Prediction of apparent shear stress in an asymmetric compound channel

Abstract

There is always an exchange of momentum between the deep main channel and its shallow floodplains of a compound channel section. When rivers have single side floodplains, they are known as asymmetric compound channels. Momentum transfer phenomenon has the effect of increasing floodplain shear and decreasing the main channel shear. In symmetrical compound channels, the momentum transfer occurs from both sides of the main channel to the floodplains whereas, for an asymmetrical compound channel, there is a stronger interaction takes place as compared to the symmetrical case. This causes more non-uniform boundary shear stress distribution as compared to the symmetrical cases. Experiments are conducted to measure the boundary shear stress distribution of an asymmetric compound channel that helps to quantify the momentum transfer in terms of apparent shear stress at the interface. Analysis of the apparent shear is useful in deciding the choice of appropriate interface planes for stage–discharge relationship of a compound channel. In the present work, an improved expression to predict the apparent shear stress, especially in an asymmetrical compound channel is developed. The strength of the new expression to predict apparent shear stress is also found to be better than the models of other investigators.