Disaster Mitigation of Debris Flows, Slope Failures and Landslides 223 Results of Real Size Rockfall Experiments on Forested and Non-Forested Slopes

At the scale of forest stands, there is a lack of quantitative, statistically valid data on the protective effect of forests against rockfall. Therefore, the first objective of this study was to quantify the velocities, rebound heights as well as the residual hazard of rockfall on a forested and a non-forested slope. The second objective was to evaluate existing rockfall protection forest management guidelines, as well as the underlying criteria. We carried out, filmed and analysed 100 real size rockfall experiments at a non-forested site (Site 1) and 102 identical experiments at a forested site (Site 2) on the same slope. At the non-forested site, results show that the mean maximum velocity is 15.4 m s−1 compared to 11.7 m s−1 at the forested site. The maximum rebound height decreases from 8 m (Site 1) to 2 m (Site 2) and the number of rocks that surpass the 223.5 m slope distance decreases from 95 out of 100 (Site 1) to 35 out of 102 (Site 2). A major effect of rockfall on a forested slope is the development of a treeless rockfall path or couloir, which had evolved after releasing 78 rocks at Site 2. During our experiments, none of the rocks attained their maximal velocity within the first 40 m. They did, however, attain destructive velocities (11–15 m s−1) within that distance. Finally, the results proved that forests can provide effective protection against rockfall