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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union
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Volume 6, issue 2 | Copyright
Earth Surf. Dynam., 6, 389-399, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 15 May 2018

Research article | 15 May 2018

Advection and dispersion of bed load tracers

Eric Lajeunesse1, Olivier Devauchelle1, and François James2 Eric Lajeunesse et al.
  • 1Institut de Physique du Globe de Paris – Sorbonne Paris Cité, Équipe de Dynamique des Fuides Géologiques, 1 rue Jussieu, 75238 Paris CEDEX 05, France
  • 2Institut Denis Poisson, Université d'Orléans, Universitéde Tours, CNRS, Route de Chartres, BP 6759, 45067 Orléans CEDEX 2, France

Abstract. We use the erosion–deposition model introduced by Charru et al. (2004) to numerically simulate the evolution of a plume of bed load tracers entrained by a steady flow. In this model, the propagation of the plume results from the stochastic exchange of particles between the bed and the bed load layer. We find a transition between two asymptotic regimes. The tracers, initially at rest, are gradually set into motion by the flow. During this entrainment regime, the plume is strongly skewed in the direction of propagation and continuously accelerates while spreading nonlinearly. With time, the skewness of the plume eventually reaches a maximum value before decreasing. This marks the transition to an advection–diffusion regime in which the plume becomes increasingly symmetrical, spreads linearly, and advances at constant velocity. We analytically derive the expressions of the position, the variance, and the skewness of the plume and investigate their asymptotic regimes. Our model assumes steady state. In the field, however, bed load transport is intermittent. We show that the asymptotic regimes become insensitive to this intermittency when expressed in terms of the distance traveled by the plume. If this finding applies to the field, it might provide an estimate for the average bed load transport rate.

Publications Copernicus
Short summary
Tracking the position of tracer particles entrained in a river is a popular method to investigate sediment transport. Using numerical simulations, we study the propagation of these tracers and find a transition between two regimes: an early regime in which the tracers are progressively set into motion and a late regime in which the tracers spread linearly. We derive analytical expressions for the behavior of the tracers in each regime. These expressions might help to interpret field data.
Tracking the position of tracer particles entrained in a river is a popular method to...