EVOLUTION MECHANISM OF LARGE-SCALE COHERENT STRUCTURE IN OPEN-CHANNEL FLOW WITH SUBMERGED VEGETATION

Abstract

The importance of flow and turbulence to the ecology of aquatic benthic organism has been widely reported. Aquatic vegetation is one of environmental variables that influence turbulence and the ecological condition of rivers. Coherent motions are generated near the vegetation edge and these large-scale eddies control the vertical exchange of mass and momentum between the over- and within-canopies. Therefore, it is of great importance to reveal the coherent eddies in vegetated flows. However, the transition from boundary-layer flow upstream of the canopy region to a mixing-layer-type flow within the canopy has not been fully investigated. So, in this study, turbulence measurements were conducted intensively in vegetated open-channel flows by using PIV. Velocity profiles were measured at 33 positions in a longitudinal direction to examine the evolution mechanism of the coherent structure near the vegetation edge. The present PIV data confirmed efficiency of mixing layer analogy and provide insight into spatial evolution of coherent structure.