GPR INVESTIGATIONS OF BURIED KARST FEATURES ALONG THE WITHLACOOCHEE RIVER, GEORGIA, USA

Ground-penetrating radar (GPR) investigations in the Georgia Coastal Plain along the Withlacoochee River show buried karst features which have implications for groundwater and surface water hydrology as well as local landscape history. The river interacts directly with the Upper Floridan aquifer in the reaches studied. It frequently "disappears" into subsurface caverns, and it also receives inputs from small ponds and "bays" which in turn receive spring and seep groundwater inputs. Investigations using a Malå 100 MHz GPR system have identified karst topography at the "top of rock" at depths ranging from 3-10 m beneath sandy surficial deposits. By collecting GPR data on a 1 x 1 m grid from an area of 3700 square meters in the floor of one large depression, deeply buried fissures and sinkholes have been identified which in turn connect this feature's hydrology with the underlying Upper Floridan aquifer. Somewhat smaller scale karst topography has also been mapped beneath an alluvial terrace in linear transects along the banks of the Withlacoochee River itself. ArcGIS was used to develop a three dimensional model using kinks in the GPR traces that result from strong contrasts in dielectric potential at the top of limestone rock. A GIS database on the cave systems within the Upper Floridan aquifer is also being tapped to examine regional relationships between those caves and the Withlacoochee River channel, floodplain, and buried karst features.