Braking Mounds in Avalanche Simulations - A Samosat Case Study.

132-138

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200204828

ABSTRACT: The town of Innsbruck is characterised by the mountain range ‘Nordkette’, which comprises some major avalanche tracks. The Arzler-Alm avalanche, reached the district of M¨uhlau in 1935. Since then, several generations of defence structures, such as braking mounds, as well as deflection and retention dams have been built. Several well-documented avalanche events allowed observing the effectiveness of the braking mounds in the Arzler-Alm run-out zone. On the 21 January 2018 the Arzler-Alm avalanche released, nearly reaching the retention dam at the bottom of the run-out zone (1000m a.s.l.). During the descent, the avalanche partly overflowed several braking mounds, located in the avalanche path and the run-out zone. These structures affected the avalanche flow. Aerial photographs were taken from manned and unmanned platforms over the release area and the deposition on 24 January 2018. They were used to map the affected area, thus providing a basis for the evaluation of the effectiveness of these defence structures and representing a well-documented case study for the simulation of dense snow avalanches and their interaction with defence structures. Back calculations of the avalanche event were performed with SamosAT, considering the defence structures in different ways: a) braking mounds represented as part of the natural terrain by including a DTM with high spatial resolution (1m ground sampling distance); b) areas with higher artificial resistance represent the braking mounds in the simulations. The simulations were compared to a reference simulation, where defence structures were omitted. Both investigated methods showed an influence on flow patterns and led to reduced avalanche velocities in the area next to the Arzler-Alm hut, compared to the reference simulation.
Keywords: avalanche simulation, defence structures, braking mounds