Investigation of Coherent Vortices in Partly Vegetated Open-channel Flows with a Particle-Image Velocimetry

In this study, images of very small 75μm diameter particles uniformly scattered in vegetated open-channel flows were taken using a CCD camera and 2W Argon-Ion laser light sheet. Instantaneous velocities at manypoints in the laser slit plane were obtained from these continuous two images of particles. This new method iscalled the “Particle-Image Velocimetry (PIV)”, and seems to be very powerful to investigate coherent vortices inspace and time, because simultaneous velocities at every point can be obtained easily. It was found that thedensity of vegetation affects on turbulent structures such as instantaneous vectors and vorticities.