DEVELOPMENT AND CALIBRATION OF AN INTEGRATED SURFACE- AND GROUND-WATER MODEL OF BISCAYNE BAY AND SURROUNDING AREAS

Southeastern Florida's hydrology is unique due to the dynamic interaction between ground water and surface water. This interaction is prominent in Miami-Dade County and Biscayne National Park (BNP), where surface-water systems, composed of highly managed canals, are fed by water from upstream sources and the Biscayne aquifer. The construction of the canal systems modified the hydrology of the area by decreasing ground-water levels and therefore reducing the groundwater flowing from springs into Biscayne Bay. The Comprehensive Everglades Restoration Plan aims to partially reestablish predevelopment wetlands and flow conditions in the Everglades system and surrounding areas including Biscayne Bay. These changes could have significant effects upon the hydrologic system. Extreme outflow conditions to Biscayne Bay could be ameliorated, and hydroperiods and flow distribution through coastal wetlands could also be restored toward historic natural conditions. Another potential effect of restoration activities may be increasing the rate of coastal groundwater discharge, aiding the transport of anthropogenic contaminants into the offshore marine ecosystem. This could cause significant harm to the habitat of many threatened or endangered species of plants and animals that reside in BNP and on the coral reef tract. Therefore, it is extremely important to study the hydrologic conditions of both the surface water- and ground-water systems.

The U.S. Geological Survey (USGS) has developed a coupled surface-water/ground-water numerical code known as the Flow and Transport in a Linked Overland/Aquifer Density-Dependent System (FTLOADDS) to represent the hydrologic conditions in south Florida. FTLOADDS was used to create a simulation of Biscayne Bay and surrounding areas. The model consists of a uniform 500m horizontal grid, with 20 vertical layers, each 2.75m. This model simulates the period from 1996-2004. Freshwater discharges to the bay, salinity transport, and ground-water flow rates and contaminant paths in the aquifer can be simulated with the model. Preliminary calibration results indicate a good fit to field data. In the future the model can be linked with local regional scale models that are currently running restoration scenarios to estimate the potential effects of the proposed restoration schemes.