Regime shifts in the Changjiang (Yangtze River) Estuary

The role of concentrated benthic suspensions

Journal Article (2021)
Author(s)

J. Lin (TU Delft - Coastal Engineering, East China Normal University)

BC Van Prooijen (TU Delft - Environmental Fluid Mechanics)

Leicheng Guo (East China Normal University)

C. Zhu (TU Delft - Coastal Engineering, East China Normal University)

Qing He (East China Normal University)

Z. B. Wang (East China Normal University, Deltares, TU Delft - Coastal Engineering)

Research Group
Coastal Engineering
Copyright
© 2021 J. Lin, Bram van Prooijen, Leicheng Guo, C. Zhu, Qing He, Zhengbing Wang
DOI related publication
https://doi.org/10.1016/j.margeo.2020.106403
More Info
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Publication Year
2021
Language
English
Copyright
© 2021 J. Lin, Bram van Prooijen, Leicheng Guo, C. Zhu, Qing He, Zhengbing Wang
Research Group
Coastal Engineering
Bibliographical Note
Green Open Access added to TU Delft Institutional Repository ‘You share, we take care!’ – Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.@en
Volume number
433
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Abstract

Channel deepening often triggers positive feedback between tidal deformation, sediment import and drag reduction, which leads to the regime shift in estuaries from low-turbid to hyper-turbid state. In this study, a transition in profiles of suspended sediment concentration (SSC) is hypothesised by including a positive feedback loop of vertical mixing and settling. Such a hypothesis is validated by the historical observations in the North Passage of Changjiang (Yangtze River) Estuary, with decreasing SSC in mid-lower layers and increasing SSC near the bed after the deepening. A mobile pool of concentrated benthic suspensions (CBS) develops in the North Passage, with a tidally averaged length of ~20 km and a mean thickness of ~4 m. The width of the CBS pool is limited (<1 km) as the CBS is concentrated in the Deepwater Navigational Channel. The movements of the CBS pool, combined with tidal asymmetry (e.g., slack-water asymmetry and lateral flow asymmetry), results in sediment trapping in the middle reaches and on the south flank of the channel. Observations by a bottom tripod system show the response of friction/drag coefficient to sediment concentration: (1) nearly linear decrease within low SSC (<10 kg/m3); (2) constant and minimum coefficient (with drag reduction up to 60–80%) in the presence of CBS (10–80 kg/m3). An empirical relationship was derived, which can be used to predict the friction coefficient and the magnitude of drag reduction for sediment transport studies, particularly for modelling regime shifts in estuaries.

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