On the Prediction of the Characteristic Times of River Meander Cutoff Sequence: Theoretical Model and Comparison With Laboratory and Field Observations

Abstract

Natural evolution of lowland rivers typically involves the continuous elongation of their axis, the formation of simple or compound loops, and the occurrence of cutoffs. Cutoff is the bypass of a meander loop by a shorter straight path and the consequent formation of an abandoned reach, the so-called oxbow lake. Meander cutoffs in alluvial valleys form either by the progressive narrowing of the neck until the two opposite limbs meet, or by the formation of a chute channel directly across the meander neck itself. Lewis and Lewin (1983) reserve the term "neck cutoff" to cases in which the opposite limbs of the bend were considerably less than a channel width apart at the time of breaching, while using "chute cutoff" for cases in which a much longer breach channel was created. Since cutoff events are cyclically sporadic and are recognized to trigger important geomorphologic processes (Mosley, 1975), their occurrence practically identifies two different characteristic timescales: a short timescale, which refers to the evolution of single meanders before the cutoff, and a long timescale, which includes multiple, more or less periodic cutoffs (see also Camporeale et al., 2005;Hooke, 2004).The study of the role of cutoff occurrence at large river dynamics timescales is usually carried out according to two different though interconnected approaches: the descriptive/experimental and the numerical method. The descriptive method dates back to very classical studies, where it was aimed at deriving some empirical laws that could relate the hydraulics of the process to the representative geomorphological parameters (e.g., Carlston, 1965;Hansen, 1967;Leopold & Wolman, 1960). From then, several laboratory/field surveys concerning cutoff (chute or neck) events, oxbow lake formation and post-cutoff adjustments have been carried out (e.g.,

Numerical modeling of two-dimensional hydrodynamics in an artificial chute cutoff under different hydrologic conditions

“…Cutoff represents an abrupt alteration in the evolution of meandering rivers 1 , resulting in rapid reductions in their length and constraining their curvature and morphological intricacy [2][3][4] . It is an efficient method of rectifying bends to flooding control, irrigation, and instream navigation.…”

High-resolution modeling of meander neck cutoffs: laboratory and field scales

“…Sustainable river management and restoration planning require spatiotemporal modeling of channels (Pannone and De Vincenzo, 2022), and cutoffs need to be accounted for long-term meandering evolution (Bogoni et al, 2017). Several river evolution models have successfully represented the statistical properties of river sinuosity, as well as pool and point bar development (Sun et al, 1996;Howard, 1996;Darby et al, 2002;Lancaster and Bras, 2002;Abad and Garcia, 2006;Seminara, 2006;Crosato, 2008;Frascati and Lanzoni, 2010;Motta et al, 2012b,a;Asahi et al, 2013;Schwenk et al, 2015;Bogoni et al, 2017;Sylvester et al, 2019).…”

“…When the centerline of the bends gets closer than a specified distance, typically the channel width, it is assumed that the cutoff occurs, and the loop is deleted from the simulation (Howard and Knutson, 1984). Pannone and De Vincenzo (2022) proposed a 1D theoretical model for meander growth and death, when tested with field data, the results had agreement with the time elapses of the real cutoff. Geometrical schemes of cutoff neglect the spatially and temporally elaborate in-channel cutoff sequence reported by field studies such as Kiss and Sipos (2015) in Hungary, Gay et al (1998) in the Power River (Montana, United States), Micheli and Larsen (2011) in the Sacramento River (California, United States), Richards and Konsoer (2020) in the White River (Arkansas, United States), and Abad et al (2022) in the Ucayali River (Loreto, Peru).…”

How Is Time Distributed in a River Meander Belt?

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Neck cutoff is fundamental to the planform evolution of meandering rivers, and takes place when a mature loop is isolated by the connection of its two adjacent bends. Neck cutoff completes a meander's life cycle by isolating it from the active channel (Hooke, 2013;Pannone & De Vincenzo, 2022), and maintains the river's steady state planform (Stølum, 1996). Cutoffs generate perturbations in channel slope (and thus bed stresses) as the river diverts to a shorter and steeper path, as well as in sediment supply due to neck failure (Monegaglia & Tubino, 2019;Zinger et al, 2011).

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