Depth averaged velocity and stage-discharge relationships in compound channels with composite roughness

The present study discusses and analyses the influence of composite roughness on the stage-discharge relationships and flow characteristics in compound channels with different channel roughness. An analytical solution to predict depth-averaged velocity, non-dimensional coefficient, integration constants and composite roughness is developed by considering the shear forces acting on the channel beds and walls. The model was applied to three different new experiments and two previous experiments. It indicates that the composite roughness is the key flow resistance parameter that influences the depth-averaged velocity, boundary shear stress distributions, and stage-discharge relationships. The result shows that, in a rough bed, the boundary shear stress in the floodplain was significantly higher than in a heterogeneous and smooth bed. The error analysis is also discussed, and the present model error is the least. Thus, the present analytical solution gives a good prediction of the stage-discharge relationships when compared with experimental data.