Geology topics

Aaron L. Pugh

Publications and source records attributed to Aaron L. Pugh.

At least 19 recordsLinked to original sources

USGS2025

Regional hydraulic geometry characteristics of stream channels in the Boston Mountains in Arkansas

Many stream-channel infrastructure, habitat enhancement, and restoration projects are undertaken on streams throughout Arkansas by Federal, State, and local agencies as well as by private organizations and businesses with limited data on local geomorphology and streamflow conditions. Equations that relate drainage area above stable stream reaches to the basin characteristics, bankfull streamflow, and the associated channel dimensions can be used to estimate stream conditions. These equations, along with streambed material particle information, provide information that can be used to improve stream-channel projects. The U.S. Geological Survey, in cooperation with the U.S. Army Corps of Engineers, Little Rock District, completed a study to develop these equations for streams in the Boston Mountains in Arkansas. Fourteen U.S. Geological Survey streamgages and stream reaches located in the Boston Mountains were selected for analysis. Geomorphic parameters of streams, including the mean bankfull channel dimensions (cross-sectional area, top width, mean depth, and streamflow), and the contributing drainage areas were investigated. Streambed materials were collected at eight of these sites to develop descriptive statistics of the streambed particle-size distributions and percentages of substrate type. Stream reaches at each study site were classified to Rosgen level II stream type based on the averages of stream-channel metrics collected from site cross sections and profiles. Of the 14 selected Boston Mountain stream reaches, 7 were classified as B-type streams, and 7 were classified as C-type streams. For these streams, the significant differences in measured parameters between stream types were that the B-type streams had greater depth, hydraulic radii, and bar D50 and D85 particle sizes, while C-type streams had greater watershed slopes. Streambed material particle size decreased with mean drainage basin elevation and decreased with increasing entrenchment ratios. Bar sediment size exhibited decreasing size with increasing sinuosity. Regional hydraulic geometry curves were constructed for the streams in the Boston Mountains by plotting measured bankfull geometry dimensions from stable reaches and the associated bankfull streamflow against the contributing drainage area.

Arkansas, Oklahoma↗

USGS2025

Hydraulic conductivity and transmissivity estimates from slug tests in wells within the Mississippi Alluvial Plain, Arkansas and Mississippi, 2020

During the spring and summer of 2020, the U.S. Geological Survey conducted single-well slug tests on selected observation wells within the Mississippi Alluvial Plain in Arkansas and Mississippi to estimate hydraulic conductivity and transmissivity values for the Mississippi River Valley alluvial and middle Claiborne aquifers. Well and aquifer data were collected from field measurements, well-construction reports, and published aquifer-thickness information. A total of 324 slug-in and slug-out tests were conducted on 48 wells by using mechanical slugs to displace the water column and submersible pressure transducers to record changes in water levels in the wells. Hydraulic conductivity of the aquifers in which the wells are screened was estimated by curve fitting the water-level-change data using aquifer test analysis software. Estimates of aquifer transmissivity were made by multiplying the estimated hydraulic conductivity value by the aquifer thickness at well locations. Mean hydraulic conductivity estimates for 44 observation wells screened in the Mississippi River Valley alluvial aquifer range from 3 to 401 feet per day, and mean transmissivity estimates range from 285 to 80,559 feet squared per day. Mean hydraulic conductivity estimates for four observation wells screened in units of the middle Claiborne aquifer range from 0.14 to 183 feet per day, and mean transmissivity estimates range from 55 to 67,913 feet squared per day. The results from these tests can be used to improve the understanding of water availability and groundwater migration, to refine groundwater models, and to ultimately provide stakeholders and decisionmakers better information for management of the groundwater resources within the Mississippi Alluvial Plain.

Arkansas, Mississippi↗

USGS2021

Effects of culvert construction on streams and macroinvertebrate communities at selected sites in the East Gulf Coastal Plain of Alabama, 2010–19

The U.S. Geological Survey, in cooperation with the Alabama Department of Transportation, evaluated the role of culvert construction in altering streams and habitats of benthic macroinvertebrate communities at selected study sites in the northern East Gulf Coastal Plain of Alabama during 2011–19. Analysis included examinations of changes in stream channel geometry, suspended sediment, turbidity, and benthic macroinvertebrate communities. Topographic surveys of stream channel cross sections, upstream and downstream of the culvert, were conducted before and after construction. Changes in channel geometry (cross-sectional area, top width, mean depth, and thalweg slope) were assessed by using paired sample t-tests to compare before- and after-construction channel geometry measurements. Statistically significant changes in stream channel geometry between the before- and after-construction measurements were observed at four of the six study sites. Analysis of the channel geometry data indicates that 1 site had no measured changes, and thalweg reach slopes were inverted at 4 of the 12 study reaches—2 measured in before-construction reaches and 2 measured in after-construction reaches. Surface-water samples were collected during selected storm events for suspended sediment and turbidity analyses. Samples were simultaneously collected upstream and downstream of the culvert construction reaches during all three phases of construction (before, during, and after). Analysis focused on the parity of upstream to downstream simultaneous samples. The mean upstream to downstream paired ratios of sediment concentrations and turbidity from the after-construction phase indicate that colloidal and noncolloidal sediments were passing through the construction reaches at two of the six sites, noncolloidal sediments were being trapped in the construction reaches at two sites, and colloidal and noncolloidal sediments were being removed from the construction reach at two sites. Benthic macroinvertebrates were collected and identified at five of the six sites from instream habitats that were available in sampled areas both upstream and downstream of the culvert construction reaches. Differences between upstream and downstream reaches and the Wilcoxon rank sum statistic were used to examine changes in metrics of benthic macroinvertebrate communities between before- and after-construction phases. Benthic macroinvertebrate sampling results did not indicate that culvert construction caused impairment to communities at study sites. No tolerance metrics suggested a major change in the pollution tolerance of the communities. The same upstream to downstream patterns in abundance-weighted tolerance values were observed in the before- and after-construction periods at each site. At one site, the difference between upstream and downstream richness-based tolerance values increased, but the after-construction upstream and downstream richness-based tolerance values were lower (indicating a less pollution-tolerant macroinvertebrate community) than in the before-construction period.

Alabama↗

USGS2019

Regional hydraulic geometry characteristics of stream channels in the Ouachita Mountains of Arkansas

Many stream channel infrastructure, habitat, and restoration projects are being undertaken on small streams throughout Arkansas by various Federal, State, and local agencies and by private organizations and businesses with limited data on local geomorphology and streamflow relations. Equations are needed that relate drainage area above stable stream reaches and the associated basin characteristics to bankfull streamflow and the associated channel dimensions. These equations, along with streambed material particle information, provide information that can improve stream channel projects. The U.S. Geological Survey and the Arkansas Natural Resources Commission in cooperation with the U.S. Army Corps of Engineers, Little Rock District, undertook a study to develop these equations for streams in the Ouachita Mountains of Arkansas. Seventeen streamgages operated by the U.S. Geological Survey, located on streams in the Ouachita Mountains, were selected for analysis. Regional hydraulic geometry curves that express the mathematical relation between the bankfull channel dimensions (cross-sectional area, top width, mean depth, and streamflow) and the contributing drainage areas were developed. Streambed material measurements were collected to develop descriptive statistics of the streambed particle-size distributions and percentages of substrate type at each study site. Stream reaches at each study site were classified to the Rosgen level II stream type based on the average of stream channel metrics collected from site cross sections and profiles. Of the 17 selected Ouachita Mountain stream reaches, 6 were classified as B stream types, and 11 were classified as C stream types. The B stream types have infrequently spaced pools; very stable plan forms, profiles, and banks; and narrow, gently sloping valleys, where bank vegetation is a moderate component of stability. The C stream types are meandering, point bar, riffle-pool channels associated with broad valleys having well-defined flood plains and terraces composed of alluvial soils, where bank vegetation is typically a high component of stability.

Arkansas↗

USGS2015

Estimated water use in Arkansas, 2010

The Arkansas Natural Resources Commission (ANRC) conducts an annual inventory of reported groundwater and surface-water withdrawals in Arkansas in cooperation with the U.S. Geological Survey (USGS). This report describes withdrawals from groundwater and surface-water resources in Arkansas for 2010. The report compiles withdrawals by county for 10 categories of water use—public supply, domestic (self-supplied), commercial (self-supplied), industrial (self-supplied), mining, livestock, aquaculture, irrigation, duck (hunting) clubs, and thermoelectric power generation. Water-use trends in Arkansas from 1965 to 2010 and sources of groundwater withdrawals also are described. During 2010, total withdrawals from groundwater and surface-water sources in Arkansas were 11,300 million gallons per day (Mgal/d). Of the total withdrawn, about 69 percent (7,790 Mgal/d) was from groundwater. Public-supply systems served about 94 percent of Arkansas’ population. Public-supply total withdrawals were 429 Mgal/d, with about 69 percent from surface-water sources. The statewide average of per capita residential use from public-supply systems was about 155 gallons per day (gal/d). The domestic (self-supplied) water use was 12.8 Mgal/d. Total commercial (self-supplied) water use was 11.7 Mgal/d. Total industrial (self-supplied) water use was 276 Mgal/d. Total mining water use was 44.3 Mgal/d. Total livestock water use was 39.0 Mgal/d. Total aquaculture water use was 268 Mgal/d. Irrigation water use totaled 8,720 Mgal/d. Total duck (hunting) club water use was 216 Mgal/d. Total thermoelectric power water use was 1,540 Mgal/d. The three water-use categories with the largest withdrawals and their effects on total water use were examined. Total water use in Arkansas has increased about 428 percent between 1965 and 2010. Total groundwater use increased about 533 percent and total surface-water use increased about 289 percent. Since about 2000, total water use in Arkansas has plateaued, peaking in 2005. The plateauing of total water use is the result of decreasing surface-water use in the irrigation, thermoelectric power, and public-supply categories offsetting the continuing increases in groundwater use in the irrigation category. An examination of total water use and irrigation water-use changes over time demonstrates the increasing dominance of groundwater withdrawals for irrigation on Arkansas’ total water use. Total irrigation water use in Arkansas between 1965 and 2010 has increased about 652 percent. Withdrawals for thermoelectric power water use in Arkansas have continuously accounted for about half of the State’s total surface-water use for the period 1965–2010. Thermoelectric power water use in Arkansas between 1965 and 2010 increased 264 percent. The percent of Arkansas’ population served by public water suppliers has continued to increase while the percentage of the State’s total water use withdrawn by public water suppliers has remained relatively constant. Public-supply water use in Arkansas between 1965 and 2010 increased about 238 percent. Regardless of continuing increases in population, since about 2000, total public-supply water use in Arkansas has plateaued at about 425 Mgal/d. Groundwater withdrawals comprised about 69 percent of the total amount of water used in Arkansas in 2010. Four aquifers in Arkansas account for more than 99 percent of the total groundwater withdrawals. The aquifers in deposits of Quaternary age supplied about 97 percent of all groundwater withdrawals. The Sparta-Memphis aquifer supplied about 2.5 percent of all groundwater withdrawals, the Wilcox aquifer supplied about 0.5 percent of all groundwater withdrawals, and the Paleozoic aquifer supplied about 0.3 percent of all groundwater withdrawals.

Arkansas↗

USGS2014

Arkansas StreamStats: A U.S. Geological Survey web map application for basin characteristics and streamflow statistics

The U.S. Geological Survey (USGS) provides streamflow and other related information needed by water-resource managers responsible for protecting people and property from floods, planning and managing water-resource activities, and protecting water quality. Streamflow statistics provided by the USGS, such as the 1-percent annual exceedance probability (100-year flood) and the 7-day 10-year low flow, are frequently used by engineers, flood forecasters, land managers, biologists, and others to guide their everyday decisions. Additionally, resource managers often need to know basin characteristics, the physical and climatic characteristics of a drainage basin, to help understand the mechanisms that control water availability, water quality, and aquatic habitats at various locations. Users of streamflow information often require streamflow statistics and basin characteristics at various locations along a stream. The USGS periodically calculates and publishes streamflow statistics and basin characteristics for streamflowgaging stations and partial-record stations, but these data commonly are scattered among many reports that may or may not be readily available to the public. The USGS also provides and periodically updates regional analyses of streamflow statistics that include regression equations and other prediction methods for estimating statistics for ungaged and unregulated streams across the State. Use of these regional predictions for a stream can be complex and often requires the user to determine a number of basin characteristics that may require interpretation. Basin characteristics may include drainage area, classifiers for physical properties, climatic characteristics, and other inputs. Obtaining these input values for gaged and ungaged locations traditionally has been time consuming, subjective, and can lead to inconsistent results.

Arkansas↗

USGS2014

Arkansas Groundwater-Quality Network

Arkansas is the fourth largest user of groundwater in the United States, where groundwater accounts for two-thirds of the total water use. Groundwater use in the State increased by 510 percent between 1965 and 2005 (Holland, 2007). The Arkansas Groundwater-Quality Network is a Web map interface ( http://ar.water.usgs.gov/wqx ) that provides rapid access to the U.S. Geological Survey’s (USGS) National Water Information System (NWIS) and the U.S. Environmental Protection Agency’s (USEPA) STOrage and RETrieval (STORET) databases of ambient water information. The interface enables users to perform simple graphical analysis and download selected water-quality data.

Arkansas↗

USGS2014

Mean annual, seasonal, and monthly precipitation and runoff in Arkansas, 1951-2011

This report describes long-term annual, seasonal, and monthly means for precipitation and runoff in Arkansas for the period from 1951 through 2011. Precipitation means were estimated using data from the Parameter-elevation Regressions on Independent Slopes Model database; while total runoff, groundwater runoff, and surface runoff means were estimated using data from 123 active and inactive U.S. Geological Survey continuous-record streamflow-gaging stations located in Arkansas and surrounding States. Annual precipitation in Arkansas for the period from 1951 through 2011 had a mean of 49.8 inches. Of the six physiographic sections in Arkansas, the Ouachita Mountains had the largest mean annual precipitation at 53.0 inches, while the Springfield-Salem plateaus had the smallest mean annual precipitation at 45.5 inches. The mean annual total runoff for Arkansas was 17.8 inches. The Ouachita Mountains had the largest mean annual total runoff at 20.4 inches, while the Springfield-Salem plateaus had the smallest mean annual total runoff at 15.0 inches. Runoff is diminished during the dry season, which is attributed to increased losses from evapotranspiration, consumptive uses including irrigation, and increased withdrawals for public and private water supplies. The decline in runoff during the dry season is observed across the State in all physiographic sections. Spatial results for precipitation and runoff are presented in a series of maps that are available for download from the publication Web page in georeferenced raster formats.

Arkansas↗

USGS2014

Potentiometric surface of the Ozark aquifer in northern Arkansas, 2010

The Ozark aquifer in northern Arkansas is composed of dolomite, limestone, sandstone, and shale of Late Cambrian to Middle Devonian age and ranges in thickness from approximately 1,100 feet to more than 4,000 feet. Hydrologically, the aquifer is complex, characterized by discrete and discontinuous flow components with large variations in permeability. The potentiometric-surface map, based on 56 well and 5 spring water-level measurements made in 2010 in Arkansas and Missouri, has a maximum water-level altitude measurement of 1,174 feet in Carroll County and a minimum water-level altitude measurement of 120 feet in Randolph County. Regionally, the flow within the aquifer is to the south and southeast in the eastern and central part of the study area and to the west, northwest, and north in the western part of the study area. Water-level altitudes changed 0.5 feet or less in 31 out of 56 wells measured between 2007 and 2010. Despite rapidly increasing population within the study area, the increase appears to have minimal effect on groundwater levels, although the effect may have been minimized by the development and use of surface-water distribution infrastructure, suggesting that most of the incoming populations are fulfilling their water needs from surface-water sources. The conversion of some users from groundwater to surface water may be allowing water levels in some wells to recover (rise) or decline at a slower rate in some areas such as in Benton, Carroll, and Washington Counties.

Arkansas↗

USGS2010

Potentiometric Surfaces and Water-Level Trends in the Cockfield (Upper Claiborne) and Wilcox (Lower Wilcox) Aquifers of Southern and Northeastern Arkansas, 2009

Eocene-age sand beds near the base of the Cockfield Formation of Claiborne Group constitute the aquifer known locally as the Cockfield aquifer. Upper-Paleocene age sand beds within the lower parts of the Wilcox Group constitute the aquifer known locally as the Wilcox aquifer. In 2005, reported water withdrawals from the Cockfield aquifer in Arkansas totaled 16.1 million gallons per day, while reported water withdrawals from the Wilcox aquifer in Arkansas totaled 27.0 million gallons per day. Major withdrawals from these units were for industrial and public water supplies with lesser but locally important withdrawals for commercial, domestic, and agricultural uses. During February 2009, 56 water-level measurements were made in wells completed in the Cockfield aquifer and 57 water-level measurements were made in wells completed in the Wilcox aquifer. The results from the 2009 water-level measurements are presented in potentiometric-surface maps and in combination with previous water-level measurements. Trends in water-level change over time within the two aquifers are investigated using water-level difference maps and well hydrographs. Water-level difference maps were constructed for each aquifer using the difference between depth to water measurements made in 2003 to 2009. Well hydrographs for each aquifer were constructed for wells with 20 or more years of historical water-level data. The hydrographs were evaluated individually using linear regression to calculate the annual rise or decline in water levels, and by aggregating the regression results by county and statistically summarizing for the range, mean, and median water-level change in each county. The 2009 potentiometric surface of the Cockfield aquifer map indicates the regional direction of groundwater flow generally towards the east and southeast, except in two areas of intense groundwater withdrawals that have developed into cones of depression. The lowest water-level altitude measured was 43 feet and the highest water-level altitude measured was 351 feet. A water-level difference map was constructed from 54 wells completed in the Cockfield aquifer within Arkansas. The largest rise in water level was 14.9 feet and the largest decline was 27.4 feet. Seven wells had a rise in water level, and the remaining 47 wells had a decline in water level. Hydrographs for 33 wells completed in the Cockfield aquifer were developed. Hydrographs indicate water-level changes in individual wells ranged from rises of 0.33 feet per year to declines of 1.21 feet per year over the 20-year period (1990-2009). County summaries of the linear regression analysis indicate Cleveland and Columbia Counties have mean annual rises. Arkansas, Ashley, Bradley, Calhoun, Chicot, Desha, Drew, Lincoln, and Union Counties have mean annual declines. The potentiometric surface for the Wilcox aquifer is presented using two maps, one for a southern area and another for a northeastern area, because of the absence of water-level data in the central part of the State. The direction of groundwater flow in the southern area is generally the east, except around two cones of depression and around two mounds of elevated water levels. Water-level altitudes in the southern area range from 147 feet to 400 feet. The direction of groundwater flow in the northeastern area is generally to the south and southeast except in an area of intense groundwater withdrawals that has altered the flow to a westerly direction. Two water-level difference maps were constructed using water-level altitudes measured in 2003 to 2009 from 53 wells completed in the Wilcox aquifer within southern and northeastern Arkansas. In the southern area the largest rise in water level was 16.0 feet and the largest decline was 17.7 feet. Eight wells in the southern area had rising water levels and the remaining five wells had declining water levels. In the northeastern area, the largest rise in water level was 1.3 feet and the larg

Scientific Investigations Report↗

USGS2009

Hydrogeologic characteristics and water levels of Wilcox aquifer in southwestern and northeastern Arkansas

The Wilcox Group of Eocene and Paleocene age is located throughout most of southern and eastern Arkansas. The Wilcox Group in southern Arkansas is undifferentiated, while in northeastern Arkansas, the Wilcox Group is subdivided into three units: Flour Island, Fort Pillow Sand, and Old Breastworks Formation. The Wilcox Group crops out in southwestern Arkansas in discontinuous, 1 to 3 mi wide bands. In northeastern Arkansas, the Wilcox Group crops out along a narrow, discontinuous, band along the western edge of Crowleys Ridge. The Wilcox aquifer provides sources of groundwater in southwestern and northeastern Arkansas. In 2005, reported withdrawals from the Wilcox aquifer in Arkansas totaled 27.0 million gallons per day, most of which came from the northeastern area. Major withdrawals from the aquifer were for public supplies with lesser but locally important withdrawals for commercial, domestic, and industrial uses. A study was conducted by the U.S. Geological Survey in cooperation with the Arkansas Natural Resources Commission and the Arkansas Geological Survey to determine the water levels associated with the Wilcox aquifer in southwestern and northeastern Arkansas. During February 2009, 58 water-level measurements were made in wells completed in the Wilcox aquifer. The results from this study and previous studies are presented as potentiometric-surface maps, water-level difference maps, and long-term hydrographs. The direction of groundwater flow in the southwestern area is affected by two potentiometric-surface mounds, one in the north and the other in the southwest, and a cone of depression in the center. The direction of water flowing off of the northern mound of water is generally to the south and east with some to the north. The direction of water flowing off of the southwestern mound is generally to the south and east. The direction of water flowing into the cone of depression is generally from the north, west, and south. The direction of groundwater flow in the northeastern area is generally to the south and southeast, except in the northwestern part of the area where the flow is in a westerly direction towards Paragould. Large groundwater withdrawals have altered the natural direction of flow near centers of pumping at Paragould and West Memphis. Water-level difference maps for the Wilcox aquifer in Arkansas were constructed using the differences between water-level measurements made during 2003 and 2009 from 52 wells. The difference in water levels between 2003 and 2009 in the southwestern area ranged from -36.4 to 16.0 ft. Water levels rose in the northern parts of the southwestern area, while the water levels in the southern part of the area declined with the exception of one well. The differences in water levels between 2003 and 2009 in the northeastern area ranged from -21.7 to 1.3 ft. Water levels declined throughout the northeastern area with the exception of two wells. Hydrographs from 42 wells with a minimum of 20 yr of water-level measurements were constructed. Trend lines using linear regression were calculated for the period from 1990 to 2009 to determine the slope in ft/yr for water levels in each well. In the southwestern area, the county mean annual water level rose 0.15 ft/yr in Hot Spring County. County mean annual water levels declined between 0.71 ft/yr and 0.03 ft/yr in Clark, Hempstead, and Nevada counties. In the northeastern area, the county mean annual water level rose 0.46 ft/yr in Greene County. County mean annual water levels declined between 0.03 ft/yr and 2.12 ft/yr in Clay, Craighead, Crittenden, Lee, Mississippi, Poinsett, and St. Francis counties.

Arkansas↗

USGS2008

Geomorphic characterization of the Middle Fork Saline River: Garland, Perry, and Saline Counties, Arkansas

This report was prepared to help address concerns raised by local residents, State, and Federal agencies about the current geomorphic conditions of the Middle Fork Saline River. Over the past 30 years the Middle Fork Saline River Basin has experienced a marked increase in urbanization. The report summarizes the Middle Fork?s current (2003) channel characteristics at nine stream reaches in the upper 91 square miles of the basin. Assessments at each study reach included comparing measured stream geometry dimensions (cross-sectional area, top width, and mean depth) at bankfull stage to regional hydraulic geometry curves for the Ouachita Mountains Physiographic Province of Arkansas and Oklahoma, evaluations of streambed materials and sinuosity, and classification of individual stream reach types. When compared to the Ouachita Mountains? regional hydraulic geometry curves for natural, stable, stream reaches, five of the nine study reaches had slightly smaller crosssectional areas, longer top widths, and shallower depths. Streambed material analysis indicates that the Middle Fork is a bedrock influenced, gravel dominated stream with lesser amounts of sand and cobbles. Slight increases in sinuosity from 1992 to 2002 at seven of the nine study reaches indicate a slight decrease in stream channel slope. Analyses of the Middle Fork?s hydraulic geometry and sinuosity indicate that the Middle Fork is currently overly wide and shallow, but is slowly adjusting towards a deeper, narrower hydraulic geometry. Using the Rosgen system of channel classification, the two upstream study reaches classified as B4c/1 stream types; which were moderately entrenched, riffle dominated channels, with infrequently spaced pools. The downstream seven study reaches classified as C4/1 stream types; which were slightly entrenched, meandering, gravel-dominated, riffle/ pool channels with well developed flood plains. Analyses of stream reach types suggest that the downstream reaches of the Middle Fork are more vulnerable to streambank failure than the upstream reaches of the stream.

Arkansas↗

USGS2008

Potentiometric Surface of the Ozark Aquifer in Northern Arkansas, 2007

The Ozark aquifer in northern Arkansas is composed of dolomite, limestone, sandstone, and shale of Late Cambrian to Middle Devonian age, and ranges in thickness from approximately 1,100 feet to more than 4,000 feet. Hydrologically, the aquifer is complex, characterized by discrete and discontinuous flow components with large variations in permeability. The potentiometric-surface map, based on 58 well and 5 spring water-level measurements collected in 2007 in Arkansas and Missouri, has a maximum water-level altitude measurement of 1,169 feet in Carroll County and a minimum water-level altitude measurement of 118 feet in Randolph County. Regionally, the flow within the aquifer is to the south and southeast in the eastern and central part of the study area and to the west, northwest, and north in the western part of the study area. Comparing the 2007 potentiometric-surface map with a predevelopment potentiometric-surface map indicates general agreement between the two surfaces except in the northwestern part of the study area. Potentiometric-surface differences can be attributed to withdrawals related to increasing population, changes in public-supply sources, processes or water withdrawals outside the study area, or differences in data-collection or map-construction methods. The rapidly increasing population within the study area appears to have some effect on ground-water levels. Although, the effect appears to have been minimized by the development and use of surface-water distribution infrastructure, suggesting most of the incoming populations are fulfilling their water needs from surface-water sources. The conversion of some users from ground water to surface water may be allowing water levels in wells to recover (rise) or decline at a slower rate, such as in Benton, Carroll, and Washington Counties.

Scientific Investigations Report↗

USGS2008

Summary of aquifer test data for Arkansas – 1940-2006

As demands on Arkansas's ground water continue to increase, decision-makers need all available information to ensure the sustainability of this important natural resource. From 1940 through 2006, the U.S. Geological Survey has conducted over 300 aquifer tests in Arkansas. Much of these data never have been published. This report presents the results from 206 of these aquifer tests from 21 different hydrogeologic units spread across 51 Arkansas counties. Ten of the hydrogeologic units are within the Atlantic Plain of Arkansas and consist mostly of unconsolidated and semi-consolidated deposits. The remaining 11 units are within the Interior Highlands consisting mainly of consolidated rock. Descriptive statistics are reported for each hydrologic unit with two or more tests, including the mean, minimum, median, maximum and standard deviation values for specific capacity, transmissivity, hydraulic conductivity, and storage coefficient. Hydraulic conductivity values for the major water-bearing hydrogeologic units are estimated because few conductivity values are recorded in the original records. Nearly all estimated hydraulic conductivity values agree with published hydraulic conductivity values based on the hydrogeologic unit material types. Similarly, because few specific capacity values were available in the original aquifer test records, specific capacity values are estimated for individual wells.

Arkansas↗

USGS1998

Potentiometric surface of the Ozark Aquifer in northern Arkansas, 1995

The Ozark aquifer in northern Arkansas is comprised of dolostones, limestones, sandstones, and shales of Late Cambrian to Middle Devonian age, and ranges in thickness from approximately 1,100 feet to more than 4,000 feet. Hydrologically, the aquifer is complex, characterized by discrete and diffuse flow components with large spatial variations in porosity and permeability. Regionally, the flow within the aquifer is to the south and southeast in the eastern and central part of the study area and to the northwest and north in the western part of the study area. Within Arkansas, the potentiometric-surface map based on October- December 1995 data indicates maximum water-level altitudes of greater than 1,300 feet in Boone, Carroll, and Madison Counties and minimum water-level altitudes of less than 400 feet in Independence, Izard, Lawrence, Randolph, Sharp, and Stone Counties. Comparing the 1995 potentiometric-surface map with a predevelopment potentiometric- surface map (Imes, 199), indicates general agreement between the two surfaces except in parts of Benton and Sharp Counties. Water-level differences could be attributed to differences in the time of year in which the water-level data were collected, differences in pumping conditions just prior to water-level measurement, differences in interpretation resulting (in part) from greater number of water-level measurements used for this report than for Imes (1990), or erroneous water-level data.

Water-Resources Investigations Report↗

USGS1998

Altitude of the top of the Sparta Sand and Memphis Sand in three areas of Arkansas

The Sparta Sand and Memphis Sand form the second most productive aquifer in Arkansas. The Sparta Sand and Memphis Sand range in thick- ness from 0 to 900 feet, consisting of fine- to medium-grained sands interbedded with layers of silt, clay, shale, and minor amounts of lignite. Within the three areas of interest, the top surface of the Sparta Sand and Memphis Sand dips regionally east and southeast towards the axis of the Mississippi Embayment syncline and Desha Basin. Local variations in the top surface may be attributed to a combination of continued development of structural features, differential compaction, localized faulting, and erosion of the surface prior to subsequent inundation and deposition of younger sediments.

Water-Resources Investigations Report↗

USGS1998

Status of water levels and selected water-quality conditions in the Mississippi River Valley alluvial aquifer in eastern Arkansas, 1994-96

During the spring of 1994 and 1996, water levels were measured in more than 600 wells completed in the Mississippi River Valley alluvial aquifer in eastern Arkansas. Water samples were collected during the summer of 1995 from about 375 wells completed in the alluvial aquifer and measured for specific conductance. Concentrations of dissolved chloride were analyzed in 314 of the samples, and concentrations of dissolved calcium, magnesium, and sodium were analyzed in 18 of the samples. The regional direction of ground-water flow is generally to the south and east except where affected by ground-water withdrawals. A large depression in the potentiometric surface is located in Arkansas, Lonoke, and Prairie Counties. The comparison of water-level altitudes from 1994 to 1996 reveals that water levels declined and the cone of depression became larger. The water-level altitudes did not decline in every well monitored from 1994 to 1996; however, most water-level altitudes declined during this period and cones of depression became deeper. Shallower depressions are located in Poinsett, Lee, St. Francis, and Woodruff Counties. Potentiometric depressions in this aquifer generally are a result of long-term pumping and probably are affected by variations in aquifer characteristics such as thickness and hydraulic conductivity. Long-term water levels typically declined an average rate of about 1.2 feet per year in the areas of potentiometric depression. Specific conductance ranged from 81 microsiemens per centimeter at 25 degrees Celsius in Drew County to 4,640 microsiemens per centimeter at 25 degrees Celsius in Chicot County. The lowest ground-water specific-conductance values generally occur along the western border of the study area. Several areas exhibited increased specific conductance with the most prominent areas centered in Chicot, Desha, and northern Arkansas County.

Water-Resources Investigations Report↗

USGS1998

Riparian-vegetation controls on the spatial pattern of stream-channel instability, Little Piney Creek, Missouri

The role of riparian vegetation is assessed quantitatively by using a five-decade record of valley bottom vegetation and channel dynamics developed from historical aerial photography. A 12-kilometer reach of a typical Ozarks stream was mapped using aerial photographs from 1938, 1948, 1955, 1965, 1976, and 1989; maps were then analyzed in a digital geographic information system. Analysis of sequential pairs of maps provides transition frequencies for assessing the relative areal rates at which riparian woodland, grassland, and cropland have been eroded or subjected to gravel aggradation. Results indicate that cropland and grassland have been no more likely to erode than woodland; cropland and grassland are slightly more susceptible to gravel deposition than woodland. These findings underscore the potential for complex responses of streams to a cumulative history of riparian and drainage-basin disturbances.

Water Supply Paper↗