Bedload monitoring under conditions of ultra-high suspended sediment concentrations

F. Liébault, H. Jantzi, S. Klotz, J. B. Laronne, A. Recking

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

The bedload response of the Moulin Ravine, a small alluvial system draining a very active Mediterranean badlands landscape entrenched into Jurassic black marls of the Southern French Prealps, has been investigated using an automatic Reid bedload slot sampler. This site is known for its exceptional sediment transport conditions thanks to a long-term monitoring program that started in the late 1980s, revealing a mean annual bedload yield of 2810 t km−2 yr−1, and suspended sediment concentrations (SSCs) during flow events commonly reaching 100 g L−1. With the deployment of the slot sampler, it has been possible to record instantaneous bedload fluxes during 10 s time increments and to investigate bedload response under flow conditions with ultra-high SSCs. Bedload records cover 4 flashy summer flow events induced by heavy convective storms including a 20-yr return period event. Due to the very high SSC conditions these events challenge bedload monitoring. Even if slot sampling has been recognized as insensitive to fine sediments (silts and clays), it has never been tested in such exceptional muddy flow conditions. The bedload slot sampler performed well in such conditions. A flow-invariant proportion of fines (∼15–20%) was captured in the slot sampler during flows. This proportion is equivalent to its content in the active bedload layer during summer flows, suggesting that fines enter the slot embedded with coarse particles. Instantaneous bedload fluxes recorded in the Moulin are amongst the highest hitherto reported values worldwide, providing evidence of the exceptional sediment transport conditions of marly alpine badlands. The dimensionless entrainment threshold is one order of magnitude higher than commonly reported for gravel-bed rivers, likely reflecting the cohesion effect of fines intruded in the channel surface and subsurface.

Original languageEnglish
Pages (from-to)947-958
Number of pages12
JournalJournal of Hydrology
Volume540
DOIs
StatePublished - 1 Sep 2016

Keywords

  • Bedload monitoring
  • Draix observatory
  • Gully
  • Mediterranean badlands
  • Reid bedload slot sampler
  • Ultra-high suspended sediment concentration

ASJC Scopus subject areas

  • Water Science and Technology

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