The importance of vegetated zone in rivers has recently been recognized not only for river management but also for water flow environment. From this point of view, some researchers have investigated vegetated open-channel flows to clarify turbulent structures such as mean velocity profiles and turbulence intensity distributions.
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 slit illumination. Instantaneous velocities at many points in the laser slit plane were obtained from these continuous two images of particles. This new method is called the “Particle-Image Velocimetry (PIV)”, and seems to be very powerful to investigate coherent vortices in space and time, because simultaneous velocities at every point can be obtained easily. It was found that the density of vegetation effects on structures such as instantaneous vectors and vorticities.