Intense bed-load due to a sudden dam-break

Abstract

AbstractIntense bed-load, or sheet flow, occurs when a free-surface flow of water drives a thick, rapidly sheared layer of water and grains over an erodible granular bed. We examine here the transient case where flow is induced by a sudden dam-break. Aiming for greater detail than achieved previously, we investigate this case using experiment and theory. The experiments combine particle tracking velocimetry (PTV) with a novel method of concentration measurement based on recording the penetration depth of a laser light sheet. The theory incorporates more vertical detail into the shallow water equations by using piecewise linear profiles of velocity and granular concentration, constrained by constitutive relations proposed recently for intense bed-load. These relations account for Coulomb yield at the bed, immersed granular collisions at the base, and equilibration of shear rate and density stratification across the bed-load layer. Using these approaches, both experiment and theory yield time- and depth-resolved profiles of velocity and granular concentration in addition to longitudinal wave profiles. Without any parameter adjustment, the theoretical predictions are in good agreement with the experimental measurements.