INTEGRATING DIFFERENTIAL ELECTRICAL RESISTIVITY TOMOGRAPHY AND TIME DOMAIN REFLECTOMETRY AS A TOOL FOR MODELING SOIL MOISTURE AND INFILTRATION IN SINKHOLES

Sinkholes are evidence of a hydrologic connection between the surface and the subsurface in karst settings. Understanding how sinkholes function to control infiltration in a karst system is both important and challenging, though little work has been done to quantify this. To address this knowledge gap, we are working towards building a quantitative model of soil moisture, infiltration and recharge in thickly mantled sinkholes using innovative combinations of geophysical, hydrologic, and soil science methods.

At an instrumented sinkhole field site in southwestern Virginia, we are using Differential Electrical Resistivity Tomography (DERT) to monitor changes in resistivity values in sinkhole transects over time. Calibrated Time Domain Reflectometry (TDR) readings are also being used to measure soil moisture values over time. Preliminary results show that DERT can clearly model variations in soil resistivity as a result of slow summer drying events as well as rapid infiltration during recharge events. TDR readings show similar patterns of variation. Current work is focusing on correlating calibrated one-dimensional TDR moisture data and physical soil parameters with corresponding 2-D ERT data. If this calibration is successful, we will be able to create 2-D models of soil moisture which, when analyzed over time, will support building a model of infiltration volumes and rates and recharge to the underlying aquifer.