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Earth Surface Dynamics An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/esurf-2017-57
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 4.0 License.
Research article
09 Nov 2017
Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Earth Surface Dynamics (ESurf).
Advection and dispersion of bedload tracers
Eric Lajeunesse1, Olivier Devauchelle1, and François James2 1Institut de Physique du Globe de Paris – Sorbonne Paris Cité, Équipe de Dynamique des Fuides Géologiques, 1 rue Jussieu, 75238 Paris cedex 05, France
2MAPMO UMR 7349 CNRS & Université d’Orléans, Fédération Denis Poisson FR CNRS 2964, Université d’Orléans, BP 6759, 45067 Orléans cedex 2, France
Abstract. We use the erosion-deposition model introduced by Charru et al. (2004) to simulate numerically the evolution of a plume of bedload 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 bedload layer. We find a transition between two asymptotic regimes. At early time, the tracers, initially at rest, are progressively set into motion by the flow. During this entrainment regime, the plume, strongly skewed in the direction of propagation, continuously accelerates while spreading non-linearly. 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 derive analytically 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, bedload 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 bedload transport rate.

Citation: Lajeunesse, E., Devauchelle, O., and James, F.: Advection and dispersion of bedload tracers, Earth Surf. Dynam. Discuss., https://doi.org/10.5194/esurf-2017-57, in review, 2017.
Eric Lajeunesse et al.
Eric Lajeunesse et al.
Eric Lajeunesse et al.

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Short summary
Tracking the position of tracer particles entrained in a river is a popular method to investigate sediment transport in rivers. 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; a late regime in which the tracers spreads linearly. We derive analytical expressions for the behavior of the tracers in each regime.These expression might help to interpret field data.
Tracking the position of tracer particles entrained in a river is a popular method to...
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