Geophysical Monitoring of the Southwest Florida Coast

Water management decisions that impact Everglades restoration efforts require high quality data and reliable hydrologic models. Traditionally these data for hydrologic models have been obtained through observation wells. In the Everglades, this approach is limited by the difficult access due to water which covers most of the area and to the limited number of roads. Airborne geophysical techniques provide a means of accessing large parcels of land and developing three-dimensional resistivity models of the area.

The overall objective of this project is the collection of geophysical data that can be used to develop ground-water flow models of the area capable of modeling saltwater intrusion. This objective includes mapping of subsurface electrical properties of the aquifer and correlation of lateral variation in these properties to aspects of aquifer geometry and water quality that are pertinent to hydrologic model development.

Completion of combined ground and airborne geophysical surveys in Everglades National Park and Big Cypress National Preserve has shown the utility of these methods to map saltwater intrusion and provide geological information needed to develop ground-water flow models. The strategy that has been used is to interpret the HEM data as layered-earth resistivity models that slowly vary from place to place. Surface geophysical measurements (time-domain electromagnetic soundings) have been used to assist in this interpretation and provide an independent check on the HEM data. Borehole data in the form of formation resistivities and water quality sampling have allowed us to develop relationships for converting the interpreted resistivity-depth models into estimated water quality given as specific conductance (SC) or chloride concentration. This information is of great value to hydrologic modelers.

These data will be used to develop a ground-water flow model which is bounded on the north by the Tamiami Trail, on the south by Florida Bay, on the east by the Atlantic coastal ridge, and on the west by the Gulf of Mexico.