NHESS Natural Hazards and Earth System Sciences NHESS Nat. Hazards Earth Syst. Sci. 1684-9981 Copernicus Publications Göttingen, Germany 10.5194/nhess-14-2233-2014 Computational snow avalanche simulation in forested terrain Teich M. 2 1 Fischer J.-T. https://orcid.org/0000-0001-5179-6457 3 Feistl T. 4 1 Bebi P. 1 Christen M. 1 Grêt-Regamey A. 2 WSL Institute for Snow and Avalanche Research SLF, Flüelastrasse 11, 7260 Davos Dorf, Switzerland Planning of Landscape and Urban Systems PLUS, ETH Zurich, Stefano-Franscini-Platz 5, 8093 Zurich, Switzerland Austrian Research Centre for Forests – BFW, Department of Natural Hazards, Rennweg 1, 6020 Innsbruck, Austria Chair for Engineering Geology, Technical University Munich TUM, Arcisstrasse 21, 80333 Munich, Germany 27 08 2014 14 8 2233 2248 Copyright: © 2014 M. Teich et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://nhess.copernicus.org/articles/14/2233/2014/nhess-14-2233-2014.html The full text article is available as a PDF file from https://nhess.copernicus.org/articles/14/2233/2014/nhess-14-2233-2014.pdf

Two-dimensional avalanche simulation software operating in three-dimensional terrain is widely used for hazard zoning and engineering to predict runout distances and impact pressures of snow avalanche events. Mountain forests are an effective biological protection measure against avalanches; however, the protective capacity of forests to decelerate or even to stop avalanches that start within forested areas or directly above the treeline is seldom considered in this context. In particular, runout distances of small- to medium-scale avalanches are strongly influenced by the structural conditions of forests in the avalanche path. We present an evaluation and operationalization of a novel detrainment function implemented in the avalanche simulation software RAMMS for avalanche simulation in forested terrain. The new approach accounts for the effect of forests in the avalanche path by detraining mass, which leads to a deceleration and runout shortening of avalanches. The relationship is parameterized by the detrainment coefficient <i>K</i> [kg m<sup>−1</sup> s<sup>−2</sup>] accounting for differing forest characteristics. We varied <i>K</i> when simulating 40 well-documented small- to medium-scale avalanches, which were released in and ran through forests of the Swiss Alps. Analyzing and comparing observed and simulated runout distances statistically revealed values for <i>K</i> suitable to simulate the combined influence of four forest characteristics on avalanche runout: forest type, crown closure, vertical structure and surface cover, for example, values for <i>K</i> were higher for dense spruce and mixed spruce-beech forests compared to open larch forests at the upper treeline. Considering forest structural conditions within avalanche simulations will improve current applications for avalanche simulation tools in mountain forest and natural hazard management.

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