Entrainment and deposition
- There are a number of possible flow regimes for a snow avalanche from dense plug flows through partly fluidised flows to dilute suspended-particle flows.
- During a single avalanche event a number of different flow regimes may be realised successively in different segments of the track, or simultaneously in distinct vertical layers (dense-flow, saltation and suspension layers) or longitudinal sectors of the flowing material (head, body, tail).
- Snow entrainment and deposition along the track are significant in most avalanches. It has recently been shown that the flowing mass may become an order of magnitude larger than the released mass, and entrainment rates may be in excess of 100 kg m-2 s-1.
- However, virtually nothing is known about the dependence of entrainment and deposition rates on shear stresses and snow properties. Improving our knowledge of such processes is crucial for accurate prediction of avalanche mass, a critical boundary condition in numerical models of avalanche dynamics.
Interactions with obstacles
- The frictional forces differ significantly between flow regimes and between different snow types (with correspondingly large differences in velocities, impact pressures and run-out distances).
- However, there are no well-established relationships between these properties.
- Very little data are available that describe the manner in which an avalanche interacts with an obstacle such as a deflecting or retention dam.
- In particular, the flow depths and velocities for such events have not been studied effectively in the past. Hence, the design criteria for deflection and retention dams are still founded on unverified analogies with hydraulics because too little information is available on most observed events.
- The goal of the SATSIE project is to collect data that improve our knowledge of these phenomena.
- From this work, it will be possible to develop more realistic computer models of snow avalanche dynamics, which may then be used to improve hazard and risk zoning in Alpine regions.