflow information

The streamflow-gaging station network in Ohio was evaluated for its effectiveness in providing regional streamflow information. The analysis involved application of the principles of generalized least squares regression between streamflow and climatic and basin characteristics. Regression equations were developed for three flow characteristics: (1) the instantaneous peak flow with a 100-year recurrence interval (P100), (2) the mean annual flow (Qa), and (3) the 7-day, 10-year low flow (7Q10). All active and discontinued gaging stations with 5 or more years of unregulated-streamflow data with respect to each flow characteristic were used to develop the regression equations. The gaging-station network was evaluated for the current (1996) condition of the network and estimated conditions of various network strategies if an additional 5 and 20 years of streamflow data were collected. Any active or discontinued gaging station with (1) less than 5 years of unregulated-streamflow record, (2) previously defined basin and climatic characteristics, and (3) the potential for collection of more unregulated-streamflow record were included in the network strategies involving the additional 5 and 20 years of data. The network analysis involved use of the regression equations, in combination with location, period of record, and cost of operation, to determine the contribution of the data for each gaging station to regional streamflow information. The contribution of each gaging station was based on a cost-weighted reduction of the mean square error (average sampling-error variance) associated with each regional estimating equation. All gaging stations included in the network analysis were then ranked according to their contribution to the regional information for each flow characteristic. The predictive ability of the regression equations developed from the gaging station network could be improved for all three flow characteristics with the collection of additional streamflow data. The addition of new gaging stations to the network would result in an even greater improvement of the accuracy of the regional regression equations. Typically, continued data collection at stations with unregulated streamflow for all flow conditions that had less than 11 years of record with drainage areas smaller than 200 square miles contributed the largest cost-weighted reduction to the average sampling-error variance of the regional estimating equations. The results of the network analyses can be used to prioritize the continued operation of active gaging stations or the reactivation of discontinued gaging stations if the objective is to maximize the regional information content in the streamflow-gaging station network.

Water-Resources Investigations Report↗

USGS1964

Natural sources of salinity in the Brazos River, Texas with particular reference to the Croton and salt Croton Creek basins

The average daily load of the Brazos River at Possum Kingdom Reservoir is about 2,800 tons of dissolved solids, of which 1,000 tons is chloride. More than 85 percent of the chloride load is contributed by the Salt Fork Brazos River, and more than 50 percent of the chloride load of the Brazos River originates from salt springs and seeps in Croton and Salt Crotdn Creeks, which are tributaries of Salt Fork Brazos River. The rest of the chloride is contributed from many small sources. The average daily chloride load of Croton Creek is 70 tons, much of which is carried during periods of flood runoff. The average daily chloride load of Salt Croton Creek is about 480 tons. Of this total, 330 tons is contributed by the base flow, which ranges from 0.5 to 2 cubic feet per second. The principal areas of salt springs and seeps in the Croton Creek basin are Hot Springs and Short Croton Salt Flats in northeastern Kent County. In the Salt Croton Creek basin, saline water is discharged in Dove Creek Salt Flat, Dove Creek near Dove Creek Salt Flat, and three small salt flats on Haystack Creek, all in southwestern King County and northwestern Stonewall County. Salt springs and seeps discharge from the rocks of the Whitehorse Group undifferentiated in the Croton Creek basin, and from the upper part of the Dog Creek Shale of the Pease River Group in the Salt Croton Creek basin. Both groups are of Permian age. The water that is discharged by springs and seeps in the Croton Creek basin is derived from the infiltration of precipitation and seepage from streams in the Duck Creek basin. The source of the water that discharges in the Salt Croton basin is not known. The salt load contributed to the Brazos River by the springs and seeps can be reduced, although the volume of salt water for disposal probably cannot be reduced or eliminated. Collecting and disposing of the base flow of Salt Croton Creek would reduce the salt load of the Brazos River by 30 percent; disposal of the total flow of Salt Croton Creek would reduce the salt load by 45 percent. The salt water may be disposed of by impounding it in reservoirs for evaporation or by injecting it underground through oil wells, oil tests, or wells drilled for saltwater disposal. Sediments in which the salt water possibly could be injected underlie the. Dove Creek Salt Flats at depths of less than 7,000 feet.

Texas↗

USGS1993

Delineation of recharge areas for selected wells in the St. Peter-Prairie du Chien-Jordan aquifer, Rochester, Minnesota

Accurate delineation of recharge areas for wells is an important requisite to protecting ground-water quality. Zones of transport and zones of contribution are two types of recharge areas that can be delineated. Analytical-calculation, numerical-modeling, and hydrogeologic-mapping methods were used to delineate recharge areas for two high-capacity wells (greater than about 200 gallons per minute discharge) completed in a karstic aquifer in the city of Rochester, in southeastern Minnesota. One well is less than 1,000 feet from a river in an area where the aquifer is unconfined, whereas the other well is more than 2,000 feet from a stream in an area where a bedrock confining unit is present. Ground-water travel times from points along the top of the aquifer to a pumped well are identified by use of a constructed map showing lines of equal advective travel time. A zone of transport, therefore, is defined by the area bounded by lines of equal travel time. Zones of transport are delineated by analytical models (calculations) and by numerical models that account for hydrologic factors. Analytical models that were used include fixed-radius (Theis drawdown, Theis time-of-travel, and volumetric equation) and variable shape. Numerical modeling was done with the U.S. Geological Survey three-dimensional ground-water-flow model MODFLOW and particle-tracking code MODPATH. The zone-of-transport areas for each of the two wells calculated by the various analytical models were very similar. The Theis-drawdown method yielded results that compared least favorably with results from the other analytical methods. The zone-of-transport areas computed by use of the numerical model were generally larger than areas computed by use of analytical models. Hydrogeologic mapping and numerical modeling were used to delineate zones of contribution to wells, defined as all parts of a ground-water-flow system that could supply water to a well. The zones of contribution delineated by use of numerical modeling have similar orientation (parallel to regional flow directions) but significantly different areas than the zones of contribution delineated by use of hydrogeologic mapping. Differences in computed areas of recharge are attributed to the capability of the numerical model to more accurately represent (1) the three-dimensional flow system, (2) hydrologic boundaries such as streams, (3) variable recharge, and (4) the influence of nearby pumped wells, compared to the analytical models.

Minnesota↗