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At least 793 records · Page 44Linked to original sources
USGS2002

Hydrology and water quality of Geneva Lake, Walworth County, Wisconsin

As part of continuing efforts to improve the water quality of Geneva Lake, a collaborative effort between the U.S. Geological Survey, the Wisconsin Department of Natural Resources, and the Geneva Lake Environmental Agency was initiated in 1997 to document the present quality of the lake and its sediments, compute detailed hydrologic and nutrient (primarily phosphorus) budgets for the lake, estimate how changes in nutrient loading may affect water quality, and describe changes in the lake over the past 170 years by comparing water quality measured in this study with historical measurements and sediment-core information. This report presents the results of this collaborative study. Measurements collected during this study (1997.2000) indicate that the trophic status of the lake ranges from mesotrophic to oligotrophic: the mean Secchi depth was 4.8 m (meters), mean surface phosphorus concentration was 9 ?g/L (micrograms per liter), mean surface nitrogen concentration was 550 ?g/L, and mean surface chlorophyll a concentration was 3 ?g/L. Surface nitrogen: phosphorus ratios indicated that, if just these nutrients are considered, phosphorus should be the limiting nutrient. Phosphorus budgets constructed for water years 1998 and 1999 indicate that recent annual phosphorus loads were about 2,000 kg (kilograms) less than that estimated in 1975 (total annual input was about 3,200 kg in 1998 and about 8,500 kg in 1999). The major source of phosphorus to the lake was from its tributaries, which contributed about 84 percent of the total load. The primary difference from the phosphorus load estimates for 1975 was the decrease in loading from the Fontana sewage-treatment plant. Direct measurements and indirect measurements based on sediment-core analyses indicate that the water quality of Geneva Lake has degraded in the last 170 years, the greatest effects resulting from urbanization. Sedimentation rates were highest between 1900 to 1930, and phosphorus concentrations were highest between the 1930s to early 1980s. As a result of the recent reduction in phosphorus loading, in-lake near-surface phosphorus concentrations decreased from 20.25 ?g/L to about 10.15 ?g/L and are similar to those estimated for the lake in the early 1900s. Concentrations of other chemical constituents associated with urban areas, however, have continually increased, especially in Williams Bay and Geneva Bay.

Wisconsin↗
USGS1995

Ground-water-level monitoring, basin boundaries, and potentiometric surfaces of the aquifer system at Edwards Air Force Base, California, 1992

A ground-water-level monitoring program was implemented at Edwards Air Force Base, California, from January through December 1992 to monitor spatial and temporal changes in poten-tiometric surfaces that largely are affected by ground-water pumping. Potentiometric-surface maps are needed to determine the correlation between declining ground- water levels and the distribution of land subsidence. The monitoring program focused on areas of the base where pumping has occurred, especially near Rogers Lake, and involved three phases of data collection: (1) well canvassing and selection, (2) geodetic surveys, and (3) monthly ground-water-level measurements. Construction and historical water- level data were compiled for 118 wells and pi-ezometers on or near the base, and monthly ground-water-level measurements were made in 82 wells and piezometers on the base. The compiled water-level data were used in conjunction with previously collected geologic data to identify three types of no-flow boundaries in the aquifer system: structural boundaries, a principal-aquifer boundary, and ground-water divides. Heads were computed from ground-water-level measurements and land-surface altitudes and then were used to map seasonal potentiometric surfaces for the principal and deep aquifers underlying the base. Pumping has created a regional depression in the potentiometric surface of the deep aquifer in the South Track, South Base, and Branch Park well-field area. A 15-foot decline in the potentiometric surface from April to September 1992 and 20- to 30-foot drawdowns in the three production wells in the South Track well field caused locally unconfined conditions in the deep aquifer.

California↗
USGS2001

Map and map database of susceptibility to slope failure by sliding and earthflow in the Oakland area, California

Map data that predict the varying likelihood of landsliding can help public agencies make informed decisions on land use and zoning. This map, prepared in a geographic information system from a statistical model, estimates the relative likelihood of local slopes to fail by two processes common to an area of diverse geology, terrain, and land use centered on metropolitan Oakland. The model combines the following spatial data: (1) 120 bedrock and surficial geologic-map units, (2) ground slope calculated from a 30-m digital elevation model, (3) an inventory of 6,714 old landslide deposits (not distinguished by age or type of movement and excluding debris flows), and (4) the locations of 1,192 post-1970 landslides that damaged the built environment. The resulting index of likelihood, or susceptibility, plotted as a 1:50,000-scale map, is computed as a continuous variable over a large area (872 km2) at a comparatively fine (30 m) resolution. This new model complements landslide inventories by estimating susceptibility between existing landslide deposits, and improves upon prior susceptibility maps by quantifying the degree of susceptibility within those deposits. Susceptibility is defined for each geologic-map unit as the spatial frequency (areal percentage) of terrain occupied by old landslide deposits, adjusted locally by steepness of the topography. Susceptibility of terrain between the old landslide deposits is read directly from a slope histogram for each geologic-map unit, as the percentage (0.00 to 0.90) of 30-m cells in each one-degree slope interval that coincides with the deposits. Susceptibility within landslide deposits (0.00 to 1.33) is this same percentage raised by a multiplier (1.33) derived from the comparative frequency of recent failures within and outside the old deposits. Positive results from two evaluations of the model encourage its extension to the 10-county San Francisco Bay region and elsewhere. A similar map could be prepared for any area where the three basic constituents, a geologic map, a landslide inventory, and a slope map, are available in digital form. Added predictive power of the new susceptibility model may reside in attributes that remain to be explored?among them seismic shaking, distance to nearest road, and terrain elevation, aspect, relief, and curvature.

Miscellaneous Field Studies Map↗
USGS1976

Effects of local geological conditions in the San Francisco Bay region on ground motions and the intensities of the 1906 earthquake

Measurements of ground motion generated by nuclear explosions in Nevada have been completed for 99 locations in the San Francisco Bay region, California. The recordings show marked amplitude variations in the frequency band 0.25 to 3.0 Hz that are consistently related to the local geological conditions of the recording site. The average spectral amplifications observed for vertical and horizontal ground motions are, respectively: (1, 1) for granite, (1.5, 1.6) for the Franciscan Formation, (3.0, 2.7) for the Santa Clara Formation, (3.3, 4.4) for alluvium, and (3.7, 11.3) for bay mud. Spectral amplification curves define predominant ground frequencies in the band 0.25 to 3.0 E for bay mud sites and for some alluvial sites. Amplitude spectra computed from recordings of seismic background noise at 50 sites do not generally define predominant ground frequencies. The intensities ascribed to various sites in the San Francisco Bay region for the California earthquake of April 18, 1906, are strongly dependent on distance from the zone of surface faulting and the geological character of the ground. Considering only those sites (approximately one square city block in size) for which there is good evidence for the degree of ascribed intensity, the intensities for 917 sites on Franciscan rocks generally decrease with the logarithm of distance as Intensity = 2.69 - 1.90 log (Distance in kilometers). (1) For sites on other geological units, intensity increments, derived from this empirical relation, correlate strongly with the Average Horizontal Spectral Amplifications (AHSA) according to the empirical relation Intensity Increment = 0.27 + 2.70 log (AHSA). (2) Average intensity increments predicted for the various geological units are −0.3 for granite, 0.2 for the Franciscan Formation, 0.6 for the Great Valley sequence, 0.8 for the Santa Clara Formation, 1.3 for alluvium, and 2.4 for bay mud. The maximum intensity map predicted on the basis of these data delineates areas in the San Francisco Bay region of potentially high intensity for large earthquakes on either the San Andreas fault or the Hayward fault. The map provides a crude form of seismic zonation for the region and may be useful for certain general types of land-use zonation.

California↗
USGS2015

Flood-inundation Maps for the Deerfield River, Franklin County, Massachusetts, from the Confluence with the Cold River Tributary to the Connecticut River

The U.S. Geological Survey developed flood elevations in cooperation with the Federal Emergency Management Agency for a 30-mile reach of the Deerfield River from the confluence of the Cold River tributary to the Connecticut River in the towns of Charlemont, Buckland, Shelburne, Conway, Deerfield, and Greenfield in Franklin County, Massachusetts to assist land owners, and emergency management workers prepare for and recover from floods. Peak flows with 50-, 20-, 10-, 4-, 2-, 1-, 0.5-, and 0.2-percent annual exceedance probabilities were computed for the reach from updated flood-frequency analyses. These peak flows were routed through a one-dimensional step-backwater hydraulic model to obtain the corresponding peak water-surface elevations and to place the tropical storm Irene flood of August 28, 2011 into historical context. The hydraulic model was calibrated by using current [2015] stage-discharge relations at two U.S. Geological Survey streamgages in the study reach—Deerfield River at Charlemont, MA (01168500) and Deerfield River near West Deerfield, MA (01170000)—and from documented high-water marks from the tropical storm Irene flood, which had between a 1- and 0.2-percent AEP. The hydraulic model was used to compute water-surface profiles for flood stages referenced to the two streamgages. Two sets of flood-inundation map libraries were created from the modeled profiles. The library for the upstream, western portion of the modeled reach is 9.1 miles long, extends from just downstream of the confluence of the Deerfield River with the Cold River to just upstream of the confluence with Clesson Brook, and is calibrated to the Deerfield River at Charlemont, MA streamgage. The library for the downstream, eastern portion of the modeled reach is 8.9 miles long, extends from just downstream of the confluence of the Deerfield River with the South River to just upstream of the confluence with the Green River, and is calibrated to the Deerfield River near West Deerfield streamgage. Stages for mapped profiles of the upstream reach range from 8.7 feet (ft) at the local datum (525.6 ft when converted to the North American Vertical Datum of 1988 [NAVD 88]) to 25.7 ft (542.6 ft at NAVD 88) at the Charlemont streamgage, and stages for mapped profiles of the downstream reach range from 8.5 ft (165.2 ft at NAVD 88) to 29.0 ft (185.7 ft at NAVD 88) at the West Deerfield streamgage. The simulated water-surface profiles were combined with a geographic information system digital elevation model derived from 0.5-ft vertical accuracy light detection and ranging (lidar) data to create the two sets of flood-inundation maps. The availability of the flood-inundation maps at http://water.usgs.gov/osw/flood_inundation/, combined with information regarding current (near real-time) stage from the two U.S. Geological Survey streamgages in the study reach, can provide emergency management personnel and residents with information to aid in flood response activities, such as evacuations and road closures, and with postflood recovery efforts. The flood-inundation maps are nonregulatory, but provide Federal, State, and local agencies and the public with estimates of the potential extent of flooding during selected peak-flow events.

Massachusetts↗
USGS2025

Spatiotemporal patterns in urban nutrient and suspended sediment loads and stream response to watershed management implementation

In recent years, local governments have invested heavily in management practices to reduce nutrient and sediment loads. These practices provide localities with nutrient and sediment regulatory reduction credits; however, their effects on water quality are poorly understood at the watershed scale. Long-term watershed-scale monitoring is essential for assessing progress toward water-quality goals, yet it has historically been lacking in urban watersheds. Since 2007, Fairfax County, Virginia, has partnered with the US Geological Survey to monitor and evaluate water-quality conditions in 20 small urban streams. This study assessed nutrient and suspended sediment loads, trends in concentration, and trends in load. Trends in load are affected by streamflow-induced variability that must be removed through a process called “flow-normalization;” however, existing methods have neither been applied to small urban watersheds nor to loads computed on a sub-daily timestep. In this study, four such methods also were assessed, and an adaptation of the weighted regressions on time, discharge, and season approach was found to be most effective. Loads, concentrations, and trends in load were spatially and temporally variable. Differences were attributed to physical watershed features such as geology, soils, and channel geomorphology, as well as urban sources such as turfgrass fertilization and septic infrastructure. Most notably, flow-normalized suspended sediment, nitrogen, and phosphorus loads decreased in two watersheds with completed stream restorations and increased in those with few implemented practices.

Virginia↗
USGS2016

Demonstration of the Cascadia G‐FAST geodetic earthquake early warning system for the Nisqually, Washington, earthquake

A prototype earthquake early warning (EEW) system is currently in development in the Pacific Northwest. We have taken a two‐stage approach to EEW: (1) detection and initial characterization using strong‐motion data with the Earthquake Alarm Systems (ElarmS) seismic early warning package and (2) the triggering of geodetic modeling modules using Global Navigation Satellite Systems data that help provide robust estimates of large‐magnitude earthquakes. In this article we demonstrate the performance of the latter, the Geodetic First Approximation of Size and Time (G‐FAST) geodetic early warning system, using simulated displacements for the 2001 M w 6.8 Nisqually earthquake. We test the timing and performance of the two G‐FAST source characterization modules, peak ground displacement scaling, and Centroid Moment Tensor‐driven finite‐fault‐slip modeling under ideal, latent, noisy, and incomplete data conditions. We show good agreement between source parameters computed by G‐FAST with previously published and postprocessed seismic and geodetic results for all test cases and modeling modules, and we discuss the challenges with integration into the U.S. Geological Survey’s ShakeAlert EEW system.

Washington↗
USGS1977

Photo-optical enhancement of landsat imagery for land use in south-central Iowa

Because the photographic laboratory at the Jet Propulsion Laboratory found it difficult to estimate what were the optimal color renditions of the Iowa landscape for land classification purposes, the Iowa Geological Survey developed its own capability for producing color products from digitally enhanced Landsat data. Research has now shown that efficient production of enhanced images requires full utilization of both computer and photographic enhancement . procedures. Experimental photo-optical enhancement techniques carried out at the EROS Data Center (EDC) for a Landsat-1, 29 August 1972 scene, proved to be more easily interpreted for land classification purposes than the EDC standard color composite. I.f digital processing can be minimized by using photographic enhancement techniques, then costs of enhanced products could be greatly reduced. Perhaps one of the major objectives of computer processing of Landsat data should be to produce high quality cosmetically enhanced (eliminate striping and line drops) data which has a range of digital values that can be completely recorded by film media. If digital processinq can distribute reflectance data throughout the entire recording ranqe of photographic film, then photographic enhancement techniques could be employed cheaply by users familiar with the type of information they wish to extract from the imaqery. Alternatively, if custom enhanced imagery is to be produced for users not having a photographic capability, different enhancements may be tried in an iterative fashion in the photographic laboratory, without having to reprocess digital data in the computer for each iteration. The savings in time and money should be considerable using this approach.

Iowa↗
USGS2007

Streamflow of 2006 -- Water Year Summary

The maps and graphs appearing in this summary describe streamflow conditions for water-year 2006 (October 1, 2005 to September 30, 2006) in the context of the 77-year period 1930-2006, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey's (USGS) National Streamflow Information Program. The period 1930-2006 was used because prior to 1930, the number of streamgages was too small to provide representative data for computing statistics for most regions of the country. In the summary, reference is made to the term 'runoff,' which is the depth to which a river basin, State, or other geographic area would be covered with water if all the streamflow within the area during a single year was uniformly distributed upon it. Runoff quantifies the magnitude of water flowing through the Nation's rivers and streams in measurement units that can be compared from one area to another. The runoff value for a geographic area is computed as the median runoff value for all streamgages in that geographic area. For example, the runoff value for a state is the median for all streamgages in that state, and the median for the Nation is the median value for all streamgages in the Nation. Each of the maps and graphs below can be expanded to a larger view by clicking on the image. In all the graphics, a rank of 1 indicates the highest flow of all years analyzed.

Fact Sheet↗
USGS2008

Streamflow of 2007--Water year summary

The maps and graphs appearing in this summary describe streamflow conditions for water-year 2007 (October 1, 2006 to September 30, 2007) in the context of the 78-year period 1930-2007, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey's (USGS) National Streamflow Information Program. The period 1930-2007 was used because prior to 1930, the number of streamgages was too small to provide representative data for computing statistics for most regions of the country. In the summary, reference is made to the term "runoff," which is the depth to which a river basin, State, or other geographic area would be covered with water if all the streamflow within the area during a single year was uniformly distributed upon it. Runoff quantifies the magnitude of water flowing through the Nation's rivers and streams in measurement units that can be compared from one area to another. The runoff value for a geographic area is computed as the median runoff value for all streamgages in that geographic area. For example, the runoff value for a State is the median for all streamgages in that State, and the median for the Nation is the median value for all streamgages in the Nation. Each of the maps and graphs below can be expanded to a larger view by clicking on the image. In all the graphics, a rank of 1 indicates the highest flow of all years analyzed.

Fact Sheet↗
USGS2009

Streamflow of 2008--Water year summary

The maps and graphs appearing in this summary describe streamflow conditions for water-year 2008 (October 1, 2007 to September 30, 2008) in the context of the 79-year period 1930-2008, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey's (USGS) National Streamflow Information Program. The period 1930-2008 was used because prior to 1930, the number of streamgages was too small to provide representative data for computing statistics for most regions of the country. In the summary, reference is made to the term "runoff," which is the depth to which a river basin, State, or other geographic area would be covered with water if all the streamflow within the area during a single year was uniformly distributed upon it. Runoff quantifies the magnitude of water flowing through the Nation's rivers and streams in measurement units that can be compared from one area to another. The runoff value for a geographic area is computed as the median runoff value for all streamgages in that geographic area. For example, the runoff value for a State is the median for all streamgages in that State, and the median for the Nation is the median value for all streamgages in the Nation. Each of the maps and graphs below can be expanded to a larger view by clicking on the image. In all the graphics, a rank of 1 indicates the highest flow of all years analyzed.

Fact Sheet↗
USGS2011

Streamflow of 2010--Water year summary

The maps and graph in this summary describe streamflow conditions for water-year 2010 (October 1, 2009 to September 30, 2010) in the context of the 81-year period 1930-2010, unless otherwise noted. The illustrations are based on observed data from the U.S. Geological Survey's (USGS) National Streamflow Information Program. The period 1930-2010 was used because prior to 1930, the number of streamgages was too small to provide representative data for computing statistics for most regions of the country. In the summary, reference is made to the term "runoff," which is the depth to which a river basin, State, or other geographic area would be covered with water if all the streamflow within the area during a single year was uniformly distributed upon it. Runoff quantifies the magnitude of water flowing through the Nation's rivers and streams in measurement units that can be compared from one area to another. Each of the maps and graphs below can be expanded to a larger view by clicking on the image. In all the graphics, a rank of 1 indicates the highest flow of all years analyzed.

Fact Sheet↗
USGS1977

GEOTHERM user guide

GEOTHERM is a computerized geothermal resources file developed by the U.S. Geological Survey. The file contains data on geothermal fields, wells, and chemical analyses from the United states and international sources. The General Information Processing System (GIPSY) in the IBM 370/155 computer is used to store and retrieve data. The GIPSY retrieval program contains simple commands which can be used to search the file, select a narrowly defined subset, sort the records, and output the data in a variety of forms. Eight commands are listed and explained so that the GEOTHERM file can be accessed directly by geologists. No programming experience is necessary to retrieve data from the file.

Open-File Report↗
USGS1989

Indexes of hydrologic data from selected coal-mining areas in northwestern Colorado

Currently (1988), data from hydrologic studies related to coal mining that have been done in northwestern Colorado since the early 1970 's are stored in the files of private companies and government offices and in various computer systems. To compile these data for additional research, a trip to each office would have to be made to determine the availability and acceptability of the data. The U.S. Geological Survey, in cooperation with the U.S. Bureau of Land Management and the Colorado Mined Land Reclamation Division, has created a database (COALDATA) that includes stream discharge, groundwater levels, and chemical analysis of water samples that were collected by private companies and government agencies other than the U.S. Geological Survey in and near selected coal mines in northwestern Colorado. Indexes in this report list 93 surface water sites and 95 groundwater sites where hydrologic data are available in the COALDATA data base. The indexes also list 62 surface water sites and 480 groundwater sites in the U.S. Geological Survey data base, which is separate from the COALDATA data base and contains only data collected by the U.S. Geological Survey. The combined output of the COALDATA data base and the U.S. Geological Survey data base provides surface water and groundwater data that include most of the study area. (USGS)

Open-File Report↗
USGS1986

Cluster analysis of phytoplankton data collected from the National Stream Quality Accounting Network in the Tennessee River basin, 1974-81

A computer program, Numerical Taxonomy System of Multivariate Statistical Programs (NTSYS), was used with interfacing software to perform cluster analyses of phytoplankton data stored in the biological files of the U.S. Geological Survey. The NTSYS software performs various types of statistical analyses and is capable of handling a large matrix of data. Cluster analyses were done on phytoplankton data collected from 1974 to 1981 at four national Stream Quality Accounting Network stations in the Tennessee River basin. Analysis of the changes in clusters of phytoplankton genera indicated possible changes in the water quality of the French Broad River near Knoxville, Tennessee. At this station, the most common diatom groups indicated a shift in dominant forms with some of the less common diatoms being replaced by green and blue-green algae. There was a reduction in genera variability between 1974-77 and 1979-81 sampling periods. Statistical analysis of chloride and dissolved solids confirmed that concentrations of these substances were smaller in 1974-77 than in 1979-81. At Pickwick Landing Dam, the furthest downstream station used in the study, there was an increase in the number of genera of ' rare ' organisms with time. The appearance of two groups of green and blue-green algae indicated that an increase in temperature or nutrient concentrations occurred from 1974 to 1981, but this could not be confirmed using available water quality data. Associations of genera forming the phytoplankton communities at three stations on the Tennessee River were found to be seasonal. Nodal analysis of combined data from all four stations used in the study did not identify any seasonal or temporal patterns during 1974-81. Cluster analysis using the NYSYS programs was effective in reducing the large phytoplankton data set to a manageable size and provided considerable insight into the structure of phytoplankton communities in the Tennessee River basin. Problems encountered using cluster analysis were the subjectivity introduced in the definition of meaningful clusters, and the lack of taxonomic identification to the species level. (Author 's abstract)

Tennessee↗
USGS1975

Estimates of temperature and precipitation for northeastern Utah

Estimates of temperature and precipitation were made for northeastern Utah from information that was collected at 67 locations. The variable-length records were converted to the common-time base of 1941-70; then general relations were developed to extend the converted point values to unsampled sites. Regression techniques were used to fill voids in the temperature-data base. Incomplete precipitation records were adjusted to the 1941-70 average on the assumption that the ratio of concurrent data is directly proportional to the ratio of the respective 1941-70 average annual values at nearby sites. Equations were then developed through a computer program to express the relationship of temperature and precipitation with altitude and location and to extend the information to unsampled sites. Two-thirds of the observed and estimated average annual temperature and precipitation values are within ±1.5°F (1.0°C) and 2.08 in (53 mm), respectively, of the calculated averages. Schematic diagrams, plotted by computer, were prepared to show variations of altitude, temperature, and precipitation; and maps, also plotted by computer, show lines of equal altitude, precipitation, and temperature.

Utah↗
USGS2000

A method for producing digital probabilistic seismic landslide hazard maps

The 1994 Northridge, California, earthquake is the first earthquake for which we have all of the data sets needed to conduct a rigorous regional analysis of seismic slope instability. These data sets include: (1) a comprehensive inventory of triggered landslides, (2) about 200 strong-motion records of the mainshock, (3) 1:24 000-scale geologic mapping of the region, (4) extensive data on engineering properties of geologic units, and (5) high-resolution digital elevation models of the topography. All of these data sets have been digitized and rasterized at 10 m grid spacing using ARC/INFO GIS software on a UNIX computer. Combining these data sets in a dynamic model based on Newmark's permanent-deformation (sliding-block) analysis yields estimates of coseismic landslide displacement in each grid cell from the Northridge earthquake. The modeled displacements are then compared with the digital inventory of landslides triggered by the Northridge earthquake to construct a probability curve relating predicted displacement to probability of failure. This probability function can be applied to predict and map the spatial variability in failure probability in any ground-shaking conditions of interest. We anticipate that this mapping procedure will be used to construct seismic landslide hazard maps that will assist in emergency preparedness planning and in making rational decisions regarding development and construction in areas susceptible to seismic slope failure. ?? 2000 Elsevier Science B.V. All rights reserved.

Engineering Geology↗
USGS2015

Dry season mean monthly flow and harmonic mean flow regression equations for selected ungaged basins in Arkansas

The U.S. Geological Survey, in cooperation with the Arkansas Department of Environmental Quality, Southwestern Energy, the Arkansas Natural Resources Commission, and the Arkansas Game and Fish Commission, developed regression equations for estimation of dry season mean monthly flows and harmonic mean flows that are representative of natural streamflow conditions at selected ungaged basins in Arkansas. Observed values of dry season mean monthly flow and harmonic mean flow computed from daily-mean flow data were used with basin characteristics to identify significant explanatory variables for multiple-linear-regression equations to estimate predicted values of dry season mean monthly flow and harmonic mean flow. Five dry season mean monthly flow regression equations and two harmonic mean flow regression equations were developed using dry season mean monthly flows and harmonic mean flows established for 91 and 93 U.S. Geological Survey continuous-record streamflow-gaging stations, respectively. The dry season in Arkansas is defined as the months of July through November for this study. For harmonic mean flow calculations and regression equations, the study area is composed of the Springfield-Salem Plateaus (Arkansas and Missouri), Boston Mountains, Arkansas Valley, Ouachita Mountains (Arkansas and Oklahoma), and West Gulf Coastal Plain (Arkansas) physiographic sections. All continuous-record streamflow-gaging stations used to compute dry season mean monthly flows were located within Arkansas. Equations for two regions were found to be statistically significant for developing regression equations for estimating harmonic mean flows at ungaged basins; thus, equations are applicable only to streams in those respective regions in Arkansas. Regression equations for dry season mean monthly flows are applicable only to streams located throughout Arkansas. All regression equations are applicable only to unaltered streams where flows were not significantly affected by regulation, diversion, or urbanization. The median number of years used for dry season mean monthly flow calculation was 43, and the median number of years used for harmonic mean flow calculations was 34 for region 1 and 43 for region 2.

Arkansas↗