CHARACTERIZING RAPID POINT-RECHARGE TO THE FLORIDAN AQUIFER IN THE WOODVILLE KARST PLAIN OF NORTH FLORIDA: IMPLICATIONS FOR PROTECTING WAKULLA SPRING

The Woodville Karst Plain (WKP) is a broad lowland that extends from just south of Tallahassee, Florida to the Gulf of Mexico, where the Floridan aquifer is either unconfined or poorly confined. Ground-water flow in the aquifer here is controlled by several large cinduits, 10-80 m in diameter and as much as 15 km long, that make up one of the largest flooded cave systems in the world. Water in these conduits discharges from springs, some 1st magnitude springs, such as Spring Creek and Wakulla springs that are the first and third largest springs in Florida. Protecting the aquifer and springs like these from contamination from surface sources has become a central focus for state and local authorities. A critical scientific aspect of those efforts is the characterization of flow paths and velocities for numerous disappearing streams in the basin.

Two quantitative groundwater tracing experiments have been conducted in the WKP to delineate flow paths and velocities from 2 of the 3 largest disappearing streams in the northwestern part of the basin: Fisher Creek and Black Creek, both tannic streams. In both experiments, relatively small masses of fluorescent dye (1-3 kg) were added to the flow of the disappearing streams during low-flow conditions. Automated sampling stations were established on the surface at numerous karst windows along the main mapped conduits. The results of the two tests confirmed some of the input locations of dark (tannic) water where center of mass travel-times were about 40 and 60 hours for flow paths of approximately 1.7 and 2.3 km respectively. Breakthrough curves at sinks and windows in the flow system have yielded information about hydraulic parameters including velocity, dispersion coefficient, and a Reynolds number. These parameters will enable predictions to be made about how surface water and contaminants enter the aquifer and affect the springs. Further information on the groundwater tracing experiments in the WKP is available at: www.hazlett-kincaid.com/FGS/.