Back-Calculations of Observed Avalanches Against Natural Deflecting Dams

The objective of this study is to assess the reliability of presently available numerical avalanche models in predicting avalanche flow about deflecting natural terrain features such as large boul- ders or moraine ridges. Field observations from Norway have been back-calculated using RAMMS. The observations vary in quality, but the main features of the avalanches regarding release, track and runout have been documented. The quality of the available digital elevation model is critical for the model results. For the two smallest avalanches, good agreement between simulation and observation of both run-up height and runout distance required substantially higher values than commonly used for the friction parameters and . This has the effect of increasing the velocity in the track and shortening the stopping distance.