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
Snow drift measures as protection against snow avalanches in
Iceland
Kristín Martha Hákonardóttir 1* , Stefan Margreth 2 , Gunnar Guðni Tómasson 4 , Hallgrímur
Daði Indriðason 1 and Skúli Þórðarson 3
1 VST Consulting Engineers Ltd., Ármúli 4, IS-104 Reykjavík, ICELAND
2 WSL. Institut fur Schnee- und Lawinenforschung, Fluelastr. 11, CH-7260 Davos Dorf, SWITZERLAND
3 Vegsýn, Reykjavíkurvegur 60, 220 Hafnarfjörður, ICELAND
4 Reykjavík University, Kringlan 1, 103 Reykjavík, ICELAND
*Corresponding author, e-mail: kmh (at) vst.is
ABSTRACT
Snow drift measures have been proposed as a part of a protection plan above the avalanche
prone Urðir area in Patreksfjörður in western Iceland. The appraisal study was conducted by
VST Consulting engineers Ltd. in co-operation with a specialist on snow drift measures at the
SLF in Switzerland. Snow drift is the main reason for snow accumulation in starting zones of
avalanches in the area and the break up of cornices is known to have initiated some of the
largest avalanches in the area. The flat mountain plateau above Patreksfjörður, coupled with
the local weather conditions lead to feasible conditions for the construction of snow fences in
order to reduce snow drift into the avalanche starting zone below the mountain plateau. Wind
baffles at the edge of the plateau are additionally proposed to prevent the formation of large
continuous cornices in the cliffs above the starting zone. High wind speeds on mountaintops
in Iceland pose a problem to the design of the structures. The snow drift measures are
considered to be extremely valuable to additionally reduce the avalanche risk in the complex
situation of constructing suitable protection dams in the Urðir area. Snow drift measures have
not yet been built as integrative avalanche protections above inhabited areas in Iceland and
experience on optimal design and durability is thus lacking.
1. INTRODUCTION
The avalanche situation in the Urðir area above Patreksfjörður is severe. The risk associated
with the avalanche path is one of the highest of such paths in Iceland creating an
approximately 200 m wide gap in the village where the older part is to the east and a newer
residential area to the west of the path. Residential houses have been built increasingly closer
to the avalanche path and the mountainside making it hard and complicated to protect the area
sufficiently with dams. The plateau above the mountain acts as a large catchment area for
snow drift which accumulates in the starting zone below the plateau. The conditions at the
mountaintop are favourable for constructing snow fences to prevent snow from drifting into
the starting zone.
Snow drift measures have not been built in Iceland yet as snow avalanche defence measures
above inhabited areas, they are however widely used as such elsewhere, e.g. in the Alps. The
climatic conditions in Iceland differ somewhat from the Alps, especially regarding higher
wind speeds on mountain tops. The high wind speeds could pose problems to durability and
effectiveness of the structures.
Hákonardóttir, Margreth, Tómasson, Indriðason and Þórðarson 85