Preprints
https://doi.org/10.5194/esurf-2021-77
https://doi.org/10.5194/esurf-2021-77

  10 Nov 2021

10 Nov 2021

Review status: this preprint is currently under review for the journal ESurf.

Entrainment and deposition of boulders in a gravel bed river

Pascal Allemand1, Eric Lajeunesse2, Olivier Devauchelle2, and Vincent Langlois1 Pascal Allemand et al.
  • 1Université Claude Bernard Lyon 1, ENS Lyon, Université Jean Monnet Saint-Étienne & CNRS, Laboratoire de Géologie de Lyon, Terre Planètes Environnement, UMR 5276, 69100 Villeurbanne, France
  • 2Université de Paris, Institut de Physique du Globe de Paris, CNRS, F-75005, Paris, France

Abstract. Rivers transports coarse sediment (gravel, cobbles, or boulder) as bedload. During a flood, when the discharge is high enough, the sediment grains move by rolling and bouncing on the river bed. Measuring bedload transport in the field is notoriously difficult. Here, we propose a new method to characterize bedload transport by floods. Using a drone equipped with a high resolution camera, we recorded yearly images of a bar of the Vieux-Habitants river, a gravel-bed river located on Basse-Terre Island (Guadeloupe, French West Indies). These images, combined with high frequency measurements of the river discharge, allow us to monitor the evolution of the population of boulders on the river bed. Based on this dataset, we estimate the smallest discharge that can move the boulders, and calculate the effective transport time of the river. We find that transport occurs about 10 hours per year. When plotted as a function of this effective transport time, likelihood of a given boulder remaining at the same location decreases exponentially, with an effective residence time of 17 hours. We then propose a rough estimate of the average number of boulders that the river carries every year.

Pascal Allemand et al.

Status: open (until 08 Jan 2022)

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Pascal Allemand et al.

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Entrainment and deposition of boulders in a gravel bed river Pascal Allemand, Eric lajeunesse, Olivier Devauchelle, Vincent Langlois https://dataverse.harvard.edu/dataset.xhtml?persistentId=doi:10.7910/DVN/QRHM8E

Pascal Allemand et al.

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Short summary
We recorded yearly images of a bar of the Vieux-Habitants river, a river located on Basse-Terre (Guadeloupe). These images, combined with measurements of the river discharge, allow us to monitor the evolution of the population of boulders. We estimate the smallest discharge that can move the boulders, and calculate the effective transport time. We show that likelihood of a given boulder remaining at the same location decreases exponentially, with an effective residence time of 17 hours.