Surface morphology and internal composition of large rockslide deposits have been frequently studied, but their hydrogeologic conditions and consequences for (drinking) water quality and quantity on such deposits are largely unknown. In this study we provide first information on this critical relationship for two large rockslide deposits in the Khumbu Himal (Nepal), which are at the same time the main settlement areas in the region. In the first step, we investigated the Lukla and the Namche-Khumjung rockslides with respect to their dimensions and internal composition based on orthophotos and digital elevation models, geomorphologic field mapping, and the analysis of rockslide outcrops. Secondly, we studied their hydrogeologic characteristics by means of spring water mapping, sampling and analyses. As a consequence of the fragmented and highly shattered rockslide material, both deposits are characterized by 1) effective infiltration, 2) short residence times of percolating water and 3) by only small amounts of available spring water and surface runoff at all. Human activity on the studied rockslide deposits can therefore be described as an ambivalent relationship: On the one hand, the rockslide deposits provide a gentle topography and the only available areas for extensive settlements and agriculture in the steep upper DudhKosi catchment; On the other hand, their internal composition accounts for water scarcity-a critical issue for the local population demanding for adaptation strategies, especially in the light of the ever-increasing trekking and expedition tourism in the region.

Glacially formed slopes in the Mondsee catchment close to Koppl, Austria, expose high hydrological dynamics after intense rainfall events. We use Electrical Resistivity Tomography (ERT) to identify the subsurface geological structure relevant for springs causing surface runoff during storm events at times of fully saturated soils. To identify the horizontal and vertical distribution of subsurface structures, we use 26 parallel ERT profile lines with 6m spacing, and 4m electrode spacing, over a total length of 88m. After 3D inversion, the electrical resistivity values in the generated model comprise 10 to 1132 Ωm. Sections with resistivity values between 10 and 100 Ωm, classified as water-saturated material, dominate the uppermost 3m of the model. Highest resistivity (>200 Ωm) materials are classified as moraine material, which forms the steepest part of the slope covered by a coppice belt. Linear features with lowest resistivity values show congruencies with streams from runoff modelling and crop-out of springs. Finally, the model enables the identification of aquifers and aquicludes relevant for further 3D hydrological modelling.