Dispersion in Submerged Vegetated Flow with Coherent Vortices

Abstract

The presence of submerged vegetation divides flow velocity vertically into overflow and vegetation velocities connected by a strong shear. In addition, the flow structure exhibits periodic oscillations at the interface called Kelvin-Helmholtz vortices. The entire flow is divided into a combined vortex-overflow region that covers the overflow and upper part of the vegetation and a lower vegetation region below the vortices. A closed-form solution for longitudinal dispersion in this flow field is derived, which is an addition of the steady flow dispersion in the two regions and the dispersion caused by inefficient exchange between the two regions. The shear velocities in both the regions are modeled by using power law, whereas the vortices are modeled by the periodic components of the combined vortex-overflow stream function. The proposed dispersion model depicts shear-induced steady flow dispersion and vortex-induced dispersion caused by the inefficient exchange and shows reasonable agreement with past data.