Water-Resources Investigations Report 00-4084
This report is available online in pdf format (6 MB): USGS WRIR00-4084 (
)
John S. Clarke and Richard E. Krause
U.S. Geological Survey Water-Resources Investigations Report 00-4084, 92 pages (Published 2000)
Ground-water flow models of the Floridan aquifer
system in the coastal area of Georgia and adjacent parts of
South Carolina and Florida, were revised and updated to
ensure consistency among the various models used, and to
facilitate evaluation of the effects of pumping on the groundwater
level near areas of saltwater contamination. The
revised models, developed as part of regional and areal
assessments of ground-water resources in coastal Georgia,
are—the Regional Aquifer-System Analysis (RASA) model,
the Glynn County area (Glynn) model, and the Savannah
area (Savannah) model. Changes were made to hydraulicproperty
arrays of the RASA and Glynn models to ensure
consistency among all of the models; results of theses
changes are evidenced in revised water budgets and
calibration statistics.
Following revision, the three models were used to simulate 32 scenarios of hypothetical changes in pumpage that ranged from about 82 million gallons per day (Mgal/d) lower to about 438 Mgal/d higher, than the May 1985 pumping rate of 308 Mgal/d. The scenarios were developed by the Georgia Department of Natural Resources, Environmental Protection Division and the Chatham County-Savannah Metropolitan Planning Commission to evaluate water-management alternatives in coastal Georgia. Maps showing simulated ground-water-level decline and diagrams presenting changes in simulated flow rates are presented for each scenario.
Scenarios were grouped on the basis of pumping location—entire 24-county area, central subarea, Glynn- Wayne-Camden County subarea, and Savannah-Hilton Head Island subarea. For those scenarios that simulated decreased pumpage, the water level at both Brunswick and Hilton Head Island rose, decreasing the hydraulic gradient and reducing the potential for saltwater contamination. Conversely, in response to scenarios of increased pumpage, the water level at both locations declined, increasing the hydraulic gradient and increasing the potential for saltwater contamination. Pumpage effects on ground-water levels and related saltwater contamination at Brunswick and Hilton Head Island generally diminish with increased distance from these areas.
Additional development of the Upper Floridan aquifer may be possible in parts of the coastal area without affecting saltwater contamination at Brunswick or Hilton Head Island, due to the presence of two hydrologic boundaries—the Gulf Trough, separating the northern and central subareas; and the hypothesized “Satilla Line,” separating the central and southern subareas. These boundaries diminish pumpage effects across them; and may enable greater ground-water withdrawal in areas north of the Gulf Trough and south of the “Satilla Line” without producing appreciable drawdown at Brunswick or Hilton Head Island.
Abstract
Introduction
Purpose and scope
Description of study area
Hydrogeologic setting
Ground-water flow
Acknowledgments
Design and revision of ground-water flow models
Regional Aquifer-System Analysis (RASA) model
Subregional models
Telescoping model approach
Model revisions
Changes to model input data
Effects on simulated water levels and water budget
Simulation of ground-water management scenarios
Scenarios for the 24-county area
Scenarios for the central subarea
Scenarios for the Glynn-Wayne-Camden County area
Scenarios for the Savannah-Hilton Head Island area
Potential for ground-water development
Limitations of model application
Summary
Selected references
Appendix A—Difference in observed and simulated water levels for the upper floridan aquifer (model layer A2), May 1985, for the revised Regional Aquifer-System (RASA) model
Appendix B—Difference in observed and simulated water levels for the upper Floridan aquifer (model layer A2), May 1985, for revised Glynn County model
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