Sediment Transport of Fine Sand to Fine Gravel on Transverse Bed Slopes in Rotating Annular Flume Experiments

Baar, Anne W.; de Smit, Jaco; Uijttewaal, Wim S. J.; Kleinhans, Maarten G.

Abstract

Large‐scale morphology, in particular meander bend depth, bar dimensions, and bifurcation dynamics, are greatly affected by the deflection of sediment transport on transverse bed slopes due to gravity and by secondary flows. Overestimating the transverse bed slope effect in morphodynamic models leads to flattening of the morphology, while underestimating leads to unrealistically steep bars and banks and a higher braiding index downstream. However, existing transverse bed slope predictors are based on a small set of experiments with a minor range of flow conditions and sediment sizes, and in practice models are calibrated on measured morphology. The objective of this research is to experimentally quantify the transverse bed slope effect for a large range of near‐bed flow conditions with varying secondary flow intensity, sediment sizes (0.17–4 mm), sediment transport mode, and bed state to test existing predictors. We conducted over 200 experiments in a rotating annular flume with counterrotating floor, which allows control of the secondary flow intensity separate from the streamwise flow velocity. Flow velocity vectors were determined with a calibrated analytical model accounting for rough bed conditions. We isolated separate effects of all important parameters on the transverse slope. Resulting equilibrium transverse slopes show a clear trend with varying sediment mobilities and secondary flow intensities that deviate from known predictors depending on Shields number, and strongly depend on bed state and sediment transport mode. Fitted functions are provided for application in morphodynamic modeling

Citation

Baar, A. W., de Smit, J., Uijttewaal, W. S. J., & Kleinhans, M. G. (2018). Sediment Transport of Fine Sand to Fine Gravel on Transverse Bed Slopes in Rotating Annular Flume Experiments. Water Resources Research, 54(1), 19-45. https://doi.org/10.1002/2017WR020604

• Journal Article Type: Article
• Acceptance Date: Dec 17, 2017
• Online Publication Date: Jan 4, 2018
• Publication Date: 2018-01
• Deposit Date: Dec 6, 2019
• Publicly Available Date: Dec 9, 2019
• Journal: Water Resources Research
• Print ISSN: 0043-1397
• Publisher: American Geophysical Union
• Peer Reviewed: Peer Reviewed
• Volume: 54
• Issue: 1
• Pages: 19-45
• DOI: https://doi.org/10.1002/2017WR020604
• Keywords: Transverse slope; Sediment transport; Annular flume; Experiments; Bend flow
• Public URL: https://hull-repository.worktribe.com/output/2851572
• Publisher URL: https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2017WR020604
• Contract Date: Dec 9, 2019