Coupled Hydrogeophysical Inversion for Top Soil Hydraulic Properties Using Electrical Resistivity Tomography

Accurate determination of soil hydraulic properties is essential for understanding subsurface flow and transport processes which can help mitigate soil and groundwater pollution.For a borehole infiltration experiment, it is numerically demonstrated in this study that surface Electrical resistivity tomography(ERT) contains enough information to physically constrain the inversion for top soil Mualem-Van Genuchten parameters provided there is a good knowledge of the soil petrophysics. This was achieved by coupling a forward geoelectric model to a vadose borehole infiltration model based on 2D axisymetric Richard's equation with the use of a suitable petrophyical relationship like the the Archie's law.The simulated water content is converted to bulk electrical resistivity of the soil using Archie's law.The simulated bulk electrical resistivity is then converted to simulated ERT-data(electrical transfer resistances) using the foward geophysical model based on the Poisson equation.The misfit between the simulated and measured ERT-Data is evaluated.The hydraulic parameters are perturbed and the whole process is repeated until a close fit is found between the measured and the simulated ERT-data.The uniqueness of the parameter estimates are improved when both ERT and Infiltration are used within this hydrogeophysical inversion framework.