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
two 100 m long and 10 m high earth filled deflecting dams which form a wedge shaped
structure directly above the facility (figure 2). The front of the wedge (the “bow”) is steep
over a 50 m long section but the rest of the dams is built with rock fill and a conventional
slope of the fill material used. Construction of the steep part of the dams was completed in
1998 and the complete structure in 2002.
Figure 2 Deflecting dams in Engidalur, Ísafjörður. The dams form a wedge shaped
structure (photos: Hallgrímur D. Indriðason).
The dams have repeatedly been hit by avalanches from Kirkjubólshlíð. The first one fell in
February 1999 prior to the full completion of the dams, followed by avalanches in: April
2001, January 2004, January 2005 and March 2007. The dams have on all occasions
prevented accidents to employees and damages to the facility (IMO, 2003; Arnalds and
others, 2007; IMO, 2005).
4.3 Neskaupstaður
4.3.1 Drangagil area
The town of Neskaupstaður is located in the east fjords of Iceland. A large part of the
residential area is threatened by avalanches from several well defined avalanche paths.
Preparation for the construction of avalanche defences in the Drangagil area was initiated in
1997. Defence structures in the Drangagil area are of three types: 1) Supporting structures, 2)
braking mounds and 3) a catching dam. The supporting structures are located in the starting
zone of Drangagil and include approximately 1000 m of 3.5−4.0 m high avalanche nets. The
braking mounds are positioned in two rows above the residential area, a total of 13 mounds
(Tómasson and others, 1998a). The mounds have a steep front facing the mountain, are 10 m
high and each mound is approximately 10−12 m wide at the top. The 400 m long catching
dam is located at a distance of 100 m from the residential area. The dam is 17 m high with a
steep front facing the mountain (see figure 3). The total volume of earth fill comprising the
catching dam and the braking mounds is approximately 260,000 m 3 . The steep dam fronts
facing the mountain are built with earth reinforcement system made of steel. The avalanche
defences were inducted in 2002.
4.4 Tröllagil area
The most extensive appraisal study yet, carried out by VST, is a proposal for the Tröllagilarea
in Neskaupstaður, which was completed in 2003 (Sigurðsson and others, 2003). Following
construction of avalanche defences in the Drangagil area in Neskaupstaður, defence
options in the Tröllagil area (western most part of the residential area) were considered. Emp-
Indriðason, Sigurðsson, Tómasson and Hákonardóttir 127