Abstract
Horizontal, periodic vortices generated at the boundary of vegetated area along river bank was studied in terms of linear stability analysis using Rayleigh equation. A dimensionless angular frequency, at which an infinitesimal disturbance takes the maximum growth rate, is found to be uniquely correlated with a dimesionless parameter for the vegetation density. Laboratory tests were also performed, in which the periodic vortices were observed by dye injection into the flow field and the period was measured using a wave gage. The measured period of vortex generation was explained very well by the linear stability analysis. The present study reveals that the periodic vortices are generated by instability induced by the existence of an inflection point in the lateral distribution of depth-averaged flow velocity.
