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At least 397 records · Page 22Linked to original sources
USGS2011

Discrete and continuous water-quality data and hydrologic parameters from seven agricultural watersheds in the United States, 2002-09

Field and analytical methods; discrete organic and non-organic water-quality data and associated quality-control data; and continuous hydrologic and water-quality parameters are reported for sites in California, Indiana, Iowa, Maryland, Mississippi, Nebraska, and Washington. The sites were sampled as part of the U.S. Geological Survey National Water-Quality Assessment Program?s Agricultural Chemicals Team study to better understand how environmental processes and agricultural practices interact to determine the transport and fate of agricultural chemicals in the environment.

Data Series↗
USGS2001

Facies analysis of Tertiary basin-filling rocks of the Death Valley regional ground-water system and surrounding areas, Nevada and California

Existing hydrologic models of the Death Valley region typically have defined the Cenozoic basins as those areas that are covered by recent surficial deposits, and have treated the basin-fill deposits that are concealed under alluvium as a single unit with uniform hydrologic properties throughout the region, and with depth. Although this latter generalization was known to be flawed, it evidently was made because available geologic syntheses did not provide the basis for a more detailed characterization. As an initial attempt to address this problem, this report presents a compilation and synthesis of existing and new surface and subsurface data on the lithologic variations between and within the Cenozoic basin fills of this region. The most permeable lithologies in the Cenozoic basin fills are freshwater limestones, unaltered densely welded tuffs, and little-consolidated coarse alluvium. The least permeable lithologies are playa claystones, altered nonwelded tuffs, and tuffaceous and clay-matrix sediments of several types. In all but the youngest of the basin fills, permeability probably decreases strongly with depth owing to a typically increasing abundance of volcanic ash or clay in the matrices of the clastic sediments with increasing age (and therefore with increasing depth in general), and to increasing consolidation and alteration (both hydrothermal and diagenetic) with increasing depth and age. This report concludes with a categorization of the Cenozoic basins of the Death Valley region according to the predominant lithologies in the different basin fills and presents qualitative constraints on the hydrologic properties of these major lithologic categories.

Open-File Report↗
USGS1949

Progress report on the geology and ground-water hydrology of the Lower Missouri-Souris Unit; Part 1, Crosby-Mohall area, North Dakota

The Crosby-Mohall area covers about 2,700 square miles in the north- western part of North Dakota. This area is included in the 2,500,000-acre Missouri-Souris and Garrison Diversion irrigation projects,which are im portant units in the general plans for development of the water resources of the Missouri River Basin. Although the Crosby-Mohall area lies outside the drainage basin of the Missouri River, plans have been made for the irrigation of about 1,000,0)0 acres (equivalent to 1,560 square miles) of the most suitable land, with water brought by canal from the Missouri River in Montana. The studies that have been undertaken in the area by the Division of Ground Water of the United States Geological Survey form a part of the investigations which have been initiated by the Survey and several other bureaus of the Department of the Interior, especially the Bureau of Reclamation. The studies on which the present report is bas2 were made during the field seasons of 1945, 1946 and 1947, to obtain information on the occurrence, movement, quantity, and quality of the ground water. The report contains data on the several kinds of water-bearing materials, water analyses, and well logs; the records of fluctuation of water level in about 400 wells; and an inventory of 4,636 wells and test holes. Later studies for the whole of the Missouri-Souris Unit will supply additional data on ground-water levels and piezometric surfaces, more extensive information on quality of water, a complete inventory of wells, and further geologic information relating to ground-water supplies. Other work that is planned also includes the drilling of additional test holes and the analysis of water samples from representative wells throughout the area.

North Dakota↗
USGS2002

Geologic framework of the regional ground-water flow system in the Upper Deschutes Basin, Oregon

Ground water is increasingly relied upon to satisfy the needs of a growing population in the upper Deschutes Basin, Oregon. Hydrogeologic studies are being undertaken to aid in management of the ground-water resource. An understanding of the geologic factors influencing ground-water flow is basic to those investigations. The geology of the area has a direct effect on the occurrence and movement of ground water. The permeability and storage properties of rock material are influenced by the proportion, size, and degree of interconnection of open spaces the rocks contain. These properties are the result of primary geologic processes such as volcanism and sedimentation, as well as subsequent processes such as faulting, weathering, or hydrothermal alteration. The geologic landscape in the study area evolved during about 30 million years of volcanic activity related to a north-south trending volcanic arc, the current manifestation of which are today’s Cascade Range volcanoes. The oldest rock unit in the upper Deschutes Basin study area, the John Day Formation, is a sequence of upper Eocene to lower Miocene volcanic and sedimentary rocks. Weathering and alteration of the rocks has resulted in very low permeability; consequently, the unit forms the hydrologic basement for the regional ground- water flow system throughout much of the area. The Deschutes Formation and age-equivalent deposits that overlie the John Day Formation, in contrast, are highly permeable and are the most widely used ground-water-bearing units in the study area. The Deschutes Formation consists of a variety of volcanic and sedimentary deposits ranging in age from late Miocene to Pliocene (approximately 7.5 to 4.0 million years). Three distinct depositional environments previously described for the formation provide useful hydrogeologic subdivisions. The ancestral Deschutes River deposits and some units within the arc- adjacent alluvial-plain region are among the highest yielding units within the Deschutes Formation, with some wells producing up to a few thousand gallons per minute. Opal Springs basalt, Pelton basalt, and the rhyodacite dome complex near Steelhead Falls are particularly productive subunits within the Deschutes Formation and provide tens to hundreds of cubic feet per second of ground-water discharge to the Deschutes and Crooked Rivers, upstream of Round Butte Dam. Most ground-water recharge in the upper Deschutes Basin occurs in Quaternary deposits of the Cascade Range and Newberry Volcano. These deposits are highly permeable, and the fractured character of the lava flows facilitates rapid infiltration of precipitation and snowmelt, as well as movement of ground water to lower elevations. Additional recharge from canal leakage occurs along sections of unlined canals near Bend, constructed on lava flows from Newberry Volcano. Hydrothermal alteration and secondary mineralization at depth beneath the Cascade Range and Newberry Volcano has drastically reduced the permeability of the material in those regions, effectively restricting most ground water to the strata above the altered rocks. The top of the hydrothermally altered region is considered the base of the regional ground-water system beneath the Cascade Range and Newberry Volcano. Structural features influence ground-water flow within the upper Deschutes Basin mainly by juxtaposing materials with contrasting permeability. This juxtaposition can be caused by fault movement or by the influence of a fault on subsequent deposition. Several depositional centers have formed along the base of fault-line scarps or in grabens within the study area, and the infilling sedimentary deposits have permeability that differs from the surrounding rocks. The effects of faults on ground-water flow may be masked in some areas. For example, the water-table gradient changes slope in the vicinity of the Sisters fault zone, but the slope change also corresponds with a major precipitation gradient change; therefore, any influence of the fault zone is unclear. Geologic units in the Deschutes Basin were divided into several distinct hydrogeologic units. In some instances the units correspond to existing stratigraphic divisions. In other instances, hydrogeologic units correspond to different facies within a single stratigraphic unit or formation. The hydrogeologic units include Quaternary sediment, deposits of the Cascade Range and Newberry Volcano, four zones within the Deschutes Formation and age-equivalent rocks that roughly correspond with depositional environments, and pre-Deschutes-age strata.

Water-Resources Investigations Report↗
USGS2025

Water supply in the conterminous United States, Alaska, Hawaii, and Puerto Rico, water years 2010–20

We present an assessment of water supply across the conterminous United States (CONUS), Alaska, Hawaii, and Puerto Rico covering water years 2010–20. Our analysis drew on two national hydrologic models, the National Hydrologic Model Precipitation-Runoff Modeling System and the Weather Research and Forecasting model hydrologic modeling system. Both models produced estimates of streamflow, evapotranspiration, soil moisture, snow water equivalent, and other hydrologic states and fluxes. The models were driven by the bias-adjusted 4-kilometer-resolution, long-term regional hydroclimate simulation over the conterminous United States dataset (CONUS404). We assessed spatial and temporal error distributions by comparing monthly simulations at the 12-digit hydrologic unit code and regional scale from both models against external benchmarking datasets. Results showed that average annual rainfall across the CONUS was 857 millimeters per year for the period of analysis, with water year 2012 the driest year (729 millimeters) and water year 2019 the wettest year (995 millimeters). Key interannual variability results included the following: (1) the California–Nevada hydrologic region had the highest variability in precipitation and snow accumulation, and (2) the Texas hydrologic region was among hydrologic regions with the highest variability in precipitation. We related interannual variability in precipitation to storage volumes in soil moisture, snow water equivalent, and lakes and reservoirs to highlight areas with little storage and large year-to-year variability in precipitation. These areas included the Southern High Plains, Central High Plains, Texas, Souris–Red–Rainy, Mississippi Embayment, and Midwest regions. Our analysis of groundwater-level data showed that several of these areas overlap aquifers where groundwater levels were considerably lower than historical averages, including the Colorado Plateaus aquifers, the Rio Grande aquifer system, and the Central and Southern regions of the High Plains aquifer. Many of these lowered groundwater levels are continuations of decades-long declines from overpumping that started well before the assessment period. The resulting water budgets and their analyses provide a high-resolution foundational assessment of the mean state and variability of the terrestrial hydrologic cycle across the CONUS and Alaska, Hawaii, and Puerto Rico to support a wide range of water resource management applications.

Professional Paper↗
USGS2019

Estimation of base flow by optimal hydrograph separation for the conterminous United States and implications for national-extent hydrologic models

Optimal hydrograph separation (OHS) uses a two-parameter recursive digital filter that applies specific conductance mass-balance constraints to estimate the base flow contribution to total streamflow at stream gages where discharge and specific conductance are measured. OHS was applied to U.S. Geological Survey (USGS) stream gages across the conterminous United States to examine the range/distribution of base flow inputs and the utility of this method to build a hydrologic model calibration dataset. OHS models with acceptable goodness-of-fit criteria were insensitive to drainage area, stream density, watershed slope, elevation, agricultural or perennial snow/ice land cover, average annual precipitation, runoff, or evapotranspiration, implying that OHS results are a viable calibration dataset applicable in diverse watersheds. OHS-estimated base flow contribution was compared to base flow-like model components from the USGS National Hydrologic Model Infrastructure run with the Precipitation-Runoff Modeling System (NHM-PRMS). The NHM-PRMS variable gwres_flow is most conceptually like a base flow component of streamflow but the gwres_flow contribution to total streamflow is generally smaller than the OHS-estimated base flow contribution. The NHM-PRMS variable slow_flow , added to gwres_flow , produced similar or greater estimates of base flow contributions to total streamflow than the OHS-estimated base flow contribution but was dependent on the total flow magnitude.

conterminous United States↗
USGS2011

Geologic framework and hydrogeology of the middle Carson River Basin, Eagle, Dayton, and Churchill Valleys, West-Central Nevada

Changes in land use and water use and increasing development of water resources in the middle Carson River basin may affect flow of the river and, in turn, affect downstream water users dependent on sustained river flows to Lahontan Reservoir. The U.S. Geological Survey, in cooperation with the Bureau of Reclamation, began a study in 2008 of the middle Carson River basin, extending from Eagle Valley to Churchill Valley. Various types of geologic and hydrologic data were compiled from previous studies, collected for this study, and compiled and analyzed to provide a framework for development of a numerical model of the groundwater and surface-water flow systems of the basin. Geologic units that are assumed to have similar hydrologic characteristics were grouped into hydrogeologic units comprised of consolidated rocks of pre-Cenozoic age that underlie a unit of consolidated volcanic rock and semi-consolidated sediments of Tertiary age. The principal aquifer in the study area is comprised of unconsolidated sediments of Quaternary age. The Quaternary sediments include alluvial fan, fluvial, and lake sediments, and were grouped into a basin-fill hydrogeologic unit that overlies the pre-Cenozoic and Tertiary hydrologic units. The thickness of the combined section of Tertiary volcanic and sedimentary rocks and Quaternary basin-fill deposits previously was estimated to range from zero where pre-Cenozoic rocks are exposed to greater than 10,000 feet in the Bull Canyon subbasin, and greater than 6,000 feet on the western side of Churchill Butte and beneath the Desert Mountains. The thickness of Quaternary basin-fill sediments was estimated using gravity data and lithologic descriptions from driller’s logs. The most permeable parts of basin-fill sediments are greater than 1,000 feet thick in the Carson Plains subbasin, greater than 800 feet and 600 feet thick in the western and northeastern parts of the Stagecoach subbasin, and greater than 1,000 feet and 800 feet thick in the northern and southern parts of Churchill Valley, respectively. The distribution of aquifer properties was estimated for basin-fill sediments using slug-test and aquifer test data, and the lithologic descriptions of previously mapped geologic units. Slug-test data show hydraulic conductivity is greater than 10 to greater than 100 feet per day for fluvial sediments near the flood plain, less than 10 feet per day for basin-fill sediments outside the flood plain, and less than 1 foot per day for consolidated rocks. Estimates of transmissivity exceed 20,000 feet squared per day near the Carson River in Dayton, Churchill, and western Lahontan Valleys and in the northern part of the Stagecoach subbasin, and exceed 10,000 feet squared per day in the western part of Churchill Valley. A transmissivity of 90,000 feet squared per day was estimated from results of an aquifer test in the Carson Plains subbasin, indicating that permeable gravel and cobble zones at depths greater than 400 feet supplied water to the pumping well. Estimates of specific yield ranged from less than 1 to 2 percent for most consolidated rocks, from 1 to 15 percent for semi-consolidated Tertiary sediments, and from 10 to 40 percent for unconsolidated basin-fill sediments. Water-level altitude maps based on measurements at about 300 wells in 2009 show water levels have declined as much as 70 feet since 1964 on the northwestern side of Eagle Valley, about 10 feet since 1995 near Dayton in the Carson Plains subbasin, and from 5 to 10 feet since 1982 in the western and northeastern parts of the Stagecoach subbasin and the northwestern part of Churchill Valley. The declines are likely the result of municipal and agricultural pumping. The maps show a groundwater divide between the Carson Plains and Stagecoach subbasins, and a continuous hydraulic gradient between the Stagecoach subbasin and Churchill Valley. Groundwater flow directions are uncertain beneath parts of the boundary of Churchill Valley. The altitude of the top of pre-Cenozoic rocks shows thick sections of saturated Tertiary rocks and sediments south of the Dead Camel Mountains and beneath the eastern part of the Desert Mountains through which groundwater flow between Churchill Valley, Mason Valley, and Lahontan Valley may take place. North of Lahontan reservoir, beneath the Dead Camel Mountains, and beneath the southern part of Adrian Valley, the altitude of pre-Cenozoic rocks indicates groundwater flow between the three valleys is minimal. Streamflow measurements, supported by data on the deuterium content and specific conductance of surface-water samples, indicate a loss of Carson River streamflow in the Riverview subbasin, streamflow gains in the Moundhouse subbasin and the eastern part of the Carson Plains subbasin, and streamflow losses in the Bull Canyon subbasin. Comparisons of fluctuations in groundwater levels to those in stream stage in the Carson Plains subbasin indicate that streamflow lost to infiltration from the Carson River, from irrigation ditches, and from irrigated fields is an important source of groundwater recharge. Fluctuations in groundwater levels compared with the stage of Lahontan Reservoir in Churchill Valley indicate losses to infiltration from the reservoir during high stage and groundwater seepage to the reservoir during low stage.

Nevada↗
USGS2015

Underpressure in Mesozoic and Paleozoic rock units in the Midcontinent of the United States

Potentiometric surfaces for Paleozoic strata, based on water well levels and selected drill-stem tests, reveal the control on hydraulic head exerted by outcrops in eastern Kansas and Oklahoma. From outcrop in the east, the westward climb of hydraulic head is much less than that of the land surface, with heads falling so far below land surface that the pressure:depth ratio in eastern Colorado is less than 5.7 kPa/m (0.25 psi/ft). Permian evaporites separate the Paleozoic hydrogeologic units from a Lower Cretaceous (Dakota Group) aquifer, and a highly saline brine plume pervading Paleozoic units in central Kansas and Oklahoma is attributed to dissolution of Permian halite. Underpressure also exists in the Lower Cretaceous hydrogeologic unit in the Denver Basin, which is hydrologically separate from the Paleozoic units. The data used to construct the seven potentiometric surfaces were also used to construct seven maps of pressure:depth ratio. These latter maps are a function of the differences among hydraulic head, land-surface elevation, and formation elevation. As a consequence, maps of pressure:depth ratio reflect the interplay of three topologies that evolved independently with time. As underpressure developed, gas migrated in response to the changing pressure regime, most notably filling the Hugoton gas field in southwestern Kansas. The timing of underpressure development was determined by the timing of outcrop exposure and tilting of the Great Plains. Explorationists in western Kansas and eastern Colorado should not be surprised if a reservoir is underpressured; rather, they should be surprised if it is not.

Arkansas, Colorado, Kansas, Iowa, Missouri, Nebras↗
USGS1988

Bottom sediments and nutrients in the tidal Potomac system, Maryland and Virginia

The characteristics and distributions of near-surface bottom sediments and of nutrients in the sediments provide information on modern sediment and nutrient sources, sedimentation environments, and geochemical reactions in the tidal Potomac system, Maryland and Virginia. This information is fundamental to an improved understanding of sedimentation and eutrophication problems in the tidal Potomac system. The tidal Potomac system consists of 1,230 square kilometers of intertidal to subtidal Potomac mainstem and tributary streambed from the heads-of-tides to Chesapeake Bay. Tidal Potomac sediments are dominantly silt and clay except in local areas. An average sediment sample is about two-thirds silt and clay (fine) particles and one-third sand (coarse) particles. The mean of the median size of all samples is 6.60 phi, or 0.010 millimeters. Sorting generally is poor and the average sediment is skewed toward the fine tail of the size-distribution curve. Mean particle-size measures have large standard deviations. Among geomorphic units, two distinctly different size populations are found; fine (median phi about 9), and poorly sorted (sorting about 3) sediments in the channel and the smooth flat, and coarse (median phi about 2), and well sorted (sorting about 1) sediments in the shoreline flat and the irregular slope. Among mainstem hydrologic divisions, an average sediment from the river and the estuary division is coarser and more variable than an average sediment from the transition division. Substantial concentrations of total carbon, total nitrogen, and total phosphorus, and limited amounts of inorganic carbon, ammonia nitrogen and nitrite plus nitrate nitrogen occur in tidal Potomac sediments. An average tidal Potomac sediment sample weighing 1 kilogram contains about 21,000 milligrams of total carbon, 2,400 milligrams of total nitrogen, 1,200 milligrams of total phosphorus, 600 milligrams of inorganic carbon, 170 milligrams of ammonia nitrogen, and 2 milligrams of nitrite plus nitrate nitrogen. Total carbon, nitrogen, and phosphorus have an average ratio by weight of 18:2:1 and an average ratio by atoms of 94:8:1. Nutrient concentrations and nutrient ratios have large ranges and standard deviations. Nutrient concentrations usually are closely related to particle size; large concentrations are characteristic of fine sediments in the channel and the smooth flat, and small concentrations are typical of coarse sediments in the shoreline flat and the irregular slope. Concentrations typically decrease from the river division to the estuary division. Mainstem and tributaries show no statistically significant difference in mean particle-size measures or mean nutrient concentrations. Tributaries do not contribute large quantities of sediment with diverse texture or nutrient content to the Potomac mainstem. Particle-size measures and nutrient concentrations in the mainstem are significantly related to hydrologic divisions and geomorphic units; that is, particle size and nutrients vary significantly along and across the Potomac mainstem. Lateral variations in particle size and nutrient content are more pronounced and contribute more to significant relations than longitudinal variations contribute. The mean values for the median particle size and for the percentage of sand indicate significant variations among hydrologic divisions for samples from a geomorphic unit, and among geomorphic units, for samples from a hydrologic division. Sediments of channels and smooth flats in the river division commonly are coarser than sediments of channels and smooth flats in the transition and the estuary divisions. Shoreline flats in the estuary division are coarser than shoreline flats in the river division. Shoreline flats and irregular slopes in each hydrologic division generally are significantly coarser than channels and smooth flats. Relations between particle-size measures and geomorphic units show progressively larger cor

Water Supply Paper↗
USGS1982

Hydrologic analysis of the upper San Pedro basin from the Mexico-United States international boundary to Fairbank, Arizona

A definition of the hydrologic system of the upper San Pedro basin was obtained by developing a numerical ground-water model to evaluate a conceptual model of the system. Information on hydraulic properties of the basin fill, recharge from bordering mountain ranges, discharge by evapotranspiration, and exchange of water between aquifer and stream was available from previous measurements or estimates. The steady-state calibration procedure and subsequent transient simulations demonstrated that the original conceptualization can be reasonably simulated. An analysis of model sensitivity to increases and decreases in certain hydraulic properties indicated a low sensitivity to aquifer anisotropy and a low to moderate sensitivity to stream leakance and evapotranspiration rate. An analysis to investigate the effects of generalizing aquifer conductivity and recharge showed that flow components and water-level response to stress could be simulated adequately but that steady-state water-level conditions could not. During equilibrium conditions, recharge to and discharge from the basin was about 16,500 acre-feet per year. Modeling results indicated that by 1978 the storage depletion rate had reached 5,600 acre-feet per year resulting from a ground-water withdrawal rate of 10,500 acre-feet per year. (USGS)

Arizona↗
USGS2000

Water-quality assessment of part of the Upper Mississippi River Basin, Minnesota and Wisconsin - Ground-water quality in an agricultural area of Sherburne County, Minnesota, 1998

The quality of shallow ground water in a 75-mi 2 agricultural area of the Anoka Sand Plain aquifer in central Minnesota is described as part of the National Water Quality Assessment (NAWQA) Program - a national-scale assessment of the quality of water resources within large study units in various hydrologic settings. Data were collected during 1998 from 29 wells completed in the aquifer, which predominantly consists of surficial glacial sand and gravel sediments. The depth below land surface to the water table ranged from 3.3 to 44 ft (median of 15.5 ft). Ground water was of the calciummagnesium bicarbonate type. Ionic constituents also included sodium, sulfate, and chloride. Iron and manganese concentrations generally were not greater than their U.S. Environmental Protection Agency (USEPA) Secondary Maximum Contaminant Levels (300 and 50 ug/L, respectively). About 38 percent of 29 samples had nitrate-N (nitrogen) concentrations greater than the USEPA Maximum Contaminant Level (MCL) of 10 mg/L. About 72 percent of the samples had nitrate-N concentrations greater than the presumed natural background level of 3 mg/L. The maximum nitrate-N concentration was 47 mg/L. The median nitrate-N concentration of 7.1 mg/L, although not greater than the MCL, exceeded the natural background level. Nitrogen isotope ratios indicate that the sources of nitrate were commercial fertilizer and soil organic matter. Concentrations of total dissolved phosphorus and orthophosphate were generally less than 1 mg/L. About 86 percent of 29 samples had detectable concentrations of at least 1 of 13 pesticide compounds. The samples were analyzed for 83 pesticide compounds. Frequencies of detection of these compounds were: deethylatrazine-79 percent; atrazine-76 percent; metolachlor-41 percent; metribuzin and bentazon-21 percent; prometon-10 percent; tebuthiuron-7 percent; and alachlor, 2,6-diethylaniline, dicamba, dinoseb, malathion, and simazine-3 percent. The detected pesticide compounds had concentrations less than 1 ug/L. Detected compounds with USEPA MCLs (atrazine, bentazon, alachlor, dinoseb, and simazine) had concentrations less than their respective MCLs. About 50 percent of 20 samples analyzed for 86 volatile organic compounds (VOCs) had detectable concentrations of at least 1 of 7 VOCs. Frequencies of detection of these 7 VOCs were: 1,2,3,4-tetramethylbenzene-40 percent; and trichlorofluoromethane, styrene, chloromethane, benzene, methylbenzene, and trichloromethane-5 percent. The detected VOCs had concentrations less than 0.120 ug/L. Detected VOCs with USEPA MCLs - styrene, benzene, methylbenzene, and trichloromethane - were present at concentrations 2-4 orders of magnitude less than their respective MCLs. Tritium concentrations had a range of from 7.5 to 18.8 tritium units (TUs) and a median of 12.5 TUs. These concentrations indicate that the ground water predominantly recharged after testing of thermonuclear weapons during the early 1950's.

Minnesota↗
USGS2020

Brianna postcard

Brianna is a hydrologist in the Hydrologic Investigations (Studies) Unit. She received a bachelor of science degree in chemical engineering and a master’s degree in civil engineering from the University of Kansas.

General Information Product↗
USGS2002

Hydrostructural maps of the Death Valley regional flow system, Nevada and California

The locations of principal faults and structural zones that may influence ground-water flow were compiled in support of a three-dimensional ground-water model for the Death Valley regional flow system (DVRFS), which covers 80,000 square km in southwestern Nevada and southeastern California. Faults include Neogene extensional and strike-slip faults and pre-Tertiary thrust faults. Emphasis was given to characteristics of faults and deformed zones that may have a high potential for influencing hydraulic conductivity. These include: (1) faulting that results in the juxtaposition of stratigraphic units with contrasting hydrologic properties, which may cause ground-water discharge and other perturbations in the flow system; (2) special physical characteristics of the fault zones, such as brecciation and fracturing, that may cause specific parts of the zone to act either as conduits or as barriers to fluid flow; (3) the presence of a variety of lithologies whose physical and deformational characteristics may serve to impede or enhance flow in fault zones; (4) orientation of a fault with respect to the present-day stress field, possibly influencing hydraulic conductivity along the fault zone; and (5) faults that have been active in late Pleistocene or Holocene time and areas of contemporary seismicity, which may be associated with enhanced permeabilities. The faults shown on maps A and B are largely from Workman and others (in press), and fit one or more of the following criteria: (1) faults that are more than 10 km in map length; (2) faults with more than 500 m of displacement; and (3) faults in sets that define a significant structural fabric that characterizes a particular domain of the DVRFS. The following fault types are shown: Neogene normal, Neogene strike-slip, Neogene low-angle normal, pre-Tertiary thrust, and structural boundaries of Miocene calderas. We have highlighted faults that have late Pleistocene to Holocene displacement (Piety, 1996). Areas of thick Neogene basin-fill deposits (thicknesses 1-2 km, 2-3 km, and >3 km) are shown on map A, based on gravity anomalies and depth-to-basement modeling by Blakely and others (1999). We have interpreted the positions of faults in the subsurface, generally following the interpretations of Blakely and others (1999). Where geophysical constraints are not present, the faults beneath late Tertiary and Quaternary cover have been extended based on geologic reasoning. Nearly all of these concealed faults are shown with continuous solid lines on maps A and B, in order to provide continuous structures for incorporation into the hydrogeologic framework model (HFM). Map A also shows the potentiometric surface, regional springs (25-35 degrees Celsius, D'Agnese and others, 1997), and cold springs (Turner and others, 1996).

Nevada;California↗
USGS2023

Regional streamflow drought forecasting in the Colorado River Basin using Deep Neural Network models

Process-based, large-scale (e.g., conterminous United States [CONUS]) hydrologic models have struggled to achieve reliable streamflow drought performance in arid regions and for low-flow periods. Deep learning has recently seen broad implementation in streamflow prediction and forecasting research projects throughout the world with performance often equaling or exceeding that of process-based models. Deep learning models are a possible approach to increase the accuracy of streamflow drought predictions and to expand the spatial coverage of river locations with available streamflow drought forecasts. As part of a multi-component Data-Driven Drought Prediction project, the U.S. Geological Survey is developing and testing deep learning models for streamflow drought forecasting. In this work, we present preliminary results of a deep learning model capable of predicting streamflow drought occurrence at ungaged locations for the Colorado River Basin (CRB). A long short-term memory (LSTM) neural network model was trained using 40 years (1980-2020) of daily streamflow data from 425 streamgages within and surrounding the CRB using static watershed attributes as well as meteorological and remotely sensed dynamic forcing inputs. Model tests were performed to evaluate model accuracy for now-casting streamflow drought conditions at ungaged locations and for forecasting drought conditions at lead times ranging from 0 to 14 days. Nearly all model configurations showed behavioral performance for predicting daily streamflow percentiles. Comparisons of LSTM model performance for predicting drought using fixed drought thresholds (calculated over all days and years) and variable drought thresholds (unique threshold calculated for each day of the year) identify differences in model skill between locations with implications for model design.

Colorado River basin↗
USGS1969

Hydrology of carbonate rock terranes — A review: With special reference to the United States

Limestone and other carbonate rocks are characterized by many unusual features and extreme conditions, either involving the hydrologic system within them or wrought by hydrologic conditions on them or through them. Perhaps there could be little agreement as to what is typical or average for the many features of carbonate rocks, as indicated by the following conditions: bare rock and thin soils are common, but so are thick soils; very highly permeable limestones are common, but so are poorly permeable ones; and rugged karst topographic features with underlying solution caverns are common, but so are flat, nearly featureless topographic conditions. Some conditions of carbonate terranes are suitable to man's needs and interests, such as the use of some permeable aquifers for water supply and the exploitation of caves for tourist attractions. On the other hand, many problems may exist, including: permeability too low for adequate water supply or so high that the aquifer retains too little water for use during periods of fair weather, soils too thin for growing of crops and for adequate filtration of wastes near the ground surface, instability of the ground for buildings and foundations in sinkhole areas, and unusually rugged topography. Some of the many variable conditions are readily observable, but others can be determined only by careful geologic and hydrologic studies. The need for knowing the specific geologic and hydrologic conditions at various places in limestone terranes, as well as the variations in hydrologic conditions with changing conditions and time, has resulted in many published reports on local areas and on special topical problems of limestone hydrology. Many of these reports have been used to advantage by the present writers in preparing this paper. The concept that secondary permeability is developed by circulation of water through openings with the accompanying enlargement of these openings by solution is now universally accepted in limestone terranes. Emphasis is placed on the hydrogeologic framework, or structural setting, in relation to the ease or difficulty of water to move from a source of recharge, through a part of the limestone, to a discharge area. Parts of the limestone favored by circulating ground water tend to develop solution openings, commonly in the upper part of the zone of saturation; as base level is lowered (sea level or perennial stream level), the related water table lowers in the limestone leaving air-filled caverns above the present zone of saturation in sinkhole areas. Reconstruction of the geologic and hydrologic history of a limestone area aids in determining the extent of development and the positions of fossil and present permeability. References are made to the hydrology of many limestone regions, especially those of the United States.

Journal of Hydrology↗
USGS1996

Plan for assessment of the occurrence, status, and distribution of volatile organic compounds in aquifers of the United States

The occurrence of volatile organic compounds (VOCs) in water is of national concern because of their relatively high aqueous solubility, mobility, and persistence, because many are known or suspected carcinogens, because of their widespread use, and because they have been found in drinking-water supplies. Because of this national concern, VOCs were selected for National investigation (hereafter termed "National Synthesis") by the U.S. Geological Survey's National Water-Quality Assessment (NAWQA) Program in 1994. The broad goals of this National Synthesis are to: (1) describe current water- quality conditions with respect to VOCs; (2) define trends, or lack of trends, in VOCs in surface and ground water; and (3) identify, describe, and explain causal relations among the occurrence and distribution of VOCs in surface water and ground water, and natural and human factors. The National Synthesis of VOCs in ground water has three objectives: (1) to describe their occurrence, status, and distribution; (2) to determine relations among VOCs in shallow ground water and natural and human factors; and (3) to determine, compare, and contrast the occurrence, transformation, transport, and fate of selected VOCs in the hydrologic cycle for several regionally or nationally important aquifer systems. The description of VOC occurrence, status, and distribution in ground water focuses on major aquifers of the United States. Occurrence describes the presence or absence of VOCs, their frequency of occurrence, and their ranges of concentrations. Status compares the concentrations of VOCs detected in relation to water-quality regulations or advisories, such as Maximum Contaminant Levels, Proposed Maximum Contaminant Levels, Maximum Contaminant Level Goals, and Health Advisories. Distribution describes the variability of VOCs in ground water, areally and by depth. This report describes the study design for conducting such an assessment. The assessment focuses on aquifers, or parts of aquifers, that are currently used or have the potential to be used as sources of water supplies, using data collected as part of local, State, and Federal ground-water monitoring programs since 1985. Assessment by aquifer and comparison of results among aquifers will be completed for those aquifers for which adequate spatial or depth-related data are available. Assessment of VOCs in aquifers also will be completed at regional and national scales. A set of criteria for well-network design, well construction, sample-collection methods, and methods of laboratory analysis must be met before VOC data are used for assessment. An appropriate well-network design will provide a generally unbiased, random, equal-area distribution of sampling sites throughout the aquifer, or part of the aquifer, of interest. Well-construction information must be sufficient to ensure that the hydrogeologic unit (or units) represented by the water level measured and the hydrologic unit (or units) contributing water to the well are known. In addition, the well construction and pumping equipment in the well need to be of a type that are not likely to affect concentrations of VOCs in the water sample. VOC data will be considered suitable for use in the occurrence assessment if nationally accepted methods for collection and analysis were used and if the quantitation level for VOC analytes was less than about 5 micrograms per liter; laboratory analysis was done by a laboratory certified by the U.S. Environ- mental Protection Agency; and the sample was collected from untreated (raw) water at or near the well head before being held in a pressure tank or holding tank.

Open-File Report↗
USGS1996

Hydrology of the southeastern Coastal Plain aquifer system in South Carolina and parts of Georgia and North Carolina

The wedge of sediments present beneath the Coastal Plain of South Carolina and adjacent parts of Georgia and North Carolina consists of sand, silt, clay, and limestone. These strata have been subdivided into six regional aquifers: the surficial aquifer, the Floridan aquifer system, the Tertiary sand aquifer, the Black Creek aquifer, the Middendorf aquifer, and the Cape Fear aquifer. Intervening confining units separate the aquifers, except for the Floridan aquifer system and the Tertiary sand aquifer, which together function as a single hydrologic unit. The quality of ground water from the Coastal Plain aquifers of South Carolina generally is acceptable for most uses in most areas. The water in most aquifers under most of the Coastal Plain contains low concentrations of dissolved solids (less than 500 milligrams per liter) and no dominant constituents in the recharge areas. Downgradient, the water is a calcium bicarbonate or sodium bicarbonate type throughout most of the Coastal Plain. Sodium-chloride-type water is present still farther downgradient, near the coast. A quasi-three-dimensional, finite-difference digital ground-water flow model was constructed to simulate flow in the Coastal Plain aquifers prior to development. The model also was used to evaluate the hydraulic responses to pumping that have occurred up to November 1982. The model consisted of five layers and a 48 by 63 node grid with a uniform square grid cell of 4 miles on a side. The Coastal Plain aquifers are recharged primarily by precipitation in their outcrop areas. Discharge is primarily as base flow to upper Coastal Plain rivers, to overlying aquifers by leakage through confining units, and to wells. Total simulated flow in the deep ground-water system was 967 cubic feet per second at the end of the transient simulation (1982). Recharge to the deep flow system simulated by the model was 793 cubic feet per second in the study area in 1982. Simulated aquifer discharge to large rivers was 660 cubic feet per second. Discharge to smaller rivers was not simulated because of the scale of the model. Changes resulting from ground-water pumping were significant as of 1982. The simulated water budget indicates that in 1982, 249 cubic feet per second were discharged from the aquifer system by wells. This pumping was balanced by the following changes from predevelopment conditions: 110 cubic feet per second derived from storage, 67 cubic feet per second decrease in aquifer-to-river discharge, 44 cubic feet per second increase in net inflow from source-sinks, and a net increase in inflow of 28 cubic feet per second across boundaries. Head declines in the Black Creek and Middendorf aquifers have occurred throughout much of the eastern part of the Coastal Plain of South Carolina as a result of pumping in the Myrtle Beach and Florence areas. Simulation indicates that the dominant sources of water for upper Coastal Plain pumping centers such as the city of Florence are decrease in flow to rivers in the upper Coastal Plain and water derived from storage. The dominant sources of water for pumping centers in the Myrtle Beach area are water derived from storage, leakage from overlying aquifers, and net increases in inflow across boundaries. Transmissivity values used in the flow simulation range from less than 1,000 feet squared per day near the updip limit of most aquifers to about 30,000 feet squared per day in the Middendorf aquifer in the Savannah River Plant area. Vertical hydraulic conductivity values used in simulation of confining units range from about 6x10 -7 feet per day for the confining unit between the Middendorf and Black Creek aquifers in coastal areas to 3x10 -2 feet per day for most of the confining units near their updip limits. Storage coefficients used in transient simulations were 0.15 where unconfined conditions exist and 0.0005 where confined conditions exist.

Georgia, North Carolina, South Carolina↗