MODELING OF SUBMARINE GROUNDWATER DISCHARGE AT TURKEY POINT, FLORIDA

A hydrogeologic model of submarine groundwater discharge (SGD) at Turkey Point in Florida, located 60 km south of Tallahassee on the Gulf of Mexico, is presented. Installations at the site include 18 piezometers, the majority of which are located offshore. As part of a SGD intercomparison experiment in August 2000, an extensive set of seepage meter measurements were obtained. Estimates of SGD using seepage meters, for a zone that extends 200 m offshore, and 100 m along the beach, are in the range from 2300 - 3600 m3/day. These values are consistent with other estimates of SGD derived from radon-222 and radium isotope methods. Assuming a conceptual hydrogeologic model where the freshwater discharge originates as recharge in the local surficial aquifer, numerical simulations with a density-dependent flow model yield SGD estimates in the range from 10 - 200 m3/day, with the discharge occurring predominantly on the seepage face of the beach. The flux predicted in the zone where the seepage meters were primarily located is negligible. The hydrogeologic model has been extended to include leakage across the underlying Intracoastal Formation from the Upper Floridian aquifer, however, it has not been possible to simultaneously match the seepage meter discharge estimates and the sub-seabed salinity profiles. Work is continuing to understand this discrepancy between model-predicted discharge, and that measured by experiment.