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
areas, roads and other places where more frequent avalanches are acceptable than around
settlements. The hazard mapping process for ski areas is in many ways different from e.g.
hazard mapping for settlements. Due to the proximity of avalanche starting zones to
constructions and ski-paths, smaller release areas and more frequent events in known
avalanche paths have to be considered. The primary result of exploratory simulations of small
to medium-size Icelandic avalanches is that they can be simulated with reasonable realism
with samosAT.
This approach is based on a classification of the release areas with respect to their physical
properties such as inclination, aspect and shape. The release areas are assigned a single
number referred to as the starting zone index and are thereby ranked by their likelihood of
releasing an avalanche with a comparatively large run-out. It is not the goal to fully automate
the hazard zoning process. The method is rather an attempt to provide some overview of the
avalanche conditions of the area under scope and establish a basis for further analysis.
3.3 Design of deflecting dams
The effects of deflecting dams can by assessed with two-dimensional avalanche models by
simulating the flow of an avalanche with given parameters using digital terrain model that
includes the structure of consideration and compare it to equivalent simulation on untouched
ground. The run-out index scale is useful to determine an appropriate design avalanche and to
simulate the performance of the structure as the events gradually become larger.
Figure 4 Distribution of 2D run-out indices around the opening of the Hnífsdalur-Bolungarvík
tunnel with (blue curves) and without (purple curves) the deflecting dam.
The extent of the January 2005 avalanche is shown as a red curve.
The samosAT has been run to constrain the design of a deflecting dam in relation to a construction
of a road tunnel connecting Hnífsdalur and Bolungarvík in the northwestern part of
Iceland. The planned location of one of the openings of the tunnel is in an area with well
known history of avalanches. An avalanche recorded in January 2005 was chosen as a
reference event. It reached the 2D run-out index 13 and has an estimated return period of
approximately 15 years.
Gíslason 167