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
6.3 Braking system in the middle of the canyon
A third scenario is to increase friction within the long gorge and to stop the avalanche before
reaching the settlement (Fig. 1). In the centre part of the path between station km 2.3 and
station km 1.7, the longitudinal section has its lowest inclination (14°), as well as two
constrictions at km 2.2 and km 1.90. In this part of the canyon it would be most successful to
build 2 braking dams to increase the braking efficiency of the path. The cost of them comes to
EUR 5.340.000. This scenario would not affect the groundwater protection zone of Innsbruck,
because the construction sites would be situated far beneath the wells. The environmental
aspect is taken into account because the dam can only be seen from special locations in Innsbruck
and the size of the affected area is limited. The simulation with FIRE (Schaffhauser,
1997) and SAMOS AT (Herbert and others, 2007) confirm the expected significant influence
of both constructions on the impact of the avalanche in the settled area.
7. ASSESSMENT OF THE SCENARIOS
Table 2: Ranking of protection measures (Assessment scheme Vogl WLV/Innsbruck, 2007).
Comparison of versions
Categories with
weighting
Mühlauer-Klamm - avalanche
Remaining risk
Costs
Follow-up costs
Ecologie 1
Asssessment
Rank
Assessment
2
1
1
0 Variant Variant 1 Variant 2 Variant 3
no measurements supporting structures Deflecting dam Breaking system.
10 (5) 4 (2) 10 (5)
2
Szenarios
1 5 2
5 2 5
18 15 20 12
3 2 4 1
positive negative
1 2 3 4 5
Manfred Pittracher 63
4 (2)
4 3 2
Due to the assessment scenario 3, the braking system, came into consideration. This measure
is nearly as effective as defence structures to stabilize the snow cover, but is less expensive,
has no influence on the groundwater protection zone and hardly a consequence seen from the
environmental aspect.
8. DESCRIPTION OF THE BRAKING SYSTEM MÜHLAUER-KLAMM-
AVALANCHE
The braking effect of the gorge in the middle section will be enforced by the building of two
dams at its beginning and end. The upper dam (Fig. 3) should prevent the filling of the
braking section below by smaller avalanches and reduce the speed of the bigger ones. The
lower dam (Fig. 2) has to catch as much avalanche mass as possible, so that the dense layer is
separated from the suspension layer. Avalanches, which nevertheless go further down the
3
3