Inter-Basin groundwater flow in West-Central Florida

Abstract

The mean annual values of inter-basin groundwater flow (IGF) for 172 watersheds in west-central Florida were estimated using the Integrated Northern Tampa Bay (INTB) model, which is an application of the Integrated Hydrologic Model dynamically coupling HSPF and MODFLOW. The estimated IGF for the scenario without human fluxes shows spatial heterogeneity in the model domain ranging from −1291 mm/year to 4808 mm/year, and the variability of IGF decreases with increasing spatial scales. A region with gaining IGF is defined as groundwater importer and a region with losing IGF is defined as a groundwater exporter. The characteristics of IGF are dominated by hydrogeology: 1) The subregion with unconfined Upper Floridan Aquifer (UFA), where runoff essentially occurs through the groundwater system by point discharge through springs and by diffuse discharge, serves as a groundwater importer; 2) The subregions with confined UFA are dominated by IGF exporters, particularly the subregion with large local recharge; and 3) Both IGF importers and exporters exist in the subregion with semi-confined UFA, but the watersheds near the Hillsborough River tend to be IGF importers. IGF plays a major role in the mean annual water balance at the watershed scale by modulating the available water for partitioning. The mean annual precipitation in the study watersheds varies from 1180 to 1495 mm/year, while the available water has a wider range from 80 to 6198 mm/year. Moreover, the climate aridity index ranges from 0.94 to 1.18, but the watershed aridity index exhibits enhanced variability, ranging from 0.23 to 2.07, due to existence of IGF. Human activities are also found to affect available water directly since human flux is a component of available water and indirectly since IGF is affected by human flux, which counteracts the impact of groundwater pumping on available water in watersheds.