No abstract

<p>Perennial landslide dams interrupt the sediment connectivity of rivers. Although most landslide dams do not persist for more than a few days, those that do can exhibit significant sediment trapping capacity. While water can pass through or over the dam, the sediment load is trapped upstream of the dam until the dam breaks or gradually erodes, or is completely filled with deposits. The volume of sediment stored in this way can reach up to three times the volume of impounded water, as we find by back-analyzing the lake Hintersee<span lang="EN-GB"> in southeastern Germany</span>. In this work, we reconstruct the pre-landslide topography using Petrel and then use the Gerris shallow-water flow solver with a Voellmy rheology to back-analyze this landslide-dammed lake in the Bavarian Alps. We test several landslide release scenarios and different landslide rheologies to obtain the best-fitting reconstruction of the dam topography. We then fill the landslide dam with water and sediment using simple slope algorithms and validate the results against the current topography. Finally, we compare the landslide deposit thicknesses, water depths, and trapped sediment thicknesses of our different scenarios in order to provide new insight into the damming and sediment trapping capacity of landslides.</p>

<p><span xml:lang="EN-US" data-contrast="none"><span>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, </span></span><span xml:lang="EN-US" data-contrast="none"><span>the dams </span></span><span xml:lang="EN-US" data-contrast="none"><span>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 </span></span><span xml:lang="EN-US" data-contrast="none"><span>Hintersee</span></span><span xml:lang="EN-US" data-contrast="none"><span> lake in the </span></span><span xml:lang="EN-US" data-contrast="none"><span>Berchtesgadener</span></span><span xml:lang="EN-US" data-contrast="none"><span> Land</span></span><span xml:lang="EN-US" data-contrast="none"><span>, Germany, and aim to determine the sediment budget of the infilled lake and the dam</span></span><span xml:lang="EN-US" data-contrast="none"><span> duration </span></span><span xml:lang="EN-US" data-contrast="none"><span>before breaching. This landslide dam formed 3520 years BP from a rockslide of 15-18 x 10</span></span><sup><span xml:lang="EN-US" data-contrast="none"><span>6</span></span></sup><span xml:lang="EN-US" data-contrast="none"><span> m</span></span><sup><span xml:lang="EN-US" data-contrast="none"><span>3</span></span></sup><span xml:lang="EN-US" data-contrast="none"><span>. We propose to reproduce the formation of the </span></span><span xml:lang="EN-US" data-contrast="none"><span>Hintersee</span></span><span xml:lang="EN-US" data-contrast="none"><span> 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 </span></span><span xml:lang="EN-US" data-contrast="none"><span>Gerris</span></span><span xml:lang="EN-US" data-contrast="none"><span> shallow water flow solver to simulate the landslide runout and to recreate the landslide dam deposition characteristics from the different source topographies and several </span></span><span xml:lang="EN-US" data-contrast="none"><span>Voellmy</span></span><span xml:lang="EN-US" data-contrast="none"><span> </span></span><span xml:lang="EN-US" data-contrast="none"><span>rheologies</span></span><span xml:lang="EN-US" data-contrast="none"><span>. We </span></span><span xml:lang="EN-US" data-contrast="none"><span>choose</span></span><span xml:lang="EN-US" data-contrast="none"><span> the best-fitting scenario to assess </span></span><span xml:lang="EN-US" data-contrast="none"><span>a sediment budget of the </span></span><span xml:lang="EN-US" data-contrast="none"><span>Hintersee</span></span><span xml:lang="EN-US" data-contrast="none"><span> landslide-dammed lake.</span></span></p>