Entrainment and adaptation processes in the evolution of collisional bedload layers

Abstract

We performed laboratory experiments which describe the evolution, from triggering until full formation, of a bedload layer. The phenomenon is driven by a turbulent open-channel flow at about constant discharge since the very initiation of the process. The flow stays uniform and the slope constant during the transient phase, during which we measured the instantaneous velocity and concentration profiles of the solid phase within the bedload layer. The timing of the process is governed by inertia and resistance forces. The bedload layer progressively thickens, fed by sediments entrained from the bed, which is progressively eroded, until the final steady uniform condition (i.e., equilibrium) is reached. We then applied a recent numerical model, able to cope with collisional suspensions using extended kinetic theories, to replicate the experimental results. The model results are used to further analyze and discuss the physical processes within the flow.