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At least 1,261 records · Page 70Linked to original sources
USGS1996

Remote mineralogic and lithologic mapping of the Ice River alkaline complex, British Columbia, Canada, using AVIRIS data

The Ice River Alkaline Complex is a late Paleozoic intrusion of mafic alkaline rocks, syenite, and carbonatite exposed in southeastern British Columbia, Canada. The complex intrudes Cambrian and Ordovician shales, slates, and limestones of the Chancellor and Ottertail Formations and the McKay Group. We examined the alkaline complex and adjacent country rocks using Airborne Visible-Infrared Imaging Spectrometer (AVIRIS) data. The data were first calibrated to relative reflectance and then used to spectrally map mineralogies in the study area by using a linear spectral unmixing program. This technique models each pixel spectrum in an AVIRIS image as a linear combination of unique endmember spectra. We selected endmember spectra from well-exposed and spectrally distinct mineralogic units, vegetation, and snow. Four of the endmembers reflect mineralogic variations within the McKay group in the study area, and may represent lateral and vertical variations of sedimentary or metamorphic facies. Otherwise, the resultant spatial distribution of endmembers shows generally close agreement with the published geologic map, although, in several places, our image-map is more accurate than the published map.

Photogrammetric Engineering and Remote Sensing↗
USGS2007

The Pennsylvanian-early permian bird spring carbonate shelf, Southeastern California: Fusulinid biostratigraphy, paleogeographic evolution, and tectonic implications

The Bird Spring Shelf in southeastern California, along with coeval turbidite basins to the west, records a complex history of late Paleozoic sedimentation, sea-level changes, and deformation along the western North American continental margin. We herein establish detailed correlations between deposits of the shelf and the flanking basins, which we then use to reconstruct the depositional history, paleogeography, and deformational history, including Early Permian emplacement of the regionally significant Last Chance allochthon. These correlations are based on fusulinid faunas, which are numerous both on the shelf and in the adjoining basins.

Special Paper of the Geological Society of America↗
USGS2010

Assessment of nonpoint source chemical loading potential to watersheds containing uranium waste dumps and human health hazards associated with uranium exploration and mining, Red, White, and Fry Canyons, southeastern Utah, 2007

During May, June, and July 2007, 58 solid-phase samples were collected from abandoned uranium mine waste dumps, background sites, and adjacent streambeds in Red, White, and Fry Canyons in southeastern Utah. The objectives of this sampling program were to (1) assess the nonpoint-source chemical loading potential to ephemeral and perennial drainage basins from uranium waste dumps and (2) assess potential effects on human health due to recreational activities on and around uranium waste dumps on Bureau of Land Management property. Uranium waste-dump samples were collected using solid-phase sampling protocols. After collection, solid-phase samples were homogenized and extracted in the laboratory using a leaching procedure. Filtered (0.45 micron) water samples were obtained from the field leaching procedure and were analyzed for major and trace elements at the Inductively Coupled Plasma-Mass Spectrometry Metals Analysis Laboratory at the University of Utah. A subset of the solid-phase samples also were digested with strong acids and analyzed for major ions and trace elements at the U.S. Geological Survey Geologic Division Laboratory in Denver, Colorado. For the initial ranking of chemical loading potential for uranium waste dumps, results of leachate analyses were compared with existing aquatic-life and drinking-water-quality standards. To assess potential effects on human health, solid-phase digestion values for uranium were compared to soil screening levels (SSL) computed using the computer model RESRAD 6.5 for a probable concentration of radium. One or more chemical constituents exceeded aquatic life and drinking-water-quality standards in approximately 64 percent (29/45) of the leachate samples extracted from uranium waste dumps. Most of the uranium waste dump sites with elevated trace-element concentrations in leachates were located in Red Canyon. Approximately 69 percent (31/45) of the strong acid digestible soil concentration values were greater than a calculated SSL. Uranium waste dump sites with elevated leachate and total digestible concentrations may need to be further investigated to determine the most appropriate remediation method.

Utah↗
USGS1988

Tectonic significance of dikes of Westerly Granite, southeastern Connecticut and southwestern Rhode Island

Undeformed Early Permian Westerly Granite dikes cut gneisses of the southeastern New England Avalon zone along coastal southeastern Connecticut and adjacent Rhode Island. Most dikes dip southward at a low angle. The Westerly dikes were emplaced in relatively warm rock penecontemporaneously with the Narragansett Pier Granite during a narrow time interval shortly after cessation of pervasive Alleghanian ductile deformation but probably before final localized movement on major shear zones. The gentle dips indicate subhorizontal release at the end stage of the Alleghanian compressive event. Doming, intrusion of granite, and subsequent rapid uplift and cooling are attributed to the underplating of Avalonian crust by an African plate during the Alleghanian. -Author

Northeastern Geology↗
USGS2020

Salt flushing, salt storage, and controls on selenium: A 31-year mass-balance analysis of an irrigated, semiarid valley

Salinity, selenium, and uranium pose water‐quality challenges for the Arkansas River in southeastern Colorado and other rivers that support irrigation in semiarid regions. This study used 31 years of continuous discharge and specific conductance (SC) monitoring data to assess interannual patterns in water quality using mass balance on a 120‐km reach of river. Discrete sampling data were used to link the SC records to salinity, selenium, and uranium. Several important patterns emerged. Consumptive use reduced discharge by a median value of 33% and drove corresponding increases in salinity and uranium concentrations. Increased water availability for irrigation from rainfall and upstream snowpack in 1995–1999 flushed additional salinity and uranium into the river in 1996–2000; average annual total dissolved solids (salinity) concentrations increased 25%, and loads increased 131%. Smaller flushing events have occurred, sometimes lagging an increase in water availability by about one year. The pattern indicates flushing of salts temporarily stored, evaporatively concentrated, or of geologic origin. Mobilization of selenium from the reach was minor compared to salinity and uranium, and net selenium removal from the river was suggested in some years. Several processes related to irrigation could be removing selenium. The results provide context for efforts to improve water quality in the Arkansas River and rivers in other semiarid regions.

Colorado↗
USGS1997

Ground Water Atlas of the United States: Segment 3, Kansas, Missouri, Nebraska

The three States-Kansas, Missouri, and Nebraska-that comprise Segment 3 of this Atlas are in the central part of the United States. The major rivers that drain these States are the Niobrara, the Platte, the Kansas, the Arkansas, and the Missouri; the Mississippi River is the eastern boundary of the area. These rivers supply water for many uses but ground water is the source of slightly more than one-half of the total water withdrawn for all uses within the three-State area. The aquifers that contain the water consist of consolidated sedimentary rocks and unconsolidated deposits that range in age from Cambrian through Quaternary. This chapter describes the geology and hydrology of each of the principal aquifers throughout the three-State area. Some water enters Segment 3 as inflow from rivers and aquifers that cross the segment boundaries, but precipitation, as rain and snow, is the primary source of water within the area. Average annual precipitation (1951-80) increases from west to east and ranges from about 16 to 48 inches (fig. 1). The climate of the western one-third of Kansas and Nebraska, where the average annual precipitation generally is less than 20 inches per year, is considered to be semiarid. This area receives little precipitation chiefly because it is distant from the Gulf of Mexico, which is the principal source of moisture-laden air for the entire segment, but partly because it is located in the rain shadow of the Rocky Mountains. Average annual precipitation is greatest in southeastern Missouri. Much of the precipitation is returned to the atmosphere by evapotranspiration, which is the combination of evaporation from the land surface and surface-water bodies, and transpiration from plants. Some of the precipitation either flows directly into streams as overland runoff or percolates into the soil and then moves downward into aquifers where it is stored for a time and subsequently released as base flow to streams. Average annual runoff, which is the total discharge into a stream from surface- and ground-water sources, ranges from about 0.2 inch in the western part of the area to about 20 inches in southeastern Missouri (fig. 2). Average annual runoff generally reflects the distribution of average annual precipitation during the same period. However, runoff is less than precipitation everywhere and ranges from less than 5 to about 35 percent of the average annual precipitation. Evapotranspiration rates are high, especially in the western one-half of the area; thus, only a small percentage of the precipitation is available to recharge aquifers in most places. Locally, however, runoff might be significantly less than shown in figure 2, and ground-water recharge, greater, especially where highly permeable rocks or deposits at the land surface allow precipitation to rapidly infiltrate. Examples of such places are the Sand Hills area of Nebraska, which is blanketed by permeable windblown sands, and parts of southern Missouri, where permeable limestone is at or near the land surface. The land surface of Segment 3 generally slopes gradually from west to east. In the Great Plains Physiographic Province (fig. 3), the altitude of the flat land surface locally is about 5,000 feet above sea level in westernmost Nebraska. By contrast, in the flat Coastal Plain Physiographic Province of eastern Missouri, the altitude is about 500 feet above sea level. The land surface is gently rolling in the Central Lowland Province except where major rivers and their tributaries are deeply incised. In the Ozark Plateaus Physiographic Province, rugged topography has developed where the underlying rocks have been uplifted and deeply eroded.

Kansas, Missouri, Nebraska↗
USGS1999

Quality of life on the Colorado Plateau: A report to camera-survey collaborators in southeast Utah

What constitutes quality of life among community residents in southeastern and central Utah? What critical areas, elements, and special outdoor places are essential to quality of life in those areas? Answering these questions was the goal of this "quality-of-life" research collaboration in the Colorado Plateau region. Collaborators include the Utah Travel Council (UTC), Canyon Country Partnership, Utah State University, and the county governments of Carbon, Emery, Grand, San Juan, and Wayne counties. In recent years, the goal of the UTC has changed from simply encouraging tourism development to understanding the relationship between tourism and community quality of life. Elements of the new UTC mission include: “make Utah a better place to live by increasing the economic contribution of tourism,” and “protect base resources and maintain quality of life for residents and visitors alike” (Utah Division of Travel Development, 1997). The Social, Economic, and Institutional Analysis Section [SEIAS]/ Midcontinent Ecological Science Center/U.S. Geological Survey conducted this research in late spring through winter of 1997 in an effort to answer those questions posed by the collaboration. This report provides an overview of the research and presents summary results.

Utah↗
USGS2018

Geologic map of the Hayfield quadrangle, Frederick County, Virginia

The Hayfield 7.5-minute quadrangle is located within the Valley and Ridge physiographic province of northern Virginia. The quadrangle includes the topographical lowland area of the northern Great Valley to the southeast, the narrow ridge of Little North Mountain along the western edge of the Great Valley, and the broad region of elongated valleys and ridges west of Little North Mountain. The most prominent physiographic feature within the quadrangle is Great North Mountain, which extends across the northwestern portion of the quadrangle. All exposed bedrock units are Paleozoic sedimentary rocks ranging from Middle Cambrian to Late Devonian, approximately 513 to 359 Ma. The clastic and carbonate sedimentary strata in the quadrangle reflect nearshore and offshore marine and deltaic depositional environments. The deposits indicate minor sea level transgression and regression cycles along a passive continental margin during the Late Cambrian to Middle Ordovician, and major sea level changes resulting from tectonic uplift during the Late Ordovician Taconian orogeny and the Middle to Late Devonian Acadian orogeny. Compressive forces caused by the continental collision during the Paleozoic Alleghanian orogeny resulted in folding and faulting of the sedimentary rock strata, with northwestward tectonic transport. The North Mountain fault zone, spanning across the southeastern part of the quadrangle, forms the western border of the Great Valley in northern Virginia and is a series of northeast-trending thrust faults with multiple splays that separate the Silurian and Devonian shales, siltstones, and sandstones from the Cambrian and Ordovician carbonate rocks and shales. Topographic ridges in the quadrangle are primarily held up by sandstones and orthoquartzites that are relatively resistant to erosion. Surficial materials include unconsolidated alluvium, colluvium, debris flow, and terrace deposits that are assumed to be of Quaternary age. Alluvium was mapped along the larger streams; locally, some low alluvial terraces exist but have not been broken out within this unit. Debris flow deposits were mapped where recognized in the lidar-derived topographic imagery on the flanks of Great North Mountain. Colluvium (not mapped separately) covers most of the steeper slopes and fills the bottoms of many of the mountain hollows, and is composed mainly of sandstone boulders and cobbles, and fragments of chert.

Virginia↗
USGS2020

The water-year water balance of the Colorado River Basin

Model‐estimated monthly water balance components (i.e., potential evapotranspiration, actual evapotranspiration, and runoff ( R )) for 146 United States (U.S.) Geological Survey 8‐digit hydrologic units located in the Colorado River Basin (CRB) are used to examine the temporal and spatial variability of the CRB water balance for water years 1901 through 2014 (a water year is the period from October 1 of one year through September 30 of the following year). Results indicate that the CRB can be divided into six subregions with similar temporal variability in monthly R . The water balance analyses indicated that approximately 75% of total water‐year R is generated by just one CRB subregion and that most of the R in the basin is derived from surplus ( S ) water generated during the months of October through April. Furthermore, the analyses show that temporal variability in S is largely controlled by the occurrence of negative atmospheric pressure anomalies over the northwestern conterminous U.S. (CONUS) and positive atmospheric pressure anomalies over the southeastern CONUS. This combination of atmospheric pressure anomalies results in an anomalous flow of moist air from the North Pacific Ocean into the CRB, particularly the Upper CRB. Additionally, the occurrence of extreme dry and wet periods in the CRB appears to be related to variability of the Atlantic Multidecadal Oscillation and the Pacific Decadal Oscillation.

Arizona, California, Colorado, Nevada, New Mexico,↗
USGS2014

Effects of hydrologic modifications on salinity and formation of hypoxia in the Mississippi River-Gulf Outlet and adjacent waterways, southeastern Louisiana, 2008 to 2012

The Mississippi River-Gulf Outlet (MRGO) was constructed between 1958 and 1968 to provide a safer and shorter route between the Gulf of Mexico and the Port of New Orleans for ocean-going vessels. In 2006, the U.S. Congress directed the U.S. Army Corps of Engineers (USACE) to develop and implement a plan to deauthorize a portion of the MRGO ship channel from its confluence with the Gulf Intracoastal Waterway to the Gulf of Mexico. In 2009, in accordance with plans submitted to Congress, the USACE built a rock barrier across the MRGO near Hopedale, Louisiana. Following Hurricane Katrina, Congress also authorized the USACE to implement the Hurricane Storm Damage Risk Reduction System (HSDRRS) by building structures in the MRGO and adjacent surface waters, to reduce vulnerability of this area to storm surge. The HSDRRS includes the Gulf Intracoastal Waterway-Lake Borgne Surge Barrier and Gate Complex near mile 58 of the deauthorized portion of the MRGO and the Seabrook Gate Complex on the Inner Harbor Navigation Canal (IHNC). By blocking or limiting tidal exchange in the MRGO, these barriers could affect water quality in the MRGO and nearby waters including Lake Pontchartrain, the IHNC, and Lake Borgne. In 2008, the U.S. Geological Survey, in cooperation with the USACE, began a study to document the effects of the construction activities on salinity and dissolved oxygen in these surface waters. Data were collected from August 2008 through October 2012. Completion of the rock barrier in the vicinity of mile 35 in July 2009 reduced hydrologic circulation and separated the MRGO into two distinct salinity regimes, with substantially fresher conditions prevailing upstream from the rock barrier. The rock barrier also contributed to a zone of hypoxia (dissolved oxygen less than 2 milligrams per liter) that formed along the channel bottom during the warmer summer months in each year of this monitoring; the zone was much more developed downstream from the rock barrier. The most extensive hypoxic zone was measured in October 2009 when it extended at least 34 miles in the MRGO, from mile 20 to mile 54. Construction of the surge barrier and flood gates did not affect salinity or dissolved oxygen in any comparable manner. The factors that contributed the most to hypoxia in the MRGO were the reductions in tidal water movement there after completion of the rock barrier combined with the channel depth in the MRGO, in places 10 to 30 feet deeper than surrounding surface water bodies. These factors helped to stratify salinity by reducing vertical mixing in the water column.

Louisiana↗
USGS2021

Hydrology and water quality of the Great Dismal Swamp, Virginia and North Carolina, and implications for hydrologic-management goals and strategies

The Great Dismal Swamp is a peat wetland in the Coastal Plain of southeastern Virginia and northeastern North Carolina. Timber harvesting and the construction of ditches to drain the swamp and facilitate the harvesting are collectively implicated in changes that altered the wetland forests, caused subsidence and decomposition of the peat, and increased the risk of fire. In response to these changes, managers have implemented strategies to control water levels and rewet the swamp using a network of 64 adjustable-height, water-control structures on the ditches. Rewetting the swamp is intended to re-establish the original wetland-forest types, reduce the risk of fire, reduce subsidence and decomposition of the peat, enhance peat accretion, and reduce the risk of fire. Knowledge of responses of the swamp to hydrologic controls, however, is critical to developing and implementing effective management goals and strategies. Because the 2008 South One fire reemphasized the need for this knowledge, the U.S. Geological Survey in cooperation with the U.S. Fish and Wildlife Service began studies in 2009 to identify critical hydrologic controls and responses to these controls. These studies identified water sources, topography, the two-layered hydraulic characteristics of the peat, the absence of peat in some areas, the ditch and road network, water-control structures on the ditches, the Dismal Swamp Canal and associated infrastructure, and wetland forests as the primary hydrologic controls. Precipitation is the only water source across much of the swamp. The eastward flow of streams and groundwater from the Isle of Wight Plain, across the Suffolk scarp, and into the swamp are additional water sources to the western part of the swamp. Vertical differences in the hydraulic characteristics of the peat reflect an upper peat having a high hydraulic conductivity and specific yield overlying a lower peat and sand having lower hydraulic conductivity and specific yield. The upper peat forms the main aquifer for the storage, flow, and release of water from the swamp. Maintaining water in the upper peat is critical to water availability to the wetland forests because of these properties. Groundwater flows from the swamp into the ditches and the Dismal Swamp Canal where it discharges into nearby streams. Discharge typically is to the closest ditch except where a spoil-pile road that impedes flow intervenes between the swamp and the ditch. When groundwater levels in a ditch are about 2 feet lower than levels in the other three ditches surrounding a part of the swamp, however, most groundwater typically discharges to the ditch having the lower level. This occurs even if a spoil-pile road intervenes between the swamp and the ditch having the lower level. Flow to a single ditch shifts watershed boundaries and groundwater divides toward the ditches having higher water levels and demonstrates how flow and discharge are controlled by ditch water levels. Consequently, managing water levels based on these and other hydrologic controls and responses is critical to achieving management objectives. The chemistry of water across the swamp shows the effects of the peat. Dissolved organic carbon concentrations in the groundwater are among the highest reported globally, ranging from 55 to 195 milligrams per liter. The pH of groundwater and ditch water is commonly less than 4.0 standard units because of organic acids. A relation between the pH and specific conductance of groundwater and ditch water reflects water sources, flow paths, and the chemical evolution, as waters from the different sources mix and flow along the paths.

North Carolina, Virginia↗
USGS2008

Water Levels and Selected Water-Quality Conditions in the Mississippi River Valley Alluvial Aquifer in Eastern Arkansas, 2006

During the spring of 2006, the U.S. Geological Survey, in cooperation with the Arkansas Natural Resource Commission and the Arkansas Geological Survey, measured water levels in 707 wells completed in the Mississippi River Valley alluvial aquifer in eastern Arkansas. Ground-water levels are affected by ground-water withdrawals resulting in depressions. In 2006, the lowest water-level altitude was 76 feet above the National Geodetic Vertical Datum of 1929 in the center of Arkansas County. The highest water-level altitude was 289 feet above the National Geodetic Vertical Datum of 1929 in northeastern Clay County on the west side of Crowleys Ridge. Two large depressions in the potentiometric surface are located in Arkansas, Lonoke, and Prairie Counties and west of Crowleys Ridge in Craighead, Cross, Lee, Monroe, Poinsett, St. Francis, and Woodruff Counties. The elongated depression in Arkansas, Lonoke, and Prairie Counties has changed in areal extent or depth when compared to previous conditions of the aquifer. The area in Arkansas County at the southeastern half of the depression has not expanded horizontally during recent years, although the center of the depression has deepened. The area in Lonoke and Prairie Counties in the northwestern half of the depression has expanded horizontally in the deeper part of the depression. The 90-foot contour has expanded north and east in Lonoke County when compared with the 2004 potentiometric surface. Along the west side of Crowleys Ridge the 2006 potentiometric-surface map shows very little change in the area of this depression, although the deeper areas within the depression have expanded. A map showing the difference in water level was constructed using 645 differences in water-levels measured in 633 wells during 2002 and 2006. The difference in measured water levels from 2002 to 2006 ranged from -24.0 feet to 25.0 feet, with a mean of -2.0 feet. The largest decline of -24.0 feet occurred in Poinsett County and the largest rise of 25.0 feet occurred in Randolph County. Out of the 645 differences, 481 were declines (74.6 percent), 12 were no difference (values of 0.0 ft) (1.8 percent), and 152 were rises (23.6 percent). Long-term water-level trends were evaluated using hydrographs from 152 wells completed in the Mississippi River Valley alluvial aquifer for the period 1982 to 2006. The mean annual rise or decline in water level for the entire study area was -0.32 feet per year with a range of -1.28 to 0.77 feet per year. Independence and White Counties are the only counties with a mean annual rise from 1982 to 2006. Mean annual declines between -0.50 feet per year and 0.00 feet per year occurred in Arkansas, Ashley, Chicot, Clay, Craighead, Crittenden, Drew, Jefferson, Lee, Mississippi, Monroe, Phillips, Poinsett, Prairie, Pulaski, Randolph, and Woodruff Counties. Mean annual declines between -1.00 feet per year and -0.50 feet per year occurred in Cross, Desha, Greene, Jackson, Lincoln, Lonoke, and St. Francis Counties. The analysis of long-term water-level changes in Arkansas, Lonoke, and Prairie Counties shows the elongation of the depression in these three counties. Both Arkansas and Prairie Counties have two different rates of annual decline for the two hydrographs shown for each county. Water levels in the two wells near the Arkansas and White Rivers either have risen or declined at a slower rate than in the three wells in the center, northern, and western part of the depression. These rates of water-level change indicate that this depression is expanding in an elongated direction north and west into Lonoke and Prairie Counties. The depression west of Crowleys Ridge has five wells with hydrographs in or near the depression that can be used to characterize the rates of water-level change within the depression. Water samples were collected from 65 wells completed in the Mississippi River Valley alluvial aquifer and measured onsite for specific conductance and tempera

Scientific Investigations Report↗
USGS1978

Channel migration of the White River in the eastern Uinta Basin, Utah and Colorado

The White River is the largest stream in the southeastern part of the Uinta Basin in Utah and Colorado. This map shows the changes that have occurred in the location of the main channel of the river from 1936 to 1974. The map indicated that certain reaches of the river are subject to different rates of channel migration. Also shown is the boundary of the flood plain, which is mapped at the point of abrupt break in slope. This map documents the position of the river channel prior to any withdrawals of water or alteration of the flow characteristics of the white river that may occur in order to meet water requirements principally associated with the proposed oil-shale industry or other development in the area. The channel locations were determined from aerial photographs taken at four different time periods for the following Federal agencies: In 1936, U.S. Soil Conservation Services; 1953, U.S. Corps of Engineers; 1965, U.S. Geological Survey; and in 1974, U.S. Bureau of Land Management. The 1936 delineation, which is actually based upon photographs that were taken in 1936 and 1937, was made by projection of the original photographs on a base map that was prepared from 1:24,000 scale topographic maps. The 1953, 1965, and 1974 delineations were produced from stereographic models. The 1965 delineation was compiled from photographs that were taken during 1962-65. The delineation is labeled as 1965 for simplicity, however, because the photographs for 1965 cover about 60 percent of the study read of the river, and because no changed were discernable in those areas of repetitive photographic coverage.

Colorado, Utah↗
USGS2010

Water levels and selected water-quality conditions in the Mississippi River Valley alluvial aquifer in Eastern Arkansas, 2008

During the spring of 2008, the U.S. Geological Survey, in cooperation with the Arkansas Natural Resources Commission and the Arkansas Geological Survey, measured 670 water levels in 659 wells completed in the Mississippi River Valley alluvial aquifer in eastern Arkansas. Groundwater levels are affected by groundwater withdrawals resulting in potentiometric-surface depressions. In 2008, the lowest water-level altitude was 69 feet above National Geodetic Vertical Datum of 1929 in the center of Arkansas County. The highest water-level altitude was 288 feet above National Geodetic Vertical Datum of 1929 in northeastern Clay County on the west side of Crowleys Ridge. Two large depressions in the potentiometric surface are located in Arkansas, Lonoke, and Prairie Counties and west of Crowleys Ridge in Craighead, Cross, Lee, Monroe, Poinsett, St. Francis, and Woodruff Counties. The elongated depression in Arkansas, Lonoke, and Prairie Counties has two areas that have changed in horizontal area or depth when compared to previous conditions of the aquifer. The area in Arkansas County in the southeastern half of the depression has not expanded horizontally from recent years, although the center of the depression has deepened. The area in Lonoke and Prairie Counties in the northwestern half of the depression has not expanded and water level in the deeper part of the depression has risen. In Lonoke and Prairie Counties in the northwestern half of the depression, the 90-foot contour shown on the 2006 potentiometric-surface map is not shown on the 2008 potentiometric-surface map. Along the west side of Crowleys Ridge, the area enclosed by 140-foot contour in Cross and Poinsett Counties has expanded further south into Cross County. The 130-foot contour in Poinsett County expanded north in 2008. The 130-foot contour is shown in Cross County, which was not evident in previous years. The 130-foot contour in St. Francis, Monroe, and Woodruff Counties in 2006 is not shown on the 2008 potentiometric-surface map. A map showing the difference in water level was constructed using 595 differences in water levels measured in 585 wells during 2008 and 2004. The difference in measured water levels from 2004 to 2008 ranged from -20.6 feet to 25.9 feet, with a mean of -1.6 feet. The largest decline of -20.6 feet occurred in Randolph County and the largest rise of 25.9 feet occurred in Prairie County. Out of the 595 differences, 442 were declines (74.3 percent), 10 were no difference (values of 0.0 ft) (1.7 percent), and 143 were rises (24.0 percent). Five areas are dominated by declines that are west of Crowleys Ridge; in eastern Craighead County; in southern Mississippi and Crittenden Counties; in eastern Lonoke and western Prairie Counties; and in Arkansas, Ashley, Chicot, Desha, Drew, and Lincoln Counties. Long-term water-level changes were evaluated using hydrographs from 173 wells in the Mississippi River Valley alluvial aquifer for the period 1984 to 2008. The mean annual rise or decline in water level for the entire study area was -0.38 feet per year (ft/yr) with a range of -4.86 to 0.58 ft/yr. Independence and White Counties are the only counties with a mean annual rise from 1984 to 2008. Mean annual declines between -0.50 ft/yr and 0.00 ft/yr occurred in Arkansas, Chicot, Clay, Craighead, Crittenden, Drew, Greene, Jefferson, Mississippi, Monroe, Phillips, Poinsett, Prairie, Pulaski, Randolph, and Woodruff Counties. Mean annual declines between -1.00 ft/yr and -0.50 ft/yr occurred in Ashley, Desha, Jackson, Lee, Lincoln, and St. Francis Counties. Mean annual declines between -1.50 ft/yr and -1.00 ft/yr occurred in Cross and Lonoke Counties. The analysis of long-term water-level changes in Arkansas, Lonoke, and Prairie Counties shows the elongation of the depression in these three counties. Arkansas and Prairie Counties have two different rates of annual decline for the two hydrographs shown for each county. Water levels in the two we

Scientific Investigations Report↗
USGS2014

Analysis of potential water-supply management options, 2010-60, and documentation of revisions to the model of the Irwin Basin Aquifer System, Fort Irwin National Training Center, California

The Fort Irwin National Training Center is considering several alternatives to manage their limited water-supply sources in the Irwin Basin. An existing three-dimensional, finite-difference groundwater-flow model—the U.S. Geological Survey’s MODFLOW—of the aquifer system in the basin was updated and the initial input dataset was supplemented with groundwater withdrawal data for the period 2000–10. The updated model was then used to simulate four combinations, or scenarios, of groundwater withdrawal and recharge over the next 50 years (January 2011 through December 2060). The scenarios included combinations of continuing withdrawals from currently active production wells, supplementing any increases in demand with withdrawals from an inactive production well, reducing withdrawal amounts and rates, and reducing the discharge of treated wastewater to infiltration ponds that provide a recharge source to the underlying aquifer. Results of the simulations indicated that, depending on the scenario implemented, groundwater levels would rise (over the next 50 years) from 40 feet to as much as 65 feet in the northwestern part of the Irwin Basin, and from 5 feet to 10 feet in the southeastern part.

California↗
USGS1997

Digital data set that describe aquifer characteristics of the Antlers aquifer in southeastern Oklahoma

The data sets in this report include digitized aquifer boundaries and maps of hydraulic conductivity, recharge, and ground-water level elevation contours for the Antlers aquifer in southeastern Oklahoma. The Early Cretaceous-age Antlers Sandstone is an important source of water in an area that underlies about 4,400-square miles of all or part of Atoka, Bryan, Carter, Choctaw, Johnston, Love, Marshall, McCurtain, and Pushmataha Counties. The Antlers aquifer consists of sand, clay, conglomerate, and limestone in the outcrop area. The upper part of the Antlers aquifer consists of beds of sand, poorly cemented sandstone, sandy shale, silt, and clay. The Antlers aquifer is unconfined where it outcrops in an area of about 1,800-square miles (Morton, 1992). The recharge, hydraulic conductivity, and aquifer boundaries data sets include the outcrop area of the Antlers Sandstone in Oklahoma and areas where the Antlers is overlain by alluvial and terrace deposits and a few small thin outcrops of the Goodland Limestone. Most of the lines in the data sets are from the digital data of the surficial geology of the Antlers Sandstone from Cederstrand (1996a, 1996b) except where the Antlers aquifer is overlain by alluvial and terrace deposits near streams and rivers. Morton (1992) interpolated the Antlers aquifer boundaries under the alluvial and terrace deposits where streams cross the aquifer outcrop. Aquifer boundary lines for areas where the aquifer is overlain by alluvial and terrace deposits were digitized and are similar to the aquifer boundaries shown in Morton (1992). A few polygons in this data set represent small and thin outcrops of the Goodland Limestone overlying the Antlers aquifer. The Antlers aquifer in Texas (Morton, 1992) is not included in this data set. The maps from which this data set was derived were scanned or digitized from maps published at a scale of 1:250,000. Hydraulic conductivity and recharge values were used as input to the ground-water model report for the Antlers aquifer by Morton (1992). The water-level elevation contours were digitized from a mylar map at a scale of 1:250,000 that was used to prepare the final map that was published as plate 1, map A, "Observed potentiometric surface, 1970, Antlers aquifer" at a scale of 1:500,000 in Morton (1992). Morton (1992) used water levels measured in wells in 1970 to construct the map. The water-level elevation contours for the Antlers aquifer in Texas (Morton, 1992) are not included in this data set. Ground-water flow models are numerical representations that simplify and aggregate natural systems. Models are not unique; different combinations of aquifer characteristics may produce similar results. The hydraulic conductivity and recharge are closely interrelated. As long as these two model inputs are in balance the model has a small mean residual; it represents the natural system numerically. If the hydraulic conductivity is accurately known, the model can be used to accurately determine recharge. Likewise, if the hydraulic conductivity is poorly known, then the recharge will be poorly determined. Therefore, values of hydraulic conductivity and recharge used in the model and presented in this data set are not precise, but are within a reasonable range when compared to independently collected data. In most aquifers, hydraulic conductivity measurements made in wells or in cores will range over several orders of magnitude, even over short horizontal and vertical distances. Hydraulic conductivity values derived from ground-water flow models represent areal generalizations and do not reflect the large local variance in well or core measurements. Recharge probably varies considerably over the local area, and model recharge is at best an average over an area at least as large as the model grid (and probably much larger than a single cell). Compilation of the data sets was funded under a cooperative Joint Funding Agreement between the U.S. Geological Survey and the State of Oklahoma, Office of the Secretary of Environment.

Oklahoma↗
USGS2015

Occurrence of pesticides in groundwater underlying areas of high-density row-crop production in Alabama, 2009-2013

The U.S. Geological Survey, in cooperation with the Alabama Department of Agriculture and Industries, sampled a network of 15 wells for up to 167 pesticides and pesticide degradates from 2009 through 2013 in three areas of high-density row-crop agriculture in Alabama. Eighteen herbicides, 2 fungicides, and 9 degradates were detected in water from the sampled wells. The highest concentration of a detected pesticide was 4.49 micrograms per liter of bentazon in Baldwin County, Alabama, which was well below the lifetime health advisory level of 200 micrograms per liter. None of the measured pesticide concentrations exceeded a human-health benchmark. Insecticides were not detected. Relatively flat land and permeable soils prevalent in each of the three areas facilitate the transport of pesticides through the unsaturated zone into the underlying aquifers. Pesticides and the degradate, deethylatrazine, were more frequently detected in groundwater from wells located in northern Alabama than in southeastern Alabama and Baldwin County, Alabama. Greater amounts of pesticide usage and shallow well depths in northern Alabama likely explain the detection of pesticides in that area. Pesticides were detected in two of the shallowest sampled wells in southeastern Alabama, and the detected pesticides have been extensively used on the crops grown in this area. Total pesticide use among the three areas was lowest in Baldwin County; however, fungicides were detected more often in Baldwin County, which is indicative of peanut crops planted in that area. Concentrations of metolachlor and atrazine have substantially decreased in the northern Alabama wells since 2000. A decline in use of metolachlor and atrazine from a high in the late-1990s and a high in 2004, respectively, in northern Alabama could account for the lower concentrations. Fluometuron use has also declined since 1998, but the relation between time and concentrations differed in the five northern Alabama wells. Fluometuron concentrations in three of the five wells have been decreasing over time, while concentrations in the remaining two wells have been increasing.

Alabama↗
USGS2014

Floods of 2011 in New York

Record rainfall combined with above-average temperatures and substantial spring snowmelt resulted in record flooding throughout New York during 2011. Rainfall totals in eastern New York were the greatest since 1895 and as much as 60 percent above the long-term average within the Catskill Mountains area and the Susquehanna River Basin. This report documents the three largest storms and resultant flooding during the year: (1) spring storm during April and May, (2) Tropical Storm Irene during August, and (3) remnants of Tropical Storm Lee during September. According to the Federal Emergency Management Agency (FEMA), the cost of these three storms exceeded $1 billion in Federal disaster assistance. A warm and wet spring in northern New York resulted in record flooding at 21 U.S. Geological Survey (USGS) active streamgages during late April to early May with the annual exceedance probabilities (AEPs) of 11 peak discharges equaling or exceeding 1 percent. Nearly 5 inches of rain during late April combined with a rapidly melting snowpack caused widespread flooding throughout northern New York, resulting in many road closures, millions of dollars in damages, and 23 counties declared disaster areas and eligible for public assistance. On May 6, Lake Champlain recorded its highest lake level in over 140 years. Hurricane Irene entered New York State on August 28 as a tropical storm and traveled up the eastern corridor of the State, leaving a path of destruction and damage never seen in many parts of New York. Thirty-one counties in New York were declared disaster areas with damages of over $1.3 billion dollars and 10 reported deaths. Storm rainfall exceeded 18 inches in the Catskill Mountains area of southeastern New York with many other areas of eastern New York receiving over 7 inches. Catastrophic flooding resulted from the extreme rainfall in many locations, including Schoharie Creek and its tributaries, the eastern Delaware River Basin, the Ausable and Bouquet River Basins in northeastern New York, and several other stream basins throughout southeastern New York. Downstream reaches of the Mohawk River also had substantial flooding. Sixty-two USGS streamgages throughout eastern New York documented record high stream flows and elevations with AEPs of 25 peak discharges equaling or exceeding 1 percent. The USGS streamgage for the Schoharie Creek at Prattsville recorded its greatest peak discharge in 109 years of record at 120,000 cubic feet per second (greater than the 0.2-percent AEP discharge) on August 28. The peak water-surface elevation at the streamgage in Prattsville was 5 feet higher than its previous record in 1996. USGS personnel surveyed 184 high-water marks (HWMs) at 30 locations along an 84-mile reach of Schoharie Creek and compared the elevations to those published by FEMA for the 10-, 2-, 1-, and 0.2-percent AEP floods. Elevations in the lower reaches of the basin exceeded published elevations for the 0.2-percent AEP flood. Remnants of Tropical Storm Lee brought a third major storm to New York in September 2011. Moisture from Lee began moving into New York on September 7 and intensified over the already saturated Susquehanna River Basin. Most of the rain fell on September 8 with storm totals nearing 13 inches in some areas (12.73 inches at Apalachin in Tioga County). Major disaster declarations were issued for 15 counties in and around central New York, making them eligible for individual or public assistance. Ten USGS streamgages within the Susquehanna River Basin documented record-high stream discharges and elevations on September 8, and all were greater than the 1-percent AEP discharge. USGS personnel surveyed 20 HWMs at 18 locations along a 114- mile reach of the Susquehanna River and compared the elevations to those published by FEMA for the 10-, 2-, 1-, and 0.2-percent AEP floods. Several of the surveyed HWMs exceeded published elevations for the 0.2-percent AEP flood.

New York↗