By Carol J. Becker, Donna Runkle, and Alan Rea
U.S. Geological Survey Open-File Report 96-452
Prepared in cooperation with the
State of Oklahoma, Office of the Secretary of Environment
Oklahoma City, Oklahoma
The data sets in this report include digitized aquifer boundaries and maps of hydraulic conductivity, recharge, and ground-water level elevation contours for the Tillman terrace and alluvial aquifer in southwestern Oklahoma. The ground-water flow model of the Tillman terrace and alluvial aquifer in a thesis by Al-Sumait (1978) encompasses the unconsolidated terrace deposits and alluvium associated with the North Fork of the Red River and the Red River in the western half of Tillman County. These sediments consist of discontinuous layers of clay, sandy clay, sand, and gravel (Al-Sumait, 1978). The aquifer extends over an area of 285 square miles and is used for irrigation and domestic purposes. Granite and the Hennessey Formation outcrop in northern parts of the aquifer where alluvial deposits are absent. These outcrops were modeled by Al-Sumait (1978) as part of the aquifer.
Most of the aquifer boundaries and some of the lines in the hydraulic conductivity and recharge data set were extracted from a digital surficial geology data set titled, "Digital geologic map of Lawton quadrangle, southwestern Oklahoma," by Cederstrand (1996) that is based on a scale of 1:250,000. The aquifer boundaries are shown in the thesis, "A computer ground-water model for the Tillman alluvium in Tillman County, Oklahoma," by Al-Sumait (1978, fig. 2, p. 11). Most of the lines in the hydraulic conductivity, recharge, and 1969 water-level elevation contour data set were digitized from a paper map published at a scale of 1:249,695 in the thesis by Al-Sumait (1978, fig. 4).
The hydraulic conductivity value for the aquifer is 92.5 feet per day and the recharge rate is 2.87 inches per year and are reported in the thesis by Al-Sumait (1978). The recharge rate and aquifer boundary maps also are published in the ground-water modeling report, "Results of computer modeling of alluvium and terrace deposts in western Tillman County and along the Washita River, southwestern Oklahoma, for water supply capability," by Kent and Naney (1978).
Ground-water flow models are numerical representations that simplify and aggregate natural systems. Models are not unique; different combinations of aquifer characteristics may produce similar results. The hydraulic conductivity and recharge are closely interrelated. As long as these two model inputs are in balance the model has a small mean residual; it represents the natural system numerically. If the hydraulic conductivity is accurately known, the model can be used to accurately determine recharge. Likewise, if the hydraulic conductivity is poorly known, then the recharge will be poorly determined. Therefore, values of hydraulic conductivity and recharge used in the model and presented in this data set are not precise, but are within a reasonable range when compared to independently collected data.
In most aquifers, hydraulic conductivity measurements made in wells or in cores will range over several orders of magnitude, even over short horizontal and vertical distances. Hydraulic conductivity values derived from ground-water flow models represent areal generalizations and do not reflect the large local variance in well or core measurements. Recharge probably varies considerably over the local area, and model recharge is at best an average over an area at least as large as the model grid (and probably much larger than a single cell).
Compilation of the data sets was funded under a cooperative Joint Funding Agreement between the U.S. Geological Survey and the State of Oklahoma, Office of the Secretary of Environment.
These data sets were created for a project to develop data sets to support ground-water vulnerability analysis. The objective was to create and document digital geospatial data sets from published reports or maps, or existing digital geospatial data sets that could be used in ground-water vulnerability analysis.
The data sets provided in this report are available in nonproprietary and ARC/INFO export file formats. (See NOTES section.) Files, except those with ".GIF" or ".GZ" extensions, are ASCII format files.
The data sets stored in the generic, public-domain Digital Line Graph (DLG-3) Version 3, Optional format have file extensions of ".DLG". Designed for data interchange, the DLG-3 format allows the simple creation of a vector polygon or line data structure. The topological linkages are explicitly encoded for node, area, and line elements. The files are composed of 8-bit ASCII characters organized into fixed logical records of 80 bytes. A detailed description of the DLG-3 Optional format may be found in the data users guide 3, Digital Line Graphs from 1:2,000,000-scale maps (U.S. Geological Survey, 1990).
The ARC/INFO export files are ASCII files that utilize a proprietary format. The "NONE" compression option was used with the ARC/INFO EXPORT command. The ARC/INFO export files have file extensions of ".E00".
The data set files have ".GZ" extensions and were compressed for distribution. These files need to be uncompressed to access the digital data. The GUNZIP utility is an MS-DOS executable program that will uncompress the data files. To uncompress a file, type at the MS-DOS prompt:
GUNZIP -aN AQBOUND.GZ
This command will uncompress the file and restore its original name. For example: "AQBOUND.DLG" or "AQBOUND.E00".
A documentation file (known as metadata) is provided for each data set. The documentation files comply with the Federal Geographic Data Committee (FGDC) Content Standards for Digital Geospatial Metadata (Federal Geographic Data Committee, 1994). The FGDC-compliant metadata files contain detailed descriptions of the data sets, and include narrative sections that describe the procedures used to produce the data sets in digital form.
A graphic image also is provided in a Graphics Interchange Format (GIF) file. GIF files are easily displayed on a variety of computer systems that use readily available display software including Internet browser software. This image provides a simplified view of the data sets, and may be used for browsing purposes. The GIF file portrays significantly less spatial resolution and information content than the actual data sets.
No software is provided with these data sets. Users will need GIS software to use the data sets. The U.S. Geological Survey does not recommend or endorse any particular software package for use with these data sets. For some links to more information on GIS software and capabilities, see: The GIS FAQ (Frequently Asked Questions), GIS Companies on the WWW, USGS GIS Information.
The Albers Equal Area map projection (Snyder, 1987) was chosen for the data sets. This projection is appropriate for maps of the conterminous United States because of the visual presentation and equal-area characteristics, which facilitates areal analysis. The projection is cast on the North American Datum of 1983. This projection slightly distorts shapes and distances (scale) in order to maintain equal-area properties. Scale is true along the standard parallels, which are to the north and south of Oklahoma. Scale distortion in Oklahoma reaches a maximum of slightly less than one percent at the northern border of the state. The following table provides map projection information.
|First standard parallel||29 30 00 North|
|Second standard parallel||45 30 00 North|
|Central meridian||96 00 00 West|
|Latitude of projection origin||23 00 00 North|
|Coordinate system parameters:|
|Planimetric units of measure ||meters|
Use of trade names is for descriptive purposes only, and does not imply endorsement by the U.S. Government.
ARC/INFO software was used in the development of the data sets. The data sets were processed using the ARC/INFO Revision 7.0.3 software package, running on a Data General AViiON workstation. Further processing was done using ARC/INFO Revisions 7.0.4 and 7.1.1 on a SUN Enterpise 4000 running Solaris Version 2.5.1. File names in this document are enclosed in quotation marks and type set in upper case.
Al-Sumait, A.J., 1978, A computer ground-water model for the Tillman alluvium in Tillman County, Oklahoma: Stillwater, OK, Oklahoma State University, master's thesis, 152 p., 48 figs.
Cederstrand, J.R., 1996, Digital geologic map of Lawton quadrangle, southwestern Oklahoma: U.S. Geological Survey Open-File Report 96-376, based on a scale of 1:250,000, 3 diskettes. (Available in nonproprietary and ARC/INFO formats.)
Federal Geographic Data Committee, 1994, Content standards for digital geospatial metadata (June 8): Federal Geographic Data Committee, Washington, D.C., 78 p.
Kent, D.C., and Naney, J.W., 1978, Results of computer modeling of alluvium and terrace deposits in western Tillman County and along the Washita River, southwestern Oklahoma, for water supply capability: Stillwater, OK, Final Report submitted to the Oklahoma Water Resources Board, administrative report by Oklahoma State University and Scientific and Education Administration: 52 p., 35 figs.
Snyder, J.P., 1987, Map projections--A working manual: U.S. Geological Survey Professional Paper 1395, 383 p.
U.S. Geological Survey, 1990, Digital line graphs from 1:2,000,000-scale maps, data users guide 3: U.S. Geological Survey National Mapping Program Technical Instruction, 70 p.