Bifurcation instability and chute cutoff development in meandering gravel-bed rivers

Abstract

. (2014) 'Bifurcation instability and chute cuto development in meandering gravel-bed rivers. ', Geomorphology., Further information on publisher's website:http://dx.doi.org/10.1016/j.geomorph.2014.01.018Publisher's copyright statement: NOTICE: this is the author's version of a work that was accepted for publication in Geomorphology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reected in this document. Changes may have been made to this work since it was submitted for publication. A denitive version was subsequently published in Geomorphology, 213, 15 May 2014, 10.1016/j.geomorph.2014.01.018. Additional information:Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. AbstractChute cutoffs reduce sinuosity of meandering rivers and potentially cause a transition from a single to a multiple channel river. The channel bifurcation of the main channel and the mouth of the incipient chute channel controls sediment and flow partitioning and development of the chute. Recent channel bifurcation models suggest that upstream bend radius, gradient advantage, inlet step, and upstream sediment supply at the bifurcation are important factors in the evolution of bifurcations. Our objective is to unravel the relative importance of these factors for chute cutoff success and development. We compare results from a morphodynamic three-dimensional (3D) model and a one-dimensional (1D) model with nodal-point relation with field observations of chute cutoffs in a meandering gravel-bed river. The balance between increased gradient advantage and flow curvature upstream of the chute channel bifurcation was systematically investigated with the 1D model. The 3D model runs and the field observations show the development of two types of chute cutoffs: a scroll-slough cutoff and a bend cutoff. The morphodynamic 3D model demonstrates that chutes are initiated when flow depth exceeds the floodplain elevation. Overbank flow and a significant gradient advantage result in a bend cutoff. The outcome of the 1D model shows that channel curvature at the bifurcation determines the success or failure of the chute cutoff when the chute channel is located at the inner bend, as in the case of scrollslough cutoffs. We conclude that chute initiation depends on floodplain characteristics, i.e., floodplain elevation, sediment composition, and the presence of vegetation. Chute cutoff success or failure is determined by the dynamics just upstream of the channel bi...

Free and forced morphodynamics of river bifurcations

“…For example, in the depositional systems investigated by Salter et al (2018), the interaction between the bifurcation and the downstream bifurcates leads to autogenic temporal oscillations of channel slope and discharge asymmetry. An analogous concept is at the core of classical theoretical studies on bar-bend interactions in river meanders (e.g., Tubino and Seminara, 1990), which pointed out how the dynamics of sediment bars inside meandering channels depends on the interaction between the free instability mechanisms that causes spontaneous development of migrating bars, and the effect of the variable meander curvature. Therefore, focusing on the local behaviour of the bifurcation node, such downstream mechanisms can be considered as an external forcing effect, coherently with the definition adopted in the present work.…”

“…Van der Mark and Mosselman, 2013;van Dijk et al, 2014;Le et al, 2018aLe et al, , 2018bSalter et al, 2018). Van der Mark and Mosselman, 2013;van Dijk et al, 2014;Le et al, 2018aLe et al, , 2018bSalter et al, 2018).…”

“…Understanding their dynamics is therefore important for managing water resources and the flooding risk, predicting the long-term morphological evolution of channel networks and evaluating the effectiveness over time of river restoration projects aimed at reactivating a multi-thread configuration (e.g. Bifurcation dynamics also control instream processes in meander bends that mitigate the development of channel sinuosity through the occurrence of short cuts through point bars (Grenfell et al, 2012;van Dijk et al, 2014). Bifurcation dynamics also control instream processes in meander bends that mitigate the development of channel sinuosity through the occurrence of short cuts through point bars (Grenfell et al, 2012;van Dijk et al, 2014).…”

“…Similar approaches have proven to provide thorough insight into the study of other morphodynamic processes, like the dynamics of river bars in curved or meandering channels (Seminara and Tubino, 1989), where migrating free bars develop on a much faster scale than that required to shape the meander planform (Tubino and Seminara, 1990). This methodological distinction is based on the recognition that free and forced mechanisms display substantial differences in their evolutionary temporal and spatial scales.…”

Response of braiding channel morphodynamics to peak discharge changes in the Upper Yellow River

“…However, elevated land surface, vegetation and numerous kinds of structures in the floodplains might limit the formation of chute channels on the floodplains (Van Dijk and Schuurman, 2014;van Oorschot et al, 2016) and thus reduce the impact of higher peak discharges. The loss of valuable land on the floodplains by the channel widening and chute channels is socially and economically undesirable.…”