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It is very important in river management and hydraulic engineering to investigate the hydrodynamic properties in vegetated open-channel flows. There are a lot of experimental and numerical studies on open-channel flows over vegetated canopies, in which velocity distributions are largely varied with not only vertical but also streamwise and spanwise diretions. In particular, it is needed to reveal such dispersive properties of velocity components, because it is considered that the velocity dispersion has significant relations with turbulence transport and generation due to vegetations. Therefore, in this study, turbulence measurements were conducted in vegetated canopy open-channel flows by using two-component laser Doppler anemometer, and turbulence structure and dispersive effects were revealed experimentally.

Turbulence characteristics of open-channel flows with the vegetated zone are greatly affected by whether the vegetation is completely soaked or not. Structures in this kind of flows become not two-dimensional, but three-dimensional, when all part of the vegetation is in the water. In spite of many studies investigating these three-dimensional structures, little is examined concerning the structure near the water-surface. In this study, we simultaneously measured water-surface fluctuations and velocity in open-channel flows with the vegetated zone at the half channel width using an ultrasonic sensor measuring water-surface and a laser Doppler anemometer (LDA), and examined effects of the water-surface on three-dimensional turbulent structures. The experimental results revealed the characteristics of surface waves and correlation properties between surface waves and velocity fluctuations. Consequently, it was found how they contribute the transverse momentum mixing between the vegetated and non-vegetated zones.

This paper describes the numerical simulation results of cavity in open-channel flows by means of Large Eddy Simulation (LES). The comparison, between numerical simulation and turbulence measurements conducted by making use of a two component fiber-optic laser Doppler anemometer (FLDA), was carried out in two cases. The results indicate that LES can reproduce the variations of mean velocities and turbulent statistics by trench length changes, and these variations may be relevant to the cycle of separated vortices and the position and size of the large circulating vortex.

It is very important in River Engineering and Hydraulic Engineering to investigate the effects of side-bank angle q between the main channel and flood plain on velocity profiles and secondary currents in compound open-channel flows. In the present study, very accurate turbulence measurements were conducted with a new twocomponent fiber-optic laser Doppler anemometer (FLDA). Because the measuring points were about 500, accurate contour lines of velocity and vector plot of secondary currents could be obtained and analyzed in detail. Of particular significance is the shift of velocity-dip phenomenatowards the main channel as the flood-plain angle decreases.

Turbulent structures in compound open channel flows were calculated by the energy dissipation model, combined with the algebraic stress model suggested by Naot & Rodi (1982). The three-dimensional flow with secondary currents was solved numerically using the SIMPLE algorithm. These numerical simulations coincide well with the experimental data which were obtained with a two-component fiber-optic laser Doppler anemometer (FLDA) by Tominaga & Nezu (1991).

lt is very important in Hydraulic Engineering as well as, in Fluid Hechanics to reveal the response of velocity profiles and bed shear stress to abrupt change of bed roughness in open chamlel flows. ln the present study, accurate velocity measurements over abrupt1y changed k-type roughness elements were conducted in open channel flows by making use of two-component laser Doppler anemometer. An inmer boundary layer develops from the boundary point (x=0) between smooth and rough beds. The velocity and turbulence distrlbutions in the inner boundary layer rapidly respond to abruptly changed roughness. of particular significance is that the bed shear stress overshoots immed iately downstream of the abrupt roughness change.This finding is very important to construct bed protection works in rivers.