Formation of dry granular fronts and watery tails in debris flows

Debris flows are particle–fluid mixtures that pose a significant hazard to many communities throughout the world. Bouldery debris often characterised by deep dry granular flow front, which is followed progressively thinner and increasingly watery tail. The formation of highly destructive bouldery wave fronts usually attributed particle-size segregation. However, moving-bed flume experiments Davies ( N. Z. J. Hydrol. , vol. 29, 1990, pp. 18–46) show discrete surges with tails also form in monodisperse mixtures. These observations motivate development new depth-averaged mixture theory for flows, explicitly takes account differing phreatic surfaces, velocity shear, relative motion between grains fluid explain these phenomena. consists four coupled conservation laws describe spatial temporal evolution grain water thicknesses velocities. This system enables travelling solutions be constructed consist (i) large amplitude front smoothly transitions (ii) an undersaturated body, (iii) oversaturated region then (iv) pure It shown good quantitative agreement Davies’ at high bed speeds slope inclinations. At lower inclinations, produces connect steady-uniform upstream flow, may or not have bulbous consistent observations.