U.S Geological Survey, South Florida Ecosystem Program: Place-Based Studies

Project: Impact of 20th Century Water-Management and Land-Use Practices on the Coastal Hydrology of Southeast Florida

Web Site: Synthesis on the impact of 20th Century water-management and land-use practices on the coastal hydrology of southeast Florida

Location: Greater Everglades Subregion 4 (Southeast Coast); Palm Beach, Broward, and Miami-Dade Counties

Principal Investigator: Robert A. Renken, rarenken@usgs.gov 954.349.7801

Project Personnel: John Koehmstedt, jkoehmst@usgs.gov 703.648.4619; Scott Ishman, sishman@geo.siu.edu 618.453.3351; Joann Dixon, jdixon@usgs.gov 305.717.5800

Other Supporting Organizations: None

Associated Projects: None

Overview & Status: (Final year of a three year project): Saltwater intrusion into the surficial aquifer is a direct consequence of water-management practices, concurrent agricultural and urban development, and natural drought conditions. This synthesis will: (1) provide a temporal (predevelopment to present-day conditions) and spatial overview of coastal saltwater intrusion in south Florida; (2) identify the principal factors that control the extent of saltwater intrusion; (3) evaluate long-term trends in ground-water withdrawal rates, ground-water level change, rainfall, and increases in chloride concentration; (4) illustrate causal relations between the position of the saltwater interface, water-management practices, and the expansion of agricultural and urban areas; and (5) discuss Everglades restoration scenarios and their anticipated effect on saltwater intrusion. A wide variety of maps and other analyses being conducted to examine anthropogenic changes and possible causal relations between movement of the interface. An important part of this synthesis is to link water-management practices (canal-discharge), consumptive water use, water levels within the surficial aquifer system, chloride concentrations, ground-water discharge, and Holocene paleohistory of the Florida Bay and Biscayne Bay. For example, a series of water table maps for specific selected 5-year increments have been developed to spatially identify the areal extent where long-term water levels within the surficial aquifer has declined and to compare these changes with movement of the interface. Such changes are also being compared with changes in coastal outflows from major canals to distinquish between long-term declines caused by regional drainage and a large number of municipal pumping centers. Paleontologic data are being used to prepare maps illustrate temporal changes in salinity within the Biscayne Bay over the last 150 years. Salinity changes within the bay are largely attributed to a decrease in ground-water and surface water discharge.

Needs & Products: The major product from this synthesis will be a U.S.G.S. Circular which will help these decision makers not only with Everglades restoration, but with planning and maintaining a balance between water needs of the environment, urban areas and agricultural areas for the next millennium. The report will contain figure-size maps, tables, and other charts that illustrate and define historic and present-day hydrologic conditions in the eastern agricultural and urban corridor.

Application to Everglades Restoration: The urban-agricultural corridor of South Florida has a unique geographic setting given its close proximity to both the Florida Everglades, offshore reefs, critical estuaries and bays. Rapid urban development and population growth have placed extraordinary demands on the environment. Therefore, a synthesis that provides both a historical and synoptic (predevelopment to 1990's) view of the hydrologic system is of great importance to water managers and for urban and environmental planners.