Abstract
Significant contributions of flow and turbulence to ecology related to aquatic benthic organism has been widely reported. Aquatic vegetation is one of environmental variables that influence turbulence and the ecological condition of rivers. Coherent turbulent motions are generated near the vegetation edge and these large-scale coherent eddies control the vertical exchange of mass and momentum between the over- and within-canopies. However, the effect of the submerged vegetation on the turbulent mixing process has not been fully investigated. Therefore, continuous dye-injection experiments were conducted to evaluate the vertical mass transport in open-channel flow with rigid vegetation models. The combination of PIV (Particle Image Velocimetry) and planar LIF (Laser-induced Fluorescene) technique is applied to reveal mass transfer in the vegetated open-channel flows. Two-dimensional data allow the identification of coherent structures and quantification of the vertical mass transport. The results revealed that the vortex structure lose coherence for flexible vegetation flow as compared to rigid vegetation flow. The values of the turbulence diffusivity become larger for rigid vegetation flow than those for flexible vegetation flow.
