Landslide dams acting as sediment traps: Example of the lake Hintersee, Berchtesgadener Land, south-eastern Germany

Landslide dams occur when a landslide deposits in the riverbed and stop the river flow, creating lakes. They act as big sediments traps that modify the sediment flux in the whole catchment. By changing the sediment load, the dams change the erosion rates upstream and downstream. Although most landslide-dammed lakes are ephemeral, some stay in place and disappear only when they have been filled with sediments. We study the Hintersee lake in the Berchtesgadener Land, Germany, and aim to determine the sediment budget of the infilled lake and the dam duration before breaching. This landslide dam formed 3520 years BP from a rockslide of 15-18 x 10⁶ m³. We propose to reproduce the formation of the Hintersee landslide dam and its infilling using different scenarios. We first use a 1 m resolution digital elevation model to rebuild the valley floor before the rockslide event, three different rockslide source areas and the landslide dam shape before fluvial incision. We apply the Gerris shallow water flow solver to simulate the landslide runout and to recreate the landslide dam deposition characteristics from the different source topographies and several Voellmy rheologies. We choose the best-fitting scenario to assess a sediment budget of the Hintersee landslide-dammed lake.