An Experimental Study of Channel Confluences

Abstract

The evolution and morphology of the confluences of model channels in a small flume were documented. Scour holes developed that were similar to features described at the confluences of branch channels in the braided North Saskatchewan River, North Platte River, and Medano Creek. The scour holes were maintained by turbulence and helicoidal flow cells generated by the converging flows; their depths and cross-sectional areas increase as turbulence increases. Scour hole depth increases rapidly as confluence angle increases from 15° to 90°, and more slowly up to 180°. Depth also increases as the difference between the discharges of the two confluent tributaries declines, and is a maximum when discharges are precisely equal. Depth decreases, other things being equal, as total sediment load increases. Apparently, an increase in sediment load requires an increase in shear stress for it to be transported, and therefore a constriction of flow and commensurate increase in flow velocity. Scour at the confluences of no...