Abstract

Water repellency (WR) might affect the spatial and temporal dynamics of a wetting front during infiltration and redistribution in a way that is difficult to predict with standard approaches. Therefore, the objectives of this study were to simulate the wetting plume geometry with a three-dimensional numerical model and to test whether electrical resistivity tomography (ERT) is able to illustrate the geometry under highly dynamic conditions. At our study site under agricultural use (Gleyic Podzol, groundwater affected), persistent WR in the subsoil to the 120-cm depth was responsible for a conical plume geometry observed after ponded tracer application with Brilliant Blue (BB) and bromide. The process was invasively observed with hydraulic sensors. At the same time, ERT was used to monitor a second ponded infiltration event under equal boundary conditions at the same site. Numerical simulation of the process showed that hysteresis in the water retention curve is needed to describe the specific infiltration plume geometry correctly. The main wetting function was derived from scaling the main drying curve with measured contact angle data. A comparison of wetting front arrival times among the hydraulic model, sensors, and independent ERT observations indicates an overall good agreement and shows the usefulness of ERT measurements under highly dynamic in situ conditions. Our results confirm the need to include strong hysteresis effects scaled with independent contact angle data when simulating infiltration dynamics in a water repellent soil to avoid an underestimation of the wetting front arrival.

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