On the effect of relative flood depth on flow hydraulics in meandering compound channels

The rivers, as the main watercourse and natural drainages, always play a significant role in the conveyance of flood flows. During floods, the water crosses the main section of the river and enters the floodplains. In this case the river crossing becomes a compound cross section. In present research work, by studying meandering compound channels, the effect of changing relative depth of flood currents on the hydraulic flow conditions and the rate of discharge are investigated. For this purpose, six channels with different sinusoidal rates at three relative depths with different flood rates were investigated by FLOW3D software. The results of numerical simulation show that by increasing relative depths from 0.26 to 0.45 (73% increase), the depth averaged velocity in all channels increased by 25% and the rate of discharge passing through the main channel decreased by 33%. Also, the results of this study show that the bed shear stress near the inner arch of the main channel is more than the outer arch and by reducing the relative depth in the compound channel, the amount of bed shear stress and flow velocity decreases. And the amount of shear stress of the inner arch wall of the main channel in all channels is higher than that of the outer arch wall, and by increasing the relative depth the amount of shear stress of the wall is increased.