Application of a two-dimensional numerical model in risk and hazard assessment in switzerland

Abstract

In Switzerland a well-established method for debris flow hazard assessment is in use. However the method requires delineation of endangered areas by the expected intensity for a given return period. For this reason there is a strong need for process-based models to improve the quality of hazard mapping and for planning and evaluation of mitigation measures. In this paper, we present the application of a Swiss modeling system for rapid mass movements. The RAMMS debris flow model is a two-dimensional model for simulating the runout distance, velocity, flow depth and impact pressure of debris flows. It uses the single-phase Voellmy fluid friction relation which describes the debris flow resistance as a combination of a dry Coulomb-type friction and a viscous resistance which varies with the square of the flow velocity. The model solves the depth-averaged shallow water equations for granular flows in 2D using a finite volume scheme. We present two case studies in which RAMMS was used by practitioners as a support tool in hazard management and planning mitigation measures. The first site is located in Stechelberg in the western Swiss Alps and the second one in Walchensee, Bavaria (Germany). In both examples RAMMS was found to provide valuable support for practitioners.