Apparent shear strss and boundary shear distribution in a compound channel flow

Abstract

The flow structure in any compound channel is a complicated process due to the transfer of momentum between the deep main channel section and the adjoining shallow floodplains. However, the boundary shear stress distribution in the main channel and floodplain greatly affects the momentum transfer. In the present work, commonly used equations of shear stress distributions across assumed interface plane originating from the junction between main channel and flood plain using Divided Channel Method ( DCM) are analyzed and tested for different compound channels and their flow conditions using global data. Furthermore, a modified general expression to predict the boundary shear distribution in compound channels for different width ratios is derived that is found to provide significant improvements in the results. The modified boundary shear stress distribution approach is tested for its validity using commonly used data published in the literature and compared with existing models. Analyses are also done to suitably choose an appropriate interface plane for evaluation of stage-discharge relationship for compound channels having uniform roughness. The effectiveness of commonly used stage-discharge methods using the apparent shear stress model and boundary shear distribution models are discussed.