Dense and powder avalanches: momentum reduction generated by a dam

• Published in: Annals of Glaciology
• Main Authors: Naaim Bouvet, F., Naaim, Mohamed, Faug, T.
• Other Authors: Érosion torrentielle, neige et avalanches (UR ETGR (ETNA)), Centre national du machinisme agricole, du génie rural, des eaux et forêts (CEMAGREF)
• Format: Conference Object
• Language: English
• Published: HAL CCSD 2003
• Subjects: [SDE]Environmental Sciences; Annals of Glaciology
• Online Access: https://hal.inrae.fr/hal-02586330; https://doi.org/10.3189/172756404781815185

International audience Passive protection structures reduce avalanche run-out distance and hence the potential damages brought about by an avalanche, by reducing its velocity and mass. This paper starts with a summary of the main existing results on interactions between snow avalanches and dams. In the case of dense avalanches, the effects of dams are re-examined and previous results are theoretically justified. For a powder snow avalanche a dam has two primary effects. The momentum is reduced by retarding force upstream of the dam and when the jet collides with the ground after the dam. Entrainment of air during the jet reduces its velocity since the mass increases. For a dense avalanche, there is a retarding force upstream of the dam and when the jet collides with the ground, but there is no significant effect of air entrainment. There is, however, deposition of snow which reduces the momentum of the avalanche without affecting the velocity. The reduction of the volume due to deposition reduces the spreading length and therefore the run-out distance of the avalanche. Downstream of the obstacle, the avalanche flow is regarded as an airborne jet. A comparative study shows that density and ambient fluid entrainment effects are significant for gravity currents, powder and dense snow avalanches whereas they are negligible in granular flows.