Investigation of Three-parameter Flow Resistance Model in Coarse-Bed Rivers (Case Study: Deryuk River)

Document Type : Research Paper


Department of Water and Environment, Faculty of Civil Engineering, Iran University of Science and Technology, Tehran, Iran


The most common approach adopted for flow resistance in open-channel hydraulic is the Manning equation. Since the Manning roughness coefficient considers the water depth and flow velocity as constant and the flow conditions in rivers are non-uniform, it is necessary to adjust this equation by considering the geometric and hydraulic characteristics of the rivers. Accordingly, this paper presents a three-parameter flow resistance model, which is a more general form of the Manning equation. The parameters of this model were calibrated by using measurements of 8 sections of a coarse bed-river, Deryuk in Mazandaran province, which has vegetation on its banks. Shear speed was calculated using three methods of boundary-layer characteristics; parabolic law, two-point and the implicit approach, Darcy–Weisbach. The results showed that the Darcy-Weisbach implicit method has high accuracy in estimating flow resistance. Also, the validity of the results was confirmed by comparing the flow discharge calculated by the model with the measured flow discharge. The results showed that the three-parameter model in 75% of the sections had a better estimate than the Manning equation. Also, the average error percentage of the proposed model was 24%, while this value was calculated 32% for the Manning equation.


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