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Bedload transport: a walk between randomness and determinism. Part 1. The state of the art

Author(s): Christophe Ancey

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Keywords: Bedload transport; bedload transport rate; history of hydraulics; morphodynamics; random motion; stochastic model

Abstract: This paper outlines the various approaches used to calculate bedload transport. As bedload transport exhibits considerable spatial and temporal variations, computing the bedload transport rates and morphological changes experienced by streambeds is difficult. A large body of experimental work has revealed scaling laws relating the mean transport rate qs to hydraulic conditions (that is, water discharge qw, bottom shear stress τb or stream power ω): qs∝qw, qs∝τb3/2 or qs∝ω. The most common approach used to calculate bedload transport has thus long involved determining the one-to-one function qs=f(qw) (or any other dependence of qs on τb or ω) from experiments or theoretical considerations. However, the predictive power of such relationships is limited: scientists are unable to predict qs to within better than one order of magnitude, and morphodynamic models based on qs=f(qw) fail to explain the development of bedforms without the use of additional assumptions. Progressively, other calculation approaches have appeared, with many relying on the idea that bedload transport is a macroscopic transport process that primarily reflects random particle motion at the grain scale. The present paper reviews the main ideas being explored today.


Year: 2020

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