Abstract
The phenomenology and previous mechanical theories of Alpine debris flows are reviewed. A new model for the mechanics of such debris flows is proposed which is based on the notion of dispersive pressure occurring in shear flows introduced by Bagnold. It is shown that the values of the dynamical variables required by this model are of the order of magnitude of those observed in nature.
Highlights
RIASSUNTO. — Dopo aver passato in rassegna e riesaminato la fenomenologia e le precedenti teorie meccaniche sul trasporto di detriti Alpini, gli A
A typical profile of a mountain stream prone to conducting debris flows consists of three regions: a region where the debris material is collected, a region where it moves downhill in a gorge, and a region where it is deposited in form of an alluvial blanket
We show here the drainage area of the Dürnbach in the Pinzgau in Austria (Pig. 1) and the corresponding profile (Fig. 2)
Summary
SUMMARY. — The phenomenology and previous mechanical theories of Alpine debris flows are reviewed. Alpine debris flows (in German "Mnrgang") are mixtures of water, fine materials, sand, gravel, large blocks and pieces of vegetation which move downstream with great velocity in an existing river channel. The theories purporting to explain the mechanics of debris flows have generally been based upon analogies with bed load transport in rivers. Any avocation of Bagnold's dispersive pressure as a possible mechanism of suspension and fluidization in Alpine debris flows must entail an analysis of the orders of magnitudes of the dynamical quantities involved. The debris flow, would encompass two types of materials: the continuous phase consisting of the water including the fine suspensions of viscosity rj and density p; — and the dispersed phase consisting of the large debris of median diameter D, density a and volume concentration c.
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