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South Florida's hydrologic systems

Water-quantity problems in southwest Florida

History of the Study
Regional System
Hydrologic Systems
- Importance of Water
- Aquifers
- Water Balance
- Hydrologic Changes
> Quantity Problems
- Resource Limits
- Quality
Final Word
PDF version
The prime water-supply problems of southwest Florida are related to urban growth and environmental protection. Large quantities of potable water will have to be made available to satisfy the increasing demands, if urban growth in the Naples and Fort Myers areas continues as expected. Freshwater supplies near the coast are being overtaxed as conditions in Naples and Fort Myers during the 1973-74 dry season indicated. Heavy withdrawals superimposed upon low water levels during the prolonged drought caused saltwater to move inland from the Gulf toward the Naples municipal well field. The water-supply situation was even more difficult in Fort Myers where saltwater migrated upstream above control structure S-79 on the Caloosahatchee River where the intake for the city's supplemental supply pipeline is located. For more than 2 months the chloride concentration of the river water at that point exceeded 250 mg/l.

Successive recurrence of low-water conditions comparable to those of 1973-74 could cause permanent damage to the water resources of the Naples area unless additional supplies are made available in the near future. Degradation of water quality in the aquifer beneath Naples could come from seawater intrusion along the Gulf side or migration of mineralized ground water from the area of poor quality water inland from Naples, as indicated by McCoy (1972). The remote interior area, beginning about 24 km (15 mi) east from Naples, is underlain by a highly permeable section of the shallow aquifer that is probably capable of satisfying the future municipal water demands for west Collier County, if pollution of the aquifer can be prevented and if high-water levels can be sustained (Klein, 1972). Future urbanization of that area will be a potential source of pollution from urban runoff. Provision for preventing the direct runoff from urban areas into the Golden Gate Canal and Faka Union Canal systems will minimize the problem of ground-water pollution also, since water from the lower controlled reaches of canals infiltrates the aquifer during part of the year.

The recent lowering of water levels by the Golden Gate Canal and Faka Union Canal systems should accelerate urban and agricultural growth in west Collier County, and this growth in turn will increase the demand on the water resources. Most of the urban water may be used consumptively because sewage systems may be obliged to dispose of effluents into environments other than local canals. Increased withdrawals of ground water will progressively lower water levels each dry season, unless measures are taken to progressively reduce the discharge of freshwater from the canal systems.

During the dry year from October 1970 to September 1971, the combined mean discharge of the Golden Gate Canal and the Faka Union Canal was more than 17 m3/s (600 ft3/s) or nearly 1.5 million m3 (400 million gallons) per day. This quantity is about equal to the aggregate daily pumpage of the cities along the heavily populated lower east coast for the dry season of 1974. If the elevations of weirs throughout the drainage systems were to be raised 0.3 to 0.6 m (1 to 2 ft), the reduction in runoff would salvage for potential use a large part of the flow to the sea. The resulting rise in water levels would tend to reduce damage to the environment and the possibility of seawater intrusion and would probably reinundate some of the sloughs that became dry as a result of drainage. The possibility of environmental changes in the Fakahatchee Strand, and in the Corkscrew Marsh northeast of Naples, would be reduced because diversion of freshwater toward canals would be reduced.

The water-supply problems of Fort Myers and coastal Lee County are about as serious as those of coastal Collier County, but the environmental consequences of drainage and urbanization are not as great as those in the Big Cypress Swamp. The prime problem in Fort Myers is the impaired quality of the water from the Caloosahatchee River that is used to supplement water supplies during the dry seasons. The salinity of the river depends upon the amount of freshwater released from Lake Okeechobee. During dry seasons, when releases are minimal, the lower controlled reach of the river becomes contaminated by saltwater during boat lockages at structure S-79 (Boggess, 1970). During prolonged dry seasons, the chloride concentration of the water at the pipeline intake exceeds the limit for public supplies. No improvement in the quality of the supplemental water can be expected until measures are taken to provide sustained freshwater flows from Lake Okeechobee and to restrict or reduce boat lockages during the dry season.

Preliminary hydrogeologic information shows the occurrence of permeable layers containing freshwater in the shallow aquifer in the east part of Lee County. Those aquifers may be capable of supplying the water for the future demands not only of Fort Myers but also of other coastal communities in the county whose supplies are being overdeveloped and are threatened by saltwater contamination. The extent and the potential yield of the inland parts of the shallow aquifer were undergoing evaluation in 1974.

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Last updated: 04 September, 2013 @ 02:04 PM (KP)