Numerical comparison between RAMMS debris flow simulations and actual events in the Illgraben catchment area, Switzerland

Abstract

Debris flows can become hazardous in mountainous areas when growing to large volumes. The main mechanism causing a debris flow to reach a large volume is erosion. The RAMMS model has shown to be successful in simulating debris flow events realistically. However, this model still has shortcomings, of which erosion is the most important one. At the moment, erosion in RAMMS is poorly studied. In this research, actual measured debris flows were compared to simulated debris flow events in RAMMS to take a closer look at how the RAMMS model performs in terms of erosion. Two debris flow events, one very erosive and the other less erosive, were analysed with a quantitative GIS erosion and deposition analysis. This study shows that RAMMS is able to successfully simulate less erosive debris flows, but when a debris flow is very erosive, the simulated erosion is very different from the actual event. A reason for this could be that the erosive event had certain parameters without erosive properties, or that the many check dams along the channel prevented most erosion. Nevertheless, it shows that future research on how RAMMS performs in terms of erosion is crucial for successfully forecasting debris flows in the future, as erosive debris flows can be most hazardous when they grow to large volumes.