Eddy formation

 

I was interested in the number of eddies being formed on the stream at Patterdale. It is clear that they were forming where a fast layer of water down the middle of the stream made contact with a stationary layer at the side of the stream. There must be shear forces involved. So far the best that I can find is that the process is associated with turbulent flow and a high Reynold's number but I was hoping to find out how the forces operated to pull the water first backwards and then round into the right direction.