Lois d'écoulement des laves torrentielles boueuses

Debris flow dynamics

CEMAGREF, Division Protection contre les Erosions, Domaine Universitaire, B.P. 76, 38402 St-Martin-d'Hères, France

Abstract

Debris flows are large masses of water, clay, silt, sand, pebbles and boulders which sometimes flow in mountain streams after long or intense rains and can cause much damages to inhabited areas. Muddy debris flows which are the most common in France exhibit a Herschel-Bulkley behaviour. Here we present theoretical tools for predicting steady free surface debris flows. We first show the fundamental feature of channelized debris flows : an unsheared zone (called plug) within the material. For flow on an infinitely wide plane one can easily compute flox characteristics. From these formulae we deduce an expression for the wall shear stress. We also propose other expressions, established empirically, which may be used for flow in rectangular or trapezoidal channels. We then show that global steady flow characteristics are similar to water flows (supercritical and subcritical regimes, hydraulic jump, rol waves). Nevertheless flow through singularities are somewhat different (dead zones formation).