Snow avalanche hazard modelling of large areas using shallow water numerical methods and GIS

Snow avalanches threaten settlements and roads in steep mountainous areas. Hazard mitigation strategies apply numerical models in combination with GIS-based methods to determine run out distances and pressure maps of snow avalanches in three-dimensional terrain. The snow avalanche modelling system is usually applied to study single avalanche tracks. In this paper we investigate the application of a numerical modelling system for large area hazard analysis. We begin by briefly presenting the depth-averaged equations governing avalanche flow. Then, we describe the statistical and GIS-based methods that are applied to define the initial fracture depths and release areas for snow avalanche modelling. We discuss the calibration of the avalanche model friction coefficients for extreme avalanches in function of altitude, avalanche size and topography. Seven test sites with areas between 100 and 350 km2, that are well distributed over the different snow climates and elevation ranges of Switzerland, were used to calibrate the model by comparing the simulation results with historic avalanche events and existing avalanche hazard maps. We then show how the avalanche modelling system was applied over the mountainous region of Switzerland (25,000 km2) to delineate forests with protective function against avalanches.