Design, Revision, and Application of Ground-Water Flow Models for Simulation of Selected Water-Management Scenarios in the Coastal Area of Georgia and Adjacent Parts of South Carolina and Florida

U.S. Geological Survey Water-Resources Investigations Report 00-4084, 93 pages

ABSTRACT

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 ground-water 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 hydraulic-property 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.

TABLE OF CONTENTS

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 81

Appendix B--Difference in observed and simulated water levels for the upper Floridan aquifer (model layer A2), May 1985, for revised Glynn County model 89

The full report is available in pdf format: Water-Resources Investigations Report 00-4084 (5.5 MB)
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