Author(s): M Trevisson; O Eiff

Linked Author(s):

Keywords: Static equilibrium; Rough beds; Bedload transport; Gravel bed; Sediment supply limited

Abstract: This work focuses on the morphological evolution of a gravel bed filled with sediments and eroding supply-limited conditions. A series of experiments under different flow conditions were conducted to establish whether and how an equilibrium of the bed is reached. Gravel beds can be widely found in mountainous rivers, where they represent important aquatic habitats. The release of large amounts of sediments from dams or following changes in land use can clog the gravel substrate, affecting the aquatic ecosystem. Sediment transport in rivers is usually studied assuming a well-sorted granulometry, based on classical models, which leads to unreliable sediment transport predictions of the finer mobile fractions when the bed presents a matrix made of coarse immobile particles. The transport of fine sediments is in this case thought to be influenced by three main types of possible processes: first, the mobility of the particles can be reduced by a sheltering effect due to gravel; second, flow separation around roughness elements increases locally the shear stress on the finer grains; third, by considering that the shear stress is partitioned over roughness elements and the grains, the available stress to move this sediment is reduced. In sediment supply limited environments, the overall result of these three processes considerably reduces sediment transport, as it was found in the field of aeolian sediment transport. They showed that, as the roughness elements’ protrusion from the bed increases, sediment transport tends to zero. In this work, an experimental approach is taken to investigate the possibility to reach, in sediment supply limited environments, an equilibrium of the bed, characterized by a constant fine sediment level and no sediment transport.

DOI: https://doi.org/10.3850/978-981-11-2731-1_148-cd

Year: 2018