Sediment–flow interactions at channel confluences: A flume study

Liu, Tonghuan; Bingda, Fan; Lu, J.

doi:10.1177/1687814015590525

Cited by 9 publications

(10 citation statements)

References 17 publications

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“…However, their results were only applicable to discordant confluences with a low discharge ratio, as they used a low discharge ratio of 0.11 in their experiments (discharge ratio ¼ tributary discharge/main channel discharge). The experimental studies of Liu et al (2015) and Ludeña et al (2014) had similar limitations. In short, the sediment transport pattern, especially of contaminated sediments, in confluences has not been explored fully and thus remains poorly understood, which leads to the questions:…”

Section: Introductionmentioning

confidence: 94%

“…One reason for the difficulty in disentangling these inconsistencies is most experimental confluence studies focusing on the morphodynamic features have not deeply investigated the local flow field. For example, no flow field data were provided in Borghei and Sahebari (2010), Guillén‐Ludeña et al (2016), Liu et al (2015), Ludeña et al (2014), and Nazari‐Giglou et al (2016) to help explain their morphodynamic findings. In addition, only the near‐bed 2‐D velocity was measured by Best (1987, 1988).…”

Section: Introductionmentioning

confidence: 99%

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Experiments on the Morphodynamics of Open Channel Confluences: Implications for the Accumulation of Contaminated Sediments

Yuan

Rennie

2020

JGR Earth Surface

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Contaminated sediments are common in river networks. The flow convergence and particular flow structures in confluences, such as the flow separation zone, may result in greater accumulation of contaminated sediments than in other river locations, but this issue is rarely studied. In addition, the contaminated sediment transport is driven by the particular morphodynamics occurring at confluences. This article describes a novel confluence flume experiment on both morphodynamics and deposition patterns of contaminated sediments as a function of geometric and flow conditions. The initial equilibrium bed geometry was developed from a mobile bed and then fixed, allowing for subsequent flow velocimetry and sediment feeding. Colored sediments of fine gradation, which mimic contaminated sediments, were then fed to the tributary channel. The results suggest that the junction angle primarily determines the confluence bed morphology and sediment transport pattern while the discharge ratio is a secondary factor. It was also observed that most introduced sediments tended to deposit immediately after the cessation of feeding at the stoss of the bar in the flow separation zone. The time history of the transport of the contaminated sediments was also investigated. Sediment that initially deposited at the stoss of the bar eventually moved to the lee of the bar and deposited around the bar downstream of the confluence, demonstrating that the sedimentation pattern evolved to a state similar to the equilibrium bed morphology. Plain Language Summary This article describes a novel confluence flume experiment on the bed form and contaminated sediment transport patterns. The initial bed state was developed from a flat mobile bed until stable and was then fixed for flow field measurements and sediment feeding. Dyed sediments of fine sizes, representing contaminated sediments, were fed to the tributary channel. Variables including confluence junction angle, flow discharge ratio between tributary and mean channel, and sediment feeding location were all considered and investigated. It was observed that the confluence junction angle primarily determines the bed form and sediment transport pattern, while the discharge ratio is a secondary factor. The contaminated sediment deposition pattern tended to evolve to a state that is similar to the initial bed state. This study improves understanding of confluence bed form evolution and water quality maintenance in confluences. Confluences are characterized by complex hydrodynamics associated with particular morphological structures. Based on those defined by Best (1987) and Best and Rhoads (2008), the general hydrodynamic and morphological components in confluences can be summarized as follows, with numbers indicating labels in Figure 1: ① Flow stagnation zone, where the local velocity of the fluid is close to zero (Best, 1988).

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Section: Introductionmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Experiments on the Morphodynamics of Open Channel Confluences: Implications for the Accumulation of Contaminated Sediments

Yuan

Rennie

2020

JGR Earth Surface

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“…Thus, river confluences are critical areas where rapid mutual adjustments in flow, sediment deposition, and hydraulic geometries must occur (Best, 1988;Liu et al, 2015). The mixing processes and flow structures at confluences have substantial implications for sediment transport and channel morphology (Best, 1987(Best, , 1988Boyer et al, 2006;Bradbrook et al, 1998;Leite Ribeiro et al, 2012a, 2012bLiu et al, 2015). Confluence hydraulics show complex but distinct three-dimensional flow patterns influencing local river morphology.…”

Section: Introductionmentioning

confidence: 99%

“…Intense bedload transport from steep tributaries, typically associated with high‐magnitude rainstorm events, can cause flooding at the tributary‐main channel confluence (Gems, Sturm, et al, 2014; Gems, Wörndl, et al, 2014; Roca et al, 2009). Thus, river confluences are critical areas where rapid mutual adjustments in flow, sediment deposition, and hydraulic geometries must occur (Best, 1988; Liu et al, 2015). The mixing processes and flow structures at confluences have substantial implications for sediment transport and channel morphology (Best, 1987, 1988; Boyer et al, 2006; Bradbrook et al, 1998; Leite Ribeiro et al, 2012a, 2012b; Liu et al, 2015).…”

Section: Introductionmentioning

confidence: 99%

Confluence morphodynamics in mountain rivers in response to intense tributary bedload input

Ostrander

Holzner

Mazzorana

et al. 2023

Earth Surf Processes Landf

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Coarse sediment transported by steep mountain tributaries during channelized flash flood events with intense bed load transport poses a significant threat to life, property, and infrastructure. Intense bedload transport occurring in tributary channels and insufficient transport capacity of the main channel flow can provoke flooding at the confluence. Deposition in the confluence can lead to overbank flooding and sedimentation into adjacent settlement areas. Extensive research has been carried out investigating lowland river confluences, where it has been determined that the confluence angle and discharge ratio have the most significant influence on channel morphology and hydraulics. However, there is a lack of information concerning confluences with low width and discharge ratios, high sediment concentrations, and gradients, typically found in steep mountain channels. This study presents results from large‐scale laboratory experiments coupled with numerical modelling with a standardized river confluence geometry. Bedload transport capacities, the shape, and volume of the deposition zone in the confluence, bedload dispersion characteristics, hydraulic and morphological dynamics, and spatial boundaries were analysed for various discharges and sediment concentrations. The confluence angle was 90°, sediment concentration was 5%, 7.5%, and 10%, and the discharge ratio was 0.1. The model was designed to accommodate scale factors of 20–40. With this configuration, a set of experiments based on steady‐state hydraulic conditions was accomplished. Results show that when the discharge ratio and confluence angle are constant, different morphologies occur, indicating that in addition to the confluence angle and the discharge ratio, the sediment concentration, flow velocity, and unit stream power significantly impact both hydraulic and morphologic zones in the confluences of mountain rivers. Additionally, backwater effects upstream of the confluence, and sedimentation in the tributary channel increases with increasing sediment concentration, which not only influences confluence morphodynamics and hydraulics but also the potential for overbanking of both channels.

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“…Research on confluence dynamics is a relatively recent undertaking, and the phenomenon has been studied experimentally in the laboratory, wherein several features have been identified to study the mechanism of flow patterns and bed formation. In studying the hydraulics of a confluence, the plan form angle, discharge ratio, and momentum flux ratio are considered the major controlling factors [6][7][8][9][10][11][12][13]. Several studies [14][15][16][17][18][19][20][21] conducted field investigations of natural stream confluences to assess the relevance of experimental and numerical models for flow composition and morphology under natural conditions.…”

Section: Introductionmentioning

confidence: 99%

Improving the Hydro-Morpho Dynamics of A River Confluence by Using Vanes

et al. 2019

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Controlling the flow and bed morphology in a river confluence is important in training and navigation works. The flow in river confluence is highly complex due to crucial and rapid changes associated with flow dynamics, sediment transport, and geomorphology. The flow in Malaysia’s rivers has many confluence junctions in natural drains of catchment areas. The confluence between Kurau and Ara Rivers, in Perak, Malaysia, is selected to investigate the scour hole that usually forms in the erosion zone and the bar that forms in the deposition zone. A 2D numerical model is used in simulating hydro-morpho dynamics in the rivers confluence to mitigate the erosion and deposition zones by adopting vanes as control structures. Simulation results suggest that the most effective location, dimension, and angle of vanes can be decided based on their performance in scouring and deposition zones. The distribution velocity and flow vectors can help in deciding the location of the vanes.

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Sediment–flow interactions at channel confluences: A flume study

Cited by 9 publications

References 17 publications

Experiments on the Morphodynamics of Open Channel Confluences: Implications for the Accumulation of Contaminated Sediments

Experiments on the Morphodynamics of Open Channel Confluences: Implications for the Accumulation of Contaminated Sediments

Confluence morphodynamics in mountain rivers in response to intense tributary bedload input

Improving the Hydro-Morpho Dynamics of A River Confluence by Using Vanes

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