Sediment transport by eddies formed in the boundary layer of open flows

The coherent structures formed near the bottom of the channel flow have been experimentally investigated. The experiments were conducted in decelerating flows of large aspect ratio in the (depth based) Reynolds number range of 2500–5000. The results of visualizations indicate that persistent structures near the bottom can be classified as cylindrical eddies revolving on span axis in opposite (positive and negative) directions. The negative eddies organize themselves periodically at the equal steps along the flow direction. At this moment they captures bottom particles forming parallel ridges on the flow bottom. They move along the cycloid trajectory with captured sediments losing them very slowly if circulation of the eddy is sufficiently high. Positive eddies are formed by the viscous force due to negative eddies fly out upward from the bottom. Positive eddy is visualized as dyed oval structure with one or two tails.