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Sand settling through bedform‐generated turbulence in rivers
Author(s) -
Yuill Brendan,
Wang Yushi,
Allison Mead,
Meselhe Ehab,
Esposito Chris
Publication year - 2020
Publication title -
earth surface processes and landforms
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.294
H-Index - 127
eISSN - 1096-9837
pISSN - 0197-9337
DOI - 10.1002/esp.4962
Subject(s) - settling , bedform , eddy , turbulence , geology , sediment transport , mechanics , sediment , geomorphology , environmental science , physics , environmental engineering
Fluvial bedforms generate a turbulent wake that can impact suspended‐sediment settling in the passing flow. This impact has implications for local suspended‐sediment transport, bedform stability, and channel evolution; however, it is typically not well‐considered in geomorphologic models. Our study uses a three‐dimensional OpenFOAM hydrodynamic and particle‐tracking model to investigate how turbulence generated from bedforms and the channel bed influences medium sand‐sized particle settling, in terms of the distribution of suspended particles within the flow field and particle‐settling velocities. The model resolved the effect of an engineered bedform, which altered the flow field in a manner similar to a natural dune. The modelling scenarios alternated bed morphology and the simulation of turbulence, using detached eddy simulation (DES), to differentiate the influence of bedform‐generated turbulence relative to that of turbulence generated from the channel bed. The bedform generated a turbulent wake that was composed of eddies with significant anisotropic properties. The eddies and, to a lesser degree, turbulence arising from velocity shear at the bed substantially reduced settling velocities relative to the settling velocities predicted in the absence of turbulence. The eddies tended to advect sediment particles in their primary direction, diffuse particles throughout the flow column, and reduced settling likely due to production of a positively skewed vertical‐velocity fluctuation distribution. Study results suggest that the bedform wake has a significant impact on particle‐settling behaviour (up to a 50% reduction in settling velocity) at a scale capable of modulating local suspended transport rates and bedform dynamics. © 2020 John Wiley & Sons, Ltd.