Combined Inversion of Land and Marine Electrical Resistivity Tomography for Submarine Groundwater Discharge and Saltwater Intrusion Characterization

Electrical resistivity tomography (ERT) is particularly suited for the characterization of saltwater intrusion and submarine freshwater discharge, given its sensitivity to the electrical conductivity of pore water. A comprehensive survey might combine land ERT collected during low tide and marine ERT acquired with lower sensitivity due to the presence of a seawater layer, most often, inverted separately. In this contribution, we propose a new methodology to jointly invert land and marine ERT acquired along a same profile, bringing them to a common situation at high tide. We first estimate the electrical resistivity distribution under the land profile. Then, we compute a corrected data set for land ERT, simulating a data set collected with the same level of water as the marine ERT. Finally, both land and marine ERT data sets are inverted jointly. We show that the approach allows to better image the freshwater/saltwater distribution across the shoreline.