Field Investigation of Flow Resistance Due to Vegetation Patch (Case Study: Shapur, Fahlian and Dalaki Rivers)

Flow resistance in rivers with vegetation patches is one of the challenging parameters in river engineering. This study aimed to investigate the effect of vegetation patches on flow resistance in Shapur, Fahlian, and Dalaki rivers. The data measured in this study include velocity measurement, surveying, and bed sampling. In this study, considering the simplifying assumptions, the equation for the flow resistance due to vegetation patches was derivated. Accordingly, the flow resistance due to vegetation patches was obtained by the difference in the flow resistance due to bed from the value of the total flow resistance for each section. The results show that the average percentage of vegetation patches’ contribution from the total flow resistance is 44%, which shows the significant effect of vegetation patches on flow resistance. In addition, an investigation of 71 measured velocity profiles showed the phenomenon of Dip in the velocity profiles near the vegetation patches, and by moving away from the vegetation patches, the effect of this phenomenon is reduced and the profiles become S-shaped.