Meandering Morphodynamics: Insights from Laboratory and Numerical Experiments and Beyond

This paper, written to mark the 60th anniversary of the Journal of Hydraulic Engineering, focuses on the nature of meandering flow and its coupling to bed and bank deformation. An outline of the present understanding of the kinematics of meandering flow and how the flow shapes the bed, with a view towards the conditions in real alluvial meandering rivers, is presented. The flow and its interaction with the bed are analyzed by treating separately the effects on the flow of channel curvature and streamwise variation of channel curvature and by considering the results of numerous laboratory and numerical experiments carried out to date. The approach is used to explain essential differences in meandering bed topography exhibited by streams with varying values of sinuosity and width-to-depth ratio. The paper is also used as an opportunity to address the question of why, in the absence of geological constraints, some streams tend to remain regular in plan shape (i.e., symmetric in plan view with regard to the axis of bend) even when their loops actively expand laterally, whereas others acquire irregular plan shapes. This question is considered in view of the intrinsically different mechanics of bed deformation and bank erosion and a new experiment on bank erosion. The paper suggests that differences in the erodibility of the bed and banks may be a significant contributing factor to the planimetric fate of the stream. (C) 2017 American Society of Civil Engineers.