International Symposium on Mitigative Measures against Snow ...

<strong>International</strong> <strong>Symposium</strong> on Mitigative Measures against Snow Avalanches
Egilsstaðir, Iceland, March 11–14, 2008
In the end, we expect that the impact of the jet stream below the dams cause considerable
energy dissipation. Heuberger (1952) also describes that downstream the constriction at
station km 1.9 no powder avalanche effect could be observed. Another evidence that our
theory is working, is reported by Skolaut (1997) from the WLV in Salzburg where a torrent
braking measure of similar construction stopped a powder snow avalanche. Now our district
bureau in Innsbruck tries to confirm the theory in cooperation with the BFW in Innsbruck by
water tank experiments at the University of Innsbruck. The simulations with FIRE (Schaffhauser,
1997) and SAMOS AT (Herbert and others, 2007) support the expected effects of the
concept. Based on the work of Kristín Martha Hákonardóttir and others (2001) we changed the
shape of the avalanche braking structure in km 2.2.
Figure 3 Plan view of the braking structure at station km 2.2 (Pittracher/WLV. 2007).
According to the proven effect of mounds in the run out of avalanches (Hákonardóttir and
others, 2003) we decided to build a construction which closes 50 % of the cross section of the
canyon at station km 2.2. Built of concrete a 20 m high wall propped up by an earth dam at
the downstream side closes the left side of the gorge completely. Based on the result of 3
numerical simulations with 3 avalanche of different size by SAMOS AT (Herbert and others,
2007) we decided to apply to the authorities for the approval to build the upper braking construction
as a mound. All three avalanche scenarios show that the mound in km 2.2 reduces
the speed of the avalanche significantly.
Manfred Pittracher 65