Skip to Main content Skip to Navigation
Journal articles

Entrainment, motion, and deposition of coarse particles transported by water over a sloping mobile bed

Abstract : In gravel bed rivers, bed load transport exhibits considerable variability in time and space. Recently, stochastic bed load transport theories have been developed to address the mechanisms and effects of bed load transport fluctuations. Stochastic models involve parameters such as particle diffusivity, entrainment, and deposition rates. The lack of hard information on how these parameters vary with flow conditions is a clear impediment to their application to real-world scenarios. In this paper, we determined the closure equations for the above parameters from laboratory experiments. We focused on shallow supercritical flow on a sloping mobile bed in straight channels, a setting that was representative of flow conditions in mountain rivers. Experiments were run at low sediment transport rates under steady nonuniform flow conditions (i.e., the water discharge was kept constant, but bed forms developed and migrated upstream, making flow nonuniform). Using image processing, we reconstructed particle paths to deduce the particle velocity and its probability distribution, particle diffusivity, and rates of deposition and entrainment. We found that on average, particle acceleration, velocity, and deposition rate were responsive to local flow conditions, whereas entrainment rate depended strongly on local bed activity. Particle diffusivity varied linearly with the depth-averaged flow velocity. The empirical probability distribution of particle velocity was well approximated by a Gaussian distribution when all particle positions were considered together. In contrast, the particles located in close vicinity to the bed had exponentially distributed velocities. Our experimental results provide closure equations for stochastic or deterministic bed load transport models. ©2016. American Geophysical Union. All Rights Reserved.
Document type :
Journal articles
Complete list of metadatas

https://hal-univ-rennes1.archives-ouvertes.fr/hal-01416361
Contributor : Laurent Jonchère <>
Submitted on : Wednesday, December 14, 2016 - 1:55:28 PM
Last modification on : Tuesday, March 3, 2020 - 10:35:57 AM

Links full text

Identifiers

Citation

J. Heyman, P. Bohorquez, C. Ancey. Entrainment, motion, and deposition of coarse particles transported by water over a sloping mobile bed. Journal of Geophysical Research: Earth Surface, American Geophysical Union/Wiley, 2016, 121 (10), pp.1931--1952. ⟨10.1002/2015JF003672⟩. ⟨hal-01416361⟩

Share

Metrics

Record views

118