Soil water content monitoring on a dike model using electrical resistivity tomography

We explore the viability of electrical resistivity tomography (ERT) to quantify soil water content in a full-scale dike model. While ERT is an established method to detect changes in soil water content, the retrieval of two-dimensional water content distributions from surface-based surveys is a much more challenging application. We conducted a series of experiments on a full-scale dike model comprising rainfall and flooding events. The dike was surveyed with an ERT line down the land-side slope and monitored with permanently installed spatial time-domain reflectometry (TDR) cables for comparison. Water content changes were calculated by applying Archie’s equation and agreed well with comparison measurements from spatial TDR measurements. The saturation exponent in Archie’s equation was estimated by combining spatial TDR and ERT measurements and agreed well with literature data of comparable sands. The choice of the inversion type, e.g., time-lapse inversion or least-squares versus robust constraint, as well as the influence of inversion parameters, such as regularization and the choice of convergence criterion, is discussed in the context of an apparent inversion artefact for the rainfall experiment, using forward modelling of synthetic data sets. The results indicate that ERT may be a feasible method to quantify water content changes under certain conditions, provided an initial water content estimate is available. © 2011 EAG