Abstract
The classic hydraulic resistance formulas, such as those in the Darcy-Weisbach methods, perform well in the hydraulic design with the characteristic roughness height ks smaller than the flow depth, which can be linked with the momentum roughness height based on the turbulent boundary-layer theory with the log-law formulation. However, when the roughness scale is of the same order as the flow depth, the traditional log-law formulation cannot provide satisfactory results because the flow structure is complicated and the vortices in different layers are dominated by various principles, such as the Karman streets near the channel bed, the mixing layer near the vegetation top, and a canonical turbulent boundary layer above the vegetation layer. Thus, the distribution of the streamwise velocity in the vegetated flow is a combination of the velocity profile linked with the dominant vortex and shows significant differences as compared with the traditional log-law distribution. This paper proposes a new characteristic roughness height of vegetation kv by linking vegetation attributes, especially the characteristics of the cross section in the flow within the vegetation. The power law resistance formula is derived based on a large amount of experimental data. Results show that the new formula is applicable to shallow flows with vegetation.
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Project supported by the China Postdoctoral Science Foundation (Grant No. 2017M610949), the National Natural Science Foundation of China (Grant No. 51439007).
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Wang, Wj., Peng, Wq., Huai, Wx. et al. Roughness height of submerged vegetation in flow based on spatial structure. J Hydrodyn 30, 754–757 (2018). https://doi.org/10.1007/s42241-018-0060-3
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DOI: https://doi.org/10.1007/s42241-018-0060-3