Modeling velocity in a compound channel with co-existing emergent and submerged vegetation

Abstract

Vegetation on a floodplain, which contains both emergent vegetation and submerged vegetation, has a considerable influence on the velocity profile of the channel. In this study, a modified analytical model, which considers interactions within the vegetation, is developed based on the Shiono and Knight method (SKM) and the concept of the two-layer model to obtain the transverse distribution of the depth-averaged streamwise velocity in a compound channel with emergent and submerged vegetation. This analytical model includes the influence of secondary flows, lateral shear stress, bed friction, and the drag force caused by the vegetation. The aforementioned model is then employed in a straight compound channel, which contained various types of vegetation. Using suitable boundary conditions, the calculated data are found to be consistent with the experimental data. Subsequently, the effects of dimensionless eddy viscosity coefficient (λ), the depth-averaged secondary flows coefficient, and the impact coefficient β on the model are analyzed. It finds that the λ has a clear effect on the main channel region, but the depth-averaged secondary flows coefficient (K¯) has only a definite effect in the slope sub-region. The β value is significantly less than 1 for the condition of the vegetation with a variable frontal width. The model proposed in the present work can provide a guidance for the investigation of the flow characteristics of the various vegetated channel.