Wet-snow avalanche interaction with a deflecting dam: field observations and numerical simulations in a case study

Sovilla, Betty; Sonatore, I.; Bühler, Yves; Margreth, Stefan

doi:10.5194/nhess-12-1407-2012

Cited by 9 publications

(11 citation statements)

References 27 publications

(42 reference statements)

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“…Wet-snow, plug-like avalanches hardly exceed velocities of u w = 8 m s −1 . Our calculations correspond to pressure measurements captured in the Vallee de la Sionne test site (Sovilla et al, 2010(Sovilla et al, , 2014, that could not been explained with dynamic impact formulas.…”

Section: Discussionsupporting

confidence: 66%

“…More importantly, the capacity of mountain forests to decelerate and stop avalanches requires distinguishing between when the avalanche destroys the forest and when trees can withstand the avalanche impact pressure. Impact pressures, however, are related to avalanche flow regime (Faug et al, 2010;Sovilla et al, 2014;Vera et al, 2015). Both fast-moving dry avalanches and slow moving wet snow flows can lead to widespread forest destruction.…”

Section: Introductionmentioning

confidence: 99%

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Forest damage and snow avalanche flow regime

Feistl¹,

Bebi²,

Christen³

et al. 2015

Preprint

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Abstract. Snow avalanches break, uproot and overturn trees causing damage to forests. The extent of forest damage provides useful information on avalanche frequency and intensity. However, impact forces depend on avalanche flow regime. In this paper, we define avalanche loading cases representing four different avalanche flow regimes: powder, intermittent, dry and wet. In the powder regime, the blast of the cloud can produce large bending moments in the tree stem because of the impact area extending over the entire tree crown. We demonstrate that intermittent granular loadings are equivalent to low-density uniform dry snow loadings under the assumption of homogeneous particle distributions. In the wet snow case, avalanche pressure is calculated using a quasi-static model accounting for the motion of plug-like wet snow flows. Wet snow pressure depends both on avalanche volume and terrain features upstream of the tree. Using a numerical model that simulates both powder and wet snow avalanches, we study documented events with forest damage. We find (1) powder clouds with velocities over 20 m s−1 can break tree stems, (2) the intermittent regime seldom controls tree breakage and (3) quasi-static pressures of wet snow avalanches can be much higher than pressures calculated using dynamic pressure formulas.

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Section: Discussionsupporting

confidence: 66%

Section: Introductionmentioning

confidence: 99%

Forest damage and snow avalanche flow regime

Feistl¹,

Bebi²,

Christen³

et al. 2015

Preprint

Self Cite

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show abstract

“…Sappington et al (2007) showed that the vector ruggedness measure is uncorrelated with slope. The measure has already been applied in different research fields, including, among others, animal habitat analysis (Sappington et al, 2007), avalanche dynamics (Sovilla et al, 2012) and avalanche formation (Vontobel, 2011).…”

Section: Surface Roughness Calculationmentioning

confidence: 99%

Influence of snow depth distribution on surface roughness in alpine terrain: a multi-scale approach

Veitinger¹,

Sovilla²,

Purves

2014

The Cryosphere

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Abstract. In alpine terrain, the snow-covered winter surface deviates from its underlying summer terrain due to the progressive smoothing caused by snow accumulation. Terrain smoothing is believed to be an important factor in avalanche formation and avalanche dynamics, and it affects surface heat transfer, energy balance as well as snow depth distribution. To assess the effect of snow on terrain, we use an adequate roughness definition. We developed a method to quantify terrain smoothing by combining roughness calculations of snow surfaces and their corresponding underlying terrain with snow depth measurements. To this end, elevation models of winter and summer terrain in three selected alpine basins in the Swiss Alps characterized by low, medium and high terrain roughness were derived from highresolution measurements performed by airborne and terrestrial lidar. The preliminary results in the selected basins reveal that, at basin scale, terrain smoothing depends not only on mean snow depth in the basin but also on its variability. The multi-temporal analysis over three winter seasons in one basin suggests that terrain smoothing can be modelled as a function of mean snow depth and its standard deviation using a power law. However, a relationship between terrain smoothing and snow depth was not found at pixel scale. Further, we show that snow surface roughness is to some extent persistent, even in-between winter seasons. Those persistent patterns might be very useful to improve the representation of a winter terrain without modelling of the snow cover distribution. This can for example improve avalanche release area definition and, in the long term, natural hazard management strategies.

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“…The slope angle at the location of the spruces was 10 • < γ < 20 • . The density of the avalanche deposition was estimated by Sovilla et al (2012) to be 500 kg m −3 and Vera et al (2015) estimated that the density of the flowing avalanche was slightly lower, approx. 450 kg m −3 .…”

Section: Wet Snow Avalanche Monbiel 2008mentioning

confidence: 99%

“…150 000 m 3 ) released spontaneously on 23 April 2008 near Monbiel, Switzerland and destroyed a small spruce forest before it stopped in the river bed of the Landquart. An approximation of the flow velocity (u = 5 m s −1 ) and flow height (h = 3 m) was possible by analyzing a movie documentation (Sovilla et al, 2012). The deposition height was measured using laser scan (between 2 and 7 m).…”

Section: Wet Snow Avalanche Monbiel 2008mentioning

confidence: 99%

Forest damage and snow avalanche flow regime

Feistl

Bebi²,

Christen³

et al. 2015

Nat. Hazards Earth Syst. Sci.

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Abstract. Snow avalanches break, uproot and overturn trees causing damage to forests. The extent of forest damage provides useful information on avalanche frequency and intensity. However, impact forces depend on avalanche flow regime. In this paper, we define avalanche loading cases representing four different avalanche flow regimes: powder, intermittent, dry and wet. Using a numerical model that simulates both powder and wet snow avalanches, we study documented events with forest damage. First we show that in the powder regime, although the applied impact pressures can be small, large bending moments in the tree stem can be produced due to the torque action of the blast. The impact area of the blast extends over the entire tree crown. We find that, powder clouds with velocities over 20 m s −1 can break tree stems. Second we demonstrate that intermittent granular loadings are equivalent to low-density uniform dry snow loadings under the assumption of homogeneous particle distributions. The intermittent regime seldom controls tree breakage. Third we calculate quasi-static pressures of wet snow avalanches and show that they can be much higher than pressures calculated using dynamic pressure formulas. Wet snow pressure depends both on avalanche volume and terrain features upstream of the tree.

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Wet-snow avalanche interaction with a deflecting dam: field observations and numerical simulations in a case study

Cited by 9 publications

References 27 publications

Forest damage and snow avalanche flow regime

Forest damage and snow avalanche flow regime

Influence of snow depth distribution on surface roughness in alpine terrain: a multi-scale approach

Forest damage and snow avalanche flow regime

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