A MODEL FOR PHASE-LAG OF SECONDARY FLOW IN RIVER MEANDERS

The phase lag in a meandering channel is the phase difference between the development (growth and decay) of secondary flow and the channel c urvature. The secondary flow is predominantly driven by the channel cu rvature; its phase lag behind (downstream of) the channel pattern is a n important feature in the mechanics of flow and the migration pattern of meander bends. This paper presents an analytical solution for the phase lag derived based on the mechanics of secondary flow. The physic al process for this approach is the growth and decay of secondary flow which has a basis different from flow instability used in previous ap proaches. The analytical approach employs simplifying assumptions to f ocus on the role of secondary flow; its limitations in application are described. Major variables affecting the phase lag are identified to be channel roughness, suspended sediment concentration, flow depth, an d meander arc length. It is very interesting to note that similar vari ables for the phase lag have been identified based on different physic al processes. The results of this study are compared with previous stu dies as well as laboratory and field data; they suggest that phase lag s in tight meandering channels are pronounced.