Avalanche hazard mapping using numerical Voellmy-Fluid models

Abstract

One- and two-dimensional numerical dense-snow avalanche dynamics models using a Voellmy-fluid constitutive flow law have been developed in Switzerland recently. In order to apply these models in practice, they have been embedded in a general Avalanche Hazard Mapping System. This system supports the preparation and specification of all necessary input, allows the choice between different simulation models, performs a detailed visualisation of the numerical results and generates the final avalanche hazard maps. Various avalanche events have been back-calculated using this system in order to identify the influence of the flow parameters, initial conditions and terrain undulations on predicted runout distances. The most important results of this system evaluation are stated in this paper. To illustrate the possibilities and limits of the numerical models, two examples are presented. The one-dimensional model is applied to a terrain terracing study in the Loetschental valley.. The two-dimensional model is used to calculate a large-area avalanche hazard map in the Davos region. Both examples show that numerical models bring new and valuable capabilities into the avalanche hazard zoning process. On the other hand, some older problems remain, e. g. the importance of the "correct" assumptions in the release zone or the two-dimensional spreading of the avalanche over a flat open slope.