An Approach to Modeling Multi-Aquifer Groundwater Interaction in Sinkhole Features in Central Florida

Naturally occurring sinkholes are a common geologic feature in karst regions of central Florida, where they provide a primary pathway for interaction of shallow and deeper groundwater. Ponds and lakes form in many of these circular depressions.  Of particular importance is an understanding of the degree of hydraulic communication developed between the upper and lower hydrostratigraphic units. The sinkhole lake system poses significant challenges to accurately simulate their behavior in a multi-aquifer flow system.

At the study area, the conceptual site model (CSM) suggests groundwater flow in the Surficial Aquifer System (SAS) is towards the sinkhole lake and that the potential exists for downward flow within the sinkhole. Recharge to the Upper Floridan Aquifer (UFA) system is from vertical seepage through the Hawthorn Confining Unit (HCU). The sinkhole lake and the associated multi-aquifer sinkhole system were simulated with varying hydraulic conductivity zones consistent with observed hydrogeological characteristics.

Simulated water levels from the model indicate variable groundwater flow towards and away from the sinkhole area with depth depending on the simulated hydrogeologic unit.  The observance of groundwater flow away from the sinkhole area in the UFA indicates direct recharge through the HCU from the SAS.  Because of the detailed representation of the multi-aquifer sinkhole feature, the model has been shown to accurately represent the groundwater flow dynamics around the sinkhole system and provides a more detailed understanding of the CSM.