Fluvial geomorphology: bank erosion, helical flow, and meander cutoff
Rivers meander due to secondary helical flow (Prandtl) in curved channels — centrifugal force drives surface water outward, eroding the outer bank; bottom return flow deposits sediment on the inner bank (point bar).
The Ikeda-Parker-Sawai (1981) linearized model gives meander migration via a diffusion-like PDE. Positive feedback: curvature → faster erosion → more curvature.
When a loop bends far enough, the river cuts through the narrow neck — forming an oxbow lake.