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At least 1,549 records · Page 86Linked to original sources
USGS1999

Estimates of ground-water discharge as determined from measurements of evapotranspiration, Ash Meadows area, Nye County, Nevada

Ash Meadows is one of the major discharge areas within the regional Death Valley ground-water flow system of southern Nevada and adjacent California. Ground water discharging at Ash Meadows is replenished from inflow derived from an extensive recharge area that includes the eastern part of the Nevada Test Site (NTS). Currently, contaminants introduced into the subsurface by past nuclear testing at NTS are the subject of study by the U.S. Department of Energy's Environmental Restoration Program. The transport of any contaminant in contact with ground water is controlled in part by the rate and direction of ground-water flow, which itself depends on the location and quantity of ground water discharging from the flow system. To best evaluate any potential risk associated with these test-generated contaminants, studies were undertaken to accurately quantify discharge from areas downgradient from the NTS. This report presents results of a study to refine the estimate of ground-water discharge at Ash Meadows. The study estimates ground-water discharge from the Ash Meadows area through a rigorous quantification of evapotranspiration (ET). To accomplish this objective, the study identifies areas of ongoing ground-water ET, delineates unique areas of ET defined on the basis of similarities in vegetation and soil-moisture conditions, and computes ET rates for each of the delineated areas. A classification technique using spectral-reflectance characteristics determined from satellite images recorded in 1992 identified seven unique units representing areas of ground-water ET. The total area classified encompasses about 10,350 acres dominated primarily by lush desert vegetation. Each unique area, referred to as an ET unit, generally consists of one or more assemblages of local phreatophytes. The ET units identified range from sparse grasslands to open water. Annual ET rates are computed by energy-budget methods from micrometeorological measurements made at 10 sites within six of the seven identified ET units. Micrometeorological data were collected for a minimum of 1 year at each site during 1994 through 1997. Evapotranspiration ranged from 0.6 foot per year in a sparse, dry saltgrass environment to 8.6 feet per year over open water. Ancillary data, including water levels, were collected during this same period to gain additional insight into the evapotranspiration process. Water levels measured in shallow wells showed annual declines of more than 10 feet and daily declines as high as 0.3 foot attributed to water losses associated with evapotranspiration. Mean annual ET from the Ash Meadows area is estimated at 21,000 acre-feet. An estimate of ground-water discharge, based on this ET estimate, is presented as a range to account for uncertainties in the contribution of local precipitation. The estimates given for mean annual ground-water discharge range from 18,000 to 21,000 acre-feet. The low estimate assumes a large contribution from local precipitation in computed ET rates; whereas, the high estimate assumes no contribution from local precipitation. The range presented is only slightly higher than previous estimates of ground-water discharge from the Ash Meadows area based primarily on springflow measurements.

Nevada↗
USGS1978

Computer model of two-dimensional solute transport and dispersion in ground water

This report presents a model that simulates solute transport in flowing ground water. The model is both general and flexible in that it can be applied to a wide range of problem types. It is applicable to one- or two-dimensional problems involving steady-state or transient flow. The model computes changes in concentration over time caused by the processes of convective transport, hydrodynamic dispersion, and mixing (or dilution) from fluid sources. The model assumes that the solute is non-reactive and that gradients of fluid density, viscosity, and temperature do not affect the velocity distribution. However, the aquifer may be heterogeneous and (or) anisotropic. The model couples the ground-water flow equation with the solute-transport equation. The digital computer program uses an alternating-direction implicit procedure to solve a finite-difference approximation to the ground-water flow equation, and it uses the method of characteristics to solve the solute-transport equation. The latter uses a particle- tracking procedure to represent convective transport and a two-step explicit procedure to solve a finite-difference equation that describes the effects of hydrodynamic dispersion, fluid sources and sinks, and divergence of velocity. This explicit procedure has several stability criteria, but the consequent time-step limitations are automatically determined by the program. The report includes a listing of the computer program, which is written in FORTRAN IV and contains about 2,000 lines. The model is based on a rectangular, block-centered, finite difference grid. It allows the specification of any number of injection or withdrawal wells and of spatially varying diffuse recharge or discharge, saturated thickness, transmissivity, boundary conditions, and initial heads and concentrations. The program also permits the designation of up to five nodes as observation points, for which a summary table of head and concentration versus time is printed at the end of the calculations. The data input formats for the model require three data cards and from seven to nine data sets to describe the aquifer properties, boundaries, and stresses. The accuracy of the model was evaluated for two idealized problems for which analytical solutions could be obtained. In the case of one-dimensional flow the agreement was nearly exact, but in the case of plane radial flow a small amount of numerical dispersion occurred. An analysis of several test problems indicates that the error in the mass balance will be generally less than 10 percent. The test problems demonstrated that the accuracy and precision of the numerical solution is sensitive to the initial number of particles placed in each cell and to the size of the time increment, as determined by the stability criteria. Mass balance errors are commonly the greatest during the first several time increments, but tend to decrease and stabilize with time.

Techniques of Water-Resources Investigations↗
USGS1999

Nitrate, volatile organic compounds, and pesticides in ground water — A summary of selected studies from New Jersey and Long Island, New York

This report describes the ground-water systems in the unconsolidated sand and gravel aquifers of the Coastal Plain of New Jersey and Long Island and in the fractured bedrock and valley-fill aquifers of northern New Jersey; summarizes current knowledge about the occurrence and distribution of nitrate, volatile organic compounds (VOCs), and pesticides in these systems; and explains why some ground-water systems are more vulnerable to comtamination than others. Although the vulnerability of ground water to contamination from the land surface is influenced by many factors, the degree of aquifer confinement, the depth of the well, and the surrounding land use are key factors. Unconfined aquifers generally are much more vulnerable to contamination than confined aquifers. For a well in a confined aquifer, the farther the well is from the unconfined area, the less vulnerable it is to contamination. Generally, the deeper the well, the less vulnerable it is to contamination. Finally, because human activities greatly affect the quality of water that recharges an aquifer, the amount and type of land use in the area that contributes water to the well is a key factor in determining vulnerability. Nitrate contamination of ground water typically occurs in agricultural and residential areas, especially where the aquifer is very permeable and unconfined and nitrogen-fertilizer use is high. In New Jersey and on Long Island, concentrations of nitrate exceed the U.S. Environmental Protection Agency Maximum Contaminant Level (MCL) more often than those of VOCs or pesticides. Nitrate contamination generally is associated with nonpoint sources. VOC contamination of ground water occurs primarily in urban areas, especially in mixed urban and industrial areas where chemicals are used. In general, VOC concentrations are low and do not exceed MCLs. High concentrations of VOCs generally are associated with point sources. Pesticide contamination of ground water occurs in some agricultural and residential areas, where the aquifer is very permeable and unconfined, and where the chemicals are used. Concentrations of pesticides in New Jersey and on Long Island generally are low; in agricultural areas of Long Island, however, some have been found to exceed MCLs. Pesticide contamination generally is associated with nonpoint sources.

New Jersey, New York↗
USGS2003

Hydrogeology of a Biosolids-Application Site Near Deer Trail, Colorado, 1993-99

This report presents hydrogeology data and interpretations resulting from two studies related to biosolids applications at the Metro Wastewater Reclamation District property near Deer Trail, Colorado, done by the U.S. Geological Survey in cooperation with the Metro Wastewater Reclamation District: (1) a 1993-99 study of hydrology and water quality for the Metro Wastewater Reclamation District central property and (2) a 1999 study of regional bedrock-aquifer structure and local ground-water recharge. Biosolids were applied as a fertilizer during late 1993 through 1999. The 1993 Metro Wastewater Reclamation District property boundary constitutes the study area, but hydrogeologic structure maps for a much larger area are included in the report. The study area is located on the eastern margin of the Denver Basin, a bowl-shaped sequence of sedimentary rocks. The uppermost bedrock formations in the vicinity of the study area consist of the Pierre Shale, the Fox Hills Sandstone, and the Laramie Formation, parts of which comprise the Laramie-Fox Hills hydrostratigraphic unit and thus, where saturated, the Laramie-Fox Hills aquifer. In the vicinity of the study area, the Laramie-Fox Hills hydrostratigraphic unit dips gently to the northwest, crops out, and is partially eroded. The Laramie-Fox Hills aquifer is either absent or not fully saturated within the Metro Wastewater Reclamation District properties, although this aquifer is the principal aquifer used for domestic supply in the vicinity of the study area. Yield was small from two deep monitoring wells in the Laramie-Fox Hills aquifer within the study area. Depth to water in these wells was about 110 and 150 feet below land surface, and monthly water levels fluctuated 0.5 foot or less. Alluvial aquifers also are present in the unconsolidated sand and loess deposits in the valleys of the study area. Interactions of the deeper parts of the Laramie-Fox Hills aquifer with shallow ground water in the study area include a general close hydraulic connection between alluvial and bedrock aquifers, recharge of the Cottonwood Creek and much of the Muddy Creek alluvial aquifers by the bedrock aquifer, and possible recharge of the bedrock aquifer by a Rattlesnake Creek tributary. Some areas of shallow ground water were recharged by infiltration from rain or ponds, but other areas likely were recharged by other ground water. Data for shallow ground water indicate that ground-water recharge takes less than a day at some sites to about 40 years at another site. Depth to shallow ground water in the study area ranged from about 2 feet to about 37 feet below land surface. Shallow ground-water levels likely were affected by evapotranspiration. Ground water is present in shallow parts of the bedrock aquifer or in alluvial aquifers in four drainage basins: Badger Creek, Cottonwood Creek, Muddy Creek, and Rattlesnake Creek. These drainage basins generally contained only ephemeral streams, which flow only after intense rain.

Water-Resources Investigations Report↗
USGS1984

Cost-effectiveness of the stream-gaging program in Iowa

This report documents the results of a study of the cost-effectiveness of the stream-gaging program in Iowa. Data uses and funding sources were identified for the 122 surface-water stations (including reservoir, lake, stage only, and miscellaneous stations) operated by the U. S. Geological Survey in Iowa. There are 110 continuous streamflow stations currently being operated in Iowa with an annual budget of $592,000. The average standard error of estimation in continuous streamflow records is 11.4 percent. It was shown that this overall degree of accuracy at the 110 continuous streamflow stations could be improved to 10.5 percent if the gaging schedule was optimized. A minimum budget of $543,000 is required to operate the present streamgaging program in Iowa. With this budget, routine visits to gages would be decreased to five during the open-water season and three during the winter. A budget less than this does not permit proper maintenance of the gages and recorders. At the minimum budget, the average standard error would be 12.5 percent. The maximum budget analyzed was $1,235,000, which resulted in an average standard error of 4.2 percent. A 10 percent increase in the current budget to $656,000 would result in a standard error of 8.4 percent. There are still a few basins with drainage areas greater than 200 square miles that have no continuous streamflow data. Continuous streamflow gages need to be established in these basins as funds become available. All stations in the current program need to be maintained for the forseeable future. Data simulated by using the flow-routing and regression methods for stations in 6 river basins do not meet the accuracy required for their data use. Other basins will be studied later to determine if alternative methods to meet accuracy standards are feasible.

Iowa↗
USGS1974

Low-flow characteristics of Wisconsin streams at sewage-treatment plants

Low-flow characteristics of Wisconsin streams at 415 sewage -treatment plants are presented in this report. The low-flow characteristics presented are the annual minimum 7-day mean flow that occurs on the average of once in 2 years (Q7, 2) and the annual minimum 7 -day mean flow that occurs on the average of once in 10 years (Q7, 10). The low-flow characteristics at most sewage-treatment plants were determined by correlating base-flow measurements at the sewage- treatment plants to the concurrent daily mean flow at continuous-record gaging stations in the area. The Q7, 2 and Q7, 10 discharges determined by a frequency analysis at the continuous-record gaging stations were used to estimate the Q7, 2 and Q7,10 at the sewage-treatment plants. For some sewage-treatment plants the low-flow characteristics were also determined by frequency analysis at nearby continuous -record gaging stations or correlation analysis at nearby low-flow, partial-record stations. The accuracy of the estimated low-flow characteristics is evaluated according to the type and amount of data available used to determine the low-flow characteristics. The accuracy determined by the standard error of estimate for the 10-year low flow (SE10) ranged from 18 percent at continuous -record gaging stations to 70 percent when only three base-flow measurements were available. The SE10 of 70 percent is larger than anticipated when the project was initiated. This was the result of extremely poor base-flow conditions during the 2-year data-collection period.

Wisconsin↗
USGS1995

Effects of combined-sewer overflows and urban runoff on the water quality of Fall Creek, Indianapolis, Indiana

In 1986, the U.S. Geological Survey and the Indianapolis Department of Public Works began a study to evaluate the effects of combined-sewer overflows and urban runoff discharging to Fall Geek on the White River. This report describes the effects of combined-sewer overflows and urban runoff on the water quality of Fall Creek during summer 1987 by comparing the water quality during base flow with that during storm runoff and by comparing water quality in the urbanized area with that in the less urbanized area upstream from the combined-sewer overflows. Data were collected at three streamflow-gaging stations located upstream from, downstream from, and in the middle of 27 combined-sewer overflows on Fall Creek. The most downstream station also was immediately downstream from the discharge of filter backwash from a water-treatment plant for public supply. Specific conductance and concentrations of major ions and dissolved solids in base flow increased downstream in response to surface-water withdrawn for public supply, ground-water inflow, and the discharge of filter backwash. Concentrations of dissolved oxygen were least in the reach of Fall Creek in the middle of the combined- sewer overflows where black sludge deposits covered the stream bottom. Concentrations of nitrate plus nitrite and ammonia steadily increased downstream, whereas concentrations of organic nitrogen, phosphorus, and orthophosphate only increased at the most downstream station. Nearly all concentrations of chromium, copper, lead, nickel, and zinc at the upstream and middle stations were less than the detection limit of 10 micrograms per liter. Detectable concentrations of these metals and high concentrations of suspended solids in base-flow samples at the most downstream station were caused by the discharges from the water-treatment plant. Concentrations of dissolved oxygen measured at the station in the middle of the combined-sewer overflows were less than the Indiana minimum ambient water-quality standard of 4.0 milligrams per liter during all storms. Concentrations of ammonia, oxygen demand, copper, lead, zinc, and fecal coliform bacteria at the stations downstream from the combined-sewer overflows were much higher in storm runoff than in base flow. Increased concentrations of oxygen demand in runoff probably were caused by combined-sewer overflows, urban runoff, and the resuspension of organic material deposited on the streambed. Some of the increased concentrations of lead, zinc, and probably copper can be attributed to the discharge and resuspension of filter backwash

Indiana↗
USGS1997

Full Equations (FEQ) model for the solution of the full, dynamic equations of motion for one-dimensional unsteady flow in open channels and through control structures

The Full EQuations (FEQ) model is a computer program for solution of the full, dynamic equations of motion for one-dimensional unsteady flow in open channels and through control structures. A stream system that is simulated by application of FEQ is subdivided into stream reaches (branches), parts of the stream system for which complete information on flow and depth are not required (dummy branches), and level-pool reservoirs. These components are connected by special features; that is, hydraulic control structures, including junctions, bridges, culverts, dams, waterfalls, spillways, weirs, side weirs, and pumps. The principles of conservation of mass and conservation of momentum are used to calculate the flow and depth throughout the stream system resulting from known initial and boundary conditions by means of an implicit finite-difference approximation at fixed points (computational nodes). The hydraulic characteristics of (1) branches including top width, area, first moment of area with respect to the water surface, conveyance, and flux coefficients and (2) special features (relations between flow and headwater and (or) tail-water elevations, including the operation of variable-geometry structures) are stored in function tables calculated in the companion program, Full EQuations UTiLities (FEQUTL). Function tables containing other information used in unsteady-flow simulation (boundary conditions, tributary inflows or outflows, gate settings, correction factors, characteristics of dummy branches and level-pool reservoirs, and wind speed and direction) are prepared by the user as detailed in this report. In the iterative solution scheme for flow and depth throughout the stream system, an interpolation of the function tables corresponding to the computational nodes throughout the stream system is done in the model. FEQ can be applied in the simulation of a wide range of stream configurations (including loops), lateral-inflow conditions, and special features. The accuracy and convergence of the numerical routines in the model are demonstrated for the case of laboratory measurements of unsteady flow in a sewer pipe. Verification of the routines in the model for field data on the Fox River in northeastern Illinois also is briefly discussed. The basic principles of unsteady-flow modeling and the relation between steady flow and unsteady flow are presented. Assumptions and the limitations of the model also are presented. The schematization of the stream system and the conversion of the physical characteristics of the stream reaches and a wide range of special features into function tables for model applications are described. The modified dynamic-wave equation used in FEQ for unsteady flow in curvilinear channels with drag on minor hydraulic structures and channel constrictions determined from an equivalent energy slope is developed. The matrix equation relating flows and depths at computational nodes throughout the stream system by the continuity (conservation of mass) and modified dynamic-wave equations is illustrated for four sequential examples. The solution of the matrix equation by Newton's method is discussed. Finally, the input for FEQ and the error messages and warnings issued are presented.

Water-Resources Investigations Report↗
USGS1987

Water quality of Lake Tuscaloosa and streamflow and water quality of selected tributaries to Lake Tuscaloosa, Alabama, 1982-86

Lake Tuscaloosa, created in 1969 by the impoundment of North River, provides the primary water supply for Tuscaloosa, Alabama , and surrounding areas. This report describes the percent contribution of major tributaries to the mean inflow to the lake; water quality; and changes in water quality in the lake and selected tributaries. During base flow, about 60% of the total flow into Lake Tuscaloosa is contributed by Binion and Carroll Creeks, which drain only 22% of the Lake Tuscaloosa basin. Binion and Carroll Creek basins are underlain primarily by sand and gravel deposits of the Coker Formation. Mean inflow to the lake was 1,150 cu ft/sec during 1983, a wet year, and 450 cu ft/sec during 1985, a relatively dry year. More than 80% of the total inflow during both years was contributed by North River and Binion, Cripple, and Carroll Creeks. About 59% was contributed by North River during those years. Except for pH, sulfate, and dissolved and total recoverable iron and manganese, the water quality of the tributaries is generally within drinking water limits and acceptable for most uses. The water quality of Lake Tuscaloosa is generally within drinking water limits and acceptable for most uses. The maximum and median concentrations of sulfate increased every year at the dam from 1979 to 1985 (7.2 to 18 mg/L and 6.2 to 14 mg/L, respectively). The dissolved solids concentrations for water at the dam have varied (1979-86) from 27 to 43 mg/L; the sulfate, 5.2 to 18 mg/L; and the dissolved iron, 10 to 250 micrograms/L--all within the recommended drinking water limits. However, concentrations of dissolved manganese and total recoverable iron and manganese at the dam commonly exceeded the recommended drinking water limits. In November 1985, after the summer warmup and increase in biological activity, the water quality at five depth profiles sites on Lake Tuscaloosa was acceptable for most uses, generally. However, a dissolved oxygen concentration of 1 mg/L or less was observed within 5 to 10 ft of the bottom for several depth profiles. At depths > 35 to 40 ft (out of a total depth of about 50 to 100 ft) the dissolved oxygen concentration was < 5 mg/L at several sites. By mid-January 1986, the temperature and dissolved oxygen depth profiles were virtually constant from top to bottom of the lake at all five sites; this indicated that lake turnover was complete. However, significant variation existed in pH depth profiles. (Author 's abstract)

Water-Resources Investigations Report↗
USGS2004

Water quality in Big Cypress National Preserve and Everglades National Park — Trends and spatial characteristics of selected constituents

Seasonal changes in water levels and flows in Big Cypress National Preserve (BICY) and Everglades National Park (EVER) affect water quality. As water levels and flows decline during the dry season, physical, geochemical and biological processes increase the breakdown of organic materials and the build-up of organic waste, nutrients, and other constituents in the remaining surface water. For example, concentrations of total phosphorus in the marsh are less than 0.01 milligram per liter (mg/L) during much of the year. Concentrations can rise briefly above this value during the dry season and occasionally exceed 0.1 mg/L under drought conditions. Long-term changes in water levels, flows, water management, and upstream land use also affect water quality in BICY and EVER, based on analysis of available data (1959-2000). During the 1980's and early 1990's, specific conductance and concentrations of chloride increased in the Taylor Slough and Shark River Slough. Chloride concentrations more than doubled from 1960 to 1990, primarily due to greater canal transport of high dissolved solids into the sloughs. Some apparent long-term trends in sulfate and total phosphorus were likely attributable, at least in part, to high percentages of less-than and zero values and to changes in reporting levels over the period of record. High values in nutrient concentrations were evident during dry periods of the 1980's and were attributable either to increased canal inflows of nutrient-rich water, increased nutrient releases from breakdown of organic bottom sediment, or increased build-up of nutrient waste from concentrations of aquatic biota and wildlife in remaining ponds. Long-term changes in water quality over the period of record are less pronounced in the western Everglades and the Big Cypress Swamp; however, short-term seasonal and drought-related changes are evident. Water quality varies spatially across the region because of natural variations in geology, hydrology, and vegetation and because of differences in water management and land use. Nutrient concentrations are relatively low in BICY and EVER compared with concentrations in parts of the northern Everglades that are near agricultural and urban lands. Concentrations of total phosphorus generally are higher in BICY (median values, 1991-2000, were mostly greater than 0.015 mg/L) than in EVER (median values, 1991-2000, less than 0.01 mg/L), probably because of higher phosphorus in natural sources such as shallow soils, rocks, and ground water in the Big Cypress region than in the Everglades region. Conversely, concentrations of chloride and sulfate are higher in EVER (median values in Shark River Slough, 1991-2000, mostly greater than 2 mg/L sulfate and 50 mg/L chloride) than in BICY (median values, 1991-2000, less than 1 mg/L sulfate and at most sites less than 20 mg/L chloride), probably because of the canal transport system, which conveys more water from an agricultural source into EVER than into BICY. Trace elements and contaminants such as pesticides and other toxic organic compounds are in relatively low concentrations in BICY and EVER compared with concentrations in parts of the northern Everglades near agricultural and urban sources. Concentrations rarely exceeded aquatic life criteria in BICY and EVER. Atrazine was the only pesticide found in water that exceeded the criteria (in 2 out of 304 samples). The pesticides heptachlor expoxide, lindane, and p,p?-DDE exceeded criteria in canal bed sediments in 1, 2, and 16 percent of the samples, respectively.

Florida↗
USGS1973

Sediment transport by streams in the Upper Columbia River Basin, Washington, May 1969-June 1971

This report presents the results of a reconnaissance evaluation of the fluvial-sediment transport by streams in the 28 ,000 - square-mile upper Columbia River basin in eastern Washington. The basin ranges in altitude from about 340 to 9,000 feet, and receives annual precipitation ranging from more than 150 inches in the mountains to less than 10 inches at the lower altitudes. A good vegetative cover is sustained in the mountains by the high precipitation, whereas vegeta tion is sparse in the lower semiarid parts of the basin. In the mountainous areas snowmelt runoff transports most of the sediment during April through June. In the semiarid parts of the basin, little runoff occurs during most years, and most of the sediment is transported when heavy, warm rains fall on extensive accumulations of snow. During the 1970 and 1971 water years, the measured suspended-sediment concentrations in the upper Columbia River basin ranged from less than 1 milligram per liter in many streams to more than 200,000 milligrams per liter in Providence Coulee. The estimated long-term annual suspended-sediment yields range from less than 10 tons per square mile in many basins to more than 500 tons per square mile in Providence Coulee. Man's activities have caused only a slight increase in the magnitude of the sediment discharge to the Columbia River. Although cultivation has initiated a large increase in erosion on the Columbia Plateau, and winds there move some of the loosened or easily eroded soils to depressions and runoff channels, sediment transport by streams has not increased greatly. This is because the little surface runoff on the plateau does not transport the soils to streams and to the Columbia River.

Washington↗
USGS2003

Extent of areal inundation of riverine wetlands along Cypress Creek and the Peace, Alafia, North Prong Alafia, and South Prong Alafia Rivers, west-central Florida

Riverine and palustrine system wetlands are a major ecological component of river basins in west-central Florida. Healthy wetlands are dependent upon the frequency and duration of periodic flooding or inundation. This report assesses the extent, area, depth, frequency, and duration of periodic flooding and the effects of potential surface-water withdrawals on the wetlands along Cypress Creek and the Peace, Alafia, North Prong Alafia, and South Prong Alafia Rivers. Results of the study were derived from step-backwater analysis performed at each of the rivers using the U.S. Army Corps of Engineers Hydrologic Engineering Center-River Analysis System (HEC-RAS) one-dimensional model. The step-backwater analysis was performed using selected daily mean discharges at the 10th, 50th, 70th, 80th, 90th, 98th, 99.5th, and 99.9th percentiles to compute extent of areal inundation, area of inundation, and hydraulic depth to assess the net reduction of areal inundation if 10 percent of the total river flow were diverted for potential withdrawals. The extent of areal inundation is determined by cross-sectional topography and the degree to which the channel is incised. Areal inundation occurs along the broad, low relief of the Cypress Creek floodplain during all selected discharge percentiles. However, areal inundation of the Peace and Alafia Rivers floodplains, which generally have deeply incised channels, occurs at or above discharges at the 80th percentile. The greatest area of inundation along the three rivers generally occurs between the 90th and 98th percentile discharges. The decrease in inundated area resulting from a potential 10-percent withdrawal in discharge ranged as follows: Cypress Creek, 22 to 395 acres (1.7 to 8.4 percent); Peace River, 17 to 1,900 acres (2.1 to 13.6 percent); Alafia River, 1 to 90 acres (1 to 19.6 percent); North Prong Alafia River, 1 to 46 acres (0.7 to 23.4 percent); and South Prong Alafia River, 1 to 75 acres (1.5 to 13.4 percent).

Water-Resources Investigations Report↗
USGS1995

Water levels in the Calumet aquifer and their relation to surface-water levels in northern Lake County, Indiana, 1985-92

The U.S. Geological Survey made 2,328 water-level measurements at a total of 96 ground-water and surface-water sites in northern Lake County, Indiana, from August 1985 through September 1992. This report lists and summarizes the significance of the measurements. Northern Lake County is on the southern shore of Lake Michigan and includes the cities of East Chicago, Gary, Hammond, and Whiting. The study area is underlain by the unconfined Calumet aquifer and receives about 36 inches of precipitation per year. The U.S. Geological Survey investigated ground-water levels and flow in the Calumet aquifer and the effect of Lake Michigan levels on ground-water and surface-water levels throughout the study area. Summary statistics of the water-level data were computed for each site. Ground-water levels annually reach a maximum in June or July and a minimum in September or October. Measured groundwater fluctuations in the Calumet aquifer during the study period ranged from 0.40 to 5.01 feet, and the mean ground-water fluctuation was about 2.3 feet The largest surface-water fluctuations were affected by record setting Lake Michigan levels. Midmonth daily averages for the data-collection period show that Lake Michigan fluctuated 4.14 feet Water-level fluctuations on the Grand Calumet River were from 1.06 to 2.45 feet. Analysis of water-level data indicates that the 1988 drought did not substantially affect water levels in the Calumet aquifer, but the deficit in precipitation reversed vertical flow gradients in ground water at three paired deep and shallow wells. High water levels in Lake Michigan during 1985-87 created long-term backwater effects on the Grand Calumet River as far as 11.0 miles upstream from Lake Michigan. Analysis of water-level data from the data-collection network indicates that the water table normally slopes toward streams, ditches, sewers, the Indiana Harbor Canal, and Lake Michigan. The slope of the water table toward the Grand Calumet River is greatest in the winter and can decrease to being almost horizontal in the summer. Wells near streams respond quickly to nearby surface-water-level changes. Water-table maps indicate that sewers and dewatering systems are lowering ground-water levels in large areas. Ditches, the Grand Calumet River, and the Indiana Harbor Canal connect the Lake Michigan water level to large parts of the study area. The surface-water stage in the Indiana Harbor Canal, which functions as a ditch, can equal Lake Michigan's stage up to 3.75 miles inland from the lakeshore. Human activity, the stage of Lake Michigan, and the storage capacity of the Calumet aquifer combine to reduce vertical changes in the water table in the study area.

Indiana↗
USGS1992

Techniques for estimating 7-day, 10-year low-flow characteristics for ungaged sites on streams in Mississippi

Mississippi State water laws require that the 7-day, 10-year low-flow characteristic (7Q10) of streams be used as a criterion for issuing wastedischarge permits to dischargers to streams and for limiting withdrawals of water from streams. This report presents techniques for estimating the 7Q10 for ungaged sites on streams in Mississippi based on the availability of baseflow discharge measurements at the site, location of nearby gaged sites on the same stream, and drainage area of the ungaged site. These techniques may be used to estimate the 7Q10 at sites on natural, unregulated or partially regulated, and non-tidal streams. Low-flow characteristics for streams in the Mississippi River alluvial plain were not estimated because the annual lowflow data exhibit decreasing trends with time. Also presented are estimates of the 7Q10 for 493 gaged sites on Mississippi streams. Techniques for estimating the 7Q10 have been developed for ungaged sites with base-flow discharge measurements, for ungaged sites on gaged streams, and for ungaged sites on ungaged streams. For an ungaged site with one or more base-flow discharge measurements, base-flow discharge data at the ungaged site are related to concurrent discharge data at a nearby gaged site. For ungaged sites on gaged streams, several methods of transferring the 7Q10 from a gaged site to an ungaged site were developed; the resulting 7Q10 values are based on drainage area prorations for the sites. For ungaged sites on ungaged streams, the 7Q10 is estimated from a map developed for. this study that shows the unit 7Q10 (7Q10 per square mile of drainage area) for ungaged basins in the State. The mapped values were estimated from the unit 7Q10 determined for nearby gaged basins, adjusted on the basis of the geology and topography of the ungaged basins.

Mississippi↗
USGS2000

Quality-assurance design applied to an assessment of agricultural pesticides in ground water from carbonate bedrock aquifers in the Great Valley of eastern Pennsylvania

Assessments to determine whether agricultural pesticides are present in ground water are performed by the Commonwealth of Pennsylvania under the aquifer monitoring provisions of the State Pesticides and Ground Water Strategy. Pennsylvania's Department of Agriculture conducts the monitoring and collects samples; the Department of Environmental Protection (PaDEP) Laboratory analyzes the samples to measure pesticide concentration. To evaluate the quality of the measurements of pesticide concentration for a groundwater assessment, a quality-assurance design was developed and applied to a selected assessment area in Pennsylvania. This report describes the quality-assurance design, describes how and where the design was applied, describes procedures used to collect and analyze samples and to evaluate the results, and summarizes the quality assurance results along with the assessment results. The design was applied in an agricultural area of the Delaware River Basin in Berks, Lebanon, Lehigh, and Northampton Counties to evaluate the bias and variability in laboratory results for pesticides. The design—with random spatial and temporal components—included four data-quality objectives for bias and variability. The spatial design was primary and represented an area comprising 30 sampling cells. A quality-assurance sampling frequency of 20 percent of cells was selected to ensure a sample number of five or more for analysis. Quality-control samples included blanks, spikes, and replicates of laboratory water and spikes, replicates, and 2-lab splits of groundwater. Two analytical laboratories, the PaDEP Laboratory and a U.S. Geological Survey Laboratory, were part of the design. Bias and variability were evaluated by use of data collected from October 1997 through January 1998 for alachlor, atrazine, cyanazine, metolachlor, simazine, pendimethalin, metribuzin, and chlorpyrifos. Results of analyses of field blanks indicate that collection, processing, transport, and laboratory analysis procedures did not contaminate the samples; there were no false-positive results. Pesticides were detected in water when pesticides were spiked into (added to) samples. There were no false negatives for the eight pesticides in all spiked samples. Negative bias was characteristic of analytical results for the eight pesticides, and bias was generally in excess of 10 percent from the ‘true’ or expected concentration (34 of 39 analyses, or 87 percent of the ground-water results) for pesticide concentrations ranging from 0.31 to 0.51 mg/L (micrograms per liter). The magnitude of the negative bias for the eight pesticides, with the exception of cyanazine, would result in reported concentrations commonly 75-80 percent of the expected concentration in the water sample. The bias for cyanazine was negative and within 10 percent of the expected concentration. A comparison of spiked pesticide-concentration recoveries in laboratory water and ground water indicated no effect of the ground-water matrix, and matrix interference was not a source of the negative bias. Results for the laboratory-water spikes submitted in triplicate showed large variability for recoveries of atrazine, cyanazine, and pendimethalin. The relative standard deviation (RSD) was used as a measure of method variability over the course of the study for laboratory waters at a concentration of 0.4 mg/L. An RSD of about 11 percent (or about ?0.05 mg/L)characterizes the method results for alachlor, chlorpyrifos, metolachlor, metribuzin, and simazine. Atrazine and pendimethalin have RSD values of about 17 and 23 percent, respectively. Cyanazine showed the largest RSD at nearly 51 percent. The pesticides with low variability in laboratory-water spikes also had low variability in ground water. The assessment results showed that atrazinewas the most commonly detected pesticide in ground water in the assessment area. Atrazine was detected in water from 22 of the 28 wells sampled, and recovery results for atrazine were some of the worst (largest negative bias). Concentrations of the eight pesticides in ground water from wells were generally less than 0.3 µg/L. Only six individual measurements of the concentrations in water from six of the wells were at or above 0.3 µg/L, five for atrazine and one for metolachlor. There were eight additional detections of metolachlor and simazine at concentrations less than 0.1 µg/L. No well water contained more than one pesticide at concentra-tions at or above 0.3 µg/L. Evidence exists, how-ever, for a pattern of co-occurrence of metolachlor and simazine at low concentrations with higher concentrations of atrazine. Large variability in replicate samples and negative bias for pesticide recovery from spiked samples indicate the need to use data for pesticide recovery in the interpretation of measured pesti-cide concentrations in ground water. Data from samples spiked with known amounts of pesticides were a critical component of a quality-assurance design for the monitoring component of the Pesti-cides and Ground Water Strategy. Trigger concentrations, the concentrations that require action under the Pesticides and Ground Water Strategy, should be considered maximums for action. This consideration is needed because of the magnitude of negative bias.

Water-Resources Investigations Report↗
USGS1999

Occurrence, distribution, and trends of volatile organic compounds in the Ohio River and its major tributaries, 1987-96

The Ohio River is a source of drinking water for more than 3 million people. Thus, it is important to monitor the water quality of this river to determine if contaminants are present, their concentrations, and if water quality is changing with time. This report presents an analysis of the occurrence, distribution, and trends of 21 volatile organic compounds (VOCs) along the main stem of the Ohio River and its major tributaries from 1987 through 1996. The data were collected by the Ohio River Valley Water Sanitation Commission's Organics Detection System, which monitors daily for VOCs at 15 stations. Various statistical methods were applied to basinwide data from all monitoring stations and to data from individual monitoring stations. For the basinwide data, one or more VOCs were detected in 45 percent of the 44,837 river-water samples. Trichloromethane, detected in 26 percent of the samples, was the most frequently detected VOC followed by benzene (11 percent), methylbenzene (6.4 percent), and the other 18 VOCs, which were detected in less than 4 percent of the samples. In samples from 8 of the 15 monitoring stations, trichloromethane was also the most frequently detected VOC. These stations were generally near large cities along the Ohio River. The median trichloromethane concentration was 0.3 microgram per liter (&mu;g/L), and concentrations ranged from less than 0.1 to 125.3 &mu;g/L. Most of the VOCs had median detected concentrations that ranged from 0.1 to 0.4 &mu;g/L for the basinwide data and for samples from individual stations. Samples from stations in the upstream part of the basin and from the Kanawha River had the highest median concentrations. Ninety-nine percent of the detected VOC concentrations were within U.S. Environmental Protection Agency drinking-water regulations. Of the 268 exceedances of drinking-water regulations, 188 were due to the detection of 1,2-dichloroethane prior to 1993 in samples from the monitoring station near Paducah, Ky. Time trend analyses indicated that most VOCs had no trend in samples at most monitoring stations because they were detected infrequently. At one or more stations, 14 VOCs had decreasing trends in monthly mean concentrations that ranged from -0.01 to -0.42 &mu;/L per year. Nine VOCs had significant decreasing trends in percentage detection that ranged from -1.08 to -12.90 percent per year. These trends suggest that source-control efforts are working and that water quality is improving.

Ohio River↗
USGS1987

Cost effectiveness of the U.S. Geological Survey's stream-gaging program in Wisconsin

This report presents the results of a three-step evaluation of the stream-gaging program in Wisconsin. First, data uses and funding sources were identified for the 89 continuous-record gaging stations operated during the 1984 water year. Next, alternative methods of streamflow estimation were examined for three stations. A flow-routing model was used for two of the stations and a statistical model was used for the third. The modeled discharges did not compare well enough with observed discharges to warrant elimination of any of the stations. Finally, an optimization model was used to assess the cost effectiveness of the stream-gaging process. The annual budget, in 1984 dollars, for operating the 89 continuous-record gaging stations and 65 additional stations is $557,3000. Based on a Kalman-filter analysis, the theoretical average standard error of instantaneous discharge associated with the current practice of visiting the stations is 13.8%. This overall level of accuracy could be maintained with a budget of $518,6000 if stream-gaging activities were redistributed in an optimal fashion among the gaging stations. For the current budget, the theoretical average standard error would be reduced to 10.1% if the network is operated in an optimal fashion. Furthermore, the average standard error would be reduced to 7.3% if all missing record is eliminated and the network is operated optimally. A minimum budget of $510,000 is required to operate the program; a budget less than this does not permit proper service and maintenance of the gaging stations. At this minimum budget, the theoretical average standard error of instantaneous discharge is 14.4%. The maximum budget analyzed was $650,000 and resulted in an average standard of error of instantaneous discharge of 7.2%.

Wisconsin↗
USGS1998

Base (100-year) flood elevations for selected sites in Marion County, Missouri

The primary requirement for community participation in the National Flood Insurance Program is the adoption and enforcement of floodplain management requirements that minimize the potential for flood damages to new construction and avoid aggravating existing flooding conditions. This report provides base flood elevations (BFE) for a 100-year recurrence flood for use in the management and regulation of 14 flood-hazard areas designated by the Federal Emergency Management Agency as approximate Zone A areas in Marion County, Missouri. The one-dimensional surface-water flow model, HEC-RAS, was used to compute the base (100-year) flood elevations for the 14 Zone A sites. The 14 sites were located at U.S., State, or County road crossings and the base flood elevation was determined at the upstream side of each crossing. The base (100-year) flood elevations for BFE 1, 2, and 3 on the South Fork North River near Monroe City, Missouri, are 627.7, 579.2, and 545.9 feet above sea level. The base (100-year) flood elevations for BFE 4, 5, 6, and 7 on the main stem of the North River near or at Philadelphia and Palmyra, Missouri, are 560.5, 539.7, 504.2, and 494.4 feet above sea level. BFE 8 is located on Big Branch near Philadelphia, a tributary to the North River, and the base (100-year) flood elevation at this site is 530.5 feet above sea level. One site (BFE 9) is located on the South River near Monroe City, Missouri. The base (100-year) flood elevation at this site is 619.1 feet above sea level. Site BFE 10 is located on Bear Creek near Hannibal, Missouri, and the base (100-year) elevation is 565.5 feet above sea level. The four remaining sites (BFE 11, 12, 13, and 14) are located on the South Fabius River near Philadelphia and Palmyra, Missouri. The base (100-year) flood elevations for BFE 11, 12, 13, and 14 are 591.2, 578.4, 538.7, and 506.9 feet above sea level.

Water-Resources Investigations Report↗