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
and utilisation of hazard zones, and preparation of provisional hazard zoning (Icelandic
Ministry for the Environment, 2000) which is under constant revision, the last one in 2007.
Extensive research on avalanches and protection measures and acquired experience of
structural design and constructions of avalanche defences has also lead to improvements in
the design of the defence structures (SATSIE, 2006).
2. DESIGN PROCESS
In Iceland local communities represent the buyer of avalanche defences. The bulk of the
financial contribution is originated from the Icelandic Avalanche and Landslide fund and
project management is carried out by the Government Construction Contracting Agency
(GCCA) (Framkvæmdasýsla ríkisins).
Avalanche hazard is assessed by the Icelandic Meteorological Office (IMO) prior to designing
avalanche protection and presented and attested by individual Hazard Zoning Committees.
Technical reports and hazard zoning maps are evidently the main input when designing
avalanche defences. Technical reports describe topographic and climatic conditions and
assessment on avalanche hazard based on model estimates.
The design process of avalanche protection measures can be divided into four stages: 1)
Appraisal study 2) Environmental impact assessment (EIA) 3) Technical design 4)
Construction and supervision.
Protection structures can have striking visual impact on towns and hillsides, leading to
negative discussion and criticism. Landscape architects have therefore increasingly been
involved in the design process at an early stage. This has often lead to successful integration
of defence structures into the environment in addition to creating attractive outdoor and
recreational areas for public use. The inhabitants involved should furthermore be kept
informed and involved at all stages of the design. Such successful integration along with the
added number of occasions when the protection dams have proven useful in deflecting or
controlling avalanches has helped to reduce negative criticism.
3. PROTECTION ALTERNATIVES
Avalanche protection structures are considered as a permanent control against avalanches,
preventing damage to residential properties as well as casualties or accidents. Supporting
structures are installed to support the snow pack in the starting zones. They are usually made
of steel. Two basic types include bridges (rigid steel barriers) and snow nets. Grounding
conditions and risk of rock fall are ruling factors when determining which type of supporting
structures should be selected. Deflecting dams are the most favorable type of protection
structures in the runout zone (McClung and Schaerer, 1993, SATSIE, 2006). Deflecting dams
are most frequently constructed as simple earth-fill dams with heights up to 20 m. The
steepness of the slopes is subject to the soil properties of the earth fill. Catching dams are
constructed perpendicular to avalanche paths and function as arresters (McClung and
Schaerer, 1993, SATSIE, 2006). Most catching dams are earth-fill dams and many are
designed with steep front constructed with the aid of earth reinforcement systems or concrete.
The dams have been built up to 20 m high. Braking mounds or retarders are located in
avalanche paths in order to dispatch the energy of the avalanche and reduce its speed
(Hakonardottir and others, 2003). The mounds have been built in staggered rows up to 10 m
Indriðason, Sigurðsson, Tómasson and Hákonardóttir 125