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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

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Download Circular 1134 PDF

publications > circular > Circular 1134 > the altered system > urbanization

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 urbanization
Aerial photo of urbanization


Urbanization in south Florida began along the Atlantic Coastal Ridge where the land is high and close to the marine transport that was essential to the original coastal settlements. Extension of a railroad to Miami at the turn of the century sparked phenomenal growth. Through the years, flood-control and water-management practices have made some land west of the ridge available for development. Today, more than 4 million people live in an urban complex along or near the eastern coast (fig. 29). A second urban complex of more than 0.5 million people has developed along the Gulf Coast between Charlotte Harbor and Cape Romano. The Everglades and the Big Cypress Swamp presented a formidable barrier to development between the two coasts.

The major effects of urbanization on water resources are reduction of infiltration, increase of flood potential, and degradation of the quality of water bodies receiving water. Trash and litter deposited on streets and parking lots, erosion of exposed ground as a result of construction, lawn and landscape fertilization, pet wastes, automobile emissions, atmospheric deposition from industrial and thermoelectric powerplants, and seepage from landfills, septic tanks, and disposal wells have been identified as sources of urban stormwater loads. These sources of generally distributed substances are grouped together under the classification of "nonpoint" to distinguish them from the more readily identifiable industrial- and domestic-sewage plant effluents, called "point sources" (fig. 30).

Figure showing population density
Figure 29. Population density in south Florida, 1990. (Derived from U.S. Department of Commerce, Bureau of Census, 1990 Census of Population and Housing Public Law 94-171.) Click on image to open larger picture (31.8k).
Figure showing location of major wastewater facilities and landfills
Figure 30. Location of major wastewater facilities and landfills in south Florida. (Florida Department of Environmental Protection, 1990-94.) Click on image to open larger picture (29.6k).

Consequences of drainage for urban and agricultural development have included seawater intrusion into coastal parts of the shallow aquifers. During the prolonged droughts of the 1930's and 1940's, seawater moved inland along canal channels and infiltrated aquifers. At the end of the 1945 dry season, seawater intrusion had affected large segments of the Biscayne aquifer, and several of Miami's municipal supply wells yielded salty water. Water levels in southern Dade County and in what is now the eastern part of Everglades National Park were as low as 2 ft below sea level (Parker and others, 1955).

Uncontrolled drainage in southeastern Florida was halted in 1946 by the installation of control structures (barriers) near the outlets of most drainage canals. These structures mitigated the recurring problems of seawater intrusion and excessively low water levels. During the rainy season, the controls are opened to release water for flood prevention in the urban and agricultural areas, and during the dry season, they are closed to prevent overdrainage and to retard seawater intrusion. Canal flows have been controlled since 1946, and regional water management in south-eastern Florida was begun in 1962 with storage of water in Conservation Area 3. Water control in the 1950's and management in the 1960's reduced canal outflows from the Everglades (Leach and others, 1972) but resulted in increased water losses from the coastal ridge area where flood prevention was necessary in the rapidly expanding urban areas.

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