River engineers often analyze the overbank flows using subdivision techniques through the selection of assumed interface planes. A wrong selection of interface planes between the main channel and floodplain accounts for transfer of improper momentum, which inculcates error in estimation of discharge for compound channel sec- tion. Distribution of apparent shear stress between the main channel and floodplain gives an insight into the magnitude of momentum transfer based on which the discharge estimation using divided channel methods is decided. In the present study, experimental results of momentum transfer at various interface plains for straight and meandering compound channels are presented. Momentum transfer and boundary shear distribution are found to be dependent on the dimensionless parameters viz., overbank flow depth ratio, width ratio, sinuosity, and the orientation of the interfaces. The developed equation helps to predict the discharge carried by com- pound channels of different geometry and sinuosity. The present study indicates that for a straight compound channel, the horizontal division method provides better discharge results for low overbank flow depth and diagonal division method is good for higher overbank flow depths. The best discharge results for a meandering compound channel are obtained through diagonal division method for low overbank flow depths and vertical division method is good for higher overbank flow depths. The adequacies of the present results are verified using present experimental data, and the data collected from the large channel facility (FCF) at Wallingford, UK. These methods agree well when applied to some natural river data.
apparent shear, compound channel, discharge estimation, floodplain, interface planes, main chan-nel, meandering river
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