Analytical solution for lateral depth-averaged velocity distributions in meandering compound channels with vegetated floodplains

Abstract

Meandering compound channels, which are the most common platform acquired by natural rivers, are typically equipped with vegetated floodplains that exhibit complex hydraulic characteristics and sediment transport processes. Given that studying depth-averaged streamwise velocity is the foundation for determining flood discharge performance and sediment carrying capacity, this paper presents an analytical solution to forecast the lateral velocity distribution in meandering compound channels with vegetated floodplains. The analytical model, which incorporates the effects of bed friction, vegetation-induced drag force, transverse shear turbulence, and secondary flows, is derived from the longitudinal depth-integrated Navier–Stokes equation and the continuity equation by assuming the secondary current term and additional Reynolds stress term to be laterally linear. The proposed model is then successfully applied to curved compound channels with different vegetated floodplains reported in the literature. The satisfactory agreement between predicted and experimental results of velocity distribution validates the effectiveness of the analytical model. Thereafter, the impact of varying characteristic parameters on the lateral profile of the velocity is discussed and analyzed by applying the validated analytical model. Results indicate that the secondary current coefficients and the dimensionless eddy viscosity exert more pronounced influences on the velocity distribution than the parameters associated with the vegetation-triggered drag force. Furthermore, it is found that the sizes and signs of the secondary current coefficients are contingent upon the intensities and rotational directions of the secondary flow cells. The presented model can be employed as an alternative methodology to gain insight into the flow characteristics of curved rivers with vegetated floodplains.