Principles of bedload transport of non-cohesive sediment in open-channels

This text addresses the particular case of motion and causes of motion of granular material as bedload in the fluvial domain. The aim is to perform and overview of key concepts, main achievements and recent advances on the description of the processes involved in erosion, deposition and transport of sediment in open-channels. The theoretical functional relations describing both the initiation of motion and the sediment transport are introduced. The classical problem of the initiation of motion of particles is treated at grain and at reach scales, accounting for the stochastic nature of flow. Concepts of granular kinematics and methods for quantifying the sediment transport rate in rivers are presented. The latter results from the interactions between the flow and the particles on the bed surface. The sediment transport rate, which has been shown to have a stochastic behaviour, is converted to a lumped statistic distribution. Finally, some field and laboratory techniques for measuring sediment transport, accounting for its inherent fluctuations, are introduced.Peer ReviewedPostprint (published version

Bedload transport in rivers, size matters but so does shape

International audienceBedload transport modelling in rivers takes into account the size and density of pebbles to estimate particle mobility, but does not formally consider particle shape. To address this issue and to compare the relative roles of the density and shape of particles, we performed original sediment transport experiments in an annular flume using molded artificial pebbles equipped with a radio frequency identification tracking system. The particles were designed with four distinct shapes and four different densities while having the same volume, and their speeds and distances traveled under constant hydraulic conditions were analyzed. The results show that particle shape has more influence than particle density on the resting time between particle displacement and the mean traveling distance. For all densities investigated, the particle shape systematically induced differences in travel distance that were strongly correlated (R-2 = 0.94) with the Sneed and Folks shape index. Such shape influences, although often mentioned, are here quantified for the first time, demonstrating why and how they can be included in bedload transport models