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At least 1,009 records · Page 56Linked to original sources
USGS1999

Variations in trace element geochemistry in the Seine River Basin based on floodplain deposits and bed sediments

Between 1990 and 1995 a series of bed sediment, suspended sediment and fresh floodplain samples were collected within the Seine River Basin, in France, to evaluate variations in trace element geochemistry. Average background trace element levels for the basin were determined from the collection and subsequent analyses of bed sediment samples from small rural watersheds and from a prehistoric (5000 BP) site in Paris. Concentrations are relatively low, and similar to those observed for fine-grained bed sediments from unaffected areas in the United States and Canada. However, the concentrations are somewhat higher than the reference levels presently adopted by French water authorities for areas north of the Seine Basin, which have similar bedrock lithologies. Downstream trace element variations were monitored in 1994 and 1995 using fresh surficial floodplain samples that were collected either as dried deposits a few days after peak discharge, or immediately after peak discharge (under ≤30 cm of water). Chemical comparisons between fresh floodplain deposits, and actual suspended sediments collected during flood events, indicate that, with some caveats, the former can be used as surrogates for the latter. The floodplain sediment chemical data indicate that within the Seine Basin, from the relatively unaffected headwaters through heavily affected urban streams, trace element concentrations vary by as much as three orders of magnitude. These trace element changes appear to be the result of both increases in population as well as concomitant increases in industrial activity. (This article is a US government work and is in the public domain in the United States.)

Hydrological Processes↗
USGS1997

Application of two direct runoff prediction methods in Puerto Rico

Two methods for predicting direct runoff from rainfall data were applied to several basins and the resulting hydrographs compared to measured values. The first method uses a geomorphology-based unit hydrograph to predict direct runoff through its convolution with the excess rainfall hyetograph. The second method shows how the resulting hydraulic routing flow equation from a kinematic wave approximation is solved using a spectral method based on the matrix representation of the spatial derivative with Chebyshev collocation and a fourth-order Runge-Kutta time discretization scheme. The calibrated Green-Ampt (GA) infiltration parameters are obtained by minimizing the sum, over several rainfall events, of absolute differences between the total excess rainfall volume computed from the GA equations and the total direct runoff volume computed from a hydrograph separation technique. The improvement made in predicting direct runoff using a geomorphology-based unit hydrograph with the ephemeral and perennial stream network instead of the strictly perennial stream network is negligible. The hydraulic routing scheme presented here is highly accurate in predicting the magnitude and time of the hydrograph peak although the much faster unit hydrograph method also yields reasonable results.

Journal of Hydrologic Engineering↗
USGS2022

Simulation experiments comparing nonstationary design-flood adjustments based on observed annual peak flows in the conterminous United States

While nonstationary flood frequency analysis (NSFFA) methods have proliferated, few studies have rigorously compared them for modeling changes in both the central tendency and variability of annual peak-flow series, also known as the annual maximum series (AMS), in hydrologically diverse areas. Through Monte Carlo experiments, we appraise five methods for updating estimates of 10- and 100-year floods at gauged sites using synthetic records based on sample moments and change trajectories of observed AMS in the conterminous United States (CONUS). We compare two methods that consider changes in both central tendency and variability - a Gamma generalized linear model estimated with weighted least squares and the Generalized Additive Model for Location, Scale, Shape (GAMLSS) - with a distribution-free approach (quantile regression), and baseline cases assuming stationarity or only changes in central tendency. ‘Trend-space’ plots identify realistic AMS changes for which modeling trends in both central tendency and variability were warranted based on fractional root mean squared errors (fRMSE). They also reveal statistical properties of AMS under which NSFFA models perform especially well or poorly. For instance, quantile regression performed especially well (poorly) under strong negative (positive) skewness. Although the nonstationary LP3 distribution accommodates most AMS with trends well, the sensitivity of NSFFA model performance to different sample moments and trends suggests the need for more flexibility in prescribing design-flood adjustments in the CONUS. A follow-up comparison of regional NSFFA models pooling at-site AMS would further illuminate NSFFA guidance, especially for AMS with properties less conducive to NSFFA modeling, such as positive skewness and increasing variability.

Journal of Hydrology X↗
USGS2014

Anuran site occupancy and species richness as tools for evaluating restoration of a hydrologically-modified landscape

A fundamental goal of wetland restoration is to reinstate pre-disturbance hydrological conditions to degraded landscapes, facilitating recolonization by native species and the production of resilient, functional ecosystems. To evaluate restoration success, baseline conditions need to be determined and a reference target needs to be established that will serve as an ecological blueprint in the restoration process. During the summer wet seasons of 2010 and 2011, we used automated recording units to monitor a community of calling anuran amphibians in the Picayune Strand State Forest of Southwest Florida, USA. This area is undergoing hydrological restoration as part of the Comprehensive Everglades Restoration Plan. We compared occurrence of anurans at sites in the restoration area, to nearby locations in relatively undisturbed habitat (reference sites). We assessed the utility of the latter as restoration targets, using a hierarchical model of community species occupancy to estimate the probability of occurrence of anurans in restoration and reference locations. We detected 14 species, 13 of which were significantly more likely to occur in reference areas. All 14 species were estimated by our model to occur at these sites but, across both years, only 8–13 species were estimated to occur at restoration sites. The composition and structure of these habitats within and adjacent to the Picayune Strand State Forest indicate that they are suitable targets for habitat restoration, as measured by amphibian occurrence and species richness. These areas are important sources for recolonization of anuran amphibians as the hydrologically degraded Picayune Strand undergoes restoration to mitigate the effects of overdrainage and habitat loss.

Florida↗
USGS2017

On the probability distribution of daily streamflow in the United States

Daily streamflows are often represented by flow duration curves (FDCs), which illustrate the frequency with which flows are equaled or exceeded. FDCs have had broad applications across both operational and research hydrology for decades; however, modeling FDCs has proven elusive. Daily streamflow is a complex time series with flow values ranging over many orders of magnitude. The identification of a probability distribution that can approximate daily streamflow would improve understanding of the behavior of daily flows and the ability to estimate FDCs at ungaged river locations. Comparisons of modeled and empirical FDCs at nearly 400 unregulated, perennial streams illustrate that the four-parameter kappa distribution provides a very good representation of daily streamflow across the majority of physiographic regions in the conterminous United States (US). Further, for some regions of the US, the three-parameter generalized Pareto and lognormal distributions also provide a good approximation to FDCs. Similar results are found for the period of record FDCs, representing the long-term hydrologic regime at a site, and median annual FDCs, representing the behavior of flows in a typical year.

Hydrology and Earth System Sciences↗
USGS1998

Hydrogeology and simulation of the effects of reclaimed-water application in west Orange and southeast Lake counties, Florida

Wastewater reclamation and reuse has become increasingly popular as water agencies search for alternative water-supply and wastewater-disposal options. Several governmental agencies in central Florida currently use the land-based application of reclaimed water (wastewater that has been treated beyond secondary treatment) as a management alternative to surface-water disposal of wastewater. Water Conserv II, a water reuse project developed jointly by Orange County and the City of Orlando, began operation in December 1986. In 1995, the Water Conserv II facility distributed approximately 28 Mgal/d of reclaimed water for discharge to rapid-infiltration basins (RIBs) and for use as agricultural irrigation. The Reedy Creek Improvement District (RCID) began operation of RIBs in September 1990, and in 1995 these RIBs received approximately 6.7 Mgal/d of reclaimed water. Analyses of existing data and data collected during the course of this study were combined with ground-water flow modeling and particle-tracking analyses to develop a process-oriented evaluation of the regional effects of reclaimed water applied by Water Conserv II and the RCID RIBs on the hydrology of west Orange and southeast Lake Counties. The ground-water flow system beneath the study area is a multi-aquifer system that consists of a thick sequence of highly permeable carbonate rocks overlain by unconsolidated sediments. The hydrogeologic units are the unconfined surficial aquifer system, the intermediate confining unit, and the confined Floridan aquifer system, which consists of two major permeable zones, the Upper and Lower Floridan aquifers, separated by the less permeable middle semiconfining unit. Flow in the surficial aquifer system is dominated regionally by diffuse downward leakage to the Floridan aquifer system and is affected locally by lateral flow systems produced by streams, lakes, and spatial variations in recharge. Ground water generally flows laterally through the Upper Floridan aquifer aquifer to the north and east. Many of the lakes in the study area are landlocked because the mantled karst environment precludes a well developed network of surface-water drainage. The USGS three-dimensional ground-water flow model MODFLOW was used to simulate ground-water flow in the surficial and Floridan aquifer systems. A steady-state calibration to average 1995 conditions was performed by using a parameter estimation program to vary values of surficial aquifer system hydraulic conductivity, intermediate confining unit leakance, and Upper Floridan aquifer transmissivity. The calibrated model generally produced simulated water levels in close agreement with measured water levels and was used to simulate the hydrologic effects of reclaimed-water application under current (1995) and proposed future conditions. In 1995, increases of up to about 40 ft in the water table and less than 5 ft in the Upper Floridan aquifer potentiometric surface had occurred as a result of reclaimed-water application. The largest increases were under RIB sites. An average traveltime of 10 years at Water Conserv II and 7 years at the RCID RIBs was required for reclaimed water to move from the water table to the top of the Upper Floridan aquifer. Approximately 67 percent of the reclaimed water applied at the RCID RIB site recharged the Floridan aquifer system, whereas 33 percent discharged from the surficial aquifer system to surface-water features; 99 percent of the reclaimed water applied at Water Conserv II recharged the Floridan aquifer system, whereas only 1 percent discharged from the surficial aquifer system to surface-water features. The majority of reclaimed water applied at both facilities probably will ultimately discharge from the Floridan aquifer system outside the model boundaries. Proposed future conditions were assumed to consist of an additional 11.7 Mgal/d of reclaimed water distributed by the Water Conserv II and RCID facilities. Increases of up to about 20 ft in the water table and 2 ft in the potentiometric surface of the Upper Floridan aquifer were simulated. The directions of reclaimed water movement through the ground-water system generally were similar to those under 1995 conditions. However, the greater reclaimed-water application rate at the RCID RIBs caused approximately half of the RCID reclaimed water to discharge to surface-water features and half to recharge the Floridan aquifer system.

Florida↗
USGS2010

GAGES: A stream gage database for evaluating natural and alteredflow conditions in the conterminous United States

Stream flow is a controlling element in the ecology of rivers and streams. Knowledge of the natural flow regime facilitates the assessment of whether specific hydrologic attributes have been altered by humans in a particular stream and the establishment of specific goals for stream-flow restoration. Because most streams are ungaged or have been altered by human influences, characterizing the natural flow regime is often only possible by estimating flow characteristics based on nearby stream gages of reference quality, i.e., gaged locations that are least disturbed by human influences. The ability to evaluate natural stream flow, that which is not altered by human activities, would be enhanced by the existence of a nationally consistent and up-to-date database of gages in relatively undisturbed watersheds. As part of a national effort to characterize stream-flow effects on ecological condition, data for 6785 U.S. Geological Survey (USGS) stream gages and their upstream watersheds were compiled. The sites comprise all USGS stream gages in the conterminous United States with at least 20 years of complete-year flow record from 1950–2007, and for which watershed boundaries could reliably be delineated (median size ¼ 578 km2). Several hundred watershed and site characteristics were calculated or compiled from national data sources, including environmental features (e.g., climate, geology, soils, topography) and anthropogenic influences (e.g., land use, roads, presence of dams, or canals). In addition, watersheds were assessed for their reference quality within nine broad regions for use in studies intended to characterize stream flows under conditions minimally influenced by human activities. Three primary criteria were used to assess reference quality: (1) a quantitative index of anthropogenic modification within the watershed based on GIS-derived variables, (2) visual inspection of every stream gage and drainage basin from recent high-resolution imagery and topographic maps, and (3) information about man-made influences from USGS Annual Water Data Reports. From the set of 6785 sites, we identified 1512 as reference-quality stream gages. All data derived for these watersheds as well as the reference condition evaluation are provided as an online data set termed GAGES (geospatial attributes of gages for evaluating stream flow).

Ecology↗
USGS2022

Analysis of per capita contributions from a spatial model provides strategies for controlling spread of invasive carp

Metapopulation models may be applied to inform natural resource management to guide actions targeted at location-specific subpopulations. Model insights frequently help to understand which subpopulations to target and highlight the importance of connections among subpopulations. For example, managers often treat aquatic invasive species populations as discrete populations due to hydrological (e.g., lakes, pools formed by dams) or jurisdictional boundaries (e.g., river segments by country or jurisdictional units such as states or provinces). However, aquatic invasive species often have high rates of dispersion and migration among heterogenous locations, which complicates traditional metapopulation models and may not conform to management boundaries. Controlling invasive species requires consideration of spatial dynamics because local management activities (e.g., harvest, movement deterrents) may have important impacts on connected subpopulations. We expand upon previous work to create a spatial linear matrix model for an aquatic invasive species, Bighead Carp, in the Illinois River, USA, to examine the per capita contributions of specific subpopulations and impacts of different management scenarios on these subpopulations. Managers currently seek to prevent Bighead Carp from invading the Great Lakes via a connection between the Illinois Waterway and Lake Michigan by allocating management actions across a series of river pools. We applied the model to highlight how spatial variation in movement rates and recruitment can affect decisions about where management activities might occur. We found that where the model suggested management actions should occur depend crucially on the specific management goal (i.e., limiting the growth rate of the metapopulation vs. limiting the growth rate of the invasion front) and the per capita recruitment rate in downstream pools. Our findings illustrate the importance of linking metapopulation dynamics to management goals for invasive species control.

Illinois↗
USGS2012

Regional regression models of watershed suspended-sediment discharge for the eastern United States

Estimates of mean annual watershed sediment discharge, derived from long-term measurements of suspended-sediment concentration and streamflow, often are not available at locations of interest. The goal of this study was to develop multivariate regression models to enable prediction of mean annual suspended-sediment discharge from available basin characteristics useful for most ungaged river locations in the eastern United States. The models are based on long-term mean sediment discharge estimates and explanatory variables obtained from a combined dataset of 1201 US Geological Survey (USGS) stations derived from a SPAtially Referenced Regression on Watershed attributes (SPARROW) study and the Geospatial Attributes of Gages for Evaluating Streamflow (GAGES) database. The resulting regional regression models summarized for major US water resources regions 1–8, exhibited prediction R 2 values ranging from 76.9% to 92.7% and corresponding average model prediction errors ranging from 56.5% to 124.3%. Results from cross-validation experiments suggest that a majority of the models will perform similarly to calibration runs. The 36-parameter regional regression models also outperformed a 16-parameter national SPARROW model of suspended-sediment discharge and indicate that mean annual sediment loads in the eastern United States generally correlates with a combination of basin area, land use patterns, seasonal precipitation, soil composition, hydrologic modification, and to a lesser extent, topography.

Journal of Hydrologic Engineering↗
USGS2002

The geohydrologic setting of Yucca Mountain, Nevada

This paper provides a geologic and hydrologic framework of the Yucca Mountain region for the geochemical papers in this volume. The regional geologic units, which range in age from late Precambrian through Holocene, are briefly described. Yucca Mountain is composed of dominantly pyroclastic units that range in age from 11.4 to 15.2 Ma. The principal focus of study has been on the Paintbrush Group, which includes two major zoned and welded ash-flow tuffs separated by an important hydrogeologic unit referred to as the Paintbrush non-welded (PTn). The regional structural setting is currently one of extension, and the major local tectonic domains are presented together with a tectonic model that is consistent with the known structures at Yucca Mountain. Streamflow in this arid to semi-arid region occurs principally in intermittent or ephemeral channels. Near Yucca Mountain, the channels of Fortymile Wash and Amargosa River collect infrequent runoff from tributary basins, ultimately draining to Death Valley. Beneath the surface, large-scale interbasin flow of groundwater from one valley to another occurs commonly in the region. Regional groundwater flow beneath Yucca Mountain originates in the high mesas to the north and returns to the surface either in southern Amargosa Desert or in Death Valley, where it is consumed by evapotranspiration. The water table is very deep beneath the upland areas such as Yucca Mountain, where it is 500-750 m below the land surface, providing a large thickness of unsaturated rocks that are potentially suitable to host a nuclear-waste repository. The nature of unsaturated flow processes, which are important for assessing radionuclide migration, are inferred mainly from hydrochemical or isotopic evidence, from pneumatic tests of the fracture systems, and from the results of in situ experiments. Water seeping down through the unsaturated zone flows rapidly through fractures and more slowly through the pores of the rock matrix. Although capillary forces are expected to divert much of the flow around repository openings, some may drip onto waste packages, ultimately causing release of radionuclides, followed by transport down to the water table. ?? 2002 Elsevier Science Ltd. All rights reserved.

Applied Geochemistry↗
USGS2011

Classifying the water table at regional to continental scales

Water tables at regional to continental scales can be classified into two distinct types: recharge-controlled water tables that are largely disconnected from topography and topography-controlled water tables that are closely tied to topography. We use geomatic synthesis of hydrologic, geologic and topographic data sets to quantify and map water-table type over the contiguous United States using a dimensionless criterion introduced by Haitjema and Mitchell-Bruker (2005), called the water-table ratio, which differentiates water-table type. Our analysis indicates that specific regions of the United States have broadly contiguous and characteristic water-table types. Water-table ratio relates to water-table depth and the potential for regional groundwater flow. In regions with recharge-controlled water tables, for example the Southwest or Rocky Mountains, USA, water-tables depths are generally greater and more variable and regional groundwater flow is generally more important as a percentage of the watershed budget. Water-table depths are generally shallow and less variable, and regional groundwater flow is limited in areas with topography-controlled water tables such as the Northeast USA. The water-table ratio is a simple but powerful criterion for evaluating regional groundwater systems over broad areas.

Geophysical Research Letters↗
USGS2026

Large streamflow differences between forested and urbanized watersheds in the energy-limited eastern United States: The role of evapotranspiration and impervious surfaces

Urban forests and other green infrastructures have been viewed as part of the “Nature-based Solutions” (NbS) to mitigate emerging urban environmental change. This study focuses on the role of evapotranspiration (ET) in regulating water balances of small watersheds in the eastern United States. We compared streamflow and ET patterns at daily, monthly and annual scales and linked these hydrological variables to the physical properties of 11 paired watersheds dominated by forests (FW) or urban (UW) land covers. The annual precipitation ranged from 1028 mm to 1683 mm and potential ET (PET) from 815 mm to 1450 mm. The mean annual flow/precipitation (Q/P) ratios were 0.26 ± 0.13 and 0.41 ± 0.1 for FW and UW, respectively. Overall, UW had lower annual ET (772 mm in UW vs. 947 mm in FW), but higher mean annual and (∼58% higher), monthly water yield (17%–186% higher), and peakflow rates (up to 100 times higher) than FW. The streamflow differences between FW and UW were most pronounced during the growing season and early winter (June-November). The mean Q/P ratios for 30 large hurricane events (2016–2021) were 0.12 ± 0.11 and 0.38 ± 0.23 for FW and UW, respectively. The flow rates in the dormant season (around December-May) in UW were similar or lower than FW. We developed conceptual models to explain the seasonal and storm event streamflow differences using background climate (PET), ET, and land surface characteristics. Urban NbS designs should factor in strategies that maximize ET while minimizing impervious surfaces enhancing watershed “sponge” and “pump” functions.

eastern United States↗
USGS2011

Sources and Delivery of Nutrients to the Northwestern Gulf of Mexico from Streams in the South-Central United States

SPAtially Referenced Regressions On Watershed attributes (SPARROW) models were developed to estimate nutrient inputs [total nitrogen (TN) and total phosphorus (TP)] to the northwestern part of the Gulf of Mexico from streams in the South‐Central United States (U.S.). This area included drainages of the Lower Mississippi, Arkansas‐White‐Red, and Texas‐Gulf hydrologic regions. The models were standardized to reflect nutrient sources and stream conditions during 2002. Model predictions of nutrient loads (mass per time) and yields (mass per area per time) generally were greatest in streams in the eastern part of the region and along reaches near the Texas and Louisiana shoreline. The Mississippi River and Atchafalaya River watersheds, which drain nearly two‐thirds of the conterminous U.S., delivered the largest nutrient loads to the Gulf of Mexico, as expected. However, the three largest delivered TN yields were from the Trinity River/Galveston Bay, Calcasieu River, and Aransas River watersheds, while the three largest delivered TP yields were from the Calcasieu River, Mermentau River, and Trinity River/Galveston Bay watersheds. Model output indicated that the three largest sources of nitrogen from the region were atmospheric deposition (42%), commercial fertilizer (20%), and livestock manure (unconfined, 17%). The three largest sources of phosphorus were commercial fertilizer (28%), urban runoff (23%), and livestock manure (confined and unconfined, 23%).

Texas, Oklahoma, Arkansas, Louisiana, Missouri, Ka↗
USGS2009

Prominence of ichnologically influenced macroporosity in the karst Biscayne aquifer: Stratiform "super-K" zones

A combination of cyclostratigraphic, ichnologic, and borehole geophysical analyses of continuous core holes; tracer-test analyses; and lattice Boltzmann flow simulations was used to quantify biogenic macroporosity and permeability of the Biscayne aquifer, southeastern Florida. Biogenic macroporosity largely manifests as: (1) ichnogenic macroporosity primarily related to postdepositional burrowing activity by callianassid shrimp and fossilization of components of their complex burrow systems (Ophiomorpha); and (2) biomoldic macroporosity originating from dissolution of fossil hard parts, principally mollusk shells. Ophiomorpha-dominated ichno-fabric provides the greatest contribution to hydrologic characteristics in the Biscayne aquifer in a 345 km 2 study area. Stratiform tabular-shaped units of thalassinidean-associated macroporosity are commonly confined to the lower part of upward-shallowing high-frequency cycles, throughout aggradational cycles, and, in one case, they stack vertically within the lower part of a high-frequency cycle set. Broad continuity of many of the macroporous units concentrates groundwater flow in extremely permeable passage-ways, thus making the aquifer vulnerable to long-distance transport of contaminants. Ichnogenic macroporosity represents an alternative pathway for concentrated groundwater flow that differs considerably from standard karst flow-system paradigms, which describe groundwater movement through fractures and cavernous dissolution features. Permeabilities were calculated using lattice Boltzmann methods (LBMs) applied to computer renderings assembled from X-ray computed tomography scans of various biogenic macroporous limestone samples. The highest simulated LBM permeabilities were about five orders of magnitude greater than standard laboratory measurements using air-permeability methods, which are limited in their application to extremely permeable macroporous rock samples. Based on their close conformance to analytical solutions for pipe flow, LBMs offer a new means of obtaining accurate permeability values for such materials. We suggest that the stratiform ichnogenic groundwater flow zones have permeabilities even more extreme (???2-5 orders of magnitude higher) than the Jurassic "super-K" zones of the giant Ghawar oil field. The flow zones of the Pleistocene Biscayne aquifer provide examples of ichnogenic macroporosity for comparative analysis of origin and evolution in other carbonate aquifers, as well as petroleum reservoirs. ?? 2008 Geological Society of America.

Geological Society of America Bulletin↗
USGS2017

Control of landslide volume and hazard by glacial stratigraphic architecture, Northwest Washington state, USA

Landslide volumes span many orders of magnitude, but large-volume slides tend to travel farther and consequently can pose a greater hazard. In northwest Washington State, USA, a landscape abounding with landslides big and small, the recent occurrence of the large-volume and tragically deadly State Route 530 (Oso) landslide is a stark reminder of the hazards associated with glacial terraces lining valleys of the western Cascade Range. What controls the differences in location and size of these slope failures? Here, we examine the control on landslide volume and failure style by terrace sedimentary architecture. We analyze lidar topographic data in three nearby valleys and find significant variation in landslide deposit volumes, morphology, and relative mobility in each valley. Geologic data show that each site differs in the thickness and position of outwash, tills, and glaciolacustrine clays. Combining a three-dimensional limit-equilibrium slope-stability analysis (Scoops3D) with simulations of variably saturated groundwater flow (VS2Dt), we show that landslide volumes are highly sensitive both to the distribution of material strength as well as the location of perched water tables. Modeled landslides match observed failure sizes and depths in all valleys when the effects of variably saturated groundwater flow are included. The position and thickness of low-strength strata act as first-order controls on landslide volume, with peak volumes for stratigraphic geometries similar to that of the valley containing the Oso landslide. Knowledge of feedbacks between lithology and hydrology is therefore critical to assess the landslide hazard and evolution of landscapes composed of stratigraphically layered units.

Washington↗
USGS2007

Three-dimensional geologic model of the northern Nevada rift and the Beowawe geothermal system, north-central Nevada

A three-dimensional (3D) geologic model of part of the northern Nevada rift encompassing the Beowawe geothermal system was developed from a series of two-dimensional (2D) geologic and geophysical models. The 3D model was constrained by local geophysical, geologic, and drill-hole information and integrates geologic and tectonic interpretations for the region. It places important geologic constraints on the extent and configuration of the active Beowawe geothermal system. The geologic framework represented in this model facilitates hydrologic modeling of the Beowawe geothermal system and evaluation of fluid flow in faults and adjacent rock units. Basin depths were determined using an iterative gravity-inversion technique that calculates the thickness of low-density, basin-filling deposits. The remaining subsurface structure was modeled using 2D potential-field modeling software. Crustal cross sections from the 2D models were generalized for use in the 3D model and consist of six stratigraphic layers defined as low-density basin sediments, volcanic rocks, basalt-andesite rocks of the northern Nevada rift, Jurassic and Cretaceous intrusive rocks, and Paleozoic siliceous and carbonate sedimentary rocks of the upper and lower plates of the Roberts Mountains allochthon, respectively. This simplified stratigraphy was combined with mapped surface geology and was extrapolated across the 3D model area. Features along the northern Nevada rift depicted by the model may represent preexisting crustal structures that controlled the locations and character of Tertiary tectonic and magmatic events related to Basin and Range extension and emplacement of the middle Miocene northern Nevada rift. Several of the geologic features represented are important components of the Beowawe geothermal system. Prominent ENE-trending faults (e.g., Malpais fault) that bound the southern edge of Whirlwind Valley, and older NNW-striking faults (e.g., Dunphy Pass and Muleshoe faults) that form major features of the model, are likely important pathways for geothermal fluids and groundwater flow from the Humboldt River, which may recharge the Beowawe system.

Nevada↗
USGS1998

USGS Mineral Resources Program: International Activities

The USGS is the country's leading earth science organization. Since 1879, USGS scientists have gathered and analyzed data and disseminated the results of their research on the geology, cartography, hydrology, and, more recently biology, of every continent and ocean on Earth. Multidisciplinary research both in the United States and in the international arena has been an important part of the USGS mission. The USGS Mineral Resources Program is the sole Federal agency program that provides high-quality scientific information, objective resource assessments, and unbiased research results on mineral issues

Fact Sheet↗
USGS2000

Water-quality assessment of the Eastern Iowa Basins: Hydrologic and biologic data, October 1996 through September 1998

Hydrologic and biologic data collected from October 1996 through September 1998 in the Eastern Iowa Basins study unit of the U.S. Geological Survey National Water-Quality Assessment Program are presented in this report. Monthly data collected from 12 sites on rivers and streams included measurements of physical properties and determinations of the concentrations of nutrients, major ions, organic carbon, trace elements, suspended sediment, and dissolved pesticides. Fish-tissue samples were collected at two sites in September 1997 and analyzed for organochlorine pesticides. In addition, water-quality assessments were made at 25 sites as part of a synoptic study in August 1997 and May 1998. A ground-water study was conducted to evaluate the effects of agricultural and urban land use on the water quality of shallow alluvial aquifers in the study unit. Samples were collected and analyzed from wells in 31 agricultural and 30 urban land-use areas during June-August 1997. Samples were collected and analyzed from 32 domestic wells during June-July 1998 to provide a broad assessment of the water quality of shallow alluvial aquifers throughout the study unit. Samples were collected during August 1998 from 27 shallow monitoring wells completed in the Iowa River alluvial aquifer to evaluate the effects of changing land use on shallow ground-water quality. Ground-water samples were analyzed for physical properties, nutrients, major ions, organic carbon, trace elements, dissolved pesticides, volatile organic compounds, radon-222, and tritium.

Iowa↗