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

SCHEUNER T., SCHWAB S., MCARDELL B.W. (2011)

Journal of Engineering Geology and Environment – 5th International Conference on Debris-Flow Hazards Mitigation

In Switzerland a well-established method for debrisflow 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-basedmodels 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 modelingsystem 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 singlephase Voellmy fluid friction relation which describes the debris flow resistance as a combination of a dryCoulomb-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 usedby practitioners as a support tool in hazard managementand planning mitigation measures. The first siteis located in Stechelberg in the western Swiss Alpsand the second one in Walchensee, Bavaria (Germany). In both examples RAMMS was found to providevaluable support for practitioners.