A reliable estimation of sediment transport in gravel-bed streams is
important for various practical engineering and biological studies
(e.g., channel stability design, bed degradation/aggradation,
restoration of spawning habitat). In this presentation, I will present
laboratory experiments conducted by Albert Herrero and Emeline Perret
[1] investigating the infiltration of fine sediment within a coarse
gravel bed and the transport of the resulting infiltrated gravels at low
bed shear stresses. Effects of fine sediments were examined by testing
beds with sand, artificial fine sand or cohesive silt infiltrated in the
gravel matrix.
Analysis of the experimental data revealed that the transport of gravel
particles depends upon the bed arrangement, the bed material properties
(e.g., size and shape, consolidation index, permeability) and the
concentration of fine sediments within the surface layer of moving
grains. This concentration is directly related to the distribution of
fine particles within the gravel matrix (i.e., bottom-up infiltration or
bridging) and their transport mode (i.e., bedload or suspended load).
Compared to loose beds, the mobility of gravel is reduced for packed
beds and for beds clogged from the bottom up with cohesive fine
sediments; in both cases, the bed shear stress for gravel entrainment
increases by about 12%. On the other hand, the mobility of gravel
increases significantly (bed shear stress for particle motion decreasing
up to 40%) for beds clogged at the surface by non-cohesive sand particles.
This results will be complemented by results obtained during the PhD of
Shashank Gupta [2], where infiltration of fine sediment took place on an
gravel alternated bar system instead of the flat bed explored
previously. Both infiltration paterns and sediment transport will be
presented.
[1] Perret, E., Berni, C., Camenen, B., Herrero, A., and El kadi
abderrezzak, K. (2018). Transport of moderately sorted gravel at low bed
shear stresses: The role of fine sediment infiltration. Earth Surface
Processes and Landforms 43, pp. 1414–1430
[2] Gupta, S., Laboratory experiments on fine sediment erosion and
deposition in an alternated
bar system and its impact on bar morphodynamics, PhD University Claude
Bernard, Lyon 1.