Numerical simulations of wet snow avalanches: interplay between cohesion and friction

2021 ◽  
Author(s):  
Guillaume Chambon ◽  
Thierry Faug ◽  
Mohamed Naaim
Keyword(s):  
Numerical Simulations ◽  
Flow Regimes ◽  
Liquid Water Content ◽  
Snow Avalanches ◽  
Shallow Flow ◽  
Distinctive Features ◽  
Wide Range ◽  
Wet Snow ◽  
Sensitivity Studies ◽  
Avalanche Flow

<p>Wet snow avalanches present distinctive features such as unusual trajectories, peculiar deposit shapes, and a rheological behavior displaying a combination of granular and pasty features depending on the actual snow liquid water content. Complex transitions between dry (cold) and wet (hot) flow regimes can also occur during a single avalanche flow. In an attempt to account for this complexity, we report on numerical simulations of avalanches using a frictional-cohesive rheology implemented in a depth-averaged shallow-flow model. Through extensive sensitivity studies on synthetic and real topographies, we show that cohesion plays a key role to enrich the physics of the simulated flows, and to represent realistic avalanche behaviors. First, when coupled to a proper treatment of the yielding criterion, cohesion provides a way to define objective stopping criteria for the flow, independently of the issues incurred by artificial diffusion of the numerical scheme. Second, and more importantly, the interplay between cohesion and friction gives raise to a variety of nontrivial physical effects affecting the dynamics of the avalanches and the morphology of the deposits. The relative weights of frictional and cohesive contributions to the overall stress are investigated as a function of space and time during the propagation, and related to the formation of specific features such as lateral levées, hydraulic jumps, etc. This study represents a first step towards robust avalanches simulations, spanning the wide range of possible flow regimes, through shallow-flow approaches. Future improvements involving more refined cohesion parameterizations will be discussed.</p>

Simulating the propagation of wet snow avalanches: challenges and perspectives

2020 ◽  
Author(s):  
Guillaume Chambon ◽  
Thierry Faug ◽  
Mohamed Naaim ◽  
Nicolas Eckert
Keyword(s):  
Numerical Models ◽  
Flow Simulation ◽  
Liquid Water Content ◽  
Snow Avalanches ◽  
Shallow Flow ◽  
Simulation Code ◽  
Full Spectrum ◽  
Wet Snow ◽  
Sensitivity Studies ◽  
Smooth Transitions

<p>Recent winters saw a striking increase in wet snow avalanche activity. Compared to dry avalanches, wet snow avalanches present uniquely distinctive features such as slower velocities, larger depths, unusual trajectories and deposit shapes, and a paste-like rheology that can result in large shear and normal stresses. In addition, the behavior of wet avalanches may strongly vary depending on the actual snow liquid water content. Complex transitions between dry (cold) and wet (hot) behaviors have also been observed during the propagation of single avalanche events. Current numerical models of avalanche dynamics are challenged when it comes to capturing the full spectrum of these different regimes, and the transitions in between. In this contribution, we critically review the various rheological models that have been proposed in the literature to simulate dry and wet snow avalanches in the frame of depth-averaged shallow-flow approaches. On this basis, a simplified parametric rheological law is proposed, with the objective of representing both dry-like and wet-like behaviors and allowing for smooth transitions between them. The law is implemented in a robust 2D shallow-flow simulation code, and systematic sensitivity studies are performed on synthetic and real topographies. Simulation outcomes are analysed in terms of propagation dynamics and deposition patterns, and the ability of the model to capture both dry and wet regimes is discussed. Lastly, a specific calibration methodology is proposed to infer the relevant mechanical parameters from documented avalanche events.</p>

scholarly journals Snow Avalanche Impact Measurements at the Seehore Test Site in Aosta Valley (NW Italian Alps)

Geosciences ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 471
Author(s):  
Margherita Maggioni ◽  
Monica Barbero ◽  
Fabrizio Barpi ◽  
Mauro Borri-Brunetto ◽  
Valerio De Biagi ◽  
...  
Keyword(s):  
Flow Regimes ◽  
Test Site ◽  
Snow Avalanche ◽  
Hazard Mapping ◽  
Force Measurements ◽  
Italian Alps ◽  
Scientific Discussion ◽  
Impact Forces ◽  
Wide Range ◽  
Avalanche Flow

In full-scale snow avalanche test sites, structures such as pylons, plates, or dams have been used to measure impact forces and pressures from avalanches. Impact pressures are of extreme importance when dealing with issues such as hazard mapping and the design of buildings exposed to avalanches. In this paper, we present the force measurements recorded for five selected avalanches that occurred at the Seehore test site in Aosta Valley (NW Italian Alps). The five avalanches were small to medium-sized and cover a wide range in terms of snow characteristics and flow dynamics. Our aim was to analyze the force and pressure measurements with respect to the avalanche characteristics. We measured pressures in the range of 2 to 30 kPa. Though without exhaustive measurements of the avalanche flows, we found indications of different flow regimes. For example, we could appreciate some differences in the vertical profile of the pressures recorded for wet dense avalanches and powder ones. Being aware of the fact that more complete measurements are necessary to fully describe the avalanche flows, we think that the data of the five avalanches triggered at the Seehore test site might add some useful information to the ongoing scientific discussion on avalanche flow regimes and impact pressure.

Observations of the dynamic structure of snow avalanches

1993 ◽  
Vol 18 ◽  
pp. 313-316 ◽  
Author(s):  
K. Nishimura ◽  
N. Maeno ◽  
F. Sandersen ◽  
K. Kristensen ◽  
H. Norem ◽  
...  
Keyword(s):  
Dynamic Structure ◽  
Velocity Shear ◽  
Sensor Data ◽  
Video Tape ◽  
Snow Avalanches ◽  
Western Norway ◽  
Wet Snow ◽  
Avalanche Flow ◽  
Dynamic Structures ◽  
Internal Velocity

During two winters, 1990–92, the dynamic structures of snow avalanches were studied in western Norway. Artificially released wet-snow avalanches ran down the avalanche chute and stopped in front of the retaining dam. Running velocity distributions were obtained not only by video tape recorder, but also by various other recording instruments. Internal velocity was derived for the last avalanche by frequency analysis of impact pressure and optical sensor data. The vertical velocity shear of the avalanche flow has been estimated to be in the range 1–10 s−1.

scholarly journals Forest damage and snow avalanche flow regime

2015 ◽  
Vol 15 (6) ◽  
pp. 1275-1288 ◽  
Author(s):  
T. Feistl ◽  
P. Bebi ◽  
M. Christen ◽  
S. Margreth ◽  
L. Diefenbach ◽  
...  
Keyword(s):  
Flow Regime ◽  
Dynamic Pressure ◽  
Forest Damage ◽  
Snow Avalanches ◽  
Particle Distributions ◽  
Wet Snow ◽  
Homogeneous Particle ◽  
Impact Area ◽  
Avalanche Flow ◽  
The Impact

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.

Avalanche flow regime transitions in a changing climate

2020 ◽  
Author(s):  
Camille Ligneau ◽  
Betty Sovilla ◽  
Johan Gaume
Keyword(s):  
Climate Change ◽  
Snow Cover ◽  
Flow Regime ◽  
Flow Regimes ◽  
Future Climate Change ◽  
Hazard Mapping ◽  
Snow Avalanches ◽  
Avalanche Flow ◽  
Regime Transitions ◽  
Snow Temperature

<p>In the near future, climate change will impact the snow cover in Alpine regions. Higher precipitations and warmer temperatures are expected at lower altitude, leading to larger gradients of snow temperature, snow water content and snow depth between the top and the bottom of slopes. As a consequence, climate change will also indirectly influence the behavior of snow avalanches.</p><p>The present work aims to investigate how changes in snow cover properties will affect snow avalanches dynamics. Experimental studies allowed to characterize different avalanche flow regimes which result from particular combinations of snow physical and mechanical properties. In particular, expected variations of snow temperatures with elevation will cause more frequent and more extreme flow regime transitions inside the same avalanche. For example, a fast avalanche characterized by cold and low-cohesive snow in the upper part of the avalanche track will transform more frequently into a slow flow made of wet and heavy snow when the avalanche will entrain warm snow along the slope. A better understanding of these flow regime transitions, which have already been largely reported, is crucial, because it affects both daily danger assessment (e.g. forecasting services, road controls) and hazard mapping of avalanches.</p><p>To date, most avalanche modeling methods are not considering temperature effects and are then unable to simulate flow regime transitions and unprecedented scenarios. Our goal is then to develop a model capable of simulating reported flow regimes, flow transitions and the interactions between the snow cover and the flow (erosion, entrainment). Since these elements are not yet fully understood, we firstly model these mesoscopic processes using a 2D Discrete Element Model (DEM) in which varying particle cohesion and friction mimic the effect of changes in snow temperature. Flow regimes are simulated by granular assemblies put into motion by gravity on an inclined slope, which interact with a granular and erodible bed surface. Simulations are calibrated using experimental data coming from the avalanche test site located in Vallée de la Sionne, which record avalanches since more than 20 years. This modeling will then be used as an input to improve slope-scale models and make them more appropriate for avalanche risk management in the context of climate change.</p>

scholarly journals Observations of the dynamic structure of snow avalanches

1993 ◽  
Vol 18 ◽  
pp. 313-316 ◽  
Author(s):  
K. Nishimura ◽  
N. Maeno ◽  
F. Sandersen ◽  
K. Kristensen ◽  
H. Norem ◽  
...  
Keyword(s):  
Dynamic Structure ◽  
Velocity Shear ◽  
Sensor Data ◽  
Video Tape ◽  
Snow Avalanches ◽  
Western Norway ◽  
Wet Snow ◽  
Avalanche Flow ◽  
Dynamic Structures ◽  
Internal Velocity

During two winters, 1990–92, the dynamic structures of snow avalanches were studied in western Norway. Artificially released wet-snow avalanches ran down the avalanche chute and stopped in front of the retaining dam. Running velocity distributions were obtained not only by video tape recorder, but also by various other recording instruments. Internal velocity was derived for the last avalanche by frequency analysis of impact pressure and optical sensor data. The vertical velocity shear of the avalanche flow has been estimated to be in the range 1–10 s−1.

scholarly journals Perspectives on Snow Avalanche Dynamics Research

Geosciences ◽  
2021 ◽  
Vol 11 (2) ◽  
pp. 57
Author(s):  
Kouichi Nishimura ◽  
Fabrizio Barpi ◽  
Dieter Issler
Keyword(s):  
Experimental Studies ◽  
Snow Avalanche ◽  
Particle Interactions ◽  
Snow Avalanches ◽  
Special Issue ◽  
Erosion And Deposition ◽  
Field Surveys ◽  
Wide Range ◽  
Avalanche Dynamics ◽  
Avalanche Flow

As an introduction for non-specialists to the Special Issue on snow avalanche dynamics, this paper first outlines how understanding the dynamics of snow avalanches can contribute to reducing risk for settlements and infrastructure. The main knowledge gaps in this field of research concern (i) the properties of the flow regimes and the transitions between them, and (ii) the dynamics of mass change due to erosion and deposition. These two aspects are intertwined and determine not only the reach of an avalanche, but also its velocity, course and impact pressure. Experimental studies described in this Special Issue comprise a wide range of scales from small rotating drums to real snow avalanches. In addition, several papers describe post-event field surveys of specific avalanches and analyze them using different methods and techniques, demonstrating how valuable qualitative insight can be gained in this way. The theoretical developments range from exploratory studies of fluid–particle interactions to a comprehensive review of half a century of avalanche flow modeling in Russia.

scholarly journals Slow drag in wet-snow avalanche flow

2010 ◽  
Vol 56 (198) ◽  
pp. 587-592 ◽  
Author(s):  
B. Sovilla ◽  
M. Kern ◽  
M. Schaer
Keyword(s):  
Mean Value ◽  
Immersion Depth ◽  
Snow Avalanches ◽  
Pressure Time ◽  
Large Fluctuations ◽  
Load Cells ◽  
Snow Pressure ◽  
Wet Snow ◽  
Avalanche Flow ◽  
The Mean

AbstractWe report impact pressures exerted by three wet-snow avalanches on a pylon equipped with piezoelectric load cells. These pressures were considerably higher than those predicted by conventional avalanche engineering guidelines. The time-averaged pressure linearly increased with the immersion depth of the load cells and it was about eight times larger than the hydrostatic snow pressure. At the same immersion depth, the pressures were very similar for all three avalanches and no dependency between avalanche velocity and pressure was apparent. The pressure time series were characterized by large fluctuations. For all immersion depths and for all avalanches, the standard deviations of the fluctuations were, on average, about 20% of the mean value. We compare our observations with results of slow-drag granular experiments, where similar behavior has been explained by formation and destruction of chain structures due to jamming of granular material around the pylon, and we propose the same mechanism as a possible microscale interpretation of our observations.

scholarly journals Wet-snow instabilities: comparison of measured and modelled liquid water content and snow stratigraphy

2011 ◽  
Vol 52 (58) ◽  
pp. 201-208 ◽  
Author(s):  
Christoph Mitterer ◽  
Hiroyuki Hirashima ◽  
Jürg Schweizer
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Water Flux ◽  
Liquid Water Content ◽  
Vital Role ◽  
Snow Avalanches ◽  
Wetting Front ◽  
Snow Stratigraphy ◽  
Capillary Barriers ◽  
Wet Snow

AbstarctWet-snow avalanches are difficult to forecast, as the change from stable to unstable snow conditions occurs rapidly in a wet snowpack, often in response to water production and movement. Snow stratigraphy plays a vital role in determining flux behaviour. Capillary barriers or melt–freeze crusts can impede and divert water horizontally over large areas and thus may act as a failure layer for wet-snow avalanches. We present a comparison of measured and modelled liquid water content, θw, and snow stratigraphy during periods of wet-snow instabilities. Special attention is given to the reproducibility of capillary barriers, ponding of water on melt–freeze crusts and the timing of first wetting and of water arrival at the bottom of the snowpack, because these factors are believed to play a major role in the formation of wet-snow avalanches. In situ measurements were performed in the vicinity of automatic weather stations or close to recent wet-snow avalanches in order to compare them with model results. The simulations are based on two different water flux models incorporated within the 1-D snow-cover model SNOWPACK. The comparison of the two model runs with observed θw and stratigraphy revealed that both water-transport models reproduced the ponding of water on melt–freeze crusts. However, in both models melt–freeze crusts were transformed to normal melt forms earlier than observed in nature, so still existing ponding was not captured by the models. Only one of the models was able to reproduce capillary barriers in agreement with observations. The time of the first wetting at the surface was well predicted, but the simulated arrival time of the wetting front at the bottom of the snowpack differed between the simulations; it was either too early or too late compared with the observation.

scholarly journals Point release wet snow avalanches

2015 ◽  
Vol 3 (4) ◽  
pp. 2883-2912
Author(s):  
C. Vera Valero ◽  
Y. Bühler ◽  
P. Bartelt
Keyword(s):  
Initial Conditions ◽  
Climate Change Scenarios ◽  
Snow Avalanches ◽  
Mountain Regions ◽  
Flow Temperature ◽  
Land Usage ◽  
Wet Snow ◽  
Avalanche Flow ◽  
Near Future ◽  
Small Point

Abstract. Wet snow avalanches can initiate from large fracture slabs or small point releases. Point release wet snow avalanches can reach dangerous proportions when they (1) initiate on steep and long avalanche paths and (2) entrain warm moist snow. In this paper we investigate the dynamics of point release wet snow avalanches by applying a numerical model to simulate documented case studies on high altitude slopes in the Chilean Andes (33° S). The model predicts avalanche flow temperature as well as meltwater production, given the thermal initial conditions of the release mass and snowcover entrainment. As the release mass is small, avalanche velocity and runout are primarily controlled by snowcover temperature and moisture content. We demonstrate how the interaction between terrain and entrainment processes influence the production of meltwater and therefore lubrication processes leading to longer runout. This information is useful to avalanche forecasters. An understanding of wet snow avalanche dynamics is important to study how climate change scenarios will influence land usage in mountain regions in the near future.

Sign in / Sign up

Export Citation Format

Share Document