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Summary of the Hydrology of the Floridan Aquifer System In Florida and In Parts of Georgia, South Carolina, and Alabama

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By Richard H. Johnson and Peter W. Bush
Professional Paper 1403-A

Potential for Future Development

Large quantities of fresh ground water are available for future development from the Upper Floridan aquifer. This is indicated by the fact that the original flow system has not been changed extensively by pumpage of about 3 Bgal/d, which currently represents less than 20 percent of the flow through the Floridan. However, very large withdrawals and the resulting head declines can induce poor-quality water to move into the Upper Floridan (by both lateral and upward movement of saltwater in coastal areas and by upcoming of saline waters in some inland areas). Thus the major constraint on future development is degradation of water quality rather than water-quantity limitations. Saltwater encroachment in coastal areas and upcoming of saline waters in some inland areas are important constraints to consider in planning additional development.

An appraisal of potentially favorable areas for large ground-water development is presented in Professional Paper 1403-C and summarized here. The appraisal is based primarily on minimizing head decline and thereby reducing the chances of water-quality deterioration. The potentially favorable areas were selected on the basis of aquifer and confining-unit properties, current water chemistry, heads, and pumpage. The criteria that had to be met in order for an area to be considered "highly favorable" are as follows:

    • Transmissivity greater than 50,000 ft2/d in unconfined or semiconfined areas; transmissivity greater than 100,000 ft2/d in confined areas.
    • Altitude of 1980 heads higher than 25 ft. In theory (which is conservative) this insures at least 1,000 ft of freshwater in the subsurface where permeable carbonate rock extends to that depth. This criterion is intended to eliminate all coastal areas where the potential for saltwater encroachment exists.
    • The Upper Floridan aquifer contains freshwater of acceptable quality; dissolved-solids concentrations of less than 500 mg/L as of 1980. Contamination of ground water by pesticides and other toxic chemicals, although documented in a few isolated instances, has not been considered in this regional evaluation.
    • Long-term water-level decline in the Upper Floridan due to ground-water development is less than 40 ft.
    • Pumpage during the early 1980's was light; less than 10 M gal/d within a 64-mi2 area.
    map showing potential areas for future development of large ground-water supplies from the Upper Florida Aquifer
    Plate 4. Potential areas for future development of large ground-water supplies from the Upper Florida Aquifer. [larger version]

    Plate 4 shows the extent of the highly favorable areas that meet all of the five criteria previously listed. This map is intended as a qualitative overview of promising areas where large ground-water development (as much as 100 M gal/d) can proceed with minimal detrimental effects. As shown on plate 4, most of the highly favorable areas occur in the lightly developed northern half of central peninsular Florida and adjoining south Georgia.

    Locally, of course, the effects of large future increases of ground-water pumpage will vary. To test the effects of such increases, computer simulation was applied in some of the favorable as well as less favorable areas. Discussions of various scenarios of increased pumpage are presented in Professional Paper 1403-D through F and 1403-H.

    In summary, there remains a considerable area of the Upper Floridan aquifer's extent that is highly favorable for the development of large ground-water supplies. This area is largely inland from the coasts and characterized by high transmissivity as well as minimal development in 1985.



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