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A Region Under Stress-- Home
A Region Under Stress-- Introduction

Environmental Setting-- The Natural System
Watersheds and Coastal Waters

Environmental Setting-- The Altered System
Drainage and Development
Public Lands
Water Use
Water Budget

Water and Environmental Stress
Loss of Wetlands and Wetland Functions
Soil Subsidence
Degradation of Water Quality
Mercury Contamination
Effects on Estuaries, Bays, and Coral Reefs

Summary and Research Needs

Related Links

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U.S. Department of the Interior
U.S. Geological Survey
Circular 1134

The South Florida Environment - A Region Under Stress

Environmental Setting--
The Altered System

Aerial photo of highway

The south Florida ecosystem has been greatly altered by man (fig. 23). Although the hydrology, water quality, and ecology of much of the region has been changed by drainage and development, parts of the old ecosystem remain, primarily on protected lands and in protected waters at the southern end of the peninsula.

Drainage and Development

Figure of hydrologic features in south Florida
Figure 23. Major canals, control structures, direction of water flow, and other hydrologic features in south Florida (above). Click on image to open larger picture (52.0k).
Photo of Miami Canal
Figure 24. Miami Canal in Water Conservation Area 3 (above). Click on image to open larger picture (95.2k).

Drainage of the Everglades watershed began in the early 1880's and continued into the 1960's. The first drainage canals were dug in the upper Kissimmee River and between Lake Okeechobee and the Caloosahatchee River. Beginning with the Miami River in 1903, canals were cut through the Atlantic Coastal Ridge and into the northern Everglades. By the late 1920's five canals had been dug between Lake Okeechobee and the Atlantic Ocean-one that passed north of the Everglades and connected the lake with the St. Lucie River, and four that passed through the Everglades (figs. 23, 24). Drainage has enabled agriculture to develop south of Lake Okeechobee. In the late 1920's, a low, muck levee was constructed along the southern and southwestern shore of the lake to prevent flooding; but during the hurricanes of 1926 and 1928, the levee was breached, which resulted in the destruction of property and lives. In response to these catastrophes, the Federal Government initiated flood- control measures, which included the construction of a levee around the southern shore of the lake and the enlargement of the Caloosahatchee and the St. Lucie Canals.

Drainage and development irreversibly altered the natural Everglades watershed and had severe environmental consequences. Early drainage lowered water tables up to 6 ft below predevelopment levels and resulted in conditions favorable for severe fires that damaged and eliminated vegetation (Alexander and Crook, 1973; 1975). Peat burned and oxidized, and the land subsided as much as 6 ft below predevelopment levels. Saltwater from the ocean intruded inland via canals and filtered into the previously freshwaters of the aquifer (Parker and others, 1955; Klein and others, 1975).

In 1948, Congress authorized the Central and Southern Florida Project for Flood Control and other Purposes to provide flood protection for urban and agricultural development and an adequate water supply for development. A water-management plan was adopted that included Lake Okeechobee and three water conservation areas (WCA's) and that provided flood protection and water supply through a complex series of canals, levees, pumps, and control structures. The northern Everglades was identified as an area that was suitable for agricultural development on the basis of soil thickness and geologic formations. As a result, 800,000 acres was designated agricultural land and termed the "Everglades Agricultural Area" (EAA). Subsequently, most of this land was drained and farmed. The WCA's were constructed in the central Everglades and consisted of levees and canals that enclosed areas that total about 900,000 acres (fig. 23). These areas, which were completed by 1962, provided flood protection during the wet season by storing water and discharging excess water to the ocean and supplied water during the dry season for irrigation and municipal uses (Klein and others, 1975).

Congress authorized the channelization of the Kissimmee River for flood control in 1954. Canal construction began in 1961 and was completed 10 years later. The 90-mi-long meandering river was replaced by a 52-mi- long canal, and seasonal flooding of much of the river's flood plain, which averaged about 2 mi in width, was eliminated. Flow into Lake Okeechobee was controlled by six locks and dams along the rivers (Carter, 1974).
Photo of smoke over field

Construction of the Kissimmee River Canal (C-38) considerably altered the hydrology, water quality, and wetlands in the Kissimmee Basin. The dams in the canal created pond areas that were permanently flooded, whereas farther upstream from each dam, wetlands were drained and replaced by terrestrial vegetation. As a result, about 40,000 to 50,000 acres of flood plain marsh disappeared, resulting in a significant loss of habitat for wading birds and other aquatic animals (South Florida Water Management District, 1989) and in a loss of the natural nutrient-filtering effects of these wetlands. Drainage also eliminated the river's natural oxbows and stimulated agricultural development in flood plain and adjacent wetlands, all of which have contributed to the increased nutrient loading to Lake Okeechobee (Lamonds, 1975; Federico, 1982). The environmental impacts of channelization were quickly recognized, and calls for restoration of the river began even during canal construction. Plans are underway to restore the river and its flood plain by increasing water storage in the upper Kissimmee Basin and by physical modifications to the lower basin. This will include backfilling 22 mi of C-38, recarving 9 mi of river channel, removing two water-control structures, and removing flood-plain levees. Construction will require approximately 15 years (South Florida Water Management District, written commun., 1993).

A large percentage of the water that originally flowed from the Kissimmee River and Lake Okeechobee into the Everglades is now diverted directly to the Gulf of Mexico by the Caloosahatchee Canal and to the Atlantic Ocean by the St. Lucie Canal. The remaining outflow from the lake is released in canals that pass through the EAA (South Florida Water Management District, 1989). Water is pumped from the EAA into the WCA's, but the timing and spatial distribution of this water delivery is altered from natural flows, and the amount of water discharged is greatly reduced. As a result, water levels in the Everglades generally are shallower and have shorter hydroperiods than those of predevelopment time, and the timing and distribution of flows have changed (Parker, 1974; Fennema and others, 1994). In the northern parts of the WCA's, water levels are drawn down rapidly by canals, and in the southern parts, water ponds as flow is impeded by levees (Dineen, 1972). The ponding effect began in the mid-1960's in WCA-3 and resulted in extensive flooding of tree islands. During droughts, water is released from Lake Okeechobee to the EAA and the WCA's. Most of this water, however, never reaches the interior marshes, because it is confined to canals and their nearby marshes.

Drainage of the Big Cypress Swamp began in the 1920's with the construction of the Barron River Canal (fig. 23). Subsequently, the Turner River Canal was dug 5 mi to the east. Even though these canals have not been effective in lowering water levels, both intercept substantial quantities of water from the Okaloacoochee Slough and divert them directly to the estuaries. A major drainage system, the Golden Gate Canals, was started in the Big Cypress in the early 1960's. As a result of this system, water levels in the western part of the swamp have been lowered an average of 2 ft, and seasonal flooding has been reduced.

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