projects > synthesis on the impact of 20th century water-management and land-use practices on the coastal hydrology of southeast florida > work plan
Project Work Plan
Greater Everglades Science Program: Place-Based Studies
Project Work Plan FY 2003
A. GENERAL INFORMATION:
Project Title: Impact of 20th Century water-management and land-use practices on the coastal hydrology of southeast Florida
Project Summary: 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; and (4) illustrate causal relations between the position of the saltwater interface, water-management practices, and the expansion of agricultural and urban areas. 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.
Project Objectives and Strategy: A critical aspect in any synthesis project is to consolidate seemingly disconnected technical information and present the "big picture," but at the same time be designed at a technical level useable to water managers and decision makers. This synthesis will: review the wide variety of anthropogenic stresses that have been imposed on the local environment; review changes in water quality caused by salt-water intrusion; summarize the current state-of-knowledge of the hydrologic system within the urban-agricultural corridor of eastern Dade, Broward, and Palm Beach Counties; and evaluate various inflow and outflow components of the water budget. A conceptual model of the ecosystem with an emphasis on the hydrologic system will be developed and an assessment of inflow and outflow components in the water budget will be prepared.
The synthesis will be completed using the following strategy. Most information can be obtained from previously published reports but supplemented with data from the files of the U.S. Geological Survey, South Florida Water Management District, and Dade County Department of Environmental Resources Management. For example, a literature review will be conducted to examine the historical development of water resources in eastern Dade County, and to describe how land-use management practices have impacted the ecosystem. The impact of these practices will be evaluated in terms of both water quantity and water quality. GIS coverages may be developed which include such topical categories as changes in the amount of ground-water pumpage, water use, and land use during the last 30 years. Assuming data are available, a GIS coverage showing location of point and non-point contamination will be prepared.
Present day inflow and outflow components of the hydrologic budget will be estimated integrating data available in the files of the U.S. Geological Survey and Southeast Florida Water Management District, from existing numerical models or from models which are currently under development. Some of the major inflow components to the system in the County include precipitation, levee seepage, ground-water recharge to the aquifer, and water conveyed from Lake Okeechobee to the ocean through the canal system. Depending on local hydrologic conditions, this canal system can act either as a source of water to, or a site of discharge from the underlying aquifer. Outflow components include evapotranspiration, canal outflows, municipal and agricultural well pumpage, and ground-water discharge to the Biscayne Bay.
In the past 60 years, projects executed by Federal, State, and local agencies have been conducted to determine the location of the saltwater interface. These projects have been mostly local in nature, limited to a specific county or municipality. Projects have reported the change in chloride with depth in a well or group of wells; most monitoring programs are managed by local governmental agencies. Other projects have used ground-water flow models to determine the location and movement of the interface. However, no effort has been made to link the results of these various studies or to fill in data gaps.
This synthesis will: 1) determine the overall status of saltwater intrusion in Southeast Florida; 2) map trends in water levels and the relation to intrusion; and 3) determine the possible impact on water supply and the South Florida ecosystem due to saltwater intrusion. The evaluation of saltwater intrusion in the surficial aquifers of South Florida will be made through an analysis of existing publications and data. Results from recent studies conducted along the southeast coast and in the Everglades National Park will be combined with additional data collected by other agencies to present a regional depiction of saltwater intrusion. Additional study will be conducted to determine long-term trends in the movement of the freshwater-saltwater interface. Changes in water levels will be compared with the movement of the interface.
This synthesis will also examine how water-management practices have affected water quality in the urban-agricultural corridor. Other water quality issues that will be addressed include the effects of solid-waste disposal facilities, well-field contamination caused by chemicals, the impact of stormwater runoff and septic tank effluent on water quality, and the extent of point and nonpoint contamination by agricultural chemicals. Other issues to be examined include a review of ongoing investigations that are attempting to quantify nutrient loads and other contaminants derived from urban and agricultural areas that enter lakes, estuaries, and the Biscayne Bay, and are carried by the canal system.
Potential Impacts and Major Product: The comprehensive plan will substantially improve water supplies, and improves the ability of water managers to meet public supply needs. Rerouting of surface water supplies is a major element of the plan. A historical review of urban development and water management illustrates causal relations between water conveyance, water use and land use practices on the movement of the saltwater interface; indirectly this study can be used to illustrate the impact of possible future management practices on the saltwater interface.
B. WORK PLAN