Mapping Buried Karst Features with Capacitive-Coupled Resistivity System (CCR) and Ground Penetrating Radar (GPR)

Surface near karst features in catchment areas of drinking water abstraction points are possible hotspots for groundwater contamination. In karst areas with absent or patchy cover sediments, karst features can be mapped with traditional techniques or by image processing of satellite images or aerial photographs. Karst features which are buried below thin soil or sediment cover may not necessarily be identified with these techniques. In a karst area in western Germany, geophysical surveys have been tested to identify karst features below a relatively thin soil cover, which have been refilled for agricultural purposes. Resistivity measurements (OhmMapper) and ground penetrating radar (GPR) have been applied on a site, where the presence of karst features (dolines) is historically proven. The results of the OhmMapper survey show distinct distribution of resistivity for those transects where high resistivity is interpreted as limestone and low resistivity is interpreted as soil, sediments and filled dolines. The results of the GPR survey are weak, and the structures of the filled dolines are not clearly represented by the GPR logs. This is probably due to the wet hydrological conditions during the measurement campaign. Capacitive-coupled resistivity measurement (CCR) is a suitable technique to identify surface near buried karst features. The CCR measurement can therefore be a useful supplement during the delineation of groundwater protection areas in karst areas where buried karst features are supposed.