A comparison of physical and computer-based debris flow modelling of a deflection structure at Illgraben, Switzerland

Catherine Berger, Marc Christen, Jürg Speerli, Guido Lauber, Melanie Ulrich and Brian W. McArdell

On the fan of the Illgraben (Switzerland), settlements and infrastructure are endangered by large debris flows. A protection concept was therefore elaborated to partially deflect large debris flows into a forest for deposition and in order to reduce discharge and flow volume in the channel on the fan. Because deflection structures for debris flows are uncommon, a physical model was built at a scale of 1:60 to test functionality and optimize the design. Afterwards, the computer-based model RAMMS::DEBRIS FLOW was compared with the physical model results and to further analyze functionality and robustness especially for rare debris flows. In general, the numerical model runs with RAMMS showed a similar flow behavior as in the physical experiments, and separation effects of the deflection structure were confirmed. The standard Voellmy model was not able to reproduce the constant velocities found in the experiments before the dosing structure. Therefore, a version of the Voellmy model including cohesion was used and showed good agreement with the physical modelling.

2016/1 212-220