Assessment of 3D geometry effects on 2D ERT data of a permanent monitoring system along a river embankment

Abstract

To permanently monitor a river embankment in Colorno, Italy, a customized electrical resistivity tomography (ERT) system was installed in November 2018. ERT data are measured twice a day to monitor the internal hydrogeological conditions of the embankment. In this paper, we present the initial assessment of site-specific 3D geometry effects on 2D ERT data measured with the monitoring system. Using average resistivity values of the levee material, 2D and 3D models of the embankment were reconstructed in RES2DMOD and RES3DMODx64. Apparent resistivity pseudosections were calculated for different profiles along the embankment and pseudosections of resistivity differences between 2D and 3D modellings were then calculated for all profiles. The results show that regardless of the lateral position, all measurements along the embankment are distorted by 3D effects, especially in deeper parts. For the smallest electrode spacings, the profile in the middle of the embankment measures data closer to real values. Our next research perspective is to use 3D field measurements and samples of the embankment to more precisely quantify the site-specific 3D effects. Considering that clay is one of the main materials used in constructing this embankment, we also plan to explore the 3D effects on 2D induced polarization (IP) measurements.