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1.
Snow drift transport may cause avalanches on the roads during the periods of snowfall and strong wind. To better understand the factors influencing transport we have developed a theoretical model. This model is based on the boundary layer theory, where the particle mass conservation is considered. Assuming that the saturation is reached, the concentration profile can be represented by a negative exponential law. By means of this analysis, the influence of particle characteristics is explored through the roles of threshold friction velocity and fall velocity. Using fluid mechanics laws, an analysis of the concentration profile resulting from the effect of the wind on a particle bed was also developed. For several velocities of flow and for different kinds of particles an experimental determination of the concentration profile was achieved. We used a laser visualisation and image processing technique to carry out these experiments. The obtained results fit with the values predicted by the theoretical model. 相似文献
2.
Dry and dense snow avalanches are considered as dry granular flows. Theirinteraction with dams is the main objective of this paper. We studied howvarying the dam height could shorten a granular avalanche run-out thanksto a set of simple laboratory experiments carried out on different scales.Shortening the run-out was expected to depend on two effects: (i) storageof the granular material upstream of the dam, and (ii) local energy dissipations.A scaling law is highlighted. As suggested by dimensional arguments, thecontribution of the local energy dissipation was shown to be more dominantthan the storage effects. 相似文献
3.
Bayesian optimal design of an avalanche dam using a multivariate numerical avalanche model 总被引：1，自引：1，他引：0
N. Eckert E. Parent T. Faug M. Naaim 《Stochastic Environmental Research and Risk Assessment (SERRA)》2009,23(8):1123-1141
For snow avalanches, passive defense structures are generally designed by considering high return period events. However,
defining a return period turns out to be tricky as soon as different variables are simultaneously considered. This problem
can be overcome by maximizing the expected economic benefit of the defense structure, but purely stochastic approaches are
not possible for paths with a complex geometry in the runout zone. Therefore, in this paper, we include a multivariate numerical
avalanche propagation model within a Bayesian decisional framework. The influence of a vertical dam on an avalanche flow is
quantified in terms of local energy dissipation with a simple semi-empirical relation. Costs corresponding to dam construction
and the damage to a building situated in the runout zone are roughly evaluated for each dam height–hazard value pair, with
damage intensity depending on avalanche velocity. Special attention is given to the poor local information to be taken into
account for the decision. Using a case study from the French avalanche database, the Bayesian optimal dam height is shown
to be more pessimistic than the classical optimal height because of the increasing effect of parameter uncertainty. It also
appears that the lack of local information is especially critical for a building exposed to the most extreme events only.
The residual hazard after dam construction is analyzed and the sensitivity to the different modelling assumptions is evaluated.
Finally, possible further developments of the approach are discussed. 相似文献
4.
Vito Bacchi Alain Recking Nicolas Eckert Philippe Frey Guillaume Piton Mohamed Naaim 《地球表面变化过程与地形》2014,39(8):1075-1086
In poorly mobile static armour, sorting is usually considered the result of hiding/exposure effects. We called this effect ‘static sorting’ in opposition to very efficient grain‐to‐grain mechanisms produced by a mobile mixture, called ‘kinetic sorting’. We hypothesized that kinetic sorting can be an important contributor to the morphodynamics of mountain streams and attempted to demonstrate this with new flume experiments. Two long runs were produced with natural poorly sorted sediments, and with transport stages of the coarse fraction (defined by the ratio between the shear stress and the critical shear stress for transport), smaller and higher than 1, respectively. Both runs produced an efficient transfer downstream of the injected material, but with a major difference: the first run (no kinetic sorting) produced permanent armour figuring clusters, akin to what has already been observed in similar experiments; the second run (with kinetic sorting) also produced bed armouring, but this armour was periodically totally destroyed, leading to substantial bed erosion. This phenomenon was explained by kinetic sorting, the effects of which are to produce an efficient downward migration of fine materials and bed surface armouring. The consequence is that fine materials are hidden to the flow during aggradation, allowing the slope to attain values much steeper than would have been expected at equilibrium for the mixture. However, whereas the surface armouring tends to stabilize the bed, construction of a layer of fine sediments at the subsurface also contributes to making it very unstable. These two contradictory effects explain the complex bed behaviours and the existence of very large bedload and slope fluctuations. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
5.
In order to study dry-snow avalanches, an intermediate scale device was built atthe “col du lac blanc”, a pass near the Alpe d'Huez ski resort, in the French Alps.It consists of a flow channel that can be artificially fed with snow through a hopper.The channel has been instrumented so as to measure height, normal and shear stressesat the bottom, and velocity profile within the flow. Through the variations in channelinclination and feeding rate, access to a wide range of slopes and heights is available.These measurements have been taken for a few dry snow flows at the end of the2001–2002 winter. The first results are presented here. 相似文献
6.
In this paper, we considered dense avalanches made of dry and cohesion-less snow as gravitational granular flows. We used an effective friction law derived from the recent progress on granular behaviour research to represent momentum loss. We formulated a simple erosion and deposition model where the eroded and deposited mass fluxes are estimated from the knowledge of the starting and stopping conditions on a given slope angle. We adopted the shallow water hypothesis and introduced the new formulation of erosion and deposition processes. We solved the equations thanks to an accurate finite volumes solver scheme, using a non-structured mesh. This allows an easy integration of defence structures and singularities. Each component of this model was tested using analytical solutions and experimental laboratory data. Finally, we used the February 1999 Taconnaz avalanche event to test this model on a real snow avalanche case. These tests gave promising results. 相似文献
7.
SPH-based numerical investigation of mudflow and other complex fluid flow interactions with structures 总被引：3，自引：0，他引：3
The understanding of mudflow–structure interactions and debris–flow structure interactions is of paramount importance for
the rational design of technical countermeasures. However, to date, only a limited number of studies have investigated this
subject. We propose here a numerical approach to this topic using a 2D vertical numerical model based on the smoothed particle
hydrodynamics (SPH) method. First, we will test the capacity of the model to simulate unsteady free-surface flows of water
and viscoplastic fluid in comparison to laboratory experiments. Then, we will use it prospectively, based on a series of simulations
of Bingham fluid free-surface propagations, to determine the momentum reduction resulting from the presence of a simple obstacle
perpendicular to the direction of propagation and to determine the characteristics of stresses applied to this obstacle in
terms of peak pressure and evolution over time. 相似文献
8.
Bayesian stochastic modelling for avalanche predetermination: from a general system framework to return period computations 总被引：1，自引：1，他引：0
N. Eckert E. Parent M. Naaim D. Richard 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(2):185-206
Stochastic models are recent but unavoidable tools for snow avalanche hazard mapping that can be described in a general system
framework. For the computation of design return periods, magnitude and frequency have to be evaluated. The magnitude model
consists of a set of physical equations for avalanche propagation associated with a statistical formalism adapted to the input–output
data structure. The friction law includes at least one latent friction coefficient. The Bayesian paradigm and the associated
simulation techniques assist considerably in performing the inference and taking estimation errors into account for prediction.
Starting from the general case, simplifying hypotheses allows computing the predictive distribution of high return periods
on a case-study. Only release and runout altitudes are considered so that the model can use the French database. An inversible
propagation model makes it possible to work with the latent friction coefficient as if it is observed. Prior knowledge is
borrowed from an avalanche path with similar topographical characteristics. Justifications for the working hypotheses and
further developments are discussed. In particular, the whole approach is positioned with respect to both deterministic and
stochastic hydrology. 相似文献
9.
Alexandra Carriere Caroline Le Bouteiller Gregory E. Tucker Sebastien Klotz Mohamed Naaim 《地球表面变化过程与地形》2020,45(5):1085-1099
While it is well recognized that vegetation can affect erosion, sediment yield and, over longer timescales, landform evolution, the nature of this interaction and how it should be modeled is not obvious and may depend on the study site. In order to develop quantitative insight into the magnitude and nature of the influence of vegetation on catchment erosion, we build a landscape evolution model to simulate erosion in badlands, then calibrate and evaluate it against sediment yield data for two catchments with contrasting vegetation cover. The model couples hillslope gravitational transport and stream alluvium transport. Results indicate that hillslope transport processes depend strongly on the vegetation cover, whereas stream transport processes do not seem to be affected by the presence of vegetation. The model performance in prediction is found to be higher for the denuded catchment than for the reforested one. Moreover, we find that vegetation acts on erosion mostly by reducing soil erodibility rather than by reducing surface runoff. Finally, the methodology we propose can be a useful tool to evaluate the efficiency of previous revegetation operations and to provide guidance for future restoration work. © 2019 John Wiley & Sons, Ltd. 相似文献
10.
As part of the European project CADZIE, the interactionbetween powder avalanches and dams has been studied. First, we simulated a powder avalancheusing a heavy salt solution in a water tank. These experiments showed that (1) the ratio betweenthe maximum velocity parallel to the slope and the front velocity is greater than 1 (up to 1.5),and that (2) the velocity normal to the slope can rise to 74% of the front velocity. The presence ofa dam leads to a reduction of front velocity. The ratio between the maximum horizontal velocityand the front velocity increases with the dam height and reaches a maximum value of 1.9. Aswe did not have access to the density distribution in our experimental set-up, we calibrateda numerical model thanks to the experiments and we deduced the dynamic pressure. Our resultsshowed that, for an avalanche without obstacle, AVAER (Rapin, 1995) and Beghin and Closet'shypothesis (1990) lead to an overestimation of the dynamic pressure in the lower partof the flow as well as in the upper part, and that the use of front velocity for estimating the lossof kinetic energy leads to an overestimation of the dam's effectiveness. 相似文献