Turbulent structures in partly vegetated open-channel flows with LDA and PI V measurements

Abstract

The effects of vegetation growing in rivers in and at ihe edge of the water on turbulent structures and the associated sediment transport are not claritied yet. in spite of their importance for hydraulics and river engineering. In this study, turbulence measurements of open-channel flows with a vegetated zone at a half channel width were conducted by making use of both, a laser Doppler anemometer! LDA) and the particle-image velocinietry(PIV). It was found that the intensities of ihe secondary currents and the turbulent energy increase with an increase of the Froude number. The turbulence is adveeted span wisely near the free surface by the secondary currents, which are generated by the anisotropy of turbulence. The horizontal vortices near the free surface are generated by the velocity inflectional instability, which increases w ith an increase of Froude number and the vegetation density. The bed (wall) shear stress in the vegetated zone was calculated by the Reynolds equation with the aid of the empirical drag coefficient.