Sediment Transport of Fine Sand to Fine Gravel on Transverse Bed Slopes in Rotating Annular Flume Experiments. Issue 1 (4th January 2018)

• Record Type: Journal Article
• Authors: Baar, Anne W.; de Smit, Jaco; Uijttewaal, Wim S. J.; Kleinhans, Maarten G.
• Is Part Of: Water resources research. Volume 54:Issue 1(2018)
• Page Start: 19
• Page End: 45
• Publication Date: 2018-01-04
• Subjects: transverse slope -- sediment transport -- annular flume -- experiments -- bend flow; Hydrology -- Periodicals; 333.91
• DOI: 10.1002/2017WR020604
• Languages: English
• ISSNs: 0043-1397

Abstract

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. Key Points: Transverse slope effects are quantified for a large range in helical flow intensity and sediment mobility using a rotating annular flume The resulting trend in slope effect deviates from typical power relations with Shields number and is grainsize‐dependent The relatively low slope effects are in contrast with the tendency to increase slope effects in current morphodynamic models