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Simulating the role of tides and sediment characteristics on tidal flat sorting and bedding dynamics

Simulating the role of tides and sediment characteristics on tidal flat sorting and bedding dynamics
Simulating the role of tides and sediment characteristics on tidal flat sorting and bedding dynamics

Understanding sediment sorting and bedding dynamics has high value to unravelling the mechanisms underlying geomorphological, geological, ecological and environmental imprints of tidal wetlands and hence to predicting their future changes. Using the Nanhui tidal flat on the Changjiang (Yangtze) Delta, China, as a reference site, this study establishes a schematized morphodynamic model coupling flow, sediment dynamics and bed level change to explore the processes that govern sediment sorting and bedding phenomena. Model results indicate an overall agreement with field data in terms of tidal current velocities, suspended sediment concentrations (SSCs), deposition thicknesses and sedimentary structures. Depending on the variation of tidal current strength, sand-dominated layers (SDLs) and mud-dominated layers (MDLs) tend to form during spring and neap tides, respectively. Thinner tidal couplets are developed during daily scale flood–ebb variations. A larger tidal level variation during a spring–neap tidal cycle, associated with a stronger tidal current variation, favours the formation of SDLs and tidal couplets. A larger boundary sediment supply generally promotes the formation of tidal bedding, though the bedding detail is partially dependent on the SSC composition of different sediment types. Sediment properties, including for example grain size and settling velocity, are also found to influence sediment sorting and bedding characteristics. In particular, finer and coarser sediment respond differently to spring and neap tides. During neap tides, relatively small flow velocities favour the deposition of finer sediment, with limited coarser sediment being transported to the upper tidal flat because of the larger settling velocity. During spring tides, larger flow velocities transport more coarser sediment to the upper tidal flat, accounting for distinct lamination formation. Model results are qualitatively consistent with field observations, but the role of waves, biological processes and alongshore currents needs to be included in further studies to establish a more complete understanding.

morphodynamic modelling, sediment sorting, sedimentary structure, tidal bedding, tidal flats, tidal rhythmite
0197-9337
2163-2176
Zhou, Zeng
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Liu, Qian
68aeec50-d19c-4e3a-8e5b-5b0692f57e1f
Fan, Daidu
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Coco, Giovanni
8a6c97e1-2a44-4f03-ad8d-e03dbc2908db
Gong, Zheng
8fec227f-4dcc-431e-85c3-13a520574886
Möller, Iris
68c755a3-3856-44bd-a901-53f4f840da1f
Xu, Fan
a74a50aa-98c4-4457-a767-f0fe8820c535
Townend, Ian
f72e5186-cae8-41fd-8712-d5746f78328e
Zhang, Changkuan
dfdb560e-6606-4ba2-86be-f7068ef48393
Zhou, Zeng
a167cd81-84c7-4e55-9e28-4529e26e7c01
Liu, Qian
68aeec50-d19c-4e3a-8e5b-5b0692f57e1f
Fan, Daidu
7080e88e-0ffe-42da-a08a-e8c36e1a6564
Coco, Giovanni
8a6c97e1-2a44-4f03-ad8d-e03dbc2908db
Gong, Zheng
8fec227f-4dcc-431e-85c3-13a520574886
Möller, Iris
68c755a3-3856-44bd-a901-53f4f840da1f
Xu, Fan
a74a50aa-98c4-4457-a767-f0fe8820c535
Townend, Ian
f72e5186-cae8-41fd-8712-d5746f78328e
Zhang, Changkuan
dfdb560e-6606-4ba2-86be-f7068ef48393

Zhou, Zeng, Liu, Qian, Fan, Daidu, Coco, Giovanni, Gong, Zheng, Möller, Iris, Xu, Fan, Townend, Ian and Zhang, Changkuan (2021) Simulating the role of tides and sediment characteristics on tidal flat sorting and bedding dynamics. Earth Surface Processes and Landforms, 46 (11), 2163-2176. (doi:10.1002/esp.5166).

Record type: Article

Abstract

Understanding sediment sorting and bedding dynamics has high value to unravelling the mechanisms underlying geomorphological, geological, ecological and environmental imprints of tidal wetlands and hence to predicting their future changes. Using the Nanhui tidal flat on the Changjiang (Yangtze) Delta, China, as a reference site, this study establishes a schematized morphodynamic model coupling flow, sediment dynamics and bed level change to explore the processes that govern sediment sorting and bedding phenomena. Model results indicate an overall agreement with field data in terms of tidal current velocities, suspended sediment concentrations (SSCs), deposition thicknesses and sedimentary structures. Depending on the variation of tidal current strength, sand-dominated layers (SDLs) and mud-dominated layers (MDLs) tend to form during spring and neap tides, respectively. Thinner tidal couplets are developed during daily scale flood–ebb variations. A larger tidal level variation during a spring–neap tidal cycle, associated with a stronger tidal current variation, favours the formation of SDLs and tidal couplets. A larger boundary sediment supply generally promotes the formation of tidal bedding, though the bedding detail is partially dependent on the SSC composition of different sediment types. Sediment properties, including for example grain size and settling velocity, are also found to influence sediment sorting and bedding characteristics. In particular, finer and coarser sediment respond differently to spring and neap tides. During neap tides, relatively small flow velocities favour the deposition of finer sediment, with limited coarser sediment being transported to the upper tidal flat because of the larger settling velocity. During spring tides, larger flow velocities transport more coarser sediment to the upper tidal flat, accounting for distinct lamination formation. Model results are qualitatively consistent with field observations, but the role of waves, biological processes and alongshore currents needs to be included in further studies to establish a more complete understanding.

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Accepted/In Press date: 9 May 2021
e-pub ahead of print date: 19 May 2021
Published date: 15 September 2021
Keywords: morphodynamic modelling, sediment sorting, sedimentary structure, tidal bedding, tidal flats, tidal rhythmite

Identifiers

Local EPrints ID: 450445
URI: http://eprints.soton.ac.uk/id/eprint/450445
ISSN: 0197-9337
PURE UUID: f411b912-6ff6-4ee7-a07e-0bee2ca283ed
ORCID for Ian Townend: ORCID iD orcid.org/0000-0003-2101-3858

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Date deposited: 28 Jul 2021 16:31
Last modified: 17 Mar 2024 06:42

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Contributors

Author: Zeng Zhou
Author: Qian Liu
Author: Daidu Fan
Author: Giovanni Coco
Author: Zheng Gong
Author: Iris Möller
Author: Fan Xu
Author: Ian Townend ORCID iD
Author: Changkuan Zhang

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