Preprints
https://doi.org/10.5194/nhess-2021-289
https://doi.org/10.5194/nhess-2021-289

  06 Oct 2021

06 Oct 2021

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

Detrainment and braking of snow avalanches interacting with forests

Louis Védrine1,2, Xingyue Li1, and Johan Gaume1,3 Louis Védrine et al.
  • 1École polytechnique fédérale de Lausanne, Lausanne, Switzerland
  • 2ENS Paris-Saclay, Gif-sur-Yvette, France
  • 3WSL Institute for Snow and Avalanche Research SLF, Davos, Switzerland

Abstract. Mountain forests provide natural protection against avalanches. They can both prevent avalanche formation in release zones and reduce avalanche mobility in runout areas. Although the braking effect of forests has been previously explored through global statistical analyses on documented avalanches, little is known about the mechanism of snow detrainment in forests for small and medium avalanches. In this study, we investigate the detrainment and braking of snow avalanches in forested terrain, by performing three-dimensional simulations using the Material Point Method (MPM) and a large strain elastoplastic snow constitutive model based on Critical State Soil Mechanics. First, the snow internal friction is evaluated using existing field measurements based on the detrainment mass, showing the feasibility of the numerical framework and offering a reference case for further exploration of different snow types. Then, we systematically investigate the influence of snow properties and forest parameters on avalanche characteristics. Our results suggest that, for both dry and wet avalanches, the detrainment mass decreases with the square of the avalanche front velocity before it reaches a plateau value. Furthermore, the detrainment mass significantly depends on snow properties. It can be as much as ten times larger for wet snow compared to dry snow. By examining the effect of forest configurations, it is found that forest density and tree diameter have cubic and square relations with the detrainment mass, respectively. The outcomes of this study may contribute to the development of improved formulations of avalanche–forest interaction models in popular operational simulation tools and thus improve hazard assessment for alpine geophysical mass flows in forested terrain.

Louis Védrine et al.

Status: open (until 17 Nov 2021)

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Louis Védrine et al.

Louis Védrine et al.

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Short summary
This study investigates how forests affect the behavior of snow avalanches through the evaluation of the amount of snow stopped by the trees and the analysis of energy dissipation mechanisms. Different avalanche features and tree configurations have been examined, leading to the proposal of a unified law for the detrained snow mass. Outcomes from this study can be directly implemented in operational models for avalanche risk assessment and contribute to improved forest management strategy.
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