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USGS1994

Hydrogeologic analysis of the saturated-zone ground-water system, under Yucca Mountain, Nevada

The configuration of the southward-sloping water table under Yucca Mountain is dominated by an abrupt decline of 300 m over a distance of less than 2 km. This northeast-striking zone of large hydraulic gradient (of 0.15 or more) separates an area of moderate gradient (of about 0.015) to the north from an area of very small gradient (0.0001) to the south. The position of the large gradient does not correlate well with any evident geologic feature in the upper 0.5 km of the mountain, but we suggest that buried geologic features are present that can explain all the geohydrologic observations. The three areas of differing hydraulic gradient under Yucca Mountain are parts of hydrogeologic domains that extend more than 70 km to the northeast. On a regional basis, the moderate and very small gradients generally correspond to areas underlain by exceptionally thick Tertiary volcanic sections and a highly transmissive Paleozoic carbonate aquifer, respectively. The regional large gradient and water-table decline are spatially associated with a contact in the Paleozoic rocks between clastic rocks and carbonates. This contact marks a large abrupt drop in the effective base of the hydrologic system because it is the upgradient boundary of the deep carbonate aquifer, which has a thickness of 5 km. An aeromagnetic high follows the regional-scale domain of large gradient under northern Yucca Mountain from outcrops of a magnetite-bearing clastic confining unit to the east, indicating that the regional correlation of the steep water-table decline with the upgradient boundary of the deep carbonate aquifer may extend to Yucca Mountain. Five additional features may be related to an explanation for the large hydraulic gradient: (1) anomalously low heat flow has been measured deep in the volcanic section south of the water-table decline, suggesting underflow of cool water in the deep carbonate aquifer; (2) the lower tuff sequence, of 0.5–1 km in thickness, which underlies most of Yucca Mountain, is largely replaced in the volcanic section by lavas in the area of the large gradient; (3) an analysis of the hydrogeology of the tuff section under Yucca Mountain indicates that transmissivity in the tuffs increases to the south; (4) a northeast-trending gravity low is present immediately south of the water-table decline; (5) units in the lower part of the volcanic section are 50–100% thicker in the area of the gravity low than to the north and south. The abrupt stratigraphic thickening into the area of the gravity low indicates that the low represents a buried graben with its northern bounding fault centered beneath the abrupt water-table decline. These geologic features of the zone of large gradient under Yucca Mountain suggest two possible hydrogeologic models. First, the northern bounding fault of the buried graben may provide a highly permeable pathway (a drain) through the brittle lavas in the lower part of the volcanic section under northern Yucca Mountain. The drain would allow flow from the tuff aquifer north of the decline to be captured by the deep carbonate aquifer, resulting in the heat-flow low, the abrupt water-table decline, and the transition to a very small hydraulic gradient. Alternatively, the northern bounding fault of the buried graben may be the effective northern limit of the tuff aquifer under Yucca Mountain because the permeability in the tuffs north of the fault may have been diminished by hydrothermal alteration. In this second model, the large gradient marks the point where the small southward flow of water through the altered volcanic rocks to the north abruptly drops into the tuff aquifer. In either case, heads in the tuff aquifer in the area of very small gradient may be regulated partly by upward flow from the deep carbonate aquifer. This upward flow under southern Yucca Mountain is indicated by linear thermal highs along fault zones, by ground-water isotopic data suggesting inmixing of waters from the deep carbonate aquifer into the tuff aquifer, and by the upward hydraulic gradient found in a drill hole that penetrates the deep carbonate aquifer under southern Yucca Mountain.

Journal of Hydrology↗

USGS2025

Evaluating trends using total impervious cover as a metric for degree of urbanisation

Impervious cover (IC) is a common metric for assessing the degree of urbanisation in watersheds. However, there are different methods for determining IC, and use of IC correlation with urban watershed response to hydrologic and geochemical inputs can be strongly influenced by the end members (IC below 10% and above 40%). The resolution of the imagery (e.g., 1 m vs. 30 m) used to measure IC can influence the estimate of IC, with differences up to 15% observed between these two resolutions for 21 watersheds along the east coast of the United States. The differences are greatest in the middle range between 10% and 40% IC. When using IC for correlation with urban watershed responses such as discharge flashiness or median solute concentrations, fits with R 2 between 0.4 and 0.78 were obtained when including end members of IC from 0% to 50%. However, when trying to distinguish behaviour between urban watersheds that fall in the middle ranges of IC, these same parameters do not correlate well with IC. Correlations fail significance tests, can switch direction, and fall below an R 2 of 0.1 without the end members of very low or very high IC. Because of improved accuracy, the finest resolution is preferred when available, and mixing IC estimation methods should be avoided. Furthermore, using regressions that include end members may not contribute to differentiating how IC in the 10%–40% range impacts hydrologic and geochemical responses in urban watersheds. Understanding this middle range of IC is important for comparing urban and suburban watersheds or planning watershed development to minimise impacts.

Delaware, Georgia, Maryland, New Jersy, New York, ↗

USGS1982

Regional hydrology of the Green River-Moab area, northwestern Paradox basin, Utah

The Green River-Moab area encompasses about 7,800 square kilometers or about 25 percent of the Paradox basin. The entire Paradox basin is a part of the Colorado Plateaus that is underlain by a thick sequence of evaporite (salt) beds of Pennsylvanian age. The rock units that underlie the area have been grouped into hydrogeologic units based on their water-transmitting ability. Confining beds consist of evaporite beds of mostly salt, and over- lying and underlying thick sequences of rocks with minimal permeability; above and below these confining beds are aquifers. The upper Mesozoic sand- stone aquifer, probably is the most permeable hydrogeologic unit of the area and is the subject of this investigation. The principal component of ground- water outflow from this aquifer probably is subsurface flow to regional streams (the Green and Colorado Rivers) and is about 100 million cubic meters per year. All other components of outflow are relatively small. The average annual recharge to the aquifer is about 130 million cubic meters, of which about 20 million cubic meters is from local precipitation. For the lower aquifer, all recharge and discharge probably is by subsurface flow and was not estimated. The aquifers are generally isolated from the evaporite beds by the bounding confining beds; as a result, most ground water has little if any contact with the evaporites. Brines are present in the confining beds, but solution of beds o£ salt probably is very slow in most parts of the area. No brine discharges' have been identified.

Utah↗

USGS2010

Attributes for NHDPlus Catchments (Version 1.1) for the Conterminous United States: Average Atmospheric (Wet) Deposition of Inorganic Nitrogen, 2002

This data set represents the average atmospheric (wet) deposition, in kilograms per square kilometer, of inorganic nitrogen for the year 2002 compiled for every catchment of NHDPlus for the conterminous United States. The source data set for wet deposition was from the USGS's raster data set atmospheric (wet) deposition of inorganic nitrogen for 2002 (Gronberg, 2005). The NHDPlus Version 1.1 is an integrated suite of application-ready geospatial datasets that incorporates many of the best features of the National Hydrography Dataset (NHD) and the National Elevation Dataset (NED). The NHDPlus includes a stream network (based on the 1:100,00-scale NHD), improved networking, naming, and value-added attributes (VAAs). NHDPlus also includes elevation-derived catchments (drainage areas) produced using a drainage enforcement technique first widely used in New England, and thus referred to as "the New England Method." This technique involves "burning in" the 1:100,000-scale NHD and when available building "walls" using the National Watershed Boundary Dataset (WBD). The resulting modified digital elevation model (HydroDEM) is used to produce hydrologic derivatives that agree with the NHD and WBD. Over the past two years (2007-2008), an interdisciplinary team from the U.S. Geological Survey (USGS), and the U.S. Environmental Protection Agency (USEPA), and contractors, found that this method produces the best quality NHD catchments using an automated process (USEPA, 2007). The NHDPlus dataset is organized by 18 Production Units that cover the conterminous United States. The NHDPlus version 1.1 data are grouped by the U.S. Geologic Survey's Major River Basins (MRBs, Crawford and others, 2006). MRB1, covering the New England and Mid-Atlantic River basins, contains NHDPlus Production Units 1 and 2. MRB2, covering the South Atlantic-Gulf and Tennessee River basins, contains NHDPlus Production Units 3 and 6. MRB3, covering the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy River basins, contains NHDPlus Production Units 4, 5, 7 and 9. MRB4, covering the Missouri River basins, contains NHDPlus Production Units 10-lower and 10-upper. MRB5, covering the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf River basins, contains NHDPlus Production Units 8, 11 and 12. MRB6, covering the Rio Grande, Colorado and Great Basin River basins, contains NHDPlus Production Units 13, 14, 15 and 16. MRB7, covering the Pacific Northwest River basins, contains NHDPlus Production Unit 17. MRB8, covering California River basins, contains NHDPlus Production Unit 18.

Data Series↗

USGS2010

Attributes for NHDPlus Catchments (Version 1.1): Basin Characteristics, 2002

This data set represents basin characteristics, compiled for every catchment in NHDPlus for the conterminous United States. These characteristics are basin shape index, stream density, sinuosity, mean elevation, mean slope, and number of road-stream crossings. The source data sets are the U.S. Environmental Protection Agency's NHDPlus and the U.S. Census Bureau's TIGER/Line Files. The NHDPlus Version 1.1 is an integrated suite of application-ready geospatial datasets that incorporates many of the best features of the National Hydrography Dataset (NHD) and the National Elevation Dataset (NED). The NHDPlus includes a stream network (based on the 1:100,00-scale NHD), improved networking, naming, and value-added attributes (VAAs). NHDPlus also includes elevation-derived catchments (drainage areas) produced using a drainage enforcement technique first widely used in New England, and thus referred to as "the New England Method." This technique involves "burning in" the 1:100,000-scale NHD and when available building "walls" using the National Watershed Boundary Dataset (WBD). The resulting modified digital elevation model (HydroDEM) is used to produce hydrologic derivatives that agree with the NHD and WBD. Over the past two years, an interdisciplinary team from the U.S. Geological Survey (USGS), and the U.S. Environmental Protection Agency (USEPA), and contractors, found that this method produces the best quality NHD catchments using an automated process (USEPA, 2007). The NHDPlus dataset is organized by 18 Production Units that cover the conterminous United States. The NHDPlus version 1.1 data are grouped by the U.S. Geologic Survey's Major River Basins (MRBs, Crawford and others, 2006). MRB1, covering the New England and Mid-Atlantic River basins, contains NHDPlus Production Units 1 and 2. MRB2, covering the South Atlantic-Gulf and Tennessee River basins, contains NHDPlus Production Units 3 and 6. MRB3, covering the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy River basins, contains NHDPlus Production Units 4, 5, 7 and 9. MRB4, covering the Missouri River basins, contains NHDPlus Production Units 10-lower and 10-upper. MRB5, covering the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf River basins, contains NHDPlus Production Units 8, 11 and 12. MRB6, covering the Rio Grande, Colorado and Great Basin River basins, contains NHDPlus Production Units 13, 14, 15 and 16. MRB7, covering the Pacific Northwest River basins, contains NHDPlus Production Unit 17. MRB8, covering California River basins, contains NHDPlus Production Unit 18.

Data Series↗

USGS2013

Inorganic carbon loading as a primary driver of dissolved carbon dioxide concentrations in the lakes and reservoirs of the contiguous United States

Accurate quantification of CO 2 flux across the air-water interface and identification of the mechanisms driving CO 2 concentrations in lakes and reservoirs is critical to integrating aquatic systems into large-scale carbon budgets, and to predicting the response of these systems to changes in climate or terrestrial carbon cycling. Large-scale estimates of the role of lakes and reservoirs in the carbon cycle, however, typically must rely on aggregation of spatially and temporally inconsistent data from disparate sources. We performed a spatially comprehensive analysis of CO 2 concentration and air-water fluxes in lakes and reservoirs of the contiguous United States using large, consistent data sets, and modeled the relative contribution of inorganic and organic carbon loading to vertical CO 2 fluxes. Approximately 70% of lakes and reservoirs are supersaturated with respect to the atmosphere during the summer (June–September). Although there is considerable interregional and intraregional variability, lakes and reservoirs represent a net source of CO 2 to the atmosphere of approximately 40 Gg C d –1 during the summer. While in-lake CO 2 concentrations correlate with indicators of in-lake net ecosystem productivity, virtually no relationship exists between dissolved organic carbon and p CO 2,aq . Modeling suggests that hydrologic dissolved inorganic carbon supports p CO 2,aq in most supersaturated systems (to the extent that 12% of supersaturated systems simultaneously exhibit positive net ecosystem productivity), and also supports primary production in most CO 2 -undersaturated systems. Dissolved inorganic carbon loading appears to be an important determinant of CO 2 concentrations and fluxes across the air-water interface in the majority of lakes and reservoirs in the contiguous United States.

Global Biogeochemical Cycles↗

USGS2014

Collaborative modelling and integrated decision support system analysis of a developed terminal lake basin

A terminal lake basin in west-central Nevada, Walker Lake, has undergone drastic change over the past 90 yrs due to upstream water use for agriculture. Decreased inflows to the lake have resulted in 100 km 2 decrease in lake surface area and a total loss of fisheries due to salinization. The ecologic health of Walker Lake is of great concern as the lake is a stopover point on the Pacific route for migratory birds from within and outside the United States. Stakeholders, water institutions, and scientists have engaged in collaborative modeling and the development of a decision support system that is being used to develop and analyze management change options to restore the lake. Here we use an integrated management and hydrologic model that relies on state-of-the-art simulation capabilities to evaluate the benefits of using integrated hydrologic models as components of a decision support system. Nonlinear feedbacks among climate, surface-water and groundwater exchanges, and water use present challenges for simulating realistic outcomes associated with management change. Integrated management and hydrologic modeling provides a means of simulating benefits associated with management change in the Walker River basin where drastic changes in the hydrologic landscape have taken place over the last century. Through the collaborative modeling process, stakeholder support is increasing and possibly leading to management change options that result in reductions in Walker Lake salt concentrations, as simulated by the decision support system.

Nevada↗

USGS2021

Hydrogeomorphic recovery and temporal changes in rainfall thresholds for debris flows following wildfire

Wildfire-induced changes to soil and vegetation promote runoff-generated debris flows in steep watersheds. Postfire debris flows are most commonly observed in steep watersheds during the first wet season following a wildfire, but it is unclear how long the elevated threat of debris flow persists and why debris-flow potential changes in recovering burned areas. This work quantifies how rainfall intensity-duration (ID) thresholds for debris-flow initiation change with time since burning and provides a mechanistic explanation for these changes. We constrained a hydrologic model using field and remotely sensed measurements of soil-infiltration capacity, vegetation cover, runoff, and debris-flow activity. We applied this model to estimate rainfall ID thresholds for debris-flow initiation within three burned areas in the southwestern United States over a postfire recovery period of three to four years. Modeling suggests ID thresholds are lowest immediately following the fire (below a one-year recurrence interval [RI] storm) and increase with time, such that a 10- to 25-year RI storm would be required to generate a debris flow after three years of recovery. Modeled changes in rainfall ID thresholds result from increases in soil infiltration capacity, canopy interception, hydraulic roughness, and median grain size of sediment entrained in an incipient debris flow. The relative importance of each of these factors varied among our three sites. Results improve our ability to assess temporal changes in postfire debris-flow potential, highlight how site-specific factors may alter the persistence of postfire debris-flow hazards, and provide additional constraints on the timescale of recovery following wildfire.

Arizona, California, New Mexico↗

USGS2015

First steps of integrated spatial modeling of titanium, zirconium, and rare earth element resources within the Coastal Plain sediments of the southeastern United States

The Coastal Plain of the southeastern United States has extensive, unconsolidated sedimentary deposits that are enriched in heavy minerals containing titanium, zirconium, and rare earth element resources. Areas favorable for exploration and development of these resources are being identified by geochemical data, which are supplemented with geological, geophysical, hydrological, and geographical data. The first steps of this analysis have been completed. The concentrations of lanthanum, yttrium, and titanium tend to decrease as distance from the Piedmont (which is the likely source of these resources) increases and are moderately correlated with airborne measurements of equivalent thorium concentration. The concentrations of lanthanum, yttrium, and titanium are relatively high in those watersheds that adjoin the Piedmont, south of the Cape Fear Arch. Although this relation suggests that the concentrations are related to the watersheds, it may be simply an independent regional trend. The concentration of zirconium is unrelated to the distance from the Piedmont, the equivalent thorium concentration, and the watershed. These findings establish a foundation for more sophisticated analyses using integrated spatial modeling.

Open-File Report↗

USGS1972

Generalized subsurface geology of the water-bearing deposits, northern San Joaquin Valley, California

The study area includes about 5,000 square miles of the northern part of the San Joaquin Valley, a broad structural trough drained by the San Joaquin River. Fresh ground water is mostly in unconsolidated deposits derived from the Coast Ranges on the west and the Sierra Nevada on the east.. The interfingering of Coast Range and Sierran alluvium, together with the variability and lenticularity of each, causes variation in the hydrologic properties both vertically and horizontally in San Joaquin Valley deposits. A persistent confining stratum, the Corcoran Clay Member of the Tulare Formation, can be correlated through most of the study area. Informally, the deposits above the clay are termed the upper units the clay is termed the confining clay stratums and the deposits from the bottom of the clay to the base of fresh water, where known, are termed the lower unit. The upper unit is composed of beds, lenses, and tongues of gravel, sand, and clay ranging in thickness from about 100 feet in the north to 500 feet at the south end of the study area. A distinctive white clay, at or near the base of the upper unit, can be traced across the center of the valley. The confining clay stratum is the greenish to bluish gray lacustrine Corcoran Clay Member of the Tulare Formation; it ranges from 0 to 130 feet in thickness. No attempt to delineate the top and bottom of the Tulare Formation was made because of the thickness and similarity of deposits overlying and underlying the Corcoran. The lower unit is lithologically similar to the upper unit and ranges in thickness, where the base of fresh water has been mapped, from 90 to more than 1,400 feet.

California↗

USGS1984

Maximum known stages and discharges of New York streams through September 1983

This report lists the maximum known stages and discharges of New York streams through September 1981. The data represent 1,189 sites. Most data were obtained from files of the U.S. Geological Survey, but some were provided by other Federal, State, and private organizations. The information is grouped by major drainage basins and listed by U.S. Geological Survey station number in downstream order. Given are county names, drainage area (in square miles), period of record, type of site (continuous record, partial record, miscellaneous measurement), date of discharge, stage, elevation, discharge, and remarks. An envelope curve for the New York data was developed from a plot of maximum known discharge versus drainage area, and was compared with a like curve derived from maximum known discharge data gathered throughout the United States. The national curve ranges from about 3.0 times higher than the New York curve at a drainage area of 1.0 square mile to about 4.5 times higher at 1 ,000 square miles. The relative magnitude of flood discharges in four hydrologic regions of New York (west, north, southeast, Long Island) is shown in graphs relating maximum known discharge to drainage area. (USGS)

Open-File Report↗

USGS2003

Irrigation-induced contamination of water, sediment, and biota in the western United States-synthesis of data from the National Irrigation Water Quality Program

In October 1985 the U.S. Department of the Interior (DOI), through the National Irrigation Water Quality Program (NIWQP), began a series of field investigations at 26 areas in the Western United States to determine whether irrigation drainage has had harmful effects on fish, wildlife, and humans or has reduced beneficial uses of water. In 1992 NIWQP initiated the Data Synthesis Project to evaluate data collected during the field investigations. Geologic, climatologic, and hydrologic data were evaluated and water, sediment, and biota from the 26 areas were analyzed to identify commonalities and dominant factors that result in irrigation-induced contamination of water and biota. Data collected for the 26 area investigations have been compiled and merged into a common data base. The structure of the data base is designed to enable assessment of relations between contaminant concentrations in water, sediment, and biota. The data base is available to the scientific community through the World Wide Web at URL http://www.usbr.gov/niwqp. Analysis of the data base for the Data Synthesis included use of summary statistics, factor analysis, and logistic regression. A Geographic Information System was used to store and analyze spatially oriented digital data such as land use, geology and evaporation rates. In the U.S. Department of the Interior (DOI) study areas, samples of water, bottom sediment, and biota were collected for trace-element and pesticide analysis. Contaminants most commonly associated with irrigation drainage were identified by comparing concentrations in water with established criteria. For surface water, the criteria used were typically chronic criteria for the protection of freshwater aquatic life. Because ground water can discharge to the surface where wildlife can be exposed to it, the criteria used for ground water were both the maximum contaminant levels (MCL's) for drinking water and the chronic criteria for the protection of freshwater aquatic life. Data collected by the NIWQP studies indicated that, in surface water, filtered and unfiltered samples had nearly the same concentrations of arsenic, boron, molybdenum, and selenium for concentrations greater than about 10 micrograms per liter. Therefore, in this concentration range, filtered concentrations can be directly compared to biological-effect levels developed for unfiltered samples. In the range of 1 to 10 micrograms per liter there may be a tendency for unfiltered arsenic concentrations to be greater than filtered concentrations. For selenium, however, the data suggest differences from equality in that range result from analytical imprecision and not a general tendency for unfiltered concentrations to be greater than filtered concentrations. This relation may not be true in lentic, nutrient-rich waters because in such settings algae can bioaccumulate large amounts of selenium and other trace elements. Selenium was the trace element in surface water that most commonly exceeded chronic criteria for the protection of freshwater aquatic life; more than 40 percent of the selenium concentrations in surface-water samples exceeded the U.S. Environmental Protection Agency (USEPA) aquatic-life chronic criterion (5 micrograms per liter). In 12 of the 26 areas at least 25 percent of the surface water-samples had selenium concentrations that either equaled or exceeded the chronic criterion (5 micrograms per liter). More than 28 percent of boron concentrations and almost 17 percent of the molybdenum concentrations exceeded the aquatic life criteria established by the State of California (550 and 19 micrograms per liter, respectively). In ground water, more than 22 percent of the arsenic concentrations and more than 35 percent of the selenium concentrations exceeded the MCL (10 and 50 micrograms per liter, respectively). Few samples of uranium in surface water exceeded a criterion for the protection of aquatic life (300 micrograms per liter), but 44 percent

Professional Paper↗

USGS2025

The National integrated water availability assessment, water years 2010–20

Water availability is fundamentally important to human well-being, economic vitality, and ecosystem health. Because of its central importance, the U.S. Congress tasked the U.S. Geological Survey (USGS) and other Federal agencies with conducting regular, comprehensive assessments of water availability in the United States through the requirements under the SECURE Water Act. In response to this mandate, the USGS has developed the U.S. Geological Survey Integrated Water Availability Assessment—2010–20, which addresses aspects of water supply, quality, and use related to water availability in the United States. This is the first chapter of that report. The major climatic factors affecting water availability are also described. Multiple aspects of water availability are integrated to produce a more comprehensive analysis of water availability in the United States. This chapter enumerates the development, organization, and tools used in the USGS Integrated Water Availability Assessment. SECURE Water Act reports, developed by the Department of Energy Hydropower Climate Change Assessment and the Bureau of Reclamation West-Wide Climate and Hydrology Assessment, are also described. A distilled list of key findings from the overall report is also provided, serving as an introduction to each topic along with the most important high-level information.

conterminous United States↗

USGS2024

Data and knowledge gaps of a water bottling facility inventory and select water-use dataset, United States

In 2023, the U.S. Geological Survey developed a national inventory of water bottling facilities for the United States, including information about locations, water sources, water use, and a collection of other attributes. The purpose of the inventory was to provide information about water bottling facilities needed to assess and improve understanding of local-, regional-, and national-scale hydrologic and socioeconomic effects resulting from water extraction for bottling. Beverage types coded in the North American Industry Classification System under subsector 312 (Beverage and Tobacco Product Manufacturing) were compiled; however, facility information was often not publicly available, time intensive to search manually, and difficult to verify because there are no nationally available facility lists. A separate evaluation of facilities in the Great Lakes region identified some facilities that were missing and some with incorrect information. Ancillary facility attributes were primarily available from a proprietary business dataset and water-use data could only be acquired for a small subset of facilities. These limitations and deficiencies may affect the types of analyses that can be done using the inventory information. Therefore, the following data-quality aspects are used to describe the information compiled in the facility and water-use tables: completeness, uniqueness, validity, timeliness, accuracy, consistency, and accessibility. The resulting implications of the data and knowledge gaps are that users of the data may need to make additional evaluations of the inventory information for some analyses.

Scientific Investigations Report↗

USGS2013

Stochastic empirical loading and dilution model (SELDM) version 1.0.0

The Stochastic Empirical Loading and Dilution Model (SELDM) is designed to transform complex scientific data into meaningful information about the risk of adverse effects of runoff on receiving waters, the potential need for mitigation measures, and the potential effectiveness of such management measures for reducing these risks. The U.S. Geological Survey developed SELDM in cooperation with the Federal Highway Administration to help develop planning-level estimates of event mean concentrations, flows, and loads in stormwater from a site of interest and from an upstream basin. Planning-level estimates are defined as the results of analyses used to evaluate alternative management measures; planning-level estimates are recognized to include substantial uncertainties (commonly orders of magnitude). SELDM uses information about a highway site, the associated receiving-water basin, precipitation events, stormflow, water quality, and the performance of mitigation measures to produce a stochastic population of runoff-quality variables. SELDM provides input statistics for precipitation, prestorm flow, runoff coefficients, and concentrations of selected water-quality constituents from National datasets. Input statistics may be selected on the basis of the latitude, longitude, and physical characteristics of the site of interest and the upstream basin. The user also may derive and input statistics for each variable that are specific to a given site of interest or a given area. SELDM is a stochastic model because it uses Monte Carlo methods to produce the random combinations of input variable values needed to generate the stochastic population of values for each component variable. SELDM calculates the dilution of runoff in the receiving waters and the resulting downstream event mean concentrations and annual average lake concentrations. Results are ranked, and plotting positions are calculated, to indicate the level of risk of adverse effects caused by runoff concentrations, flows, and loads on receiving waters by storm and by year. Unlike deterministic hydrologic models, SELDM is not calibrated by changing values of input variables to match a historical record of values. Instead, input values for SELDM are based on site characteristics and representative statistics for each hydrologic variable. Thus, SELDM is an empirical model based on data and statistics rather than theoretical physiochemical equations. SELDM is a lumped parameter model because the highway site, the upstream basin, and the lake basin each are represented as a single homogeneous unit. Each of these source areas is represented by average basin properties, and results from SELDM are calculated as point estimates for the site of interest. Use of the lumped parameter approach facilitates rapid specification of model parameters to develop planning-level estimates with available data. The approach allows for parsimony in the required inputs to and outputs from the model and flexibility in the use of the model. For example, SELDM can be used to model runoff from various land covers or land uses by using the highway-site definition as long as representative water quality and impervious-fraction data are available.

Techniques and Methods↗

USGS2010

Estimating salinity intrusion effects due to climate change along the Grand Strand of the South Carolina coast

The ability of water-resource managers to adapt to future climatic change is especially challenging in coastal regions of the world. The East Coast of the United States falls into this category given the high number of people living along the Atlantic seaboard and the added strain on resources as populations continue to increase, particularly in the Southeast. Increased temperatures, changes in regional precipitation regimes, and potential increased sea level would have a great impact on existing hydrological systems in the region. Six reservoirs in North Carolina discharge into the Pee Dee River, which flows 160 miles through South Carolina to the coastal communities near Myrtle Beach, SC. During the Southeast’s record-breaking drought from 1998 to 2002, salinity intrusions inundated a coastal municipal freshwater intake, limiting water supplies. Salinity intrusion results from the interaction of three principal forces - streamflow, mean tidal water levels, and tidal range. To analyze, model, and simulate hydrodynamic behaviors at critical coastal streamgages along the Atlantic Intracoastal Waterway (AIW) near Myrtle Beach, SC, data-mining techniques were applied to over 20 years of hourly streamflow, coastal water-quality, and water-level data. Artificial neural network (ANN) models were trained to learn the variable interactions that cause salinity intrusions. Streamflow from the 12,700 square-mile Pee Dee River Basin that flows into the AIW are input to the model as time-delayed variables and accumulated tributary inflows. Tidal inputs to the models were obtained by decomposing tidal water-level data into a “periodic” signal of tidal range and a “chaotic” signal of mean water levels. The ANN models were able to convincingly reproduce historical behaviors and generate alternative scenarios of interest. To evaluate the impact of climate change on salinity intrusion, inputs of streamflows and mean tidal water levels were modified to incorporate estimated changes in precipitation patterns and sea-level rise appropriate for the Southeastern United States. Changes in mean tidal water levels were changed parametrically for various sea-level rise conditions. Preliminary model results at the U.S. Geological Survey Pawleys Island streamgage (station 02110125) near a municipal freshwater intake indicate that a sea-level rise of 1 foot (ft, 30.5 centimeters [cm]) would double the frequency of water with a specific conductance value of 2,000 microsiemens per centimeter close to 4 percent. A 2 ft (61 cm) sea-level rise would quadruple the frequency to 9 percent.

South Carolina↗

USGS2010

Geohydrology of the Aucilla-Suwannee-Ochlockonee River Basin, south-central Georgia and adjacent parts of Florida

Major streams and tributaries located in the Aucilla-Suwannee-Ochlockonee (ASO) River Basin of south-central Georgia and adjacent parts of Florida drain about 8,000 square miles of a layered sequence of clastic and carbonate sediments and carbonate Coastal Plain sediments consisting of the surficial aquifer system, upper semiconfining unit, Upper Floridan aquifer, and lower confining unit. Streams either flow directly on late-middle Eocene to Oligocene karst limestone or carve a dendritic drainage pattern into overlying Miocene to Holocene sand, silt, and clay, facilitating water exchange and hydraulic connection with geohydrologic units. Geologic structures operating in the ASO River Basin through time control sedimentation and influence geohydrology and water exchange between geohydrologic units and surface water. More than 300 feet (ft) of clastic sediments overlie the Upper Floridan aquifer in the Gulf Trough-Apalachicola Embayment, a broad area extending from the southwest to the northeast through the center of the basin. These clastic sediments limit hydraulic connection and water exchange between the Upper Floridan aquifer, the surficial aquifer system, and surface water. Accumulation of more than 350 ft of low-permeability sediments in the Southeast Georgia Embayment and Suwannee Strait hydraulically isolates the Upper Floridan aquifer from land-surface hydrologic processes in the Okefenokee Basin physiographic district. Burial of limestone beneath thick clastic overburden in these areas virtually eliminates karst processes, resulting in low aquifer hydraulic conductivity and storage coefficient despite an aquifer thickness of more than 900 ft. Conversely, uplift and faulting associated with regional tectonics and the northern extension of the Peninsular Arch caused thinning and erosion of clastic sediments overlying the Upper Floridan aquifer southeast of the Gulf Trough-Apalachicola Embayment near the Florida-Georgia State line. Limestone dissolution in Brooks and Lowndes Counties, Ga., create karst features that enhance water-transmitting and storage properties of the Upper Floridan aquifer, promoting groundwater recharge and water exchange between the aquifer, land surface, and surface water. Structural control of groundwater flow and hydraulic properties combine with climatic effects and increased hydrologic stress from agricultural pumpage to yield unprecedented groundwater-level decline in the northwestern and central parts of the ASO River Basin. Hydrographs from continuous-record observation wells in these regions document declining groundwater levels, indicating diminished water-resource potential of the Upper Floridan aquifer through time. More than 24 ft of groundwater-level decline occurred along the basin's northwestern boundary with the lower Apalachicola-Chattahoochee-Flint River Basin, lowering hydraulic gradients that provide the potential for groundwater flow into the ASO River Basin and southeastward across the Gulf Trough-Apalachicola Embayment region. Slow-moving groundwater across the trough-embayment region coupled with downward-vertical flow from upper to lower limestone units composing the Upper Floridan aquifer resulted in 40-50 ft of groundwater-level decline since 1969 in southeastern Colquitt County. Multi-year episodes of dry climatic conditions during the 1980s through the early 2000s contributed to seasonal and long-term groundwater-level decline by reducing recharge to the Upper Floridan aquifer and increasing hydrologic stress by agricultural pumpage. Unprecedented and continued groundwater-level decline since 1969 caused 40-50 ft of aquifer dewatering in southeastern Colquitt County that reduced aquifer transmissivity and the ability to supply groundwater to wells, resulting in depletion of the groundwater resource.

Florida, Georgia↗

USGS2010

Attributes for NHDPlus Catchments (Version 1.1)for the Conterminous United States: Contact Time, 2002

This data set represents the average contact time, in units of days, compiled for every catchment of NHDPlus for the conterminous United States. Contact time, as described in Wolock and others (1989), is the baseflow residence time in the subsurface. The source data set was the U.S. Geological Survey's (USGS) 1-kilometer grid for the conterminous United States (D.M. Wolock, U.S. Geological Survey, written commun., 2008). The grid was created using a method described by Wolock and others (1997a; see equation 3). In the source data set, the contact time was estimated from 1-kilometer resolution elevation data (Verdin and Greenlee, 1996 ) and STATSGO soil characteristics (Wolock, 1997b). The NHDPlus Version 1.1 is an integrated suite of application-ready geospatial datasets that incorporates many of the best features of the National Hydrography Dataset (NHD) and the National Elevation Dataset (NED). The NHDPlus includes a stream network (based on the 1:100,00-scale NHD), improved networking, naming, and value-added attributes (VAAs). NHDPlus also includes elevation-derived catchments (drainage areas) produced using a drainage enforcement technique first widely used in New England, and thus referred to as "the New England Method." This technique involves "burning in" the 1:100,000-scale NHD and when available building "walls" using the National Watershed Boundary Dataset (WBD). The resulting modified digital elevation model (HydroDEM) is used to produce hydrologic derivatives that agree with the NHD and WBD. Over the past two years, an interdisciplinary team from the U.S. Geological Survey (USGS), and the U.S. Environmental Protection Agency (USEPA), and contractors, found that this method produces the best quality NHD catchments using an automated process (USEPA, 2007). The NHDPlus dataset is organized by 18 Production Units that cover the conterminous United States. The NHDPlus version 1.1 data are grouped by the U.S. Geologic Survey's Major River Basins (MRBs, Crawford and others, 2006). MRB1, covering the New England and Mid-Atlantic River basins, contains NHDPlus Production Units 1 and 2. MRB2, covering the South Atlantic-Gulf and Tennessee River basins, contains NHDPlus Production Units 3 and 6. MRB3, covering the Great Lakes, Ohio, Upper Mississippi, and Souris-Red-Rainy River basins, contains NHDPlus Production Units 4, 5, 7 and 9. MRB4, covering the Missouri River basins, contains NHDPlus Production Units 10-lower and 10-upper. MRB5, covering the Lower Mississippi, Arkansas-White-Red, and Texas-Gulf River basins, contains NHDPlus Production Units 8, 11 and 12. MRB6, covering the Rio Grande, Colorado and Great Basin River basins, contains NHDPlus Production Units 13, 14, 15 and 16. MRB7, covering the Pacific Northwest River basins, contains NHDPlus Production Unit 17. MRB8, covering California River basins, contains NHDPlus Production Unit 18.

Data Series↗