GROUNDBREAKING CHARACTERIZATION OF THE KARSTIFIED FLORIDAN AQUIFER IN THE WOODVILLE KARST PLAIN OF NORTH FLORIDA

A comprehensive effort to study the mechanics of karst aquifers is underway in the Woodville Karst Plain (WKP) of North Florida that combines detailed quantitative groundwater tracing and real-time data from a network of in-cave underwater hydrologic meters. Quantitative groundwater tracing experiments have successfully delineated flow paths that connect the two largest underwater cave systems in the basin, which constitute more than 40 km of individual conduits that average 10-80 m in diameter, and the large disappearing streams to Wakulla spring, which discharges approximately 15 m3/s on average. Tracer breakthrough curves have established minimum through-conduit groundwater velocities of between 800 and 6000 m/day which equate to travel-times (age) of one component of spring discharge to be about 10 days. Other hydraulic parameters such as dispersion coefficients and a Reynolds numbers have also been resolved from the breakthrough curves.

Seven in-cave meters have been installed at locations within the largest underwater cave in the basin, Wakulla Cave, up to 1,500 m from the cave entrance at Wakulla Spring. The meters are recording velocity, converted to flow with cross-sectional measurements of the conduits made by research divers, temperature, and conductivity, at 15 minute intervals. The data clearly identify three sources of the water discharging at Wakulla spring, one or more disappearing streams, and two separate sources of groundwater that differ significantly in temperature indicating different circulation depths. Both the flow and temperature data also display a diurnal signal roughly correlate to tidal measurements in the Gulf of Mexico, approximately 16 km to the south.

Both the tracing and meter data have significantly improved our understanding of flow patterns in the WKP and raised significant awareness about the critical need for improved groundwater protection efforts in the karst regions of Florida. The data is now being used to construct and calibrate new numerical and statistical models of flow through the karst basin, which will provide a valuable planning tool for ensuing protection efforts. Further details about both the tracing and meter data are available at www.hazlett-kincaid.com/FGS.