Velocity distribution in non-prismatic compound channels

River-flow modelling relies on accurate prediction of the stage-discharge relationship. Additionally, the lateral distribution of the longitudinal velocity component should be estimated for sediment transport investigations. In compound channels, the shear stress at the interface between the floodplains and the main channel strongly affects both conveyance and velocity distribution. This effect is reinforced when mass transfer occurs between subsections due to channel non-prismaticity. The stage-discharge relationship and the velocity distribution in prismatic compound channels can be computed using the lateral distribution method (LDM). The present paper investigates an extension of the LDM to non-prismatic channels. The physical meaning of the so-called secondary-current term is discussed. Numerical results are compared with previous velocity measurements in a symmetrically narrowing compound channel and to new bed shear-stress measurements in the same geometry.