Home Introduction Physical Setting Urbanization Natural Hazards Mineral Resources Water System - Problems > Mgmt. Alternatives Environmental Quality Outdoor Recreation Everglades N.P. Coastal Zone Fish & Wildlife Miccosukee Indians Conclusion References

Projected growth in south Dade County will further stress the water resources. Implementation plans to increase the capacity of the Levee 31 Canal will facilitate movement of water from the water storage areas to south Dade County. However, increasing the capacity of the delivery system will be of little consequence if water is not available for transport.

Water needs for a growing population can be at least partly satisfied by conserving for use during dry season excess water that otherwise would flow to the ocean during the rainy season. However, conserving this water could change the amount and distribution of water in the aquatic environs with resultant effects on plants and animals.

One way to alleviate water shortages during droughts is to backpump to the water-conservation areas part of the excess storm water currently being discharged to the ocean during rainy seasons. [larger image]

During the past 12 years, seaward flow from canals in Dade County north of Snapper Creek Canal was about 1,200 cfs (cubic feet per second). In the lowest year, it averaged about 600 cfs. If only half of this minimum flow were backpumped, an additional 200 mgd could be recovered for use. Based upon present water consumption rates in Dade County ^9/, the hydrologic system within Dade County augmented by backpumping could sustain a total county population of 2.5 million, without further stress on the water resources. The water backpumped, however, must be of acceptable quality. Excessive nutrients, pesticides, or toxic metals in the water could change or adversely affect aquatic life in Conserve Area 3 and Everglades National Park.

Another alternative is forward pumping which involves the eastward pumping from surface and underground storage in the conservation areas into the urban canal system to augment coastal water supplies. [larger image]

Forward pumping would salvage water that is ordinarily lost by evapotranspiration in Conservation Area 3 ^9/. However, prolonged pumping would further reduce the water in storage and could result in changes in the biota in Conservation Area 3 and the interior of Everglades National Park. On the other hand, forward pumping to south Dade County would benefit biologic communities in the southeast panhandle of the Everglades National Park.

To sustain proper water levels at coastal control structures in the selected canals, the quantity of water to be pumped forward would have to equal the quantity of water lost by seepage at the coastal controls (about 50 cfs per canal) plus the quantity diverted by well field withdrawals ^4/. The lowering of water levels in Conservation Area 3 would be seasonal, as water lost from Conservation Area 3 by forward pumping would be replenished during the rainy season.

Water levels can be stepped up from the coast to the water storage areas by inland control structures in canals. [larger image]

Inland control structures in south Dade canals are less effective in reducing fresh-water losses to the ocean than those in other areas because of the higher permeability of the Biscayne aquifer there. The high permeability allows more water to seep around the structures and out of the controlled reaches of canal. Despite this high permeability, additional structures on Snapper Creek and Black Creek Canals would help delay runoff and conserve fresh water.

Reducing fresh-water discharge to the ocean would not only decrease the rate at which water levels decline but also would reduce the period that water levels in the south part of the area and Everglades National Park are below sea level. High water levels may make it more difficult to urbanize some interior areas but would benefit aquatic environments. Water conserved through operation of inland control structures could complement the backpumping plan for water conservation.

Further saving of water in the controlled reaches of the canals might be accomplished by grouting the limestone at the control structures or by lining the canals upstream from the structures to reduce seepage.

Urbanization of coastal areas requires filling to elevations above tidal flood levels. [larger image]

Land-use and population projections indicate that agriculture areas in south Dade will gradually be urbanized. To accommodate urban development, lowlying lands have to be raised to meet county flood-criteria elevations. Water levels at costal structures in the major canals (Black Creek, Canal 102, and Mowry) could then be raised from the present operating level of 1.5 feet above sea level to 3.0 or possibly 3.5 feet above sea level. At these higher levels, the coastal controls would have to be opened for short periods to discharge flood water but, at other times, the controls would be closed. Thus, much of the water now discharged to the ocean could be conserved.

Raising water levels by coastal control structures will also raise water levels in the interior and reduce seepage from Conservation Area 3. These higher coastal levels would probably move the salt front in the Biscayne aquifer toward the sea. Unless carefully controlled, development would destroy the salt marsh-mangrove environment that fringes the coast. Dredging and filling necessary for development would damage the coastal zone. Permanent environmental degradation such as that experienced in north Biscayne Bay could occur. The reduced flow to south Biscayne Bay as a result of increased water levels would approximate the flows before the canals, and thus little alteration in the bay environment would be expected.

In the past, flooded land was drained by canals to permit urban development. In the future, because of impending water shortages, development of inland marginal and flood-prone areas will probably be by borrow-and-fill method which raises land above flood levels ^11/. Although this will minimize water losses and damage to aquatic environments, it will increase costs of land preparation, building, and installing utilities and roads. Most of the area developable by borrow-and-fill is west of the levee system.

Injection of excess storm water into deep wells in the Floridan aquifer is a potential although untested method of storing fresh water for use during the dry season. [larger image]

This aquifer underlies the Biscayne aquifer and is separated from it by an 800-foot-thick confining layer. The part of the aquifer between depths of 800 feet and 1,500 feet appears especially suited to injection, storage, and recovery of fresh water. Yields from large-diameter wells in this aquifer are more than 2,000 gallons per minute of brackish water of 2,000 to 5,000 milligrams per liter of chloride. Therefore, it is theoretically possible to inject under pressure fresh water at similar rates. The injected water should maintain itself as a lens of recoverable fresh water. As the aquifer is under high artesian head (40 feet above sea level), the water could be recovered by natural flow. This type of storage would eliminate evapotranspiration losses and could compliment backpumping programs in a comprehensive water-management program.

Water would be injected during the rainy season from canals or from shallow wells in the Biscayne aquifer adjacent to canals. Pumping from shallow wells probably would minimize well clogging, a problem which reduces injection capacity.

The quantity of water pumped into storage over a period of years could be large enough to sustain needs in selected areas during an entire dry season or longer. In south Dade County clusters of injection-recovery wells located near the Orr-Southwest well fields, the Homestead Air Force Base well field, and the Homestead and Key West well fields could meet needs for future increases in municipal water supplies. Fresh water recovered from the Floridan aquifer could also supplement flows in some south Dade County canals during severe drought.

Further studies on the characteristics of the Floridan aquifer are needed to determine the practicability of this method.

In 1970, sewage treatment plants in Dade County charged about 90 mgd of wastewater to ocean outfalls and about 10 mgd to inland canals ^9/. By 1990, 325 mgd of wastewater will be produced, of which 90 percent discharged to ocean outfalls. Water discharge to the ocean is lost. Wastewater, however, if adequately treated, is a source of fresh water for well-field replenishment, for salinity control, for irrigation, and for maintaining wetlands. Although wastewater currently discharged into canals help maintain higher water levels at control structure during the dry season, the water is of low quality and contaminates the waterways.

Properly treated wastewater could be piped from central treatment plants to the coast and injected into the Biscayne aquifer to help retard sea-water intrusion. Wastewater treated for removal of nutrients, toxic chemicals, and bacterial contamination also could be discharged directly to canals to insure continual recharge of the Biscayne aquifer.

Treated wastewater could also be piped inland to water conservation areas or to wetlands west of Levee 31 (see illustration). This would retard recession of water levels in these areas and help sustain flows to Everglades National Park as well as to canals. If, however, the wastewater contained nutrients the growth of vegetation in the wetland areas would be stimulated.

Treated wastewater could be backpumped to Conservation Area 3 or other interior wetlands to maintain water levels. The quality of the water, however, may affect plants and animals in the area. [larger image]

Other methods of increasing the availability of water in southeast Florida would affect the south Dade area. Proposed methods include backpumping in counties north of Dade County, ^14/ raising water levels in Lake Okeechobee, desalting water from the sea or from the Floridan aquifer, use of evaporation suppressants, and weather modification. Backpumping or raising water levels in Lake Okeechobee would reduce canal discharge to the ocean and require pump installations and other construction. Deterioration of the water quality of Lake Okeechobee is probable if the water backpumped is enriched with nutrients and other contaminants from agricultural and urban areas. The rise in lake level probably would alter perimeter marshes, which if destroyed would adversely affect water quality.

Treated wastewater could be piped to the coast and injected into shallow wells in the Biscayne aquifer to retard sea-water intrusion in selected areas. 12/ [larger image]		Artesian water of relatively low salinity from deep wells could be injected into shallow wells along the coast to retard seawater intrusion in the Biscayne aquifer. [larger image]

The current water-management system for south Florida is a complex network of water-conservation areas, canals, salt-water barriers, and other physical features. Both the existing system and a system with modifications offer opportunity for alternatives to management.

Assessment of alternatives for future management procedures will require close coordination with planning agencies so that realistic objectives and alternatives for implementation can be formulated. Limitations on available water will undoubtedly affect land-use planning; similarly, land-use decisions will influence the selection of management alternatives.

Go back to Problems | Go ahead to Ecosystem Impact