A model for phase lag of secondary flow in river meanders

Abstract

The phase lag in a meandering channel is the phase difference between the development (growth and decay) of secondary flow and the channel curvature. The secondary flow is predominantly driven by the channel curvature; its phase lag behind (downstream of) the channel pattern is an 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 physical process for this approach is the growth and decay of secondary flow which has a basis different from flow instability used in previous approaches. The analytical approach employs simplifying assumptions to focus 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, and meander arc length. It is very interesting to note that similar variables for the phase lag have been identified based on different physical processes. The results of this study are compared with previous studies as well as laboratory and field data; they suggest that phase lags in tight meandering channels are pronounced.