Georgia Water Science Center

USGS Open-File Report 96-492


This report is available online in pdf format (2.7 MB): USGS OFR 96-492 (Opens the PDF file in a new window. )

Melinda J. Chapman and Michael F. Peck

U.S. Geological Survey Open-File Report 96-492, 48 pages (Published 1997)


Drought conditions in the 1980’s focused attention on the multiple uses of the surface- and ground-water resources in the Apalachicola-Chattahoochee-Flint (ACF) and Alabama-Coosa-Tallapoosa (ACT) River basins in Georgia, Alabama, and Florida. State and Federal agencies also have proposed projects that would require additional water resources and revise operating practices within the river basins. The existing and proposed water projects create conflicting demands for water by the States and emphasize the problem of water-resource allocation. This study was initiated to describe ground-water availability in the middle Chattahoochee River in Georgia and Alabama, and upper Flint River in Georgia, Subarea 2 of the ACF and ACT River basins, and to estimate the possible effects of increased ground-water use within the basin.

Subarea 2 encompasses about 4,100 square miles (mi2), which includes about 2,250 mi2 of the Chattahoochee River basin and 1,850 mi2 of the Flint River basin in the Piedmont physiographic province of west-central Georgia and eastern Alabama. Subarea 2 includes about 26 percent of the total 8,740 square-mile area of the Chattahoochee River basin and about 22 percent of the total 8,460 square-mile area of the Flint River basin. The study area is under-lain by a two-component aquifer system composed of a fractured, crystalline-rock aquifer characterized by little or no primary porosity or permeability; and the overlying weathered regolith (saprolite), which generally behaves as a porous-media aquifer. In some areas, a transition zone lies between the regolith and unweathered crystalline bedrock.

The conceptual model described for this study qualitatively subdivides the ground-water flow system into local (shallow), intermediate, and regional (deep) flow regimes. Ground-water discharge to tributaries mainly is from local and intermediate flow regimes and varies seasonally. The regional flow regime probably represents steady-state conditions and discharges chiefly to major drains such as the Chattahoochee and Flint Rivers. Ground-water discharge to major drains originates from all flow regimes. Mean-annual ground-water discharge to streams (baseflow) is considered to represent the long-term, average recharge to ground water. The mean-annual baseflow was estimated using an automated hydrograph-separation method, and represents discharge from the local, intermediate, and regional flow regimes of the ground-water flow system. Mean-annual baseflow exiting Subarea 2 was estimated to be 5,800 cubic feet per second. Mean-annual baseflow represented about 68 percent of total mean-annual stream discharge in the Chattahoochee River basin and 49 percent in the Flint River basin at the Subarea 2–Subarea 3 boundary.

Stream discharge for selected sites on the Chattahoochee River and its tributaries were compiled for the years 1941, 1954, and 1986, during which sustained severe droughts occurred throughout most of the ACF-ACT area. Stream discharge was assumed to be sustained entirely by baseflow during the latter periods of these droughts. Estimated baseflow (unregulated) near the end of the individual drought years averaged about 13 percent of the estimated mean-annual baseflow in the Chattahoochee River basin and 8.7 percent in the Flint River basin in Subarea 2.

The potential exists for the development of ground-water resources on a regional scale throughout Subarea 2. Estimated ground-water use in 1990 was about 1.2 percent of the estimated mean-annual baseflow in Georgia and 1.7 percent in Alabama; and 11.4 and 14.5 percent of the average drought flow in Georgia and Alabama, respectively. Because ground-water use in Subarea 2 represents a relatively minor percentage of ground-water recharge, even a large increase in ground-water use in Subarea 2 in one State is likely to have little effect on ground-water and surface-water occurrence in the other. Indications of long-term ground-water level declines were not observed; however, the number and distribution of observation wells for which long-term water-level measurements are available in Subarea 2 are insufficient to draw conclusions.




Purpose and scope

Physical setting of study area



Ground-water use

Previous investigations

Well and surface-water station numbering systems

Approach and methods of study

Mean-annual baseflow analysis

Drought-flow analysis


Conceptual model of ground-water flow and stream-aquifer relations

Hydrologic setting

Ground-water system



Ground-water levels

Regolith wells

Bedrock wells

Surface-water system

Ground-water discharge to streams

Mean-annual baseflow

Drought flow for 1941, 1954, and 1986

Ground-water utilization and general development potential

Ground-water exploration-program example


Suggestions for further study

Selected references



This report is available online in pdf format (2.7 MB): USGS OFR 96-492 (Opens the PDF file in a new window. )
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