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At least 361 records · Page 20Linked to original sources
USGS2014

Sediment source apportionment in Laurel Hill Creek, PA, using Bayesian chemical mass balance and isotope fingerprinting

A Bayesian chemical mass balance (CMB) approach was used to assess the contribution of potential sources for fluvial samples from Laurel Hill Creek in southwest Pennsylvania. The Bayesian approach provides joint probability density functions of the sources' contributions considering the uncertainties due to source and fluvial sample heterogeneity and measurement error. Both elemental profiles of sources and fluvial samples and 13 C and 15 N isotopes were used for source apportionment. The sources considered include stream bank erosion, forest, roads and agriculture (pasture and cropland). Agriculture was found to have the largest contribution, followed by stream bank erosion. Also, road erosion was found to have a significant contribution in three of the samples collected during lower-intensity rain events. The source apportionment was performed with and without isotopes. The results were largely consistent; however, the use of isotopes was found to slightly increase the uncertainty in most of the cases. The correlation analysis between the contributions of sources shows strong correlations between stream bank and agriculture, whereas roads and forest seem to be less correlated to other sources. Thus, the method was better able to estimate road and forest contributions independently. The hypothesis that the contributions of sources are not seasonally changing was tested by assuming that all ten fluvial samples had the same source contributions. This hypothesis was rejected, demonstrating a significant seasonal variation in the sources of sediments in the stream.

Pennsylvania↗
USGS2015

Groundwater/surface-water interactions in the Bad River Watershed, Wisconsin

A groundwater-flow model was developed for the Bad River Watershed and surrounding area by using the U.S. Geological Survey (USGS) finite-difference code MODFLOW-NWT. The model simulates steady-state groundwater-flow and base flow in streams by using the streamflow routing (SFR) package. The objectives of this study were to: (1) develop an improved understanding of the groundwater-flow system in the Bad River Watershed at the regional scale, including the sources of water to the Bad River Band of Lake Superior Chippewa Reservation (Reservation) and groundwater/surface-water interactions; (2) provide a quantitative platform for evaluating future impacts to the watershed, which can be used as a starting point for more detailed investigations at the local scale; and (3) identify areas where more data are needed. This report describes the construction and calibration of the groundwater-flow model that was subsequently used for analyzing potential locations for the collection of additional field data, including new observations of water-table elevation for refining the conceptualization and corresponding numerical model of the hydrogeologic system. The study area can be conceptually divided into three primary hydrogeologic environments. The first encompasses the southern uplands with relatively low topographic relief, where groundwater-flow is unconfined and occurs primarily in sandy till and glacial outwash overlying Archean-aged crystalline bedrock. The second includes a transitional area of higher topographic relief and shallow depth to bedrock, in the vicinity of ridges formed by steeply dipping, early-Proterozoic aged metasedimentary units of the Marquette Range Supergroup (including the Ironwood Formation), and late-Proterozoic igneous units associated with the Midcontinent Rift System (MRS). Groundwater-flow in this area likely occurs primarily through connected networks of bedrock fractures that are not well characterized, and also in isolated pockets of Quaternary deposits. The third and last hydrogeologic environment includes lowlands along Lake Superior where a deep sandstone aquifer is confined by thick deposits of clay-rich till. Model input was compiled by using both published and unpublished data. Constant flux boundary conditions for the model perimeter were developed from a regional analytic element model described in appendix 1 of this report. Pumping from 26 high-capacity wells within the model area was included. The SFR stream network was developed from the National Hydrography Dataset (NHDPlus Version 2) and hydrography from the Wisconsin Department of Natural Resources (WDNR). Hydraulic conductivity values were determined for each model cell by interpolation from a network of pilot points, within zones representing major hydrogeologic units. Recharge to the groundwater system was estimated on a cell-by-cell basis by using the Soil Water Balance code (SWB), with gridded daily temperature and precipitation data for the period 1980–2011, and GIS coverages of soil and land-surface conditions. Estimated recharge varies considerably, following spatial patterns in the precipitation and soil hydrologic group inputs. The lowest recharge values occur in the Superior lowlands, whereas the highest values occur in the upland areas, especially those underlain by sandy soils, and in the vicinity of bedrock hills. The model was calibrated to groundwater-levels and base flows obtained from the USGS National Water Information System (NWIS) database, and groundwater-levels obtained from the WDNR and Band River Band well-construction databases. Calibration was performed via nonlinear regression by using the parameter-estimation software suite PEST. Groundwater levels and base-flow observations in the calibration dataset were well simulated by the calibrated model, with reasonable values of hydraulic conductivity. The pilot-point parameters that were most constrained by observations during model calibration coincided with the locations containing the most wells (head observations)—especially the population centers of Ashland, Mellen, and other communities along the major highway corridors. Results from the calibrated model illustrate differences in the nature of groundwater-flow within the watershed. In the southern part of the watershed, where bedrock is shallow, groundwater flow paths are relatively short, extending from local recharge areas to adjacent first and second-order streams. In contrast, laterally continuous deposits of clay-rich till covering the Superior Lowlands isolate most smaller streams from the sandstone aquifer, allowing for longer flow paths toward larger streams such as the Bad, Marengo, and White Rivers. Approximately three-quarters of all first-order stream cells were dry in the Superior Lowlands, compared to only half of first-order stream cells in the southern bedrock uplands. The model was used to delineate the groundwatershed for the Bad and Kakagon Rivers. “Groundwatershed” is defined as the area contributing groundwater discharge to one of these streams and their tributaries. The groundwatershed was found to align closely with the surface-watershed, with the most notable exception occurring along the southwestern half of Birch Hill, where surface water drains southwest towards the Potato River, and groundwater flows north and east towards Lake Superior. Similarly, the contributing area of groundwater-flow to the Reservation was delineated. Results indicate the off-Reservation groundwater contributing area to be limited in comparison to the extent of the watershed, extending southward into the highlands underlain by MRS igneous rock units, but not further into the area underlain by the Marquette Range Supergroup. Stable isotope samples were collected from 54 wells within the watershed, to investigate sources of groundwater. Oxygen-18 (δ 18 O) values lower than -13.0 per mil were documented in the sampling, and likely indicate the presence of recharge water from the last glacial period (>9,500 years old) beneath the northern portion of the Reservation, in the vicinity of Odanah, Wisconsin. Finally, a new data-worth analysis of potential new monitoring-well locations was performed by using the model. The relative worth of new measurements was evaluated based on their ability to increase confidence in model predictions of groundwater levels and base flows at 35 locations, under the condition of a proposed open-pit iron mine. Results of the new data-worth analysis, and other inputs and outputs from the Bad River model, are available through an online dynamic web mapping service at ( http://wim.usgs.gov/badriver/ ).

Wisconsin↗
USGS2003

Ground-water flow and ground- and surface-water interaction at McBaine Bottoms, Columbia, Missouri-2000-02

McBaine Bottoms southwest of Columbia, Missouri, is the site of 4,269 acres of the Eagle Bluffs Conservation Area operated by the Missouri Department of Conservation, about 130 acres of the city of Columbia wastewater-treat-ment wetlands, and the city of Columbia munici-pal-supply well field. The city of Columbia wastewater-treatment wetlands supply treated effluent to the Eagle Bluffs Conservation Area. The presence of a sustained ground-water high underlying the Eagle Bluffs Conservation Area has indicated that ground-water flow is toward the municipal well field that supplies drinking water to the city of Columbia. The U.S. Geological Survey, in cooperation with the Missouri Department of Conservation and the city of Columbia, measured the ground-water levels in about 88 monitoring wells and the surface-water elevation at 4 sites monthly during a 27-month period to determine the ground-water flow and the ground- and surface-water interaction at McBaine Bottoms. Lateral ground-water flow was dominated by the presence of a ground-water high that was beneath the Eagle Bluffs Conservation Area and the presence of a cone of depression in the northern part of the study area. The ground-water high was present during all months of the study. Ground-water flow was radially away from the apex of the ground-water high; west and south of the high, flow was toward the Missouri River, east of the high, flow was toward Perche Creek, and north of the high, flow was toward the north toward the city of Columbia well field. The cone of depression was centered around the city of Columbia well field. Another permanent feature on the water-level maps was a ground-water high beneath treatment wetland unit 1. Although the ground-water high beneath the Eagle Bluffs Conservation Area was present throughout the study period, the configuration of the high changed depending on hydrologic conditions. Generally in the spring, the height of the ground-water high began to decrease and hydraulic gradients around the high became more shallow than in the winter months. In early summer, the high was the least pronounced. During mid-sum-mer, the high became more pronounced, and it continued to become higher, increasing until it reached its maximum height in late fall or early winter. Fluctuations in the ground-water high were partially produced by the cycle of flooding of the Eagle Bluffs Conservation Area wetland pools in the fall and subsequent drainage so crops could be planted in many of the wetland pools. The cone of depression in the northern part of the study area generally extended from the base of the ground-water high in the northern part of the Eagle Bluffs Conservation Area throughout the rest of the study area. The depth of the cone primarily was affected by the altitude of the Missouri River and the quantity of water being pumped from the alluvial aquifer by the city of Columbia well field. Ground-water flow in the alluvial aquifer in McBaine Bottoms in the late 1960?s before the development of the city of Columbia well field and the Eagle Bluffs Conservation Area was from northwest to southeast approximately parallel to the Missouri River. The ground-water high beneath the Eagle Bluffs Conservation Area and the cone of depression around the city of Columbia well field were not present in water-level maps for 1968 and 1978. The Missouri River can be a source of recharge to the alluvial aquifer. Generally the altitude of the river in the northern part of the study area was higher than the water table in the aquifer. Ground-water flow in this area was from the river into the alluvial aquifer. In the southern part of the study area adjacent to the Eagle Bluffs Conservation Area, the Missouri River was lower than the water table in the alluvial aquifer, indicating that the river was receiving water from the alluvial aquifer beneath the Eagle Bluffs Conservation Area.

Missouri↗
USGS1977

Quality of rivers of the United States, 1975 water year; based on the National Stream Quality Accounting Network (NASQAN)

The National Stream Quality Accounting Network (NASQAN) was established by the U.S. Geological Survey to provide a nationally uniform basis for continuously assessing the quality of U.S. rivers. Stations generally are at the downstream end of hydrologic accounting units in order to measure the quantity and quality of water flowing from the units. The 1975 water year was the first year of operation of the network that represents essentially all of the accounting units and thereby describes the water- quality of the entire country. Data are available on a large number of water-quality constituents measured at 345 stations during the 1975 water year. Temperature data (usually continuous or daily measurements) from NASQAN stations were fitted to a first order harmonic equation and the parameters for the harmonic function are reported for each station. Mean temperatures generally range from 5°-10°C in the North to more than 20°C along the southern border of the continental United States and in Hawaii and Puerto Rico; means were less than 10°C at 63 stations and greater than 25°C at only 7 stations. Amplitudes of the temperature curves are greatest (greater than 12°C) for the streams at midlatitudes and in the Great and Central Plains, and they are smallest for the subtropical and cold-climate streams. Considering chemical and biological characteristics of U.S. streams as described by NASQAN data, water quality is best (by many standards) in the Northeast, Southeast, and Northwest. Waters there generally are low in dissolved solids and major and minor chemical constituents, generally are soft (except in Florida), and carry relatively small amounts of sediment. These conditions mainly reflect the geology of the regions and the relatively large amounts of precipitation. However, many of these waters show the effects of pollution and carry moderate or high levels of major nutrients and have correspondingly high populations of attached and floating plants. High counts of indicator bacteria also show signs of local pollution, particularly in regions of the country with large human and animal populations. In the Northeast, some heavy metals are at moderate levels, but not above most water-quality criteria. Rivers of most of the Mid-Continent and Southwest reflect the arid or semi-arid climate, erodible soils, and agricultural activities. They are characterized by moderate to high levels of dissolved major and minor constituents, sediment, major nutrients, and biota (floating and attached aquatic plants and indicator bacteria). In addition, the most incidences of pesticides in stream and bottom sediments were found in these regions. A special analysis was made to study the patterns of dissolved solids, major nutrients, phytoplankton, and zinc in the Mississippi River above Memphis, Tennessee. It was found that flow volume is an important factor in influencing river quality, and that stations with low concentration of major nutrients generally had low phytoplankton populations as well.

Open-File Report↗
USGS2005

Hydrogeology and simulation of source areas of water to production wells in a colluvium-mantled carbonate-bedrock aquifer near Shippensburg, Cumberland and Franklin Counties, Pennsylvania

This report presents the results of a study by the U.S. Geological Survey in cooperation with the Shippensburg Borough Authority to evaluate the source areas of water to production wells in a colluvium-mantled carbonate-bedrock aquifer in Cumberland and Franklin Counties, Pa. The areal extent of the zone of contribution was simulated for three production wells near Shippensburg, Pa. by use of a ground-water-flow model. A 111-square-mile area was selected as the model area and includes areas of the South Mountain Section and the Great Valley Section of the Valley and Ridge Physiographic Province. Within the model area, the geologic units in the South Mountain area are predominantly metamorphic rocks and the geologic units in the Great Valley are predominantly carbonate rocks. Hydrologic and geologic information were compiled to establish a conceptual model of ground-water flow. Characteristics of aquifer materials were determined, and streamflow and water levels were measured. Streamflow measurements in November 2003 showed all streams lost water as they flowed from South Mountain over the colluvium-mantled carbonate aquifer into the Great Valley. Some streams lost more than 1 cubic foot per second to the aquifer in this area. The Shippensburg Borough Authority owns three production wells in the model area. Two wells, Cu 969 and Fr 823, are currently (2004) used as production wells and produce 500,000 and 800,000 gallons per day, respectively. Well Cu 970 is intended to be brought on line as a production well in the future. Water levels were measured in 43 wells to use for model calibration. Water-level fluctuations and geophysical logs indicated confined conditions in well Cu 970. Ground-water flow was simulated with a model that consisted of two vertical layers, with five zones in each layer. The units were hydrostratigraphic units that initially were based on geologic formations, but boundaries were adjusted during model calibration. Model calibration resulted in a root mean square error of 9.8 feet. A parameter-estimation package was used during model calibration to estimate three parameters. The parameter estimation resulted in a value of 233 feet per day for horizontal hydraulic conductivity of the highly fractured carbonate rocks and sandy colluvium in layer 1; 3.97 feet per day for horizontal hydraulic conductivity of the ridge-forming unit in layer 1; and a value of 1.73 for horizontal anisotropy in both layers. The calibrated model was used to delineate the areal extent of the zone of contribution for wells Cu 969 and Fr 823. Although well Cu 970 is not currently (2004) being used, the areal extent of its zone of contribution also was simulated without additional model calibration. The shape of the areal extent of the zone of contribution was similar for each well and included an area that extended from the well southwest along the Tomstown Formation, and then extended southeast into the metamorphic rocks of South Mountain. The contributing areas from the watersheds of losing streams were also delineated because losing stream reaches bisect the areal extent of the zones of contribution. Spatial uncertainty of the areal extent of the zone of contribution was illustrated using a Monte-Carlo analysis. The model was run 1,000 times using randomly generated parameter sets that were normally distributed within the confidence interval around the optimal values for the three estimated parameters. The model converged and had a reasonable water budget for 980 of the model runs. For each of those 980 model runs, the recharge area was determined, and the results for all runs were compiled and contoured. The results of the Monte-Carlo analysis were compared to the results of the deterministic model, illustrating that the deterministic model has the greatest certainty in the area closest to each well in the Tomstown Formation. The areas farther from the well, upgradient, and in the metamorphic rocks have a higher degree

Pennsylvania↗
USGS2026

Groundwater drought in the United States: Spatial and temporal variability

Many communities and ecosystems in the United States that are dependent on groundwater are potentially adversely affected by groundwater drought. We computed yearly groundwater-drought metrics and mean groundwater levels at well locations across the conterminous United States (CONUS), using data from wells and remotely sensed and modeled Gravity Recovery and Climate Experiment Drought Monitor Data Assimilation (GRACE-DADM). We also modeled the probability of low or high human impact at each well location. The spatial distribution of groundwater-drought duration and severity from 2001 to 2020 for 1,510 wells shows longer maximum duration and higher maximum severity events in drier regions like the Southwest than in wetter regions like the Northeast. Based on 613 wells in CONUS from 1981 to 2020, there are many significant decreases in drought duration and severity in the Northeast and many significant increases in annual-mean groundwater levels. In contrast, there are many significant increases in drought metrics and decreases in mean water levels in parts of the Southeast. There are major differences in trends from 2001 to 2020 between well-based and GRACE-DADM-based groundwater metrics in some CONUS regions and a very low correlation between trends at individual locations across CONUS. A potential reason for this disparity is the low GRACE-DADM resolution (∼12 km) and the potential for a large amount of groundwater variation at the local scale. Also, GRACE-DADM represents shallow, unconfined aquifers which may not match the screened interval of the monitoring wells we evaluated. Large spatial gaps in long-term, high frequency, and quality-assured groundwater-well monitoring data present a challenge for understanding groundwater-drought variability across CONUS. Remote sensing tools such as GRACE can help but cannot fully replace well monitoring, as highlighted by our study results. Substantially more long-term monitoring wells would more accurately represent groundwater-drought trends and spatial variability across CONUS, particularly in western regions.

conterminous United States↗
USGS2014

Groundwater quality at Alabama Plating and Vincent Spring, Vincent, Alabama, 2007–2008

The former Alabama Plating site in Vincent, Alabama, includes the location where the Alabama Plating Company operated an electroplating facility from 1956 until 1986. The operation of the facility generated waste containing cyanide, arsenic, cadmium, chromium, copper, lead, zinc, and other heavy metals. Contamination resulting from the site operations was identified in groundwater, soil, and sediment. Vincent Spring, used as a public water supply by the city of Vincent, Alabama, is located about ½ mile southwest of the site. The U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, conducted an investigation at Vincent Spring and the Alabama Plating site, Vincent, Alabama, during 2007–2008 to evaluate the groundwater quality and evaluate the potential effect of contaminated groundwater on the water quality of Vincent Spring. The results of the investigation will provide scientific data and information on the occurrence, fate, and transport of contaminants in the water resources of the area and aid in the evaluation of the vulnerability of the public water supply to contamination. Samples were analyzed to evaluate the water quality at the former plating site, investigate the presence of possible contaminant indicators at Vincent Spring, and determine the usefulness of stable isotopes and geochemical properties in understanding groundwater flow and contaminant transport in the area. Samples collected from 16 monitor wells near the plating site and Vincent Spring were analyzed for major constituents, trace metals, nutrients, and the stable isotopes for hydrogen ( 2 H/H) and oxygen ( 18 O/ 16 O). Groundwater collected from Vincent Spring was characterized as a calcium-magnesium-bicarbonate water type with total dissolved solids concentrations ranging from 110 to 120 milligrams per liter and pH ranging from about 7.5 to 7.9 units. Groundwater chemistry at the monitor wells at the Alabama Plating site was highly variable by location and depth. Dissolved solids concentrations ranged from 28 to 2,880 milligrams per liter, and the water types varied from calcium-magnesium-bicarbonate-chloride, to calcium-sulfate or calcium-magnesium-sulfate, to sodium-chloride water types. The stable isotope ratios for hydrogen ( 2 H/H) and oxygen ( 18 O/ 16 O) for water from the monitor wells and from Vincent Spring, based on a single sampling event, can be separated into three groups: (1) Vincent Spring, (2) monitor wells MW03 and MW28, and (3) the remaining Alabama Plating monitor wells. The geochemical and stable isotope analyses indicate that water from Vincent Spring is distinct from water from the Alabama Plating monitor wells; however, this evaluation is based on a single sampling event. Although the water from Vincent Spring, for this sampling event, is different and does not seem to be affected by contaminated groundwater from the Alabama Plating site, additional hydrologic and water-quality data are needed to fully identify flow paths, the potential for contaminant transport, and water-quality changes through time.

Alabama↗
USGS1997

Eutrophication potential of Payette Lake, Idaho

Payette Lake was studied during water years 1995-96 to determine the 20.5-square-kilometer lake's assimilative capacity for nutrients and, thus, its eutrophication potential. The study included quantification of hydrologic and nutrient budgets, characterization of water quality in the limnetic and littoral zones, development of an empirical nutrient load/lake response model, and estimation of the limnological effects of a large-scale forest fire in the lake's 373-square-kilometer watershed during the autumn of 1994. Streamflow from the North Fork Payette River, the lake's primary tributary, delivered about 73 percent of the lake's inflow over the 2 years. Outflow from the lake, measured since 1908, was 128 and 148 percent of the long-term average in 1995 and 1996, respectively. The larger volumes of outflow reduced the long-term average water- residence time of 2.35 years to 1.84 and 1.42 years for 1995 and 1996, respectively. The lake retained 54 percent of its 1995-96 influent load of nitrogen and 79 percent of its influent load of phosphorus. The North Fork Payette River contributed an average of 69.4 percent of the lake's nitrogen load and 28.2 percent of its phosphorus load. The 1994 forest fires substantially increased the loads of nitrogen and phosphorus delivered to the lake; however, only nitrogen concentrations were noticeably increased in the lake. Payette Lake was classified as oligotrophic on the basis of annual geometric mean concentrations, in micrograms per liter, of total phosphorus (4.7), total nitrogen (225), and chlorophyll- a (1.3) during 1995-96. Secchi-disc transparencies ranged from 2.3 to 8.0 meters, indicative of mesotrophic conditions. Median ratios of dissolved inorganic nitrogen to dissolved orthophosphorus ranged from 38 to 254, thereby indicating phosphorus limitation of phytoplankton growth. Phytoplankton populations were taxonomically dominated by diatoms; blue-green algae were rare. One diatom, Tabellaria fenestrata , contributed 52 percent of the biovolume. Within the littoral zone, median periphyton production, normalized to photosynthetically active radiation input, ranged from 0.0007 to 0.02 milligrams of chlorophyll- a per square meter per Einstein, a difference of 28.6 times. Multiple linear regression analysis failed to detect any significant relation between periphyton production and various indices of nearshore development. Nine genera of aquatic macrophytes were identified, including Eurasian milfoil ( Myriophyllum spicatum var. spicatum ), which is considered a nuisance aquatic plant. Despite its oligotrophy, Payette Lake had substantial dissolved-oxygen deficits in 1995-96, which led to 4-month periods of anoxia in the near-bottom waters of its southwest basin. The hypolimnetic dissolved-oxygen deficit was much larger than that predicted by the nutrient load/lake response model. The southwest basin's propensity for developing anoxia was related to the lengthy water-residence time and incomplete water-column circulation and reaeration during the spring and autumn, coupled with a long-term accumulation of oxygen- demanding organic matter produced within the lake or delivered by its watershed.

Idaho↗
USGS2001

Hydrologic and salinity characteristics of Currituck Sound and selected tributaries in North Carolina and Virginia, 1998–99

Data collected at three sites in Currituck Sound and three tributary sites between March 1, 1998, and February 28, 1999, were used to describe hydrologic and salinity characteristics of Currituck Sound. Water levels and salinity were measured at West Neck Creek at Pungo and at Albemarle and Chesapeake Canal near Princess Anne in Virginia, and at Coinjock, Bell Island, Poplar Branch, and Point Harbor in North Carolina. Flow velocity also was measured at the West Neck Creek and Coinjock sites. The maximum water-level range during the study period was observed near the lower midpoint of Currituck Sound at Poplar Branch. Generally, water levels at all sites were highest during March and April, and lowest during November and December. Winds from the south typically produced higher water levels in Currituck Sound, whereas winds from the north typically produced lower water levels. Although wind over Currituck Sound is associated with fluctuations in water level within the sound, other mechanisms, such as the effects of wind on Albemarle Sound and on other water bodies south of Currituck Sound, likely affect low-frequency water-level variations in Currituck Sound. Flow in West Neck Creek ranged from 313 cubic feet per second to the south to -227 cubic feet per second to the north (negative indicates flow to the north). Flow at the Coinjock site ranged from 15,300 cubic feet per second to the south to -11,700 cubic feet per second to the north. Flow was to the south 68 percent of the time at the West Neck Creek site and 44 percent of the time at the Coinjock site. Daily flow volumes were calculated as the sum of the instantaneous flow volumes. The West Neck Creek site had a cumulative flow volume to the south of 7.69 x 108 cubic feet for the period March 1, 1998, to February 28, 1999; the Coinjock site had a cumulative flow volume to the north of -1.33 x 1010 cubic feet for the same study period. Wind direction and speed influence flow at the West Neck Creek and Coinjock sites, whereas precipitation alone has little effect on flow at these sites. Flow at the West Neck Creek site is semidiurnal but is affected by wind direction and speed. Flow to the south (positive flow) was associated with wind speeds averaging more than 15 miles per hour from the northwest; flow to the north (negative flow) was associated with wind speeds averaging more than 15 miles per hour from the south and southwest. Flow at the Coinjock site reacted in a more unpredictable manner and was not affected by winds or tides in the same manner as West Neck Creek, with few tidal characteristics evident in the record. Throughout the study period, maximum salinity exceeded 3.5 parts per thousand at all sites; however, mean and median salinities were below 3.5 parts per thousand at all sites except the Point Harbor site (3.6 and 4.2 parts per thousand, respectively) at the southern end of the sound. Salinities were less than or equal to 3.5 parts per thousand nearly 100 percent of the time at the Bell Island and Poplar Branch sites in Currituck Sound and about 86 percent of the time at the Albemarle and Chesapeake Canal site north of the sound. Salinity at the West Neck Creek and Coinjock sites was less than or equal to 3.5 parts per thousand about 82 percent of the time. During this study, prevailing winds from the north were associated with flow to the south and tended to increase salinity at the West Neck Creek and the Albemarle and Chesapeake Canal sites. Conversely, these same winds tended to decrease salinity at the other sites. Prevailing winds from the south and southwest were associated with flow to the north and tended to increase salinity at the Poplar Branch and Point Harbor sites in Currituck Sound and at the Coinjock site, but these same winds tended to decrease salinity at the West Neck Creek and the Albemarle and Chesapeake Canal sites. The greatest variations in salinity were observed at the northernmost site, West Neck Creek, and thesouthernmost site, Point Harbor. The least variation in salinity was observed at the upper midpoint of the sound at the Bell Island site. Daily salt loads were computed for 364 days at the West Neck Creek site and 348 days at the Coinjock site from March 1, 1998, to February 28, 1999. The cumulative salt load at West Neck Creek was 28,170 tons to the south, and the cumulative salt load at the Coinjock site was -872,750 tons to the north. The cumulative salt load passing the West Neck Creek site during the study period would be 0.01 part per thousand if uniformly distributed throughout the sound (approximately 489,600 acre-feet in North Carolina). If the cumulative salt load passing the Coinjock site were uniformly distributed throughout the sound, the salinity in the sound would be 0.32 part per thousand. The net transport at the West Neck Creek and Coinjock sites indicates inflow of salt into the sound. A constant inflow of freshwater from tributaries and ground-water sources also occurs; however, the net flow volumes from these freshwater sources are not documented, and the significance of these freshwater inflows toward diluting the net import of salt into the sound is beyond the scope of this study.

North Carolina, Virginia↗
USGS2008

Glaciers of North America - Glaciers of Alaska

Glaciers cover about 75,000 km 2 of Alaska, about 5 percent of the State. The glaciers are situated on 11 mountain ranges, 1 large island, an island chain, and 1 archipelago and range in elevation from more than 6,000 m to below sea level. Alaska's glaciers extend geographically from the far southeast at lat 55 deg 19'N., long 130 deg 05'W., about 100 kilometers east of Ketchikan, to the far southwest at Kiska Island at lat 52 deg 05'N., long 177 deg 35'E., in the Aleutian Islands, and as far north as lat 69 deg 20'N., long 143 deg 45'W., in the Brooks Range. During the 'Little Ice Age', Alaska's glaciers expanded significantly. The total area and volume of glaciers in Alaska continue to decrease, as they have been doing since the 18th century. Of the 153 1:250,000-scale topographic maps that cover the State of Alaska, 63 sheets show glaciers. Although the number of extant glaciers has never been systematically counted and is thus unknown, the total probably is greater than 100,000. Only about 600 glaciers (about 1 percent) have been officially named by the U.S. Board on Geographic Names (BGN). There are about 60 active and former tidewater glaciers in Alaska. Within the glacierized mountain ranges of southeastern Alaska and western Canada, 205 glaciers (75 percent in Alaska) have a history of surging. In the same region, at least 53 present and 7 former large ice-dammed lakes have produced jokulhlaups (glacier-outburst floods). Ice-capped volcanoes on mainland Alaska and in the Aleutian Islands have a potential for jokulhlaups caused by subglacier volcanic and geothermal activity. Because of the size of the area covered by glaciers and the lack of large-scale maps of the glacierized areas, satellite imagery and other satellite remote-sensing data are the only practical means of monitoring regional changes in the area and volume of Alaska's glaciers in response to short- and long-term changes in the maritime and continental climates of the State. A review of the literature for each of the 11 mountain ranges, the large island, the island chain, and the archipelago was conducted to determine both the individual and the regional status of Alaskan glaciers and to characterize changes in thickness and terminus position of representative glaciers in each mountain range or island group. In many areas, observations used for determining changes date from the late 18th or early 19th century. Temperature records at all Alaskan meteorological recording stations document a 20th century warming trend. Therefore, characterizing the response of Alaska's glaciers to changing climate helps to quantify potential sea-level rise from past, present, and future melting of glacier ice (deglaciation of the 14 glacierized regions of Alaska), understand present and future hydrological changes, and define impacts on ecosystems that are responding to deglacierization. Many different types of data were scrutinized to determine baselines and to assess the magnitude of glacier change. These data include the following: published descriptions of glaciers (1794-2000), especially the comprehensive research by Field (1975a) and his colleagues in the Alaska part of Mountain Glaciers of the Northern Hemisphere, aerial photography (since 1926), ground photography (since 1884), airborne radar (1981-91), satellite radar (1978-98), space photography (1984-94), multispectral satellite imagery (since 1972), aerial reconnaissance and field observations made by many scientists during the past several decades, and various types of proxy data. The published and unpublished data available for each glacierized region and individual glacier varied significantly. Geospatial analysis of digitized U.S. Geological Survey (USGS) topographic maps is used to statistically define selected glaciological parameters in the eastern part of the Alaska Range. The analysis determined that every mountain range and island group investigated can be characterized by significant glacier retreat, thinning, and (or) stagnation, especially those glaciers that end at lower elevations. At some locations, glaciers completely disappeared during the 20th century. In other areas, retreat that started as early as the early 18th century has continued into the 21st century. Ironically, in several areas, retreat is resulting in an increase in the total number of glaciers; even though individual glaciers are separating, the volume and area of ice continue to decrease.

Alaska↗
USGS2014

Wind River subbasin restoration: U.S. Geological Survey annual report November 2012 through December 2013

Executive Summary The Wind River subbasin in southwest Washington State provides habitat for a population of wild Lower Columbia River steelhead Oncorhynchus mykiss . There have been no hatchery steelhead planted in the Wind River subbasin since 1994, and hatchery adults are estimated to be less than one percent of adults in any year (pers comm. Thomas Buehrens, Washington Department of Fish and Wilflife). We used Passive Integrated Transponder (PIT)-tagging and a series of instream PIT-tag interrogation systems (PTIS) to investigate life-histories, populations, and efficacy of habitat restoration actions for these steelhead. Data from our study, and companion work by Washington Department of Fish and Wildlife (WDFW), will contribute to Bonneville Power Administration’s (BPA) Research Monitoring and Evaluation (RM&E) Program Strategy of Fish Population Status Monitoring ( www.cbfish.org/ProgramStrategy.mvc/ViewProgramStrategySummary/1 ), specifically the sub-strategies of: 1) Assessing the Status and Trends of Diversity of Natural Origin Fish Populations and to uncertainties research regarding differing life histories of a wild steelhead population, 2) Assessing the Status and Trend of Adult Natural Origin Fish Populations, and 3) Monitoring and Evaluating the Effectiveness of Tributary Habitat Actions Relative to Environmental, Physical, or Biological Performance Objectives. During summer 2013, we PIT-tagged parr steelhead in headwater areas of the Wind River subbasin to investigate variable life-histories, specifically to compare fate of those juvenile steelhead that move downstream prior to smolting with those that remain in their natal areas until smolting. A series of instream PTISs monitored movement of these fish. Detections at the instream PTISs showed trends of parr emigration during summer and fall, in addition to the expected movement of parr and smolts in spring. Long-term monitoring of PIT-tagged fish over multiple years will provide information on contribution of various life-history strategies to smolt production and adult returns, as well as helping to identify factors influencing parr movement. Movements of PIT-tagged adult steelhead were tracked with our instream PTISs. These data have provided information on timing of adult movements to various parts of the watershed, which is allowing us to assess adult returns to tributary watersheds within the Wind River subbasin. Determination of adult use of tributary watersheds has provided data that will contribute to evaluating the efficacy of the removal of Hemlock Dam from Trout Creek. Hemlock Dam, located at rkm 2.0 of Trout Creek was removed in summer 2009 and had contributed to hydrologic impairment of Trout Creek. Evaluating restoration efforts is of interest to many managers and agencies so that funding and time are allocated for best results. The evaluation of various life-histories of Lower Columbia River steelhead within the Wind River subbasin will provide information to better track populations, and to direct habitat restoration and water allocation planning. Increasingly detailed Viable Salmonid Population information, such as that provided by PIT-tagging and instream PTISs networks like those we are building and operating in the Wind River subbasin, will provide data to inform policy and management, as life-history strategies and production bottlenecks are identified and understood.

Washington↗
USGS2015

Regional variability in dust-on-snow processes and impacts in the Upper Colorado River Basin

Dust deposition onto mountain snow cover in the Upper Colorado River Basin frequently occurs in the spring when wind speeds and dust emission peaks on the nearby Colorado Plateau. Dust loading has increased since the intensive settlement in the western USA in the mid 1880s. The effects of dust-on-snow have been well studied at Senator Beck Basin Study Area (SBBSA) in the San Juan Mountains, CO, the first high-altitude area of contact for predominantly southwesterly winds transporting dust from the southern Colorado Plateau. To capture variability in dust transport from the broader Colorado Plateau and dust deposition across a larger area of the Colorado River water sources, an additional study plot was established in 2009 on Grand Mesa, 150 km to the north of SBBSA in west central, CO. Here, we compare the 4-year (2010–2013) dust source, deposition, and radiative forcing records at Grand Mesa Study Plot (GMSP) and Swamp Angel Study Plot (SASP), SBBSA's subalpine study plot. The study plots have similar site elevations/environments and differ mainly in the amount of dust deposited and ensuing impacts. At SASP, end of year dust concentrations ranged from 0.83 mg g −1 to 4.80 mg g −1 , and daily mean spring dust radiative forcing ranged from 50–65 W m −2 , advancing melt by 24–49 days. At GMSP, which received 1.0 mg g −1 less dust per season on average, spring radiative forcings of 32–50 W m −2 advanced melt by 15–30 days. Remote sensing imagery showed that observed dust events were frequently associated with dust emission from the southern Colorado Plateau. Dust from these sources generally passed south of GMSP, and back trajectory footprints modelled for observed dust events were commonly more westerly and northerly for GMSP relative to SASP. These factors suggest that although the southern Colorado Plateau contains important dust sources, dust contributions from other dust sources contribute to dust loading in this region, and likely account for the majority of dust loading at GMSP.

Hydrological Processes↗
USGS2004

Migration stopover ecology of western avian populations: A southwestern migration workshop

The importance of migration stopover sites in ensuring that migratory birds successfully accomplish their journeys between breeding and non-breeding ranges has come to the forefront of avian research. Migratory birds that breed in western United States (US) and Canada and overwinter primarily in western Mexico migrate across the arid region of northern Mexico and southwestern US. Many of these migrants use lowland riparian stopover habitats, which comprise less than 0.1% of the western U.S. landscape. These habitats represent a significant conservation priority. Recognizing the importance of migration stopover habitats in the arid southwest, the U.S. Fish and Wildlife Service (USFWS) Region 6 partnered with the U.S. Geological Survey (USGS) to support a project---“Migration stopover ecology of western avian populations: patterns of geographic and habitat distribution.” A primary objective of the project was to convene a workshop for avian researchers, conservation professionals, and land managers involved in stopover needs of migratory birds that breed in western North America. The workshop included presentations on our current state of knowledge regarding passerine migration in western North America, techniques and technologies potentially useful in researching migration, and efforts that agencies and other partners are conducting within the realm of migration. Workshop presentations provided a backdrop for subsequent discussions, the goals of which were to identify research needs and initiate a coordinated approach to research of western migration stopover ecology. Workshop presentations spanned a wide range of concerns and interests. Highlights included indications that mid- and high-elevation riparian and montane shrubland habitats may be as crucial to western migrants in fall migration as lowland riparian habitats are in spring migration. Comparisons of eastern versus western migration systems elucidated large differences in stopover habitats used and the intensity with which certain types are used, underscoring the potential need to develop separate management approaches for eastern and western stopover sites. Presentations on techniques and technology for migration research revealed that rate of lipid deposition can serve as an indicator of habitat quality; that genetics and stable isotope analyses of feathers can be valuable tools to elucidate linkages between breeding and wintering areas; that radar imagery can be used to track large-scale movement patterns and habitat use; and that there are analytical options for combining multiple sources of information. Other presentations focused on partnership perspectives (USFWS and Sonoran Joint Venture), the genesis of a western migration monitoring network, premises of Coordinated Bird Monitoring, and how collaborative efforts could benefit migration research (e.g., combined bird and bat migration studies; linking avian researchers with fluvial geomorphologists; linking research throughout western North America; linking surveys and banding). Priority research needs and questions identified during the open discussions fell into three main categories: (1) habitat/landscape/climate relationships, (2) en route bird distribution patterns, and (3) general migration ecology. Tasks within these categories included: define the relative importance of various habitat types to migrants in spring and fall, determine what distinguishes high- from poor-quality stopover habitat; determine geographic patterns of loss in stopover habitats; model landscape attributes associated with species richness and abundance; identify effects of climate change and current climate anomalies on plant phonologies, associated insect flushes, and timing of migration; and determine effects of hydrologic changes on riparian vegetation, food availability, and stopover habitat quality. Workshop participants discussed a coordinated approach for addressing immediate research needs regarding migration patterns and crucial stopover sites and types. They envisioned a three­-tiered, coordinated approach: (1) long-term research to address effects of climate change and other large-scale patterns, (2) intensive, short-term survey and monitoring efforts using a stratified random design within habitats of interest to elucidate regional patterns of distribution and habitat use, and (3) research conducted at existing survey and banding sites to address more in-depth questions (e.g., rates of lipid deposition, microhabitat use, isotope analyses). There was considerable interest in developing common research proposals to blend the broad expertise represented at this workshop. A second meeting is recommended to build on the momentum of these discussions, to facilitate collaborations, and further the goals of integrated approaches to broadscale research on migration stopover ecology.

Open-File Report↗
USGS1963

Geology and occurrence of ground water in Lyon County, Minnesota

Lyon County is in southwestern Minnesota, mostly within the drainage basin of the Minnesota River. The basement rocks in the area consist largely of Precambrian granite and quartzite. These are overlain locally by flat-lying Upper Cretaceous strata composed of thick sections of soft dark-bluish-gray shale and some thin beds of loosely consolidated sandstone. The Cretaceous strata are more than 500 feet thick near the center of the county but gradually pinch out toward the northeast and southwest against the highs of the Precambrian bedrock surface. Glacial drift overlies the Precambrian and Cretaceous rocks and forms the surface of the area. The drift consists largely of till and ranges in thickness from about 10 feet in the north and northeast to approximately 550 feet in the southwest. The most prominent surflcial glacial deposits are five southeast-trending end moraines, two of which are associated with, and parallel to, relatively extensive belts of outwash. Recent deposits averaging less than 20 feet in thickness overlie the glacial drift in stream valleys. The principal aquifers in Lyon County are glacial-melt-water deposits of sand and gravel, and sandstone of Cretaceous age. The underlying Precambrian rocks and the Recent alluvium are of only local importance as water sources. Melt-water deposits composed of stratified clay and silt as well as sand and gravel occur in channels having surficial expression, in buried channels having no direct surface expression, and as small isolated bodies within the till. Well logs of test holes show that the buried melt-water channels are generally parallel to the surflcial channels. However, melt-water deposits are not necessarily confined to the area beneath the surflcial channel but may extend laterally 1 mile or more beyond its limits. Sand and gravel are commonly interbedded with other melt-water materials. They range in thickness from 10 to 75 feet, are usually less than 1 mile in width, and may be as much as 8 miles in length. Although these aquifers are extensive, they underlie less than 10 percent of the county area. In most places, water from the drift is obtained from small isolated bodies of sand and gravel within the till. Water in the glacial drift is usually very hard (more than 500 parts per million) and low in chlorides (less than 50 parts per million). Drift wells generally yield from 2 to 30 gallons per minute; however, in areas where wells tap melt-water-channel deposits, sustained yields of as much as 500 gallons per minute are obtained. The sandstone beds of Cretaceous age occur between the Precambrian bedrock surface and an altitude of 825 feet as a basal sandstone, between altitudes of 890 and 1.020 feet, and between altitudes of 1,050 and 1,160 feet. Water-well data, supplemented by test drilling, show that each of these stratigraphic intervals is developed only in the county. The sandstone beds are of low permeability and are usually less than 2 feet thick, but they may be more than 20 feet thick in places. Water from these aquifers range in quality from soft (less than 60 parts per million) to very hard (more than 500 parts per million) and may contain excessive amounts of chloride (500 to 2,000 parts per million). Wells tapping rocks of Cretaceous age usually yield 2 to 7 gallons per minute, but in areas where the sandstone beds are thicker or hydrologically interrelated with aquifers of other geologic units, yields of as much as 75 gallons per minute have been obtained. Large quantities of ground water are available from melt-water channels in the county. Moderate quantities, adequate for domestic and small industrial needs, are available from many of the small isolated deposits of sand and gravel in the till. Small quantities of ground water, adequate only for domestic supply, generally can be obtained from Cretaceous sandstone.

Minnesota↗
USGS1996

Geohydrology and conceptual model of a ground-water-flow system near a Superfund site in Cheshire, Connecticut

Degradation of ground-water quality has been identified in an area of the north-central part of the town of Cheshire, Connecticut. An investigation by the U.S. Geological Survey, in cooperation with the U.S. Environmental Protection Agency, was done during 1994-95 to characterize the unconsolidated glacial deposits and the sedimentary bedrock, integrate the local geohydrologic conditions with the regional geohydrologic system, and develop a conceptual understanding of ground-water flow in the study area. A regional ground-water-flow model developed for the region near the study area indicates that perennial streams, including Judd Brook and the Tenmile River, form hydrologic divides that separate the larger region into hydraulically independent flow systems. In the local study area, synoptic water-level measurements made in June 1995 indicate that ground water near the water table flows west and southwestward from the low hill on the eastern side of the area toward the pond and wetlands along Judd Brook. Water-level data indicate that there is good hydraulic connection between the unconsolidated materials and underlying fractured bedrock. Unconsolidated materials in the study area consist principally of glacial stratified deposits that are fine sand, silt, and clay of glaci- olacustrine origin; locally these overlie thin glacial till. The glacial sediments range in thickness from a few feet to about 25 ft in the eastern part of the study area and are as much as 100 ft thick in the western and southern part of the study area beneath the Judd Brook and Tenmile River valleys. Fluvial redbeds of the New Haven Arkose underlie the glacial deposits in the region; in the study area, the redbeds consist of (1) channel sandstone units, which are coarse sandstone to fine conglomerate, generally in 6- to 15-ft- thick sequences; and (2) overbank mudstone units, which are siltstone and silty sandstone with some fine sandstone, generally in 6- to 50-ft-thick sequences. Thin-bedded zones of siltstone that are particularly fissile are present locally within the mudstone units. Rock units strike northward and dip eastward at about 20. The eastward-dipping strata are cut by a consistent set of west to west-northwest dipping, high-angle fractures. These fractures are oriented perpendicular to bedding and are present mostly in the channel sandstone units, but locally extend into the mudstone units as well. Borehole-geophysical logging indicates that ground water flows along bedding planes in fissile zones and between fissile zones in high-angle fractures, which are perpendicular to bedding. The combined fracture types form an aquifer system in which ground water follows a stair-step flowpath, flowing horizontally through fissile zones and vertically through high-angle fractures. Heat-pulse flow meter measurements and borehole fluid-conductivity and temperature logs indicate that only a small subset of the fissile zones and some high-angle fractures are hydraulically significant. A generalized local-scale ground-water flow model based on a nonspecific, but realistic, rock and fracture geometry was developed for the study area. Simulations show that under nonpumping conditions at a hypothetical well located in the middle of the model, ground-water flow was separated into upper and lower zones in which flow paths differed but were generally from northeast to southwest. Several short-duration aquifer tests conducted in the study area indicate that there is good hydraulic connection in the fractures between the pumping well (CS-221) and two bedrock wells located approximately 100 ft to the north and south along bedding strike. During the short duration of the aquifer tests, there was no hydraulic connection in bedrock wells located to the east, perpendicular to the strike. A range of transmissivity of 27 to 46 ft2/d was calculated from the aquifer-test data for the fractured-bedrock aquifer at CS-221 and TH-2. Individual fracture zones identified by bo

Open-File Report↗
USGS2010

Hydrothermal zebra dolomite in the Great Basin, Nevada--attributes and relation to Paleozoic stratigraphy, tectonics, and ore deposits

In other parts of the world, previous workers have shown that sparry dolomite in carbonate rocks may be produced by the generation and movement of hot basinal brines in response to arid paleoclimates and tectonism, and that some of these brines served as the transport medium for metals fixed in Mississippi Valley-type (MVT) and sedimentary exhalative (Sedex) deposits of Zn, Pb, Ag, Au, or barite. Numerous occurrences of hydrothermal zebra dolomite (HZD), comprised of alternating layers of dark replacement and light void-filling sparry or saddle dolomite, are present in Paleozoic platform and slope carbonate rocks on the eastern side of the Great Basin physiographic province. Locally, it is associated with mineral deposits of barite, Ag-Pb-Zn, and Au. In this paper the spatial distribution of HZD occurrences, their stratigraphic position, morphological characteristics, textures and zoning, and chemical and stable isotopic compositions were determined to improve understanding of their age, origin, and relation to dolostone, ore deposits, and the tectonic evolution of the Great Basin. In northern and central Nevada, HZD is coeval and cogenetic with Late Devonian and Early Mississippian Sedex Au, Zn, and barite deposits and may be related to Late Ordovician Sedex barite deposits. In southern Nevada and southwest California, it is cogenetic with small MVT Ag-Pb-Zn deposits in rocks as young as Early Mississippian. Over Paleozoic time, the Great Basin was at equatorial paleolatitudes with episodes of arid paleoclimates. Several occurrences of HZD are crosscut by Mesozoic or Cenozoic intrusions, and some host younger pluton-related polymetallic replacement and Carlin-type gold deposits. The distribution of HZD in space (carbonate platform, margin, and slope) and stratigraphy (Late Neoproterozoic Ediacaran–Mississippian) roughly parallels that of dolostone and both are prevalent in Devonian strata. Stratabound HZD is best developed in Ediacaran and Cambrian units, whereas discordant HZD is proximal to high-angle structures at the carbonate platform margin, such as strike-slip and growth faults and dilational jogs. Fabric-selective replacement and dissolution features (e.g., collapse breccias, voids with geopetal textures) are common, with remaining void space lined with light-colored dolomite crystals that exhibit zoning under cathodoluminescence. Zoned crystals usually contain tiny (<1–3 μm) fluid inclusions with vapor bubbles, requiring Th > ∼70 °C. The oxygen isotopic compositions of HZD are consistent with formation temperatures of 50–150 °C requiring brine circulation to depths of 2–5 km, or more. The few HZD occurrences with the highest concentrations of metals (especially Fe, Mn, and Zn) and the largest isotopic shifts are closely associated with Sedex or MVT deposits known to have formed from hotter brines (e.g., Th > 150–250 °C). These relationships permit that HZD formed at about the same time as dolostone, from brines produced by the evaporation of seawater during arid paleoclimates at equatorial paleolatitudes. Both dolostone and HZD may have formed as basinal brines, which migrated seaward from evaporative pans on the platform, with dolostone forming at low temperatures along shallow migration pathways through permeable limestones, and HZD forming at high temperatures along deeper migration pathways through basal aquifers and dilatant high-angle faults. The small MVT deposits were chemical traps where hot brines encountered rocks or fluids containing reduced sulfur. The abundant Sedex deposits mark sites where hot brine discharged at the seafloor in adjacent basins. Thus the distribution of HZD may map deep migration pathways and upflow zones between eastern shallow marine facies, where evaporative brine could have been generated, and western Sedex deposits, where heated brines discharged along faults into platform margin, slope, and basin facies. The small size and scarcity of Pb-Zn deposits and the abundance of barite deposits in the Great Basin suggests the brines were generally reduced, possibly due to reactions with carbonaceous rocks along deep migration pathways. While this scenario may have occurred at several times, the age and abundance of Sedex deposits suggest that such a hydrology was best developed in the Late Ordovician, Late Devonian, and Early Mississippian, possibly in response to episodes of extension and forebulge faults associated with the Antler orogeny. The improved understanding of HZD may aid future exploration for ore deposits in the Great Basin.

Nevada↗
USGS1995

Ground Water Atlas of the United States: Segment 2, Arizona, Colorado, New Mexico, Utah

This chapter of the Ground Water Atlas of the United States describes the aquifers in Arizona, Colorado, New Mexico, and Utah. These four States, which comprise Segment 2 of this Atlas, are located in the Southwestern United States and extend from the rolling grasslands of the Great Plains on the east across the Rocky Mountains and Continental Divide to the desert basins of the Southwest. The 425,000-square-mile area ranges in altitude from about 14,400 feet above sea level in the Rocky Mountains of Colorado to about 100 feet near the lower Colorado River in southwestern Arizona. All the ground water in Segment 2 ultimately is derived from infiltration of precipitation, which varies considerably with the altitude and topography of the area. The Great Plains Physiographic Province of the Central United States extends into eastern Colorado and New Mexico (fig. 1), where flat to rolling prairie (fig. 2) with scattered hills and bluffs gradually rises westward to 5,000 to 7,000 feet above sea level and abruptly gives way to the frontal ranges of the Rocky Mountains in the Southern Rocky Mountain and Basin and Range Physiographic Provinces. West of the frontal ranges in Colorado and northern New Mexico are additional and higher mountain ranges generally oriented north-south but with many spurs and extensions oriented in other directions. The many ranges of the Rocky Mountains are separated by valleys and high mountain parks (fig. 3). Colorado contains about three-fourths of the Nation's land area above 10,000 feet and has 53 mountain peaks higher than 14,000 feet. Most of these high peaks are located near the Continental Divide (fig. 1), which extends approximately north-south through central Colorado and western New Mexico. The altitude of the divide decreases in southern New Mexico to less than 4,500 feet in a few areas. Farther westward, the mountains are less prevalent and are interspersed with broad structural basins. These basins and the broad valleys of the middle Colorado River and its tributaries form the irregular intermontane topography of the Colorado Plateaus Physiographic Province (fig. 4). Plateaus and high mesas are formed where the surface has been dissected by rugged canyons carved by the Colorado River and its tributaries (fig. 5). The largest of these canyons-the Grand Canyon-extends about 220 miles southwestward from the mouth of the Little Colorado River in Arizona and ranges from 4 to 18 miles in width and from 2,700 to 5,700 feet in depth below the rim. Small mountain ranges and intervening broad desert valleys of the Basin and Range Physiographic Province are prevalent to the west and south of the Colorado Plateaus in western Utah, southern Arizona, and southern New Mexico (fig. 1). These mountain ranges generally protrude 3,000 to 6,000 feet above the surrounding valley floor (fig. 6) and commonly extend from 20 to 50 miles in a north or northwesterly direction. Small parts of the Middle Rocky Mountains and Wyoming Basin Physiographic Provinces extend into northwestern Colorado and northeastern Utah (fig. 1). The topography, geology, and hydrology of the two areas are described in Chapter 1 of this Atlas. Four of the Nation's major river systems have headwaters in the mountainous areas of Segment 2. The South Platte River of the Missouri River system drains the eastern slope of northern Colorado; the Arkansas River and its tributary, the Canadian River, drain southeastern Colorado and northeastern New Mexico; the Rio Grande and its tributary, the Pecos River, drain south-central Colorado and central New Mexico; and the Colorado River and its tributaries drain Arizona, eastern Utah, Northwestern New Mexico, and western Colorado (fig. 1). Western Utah is drained by numerous streams that terminate in local desert basins, the Great Salt Lake, or other local lakes and reservoirs. Because the Great Salt Lake lies in the Great Basin, which is the largest closed basin in North America, it has no outlet to the sea. The salinity of the lake water is about 20 percent or about 6 times the salinity of seawater. Most of Segment 2 is sparsely populated. The average population density of counties is less than 8 persons per square mile in about 65 percent of the four-State area (fig. 7). Population densities range from less than 0.5 person per square mile in a few rural counties to more than 4 ,000 persons per square mile in populous urban areas. The 1990 population of the four States was about 10 million; almost 70 percent of this population was in Arizona and Colorado. Most land in Segment 2 is undeveloped forest grassland, or desert shrubland, much of which is used for livestock grazing. Land used for production of commercial crops primarily is in eastern Colorado and eastern New Mexico.

Arizona, Colorado, New Mexico, Utah↗
USGS2003

Vulnerability of ground water to contamination, northern Bexar County, Texas

The Trinity aquifer, composed of Lower Cretaceous carbonate rocks, largely controls the ground-water hydrology in the study area of northern Bexar County, Texas. Discharge from the Trinity aquifer recharges the downgradient, hydraulically connected Edwards aquifer one of the most permeable and productive aquifers in the Nation and the sole source of water for more than a million people in south-central Texas. The unconfined, karstic outcrop of the Edwards aquifer makes it particularly vulnerable to contamination resulting from urbanization that is spreading rapidly northward across an "environmentally sensitive" recharge zone of the Edwards aquifer and its upgradient "catchment area," composed mostly of the less permeable Trinity aquifer. A better understanding of the Trinity aquifer is needed to evaluate water-management decisions affecting the quality of water in both the Trinity and Edwards aquifers. A study was made, therefore, in cooperation with the San Antonio Water System to assess northern Bexar County's vulnerability to ground-water contamination. The vulnerability of ground water to contamination in this area varies with the effects of five categories of natural features (hydrogeologic units, faults, caves and (or) sinkholes, slopes, and soils) that occur on the outcrop and in the shallow subcrop of the Glen Rose Limestone. Where faults affect the rates of recharge or discharge or the patterns of ground-water flow in the Glen Rose Limestone, they likewise affect the risk of water-quality degradation. Caves and sinkholes generally increase the vulnerability of ground water to contamination, especially where their occurrences are concentrated. The slope of land surface can affect the vulnerability of ground water by controlling where and how long a potential contaminant remains on the surface. Disregarding the exception of steep slopes which are assumed to have no soil cover the greater the slope, the less the risk of ground-water contamination. Because most soils in the study area are uniformly thin, they have only minimal effect on the vulnerability of ground water to contamination. The results of hydrogeologic mapping during the present study divide the outcrop of the Glen Rose Limestone into five mappable intervals, labeled (youngest to oldest) A through E. Of these intervals, only the middle (C) and the lowermost (E) generally provide appreciable permeability. The vulnerability assessment provided herein was determined by combining the presumed effects of selected natural features (with individual vulnerability ratings ranging from 0 through 35) using a grid-based, multilayer system of digital datasets and geographic information system analysis. The resulting vulnerability map comprises composite vulnerability ratings that range from 26 through 104. The relatively less vulnerable areas those containing no faults, sinkholes, or caves occupy about 92 percent of the study area. The most vulnerable areas are those containing both a fault and one or more caves. The distribution of the most vulnerable areas which trend from southwest to northeast, roughly parallel to the Balcones fault zone occur mainly where faults intersect caves.

Texas↗