Correction to “Channel bifurcation in braided rivers: Equilibrium configurations and stability”

Pittaluga, M. Bolla; Repetto, Rodolfo; Tubino, Marco

doi:10.1029/2003wr002754

Cited by 15 publications

(78 citation statements)

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“…Interestingly, the unbalanced configuration can also result from an inherent instability mechanism, even in the absence of external forcings, as shown theoretically by Wang et al (1995) and Bolla Pittaluga et al (2003), and later demonstrated through laboratory and numerical studies (Bertoldi and Tubino, 2007;Edmonds and Slingerland, 2008;Siviglia et al, 2013;Salter et al, 2018). More recently, Redolfi et al (2016) provided an interpretation of such 'free' bifurcations instability within the framework of the theory of morphodynamic influence of Zolezzi and Seminara (2001), showing that the unbalanced configuration arises when the bifurcation is able to exert an upstream morphodynamic influence that allows for the formation of an upstream steady bar.…”

Section: Introductionmentioning

confidence: 68%

“…Our model stems from the Bolla Pittaluga et al (2003) two-cell approach, and is formulated to incorporate both free and forced bifurcation responses, and their interaction. It allows predicting how water and sediment fluxes delivered from the upstream main channel are drained by the downstream anabranches, under different combinations of external forcings.…”

Section: Methodsmentioning

confidence: 99%

“…with no curvature or slope advantage) that follows the classic approach of Bolla Pittaluga et al (2003). with no curvature or slope advantage) that follows the classic approach of Bolla Pittaluga et al (2003).…”

Section: The Free Bifurcationmentioning

confidence: 99%

“…Lesser et al, 2004). Bolla Pittaluga et al, 2003Pittaluga et al, , 2015. sub-resonant conditions), while all the unbalanced bifurcations (open markers) are located above the dashed line (i.e.…”

Section: The Free Bifurcationmentioning

confidence: 99%

“…The analysis is based on the two-cell model originally proposed by Bolla Pittaluga et al (2003), as extended by Kleinhans et al (2008) to account for the curvature-driven FREE AND FORCED MORPHODYNAMICS OF RIVER BIFURCATIONS 975 secondary flow, and on the theoretical results of Redolfi et al (2016). The analytical model prescribes physically based, simplified nodal point relationships that enable us to explore the basic mechanisms that drive the water and sediment distribution at the node.…”

Section: Introductionmentioning

confidence: 99%

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Free and forced morphodynamics of river bifurcations

Redolfi

Zolezzi

Tubino

2019

Earth Surf Processes Landf

128

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Water and sediment distribution by river bifurcations is often highly unbalanced. This may result from a variety of factors, such as migration of bars, channel curvature and backwater effects, which promote an uneven partition of flow and sediment fluxes in the downstream branches, which we call ‘forcings’. Bifurcations also display an intrinsic instability mechanism that leads to unbalanced configurations, as occurs in the idealized case of a geometrically symmetric bifurcation, which we call ‘free’, provided the width‐to‐depth ratio of the incoming flow is large enough. Most frequently, these free and forced mechanisms coexist; however, their controlling roles in bifurcation dynamics have not been investigated so far. In this paper we address this question by proposing a unified free‐forced modelling framework for bifurcation morphodynamics. Upstream channel curvature and different slopes of downstream branches (slope advantage) are specifically investigated as forcing effects typically occurring in bifurcations of alluvial channels. The modelling strategy is based on the widely used two‐cell model of Bolla Pittaluga et al. (Water Resources Research, 2003, 39(3), 1–13), here extended to account for the spatially non‐uniform fluxes entering the bifurcation node. Results reveal that the relative role of free and forced mechanisms depends on the width‐to‐depth ratio falling above or below the resonant threshold that controls the stability of free bifurcations: when the main channel is relatively wide and shallow (super‐resonant regime) the bifurcation invariably evolves towards unbalanced configurations, whatever the combination of curvature and slope advantage values, which instead control the bifurcation response under sub‐resonant conditions. Detection of the resonant aspect ratio as a key threshold also releases the modelling approach from the need for parameter calibration that characterized previous approaches, and allows for interpreting under a unified framework the opposite behaviours shown by gravel‐bed and sand‐bed bifurcations for increasing Shields parameter values. © 2018 John Wiley & Sons, Ltd.

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Section: Introductionmentioning

confidence: 68%

Section: Methodsmentioning

confidence: 99%

Section: The Free Bifurcationmentioning

confidence: 99%

Section: The Free Bifurcationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Free and forced morphodynamics of river bifurcations

Redolfi

Zolezzi

Tubino

2019

Earth Surf Processes Landf

128

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Sediment Transport of Fine Sand to Fine Gravel on Transverse Bed Slopes in Rotating Annular Flume Experiments

Baar

Smit

Uijttewaal

et al. 2018

Water Resources Research

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Large‐scale morphology, in particular meander bend depth, bar dimensions, and bifurcation dynamics, are greatly affected by the deflection of sediment transport on transverse bed slopes due to gravity and by secondary flows. Overestimating the transverse bed slope effect in morphodynamic models leads to flattening of the morphology, while underestimating leads to unrealistically steep bars and banks and a higher braiding index downstream. However, existing transverse bed slope predictors are based on a small set of experiments with a minor range of flow conditions and sediment sizes, and in practice models are calibrated on measured morphology. The objective of this research is to experimentally quantify the transverse bed slope effect for a large range of near‐bed flow conditions with varying secondary flow intensity, sediment sizes (0.17–4 mm), sediment transport mode, and bed state to test existing predictors. We conducted over 200 experiments in a rotating annular flume with counterrotating floor, which allows control of the secondary flow intensity separate from the streamwise flow velocity. Flow velocity vectors were determined with a calibrated analytical model accounting for rough bed conditions. We isolated separate effects of all important parameters on the transverse slope. Resulting equilibrium transverse slopes show a clear trend with varying sediment mobilities and secondary flow intensities that deviate from known predictors depending on Shields number, and strongly depend on bed state and sediment transport mode. Fitted functions are provided for application in morphodynamic modeling.

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Flow structures at an idealized bifurcation: a numerical experiment

Hardy

Lane

2011

Earth Surf Processes Landf

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River bifurcations are key nodes within braided river systems controlling the flow and sediment partitioning and therefore the dynamics of the river braiding process. Recent research has shown that certain geometrical configurations induce instabilities that lead to downstream mid-channel bar formation and the formation of bifurcations. However, we currently have a poor understanding of the flow division process within bifurcations and the flow dynamics in the downstream bifurcates, both of which are needed to understand bifurcation stability. This paper presents results of a numerical sensitivity experiment undertaken using computational fluid dynamics (CFD) with the purpose of understanding the flow dynamics of a series of idealized bifurcations. A geometric sensitivity analysis is undertaken for a range of channel slopes (0.005 to 0.03), bifurcation angles (22 to 42 ) and a restricted set of inflow conditions based upon simulating flow through meander bends with different curvature on the flow field dynamics through the bifurcation. The results demonstrate that the overall slope of the bifurcation affects the velocity of flow through the bifurcation and when slope asymmetry is introduced, the flow structures in the bifurcation are modified. In terms of bifurcation evolution the most important observation appears to be that once slope asymmetry is greater than 0.2 the flow within the steep bifurcate shows potential instability and the potential for alternate channel bar formation. Bifurcation angle also defines the flow structures within the bifurcation with an increase in bifurcation angle increasing the flow velocity down both bifurcates. However, redistributive effects of secondary circulation caused by upstream curvature can very easily counter the effects of local bifurcation characteristics.

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Correction to “Channel bifurcation in braided rivers: Equilibrium configurations and stability”

Cited by 15 publications

References 0 publications

Free and forced morphodynamics of river bifurcations

Free and forced morphodynamics of river bifurcations

Sediment Transport of Fine Sand to Fine Gravel on Transverse Bed Slopes in Rotating Annular Flume Experiments

Flow structures at an idealized bifurcation: a numerical experiment

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