The Kosi River shifts laterally over the Himalaya foreland plain by continual minor cutoffs and bank cutting and by episodic major shifts across watersheds, by moving into and then out of preexisting, adjacent, less actively aggrading streams. Migration is unidirectional because after a channel is filled to instability, floodwater will drain preferentially into a new adjacent low rather than across it to the next watershed or back to the last abandoned channel. Major shifts seem stochastic and autocyclic; they do not correlate with the many severe quakes and floods that undoubtedly helped prime the system for shifts.
