Numerical simulation of flow velocity distribution and shear stress in meandering compound channels

In this research, using FLOW3D software, the flow velocity distribution and shear stress of the bed in meandering compound channels due to the change of floodplain width and relative depth were investigated. For this purpose, four sections of meandering compound channels with floodplain width having 3.3, 4.31, 5.32 and 6.33 meters and three relative depths of 0.26, 0.35 and 0.45 have been used. The results of numerical simulation show that by increasing the floodplain width, the depth averaged velocity and bed shear stress are reduced. So that with a 92% increase in floodplain width, the maximum flow velocity in the main channel decreases by 24% , and the depth averaged velocity at relative depths 0.45 and 0.26 are reduced by 17% and 21%, respectively; and the rate of change of depth averaged velocity is more noticeable due to a change in the width of floodplain for low relative depths. The effect of changing the floodplain width on the bed shear stress has the highest value in the mid-section between two apexes (CS3 section); so that by 92% increase in the floodplain width in the mid-section (CS3), the bed shear stress is reduced by 35%. Also, the amount of boundary shear stress in the inner arch wall in all channels which is higher than the boundary shear stress in the outer arch wall; and the maximum amount of wall shear stress occurs near the bankfull level of the main channel and by increasing the relative depth, the wall shear stress increases.