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
The design of avalanche protection dams.
Recent practical and theoretical developments
Tómas Jóhannesson 1 *, Peter Gauer 2 , Karstein Lied 2 , Massimiliano Barbolini 3 , Ulrik Domaas 2 ,
Thierry Faug 4 , Kristín Martha Hákonardóttir 5 , Carl. B. Harbitz 2 , Dieter Issler 2 , Florence
Naaim 4 , Mohamed Naaim 4 and Lambert Rammer 6
1 Icelandic Meteorological Office, Bústaðavegi 9, IS-150 Reykjavík, ICELAND
2 Norwegian Geotechnical Institute, PO Box 3930 Ullevål Stadion, N-0806 Oslo, NORWAY
3 FLOW-ING s.r.l. Ingegneria per l'ambiente, P.za J.F. Kennedy 27, I-19124, La Spezia, ITALY
4 Cemagref, Division Erosion torrentielle, neige et avalanches, BP 76, F-38402 Saint Martin d’He`res, FRANCE
5 VST Consulting Engineers Ltd., Ármúli 4, IS-104 Reykjavík, ICELAND
6 Department of Natural Hazards and Alpine Timberline, Federal Research Centre for Forests, Natural Hazards
and Landscape, BFW, Rennweg 1, A-6020 Innsbruck, AUSTRIA
*Corresponding author, e-mail: tj (at) vedur.is
ABSTRACT
Recent experimental and theoretical studies of the flow of avalanches against obstructions
have been used, in combination with traditional design guidelines, to formulate recommendations
for the design of dams and other protection measures in the run-out zones of wet- and
dry-snow avalanches. These recommendations deal with the design height of dams, geometry
and layout of braking mounds and impact forces on walls and other obstacles. In addition,
laws and regulations regarding hazard zoning below avalanche protection measures in different
European countries are described. The main new features of this procedure to dimension
dams are:
• The dam design is based on a consistent dynamic description of the interaction of
shallow granular flow and an obstruction.
• Shock dynamics are used to derive run-up heights on dams, which determine the
design dam height under some conditions.
• The necessary dam height to prevent supercritical overflow is also used to derive runup
heights on dams, which determines the design-dam height under other conditions.
• A maximum allowable deflecting angle, derived from shock dynamics, limits the
range of possible deflecting angles of deflecting dams.
• Momentum loss in the impact with a dam is calculated from the component of the
velocity normal to the dam in the same way for both catching and deflecting dams.
• Avalanche flow along deflecting dams becomes canalised, which may lead to a
substantial increase in run-out in the direction of the canalised flow.
• A consistent dynamic framework makes it possible to account for the slope of the
terrain where a dam is located and a curvature of the dam axis in the dam design.
1. INTRODUCTION
Dams in the run-out areas of snow avalanches are widely used as protection measure against wet-
and dry-snow avalanches (Figure 1). Several methods have been used to design avalanche dams,
based either on simple point mass considerations, widely used in Alpine countries, a description
of the dynamics of the leading edge of the avalanche or on numerical computations of the
200 The design of avalanche protection dams