projects > synthesis on the impact of 20th century water-management and land-use practices on the coastal hydrology of southeast florida > 1999 proposal
Synthesis on the impact of 20th Century water-management and land-use practices on the coastal hydrology of southeast Florida
Project Proposal for 1999
USGS Geologic Division
Geographic area: South Florida
Project chief: Robert A. Renken
Program(s): Integrated Natural Resources Science (INATURES)
Project summary: The urban and agricultural corridor of South Florida lies between the Everglades and Water Conservation areas to the west and the Atlantic Ocean to the east. This area includes eastern Dade, Broward, and Palm Beach Counties and is subject to widely conflicting stresses on the environment. The Shark River Slough, a deep water slough which historically channeled water from the eastern Everglades and moved water to the southwest, is located immediately west of this corridor. A highly controlled water management system has evolved during this century largely to provide drained land for a rapidly expanding population. Reclamation of Everglades wetland areas during the last 75 years provided the opportunity for westward expansion of agricultural, mining, and urban activities. In Water Conservation Areas that lie to the west of the protective levee system, surface water is impounded, partly to sustain an Everglades ecosystem, partly to keep overland sheet flow from moving eastward and flooding urban and agricultural areas, and partly for water supply.
In coastal areas of the urban-agricultural corridor, parallel environmental conflicts exist. Coastal residential and urban areas must be drained for flood control; the underlying aquifer system must simultaneously serve as the principal source for water supply and heads must be maintained to prevent salt water intrusion. Changes in predevelopment ground-water flow patterns and the associated reduction in ground-water discharge to coastal bays has altered salinity in and affected the local ecology.
The extensive canal network that incises the underlying unconfined aquifer has historically resulted in deleterious consequences: overdrainage, inland migration of coastal salt water and intrusion of these saline waters to nearby municipal well fields. The construction of canals and pumping from the surficial aquifer for water supply in south Florida has resulted in the lowering of water levels in the Everglades and in the aquifer. Consequently, the hydrodynamic balance between freshwater and saltwater in the ground-water flow system has changed, resulting in inland migration of saltwater into the freshwater aquifers. Coastal well fields used by many communities in South Florida are threatened, with some closed due to the inland movement of the saltwater.
Lowering of ground-water levels in the agricultural-urban areas by pumping has caused higher ground-water seepage and canal discharge along the levee system, reducing flows to the south in the water-conservation and Everglades area. As part of an Everglades ecosystem restoration plan, a buffer zone will separate the urban and wetland areas. Currently under consideration for the buffer zone in Dade County are plans for the development of a Lake Belt District formed by a series of interconnected quarries. These limestone quarries provide one-half of the limestone mined in Florida each year; of particular concern is the potential for increased seepage losses across the protective levee system immediately west of the planned Lake Belt and how these lakes may impact the recharge area of Dade Countys Northwest Well Field.
Contamination of the environment is also an important issue in the south Florida agricultural-urban corridor. The entire area is underlain by the highly prolific Biscayne aquifer; designated by the EPA as a sole source aquifer. The aquifer is unconfined and has been subject to contamination by solid waste disposal, leaking underground storage tanks, septic fields, industry, and by agricultural chemicals.
An important question in south Florida is how to best regulate an irregular temporal and spatial distribution of water, but simultaneously mitigate past environmental damage caused by tampering with natural hydropatterns. A fundamental issue is to identify the best approach to store excess water in even greater quantities without creating new environmental concerns. The Floridan aquifer system largely contains brackish or saline water in southeastern Florida. However, the upper Floridan is viewed as a potential site for the subsurface storage and recovery of excess water collected during the wet season for use during the dry season. Another critical issue being studied is whether wastes injected into the Lower Floridan aquifer can migrate upward and contaminate the upper Floridan aquifer.
This synthesis will assess the hydrogeologic character of the surficial aquifer system, review the extensive impact of water-management controls on the hydrologic system, and examine the manner in which urban and agricultural areas have effected the ambient quality of ground water. In addition, this synthesis will examine the overall status of saltwater intrusion in South Florida, potential effects of Everglades restoration scenarios on intrusion, and the impact on water supply and the South Florida ecosystem due to saltwater intrusion.
Project objectives and strategy:
A critical aspect in any synthesis project is to consolidate seemingly disconnected technical information and present the ãbig picture,ä 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 will 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 an 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 South Florida Water Management District, from existing numerical, models or from models which are currently under development. Some of the major inflow components for 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 South Florida; 2) map trends in water levels and the relation to intrusion; 3) examine potential effects of Everglades restoration scenarios on intrusion; and 4) 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 products:
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 (1990s) view of the hydrologic system is of great importance to water managers and for urban and environmental planners. 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.
South Florida Water Management District, Metro-Dade Department of EnvironmentalResources Management, Biscayne National Park, Everglades National Park, Biological ResourcesDivision, and the U.S. Army Corps of Engineer. Additional clients include the environmental regulatory agencies and municipal suppliers in Broward and Palm Beach Counties.
Time line (FY 1999 to project end):
Deliverables/products: U.S. Geological Survey Circular, FY 2000
Outreach activities: Presentations to interested parties will be made as deemed appropriate.
Proposers previous experience in the projects topic or geographic area:
PROJECT SUPPORT REQUIREMENTS
Other required expertise for which no individual has been identified (list by fiscal year for duration of project):
Major equipment/facility needs (list by fiscal year for duration of project):