New formulation for the effective relative roughness height of open channel flows with submerged vegetation

• Published in: Advances in water resources Vol. 86; pp. 46 - 57
• Main Authors: Li, Shuolin, Shi, Haoran, Xiong, Zhengwei, Huai, Wenxin, Cheng, Niansheng
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.12.2015
• Subjects: Auxiliary bed; Channels; Coefficients; Darcy–Weisbach friction factor; data collection; dynamic models; Effective relative roughness height; energy; equations; Friction; Friction factor; Mathematical models; Open channel flow; Roughness; Submerged rigid vegetation; Suspension layer; Vegetation; water resources; Suspension layer; Submerged rigid vegetation; Effective relative roughness height; Open channel flow; Auxiliary bed; Darcy–Weisbach friction factor
• ISSN: 0309-1708; 1872-9657
• DOI: 10.1016/j.advwatres.2015.09.018

•We propose an auxiliary bed in open channel flow with submerged vegetation.•We use the penetration depth to divide flow into suspension layer and basal layer.•We derive an effective relative roughness height for the suspension layer.•We obtain a series of formulae that perform better than those of previous studies. The friction factor f is a crucial parameter for scaling friction resistance and energy loss in open channel flows [11,16]. We propose an auxiliary bed for the distinctive flow structure arising from mutual effects of flow and vegetation. Using the auxiliary bed, a two-layer dynamic model with meaningful physical significance is established to modify equations for channelized flows with vegetation. This new approach divides the vegetated flow into two parts: a basal layer and a suspension layer. A parameter named ‘effective relative roughness height’, analogous to the relative roughness height of unvegetated open channels, is proposed to predict the friction factor of the suspension layer. By analyzing hundreds of datasets, a series of formulae are proposed based on the application of the effective relative roughness height. Comparisons show that the new formulae yield more precise estimates of the flow rate, Manning coefficient and Chezy coefficient than previously published formulae on the subject.