Prediction of flow velocity profiles of open-channels with submerged vegetation

For submerged vegetated flow, the vertical velocity profile can often be described by two layers, the vegetation layer in the lower region and the surface layer in the upper non-vegetated region. In this paper, based on the momentum equation of flow with an assumption of turbulent eddy viscosity being a linear relationship with the local velocity, a two-layer velocity profile for flow in an open-channel with rigid submerged vegetation is proposed. The proposed model was tested against several datasets widely used previously in literature. Our studies show that the model can predict the velocity profiles well for all datasets. In the test, it was found that the mixing length scale of eddies (λ) is well related with both vegetation height (h) and flow depth of surface layer (i.e. height of non-vegetation layer, H-h). Close examination of the length scale λ in the proposed model showed that when λ/h = 0.03(H/h-1)1/2, the model can predict velocity profiles well for all the datasets used. The datasets used include various submergence [flow depth (H)/vegetation height (h) =1.25 ~ 3.33], different vegetation densities of a =1.1 ~ 18.5 m-1 (a defined as the frontal area of the vegetation per unit volume) and bed slopes (So = 4.0x10-4 ~4.0x10-3).