U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1403-H Hydrogeology and Simulated Effects of Ground-Water Development of the Floridan Aquifer System, Southwest Georgia, Northwest Florida, and Southernmost Alabama By Morris L. Maslia, and Larry R. Hayes REGIONAL AQUIFER-SYSTEM ANALYSIS U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1403- H UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1988 DEPARTMENT OF THE INTERIOR DONALD PAUL MODEL, Secretary U.S. GEOLOGICAL SURVEY Dallas L. Peck, Director Library of Congress Cataloging in Publication Data Maslia, Morris L. Hydrogeology and simulated effects of ground-water development of the Floridan aquifer system, southwest Georgia, northwest Florida, and southernmost Alabama. (Regional aquifer-system analysis) (Geological Survey Professional Paper; 1403-H) Bibliography: p. Supt. of Docs. No.: I 19.16:1403-H 1. Aquifers Georgia. 2. Aquifers Florida. 3. Aquifers Alabama. 4. Groundwater flow Data processing. 5. Groundwater flow Mathematical models. I. Hayes, Larry R. II. Title. III. Series. IV. Series: Geological Survey Professional Paper ; 1403-H. GB1199.3.G4M37 1985 553.7'9'0975 85-600067 For sale by the Books and Open-File Reports Section, U.S. Geological Survey, Federal Center, Box 25425, Denver, CO 80225 FOREWORD THE REGIONAL AQUIFER-SYSTEM ANALYSIS PROGRAM The Regional Aquifer-System Analysis (RASA) Program was started in 1978 following a congressional mandate to develop quantitative appraisals of the major ground-water systems of the United States. The RASA Program represents a systematic effort to study a number of the Nation's most important aquifer systems, which in aggregate underlie much of the country and which represent an important component of the Nation's total water supply. In general, the boundaries of these studies are identified by the hydrologic extent of each system and accordingly transcend the political subdivisions to which investigations have often arbitrarily been limited in the past. The broad objective for each study is to assemble geologic, hydrologic, and geochemical information, to analyze and develop an understanding of the system, and to develop predictive capabilities that will contribute to the effective management of the system. The use of computer simulation is an important element of the RASA studies, both to develop an understanding of the natural, undisturbed hydrologic system and the changes brought about in it by human activities, and to provide a means of predicting the regional effects of future pumping or other stresses. The final interpretive results of the RASA Program are presented in a series of U.S. Geological Survey Professional Papers that describe the geology, hydrology, and geochemistry of each regional aquifer system. Each study within the RASA Program is assigned a single Professional Paper number, and where the volume of interpretive material warrants, separate topical chapters that consider the principal elements of the investigation may be published. The series of RASA interpretive reports begins with Professional Paper 1400 and thereafter will continue in numerical sequence as the interpre­ tive products of subsequent studies become available. Dallas L. Peck Director in CONTENTS Page Page Foreword ______________________________ III Ground-water flow models Continued Abstract ________________________________ HI Calibration procedures Continued Introduction ____________________________ 2 Dougherty Plain model calibration Continued Scope and purpose ______________________ 2 May-November 1980 transient simulation _ _ H44 Previous investigations and acknowledgments _ _ _ _ 2 Sensitivity of calibrated aquifer Rainfall _______________________________ 4 parameters ____________________ 44 Streamflow _____________________________ 4 Fort Walton Beach model calibration _______ 46 Flow duration ________________________ 4 January 1941 to March 1978 transient Base flow ___________________________ 8 calibration ____________________ 46 Hydrogeology ___________________________ 13 Predevelopment steady-state simulation using Geologic setting _______________________ 13 the transient calibrated hydrologic Minor aquifers and confining units ___________ 16 parameter values ________________ 47 Sand-and-gravel aquifer _______________ 16 Sensitivity of calibrated aquifer Upper and lower confining units __________ 16 parameters ____________________ 48 Floridan aquifer system __________________ 18 Subregional model calibration ____________ 50 Lithology, areal extent, and thickness _______ 18 Predevelopment steady-state calibration _ _ _ 51 Hydraulic properties _________________ 20 Sensitivity of calibrated aquifer Water quality ______________________ 23 parameters ____________________ 56 Pesticides Southwest Georgia ________ 23 Potential for ground-water development based Saline water Coastal Florida _________ 23 on simulations ______________________ 56 Ground-water flow ________________________ 25 Evaluation of potential development in the Predevelopment flow system _______________ 25 Dougherty Plain area ______________ 56 Present-day (1980) flow system ______________ 27 Effects of irrigation pumpage during a Southern Okaloosa and Walton Counties, consecutive three-year drought _______ 56 Florida _________________________ 28 Pumpage at 1981 withdrawal rates Southwest Georgia ___________________ 29 (assumed drought condition) _________ 57 Water use ______________________________ 31 Pumpage increased to irrigate all potential Northwest Florida ______________________ 31 agricultural land in the Dougherty Southern Okaloosa and Walton Counties, Florida _ _ 31 Plain (assumed drought condition) _____ 57 Southwest Georgia ______________________ 33 Effects of increase in irrigation pumpage Ground-water flow models ___________________ 33 for ten years (assumed average Conceptual model of the flow system __________ 33 hydrologic condition) _______________ 63 Numerical model ______________________ 36 Evaluation of potential development in the Model description ___________________ 36 Fort Walton Beach area _____________ 63 Finite-difference grids and boundary Effects of pumpage in the year 2000 ________ 63 conditions _______________________ 36 Projected pumpage at existing pumping Data requirements ___________________ 40 centers ______________________ 63 Hydraulic properties _______________ 40 Projected pumpage at relocated pumping Initial conditions _________________ 42 centers ______________________ 64 Calibration procedures ___________________ 42 Summary and conclusions ____________________ 67 Dougherty Plain model calibration _________ 43 Selected references ________________________ 70 November 1979 steady-state calibration _ _ _ 44 ILLUSTRATIONS [Plates are in pocket] PLATE 1. Streamflow hydrograph of Turkey Creek (station 02349900) showing base-flow and overland-flow components of total flow, 1978 water year. 2. Geohydrologic section from land surface to below the base of the Floridan aquifer system. VI CONTENTS PLATES 3-24. Maps showing: 3. Distribution of leakance of the upper confining unit, Floridan aquifer system 4. Top of the Floridan aquifer system 5. Thickness of the Floridan aquifer system 6. Distribution of transmissivity, Upper Floridan aquifer 7. Chloride concentrations in water from the Upper Floridan aquifer, southern Okaloosa and Walton Counties, Florida 8. Predevelopment distribution of recharge to and discharge from the Floridan aquifer system 9. Estimated predevelopment potentiometric surface, Upper Floridan aquifer 10. May 1980 potentiometric surface, Upper Floridan aquifer 11. Changes between estimated predevelopment and May 1980 potentiometric surfaces, Upper Floridan aquifer 12. March 1978 potentiometric surface of the Upper Floridan aquifer and distribution of simulated recharge and discharge, southern Okaloosa and Walton Counties, Florida 13. Pumpage from the Upper Floridan aquifer in 1980, southwest Georgia and northwest Florida 14. Finite-difference grid and model boundary conditions for the subregional model and model boundary for Dougherty Plain and Fort Walton Beach detailed models, Upper Floridan aquifer, southwest Georgia, northwest Florida, and southernmost Alabama 15. Transmissivity values used in the calibrated Dougherty Plain model, Upper Floridan aquifer, southwest Georgia 16. Transmissivity values used in the calibrated Fort Walton Beach model, Upper Floridan aquifer, southern Okaloosa and Walton Counties, Florida 17. November 1979 measured water levels and simulated potentiometric surface, Upper Floridan aquifer, southwest Georgia 18. Areal distribution of absolute head differences between the November 1979 potentiometric surface con­ structed from measured water levels and simulated heads, Upper Floridan aquifer, southwest Georgia 19. November 1980 measured water levels and simulated potentiometric surface, Upper Floridan aquifer, southwest Georgia 20. March 1978 measured water levels and simulated potentiometric surface, Upper Floridan aquifer, southern Okaloosa and Walton Counties, Florida 21. Areal distribution of absolute head differences between the March 1978 potentiometric surface constructed from measured water levels and simulated heads, Upper Floridan aquifer, southern Okaloosa and Walton Counties, Florida 22. Comparison of measured water levels for 1942 and 1947 and the simulated predevelopment potentiometric surface, Upper Floridan aquifer, southern Okaloosa and Walton Counties, Florida 23. Estimated and simulated predevelopment potentiometric surfaces, Upper Floridan aquifer, southwest Georgia, northwest Florida,