Hydrodynamics in Kinoshita-generated meandering bends: Importance for river-planform evolution

Most alluvial rivers have a tendency to meander as they flowdownslope.This process of planform evolution is controlled by several components such as flow conditions, sediment, vegetation, and geological characteristics of the channel boundaries. The interactions of these components result in a complex system, which can not be completely described yet, even with the advance of computational, experimental and field resources. Several laboratory-based studies have dealt with periodic symmetric channel configurations and have described the importance of high-amplitude and high-curvature bends in terms of flow structure and sediment redistribution. However, most rivers present not only symmetric, but also asymmetric planform configurations. This study attempts to provide some insight into the hydrodynamic description of the flow in laboratory-scaled asymmetric meandering channels (Kinoshita-generated). Sediment transport and morphological evolution are not considered in this first stage of the study; thus, the meandering channels have been described topographically by using an empirical formulation based on local curvature and channel forming discharge. Four river stages (angular sinuosity: θ =20?, 50?, 90?, 100?) are simulated numerically with the help of a state-of-the-art threedimensional CFD model. The results show the important role of convective accelerations, induced by point bars, in the redistribution of momentum, dynamics of secondary flows, and the distribution of bed shear stresses. Discussions about implications for sediment transport and river-planform evolution are presented.