THEORETICAL AND NUMERICAL MODELING OF RIVER MEANDER MIGRATION WITH FREELY-ADJUSTABLE WIDTH

Most models of river meander migration explicitly or implicitly assume that the river maintains constant width as it migrates. Here we present a model that instead allows width to self-adjust as the channel migrates. The model incorporates: a) a nonlinear, curvature-corrected, depth-averaged formulation of the hydrodynamics; b) a 2D formulation for sediment transport and bed evolution which includes the effects of both bed shear stress and gravity acting on bed sediment; and c) an innovative relation for the rate of migration normal to a given bank. Sufficiently high bed shear stress near the bank results in bank erosion, and thus migration away from the channel centerline. This erosion rate is moderated by slump block armoring. Sufficiently low bed shear stress near the bank results in bank deposition due to vegetal encroachment, and thus migration toward the centerline. The model predicts the co-evolution of channel width and meander planform. Under conditions of cyclically varied flood flow, it also predicts the formation of scroll bars.