Hydrologically driven modulation of cutoff regime in meandering rivers

Abstract

Bend cutoff is a fundamental process shaping meandering rivers. Despite the widely accepted differentiation between neck and chute cutoffs, a significant knowledge gap persists regarding the factors responsible for the occurrence of each cutoff regime and the specific conditions triggering the regime. Here, we used field and photogrammetric data derived from a global set of 22 meandering rivers, stretching more than 5500 km in total river length, to disentangle the controlling factors behind the cutoff regime in meandering rivers. We found that whether a meandering river forms a chute rather than neck meander cutoff depends primarily on the variability of overbank discharges. Short-lived, high-magnitude overbank floods promote the formation of chute cutoffs, aided by (though not required) reduced riparian vegetation density, enhanced stream power, and flow confinement within the river valley. In contrast, neck cutoffs are prevalent in rivers characterized by limited variations in bankfull hydrology, typically associated with low-magnitude, long-lasting overbank floods. Distinct cutoff regimes also discernibly affected floodplain geomorphology, with a chute regime resulting in more frequent cutoff occurrences. Our results suggest that human-induced alterations of river hydrologic regime can potentially cause fundamental shifts in the cutoff behavior of meandering rivers, thus affecting sediment residence time and carbon fluxes in alluvial floodplains.