Apparent Shear Stress in a Compound Channel

Abstract

The flow structure of a compound channel is a complicated process due to the transfer of momentum between the deep main channel and the adjoining shallow floodplains. Experiments are carried out to measure the boundary shear around the wetted perimeter of a two-stage compound channel and to quantify the momentum transfer in terms of apparent shear stress along the assumed interfaces originating from the junction between main channel and flood plain. This is further helpful for deciding appropriate interface plains for evaluation of accurate stage-discharge relationship for a compound channel of all geometry. The lateral momentum transfers are found to magnificently affect the shear stress distribution in flood plain and main channel sub sections. Knowledge of momentum transfer to different interfaces can be acquired from the distribution of boundary shear in the sub sections. In the present work, commonly used equations of shear stress distributions across assumed interface plane are analyzed and tested for various types of compound channels and their flow conditions using published data. Furthermore, a modified expression to predict the boundary shear distribution in compound channels that is good for all width ratios is derived and is found to provide significant improved results. The model are also validated using the well published data.