SSF SUBSURFACE CONTROLS: Non-invasive identification and characterization of the subsurface structures and their control on SSF processes

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The spatial heterogeneity of the hydrologically relevant soil parameters is one of the major challenges on the way towards a comprehensive understanding of SSF. It starts from the first ideas on the flow processes and proceeds to the numerical simulation of the flow and transport processes which are finally needed for a quantitative prediction of SSF. This heterogeneity involves not only a variability of the parameter values over several orders of magnitude, but also strongly organized patterns.The project addresses the current limitations in linking the experimental identification of subsurface structures to their numerical parameterization as required by numerical models working at larger scales. The central hypothesis is that the heterogeneous, but strongly organized subsurface structures play a key role in understanding SSF. This hypothesis is reflected in the following research questions:(1) What is the geo-pedological setting of the experimental sites? (2) Which role do the small-scale heterogeneity and the related patterns of the soil play for the occurrence of SSF? (3) To what extent can the small-scale heterogeneity of the soil be mapped using non-invasive methods?(4) Can we effectively generalize the information about the local soil heterogeneity to the catchment scale towards an improved catchment-scale prediction of the runoff processes?The project combines experimental, theoretical and numerical work. While classical soil mapping will be the starting point, focus will be on subsurface exploration by non-invasive geophysical methods. Several methods (in particular, electrical resistivity tomography, electromagnetic induction methods, and ground-penetrating radar) will be applied. The measurements will involve both static explorations of all experimental sites and time-lapse measurements in order to detect preferential flow patterns. As a final step, an operational framework capable of accounting for such multi-source information will be developed, supported by emerging theoretical concepts for up-scaling the physical parameters to the catchment-larger domain.