EG31: Underwater ERT method to image Karst cave distribution below the river water

Electrical resistivity tomography (ERT) was employed to locate potential karst cave areas beneath rivers. This study set up six 700-meter-long ERT survey lines across the East River. Using the specially designed 200-meter underwater cable with 5-meter electrode spacing, a pole-dipole electrode configuration was utilized to conduct observations of the underground structures. The inverted resistivity profiles revealed high-resistance anomalies in the surface layer and bedrock which were interpreted to be gravel, pebble, and limestone. Meanwhile, they delineated the spatial distribution of low-resistance anomalies such as sandstone and conglomerate. Deploying electrodes in water to observe underground resistivity structures is highly challenging, nevertheless it will provide guidance significant for subsequent underwater geological structure imaging.