Abstract ID: 3.11187 | Accepted as Poster | Poster | TBA | TBA

Forests can have a braking effect on moving snow avalanches, contributing to avalanche protection, a key ecosystem service in mountains. The magnitude of this effect depends on avalanche intensity, forest attributes, and forest position within avalanche paths. Incorporating forest effects on avalanche runout into simulation tools is crucial, since quantifying these effects provides valuable data for risk assessments. While physical process-based simulation tools are predominantly used to model avalanche-forest interaction, empirical approaches are rare. However, empirical models are a good alternative in data-scarce areas and facilitate regional-scale analyses due to their computational efficiency.

The open-source avalanche simulation framework AvaFrame provides the empirical simulation module com4FlowPy for gravitational mass flows (GMFs). It routes a GMF along an identified path in three-dimensional terrain. GMF runout and intensity are determined by geometrical runout angle (α) concepts. The Forest Friction Module in com4FlowPy calculates the effect of forests on GMF transit and runout. Required input data include a Digital Elevation Model (DEM), GMF starting zone(s) and a forest layer. In forested areas, a GMF’s energy dissipation due to forest friction is modelled by increasing pre-defined α.

To offer a comprehensive understanding of Forest Friction parameters, we performed a sensitivity analysis. We analysed modelled avalanche runout distances from varied parameter settings under different initial and boundary conditions. Parameter variation was performed in scenarios with generic topographies of different steepness but with same forest extent, and avalanche intensities. The results show that Forest Friction parameter sensitivities depend on pre-defined α and terrain steepness. Greater parameter sensitivities were observed in flatter avalanche terrain (30°) compared to steeper terrain (45°). Modelled runout lengths reacted more sensitively to lower modelled intensities (< 66 m/s) than to higher intensities (66–72 m/s) at which an avalanche enters forest. The Forest Structure Index (FSI), which describes a forest’s protective characteristics (0=no protection, 1=optimal protection), had the greatest influence on avalanche runout compared to other parameters. We summarised these insights in recommended parametrisations for different terrain and avalanche intensities and applied them in a case study where observed avalanche events were back-calculated.