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Shock waves and snow avalanches

Cui, X; Gray, JM (Wales / Manchester)
Friday 09 January 2009, 14:50-15:15

Seminar Room 1, Newton Institute


Many geophysical granular flows, such as snow slab avalanches, occur as dense free-surface flows that are driven downslope under the action of gravity. In mountainous regions, avalanche defences are often built to deflect the avalanche away from people and infrastructure, or, to stop it before it reaches them. As the avalanche is deflected there are rapid changes in the avalanche height and velocity. We apply classical oblique shock theory and use small scale experiments to investigate how weak, strong and detached shock waves are generated by a wedge and compare shock capturing numerical simulations on realistic topography to field observations from a deflecting dam in Flateyri, Iceland. These show that there is no one single set of upstream conditions that parameterises the flow behaviour, but the solution evolves as the avalanche propagates along the dam in response to the deceleration imposed by the slope. Nevertheless the classical theory still yields important order of magnitude estimates for the flow velocity and thickness immediately upstream of the shock. The numerical method is extended to handle the flow around arrays of rectangular obstacles, which are often placed in the run-out zone to slow the avalanche down. The results are also compared with small scale experiments.


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