Numerical Calculation of Snow Avalanche Runout Distances

Abstract

Snow avalanches threaten villages, roads and railways in most mountainous regions in the world. The extreme avalanche winters of 1951 and 1999 in Switzerland clearly demonstrated the importance of avalanche dynamics calculations, in preparing hazard maps for snow avalanches. Today’s hazard mitigation strategies rely both on practical experience and avalanche dynamics models that predict snow avalanche descent paths, runout distances and impact pressures. This paper discusses the practical difficulties of applying a multidimensional numerical analysis tool to predict snow avalanche runout distances. The tool is embedded in a Geographical Information System (GIS) to simplify the specification of input and to help the interpretation of numerical results. Essential for an accurate prediction of avalanche runout is not only the flow friction, but also the specification of the initial release conditions – the fracture height and area. These are semi-automatically generated with the help of the GIS system. An advanced TVD numerical finite difference scheme then solves the differential equations that govern dense snow avalanche flow in general terrain. The primary results are pressure maps that define runout distances and the extent of avalanche danger. Two example calculations are presented. The first is an application of a single avalanche track where different combinations of release zones are discussed. The second example analyses the usefulness of protective forests to reduce avalanche runout distances over a large area.