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At least 865 records · Page 48Linked to original sources
USGS2002

Atlas of natural hazards in the Hawaiian coastal zone

The purpose of this report is to communicate to citizens and regulatory authorities the history and relative intensity of coastal hazards in Hawaii. This information is the key to the wise use and management of coastal resources. The information contained in this document,we hope,will improve the ability of Hawaiian citizens and visitors to safely enjoy the coast and provide a strong data set for planners and managers to guide the future of coastal resources. This work is largely based on previous investigations by scientific and engineering researchers and county, state, and federal offices and agencies. The unique aspect of this report is that, to the extent possible, it assimilates prior efforts in documenting Hawaiian coastal hazards and combines existing knowledge into a single comprehensive coastal hazard data set. This is by no means the final word on coastal hazards in Hawaii. Every hazardous phenomenon described here, and others such as slope failure and rocky shoreline collapse, need to be more carefully quantified, forecast, and mitigated. Our ultimate goal, of course, is to make the Hawaiian coast a safer place by educating the people of the state, and their leaders, about the hazardous nature of the environment. In so doing, we will also be taking steps toward improved preservation of coastal environments, because the best way to avoid coastal hazards is to avoid inappropriate development in the coastal zone. We have chosen maps as the medium for both recording and communicating the hazard history and its intensity along the Hawaiian coast.Two types of maps are used: 1) smallscale maps showing a general history of hazards on each island and summarizing coastal hazards in a readily understandable format for general use, and 2) a large-scale series of technical maps (1:50,000) depicting coastal sections approximately 5 to 7 miles in length with color bands along the coast ranking the relative intensity of each hazard at the adjacent shoreline.

Hawaii↗
USGS2017

The Surge, Wave, and Tide Hydrodynamics (SWaTH) network of the U.S. Geological Survey—Past and future implementation of storm-response monitoring, data collection, and data delivery

After Hurricane Sandy made landfall along the northeastern Atlantic coast of the United States on October 29, 2012, the U.S. Geological Survey (USGS) carried out scientific investigations to assist with protecting coastal communities and resources from future flooding. The work included development and implementation of the Surge, Wave, and Tide Hydrodynamics (SWaTH) network consisting of more than 900 monitoring stations. The SWaTH network was designed to greatly improve the collection and timely dissemination of information related to storm surge and coastal flooding. The network provides a significant enhancement to USGS data-collection capabilities in the region impacted by Hurricane Sandy and represents a new strategy for observing and monitoring coastal storms, which should result in improved understanding, prediction, and warning of storm-surge impacts and lead to more resilient coastal communities. As innovative as it is, SWaTH evolved from previous USGS efforts to collect storm-surge data needed by others to improve storm-surge modeling, warning, and mitigation. This report discusses the development and implementation of the SWaTH network, and some of the regional stories associated with the landfall of Hurricane Sandy, as well as some previous events that informed the SWaTH development effort. Additional discussions on the mechanics of inundation and how the USGS is working with partners to help protect coastal communities from future storm impacts are also included.

Connecticut, Delaware, Maine, Maryland, Massachuse↗
USGS2005

Sediment-transport investigations of the upper Yellowstone River, Montana, 1999 through 2001: Data collection, analysis, and simulation of sediment transport

The upper Yellowstone River in Montana is an important State and national water resource, providing recreational, agricultural, and commercial benefits. Floods in 1996 and 1997, with recorded peak discharges having recurrence intervals close to 100 years, caused substantial streambank erosion and hill- slope mass wasting. Large quantities of sand-, gravel-, and cobble-sized material entrained by the flood flows became flood-bar deposits, creating a source of sediment available for transport during future floods. The flood damage and resulting sedimentation raised concerns about potential streambank-stabilization projects and how the river and riparian corridor might be managed in the future. The U.S. Geological Survey, in cooperation with the Park Conservation District, the Montana Department of Transportation, and the U.S. Army Corps of Engineers, investigated sediment transport in the upper Yellowstone River near Livingston from 1999 through 2001 as part of a cumulative effects study to provide a scientific basis for future river management decisions. The purpose of this report is to present the results of data collection, analysis, and simulation of sediment transport for the upper Yellowstone River. The study area included a 13.5-mile study reach of the upper Yellowstone River where substantial sediment transport occurred in 1996 and 1997. In this study area, the upper Yellowstone River is a high gradient, coarse-bed stream having a slope of about 0.0028 foot per foot or more than 14 feet per mile. The study area drains about 3,551 square miles, and runoff results primarily from snowmelt during the spring and summer months. As part of sediment-transport investigations, the U.S. Geological Survey surveyed river cross sections, characterized streambed-material particle size using particle counts and sieve analyses, and collected bedload- and suspended-sediment data during three runoff seasons (1999-2001). Data were collected for stream discharges that ranged from 2,220 cubic feet per second (typical of pre- and post-runoff discharge) to 25,100 cubic feet per second (about 125 percent of bankfull discharge). The distribution of streambed-material particle size was determined, and sediment-transport curves for bedload discharge, suspended-sediment discharge, and total-sediment discharge were developed. The threshold values of streamflow and average stream velocity needed for initiation of bedload transport for selected sediment-size classes showed that little to no bedload was transported for an average stream velocity below about 3 feet per second, and the only particle size transported as bedload at that velocity was sand. Over the range of stream discharges sampled and with silt- and finer-sized particles excluded, bedload discharge averaged about 18 percent of the total-sediment discharge, equal to bedload discharge plus suspended-sediment discharge. At the lowest and highest stream discharges sampled, bedload was, respectively, less than about 2 percent and about 30 percent of the total-sediment discharge. Over the range of stream discharges sampled, the sand-sized part of the total suspended-sediment discharge averaged about 48 percent, where the total suspended-sediment discharge included sand-, silt- and finer-sized particles. At the lowest and highest stream discharges sampled, the sand-sized part of the total suspended-sediment discharge was, respectively, less than about 16 percent and about 50 percent of the total suspended-sediment discharge. The sediment-transport curves were compared to curves for selected sites in the western United States having drainage areas ranging from 21 square miles to over 20,000 square miles. Daily sediment loads transported at bankfull discharge were calculated for each site and results were plotted in relation to drainage area. Results based on the 1999-2001 data-collection period indicate that the estimated daily bedload transported at bankfull discharge in the upper Yellowstone River exceeded the envelope line that bounds the upper end of the data for other selected sites in the Northern Rocky Mountains and is similar in magnitude to that for selected sites in Alaska having braided channels and glacial and snowmelt runoff. Similar comparisons for suspended sediment indicate that daily suspended-sediment load at bankfull discharge is relatively high in the upper Yellowstone River, plotting slightly above the envelope line that bounds the upper end of the data for other selected sites in the Northern Rocky Mountains. Sediment data were used to develop individual transport equations for seven size classes of sediment ranging from small cobbles to very fine sand. A step-wise regression procedure relating sediment discharge to important hydraulic variables showed that average stream velocity was the only significant variable at the 95-percent confidence level. Bedload and suspended-sediment data and equations indicate that more sand is transported for a given velocity than any other particle size, and very little sand-size sediment load is transported below an average stream velocity of about 2.5 feet per second. Transport of coarser-sized sediment (limited to bedload) becomes very little for an average velocity less than about 3.5 feet per second. Results for the 1999-2001 data-collection period indicate that sediment transport in the upper Yellowstone River tends to be limited more by the transport capacity of the stream (capacity or transport limited), than to the availability of sediment in the watershed (supply limited). Sediment data collected and analyzed were used to simulate sediment transport in the study reach using the BRIdge Stream Tube model for Alluvial River Simulation, or BRI-STARS computer model. The model was calibrated and verified using selected data from historical runoff periods. Simulated total-sediment loads, on a reach-averaged basis, were in good agreement with the total-sediment loads determined from the transport curve for the 2-year flood hydrograph but were considerably smaller for the total-sediment loads determined from the transport curve for the 50-, 100-, and 500-year flood hydrographs. The differences probably were largely due to the inability of the model to simulate streambank erosion, hillslope mass-wasting, and other channel-widening processes, which had supplied substantial quantities of sediment to the channel during the 1996 and 1997 floods, and probably continued to contribute to the sediment load in the subsequent years (1999-2001) when the data were collected. Furthermore, the transport curve was applied beyond the measured data for the highest discharges, and may thus be unreliable. Also, the transport curve derived from only limited data may not apply over the full duration of the hydrograph and sediment might be transported over only a portion of the hydrograph, especially for rivers like the upper Yellowstone where snowmelt runoff predominates. The true sediment discharge is, therefore, unknown and might be closer to the simulated values than to the values calculated from the transport curve.

Montana↗
USGS2015

Changes in data sharing and data reuse practices and perceptions among scientists worldwide

The incorporation of data sharing into the research lifecycle is an important part of modern scholarly debate. In this study, the DataONE Usability and Assessment working group addresses two primary goals: To examine the current state of data sharing and reuse perceptions and practices among research scientists as they compare to the 2009/2010 baseline study, and to examine differences in practices and perceptions across age groups, geographic regions, and subject disciplines. We distributed surveys to a multinational sample of scientific researchers at two different time periods (October 2009 to July 2010 and October 2013 to March 2014) to observe current states of data sharing and to see what, if any, changes have occurred in the past 3–4 years. We also looked at differences across age, geographic, and discipline-based groups as they currently exist in the 2013/2014 survey. Results point to increased acceptance of and willingness to engage in data sharing, as well as an increase in actual data sharing behaviors. However, there is also increased perceived risk associated with data sharing, and specific barriers to data sharing persist. There are also differences across age groups, with younger respondents feeling more favorably toward data sharing and reuse, yet making less of their data available than older respondents. Geographic differences exist as well, which can in part be understood in terms of collectivist and individualist cultural differences. An examination of subject disciplines shows that the constraints and enablers of data sharing and reuse manifest differently across disciplines. Implications of these findings include the continued need to build infrastructure that promotes data sharing while recognizing the needs of different research communities. Moving into the future, organizations such as DataONE will continue to assess, monitor, educate, and provide the infrastructure necessary to support such complex grand science challenges.

PLoS ONE↗
USGS2020

Linking monitoring and data analysis to predictions and decisions for the range-wide eastern black rail status assessment

The US Fish and Wildlife Service has initiated a re-envisioned approach for providing decision makers with the best available science and synthesis of that information, called the Species Status Assessment (SSA), for endangered species decision making. The SSA report is a descriptive document that provides decision makers with an assessment of a species’ current status and predicted future status. These analyses support all manner of decisions under the US Endangered Species Act, such as listing, reclassification, recovery planning, etc. Novel scientific analysis and predictive modeling in SSAs could be an important part of rooting species conservation decisions in current data and cutting edge analytical and modeling techniques. Here we describe a novel analysis of available data to assess current condition of eastern black rail across its range in a dynamic occupancy analysis. We used the results of the analysis to develop a site occupancy projection model where the model parameters (initial occupancy, site persistence, colonization) were linked to environmental covariates, such as land management and land cover change (sea-level rise, development, etc.). We used the projection model to predict future conditions under multiple sea-level rise and habitat management scenarios. Occupancy probability and site colonization were low in all analysis units and site persistence was also low, suggesting low resiliency and redundancy currently. Extinction probability was high for all analysis units in all simulated scenarios except one with significant effort to preserve existing habitat, suggesting low future resiliency and redundancy. With results of these data analyses and predictive modeling, the US Fish and Wildlife Service concluded that protections of the Endangered Species Act were warranted for this subspecies.

Endangered Species Research↗
USGS2006

High-resolution geologic mapping of the inner continental shelf: Boston Harbor and approaches, Massachusetts

This report presents the surficial geologic framework data and information for the sea floor of Boston Harbor and Approaches, Massachusetts (fig. 1.1). This mapping was conducted as part of a cooperative program between the U.S. Geological Survey (USGS), the Massachusetts Office of Coastal Zone Management (CZM), and the National Oceanic and Atmospheric Administration (NOAA). The primary objective of this project was to provide sea floor geologic information and maps of Boston Harbor to aid resource management, scientific research, industry and the public. A secondary objective was to test the feasibility of using NOAA hydrographic survey data, normally collected to update navigation charts, to create maps of the sea floor suitable for geologic and habitat interpretations. Defining sea-floor geology is the first steps toward managing ocean resources and assessing environmental changes due to natural or human activity. The geophysical data for these maps were collected as part of hydrographic surveys carried out by NOAA in 2000 and 2001 (fig. 1.2). Bottom photographs, video, and samples of the sediments were collected in September 2004 to help in the interpretation of the geophysical data. Included in this report are high-resolution maps of the sea floor, at a scale of 1:25,000; the data used to create these maps in Geographic Information Systems (GIS) format; a GIS project; and a gallery of photographs of the sea floor. Companion maps of sea floor to the north Boston Harbor and Approaches are presented by Barnhardt and others (2006) and to the east by Butman and others (2003a,b,c). See Butman and others (2004) for a map of Massachusetts Bay at a scale of 1:125,000. The sections of this report are listed in the navigation bar along the left-hand margin of this page. Section 1 (this section) introduces the report. Section 2 presents the large-format map sheets. Section 3 describes data collection, processing, and analysis. Section 4 summarizes the geologic history of the region and discusses geomorphic and anthropogenic features within the study area. Section 4 also provides references that contain additional information about the region. Appendix 1 provides GIS layers of all the data collected in this study, Appendix 2 contains the grain size textural analyses of sediment samples, and Appendix 3 contains bottom photographs of the sea floor in JPG format.

Massaachusetts↗
USGS2025

Unlocking ecological insights from sub-seasonal visible-to-shortwave infrared imaging spectroscopy: The SHIFT campaign

We stand at the threshold of a transformative era in Earth observation, marked by space-borne visible-to-shortwave infrared (VSWIR) imaging spectrometers that promise consistent global observations of ecosystem function, phenology, and inter- and intra-annual change. However, the full value of repeat spectroscopy, the information embedded within different temporal scales, and the reliability of existing algorithms across diverse ecosystem types and vegetation phenophases have remained elusive due to the absence of suitable sub-seasonal spectroscopy data. In response, the Surface Biology and Geology (SBG) High-Frequency Time Series (SHIFT) campaign was initiated during late February 2022 in Santa Barbara County, California. SHIFT, designed to support NASA's SBG mission, addressed mission scoping, scientific advancement, applications development, and community building. This ambitious endeavor included weekly Airborne Visible InfraRed Imaging Spectrometer-Next Generation (AVIRIS-NG) imagery acquisitions for 13 weeks (spanning February 24 to May 29, 2022), accompanied by coordinated terrestrial vegetation and coastal aquatic data collection. We describe the rich datasets collected and illustrate how the complex sub-seasonal patterns of change can be linked to biological science and applications, surpassing insights from multispectral observations. Leveraging open-source processing methods and cloud-based analysis tools, the SHIFT campaign showcases the readiness of the scientific community to harness ecological insights from remotely sensed hyperspectral time series. We provide an overview of SHIFT's goals, data collections, preliminary results, and the collaborative efforts of early career scientists committed to unlocking the transformative potential of high-frequency time series data from space-borne VSWIR imaging spectrometers.

Ecosphere↗
USGS2002

Digital data grids for the magnetic anomaly map of North America

The digital magnetic anomaly database and map for the North American continent is the result of a joint effort by the Geological Survey of Canada (GSC), U. S. Geological Survey (USGS), and Consejo de Recursos Minerales of Mexico (CRM). This integrated, readily accessible, modern digital database of magnetic anomaly data is a powerful tool for further evaluation of the structure, geologic processes, and tectonic evolution of the continent and may also be used to help resolve societal and scientific issues that span national boundaries. The North American magnetic anomaly map derived from the digital database provides a comprehensive magnetic view of continental-scale trends not available in individual data sets, helps link widely separated areas of outcrop, and unifies disparate geologic studies. This open-file report presents three unique, gridded data sets used to make the magnetic anomaly map of North America. Subsets of these three grids that span only the United States were also created, giving a total of six grids. Details on the data processing and compilation procedures used to produce the grids are described in the booklet that accompanies the North American magnetic anomaly map. All three grids have 1-km spacing and are projected to the DNAG projection (spherical transverse mercator, central meridian of 100 o W, base latitude of 0o, scale factor of 0.926 and Earth radius of 6,371,204 m.) More details are given in the metadata files that accompany the gridded data files. These grids are presented in Geosoft binary grid format, with two files describing each of the six grids (suffixes .grd and .gi). This format can be easily converted to numerous other formats using the free conversion software offered by this company at http://www.geosoft.com/. The first grids (NAmag_origmrg.grd and USmag_origmrg.grd) show the magnetic field at 305 m. above terrain. For the second grids (NAmag_hp500.grd and USmag_hp500.grd) we removed long-wavelength anomalies (500 km and greater) from the first grid. This grid was used for the published map. Although the North American merged grid represents a significant upgrade to older compilations, the existing patchwork of surveys is inherently unable to accurately represent anomalies with long (greater than roughly 150 km) wavelengths, particularly in the US and Canada (U.S. Magnetic-Anomaly Data Set Task Group, 1994). The lack of information about long wavelength anomalies is primarily related to datum shifts between merged surveys, caused by data acquisition at widely different times and by differences in merging procedures. Therefore, we removed anomalies with wavelengths greater than 500 km from the merged grid to reduce the effects caused by the spurious long wavelengths but still maintain the continuity of anomalies. The correction was accomplished by transforming the merged grid to the frequency domain, filtering the transformed data with a long-wavelength cutoff at 500 km, and subtracting the long-wavelength data grid from the merged grid. In addition to the 500-km high pass filter, an equivalent source method, based on long-wavelength characterization using satellite data (CHAMP satellite anomalies, Maus and others, 2002), was also used to correct for spurious shifts in the original magnetic anomaly grid (Ravat and others, 2002). These results are presented in the third grids (NAmag_CM.grd and USmag_CM.grd), in which the wavelengths longer than 500 km have been replaced by downward-continued satellite data. The steps used to create the third long-wavelength-corrected grid are: 0. The North American 1-km merged grid was decimated to 5 km. 1. This 5-km grid was converted to a 0.05 degree grid and was low-pass filtered using a Gaussian filter with a 500-km cutoff, then decimated to 1 degree. 2. A joint inversion of this 1-degree low-pass aeromagnetic grid and satellite data, with the aeromagnetic data weighted very low, was used to produce a stabilized downward continuation of the satellite data. 3. The inverted data were interpolated to 0.05 degrees and again low-pass filtered using the same Gaussian 500-km filter to remove short-wavelength artifacts. 4. The low-pass grid from step 1 was subtracted from the original 0.05-degree aeromagnetic grid to create a 500-km high-pass aeromagnetic grid. This grid was added to the low-pass inverted grid from step 3 to get a corrected 0.05-degree aeromagnetic grid. 5. The corrected 0.05-degree aeromagnetic grid was projected to the DNAG projection and regridded to 5 km. This was subtracted from the decimated 5-km aeromagnetic grid to generate a 5-km correction grid. A matched filter was used to remove short-wavelength artifacts resulting from the projection and regridding process. 6. The resulting 5-km correction grid was regridded to the original 1-km grid and subtracted from the original 1-km aeromagnetic grid to generate the final 1-km corrected aeromagnetic grid. The six grids described in this report are available for download. Two metadata files, one for the North American grids and one for the United States grids, are also included with the gridded data.

Open-File Report↗
USGS2023

Indicators of the effects of climate change on freshwater ecosystems

Freshwater ecosystems, including lakes, streams, and wetlands, are responsive to climate change and other natural and anthropogenic stresses. These ecosystems are frequently hydrologically and ecologically connected with one another and their surrounding landscapes, thereby integrating changes throughout their watersheds. The responses of any given freshwater ecosystem to climate change depend on the magnitude of climate forcing, interactions with other anthropogenic and natural changes, and the characteristics of the ecosystem itself. Therefore, the magnitude and manner in which freshwater ecosystems respond to climate change are difficult to predict a priori. We present a conceptual model to elucidate how freshwater ecosystems are altered by climate change. We identify eleven indicators that describe the response of freshwater ecosystems to climate change, discuss their potential value and limitations, and describe supporting measurements. Indicators are organized in three interrelated categories: hydrologic, water quality, and ecosystem structure and function. The indicators are supported by data sets with a wide range of temporal and spatial coverage, and they inform important scientific and management needs. Together, these indicators improve the understanding and management of the effects of climate change on freshwater ecosystems.

Climate Change↗
USGS2002

Of bugs and birds: Markov Chain Monte Carlo for hierarchical modeling in wildlife research

Markov chain Monte Carlo (MCMC) is a statistical innovation that allows researchers to fit far more complex models to data than is feasible using conventional methods. Despite its widespread use in a variety of scientific fields, MCMC appears to be underutilized in wildlife applications. This may be due to a misconception that MCMC requires the adoption of a subjective Bayesian analysis, or perhaps simply to its lack of familiarity among wildlife researchers. We introduce the basic ideas of MCMC and software BUGS (Bayesian inference using Gibbs sampling), stressing that a simple and satisfactory intuition for MCMC does not require extraordinary mathematical sophistication. We illustrate the use of MCMC with an analysis of the association between latent factors governing individual heterogeneity in breeding and survival rates of kittiwakes ( Rissa tridactyla ). We conclude with a discussion of the importance of individual heterogeneity for understanding population dynamics and designing management plans.

Journal of Wildlife Management↗
USGS2000

Data report: Mid-Pliocene diatom assemblages at sites 1016, 1021, and 1022

Diatom assemblages from the middle part of the Pliocene (3.2-2.5 Ma) were investigated from Ocean Drilling Program Sites 1016, 1021, and 1022 in an effort to infer paleotemperature fluctuations off California. Diatoms are very sparse in virtually all of the samples that were examined from Sites 1016 and 1021. This is presumably because these sites were seaward (west) of the coastal zone of diatom productivity during the middle part of the Pliocene. Diatoms are relatively common in the vast majority of samples that were examined from Hole 1022A. Diatom assemblages are dominated by Chaetoceros spores (a coastal upwelling component), the cold-water (subarctic) taxa Neodenticula kamtschatica and its descendant Neodenticula koizumii, and Thalassionema nitzschioides, a temperate taxon that is typically found at the seaward edge of coastal upwelling zones. Paleotemperature interpretations, however, are not possible at this time because of the scarcity of comparative modern core-top data.

Proceedings of the Ocean Drilling Program: Scienti↗
USGS1999

U.S. Geological Survey World Wide Web Information

The U.S. Geological Survey (USGS) invites you to explore an earth science virtual library of digital information, publications, and data. The USGS Internet World Wide Web sites offer an array of information that reflects scientific research and monitoring programs conducted in the areas of natural hazards, environmental resources, and cartography. This list provides gateways to access a cross section of the digital information on the USGS World Wide Web sites.

Fact Sheet↗
USGS1955

Geology of the Calamity Mesa quadrangle, Colorado

The series of Geologic Quadrangle Maps of the United States continues the series of quadrangle maps begun with the folios of the Geologic Atlas of the United States, which were published from 1894 to 1945. The present series consists of geologic maps, supplemented where possible by structure sections, columnar sections, and other graphic means of presenting geologic data, and accompanied by a brief explanatory text to make the maps useful for general scientific and economic purposes. Full description and interpretation of the geology of the areas shown on these maps are reserved for publication in other channels, such as the Bulletins and Professional Papers of the Geological Survey. Separate maps of the same areas, covering bedrock, surficial, engineering, and other phases of geology, may be published in the geologic quadrangle map series.

Colorado↗
USGS2013

Reconnaissance geologic map of Kodiak Island and adjacent islands, Alaska

Kodiak Island and its adjacent islands, located on the west side of the Gulf of Alaska, contain one of the largest areas of exposure of the flysch and melange of the Chugach terrane of southern Alaska. However, in the past 25 years, only detailed mapping covering small areas in the archipelago has been done. This map and its associated digital files (Wilson and others, 2005) present the best available mapping compiled in an integrated fashion. The map and associated digital files represent part of a systematic effort to release geologic map data for the United States in a uniform manner. The geologic data have been compiled from a wide variety of sources, ranging from state and regional geologic maps to large-scale field mapping. The map data are presented for use at a nominal scale of 1:500,000, although individual datasets (see Wilson and others, 2005) may contain data suitable for use at larger scales.

Alaska↗
USGS2018

Delineation of the hydrogeologic framework of the Big Sioux aquifer near Sioux Falls, South Dakota, using airborne electromagnetic data

The U.S. Geological Survey, in cooperation with the City of Sioux Falls, South Dakota, began developing a groundwater-flow model of the Big Sioux aquifer in 2014 that will enable the City to make more informed water management decisions, such as delineation of areas of the greatest specific yield, which is crucial for locating municipal wells. Innovative tools are being evaluated as part of this study that can improve the delineation of the hydrogeologic framework of the aquifer for use in development of a groundwater-flow model, and the approach could have transfer value for similar hydrogeologic settings. The first step in developing a groundwater-flow model is determining the hydrogeologic framework (vertical and horizontal extents of the aquifer), which typically is determined by interpreting geologic information from drillers’ logs and surficial geology maps. However, well and borehole data only provide hydrogeologic information for a single location; conversely, nearly continuous geophysical data are collected along flight lines using airborne electromagnetic (AEM) surveys. These electromagnetic data are collected every 3 meters along a flight line (on average) and subsequently can be related to hydrogeologic properties. AEM data, coupled with and constrained by well and borehole data, can substantially improve the accuracy of aquifer hydrogeologic framework delineations and result in better groundwater-flow models. AEM data were acquired using the Resolve frequency-domain AEM system to map the Big Sioux aquifer in the region of the city of Sioux Falls. The survey acquired more than 870 line-kilometers of AEM data over a total area of about 145 square kilometers, primarily over the flood plain of the Big Sioux River between the cities of Dell Rapids and Sioux Falls. The U.S. Geological Survey inverted the survey data to generate resistivity-depth sections that were used in two-dimensional maps and in three-dimensional volumetric visualizations of the Earth resistivity distribution. Contact lines were drawn using a geographic information system to delineate interpreted geologic stratigraphy. The contact lines were converted to points and then interpolated into a raster surface. The methods used to develop elevation and depth maps of the hydrogeologic framework of the Big Sioux aquifer are described herein. The final AEM interpreted aquifer thickness ranged from 0 to 31 meters with an average thickness of 12.8 meters. The estimated total volume of the aquifer was 1,060,000,000 cubic meters based on the assumption that the top of the aquifer is the land-surface elevation. A simple calculation of the volume (length times width times height) of a previous delineation of the aquifer estimated the aquifer volume at 378,000,000 cubic meters; thus, the estimation based on AEM data is more than twice the previous estimate. The depth to top of Sioux Quartzite, which ranged in depth from 0 to 90 meters, also was delineated from the AEM data.

South Dakota↗
USGS2005

Potentiometric surface of the Ozark aquifer in northern Arkansas, 2004

The Ozark aquifer in northern Arkansas comprises dolomites, limestones, sandstones, and shales of Late Cambrian to Middle Devonian age, and ranges in thickness from approximately 1,100 feet to more than 4,000 feet. Hydrologically, the aquifer is complex, characterized by discrete and discontinuous flow components with large variations in permeability. The potentiometric-surface map, based on 59 well and 5 spring water-level measurements collected in 2004 in Arkansas and Missouri, indicates maximum water-level altitudes of about 1,188 feet in Benton County and minimum water-level altitudes of about 116 feet in Randolph County. Regionally, the flow within the aquifer is to the south and southeast in the eastern and central part of the study area and to the northwest and north in the western part of the study area. Comparing the 2004 potentiometric- surface map with a predevelopment potentiometricsurface map indicates general agreement between the two surfaces. Potentiometric-surface differences could be attributed to differences in pumping related to changing population from 1990 to 2000, change in source for public supplies, processes or water use outside the study area, or differences in data-collection or map-construction methods.

Scientific Investigations Report↗
USGS2007

Development and Application of Health-Based Screening Levels for Use in Water-Quality Assessments

Health-Based Screening Levels (HBSLs) are non-enforceable water-quality benchmarks that were developed by the U.S. Geological Survey in collaboration with the U.S. Environmental Protection Agency (USEPA) and others. HBSLs supplement existing Federal drinking-water standards and guidelines, thereby providing a basis for a more comprehensive evaluation of contaminant-occurrence data in the context of human health. Since the original methodology used to calculate HBSLs for unregulated contaminants was published in 2003, revisions have been made to the HBSL methodology in order to reflect updates to relevant USEPA policies. These revisions allow for the use of the most recent, USEPA peer-reviewed, publicly available human-health toxicity information in the development of HBSLs. This report summarizes the revisions to the HBSL methodology for unregulated contaminants, and updates the guidance on the use of HBSLs for interpreting water-quality data in the context of human health.

Scientific Investigations Report↗
USGS2007

Water-resource trends and comparisons between partial-development and October 2006 hydrologic conditions, Wood River Valley, south-central Idaho

This report analyzes trends in ground-water and surface-water data, documents 2006 hydrologic conditions, and compares 2006 and historic ground-water data of the Wood River Valley of south-central Idaho. The Wood River Valley extends from Galena Summit southward to the Timmerman Hills. It is comprised of a single unconfined aquifer and an underlying confined aquifer present south of Baseline Road in the southern part of the study area. Streams are well-connected to the shallow unconfined aquifer. Because the entire population of the area depends on ground water for domestic supply, either from domestic or municipal-supply wells, rapid population growth since the 1970s has raised concerns about the continued availability of ground and surface water to support existing uses and streamflow. To help address these concerns, this report evaluates ground- and surface-water conditions in the area before and during the population growth that started in the 1970s. Mean annual water levels in three wells (two completed in the unconfined aquifer and one in the confined aquifer) with more than 50 years of semi-annual measurements showed statistically significant declining trends. Mean annual and monthly streamflow trends were analyzed for three gaging stations in the Wood River Valley. The Big Wood River at Hailey gaging station (13139500) showed a statistically significant trend of a 25-percent increase in mean monthly base flow for March over the 90-year period of record, possibly because of earlier snowpack runoff. Both the 7-day and 30-day low-flow analyses for the Big Wood River near Bellevue gaging station (13141000) show a mean decrease of approximately 15 cubic feet per second since the 1940s, and mean monthly discharge showed statistically significant decreasing trends for December, January, and February. The Silver Creek at Sportsman Access near Picabo gaging station (13150430) also showed statistically significant decreasing trends in annual and mean monthly discharge for July through February and April from 1975 to 2005. Comparisons of partial-development (ground-water conditions from 1952 to 1986) and 2006 ground-water resources in the Wood River Valley using a geographic information system indicate that most ground-water levels for the unconfined aquifer in the study area are either stable or declining. Declines are predominant in the southern part of the study area south of Hailey, and some areas exceed what is expected of natural fluctuations in ground-water levels. Some ground-water levels rose in the northern part of the study area; however, these increases are approximated due to a lack of water-level data in the area. Ground-water level declines in the confined aquifer exceed the range of expected natural fluctuations in large areas of the confined aquifer in the southern part of the study area in the Bellevue fan. However, the results in this area are approximated due to limited available water-level data.

Idaho↗