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The prediction of the transport of sediments in streams is of crucial importance for many geophysical and industrial applications. Most of the available formulas for sediment transport are empirical and apply to situations near initiation, where a few erratic particles are seen jumping and rolling over an immobile bed. However, they are commonly adopted for predicting massive transport of sediments, although more rigorous approaches exist. The latter make use of constitutive relations from kinetic theories of granular gases, but require the numerical integrations of complicated, nonlinear differential equations, hence discouraging their usage for practical purposes. A new, explicit formula for predicting intense sediment transport is proposed here, based on kinetic theories of granular gases and incorporating in a simple yet rigorous way the possibility of turbulent suspension of the particles. It is shown that this formula, unlike others, can quantitatively reproduce physical experiments on steady, uniform flows of natural and artificial particles and water over horizontal, movable beds taken from the literature. These findings suggest that granular physics is now mature enough to provide practical tools in fields that were so far mainly empirically oriented. DOI: 10.1061/(ASCE)HY.1943-7900.0000686. © 2013 American Society of Civil Engineers. CE Database subject headings: Sediment transport; Sheet flow; Kinetics; Turbulence; Predictions. Author keywords: Sediment transport; Sheet flow; Kinetic theories. Introduction and Theory Most research on sediment transport has emphasized the forces that the liquid component exerts on the particles, rather than on the particle-particle interactions. This is partially due to the fact that the laboratory experiments were mostly conducted, for prac- tical reasons, at small values of water discharge, close to the incep- tion of particle motion, where interparticle forces are negligible. At higher values of water discharge, massive transport of sediments takes place instead, and those forces cannot be ignored. Sophisti

This work deals with the evaluation of the most suitable expression for the motion resistance of a debris flow. In particular, it focuses on inertial debris flows, i.e., granular-fluid mixtures in which the particle inertia dominates both the fluid viscous force and turbulence; it provides, through an order-of-magnitude analysis, the criterion to be satisfied for a debris flow to be considered inertial and shows that most of real-scale debris flows match this description. The analytical relation between flow depth, depth-averaged velocity, and tangent of the angle of inclination of the free surface is then used in steady, uniform flow conditions to approximate the flow resistance in depth-averaged mathematical models of debris flows. That resistance formula is tested against experimental results on the longitudinal profile of steady, fully saturated waves of water and gravel over both rigid and erodible beds, and against field measurements of real events. The notable agreement, especially in compa...

This work deals with the simple shear flow of neutrally buoyant, rigid, frictionless spheres immersed in a viscous fluid that exchange momentum through inelastic collisions. It is shown how kinetic theories are able to provide a full analytical description of the flow, once the influence of the viscous fluid is taken into account in a simple way through the dependence of the collisional coefficient of restitution on the Stokes number. This allows the capture of the characteristics of the experiments performed by Bagnold 60 years ago and the interpretation of the macroviscous and inertial regimes described by the same author as the limits for the coefficient of restitution equal to zero and to the value valid in absence of the viscous fluid, respectively. DOI: 10.1061/(ASCE)HY.1943-7900.0000701. © 2013 American Society of Civil Engineers. CE Database subject headings: Shear flow; Kinetics; Rheology; Coefficients. Author keywords: Simple shear flow; Kinetic theory; Granular-fluid mixture; Rheology.