Effect of Vegetation on Shear Stress and Flow Velocity in Compound Channels Using Flow3D Model

Flow in a compound channel differs from a simple channel due to the strong interaction of flow between the main channel and the floodplain. In this research, flow pattern was investigated in a compound channel without vegetation and with vegetation by parallel arrangement. To study the effect of vegetation density on flow pattern, the ratio of inter-plant distance and plant diameter (L/D) was used, which was set to 3, 8, and 16. Results indicated that longitudinal velocity and depth-averaged velocity of flow in the main channel were lower in the non-vegetated condition than the vegetated one. However, this condition was reversed for the floodplain. Under the non-vegetated case, by moving from the center of the main channel to the floodplain, the depth-averaged velocity decreased until it increased at the interface between the main channel and the floodplain. Later the decreasing trend continued. In the parallel arrangement, with a reduction in L/D ratio, vegetation density increased while longitudinal velocity, depth-averaged velocity of flow, shear stress and flow rate at the floodplain decreased by about 65%.