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At least 397 records · Page 22Linked to original sources
USGS2023

Regression equations for estimating the 4-day, 3-year low-flow frequency and adjusted harmonic mean streamflow at ungaged sites for unregulated, perennial streams in New Mexico

The Federal Clean Water Act stipulates that States adopt water-quality standards to protect and enhance the quality of water in those States and to protect water quality through the creation of planning documents and discharge permits. Critical low-flow values, including the 4-day, 3-year low-flow frequency (4Q3) and harmonic mean streamflows, are necessary for developing those planning documents and permits. The U.S. Geological Survey computed the 4Q3 and adjusted harmonic mean streamflows using data from 96 streamgages on perennial streams, and regression equations were developed for the estimation of these parameters at ungaged, perennial streams in the State of New Mexico using weighted least-squares regression and readily accessed basin and climatic characteristics. Six equations were developed for the 4Q3 statistic, and five equations were developed for the adjusted harmonic mean statistic. Separate equations were developed for sites located in basins with mean elevations equal to or greater than 8,000 feet above the National Geodetic Vertical Datum of 1929 (except where noted as the North American Vertical Datum of 1988), as well as for sites on streams that are tributary to the San Juan River. Pseudo R-squared values ranged from 0.53 to 0.87 (4Q3) and adjusted R-squared values ranged from 0.69 to 0.89 (adjusted harmonic mean). For sites in basins with mean elevations of less than 8,000 feet above the National Geodetic Vertical Datum of 1929 (except where noted as the North American Vertical Datum of 1988), equations were developed based on contributing drainage area size. Drainage area, mean basin elevation, basinwide mean annual precipitation, and mean basin slope were found to have relations to the 4Q3; drainage area, mean basin elevation, basinwide mean annual precipitation, mean basin slope, and mean basinwide precipitation for the winter period, defined as the months of October through April, were found to have relations to the adjusted harmonic mean. Comparison to previous 4Q3 regression equations using fit statistics indicate an overall improvement in performance.

New Mexico↗
USGS2002

Hydrology and water quality of Geneva Lake, Walworth County, Wisconsin

As part of continuing efforts to improve the water quality of Geneva Lake, a collaborative effort between the U.S. Geological Survey, the Wisconsin Department of Natural Resources, and the Geneva Lake Environmental Agency was initiated in 1997 to document the present quality of the lake and its sediments, compute detailed hydrologic and nutrient (primarily phosphorus) budgets for the lake, estimate how changes in nutrient loading may affect water quality, and describe changes in the lake over the past 170 years by comparing water quality measured in this study with historical measurements and sediment-core information. This report presents the results of this collaborative study. Measurements collected during this study (1997.2000) indicate that the trophic status of the lake ranges from mesotrophic to oligotrophic: the mean Secchi depth was 4.8 m (meters), mean surface phosphorus concentration was 9 ?g/L (micrograms per liter), mean surface nitrogen concentration was 550 ?g/L, and mean surface chlorophyll a concentration was 3 ?g/L. Surface nitrogen: phosphorus ratios indicated that, if just these nutrients are considered, phosphorus should be the limiting nutrient. Phosphorus budgets constructed for water years 1998 and 1999 indicate that recent annual phosphorus loads were about 2,000 kg (kilograms) less than that estimated in 1975 (total annual input was about 3,200 kg in 1998 and about 8,500 kg in 1999). The major source of phosphorus to the lake was from its tributaries, which contributed about 84 percent of the total load. The primary difference from the phosphorus load estimates for 1975 was the decrease in loading from the Fontana sewage-treatment plant. Direct measurements and indirect measurements based on sediment-core analyses indicate that the water quality of Geneva Lake has degraded in the last 170 years, the greatest effects resulting from urbanization. Sedimentation rates were highest between 1900 to 1930, and phosphorus concentrations were highest between the 1930s to early 1980s. As a result of the recent reduction in phosphorus loading, in-lake near-surface phosphorus concentrations decreased from 20.25 ?g/L to about 10.15 ?g/L and are similar to those estimated for the lake in the early 1900s. Concentrations of other chemical constituents associated with urban areas, however, have continually increased, especially in Williams Bay and Geneva Bay.

Wisconsin↗
USGS2015

Evaluation of the U.S. Geological Survey standard elevation products in a two-dimensional hydraulic modeling application for a low relief coastal floodplain

Growing use of two-dimensional (2-D) hydraulic models has created a need for high resolution data to support flood volume estimates, floodplain specific engineering data, and accurate flood inundation scenarios. Elevation data are a critical input to these models that guide the flood-wave across the landscape allowing the computation of valuable engineering specific data that provides a better understanding of flooding impacts on structures, debris movement, bed scour, and direction. High resolution elevation data are becoming publicly available that can benefit the 2-D flood modeling community. Comparison of these newly available data with legacy data suggests that better modeling outcomes are achieved by using 3D Elevation Program (3DEP) lidar point data and the derived 1 m Digital Elevation Model (DEM) product relative to the legacy 3 m, 10 m, or 30 m products currently available in the U.S. Geological Survey (USGS) National Elevation Dataset. Within the low topographic relief of a coastal floodplain, the newer 3DEP data better resolved elevations within the forested and swampy areas achieving simulations that compared well with a historic flooding event. Results show that the 1 m DEM derived from 3DEP lidar source provides a more conservative estimate of specific energy, static pressure, and impact pressure for grid elements at maximum flow relative to the legacy DEM data. Better flood simulations are critically important in coastal floodplains where climate change driven storm frequency and sea level rise will contribute to more frequent flooding events.

North Carolina↗
USGS1977

Relation of bulk precipitation and evapotranspiration to water quality and water resources, St. Thomas, Virgin Islands

St. Thomas, Virgin Islands, lies in what can be considered a true maritime regime, being 600 miles (1000 kilometers) from the nearest continental landmass. The island is composed almost entirely of volcanic rocks mantled by a thin soil seldom more than 2 feet (60 centimeters) thick. Rainfall, averaging about 40 inches (1020 millimeters) annually, has an orographic distribution related to the central ridge of the island, altitude 600 to 1500 feet (180 to 405 meters), and the easterly to northeasterly trade winds. The mineral content of bulk precipitation falling on the island is derived principally from the sea although soil dust contributes much of the calcium, sodium, and bicarbonate. Two-thirds of the sulfate in the precipitation is provided by sea salts; the remainder is derived from other sources. The concentration of the constituents of bulk precipitation fluctuates widely month to month, but the load of the constituents shows little monthly variation. Bulk precipitation is concentrated on the land surface and in the soil zone. From there it is carried into the ground water during recharge or is removed by storm-water runoff. It is the principal source of minerals in the waters of the island. Soil-moisture demand and evaporation limits recharge to 1 to 2 inches (25 to 50 millimeters) annually for the greater part of the island. Evapotranspiration also occurs directly from the aquifer. The salts left further increase the mineralization of the ground water. Water loss from the aquifer by evapotranspiration ranges from 40 to 80 percent of the recharge. Recharge to the aquifers and evapotranspiration of ground water determined by ratios of chloride concentrations in bulk precipitation, surface water, and subsurface water agree favorably with recharge and groundwater loss computed by other means.

Water Supply Paper↗
USGS2010

Assessing the vulnerability of public-supply wells to contamination: Glacial aquifer system in Woodbury, Connecticut

This fact sheet highlights findings from the vulnerability study of a public-supply well in Woodbury, Connecticut. The well typically produces water at the rate of 72 gallons per minute from the glacial aquifer system in the Pomperaug River Basin. Water samples were collected at the public-supply well and at monitoring wells installed in or near the simulated zone of contribution to the supply well. Samples of untreated water from the public-supply wellhead contained several types of undesirable constituents, including 11 volatile organic compounds (VOCs), nitrate, pesticides, uranium, and radon. Most of these constituents were detected at concentrations below drinking-water standards, where such standards exist. Only concentrations of the VOC trichlorethylene exceeded the Maximum Contaminant Level (MCL) of 5 micrograms per liter (ug/L) established by U.S. Environmental Protection Agency for drinking water. Radon concentrations exceeded a proposed-but not finalized-MCL of 300 picocuries per liter (pCi/L). Overall, the study findings point to four main factors that affect the movement and fate of contaminants and the vulnerability of the public-supply well in Woodbury: (1) groundwater age (how long ago water entered, or recharged, the aquifer); (2) the percentage of recharge received through urban areas; (3) the percentage of recharge received through dry wells and their proximity to the public-supply well; and (4) natural geochemical processes occurring within the aquifer system; that is, processes that affect the amounts and distribution of chemical substances in aquifer sediments and groundwater. A computer-model simulation of groundwater flow to the public-supply well was used to estimate the age of water particles entering the well along the length of the well screen. About 90 percent of the simulated flow to the well consists of water that entered the aquifer 9 or fewer years ago. Such young water is vulnerable to contaminants resulting from human activities, as indicated by the solvents, fuel components, road salt, and septic-system leachate that were detected in the glacial aquifer system during the current study. Age-dating combined with chemical modeling suggests that less than 2 percent of water produced by the public-supply well is water from the deep bedrock that is "old" (water that recharged, or entered, the aquifer before 1952). Such a small percentage of old groundwater entering the public-supply well offers little potential for dilution of young waters containing contaminants from human activities. Shallow groundwater that originated as recharge through urban areas generally had higher median concentrations and more detections of volatile organic compounds (VOCs) than did groundwater from the deep glacial deposits or fractured bedrock that originated mainly as recharge through agricultural and undeveloped land. Shallow groundwater was also found to be affected by road salt and septic-system leachate. A chemical mixing model indicates that up to 15 percent of nitrate in water from the supply well is likely from septic-system leachate. The Connecticut Department of Public Health has identified several potential sources of contamination in the commercial area of Woodbury (several light industrial or commercial properties where hazardous materials and petroleum products are used and stored). To reduce stormwater runoff in the commercial area, water from the parking lots and pavement is channeled into dry wells-drains that shunt water directly into the aquifer system, bypassing the soil and unsaturated zones. A computer-model simulation of groundwater flow indicates that approximately 16 percent of the water produced by the public-supply well is derived from runoff captured by these drains. Traveltime for water from the dry wells to the public-supply well ranges from about 1.5 to less than 4 years. Dry wells have the potential to enhance contaminant movement to the supply well, suggesting that stormwater-control methods cannot be considered separately from groundwater quality—they are linked. Water-quality protection in this setting depends on the entire community. If residents and businesses take steps to reduce input of manmade contaminants to groundwater, a positive effect on quality of the supply-well water might begin to be seen in less than 10 years, owing to the short residence time of water in the aquifer.

Connecticut↗
USGS2025

Grfin Tools—User guide and methods for modeling landslide runout and debris-flow growth and inundation

The software package, Grfin Tools, can estimate potential runout from landslides or inundation from geophysical mass flows such as debris flows, lahars from volcanoes, and rock avalanches within a digital elevation model (DEM). Grfin is an acronym of gr owth + f low + in undation. The tools within this package apply simple, well-tested, empirical models of runout that are computationally efficient and require minimal parameters. These tools can be used individually (for example, to estimate debris-flow inundation) or in combination to represent a more complete series of linked processes, from landslide source areas, to unchannelized transport, to channelized flows. Grfin Tools can rapidly assess potential runout and inundation over large areas and the results are readily visualized in a geographic information system. Tools for assessing areas affected by runout and flow inundation include a height-to-length ( H / L ) ratio, angle-of-reach approach for estimating open-slope, unchannelized landslide runout, and volume-area scaling relations for assessing flow inundation in channels. Potential landslide areas that constitute the sources of runout or inundation can be delineated with topographic features, such as slope and (or) curvature, derived by the software package, or by employing potential sources derived from other landslide susceptibility models. Grfin Tools also has the capability to assess inundation from flows that grow volumetrically downstream. This is a vital feature, as larger flows commonly result in longer runout and larger inundation. The software uses empirically derived growth factors applied over upslope contributing source areas or upstream channel lengths to integrate the effects of various growth processes, such as channel entrainment, streambank failures, adjacent landslides, and hillslope erosion. Inundation follows a drainage network defined with a separate tool that uses topographic curvature to identify channel initiation locations. This document includes information on using Grfin Tools, the basis and methods underlying the tools and models, detailed descriptions of the software input and output files, and tips for handling special conditions such as roads and large water bodies. Multiple detailed examples illustrating different applications are also presented. Grfin Tools relies on the freely available TauDEM software package (Tarboton, 2005). The Grfin Tools software release is available from Cronkite-Ratcliff and others (2025).

Techniques and Methods↗
USGS1987

Shore erosion as a sediment source to the tidal Potomac River, Maryland and Virginia

The shoreline of the tidal Potomac River attained its present form as a result of the Holocene episode of sea-level rise; the drowned margins of the system are modified by wave activity in the shore zone and by slope processes on banks steepened by basal-wave erosion. Shore erosion leaves residual sand and gravel in shallow water and transports silt and clay offshore to form a measurable component of the suspended-sediment load of the tidal Potomac River. Erosion rates were measured by comparing digitized historical shoreline maps and modern maps, and by comparing stereopairs of aerial photographs taken at different points in time, with the aid of an interactive computer-graphics system and a digitizing stereoplotter. Cartographic comparisons encompassed 90 percent of the study reach and spanned periods of 38 to 109 years, with most measurements spanning at least 84 years. Photogrammetric comparisons encompassed 49 percent of the study reach and spanned 16 to 40 years. Field monitoring of erosion rates and processes at two sites, Swan Point Neck, Maryland, and Mason Neck, Virginia, spanned periods of 10 to 18 months. Estimated average recession rates of shoreline in the estuary, based on cartographic and photogrammetric measurements, were 0.42 to 0.52 meter per annum (Virginia shore) and 0.31 to 0.41 meter per annum (Maryland shore). Average recession rates of shoreline in the tidal river and transition zone were close to 0.15 meter per annum. Estimated average volume-erosion rates along the estuary were 1.20 to 1.87 cubic meters per meter of shoreline per annum (Virginia shore) and 0.56 to 0.73 cubic meter per meter of shoreline per annum (Maryland shore); estimated average volume-erosion rates along the shores of the tidal river and transition zone were 0.55 to 0.74 cubic meter per meter of shoreline per annum. Estimated total sediment contributed to the tidal Potomac River by shore erosion was 0.375 x 10 6 to 0.565 x 10 6 metric tons per annum; of this, the estimated amount of silt and clay ranged from 0.153x10 6 to 0.226x10 6 metric tons per annum. Between 49 and 60 percent of the sediment was derived from the Virginia shore of the estuary; 14 to 18 percent was derived from the Maryland shore of the estuary; and 23 to 36 percent was derived from the shores of the tidal river and transition zone. The adjusted modern estimate of sediment eroded from the shoreline of the estuary is about 55 percent of the historical estimate. Sediment eroded from the shoreline accounted for about 6 to 9 percent of the estimated total suspended load for the tidal Potomac River during water years 1979 through 1981 and for about 11 to 18 percent of the suspended load delivered to the estuary during the same period. Annual suspended-sediment loads derived from upland source areas fluctuated by about an order of magnitude during the 3 years of record (1979-81); shore erosion may have been a more important component of the sediment budget during periods of low flow than during periods of higher discharges. Prior to massive land clearance during the historical period of intensive agriculture in the 18th and 19th centuries, annual sediment loads from upland sources probably were smaller than they are at present; under these circumstances shore erosion would have been an important component of the sediment budget. At current rates of sediment supply, relative sea-level rise, and shoreline recession, the landward parts of the tidal Potomac River are rapidly being filled by sediment. If these rates were to remain constant over time, and no sediment were to escape into Chesapeake Bay, the tidal river and transition zone would be filled within 600 years, and the total system would be filled in less than 4,000 years. Given a slower rate of sediment supply, comparable to the measured rate during the low-flow 1981 water year, the volume of the tidal Potomac River might remain relatively stable or even increase over time. Changes in rates

Water Supply Paper↗
USGS2021

Cimarron River alluvial aquifer hydrogeologic framework, water budget, and implications for future water availability in the Pawnee Nation Tribal jurisdictional area, Payne County, Oklahoma, 2016–18

The Cimarron River is a free-flowing river and is a major source of water as it flows across Oklahoma. Increased demand for water resources within the Cimarron River alluvial aquifer in north-central Oklahoma (primarily in Payne County) has led to increases in groundwater withdrawals for agriculture, public, irrigation, industrial, and domestic supply purposes. The Pawnee Nation of Oklahoma (Pawnee Nation) is particularly concerned about the sustainability of the Cimarron River alluvial aquifer and whether the aquifer will continue to be a viable water resource for future generations of Tribal members and residents. To better understand current (2021) water resources and possible future water availability in the Pawnee Nation Tribal jurisdictional area, the U.S. Geological Survey, in cooperation with the Bureau of Indian Affairs and the Pawnee Nation of Oklahoma, compiled available hydrogeologic data and developed conceptual and numerical groundwater-flow models for the Cimarron River alluvial aquifer in Payne County, north-central Oklahoma, including a focus area in the Pawnee Nation Tribal jurisdictional area for the 2016–18 study period. A conceptual water budget was created to establish estimates of groundwater fluxes into and out of the aquifer through hydrologic boundaries and groundwater withdrawals for use in the numerical groundwater-flow model. The conceptual water budget focuses on the alluvial aquifer, meaning that inflows include sources of water to the aquifer and that outflows include sources of water out of the aquifer, such as base-flow contributions to the Cimarron River. The conceptual water budget was constructed by using data from 2017 (the most complete year of record for each data type included in the model) for the Pawnee Nation subdomain of the Cimarron River alluvial aquifer model extent (Pawnee Nation subdomain). Groundwater withdrawals were estimated from groundwater-withdrawal rate information for permanent and temporary permitted wells that was obtained from the Oklahoma Water Resources Board. One-half of each annual permitted groundwater-withdrawal rate allotted was used as the estimated annual groundwater-withdrawal amount. Halving the permitted groundwater-withdrawal rate was done because permitted withdrawal rates are the maximum permitted rate and actual groundwater withdrawals are generally appreciably lower than the maximum permitted rate. Total groundwater withdrawals were estimated as 1,300 acre-feet per year for the Pawnee Nation subdomain. Various hydrogeologic data were measured to assist with model development, including depth to bedrock and water-table altitude data. In support of the model development, analyses pertaining to groundwater flow, groundwater/surface-water interactions, base flows in the Cimarron River, and lithological interpretations in the Pawnee Nation Tribal jurisdictional area were used to compute a conceptual water budget applicable to the 2016–18 study period. A numerical groundwater-flow model was developed using the hydrogeologic framework of the Cimarron River alluvial aquifer and the conceptual water budget. The numerical model consists of a single layer representing alluvium and terrace deposits within the alluvial aquifer model area. Hydraulic conductivities were estimated and modeled for the alluvium and terrace deposits in the alluvial aquifer. Base-flow values were estimated using the base-flow index from streamflow data collected at U.S. Geological Survey streamgages. Stream seepage values were derived from the mean 2017 base-flow index between certain streamgages. Hydraulic conductivities were specified an initial (before calibration) value of 120 feet per day for the alluvium deposits and 16 feet per day for the terrace deposits. The simulated inflows in the numerical groundwater-flow model of the Pawnee Nation subdomain were higher than the inflows of conceptual water budget, and the simulated outflows were lower than the outflows of the conceptual water budget. Overall, simulated base flows matched closely to observed base flows for the 2016 and 2017 stress periods. Simulated streamflow tended to match better with the observed streamflow for 2017, which was the period with the most data for the Cimarron River alluvial aquifer model. Streamflow capture analysis was applied to the steady-state simulation to identify areas of the aquifer where base flows in the Cimarron River were most sensitive to groundwater withdrawals. The initial base-flow value was assigned the value obtained from streamflow-routing software used to simulate stream outflow for the calibrated steady-state base model. Subsequent simulations were run in each active cell in the Pawnee Nation subdomain for a specified groundwater-withdrawal rate of 180,000 cubic feet per day. The study area that includes the Pawnee Nation subdomain is in the upper Arkansas River Basin. A groundwater-withdrawal rate of 180,000 cubic feet per second per day represents a 34 percent increase compared to the highest permitted groundwater-withdrawal rate for the study area, which corresponds to the estimated 34 percent increase in groundwater withdrawals predicted by 2060 for the upper Arkansas River Basin. Simulated streamflow capture was highest in the alluvium deposits adjacent to the Cimarron River; that is, base flow in the Cimarron River decreased the most for simulated groundwater withdrawals in the alluvium deposits adjacent to the Cimarron River. Streamflow capture increased as the distance of a well from the Cimarron River decreased in the simulation. The northeastern part of the Pawnee Nation subdomain showed greater streamflow capture in a broader area; streamflow in that part of the Pawnee Nation subdomain is likely more sensitive to groundwater withdrawals compared to other parts of the Pawnee Nation subdomain.

Oklahoma↗
USGS2005

Water-quality assessment of Lake Houston near Houston, Texas, 2000-2004

Lake Houston is a major source of public water supply and recreational resource for the Houston metropolitan area, Texas. Water-quality issues of potential concern for the lake have included nutrient enrichment (orthophosphorus, total phosphorus, nitrite plus nitrate) and aquatic life use (dissolved oxygen). The , in cooperation with the City of Houston, collected water samples from three sites in Lake Houston and from two streams that discharge to the lake during 2000–2004. Nitrogen compounds, phosphorus, suspended sediment, organic carbon, turbidity, chlorophyll-a, and selected pesticide compounds in water were assessed for all sites. Waterquality conditions of the lake and inflow streams were assessed, and loads and yields were computed for selected constituents in the streams. Selected constituents from samples collected in Lake Houston during 1990–2004 were tested for trends. The three sites sampled in Lake Houston characterized water available to the City of Houston pumping station (site AC), water entering the lake from the largely rural eastern subbasin (site EC), and water entering the lake from the more urbanized, western subbasin (site FC). Most constituent concentrations were largest at site FC, smallest at site EC, and intermediate at site AC. Organic nitrogen was the dominant form of nitrogen in samples collected at all sites. Nitrite plus nitrate concentrations were largest at site FC. Total phosphorus concentrations in all samples were larger than that recommended by the U.S. Environmental Protection Agency to limit aquatic growth in reservoirs. There was a wide range in suspended-sediment concentrations and turbidity in the lake. Twelve pesticides were detected. Atrazine and its breakdown product, 2-chloro-4-isopropylamino-6-amino-s-triazine (CIAT), were the most commonly detected pesticides; concentrations of atrazine were larger than the U.S. Environmental Protection Agency maximum contaminant level of 3.0 micrograms per liter in two samples at site FC. The relative contributions to the water quality of Lake Houston from the eastern and western subbasins were examined by collecting water samples in Cypress Creek and East Fork San Jacinto River. Nitrate and pesticide concentrations were larger in Cypress Creek than in East Fork San Jacinto River. In Cypress Creek, nitrate was the primary form of nitrogen at low flows. Atrazine exceeded 3.0 micrograms per liter in three of 17 samples, with the maximum measured concentration of 21.3 micrograms per liter. In East Fork San Jacinto River, organic nitrogen was the primary form of nitrogen. Atrazine was detected in six of 15 samples. The maximum atrazine concentration was 0.233 microgram per liter. Constituent yields allowed direct comparison of loads from Cypress Creek and East Fork San Jacinto River. In Cypress Creek, storm yields of nitrite plus nitrate nitrogen for high flows ranged from 8 to 45 pounds per square mile per day; in East Fork San Jacinto River, the maximum storm yield for high flows was 1.47 pounds per square mile per day. At low flows, the median daily yield of dissolved phosphorus from Cypress Creek was 84 times larger than the median daily yield from East Fork San Jacinto River; at high flows, it was 16 times larger. At high flows, the maximum daily yield of atrazine from Cypress Creek was 460 times larger than the maximum daily yield at high flows from East Fork San Jacinto River. The concentrations of most constituents at Lake Houston sites showed no trend during 1990–2004; however, significant trends overall or for particular seasons, or both, were detected at some sites for nitrite plus nitrate, dissolved phosphorus, dissolved organic carbon, chlorophyll-a, and diazinon (2000–2004 data only for diazinon).

Texas↗
USGS2016

Controls on the geochemical evolution of Prairie Pothole Region lakes and wetlands over decadal time scales

One hundred sixty-seven Prairie Pothole lakes, ponds and wetlands (largely lakes) previously analyzed chemically during the late 1960’s and early to mid-1970’s were resampled and reanalyzed in 2011–2012. The two sampling periods differed climatically. The earlier sampling took place during normal to slightly dry conditions, whereas the latter occurred during and immediately following exceptionally wet conditions. As reported previously in Mushet et al. ( 2015 ), the dominant effect was expansion of the area of these lakes and dilution of their major ions. However, within that context, there were significant differences in the evolutionary pathways of major ions. To establish these pathways, we employed the inverse modeling computer code NetpathXL. This code takes the initial and final lake composition and, using mass balance constrained by the composition of diluting waters, and input and output of phases, calculates plausible geochemical evolution pathways. Despite the fact that in most cases major ions decreased, a subset of the lakes had an increase in SO 4 2− . This distinction is significant because SO 4 2− is the dominant anion in a majority of Prairie Pothole Region wetlands and lakes. For lakes with decreasing SO 4 2− , the proportion of original lake water required for mass balance was subordinate to rainwater and/or overland flow. In contrast, lakes with increasing SO 4 2− between the two sampling episodes tended to be dominated by original lake water. This suite of lakes tended to be smaller and have lower initial SO 4 2− concentrations such that inputs of sulfur from dissolution of the minerals gypsum or pyrite had a significant impact on the final sulfur concentration given the lower dilution factors. Thus, our study provides context for how Prairie Pothole Region water bodies evolve geochemically as climate changes. Because wetland geochemistry in turn controls the ecology of these water bodies, this research contributes to the prediction of the impact of climate change on this important complex of ecosystems.

North Dakota↗
USGS1975

Earthquake shaking and damage to buildings

Ground shaking close to the causative fault of an earthquake is more intense than it was previously believed to be. This raises the possibility that large numbers of buildings and other structures are not sufficiently resistant for the intense levels of shaking that can occur close to the fault. Many structures were built before earthquake codes were adopted; others were built according to codes formulated when less was known about the intensity of near-fault shaking. Although many building types are more resistant than conventional design analyses imply, the margin of safety is difficult to quantify. Many modern structures, such as freeways, have not been subjected to and tested by near-fault shaking in major earthquakes (magnitude 7 or greater). Damage patterns in recent moderate-sized earthquakes occurring in or adjacent to urbanized areas, however, indicate that many structures, including some modern ones designed to meet earthquake code requirements, cannot withstand the severe shaking that can occur close to a fault. It is necessary to review the ground motion assumed and the methods utilized in the design of important existing structures and, if necessary, to strengthen or modify the use of structures that are found to be weak. New structures situated close to active faults should be designed on the basis of ground motion estimates greater than those used in the past. The ultimate balance between risk of earthquake losses and cost for both remedial strengthening and improved earthquake-resistant construction must be decided by the public. Scientists and engineers must inform the public about earthquake shaking and its effect on structures. The exposure to damage from seismic shaking is steadily increasing because of continuing urbanization and the increasing complexity of lifeline systems, such as power, water, transportation, and communication systems. In the near future we should expect additional painful examples of the damage potential of moderate-sized earthquakes in urban areas. Over a longer time span, however, we can significantly reduce the risk to life and property from seismic shaking through better land utilization, improved building codes and construction practices, and at least the gradual replacement of poor buildings by more resistant buildings. Progress toward reducing risk from seismic shaking through better building design is slowed by deficiencies in our knowledge about the nature of damaging ground motion and the failure mechanisms in structures. For example, lacking observational data, seismologists must rely on simplified theoretical and numerical models of the earthquake process to estimate near-fault ground motion, especially for earthquakes as large as magnitude 7 and 8. Because such models have not been adequately tested against data, their reliability is unknown. Engineers lack detailed information about failure processes in structures during an earthquake. Although many structures have been instrumented to measure their response to an earthquake, few records have been obtained from buildings that actually sustained significant structural damage and few structures are properly instrumented to measure all the modes of deformation that are likely to contribute to failure. Moreover, the fact that many structures have withstood ground motion more intense than that assumed in their design indicates that conventional methods of design do not take into account important contributions to earthquake resistance by nonstructural elements and by the ability of structural elements to deform inelastically without necessarily causing failure of the structure. It is fortunate when such reserve resistance exists, but better understanding of the sources of reserve strength is needed to determine how large a margin of safety they confer and how they might be affected by changes in construction practices and materials with time. In the next few years we look forward to significant advances in knowledge and to more effective application of what is already known, largely because of substantial funding of research related to seismic engineering by the National Science Foundation . The increasing number of strong-motion seismographs operating in seismically active regions will likely provide for the first time a number of records of damaging levels of ground motion. Significant effort is being directed toward obtaining near-fault records, although many probable sites of future large earthquakes remain inadequately instrumented, especially outside the conterminous United States. New and more complete information on building response and damage mechanisms will be obtained by improved instrumentation of structures and through laboratory investigations of failure in structures and structural elements. Further developments in computer technology and in computer modeling techniques will permit more realistic simulations of the seismic response of soils and structures that take into account their inelastic behavior and their strain-dependent properties. Earthquake design codes will continually be revised to better utilize existing knowledge concerning the nature of strong ground motion and the dynamic behavior of buildings during earthquakes and to incorporate new knowledge and also experiences gained from future earthquakes. We believe that application of new knowledge, improvements in earthquake-resistant design and construction, and remedial strengthening or replacement of weak existing structures can significantly reduce our current level of exposure to earthquake hazards.

Science↗
USGS1979

Magnitudes, nature, and effects of point and nonpoint discharges in the Chattahoochee River Basin, Atlanta to West Point Dam, Georgia

During the period April 1975 to June 1978, the U.S. Geological Survey conducted a river-quality assessment of the Upper Chattahoochee River basin in Georgia. One objective of the study was to assess the magnitudes, nature, and effects of point and non-point discharges in the Chattahoochee River basin from Atlanta to the West Point Dam. On an average annual basis and during the storm period of March 1215, 1976, non-point-source loads for most constituents analyzed were larger than point-source loads at the Whitesburg station, located on the Chattahoochee River about 40 river miles downstream of Atlanta. Most of the non-point-source constituent loads in the Atlanta-to-Whitesburg reach were from urban areas. Average annual point-source discharges accounted for about 50 percent of the dissolved nitrogen, total nitrogen, and total phosphorus loads, and about 70 percent of the dissolved phosphorus loads at Whitesburg. During weekends, power generation at the upstream Buford Dam hydroelectric facility is minimal. Streamflow at the Atlanta station during dry-weather weekends is estimated to be about 1,200 ft3/s (cubic feet per second). Average daily dissolved-oxygen concentrations of less than 5.0 mg/L (milligrams per liter) occurred often in the river, about 20 river miles downstream from Atlanta during these periods from May to November. During a low-flow period, June 1-2, 1977, five municipal point sources contributed 63 percent of the ultimate biochemical oxygen demand, 97 percent of the ammonium nitrogen, 78 percent of the total nitrogen, and 90 percent of the total phosphorus loads at the Franklin station, at the upstream end of West Point Lake. Average daily concentrations of 13 mg/L of ultimate biochemical oxygen demand and 1.8 mg/L of ammonium nitrogen were observed about 2 river miles downstream from two of the municipal point sources. Carbonaceous and nitrogenous oxygen demands caused dissolved-oxygen concentrations between 4.1 and 5.0 mg/L to occur in a 22-mile reach of the river downstream from Atlanta. Nitrogenous oxygen demands were greater than carbonaceous oxygen demands in the reach from river mile 303 to 271, and carbonaceous demands were greater from river mile 271 to 235. The heat load from the Atkinson-McDonough thermoelectric power-plants caused a decrease in the dissolved-oxygen concentrations of about 0.2 mg/L. During a critical low-flow period, a streamflow at Atlanta of about 1,800 ft3/s, with present (1977) point-source flows of 185 ft3/s containing concentrations of 45 mg/L of ultimate biochemical oxygen demand and 15 mg/L of ammonium nitrogen, results in a computed minimum dissolved-oxygen concentration of 4.7 mg/L in the river downstream from Atlanta. In the year 2000, a streamflow at Atlanta of about 1,800 ft3/s with point-source flows of 373 ft3/s containing concentrations of 45 mg/L of ultimate biochemical oxygen demand and 5.0 mg/L of ammonium nitrogen, will result in a computed minimum dissolved-oxygen concentration of 5.0 mg/L. A streamflow of about 1,050 ft3/s at Atlanta in the year 2000 will result in a dissolved-oxygen concentration of 5.0 mg/L if point-source flows contain concentrations of 15 mg/L of ultimate biochemical oxygen demand and 5.0 mg/L of ammonium nitrogen. Phytoplankton concentrations in West Point Lake, about 70 river miles downstream from Atlanta, could exceed 3 million cells per milliliter during extended low-flow periods in the summer with present point- and non-point-source nitrogen and phosphorus loads. In the year 2000, phytoplankton concentrations in West Point Lake are not likely to exceed 700,000 cells per milliliter during extended low-flow periods in the summer, if phosphorus concentrations do not exceed 1.0 mg/L in point-source discharges.

Georgia↗
USGS2019

On the portability of ML-MC as a depth discriminant for small seismic events recorded at local distances

In this paper we show that M L -M C is a viable and regionally portable depth discriminant and therefore may contribute in nuclear test ban treaty verification. A recent study found that the difference between local magnitude (M L ) and coda duration magnitude (M C ) discriminates shallow seismic events (mining blasts, mining-induced earthquakes, and shallow tectonic earthquakes) from deeper tectonic earthquakes in the Utah region. The shallow seismic events had anomalously high M C values, with increasingly negative M L -M C values as depth decreased. Here we evaluate the performance of M L -M C as a depth discriminant in three new regions, finding that M L -M C increases between 0–9 km depth in all cases. Initially, we investigated M L -M C as a function of depth for naturally occurring earthquakes in the region around Yellowstone National Park, as recorded by the University of Utah Seismograph Stations. For 3,358 Yellowstone earthquakes with well-constrained depths, we found M L -M C increased 0.030 ± 0.007 magnitude units (m.u.) for each 1 km increase in depth up to 10 km depth. Next, we examined M L -M C values for anthropogenic seismicity in northern Oklahoma and southern Kansas, as recorded by the National Earthquake Information Center. For 1,628 events with well-constrained depths, we computed a slope for M L -M C of 0.022 ± 0.010 m.u./km. Finally, we analyzed M L -M C for 28,722 well-located earthquakes in Italy, as recorded by the National Institute of Geophysics and Volcanology, and found an M L -M C slope of 0.018 ± 0.001 m.u./km. In each case, the quoted error bounds represent 95% confidence regions which exclude zero, implying that the depth-dependence of M L -M C is statistically significant. We performed several robustness tests in which we varied the criterion used to define a well-constrained depth and the depth range used in the linear fit. In nearly all cases, we found a positive slope for M L -M C vs. depth at a confidence level above 95%.

Utah, Montana, Idaho, Wyoming, Kansas, Oklahoma↗
USGS2013

A regional classification of the effectiveness of depressional wetlands at mitigating nitrogen transport to surface waters in the Northern Atlantic Coastal Plain

Nitrogen from nonpoint sources contributes to eutrophication, hypoxia, and related ecological degradation in Atlantic Coastal Plain streams and adjacent coastal estuaries such as Chesapeake Bay and Pamlico Sound. Although denitrification in depressional (non-riparian) wetlands common to the Coastal Plain can be a significant landscape sink for nitrogen, the effectiveness of individual wetlands at removing nitrogen varies substantially due to varying hydrogeologic, geochemical, and other landscape conditions, which are often poorly or inconsistently mapped over large areas. A geographic model describing the spatial variability in the likely effectiveness of depressional wetlands in watershed uplands at mitigating nitrogen transport from nonpoint sources to surface waters was constructed for the Northern Atlantic Coastal Plain (NACP), from North Carolina through New Jersey. Geographic and statistical techniques were used to develop the model. Available medium-resolution (1:100,000-scale) stream hydrography was used to define 33,799 individual watershed catchments in the study area. Sixteen landscape metrics relevant to the occurrence of depressional wetlands and their effectiveness as nitrogen sinks were defined for each catchment, based primarily on available topographic and soils data. Cluster analysis was used to aggregate the 33,799 catchments into eight wetland landscape regions (WLRs) based on the value of three principal components computed for the 16 original landscape metrics. Significant differences in topography, soil, and land cover among the eight WLRs demonstrate the effectiveness of the clustering technique. Results were used to interpret the relative likelihood of depressional wetlands in each WLR and their likely effectiveness at mitigating nitrogen transport from upland source areas to surface waters. The potential effectiveness of depressional wetlands at mitigating nitrogen transport varies substantially over different parts of the NACP. Depressional wetlands are common in three WLRs covering 32 percent of the area, and have a relatively high potential to mitigate nitrogen transport from nonpoint sources. Conversely, 37 percent of the study area includes rolling hills with relatively high slope and relief, and little likelihood of depressional wetlands. The remainder of the Coastal Plain includes relatively flat watersheds with moderate to low relative likelihood of nitrogen mitigation. The delineation of WLRs in this model should be useful for targeting wetland conservation or restoration efforts, and for estimating the effects of depressional wetlands on the regional nitrogen budget, but should be considered in light of limitations and assumptions inherent in the model.

Scientific Investigations Report↗
USGS1997

Changes in bottom-surface elevations in three reservoirs on the lower Susquehanna River, Pennsylvania and Maryland, following the January 1996 flood — Implications for nutrient and sediment loads to Chesapeake Bay

The Susquehanna River drains about 27,510 square miles in New York, Pennsylvania, and Maryland, contributes nearly 50 percent of the freshwater discharge to the Chesapeake Bay, and contributes nearly 66 percent of the annual nitrogen load, 40 percent of the phosphorus load, and 25 percent of the suspended-sediment load from non-tidal parts of the Bay during a year of average streamflow. A reservoir system formed by three hydroelectric dams on the lower Susquehanna River is currently trapping a major part of the phosphorus and suspended-sediment loads from the basin and, to a lesser extent, the nitrogen loads. In the summer of 1996, the U. S. Geological Survey collected bathymetric data along 64 cross sections and 40 bottom-sediment samples along 14 selected cross sections in the lower Susquehanna River reservoir system to determine the remaining sediment-storage capacity, refine the current estimate of when the system may reach sediment-storage capacity, document changes in the reservoir system after the January 1996 flood, and determine the remaining nutrient mass in Conowingo Reservoir. Results from the 1996 survey indicate an estimated total of 14,800,000 tons of sediment were scoured from the reservoir system from 1993 (date of previous bathymetric survey) through 1996. This includes the net sediment change of 4,700,000 tons based on volume change in the reservoir system computed from the 1993 and 1996 surveys, the 6,900,000 tons of sediment deposited from 1993 through 1996, and the 3,200,000 tons of sediment transported into the reservoir system during the January 1996 flood. The January 1996 flood, which exceeded a 100-year recurrence interval, scoured about the same amount of sediment that normally would be deposited in the reservoir system during a 4- to 6-year period. Concentrations of total nitrogen in bottom sediments in the Conowingo Reservoir ranged from 1,500 to 6,900 mg/kg (milligrams per kilogram); 75 percent of the concentrations were between 3,000 and 5,000 mg/kg. About 96 percent of the concentrations of total nitrogen consisted of organic nitrogen. Concentrations of total phosphorus in bottom sediments ranged from 286 to 1,390 mg/kg. About 84 percent of the concentrations of total phosphorus were comprised of inorganic phosphorus. The ratio of concentrations of plant-available phosphorus to concentrations of total phosphorus ranged from 0.6 to 3.5 percent; ratios generally decreased in a downstream direction. About 29,000 acre-feet, or 42,000,000 tons, of sediment can be deposited before Conowingo Reservoir reaches sediment-storage capacity. Assuming the average annual sediment-deposition rate remains unchanged and no scour occurs due to floods, the reservoir system could reach sediment-storage capacity in about 17 years. The reservoir system currently is trapping about 2 percent of the nitrogen, 45 percent of the phosphorus, and 70 percent of the suspended sediment transported by the river to the upper Chesapeake Bay. Once the reservoir reaches sediment-storage capacity, an estimated 250-percent increase in the current annual loads of suspended sediment, a 2-percent increase in the current annual loads of total nitrogen, and a 70-percent increase in the current annual loads of total phosphorus from the Susquehanna River to Chesapeake Bay can be expected. If the goal of a 40-percent reduction in controllable phosphorus load from the Susquehanna River Basin is met before the reservoirs reach sediment-storage capacity, the 40-percent reduction goal will probably be exceeded when the reservoir system reaches sediment-storage capacity.

Maryland, Pennsylvania↗
USGS1985

Environmental systems and management activities on the Kennedy Space Center, Merritt Island, Florida: results of a modeling workshop

In the early 1960's, the National Aeronautics and Space Administration (NASA) began purchasing 140,000 acres on Merritt Island, Florida, in order to develop a center for space exploration. Most of this land was acquired to provide a safety and security buffer around NASA facilities. NASA, as the managing agency for the Kennedy Space Center (KSC), is responsible for preventing or controlling environmental pollution from the Federal facilities and activities at the Space Center and is committed to use all practicable means to protect and enhance the quality of the surrounding environment. The Merritt Island National Wildlife Refuge was established in 1963 when management authority for undeveloped lands at KSC was transferred to the U.S. Fish and Wildlife Service. In addition to manage for 11 Federally-listed threatened and endangered species and other resident and migratory fish and wildlife populations, the Refuge has comanagement responsibility for 19,000 acres of mosquito control impoundments and 2,500 acres of citrus groves. The Canaveral National Seashore was developed in 1975 when management of a portion of the coastal lands was transferred from NASA to the National Park Service. This multiagency jurisdiction on Merritt Island has resulted in a complex management environment. The modeling workshop described in this report was conducted May 21-25, 1984, at the Kennedy Space Center to: (1) enhance communication among the agencies with management responsibilities on Merritt Island; (2) integrate available information concerning the development, management, and ecology of Merritt Island; and (3) identify key research and monitoring needs associated with the management and use of the island's resources. The workshop was structured around the formulation of a model that would simulate primary management and use activities on Merritt Island and their effects on upland, impoundment, and estuarine vegetation and associated wildlife. The simulation model is composed of four connected submodels. The Uplands submodel calculates changes in acres and structural components of vegetation communities resulting from succession, fire, facilities development, and shuttle launch depositions, as well as the quantity and quality of surface runoff and aquifer input to an impoundment and an estuary. The Impoundment submodel next determines water quality and quantity and changes in vegetation resulting from water level manipulation and prescribed burning. The Estuary submodel than determines water quality parameters and acres of seagrass beds. Finally, the Wildlife submodel calculates habitat suitability indices for key species of interest, based on vegetation conditions in the uplands and impoundments and on several hydrologic parameters. The model represents a hypothetical management unit with 2,500 acres of uplands, a 600-acre impoundment, and a 1,500-acre section of estuary. Two management scenarios were run to analyze model behavior. The scenarios differ in the frequency of shuttle launches and prescribed burning, the extent of facilities development, the amount of land disposed waste material applied, and the nature and timing of impoundment water level control. Early in a model development project, the process of building the model is usually of greater benefit than the model itself. The model building process stimulates interaction among agencies, assists in integrating existing information, and helps identify research needs. These benefits usually accrue even in the absence of real predictive power in the resulting model. Open communication occurs among the Federal, State, and local agencies involved with activities on Merritt Island and the agencies have a cooperative working relationship. The workshop provided an opportunity for all of these agencies to meet at one time and have focused discussions on the key environmental and multiagency resource management issues. The workshop framework helped to integrate information and assumptions from a number of disciplines and agencies. This integration occurred in the computer simulation model and among workshop participants as submodel linkages were developed and scenario results discussed. A number of research needs were identified at the workshop during the model building and testing exercises and associated discussions. These needs were based on the informed judgement of researchers and managers familiar with Merritt Island or similar areas, rather than on a comprehensive literature review of sensitivity analysis of the preliminary model developed at the workshop. Some of the needs can be addressed by interpreting the results of completed studies from similar geographic areas as they relate to Merritt Island, while other will require additional research studies on Merritt Island. Major research needs associated with the Upland submodel include behavior of the near-surface aquifer, factors limiting slash pine regeneration, frequency and effects of natural fire on various cover types, cumulative effects of shuttle launches, and fate in upland soils of nitrogen and phosphorous from land applied waste material. Key Impoundment submodel needs include documentation of vegetation changes in response to altered water depth, salinity, and nutrient concentrations and better specification of the functional characteristics of impoundments as chemical filters. Important information gaps identified in the Estuary submodel include a more complete analysis of factors contributing to phytoplankton abundance, evaluation of sources of turbidity other than phytoplankton, and identification and quantification of factors limiting seagrass distribution. Primary research needs associated with the Wildlife submodel include a survey of breeding habitat, production data, and harvest data for mottled ducks; data on the emigration and immigration of juvenile mullet (and other transient fish) in the impoundment; the contribution of various seagrasses to habitat requirements of sea trout; and the effects of dissolved oxygen on survival of juvenile sea trout. Ideally, the modeling workshop process is iterative in nature. Periods between workshops are used for research, data collection, and model refinement. Each workshop integrates information collected since the last workshop and produces a more credible model that is more useful in evaluating management alternatives. Participants felt that continued application of this process would help provide ongoing integration and communication among agencies and would allow each agency's planning and management activities to be viewed within the context of an overall assessment.

Report↗
USGS2008

Geolocation of man-made reservoirs across terrains of varying complexity using GIS

The Reservoir Sedimentation Survey Information System (RESIS) is one of the world's most comprehensive databases of reservoir sedimentation rates, comprising nearly 6000 surveys for 1819 reservoirs across the continental United States. Sediment surveys in the database date from 1904 to 1999, though more than 95% of surveys were entered prior to 1980, making RESIS largely a historical database. The use of this database for large-scale studies has been limited by the lack of precise coordinates for the reservoirs. Many of the reservoirs are relatively small structures and do not appear on current USGS topographic maps. Others have been renamed or have only approximate (i.e. township and range) coordinates. This paper presents a method scripted in ESRI's ARC Macro Language (AML) to locate the reservoirs on digital elevation models using information available in RESIS. The script also delineates the contributing watersheds and compiles several hydrologically important parameters for each reservoir. Evaluation of the method indicates that, for watersheds larger than 5 km2, the correct outlet is identified over 80% of the time. The importance of identifying the watershed outlet correctly depends on the application. Our intent is to collect spatial data for watersheds across the continental United States and describe the land use, soils, and topography for each reservoir's watershed. Because of local landscape similarity in these properties, we show that choosing the incorrect watershed does not necessarily mean that the watershed characteristics will be misrepresented. We present a measure termed terrain complexity and examine its relationship to geolocation success rate and its influence on the similarity of nearby watersheds. ?? 2008 Elsevier Ltd. All rights reserved.

Computers & Geosciences↗
USGS2005

Estimating the magnitude and frequency of floods for streams in west-central Florida, 2001

Flood discharges were estimated for recurrence intervals of 2, 5, 10, 25, 50, 100, 200, and 500 years for 94 streamflow stations in west-central Florida. Most of the stations are located within the 10,000 square-mile, 16-county area that forms the Southwest Florida Water Management District. All stations had at least 10 years of homogeneous record, and none have flood discharges that are significantly affected by regulation or urbanization. Guidelines established by the U.S. Water Resources Council in Bulletin 17B were used to estimate flood discharges from gaging station records. Multiple linear regression analysis was then used to mathematically relate estimates of flood discharge for selected recurrence intervals to explanatory basin characteristics. Contributing drainage area, channel slope, and the percent of total drainage area covered by lakes (percent lake area) were the basin characteristics that provided the best regression estimates. The study area was subdivided into four geographic regions to further refine the regression equations. Region 1 at the northern end of the study area includes large rivers that are characteristic of the rolling karst terrain of northern Florida. Only a small part of Region 1 lies within the boundaries of the Southwest Florida Water Management District. Contributing drainage area and percent lake area were the most statistically significant basin characteristics in Region 1; the prediction error of the regression equations varied with the recurrence interval and ranged from 57 to 69 percent. In the three other regions of the study area, contributing drainage area, channel slope, and percent lake area were the most statistically significant basin characteristics, and are the three characteristics that can be used to best estimate the magnitude and frequency of floods on most streams within the Southwest Florida Water Management District. The Withlacoochee River Basin dominates Region 2; the prediction error of the regression models in the region ranged from 65 to 68 percent. The basins that drain into the northern part of Tampa Bay and the upper reaches of the Peace River Basin are in Region 3, which had prediction errors ranging from 54 to 74 percent. Region 4, at the southern end of the study area, had prediction errors that ranged from 40 to 56 percent. Estimates of flood discharge become more accurate as longer periods of record are used for analyses; results of this study should be used in lieu of results from earlier U.S. Geological Survey studies of flood magnitude and frequency in west-central Florida. A comparison of current results with earlier studies indicates that use of a longer period of record with additional high-water events produces substantially higher flood-discharge estimates for many gaging stations. Another comparison indicates that the use of a computed, generalized skew in a previous study in 1979 tended to overestimate flood discharges.

Scientific Investigations Report↗