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Experiments were conducted in a straight smooth compound trapezoidal main channel flanked by two symmetrical floodplains having width ratio value ≈12. The point velocities were measured throughout the compound cross section and isovel patterns were analyzed to determine the values of kinetic energy coefficient (α) and momentum coefficient (β) under varying flow conditions of Froude no. between 0.277 to 0.444 and relative depth of between 0.11 and 0.43. The values obtained for α and β are 2.09 and 1.39 respectively, which are significantly higher than their respective values reported by previous researchers for compound cross sections of different size and shape. New relations are suggested to determine approximate values of α and β with R2 values more than 0.97. It is hoped that the present findings will provide new guidelines for design and research in trapezoidal compound channels

For uniform bounded flow conditions, much of the hydraulic resistance may be attributed to grain roughness and flow characteristics with further accounting for other forces. The resistance to flow by the channel boundary is manifested in the form of distribution of boundary shear along the periphery. In the present work, the validated equations of shear stress distributions across the boundary of main channel and roughened flood plain are analyzed and tested for compound channel having high width ratio of 15.75 and their flow conditions using fresh lab data recorded for this purpose as well as for FCF data for a better comparison.

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. The boundary shear stress distribution in the main channel and floodplain greatly affects the momentum transfer. In the present work, the shear stress distributions across an assumed interface plane originating from the junction between the main channel and flood plain using the Divided Channel Method (DCM) are analyzed and tested for different compound channels and their flow conditions using global data. An improved equation to predict the boundary shear distribution in compound channels for different width ratios is derived that gives better results than other proposed models. Analyses are also done to suitably choose an appropriate interface plane for evaluation of stagedischarge relationship for compound channels having equal roughness in the channel beds and walls. The effectiveness of predicting the stage-discharge relationship using the apparent shear stress equation and boundary shear distribution models are discussed.