DOLINE AND AQUIFER CHARACTERISTICS WITHIN HERNANDO, PASCO, & NORTHERN HILLSBOROUGH COUNTIES, FLORIDA
The Upper Floridan aquifer is a limestone and dolomite aquifer approximately 300 meters to 450 meters thick, containing numerous sinkhole and karst features. Water supplies in the area are provided almost exclusively by the Upper Floridan aquifer. Hydraulic conductivities in the aquifer may vary by three orders of magnitude in the study area. The aquifer has been extensively subjected to karst activity, and the intensity of this activity is controlled largely by the distance of the aquifer from land surface, and the thickness and continuity of the clay confining unit overlying the Upper Floridan.
Using depression data derived from U.S. Geological Survey (USGS) maps, doline densities (DD) were calculated over the study area, and doline-area ratios (RD) were generated and compiled by county, physiographic province, and model-derived Kx zones. Results from these analyses indicate that areas of high DD coincide with northern portions of the study area where aquifer confinement is poor. Values of RD calculated by county also support the observation of increased karst activity in the north. Of particular significance, however, are the results indicating a positive linear correlation between RD and model-derived values of Kx (r2=0.97). These results may provide a useful technique for ground-water modelers to estimate regional-scale values of hydraulic conductivity or other hydraulic properties.