MONITORING WATER INFILTRATION IN SHALLOW KARST FEATURES USING TIME-LAPSE ELECTRICAL RESISTIVITY SURVEYS WITH PERMANENTLY INSTALLED ELECTRODES

Understanding how water infiltrates and recharges subsurface aquifers is important for protecting groundwater resources. The water infiltration process is very complex, however, especially in karst areas where many surface karst features, such as sinkholes and sinking streams, provide different pathways connecting surface water to groundwater. In this study, we deploy time-lapse electrical resistivity surveys with permanently installed electrodes to monitor the water infiltration process in Royal Spring groundwater basin in central Kentucky.

In a typical electrical resistivity survey, electrodes are placed in the ground during the survey and retrieved after the survey. For this project, we build electrodes that can be installed and left in the field for a long period to improve data accuracy and reduce field work. The electrodes are made using 10-in. stainless steel rods that are tightly wrapped with 18 AWG copper wire and secured with room-temperature-vulcanizing silicone and 0.5-in. shrink tubing. The self-made electrodes were tested successfully to conduct surface 3-D surveys. Our next step will be to use these electrodes to establish two time-lapse electrical resistivity survey sites, one at a 1-m-diameter swallet and the other in a perched aquifer; both are at the Kentucky Horse Park in Royal Spring groundwater basin. At each site, the background resistivity will first be measured, and subsequent data acquisition will focus on various storms; surveys will be conducted before, during, and after the storms. We will use the survey data to calculate temporal changes in resistivity to better understand infiltration in various shallow karst features.