Towards fully coupled finite element modelling of DC resistivity in complex seawater intrusion scenarios

Electrical geophysical techniques are increasingly utilized for delineation of seawater intrusion patterns in coastal aquifers. Geophysical data can be utilized in groundwater models for calibration and verification. In these models, geophysical signal is converted into hydraulic variables, and vice versa, using a petrophysical relationship. However, the use of separate numerical codes limits the applicability and is prone to conversion, interpolation or simulation errors, caused by the necessity of transfer of information between programmes. In-house software, on the contrary, has been used to perform coupled models, but are usually limited to synthetic and simple hydrogeological models. In this work we present a coupled modelling methodology, using a finite element code, which can be adapted to complex hydrogeological scenarios that can include heterogeneities, anisotropies, variable saturation or topographic effects. The approach overcomes limitations of back-forward mapping between codes as the petrophysical relationship is defined on a shared domain and accommodates spatially distributed parameters and state variables. As a result, both models are structurally coupled and solved at the same time in a single run. This is an important first step for the development of a coupled hydrogeophysical inversion procedure to be applied to real-world field studies in complex seawater intrusion scenarios.