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Open AccessArticle

2D Runout Modelling of Hillslope Debris Flows, Based on Well-Documented Events in Switzerland

1
geo7 AG, 3012 Bern, Switzerland
2
Swiss Federal Institute WSL, 8903 Birmensdorf, Switzerland
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Institute of Mountain Risk Engineering, University of Natural Resources and Life Sciences, 1190 Vienna, Austria
*
Author to whom correspondence should be addressed.
Geosciences 2020, 10(2), 70; https://doi.org/10.3390/geosciences10020070
Received: 20 December 2019 / Revised: 7 February 2020 / Accepted: 10 February 2020 / Published: 14 February 2020
(This article belongs to the Special Issue Numerical Modeling of Surface Processes)
In mountain areas, mass movements, such as hillslope debris flows, pose a serious threat to people and infrastructure, although size and runout distances are often smaller than those of debris avalanches or in-channel-based processes like debris floods or debris flows. Hillslope debris-flow events can be regarded as a unique process that generally can be observed at steep slopes. The delimitation of endangered areas and the implementation of protective measures are therefore an important instrument within the framework of a risk analysis, especially in the densely populated area of the alpine region. Here, two-dimensional runout prediction methods are helpful tools in estimating possible travel lengths and affected areas. However, not many studies focus on 2D runout estimations specifically for hillslope debris-flow processes. Based on data from 19 well-documented hillslope debris-flow events in Switzerland, we performed a systematic evaluation of runout simulations conducted with the software Rapid Mass Movement Simulation: Debris Flow (RAMMS DF)—a program originally developed for runout estimation of debris flows and snow avalanches. RAMMS offers the possibility to use a conventional Voellmy-type shear stress approach to describe the flow resistance as well as to consider cohesive interaction as it occurs in the core of dense flows with low shear rates, like we also expect for hillslope debris-flow processes. The results of our study show a correlation between the back-calculated dry Coulomb friction parameters and the percentage of clay content of the mobilised soils. Considering cohesive interaction, the performance of all simulations was improved in terms of reducing the overestimation of the observed deposition areas. However, the results also indicate that the parameter which accounts for cohesive interaction can neither be related to soil physical properties nor to different saturation conditions. View Full-Text
Keywords: hillslope debris flow; RAMMS; 2D runout simulation; cohesive interaction; Switzerland hillslope debris flow; RAMMS; 2D runout simulation; cohesive interaction; Switzerland
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Zimmermann, F.; McArdell, B.W.; Rickli, C.; Scheidl, C. 2D Runout Modelling of Hillslope Debris Flows, Based on Well-Documented Events in Switzerland. Geosciences 2020, 10, 70.

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