Stability of river bifurcations in ID morphodynamic models

Wang, Zheng Bing; Vries, Martijn de; Fokkink, Robbert; Langerak, Ana

doi:10.1080/00221689509498549

Cited by 130 publications

(271 citation statements)

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“…From numerical modeling results obtained in a previous study (see Figure 12 in Sassi et al [2012a]) we can conclude that the ratio between surface level elevation differences to water depth is approximately between 5% and 10%, taking mean channel depth as the reference. Consequently, hydraulic theory on gradually varied flow does not directly apply, and existing work on river bifurcation stability, such as initiated by Wang et al [1995] and extended by Bolla-Pitaluga et al [2003], cannot readily be extended to the case with tides. Results from the bifurcations studied in this manuscript suggest it can be promising to use a depth-averaged morphological model for the latter purpose, in which settling lag and scour lag effects are being accommodated implicitly [Galappatti and Vreugdenhil, 1985].…”

Section: Discussionmentioning

confidence: 99%

Sediment discharge division at two tidally influenced river bifurcations

Sassi

Hoitink

Vermeulen

et al. 2013

Water Resources Research

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[1] We characterize and quantify the sediment discharge division at two tidally influenced river bifurcations in response to mean flow and secondary circulation by employing a boatmounted acoustic Doppler current profiler (ADCP), to survey transects at bifurcating branches during a semidiurnal tidal cycle. The ADCP collecting flow velocity and acoustical backscatter data was used to quantify suspended sediment discharge, adopting a recently introduced calibration procedure. Measured profiles of flow velocity and sediment concentration allowed us to compute spatiotemporal distributions of the shear velocity, the roughness length and the Rouse number. Spatiotemporal distributions of the settling velocity were obtained by combining the Rouse number and shear velocity estimates with in situ measurements from a laser particle size analyzer. Bed-load transport rates were inferred from shear stress estimates. The concentration field shows a direct response to bed shear stress, stressing the alluvial context of the system. The flow in the bifurcation regions is characterized by counter rotating secondary-flow cells, which stretch over the full width and depth of the cross sections in the downstream branches, and persist throughout the entire tidal cycle. The pattern of secondary flow suggests the flow approaching the bifurcation is concentrated in two independent threads. A two-cell structure inhibits the exchange of sediment that would occur in case a single cell would stretch over the full channel width. The division of suspended sediment primarily depends on the upstream transverse profile of the suspended sediment concentration, which is in turn dependent on geometrical factors such as upstream curvature.

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Section: Discussionmentioning

confidence: 99%

Sediment discharge division at two tidally influenced river bifurcations

Sassi

Hoitink

Vermeulen

et al. 2013

Water Resources Research

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“…Two distributaries with identical downstream boundary conditions and a given upstream Shields stress (Q) distribute water and sediment asymmetrically because this is a stable equilibrium configuration [Wang et al, 1995;Slingerland and Smith, 1998;Bolla Pittaluga et al, 2003;Miori et al, 2006;Zolezzi et al, 2006;Bertoldi and Tubino, 2007;Edmonds and Slingerland, 2008;Kleinhans et al, 2008]. For a given Q, upstream channel roughness, and channel aspect ratio, there exists only one asymmetric discharge ratio (Q r ) for which the downstream bifurcate channels are stable to small perturbations.…”

Section: Motivationmentioning

confidence: 99%

Response of river‐dominated delta channel networks to permanent changes in river discharge

Edmonds

Slingerland

Best

et al. 2010

Geophysical Research Letters

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[1] Using numerical experiments, we investigate how river-dominated delta channel networks are likely to respond to changes in river discharge predicted to occur over the next century as a result of environmental change. Our results show for a change in discharge up to 60% of the initial value, a decrease results in distributary abandonment in the delta, whereas an increase does not significantly affect the network. However, an increase in discharge beyond a threshold of 60% results in channel creation and an increase in the density of the distributary network. This behavior is predicted by an analysis of an individual bifurcation subject to asymmetric water surface slopes in the bifurcate arms. Given that discharge in most river basins will change by less than 50% in the next century, our results suggest that deltas in areas of increased drought will be more likely to experience significant rearrangement of the delta channel network. Motivation[2] An immediate impact of climate change and human modifications to river catchments is that the long-term average discharge of most rivers will change appreciably over the next century [Nohara et al., 2006;Palmer et al., 2008]. On rivers that terminate in marine or lacustrine basins, this hydrological change also will impact their deltas, and yet no framework exists for predicting the adjustments deltas may undergo as discharge changes. Relative sea-level rise is already threatening the world's deltas [Blum and Roberts, 2009;Syvitski et al., 2009], and that problem could be further compounded if permanent changes in discharge also dramatically alter delta landscapes, which provide wetlands, biodiversity,, and homes to a significant part of the world's population [Coleman, 1988;Day et al., 2007]. Studies to date have focused on identifying which deltas are at risk [Day et al., 1995;Ericson et al., 2006] and how they might respond to perturbations such as sea-level rise [Jerolmack, 2009]. But, how deltaic distributary networks will respond to changes in river discharge remains unknown.[3] As the long-term average river discharge (Q) changes, the most dramatic response of a deltaic channel network, apart from a full avulsion caused by delta-lobe switching [Coleman, 1988], is abandonment or initiation of distributary channels. This scenario could be expected because the number of bifurcations in a distributary network correlates positively with the input Q and inversely with the power in the marine environment [Syvitski and Saito, 2007]. However, it is unclear whether an individual delta's response to changes in Q would follow the same trend between Q and channel number observed from the Syvitski and Saito delta compilation.[4] Past work has shown that the splitting of discharges at channel bifurcations is subject to fairly stringent stability conditions. Two distributaries with identical downstream boundary conditions and a given upstream Shields stress (Q) distribute water and sediment asymmetrically because this is a stable equilibrium configuration [Wang et al., 1995;S...

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“…Bifurcation development is determined by the division of water and sediment to the downstream branches in relation to their conveyance and transport capacity (Wang et al, 1995;Bolla Pittaluga et al, 2003;Hardy et al, 2011). The division of water and sediment between both branches can change over time as a result of change of the downstream branches, for example channel widening (Miori et al, 2006) or lengthening.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2014

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. (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...

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Stability of river bifurcations in ID morphodynamic models

Cited by 130 publications

References 0 publications

Sediment discharge division at two tidally influenced river bifurcations

Sediment discharge division at two tidally influenced river bifurcations

Response of river‐dominated delta channel networks to permanent changes in river discharge

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

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