Preprints
https://doi.org/10.5194/nhess-2021-319
https://doi.org/10.5194/nhess-2021-319

  12 Nov 2021

12 Nov 2021

Review status: this preprint is currently under review for the journal NHESS.

Full scale experiments to examine the role of deadwood on rockfall dynamics in forests

Adrian Ringenbach1,3, Elia Stihl1, Yves Bühler1, Peter Bebi1, Perry Bartelt1, Andreas Rigling2,3, Marc Christen1, Guang Lu1, Andreas Stoffel1, Martin Kistler1, Sandro Degonda1, Kevin Simmler1, Daniel Mader3, and Andrin Caviezel1 Adrian Ringenbach et al.
  • 1WSL Institute for Snow and Avalanche Research SLF, 7260 Davos Dorf, Switzerland
  • 2Swiss Federal Institute for Forest, Snow and Landscape Research WSL, Zürcherstrasse 111 8903 Birmensdorf, Switzerland
  • 3Department of Environmental Systems Science, Institute of Terrestrial Ecosystems, ETH Zürich, Zurich, Switzerland

Abstract. Forests are rockfall-protective ecological infrastructures, as a significant amount of kinetic energy is absorbed during consecutive rock-tree impacts. Although many recent works have considered rock impacts with standing trees, the effect of lying deadwood in forests has not yet been considered thoroughly, either experimentally or numerically. Here, we present a complete examination of induced rockfall experiments on a forested area in three different management stages. The trilogy is conducted in a spruce forest stand (i) in its original state, (ii) after a logging operation with fresh, lying deadwood and (iii) after the removal of the deadwood. The tests allow us to directly quantify the effect of fresh deadwood on overall rockfall risk for the same forest (slope, species) under three different conditions. The study yields quantitative results on the barrier efficiency of the deadwood logs as only 3.6 % of the rocks surpass the deadwood section. The mean runout distance is reduced by 42 %. Conversely, the runout distance increases by 17 % when the cleared stand is compared to the original forest. These results quantitatively confirm the benefits of nature-based mitigation measures integrated into forestry practice and we show how modern rockfall codes can be extended to incorporate such complex, but realistic forest boundary conditions.

Adrian Ringenbach et al.

Status: open (until 24 Dec 2021)

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Adrian Ringenbach et al.

Adrian Ringenbach et al.

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Short summary
The runout area of rockfalls is often forested. Due to repeated tree-rock hits, the forest has a braking effect. This effect is regularly included in the numerically simulated hazard assessment. The effect of lying deadwood, however, is often neglected. To fill this gap, 1:1 scale experiments were conducted in the original forest, in the forest including lying deadwood, and in the cleared forest. The evaluation of the deposition points shows that deadwood has a large protective effect.
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