Abstract:
This data set was created for a project to develop data sets to support ground-water vulnerability analysis. The objective was to create and document a digital geospatial data set from a published report or map, or existing digital geospatial data set that could be used in ground-water vulnerability analysis.
This data set consists of digitized polygons of a constant hydraulic conductivity value ... for the Antlers aquifer in southeastern Oklahoma. The Early Cretaceous-age Antlers Sandstone is an important source of water in an area that underlies about 4,400-square miles of all or part of Atoka, Bryan, Carter, Choctaw, Johnston, Love, Marshall, McCurtain, and Pushmataha Counties. The Antlers aquifer consists of sand, clay, conglomerate, and limestone in the outcrop area. The upper part of the Antlers aquifer consists of beds of sand, poorly cemented sandstone, sandy shale, silt, and clay. The Antlers aquifer is unconfined where it outcrops in about an 1,800-square-mile area.
The hydraulic conductivity polygons were developed from the hydraulic conductivity value used as input into a ground-water flow model and from published digital data sets of the surficial geology of the Antlers Sandstone except in areas overlain by alluvial and terrace deposits near streams. Some of the lines were interpolated where the Antlers aquifer is overlain by alluvial and terrace deposits. The interpolated lines are very similar to the aquifer boundaries shown on maps published in a ground-water modeling report for the Antlers aquifer. The constant hydraulic conductivity value used as input to the ground-water flow model was estimated as 5.74 feet per day.
Ground-water flow models are numerical representations that simplify and aggregate natural systems. Models are not unique; different combinations of aquifer characteristics may produce similar results. Therefore, values of hydraulic conductivity used in the model and presented in this data set are not precise, but are within a reasonable range when compared to independently collected data.
Use Constraints
This data set was derived from scanned maps published at a scale of 1:250,000 (Cederstrand, 1996a and 1996b), and represent the hydraulic conductivity value reported in Morton (1992). Hydraulic conductivity polygons represented at this scale are indicative of broad, regional trends and should not be interpreted as site specific. Ground-water flow ... models are numerical representations that simplify and aggregate natural systems. Models are not unique; different combinations of aquifer characteristics may produce similar results. The hydraulic conductivity and recharge are closely interrelated. As long as these two model inputs are in balance the model has a small mean residual; it represents the natural system numerically. If the hydraulic conductivity is accurately known, the model can be used to accurately determine recharge. Likewise, if the hydraulic conductivity is poorly known, then the recharge will be poorly determined. Therefore, values of hydraulic conductivity used in the model and presented in this data set are not precise, but are within a reasonable range when compared to independently collected data. In most aquifers, hydraulic conductivity measurements made in wells or in cores will range over several orders of magnitude, even over short horizontal and vertical distances. Hydraulic conductivity values derived from ground-water flow models represent areal generalizations and do not reflect the large local variance in well or core measurements.
Cederstrand, J.R., 1996a, Digital geologic map of the Ardmore-Sherman quadrangles, south-central Oklahoma: U.S. Geological Survey Open-File Report 96-370, based on a scale of 1:250,000, 3 diskettes. (Available in nonproprietary and ARC/INFO formats.) URL: <http://wwwok.cr.usgs.gov/gis/geology/index.html>
Cederstrand, J.R., 1996b, Digital geologic map of McAlester-Texarkana quadrangles, southeastern Oklahoma: U.S. Geological Survey Open-File Report 96-377, based on a scale of 1:250,000, 3 diskettes. (Available in nonproprietary and ARC/INFO formats.) URL: <http://wwwok.cr.usgs.gov/gis/geology/index.html>
Morton, R.B., 1992, Simulation of ground-water flow in the Antlers aquifer in southeastern Oklahoma and northeastern Texas: U.S. Geological Survey Water-Resources Investigations Report 88-4208, 22 p.
