Transition and development processes of turbulence structure from flat bed to vegetation flows

Abstract

A lot of aquatic plants are observed in actual rivers, and they are responsible for water quality, nutrient and particle removal, and can reduce turbidity and sediment transport. Recently, the importance of flow and turbulence to the ecology of aquatic benthic organism has been widely reported. For submerged vegetation, a shear-layer is generated near the vegetation edge, and it generates coherent vortices by Kelvin-Helmholtz (KH) instability. These large-scale eddies control mass and momentum exchange between the vegetated and non-vegetated zone, influencing the mean velocity profile, as well as the turbulent diffusivity. Therefore, it is very important to reveal the coherent eddies in vegetated flows.
However, the transition from boundary-layer flow upstream of the vegetation canopy region to a mixing-layer-type flow within the vegetation canopy has not been fully investigated. So, in this study, turbulence measurements were conducted intensively in vegetated open-channel flows by using PIV. The present data provide insight into spatial growth of coherent structure.