Modeling Debris-Flow Runout Pattern on a Forested Alpine Fan with Different Dynamic Simulation Models

Debris flows constitute a major hazard in alpine regions. Predicting potential deposition areas of future events is important for engineering hazard assessment. When using a numerical simulation model, knowledge of appropriate model parameters is essential. These parameters reflect not only the flow resistance of the material in motion, but also the resistance of the surface on which the flow is routed. In this study we used two numerical simulation models for evaluating model Voellmy model parameters to best fit runout lengths and deposition pattern of an observed past debris-flow event on an alpine fan in Austria. The simulation tool RAMMS-DF (RApid Mass MovementS-Debris Flow) is based on a Voellmy-type constitutive equation, and the software DAN3D (Dynamic Analysis of Landslides) allows selecting different rheologies, including a Voellmy-type flow law. All calculations were based on the same digital elevation model with a 1 m resolution and the same initial conditions. Our results show that both simulation tools were capable to match observed deposition pattern reasonably well. The best fit parameter set for mu and xi are 0.11 and 200 for RAMMS-DF, respectively 0.08 and 400 for DAN3D. A sensitivity analysis shows a slightly higher sensitivity of model parameters for the DAN3D model than for the RAMMS-DF model. This study shall contribute to the evaluation of realistic model parameters for simulation of debris-flows on forested and non-forested fans.