Reconnaissance of hydrology and water quality of Lake Susupe, Saipan, Commonwealth of the Northern Mariana Islands, 1990
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Water-Resources Investigations Report↗
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Sediment delivery by ungaged tributaries of the Colorado River in Grand Canyon, Arizona
Sediment input to the Colorado River in Grand Canyon, Arizona, is a valuable resource required to sustain both terrestrial and aquatic ecosystems. A total of 768 ungaged tributaries deliver sediment to the river between Glen Canyon Dan and the Grand Wash Cliffs (river miles - 15 to 276). The 32 tributaries between the dam and Lee's Ferry produce only streamflow floods, whereas 736 tributaries in Grand Canyon produce streamflow floods and debris flows. We used three techniques to estimate annual streamflow sediment yield from ungaged tributaries to the Colorado River. For the Glen Canyon and Marble Canyon reaches (river miles -15 to 61.5), respectively, these techniques indicate that 0.065 . 10 6 and 0.610 . 10 6 Mg/yr (0.68 . 10 6 Mg/yr of total sediment) enters the river. This amount is 20 percent of the sediment yield of the Paria River, the only gaged tributary in this reach and a major sediment contributor to the Colorado River. The amout of sand delivered ranges from 0.10 . 10 6 to 0.51 . 10 6 Mg/yr, depending on the sand content of streamflow sediment. Sand delivered in Glen Canyon is notably coarser (D 50 = 0.24 mm) than sand in other reaches (D 50 = 0.15 mm). A relation is given for possible variation of this sediment delivery with climate.
Arizona↗
Distribution of nitrate in ground water in the Republican River Basin, southwest Nebraska, 1996-98
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Water-Resources Investigations Report↗
Distribution, movement, and fate of nitrate in the surficial aquifer beneath citrus groves, Indian River, Martin, and St. Lucie Counties, Florida
The surficial aquifer system beneath citrus groves in Indian River, Martin, and St. Lucie Counties, Florida, was studied to determine the effects of citrus agriculture on ground-water quality. The surficial aquifer is the primary drinking-water source for Martin and St. Lucie Counties and furnishes about 33 percent of the drinking-water for Indian River County. Water-quality samples and water-level data were collected from December 1996 through October 1998. Nitrate concentrations in ground water exceeded 10 milligrams per liter (mg/L), the U.S. Environmental Protection Agency's maximum contaminant level for nitrate reported as nitrogen, in 5 percent of the samples from citrus groves. These exceedances occurred in samples from wells with depths of 10 feet or less at citrus groves, and mostly in samples collected during or immediately following fertilizer applications. Samples from wells with depths of 20-25 feet contained little or no nitrate. The decreased nitrate concentrations in ground water with depth was not consistent with chloride and dissolved-solids concentrations, two other common indicators of agricultural activity. Chloride and dissolved-solids concentrations remained elevated in ground-water samples from all depths at citrus groves; median chloride and dissolved-solids concentrations in samples from citrus sites were 125 and 779 mg/L, respectively. In comparison, samples from the reference site had maximum chloride and dissolved-solids concentrations of 61 and 366 mg/L, respectively. Based on the age of ground water at 20-25 foot depths (3-50 years, measured with tritium and helium-3 concentration ratios), nitrate concentrations also should have remained elevated with depth because fertilizers have been used for at least 20-30 years at these citrus groves. Nitrate concentrations decreased with depth as a result of denitrification. This could have occurred because favorable conditions for denitrification existed in the aquifer, including high concentrations of dissolved organic carbon and iron (median concentrations of 25.5 and 1.75 mg/L, respectively at citrus sites) and low concentrations of dissolved oxygen (median concentration of 0.9 mg/L at citrus sites), which indicates that reducing conditions were present. Evidence that denitrification occurred included the enrichment of ground water with depth in the heavier isotope of nitrogen, nitrogen-15 ( 15 N). Ground water from wells screened 10-15 feet below land surface had a median d 15 N value of 24.6 per mil, whereas ground water from wells screened 5-10 feet below land surface had a median d 15 N value of 9.4 per mil. Fertilizer samples had a median d 15 N value of 3.0 per mil. Increased d 15 N values coincident with decreased nitrate concentrations with depth indicates that fractionation occurred during denitrification reactions. Finally, excess nitrogen gas, a byproduct of denitrification reactions, was detected at concentrations ranging from 0-8 mg/L in samples from wells screened 10-25 feet below land surface.
Florida↗
Assessment of freshwater mussels in the Allegheny River at Foxburg, Pennsylvania, 1998
The upper reaches of the Allegheny River are a high-quality resource that supports populations of a number of endangered species. Two endangered species of freshwater mussel, the northern riffleshell, Epioblasma torulosa rangiana , and clubshell, Pleurobema clava , are present in this river reach. Prior to a bridge-replacement project at the Allegheny River at Foxburg, Pa. (river mile 86.2), a mussel survey was conducted to determine if either of the protected endangered species are present and to assess the quality of the mussel bed at this site. Shore and near-shore searches followed by SCUBA diving transects determined that a mussel bed is present at this location. The freshwater-mussel community consists of at least 14 species and includes both endangered species. Substrate type, stream velocity, and channel morphology combined with results from the transect searches documented that the mussel bed is largely limited to the east side of the river. A two-stage sampling design was employed to estimate the overall mussel abundance within the bed. Twelve 4-m 2 (square meter) cells were sampled with four 0.25-m 2 quadrants per cell. The mean population density within the mussel bed is 8.4 mussel per square meter. The overall mussel population in the survey area is 225,567 individuals (95-percent confidence interval, 135,973 to 374,195). River-bed scour and acid mine drainage appear to limit mussel distribution in the center and left section of the channel. Overall, a healthy and diverse mussel bed exists at this site.
Water-Resources Investigations Report↗
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↗
Natural attenuation of chlorinated volatile organic compounds in ground water at Area 6, Naval Air Station Whidbey Island, Washington
Natural attenuation is a viable alternative to pump and treat for meeting remediation objectives in the vicinity of the southern contaminant plume. The combination of historically low contaminant concentrations in ground water, a landfill cap that limits source area contributions, favorable conditions for degradation of VC, and a relatively long downgradient distance to potential receptors are all favorable for natural attenuation as a remediation alternative. Natural attenuation could effectively meet all but one remediation goal that extraction wells PW- 2, PW-4, PW-6, PW-7, PW-8 and PW-9 are currently being employed to meet. The goal of preventing migration of all VC across the site boundary could not be met by natural attenuation. Some VC would migrate south of the Navy boundary, but the potential for subsequent VC mineralization downgradient of the base and the existing institutional controls would result in minimal additional risk from using natural attenuation. In the western contaminant plume natural attenuation is not currently a viable alternative to pump and treat for meeting remediation objectives. There is a possibility that rates for reductive dechlorination of TCE and TCA could increase substantially if the plume was allowed to migrate beneath the Oak Harbor landfill, but there are not enough data to be certain of such an increase. TCA and TCE concentrations at the leading edge of the western plume need to be reduced to at least 25 and 40 µg/L, respectively, to be protective of potential downgradient receptors. Source area TCA and TCE concentrations have decreased substantially over the past ten years, and the extraction wells PW-3 and PW-5 in particular are removing a significant mass of contaminants from ground water, so natural attenuation may be a viable alternative for the western plume in the future. There would be some possible side benefits of using natural attenuation as an alternative to pump and treat in the southern contaminant plume. The first would be that the resulting decrease in the amount of treated water that would need to be recharged in the swale north of the landfill would result in less off-base migration of contamination across the western site boundary. The second benefit would be a substantial reduction in the amount of dissolved iron and manganese being extracted from the shallow aquifer and run through the treatment system. Removing that source of operation and maintenance problems would result in more effective containment and removal of contamination in the western contaminant plume. The most critical data gap identified in this evaluation is the paucity of contaminant chemistry information downgradient of the Navy boundary in the vicinity of the southern contaminant plume. Without such data, the behavior of the plume and the protectiveness of natural attenuation to downgradient receptors cannot be verified, and field attenuation rates for VC cannot be determined directly. The existing long-term monitoring plan would need to be reviewed and revised if natural attenuation is selected as a remedy for the contamination in the southern plume. In particular, additional performance monitoring wells may be required downgradient of the property.
Washington↗
Nutrients and organic compounds in Deer Creek and south branch Plum Creek in southwestern Pennsylvania, April 1996 through September 1998
This report presents results of an analysis of nutrient and pesticide data from two surface-water sites and volatile organic compound (VOC) data from one of the sites that are within the Allegheny and Monongahela River Basins study unit of the National Water-Quality Assessment Program of the U.S. Geological Survey. The Deer Creek site was located in a 27.0 square-mile basin within the Allegheny River Basin in Allegheny County. The primary land uses consist of small urban areas, large areas of residential housing, and some agricultural land in the upper part of the basin. The South Branch Plum Creek site was located in a 33.3 square-mile basin within the Allegheny River Basin in Indiana County. The primary land uses throughout this basin are mostly agriculture and forestland. Water samples for analysis of nutrients were collected monthly and during high-flow events from April 1996 through September 1998. Concentrations of dissolved nitrite, dissolved ammonia plus organic nitrogen, and dissolved phosphorus were less than the method detection limits in more than one-half of the samples collected. The median concentration of dissolved nitrite plus nitrate in South Branch Plum Creek was 0.937 mg/L and 0.597 mg/L in Deer Creek. The median concentration of dissolved orthophosphate was 0.01 mg/L in both streams. High loads of nitrate were measured in both streams from March to June. Concentrations of dissolved ammonia nitrogen, dissolved nitrate, and total phosphorus were lower during the summer months. Measured concentrations of nitrate nitrogen in both streams were well below the U.S. Environmental Protection Agency (USEPA) maximum contaminant level (MCL) of 10 mg/L. Water samples for analysis of pesticides were collected throughout 1997 in both streams and during a storm event on August 25-26, 1998, in Deer Creek. Samples were collected monthly at both sites and more frequently during the spring and early summer months to coincide with application of pesticides. Seventy-eight pesticides and 7 pesticide metabolites were analyzed in 31 samples collected in Deer Creek and in 18 samples collected in South Branch Plum Creek. Of the 85 pesticides and pesticide metabolites analyzed, 25 of the pesticides were detected at least once in Deer Creek, and 20 of the pesticides were detected at least once in South Branch Plum Creek. Atrazine was the most commonly detected pesticide in both streams. There was a distinct seasonal pattern of atrazine, simazine, and metolachlor concentrations measured at both sites. Prometon was detected in 3 of the 18 samples collected in South Branch Plum Creek in 1997 and in 28 of the 31 samples collected in Deer Creek in both 1997 and 1998. Prometon generally is applied in conjunction with asphalt paving projects and is commonly used in residential areas. The highest measured concentrations of prometon detected in Deer Creek were in the five storm samples collected on August 25-26, 1998. At the Deer Creek site, 9 of the 25 pesticides detected throughout the study were detected only in the sample collected on June 13, 1997. Those nine pesticides included acifluorfen, bentazon, bromoxynil, dicamba, dichlorprop, fenuron, linuron, MCPA, and neburon. Nine other pesticides also were detected in that sample. All concentrations of pesticides were well below established drinking-water guidelines. The maximum measured concentration of diazinon in Deer Creek (0.097 µg/L) and South Branch Plum Creek (0.974 µg/L) exceeded the aquatic life guideline of 0.009 µg/L established by the National Academy of Sciences/National Academy of Engineers. The maximum measured concentration of azinphos-methyl in South Branch Plum Creek (an estimated value of 0.033 µg/L) exceeded the chronic aquatic-life guideline of 0.01 µg/L established by the USEPA. Twenty-five samples were collected from Deer Creek and analyzed for volatile organic compounds (VOCs). Of 87 VOCs analyzed for, 22 were detected at least once, and 12 were gasoline-related compounds. Acetone, benzene, carbon disulfide, meta/paraxylene, methyl chloride, MTBE, p-isopropyl toluene, toluene, and 1,2,4-trimethylbenzene were each detected in five or more samples. VOCs generally were detected during the colder winter months and not frequently during the summer months. The maximum measured concentrations of benzene, ethylbenzene, o-dichlorobenzene, styrene, and toluene were two or more orders of magnitude lower than the MCLs established by the USEPA.
Pennsylvania↗
Evaluation of a Method of Estimating Low-Flow Frequencies from Base-Flow Measurements at Indiana Streams
A mathematical technique of estimating low-flow frequencies from base-flow measurements was evaluated by using data for streams in Indiana. Low-flow frequencies at low-flow partial-record stations were estimated by relating base-flow measurements to concurrent daily flows at nearby streamflow-gaging stations (index stations) for which low-flow- frequency curves had been developed. A network of long-term streamflow-gaging stations in Indiana provided a sample of sites with observed low-flow frequencies.Observed values of 7-day, 10-year low flow and 7-day, 2-year low flow were compared to predicted values to evaluate the accuracy of the method. Five test cases were used to evaluate the method under a variety of conditions in which the location of the index station and its drainage area varied relative to the partial-record station. A total of 141 pairs of streamflow-gaging stations were used in the five test cases. Four of the test cases used one index station, the fifth test case used two index stations. The number of base-flow measurements was varied for each test case to see if the accuracy of the method was affected by the number of measurements used. The most accurate and least variable results were produced when two index stations on the same stream or tributaries of the partial-record station were used. All but one value of the predicted 7-day, 10-year low flow were within 15 percent of the values observed for the long-term continuous record, and all of the predicted values of the 7-day, 2-year low-flow were within 15 percent of the observed values. This apparent accuracy, to some extent, may be a result of the small sample set of 15. Of the four test cases that used one index station, the most accurate and least variable results were produced in the test case where the index station and partial-record station were on the same stream or on streams tributary to each other and where the index station had a larger drainage area than the partial-record station. In that test case, the method tended to over predict, based on the median relative error. In 23 of 28 test pairs, the predicted 7-day, 10-year low flow was within 15 percent of the observed value; in 26 of 28 test pairs, the predicted 7-day, 2-year low flow was within 15 percent of the observed value. When the index station and partial- record station were on the same stream or streams tributary to each other and the index station had a smaller drainage area than the partial-record station, the method tended to under predict the low-flow frequencies. Nineteen of 28 predicted values of the 7-day, 10-year low-flow were within 15 percent of the observed values. Twenty-five of 28 predicted values of the 7-day, 2-year low flow were within 15 percent of the observed values. When the index station and the partial- record station were on different streams, the method tended to under predict regardless of whether the index station had a larger or smaller drainage area than that of the partial-record station. Also, the variability of the relative error of estimate was greatest for the test cases that used index stations and partial-record stations from different streams. This variability, in part, may be caused by using more streamflow-gaging stations with small low-flow frequencies in these test cases. A small difference in the predicted and observed values can equate to a large relative error when dealing with stations that have small low-flow frequencies. In the test cases that used one index station, the method tended to predict smaller low-flow frequencies as the number of base- flow measurements was reduced from 20 to 5. Overall, the average relative error of estimate and the variability of the predicted values increased as the number of base-flow measurements was reduced.
Indiana↗
Evaluation of the use of reach transmissivity to quantify leakage beneath Levee 31N, Miami-Dade County, Florida
A coupled ground- and surface-water model (MODBRANCH) was developed to estimate ground-water flow beneath Levee 31N in Miami-Dade County, Florida, and to simulate hydrologic conditions in the surrounding area. The study included compilation of data from monitoring stations, measurement of vertical seepage rates in wetlands, and analysis of the hydrogeologic properties of the ground-water aquifer within the study area. In addition, the MODBRANCH code was modified to calculate the exchange between surface-water channels and ground water using a relation based on the concept of reach transmissivity. The modified reach-transmissivity version of the MODBRANCH code was successfully tested on three simple problems with known analytical solutions. It was also tested and determined to function adequately on one field problem that had previously been solved using the unmodified version of the software. The modified version of MODBRANCH was judged to have performed satisfactorily, and it required about 60 percent as many iterations to reach a solution. Additionally, its input parameters are more physically-based and less dependent on model-grid spacing. A model of the Levee 31N area was developed and used with the original and modified versions of MODBRANCH, which produced similar output. The mean annual modeled ground-water heads differed by only 0.02 foot, and the mean annual canal discharge differed by less than 1.0 cubic foot per second. Seepage meters were used to quantify vertical seepage rates in the Everglades wetlands area west of Levee 31N. A comparison between results from the seepage meters and from the computer model indicated substantial differences that seemed to be a result of local variations in the hydraulic properties in the topmost part of the Biscayne aquifer. The transmissivity of the Biscayne aquifer was estimated to be 1,400,000 square feet per day in the study area. The computer model was employed to simulate seepage of ground water beneath Levee 31N. Modeled seepage rates were usually between 100 and 400 cubic feet per day per foot of levee, but extreme values ranged from about -200 to 500 cubic feet per day (positive values indicate eastward seepage beneath the levee). The modeled seepage results were used to develop an algorithm to estimate seepage based on head differential at selected monitoring stations. The algorithm was determined to adequately predict ground-water seepage.
Florida↗
Ground-water resources of Tinian, Commonwealth of the Northern Mariana Islands
Tinian, which lies in the western Pacific Ocean at latitude 15°N and longitude 145°W (fig. 1), is the second largest island (39.2 mi 2 ) in the Commonwealth of the Northern Mariana Islands (CNMI). Fresh ground water is obtained from shallow wells that tap the surface of a freshwater lends found in an aquifer composed mainly of coralline limestone. The main water-supply well withdraws water with a chloride concentration ranging from 160 to 220 mg/L. Current (1999) pumping rates adequately supply the island residents but future demand are expected to be higher.. To better understand the ground-water resources of the island and to learn more about the hydrology of oceanic islands, the U.S. Geological Survey (USGS) entered into a cooperative study with the Municipality of Tinian. The objective of the study, conducted between 1990 and 1997, was to assess the ground-water resources of the is;land. This report presents some of the results of the study including a description of the island's geology and geography, the current land use, the water-production system, the thickness and arcal extent of the freshwater lens, the water-table configuration and directions of ground-water flow. The report also discusses the relation of the changes in water-table elevation to daily and seasonal changes in ocean level.
Tinian Island↗
Flood hydrology for Dry Creek, Lake County, northwestern Montana
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Water-Resources Investigations Report↗
Use of borehole and surface geophysics to investigate ground-water quality near a road-deicing salt-storage facility, Valparaiso, Indiana
Borehole and surface geophysics were used to investigate ground-water quality affected by a road-deicing salt-storage facility located near a public water-supply well field. From 1994 through 1998, borehole geophysical logs were made in an existing network of monitoring wells completed near the bottom of a thick sand aquifer. Logs of natural gamma activity indicated a uniform and negligible contribution of clay to the electromagnetic conductivity of the aquifer so that the logs of electromagnetic conductivity primarily measured the amount of dissolved solids in the ground water near the wells. Electromagnetic-conductivity data indicated the presence of a saltwater plume near the bottom of the aquifer. Increases in electromagnetic conductivity, observed from sequential logging of wells, indicated the saltwater plume had moved north about 60 to 100 feet per year between 1994 and 1998. These rates were consistent with estimates of horizontal ground-water flow based on velocity calculations made with hydrologic data from the study area. Ratios of chloride to bromide concentrations in water samples were used to distinguish sources of chloride in the ground water?whether from road-deicing salt, domestic wastewater, or natural occurrences. Water samples identified with the chloride/bromide ratios as being affected by road-deicing salt had concentrations of dissolved solids, chloride, and sodium many times the background levels for the study area. The largest concentrations were in water from wells near the salt-storage facility?12,400 to 12,800 milligrams per liter (mg/L) dissolved solids, 6,730 to 7,230 mg/L chloride, and 3,690 to 4,400 mg/L sodium. A conceptual, multi-layer model was developed to describe the vertical extent of the saltwater plume in the vicinity of the monitoring wells. A relation was derived between average borehole electromagnetic conductivity in the screened interval of the wells in the saltwater plume and concentrations of dissolved solids in water samples from those wells. This relation was used in the model to show borehole electromagnetic conductivity in transects of wells as a zone of saline water overlain by zones of brackish water and freshwater. The thickness and altitude of the zones of saline and brackish water decreased with increased distance from the salt-storage facility. Two surface surveys of terrain electromagnetic conductivity were used to map the horizontal extent of the saltwater plume in areas without monitoring wells. Background values of terrain conductivity were measured in an area where water-quality and borehole geophysical data did not indicate saline or brackish water. Based on a guideline from previous case studies, the boundaries of the saltwater plume were mapped where terrain conductivity was 1.5 times background. The extent of the saltwater plume, based on terrain conductivity, generally was consistent with the available water-quality and borehole electromagnetic-conductivity data and with directions of ground-water flow determined from water-level altitudes.
Indiana↗
Effects of hypothetical management scenarios on simulated water temperatures in the Tualatin River, Oregon
In 1994, the U.S. Geological Survey (USGS) and the Unified Sewerage Agency of Washington County, Oregon (USA) began a cooperative study to better understand water-temperature variations in the Tualatin River and to assess mitigative water-management solutions. Continuous water-temperature data were collected at locations along the main stem of the river and along the major tributaries during the lowflow periods of 1994 and 1995. The 1994 data were used to develop and calibrate flow and water-temperature models characterizing conditions in the main stem. The models were used to simulate 10 hypotheti3 cal water-management scenarios, which would enable water managers to understand the effects of various human activities on water temperatures. Modeling results from the study are presented in Risley (1997); the data collected are presented in Risley and Doyle (1997). This report presents the water-temperature model simulation results of 16 additional hypothetical water-management scenarios using the 1994 and 1995 data. The additional modeling was funded by the USGS and the USA under a cooperative agreement. For a comprehensive description of the water-temperature models and their underlying assumptions, refer to Risley (1997).
Oregon↗
Spatial and seasonal variability of nutrients, pesticides, bacteria, and suspended sediment in the Santee River basin and coastal drainages, North and South Carolina, 1995-97
No abstract available.
North Carolina, South Carolina↗
Ground-water flow in the shallow aquifer system at the Naval Weapons Station Yorktown, Virginia
The Environmental Directorate of the Naval Weapons Station Yorktown, Virginia, is concerned about possible contamination of ground water at the Station. Ground water at the Station flows through a shallow system of layered aquifers and leaky confining units. The units of the shallow aquifer system are the Columbia aquifer, the Cornwallis Cave confining unit, the Cornwallis Cave aquifer, the Yorktown confining unit, and the Yorktown-Eastover aquifer. The Eastover-Calvert confining unit separates the shallow aquifer system from deeper confined aquifers beneath the Station. A three-dimensional, finite-difference, ground-water flow model was used to simulate steady-state ground-water flow of the shallow aquifer system in and around the Station. The model simulated ground-water flow from the peninsular drainage divide that runs across the Lackey Plain near the southern end of the Station north to King Creek and the York River and south to Skiffes Creek and the James River. The model was calibrated by minimizing the root mean square error between 4 7 measured and corresponding simulated water levels. The calibrated model was used to determine the ground-water budget and general directions of ground-water flow. A particle-tracking routine was used with the calibrated model to estimate groundwater flow paths, flow rates, and traveltimes from selected sites at the Station. Simulated ground-water flow velocities of the Station-area model were small beneath the interstream areas of the Lackey Plain and Croaker Flat, but increased outward toward the streams and rivers where the hydraulic gradients are larger. If contaminants from the land surface entered the water table at or near the interstream areas of the Station, where hydraulic gradients are smaller, they would migrate more slowly than if they entered closer to the streams or the shores of the rivers where gradients commonly are larger. The ground-water flow simulations indicate that some ground water leaks downward from the water table to the Yorktown confining unit and, where the confining unit is absent, to the Yorktown-Eastover aquifer. The velocities of advective-driven contaminants would decrease considerably when entering the Yorktown confining unit because the hydraulic conductivity of the confining unit is small compared to that of the aquifers. Any contaminants that moved with advective ground-water flow near the groundwater divide of the Lackey Plain would move relatively slowly because the hydraulic gradients are small there. The direction in which the contaminants would move, however, would be determined by precisely where the contaminants entered the water table. The model was not designed to accurately simulate ground-water flow paths through local karst features. Beneath Croaker Flat, ground water flows downward through the Columbia aquifer and the Yorktown confining unit into the Yorktown-Eastover aquifer. Analyses of the movement of simulated particles from two adjacent sites at Croaker Flat indicated that ground-water flow paths were similar at first but diverged and discharged to different tributaries of Indian Field Creek or to the York River. These simulations indicate that complex and possibly divergent flow paths and traveltimes are possible at the Station. Although the Station-area model is not detailed enough to simulate ground-water flow at the scales commonly used to track and remediate contaminants at specific sites, general concepts about possible contaminant migration at the Station can be inferred from the simulations.
Virginia↗
Estimation of peak streamflows for unregulated rural streams in Kansas
Peak streamflows were estimated at selected recurrence intervals (frequencies) ranging from 2 to 200 years using log-Pearson Type III distributions for 253 streamflow-gaging stations in Kansas. The annual peak-streamflow data, through the 1997 water year, were from streamflow-gaging stations with unregulated flow in mostly rural basins. A weighted least-squares regression model was used to generalize the coefficients of station skewness. The resulting generalized skewness equation provides more reliable estimates than the previously developed equation for Kansas. A generalized least-squares regression model then was used to develop equations for estimating peak streamflows for sites without stream gages for selected frequencies from selected physical and climatic basin characteristics for sites without stream gages. The equations can be used to estimate peak streamflows for selected frequencies using contributing-drainage area, mean annual precipitation, soil permeability, and slope of the main channel for ungaged sites in Kansas with a contributing-drainage area greater than 0.17 and less than 9,100 square miles. The errors of prediction for the generalized least-squares-generated equations range from 31 to 62 percent.
Water-Resources Investigations Report↗