An integrated method for debris flow hazard mapping using 2D runout models

Hazard mapping of rapid mass movements in Alpine regions, especially debris flows, remains a challenging task in land-use management. Physically-based 2D runout models are capable of predicting debris-flow intensities over natural topography for use in the generation of detailed hazard maps. However constitutive hypothesis underlying the models are rarely fully tested and it is difficult to consider all natural variables. Differences in simulation results among different models are not negligible, causing uncertainty in application methodology to hazard mapping and increasing the risk if the model results are not generalized appropriately in hazard map drawing. In two cases in the Swiss Alps, a pragmatic method is proposed which accounts differences in model results, herein shown using two 2D models (FLO-2D and RAMMS) and empirical equations. This approach represents an alternative or complementary way to assess the degree of uncertainty in hazard maps.