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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).
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.
U.S. Department of the Interior, U.S. Geological Survey
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Last updated: 04 September, 2013 @ 02:03 PM(KP)