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
gorge, should stop in the lower part of the canyon or should remain within the gully in the
settled area around station km 1.4.
On the one hand, the powder part of the avalanche should be separated from the dense layer
(Issler, 1999) to retard the current, on the other hand, the suspension layer is expected to
decelerate by turbulences when passing the dams.
The most effective construction suggested is a dam, which is permeable in its middle part so
that the clearance keeps open as long as possible. Both dams are 20 m high and have an
inclination on the upper side of 60°. The construction in the centre of the dams consists of 5
walls made of reinforced concrete which divide the section into 4 gaps each 4 m wide. On
both flanks, earth dams close the cross section of the gorge. In the original concept both dams
are of the same type.
Figure 2 Braking dam at station km 1.7 (photo: Gwercher/WLV Innsbruck 2007).
This complex structure of the braking dams should cause different effects on the avalanche.
Due to the gaps the centre of the avalanche should be prevented running up the upstream dam
slope. During passing the 4 gaps the dense layer should become slower because of higher
friction by splitting up into 4 parts (Kern and others, 2004). Both lateral earth dams should
stop the dense layer at the flanks and cause a run up. Such different flow behaviour should
increase the internal friction of the avalanche.
The different permeability of the cross section is expected to create higher turbulence in the
lower part of the suspension layer. Due to the effects on the dense layer, the separation of the
two layers is supposed. Both higher turbulence and loss of the matrix should weaken the
suspension before it reaches the settlement (Isssler, 1999).
64 A new avalanche braking system in the Mühlauer-Klamm