Alternate gravel bar systems

Context

We study here the formation and the evolution of alternated bars systems for alpine gravel rivers that are laterally constrained. More specifically we try to understand how fine sediments (sand and silts) can contribute to this dynamics

Scientific issues

• How do gravel bars forms and evolves?
• How fine sediments impacts this dynamics?

Methods & Results

This study combines field and lab experiments.

In the lab, we benefits from our large tilting flume with the sediment feeding system. Bars are generated by deposition of gravels under a flow, a method that was proposed by James Cooper (Cooper & Tait, ESPL 2009) to better reproduce geometric caracteristics of river beds. With this technic, the surface grain size distribution is different in troughs and crest and the grains presents strong imbrication. Over such a bed, we will then study fine sediment dynamics both in suspension and within the porous bed.We will identify preferential zones for erosion and deposits, the potential for resuspension and the possible pumping effect.

Field experiments were conducted on the Arc-Isère site. During the PhD of M. Jaballah,we studied under what conditions alternated bar system developed (width to depth ratio, reach equilibrium, etc.) and how they can evolve to a confined laterally translating system.

Typical alternated bar systme evolution in the Arc river: intially an alternated bar system with islands that disappear gradually to form an alternated bar system.

Projects

• 2019-2022: DEAR ANR project:  Deposition and erosion of fine sediment in Alpine rivers (see web site https://dear.irstea.fr/).
• 2014-2015: Water Agency project « Lidar datapost-processing for morphological studies »

PhDs and post-doctorates

• 2019-2022 : Gupta S. Dynamique des stocks de fines sur un système de bancs alternés et impact sur la morphodynamique des bancs : étude de laboratoire.
• 2010-2013 : Jaballah M. Influence des sédiments fins sur la dynamique d’une rivière de montagne aménagée : l’Arc en Maurienne. Université C. Bernard, Lyon 1. 195 p.

Publications

• Jaballah, M., Camenen, B., Pénard, L., & Paquier, A. (2015). Alternate bar development in an alpine river following engineering works. Advance in Water Res. 81:103-113.