THE EFFECTS OF SURFACE-WATER MANAGEMENT AND GROUNDWATER WITHDRAWALS ON SALTWATER INTRUSION IN THE KARST BISCAYNE AQUIFER, MIAMI-DADE COUNTY, FLORIDA, USA

Saltwater intrusion has been an issue in the Biscayne aquifer since the early 1930s as a result of low topographic relief, canal drainage, high aquifer permeability, and large groundwater withdrawals close to tidal rivers and canals. Groundwater levels in the Biscayne aquifer are managed using an extensive canal system cut into karst limestone that composes much of the aquifer and is designed to control urban flooding, supply recharge to municipal well fields, and control saltwater intrusion. Results from an integrated surface water/groundwater model of a 3,000 km² part of the Biscayne aquifer are presented to evaluate the combined effects of surface-water management and groundwater withdrawals on saltwater intrusion.

The Biscayne aquifer is discretized into a multi-layer model having a 500-m square horizontal grid spacing. All primary and secondary surface-water features in the active model domain are discretized into segments using the 500-m square horizontal grid. A 15-year period of time from 1996 to 2010 is simulated. The model includes 64 operable surface-water control structures, 127 municipal production wells, and spatially-distributed daily internal and external hydrologic stresses. Model simulations indicate that the canal system supplies a notable percentage of recharge to municipal well fields using historic and projected groundwater withdrawal rates, but management of the salinity control surface-water structures can effectively control saltwater intrusion resulting from groundwater withdrawals if projected increases in municipal well field withdrawals were to occur.