Criticality on the planform behavior of the Ganges River meanders

Abstract

The critical point of planform transition from straight to meandering in the wandering Ganges is identifiable. Maps indicate cutoffs occur at multiple decadal intervals. Recent remote-sensing data indicate that four similar meanders cutoff, or attempted to cutoff, after c. 31-35 years, primarily due to channel-aggradation. As main-channels aggrade, sinuosity is maximized for broad channel widths and small radii of curvature and relaxes for bends of greater radii. Maximized form resistance occurs close to self-organized criticality and super-elevated flows develop along the outer banks of bends and promote cutoffs. Avulsions lead to main channel narrowing and prevent further bend tightening, relaxing the system by reducing sinuosity. Thus, the wandering river oscillates in space and time across the transition from a more ordered to a more chaotic state. Planform behaviour is described by the Jerolmack-Mohrig mobility number and the Parker stability criterion. These parameters well-define meander behaviour as they approach criticality and then relax via partial or completed avulsions. The results have significance for river engineering, river network and stratigraphic modelling. Such an approach could be of practical value when predicting the behaviours of other major wandering rivers.

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ORCID for Peter Atkinson: orcid.org/0000-0002-5489-6880

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