A fully coupled hydrogeophysical inversion strategy for the calibration of groundwater models using geophysical data

The scarcity of direct hydrogeological data, such as hydraulic levels measured in boreholes, is an important limitation for the calibration of groundwater models. By using geophysical data it is possible to use additional datasets to inform hydrogeological models. However, it has been observed that the use of indirect geophysical-derived data has practical limitations derived from the characteristics of the stand-alone geophysical inversion and the selection and application of the petrophysical relationships. A proposed way forward is the use of fully coupled modelling and inversion strategy where both problems are solved simultaneously finding better correspondence in the resolved distribution of geological properties. In this work we present a fully coupled and inversion strategy implemented using PEST and COMSOL Multiphysics. Following this approach it is possible to calibrate a groundwater model with multiple hydrogeological and geophysical datasets, such as from electromagnetic or gravity surveys. As an example we apply the methodology for the calibration of an heterogeneous coastal aquifer with a saltwater intrusion problem using electrical resistivity data.