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The influence of seasonal climate on the morphology of the mouth-bar in the Yangtze Estuary, China

The influence of seasonal climate on the morphology of the mouth-bar in the Yangtze Estuary, China
The influence of seasonal climate on the morphology of the mouth-bar in the Yangtze Estuary, China
The geomorphology of the Yangtze Estuary in the Changjiang River Delta in Eastern China has been the subject of extensive research. This study extends previous work to examine the influence of wind-waves on the mouth-bar, where about half of the river-borne material settles to the bed. The site is located just outside of Changjiang River mouth, which is meso-tidal and subject to seasonally varying river flows and wind-wave conditions. Modeling was performed with a coupled wave-current hydrodynamic model using TELEMAC and TOMAWAC and validated against observed data. Bottom Shear Stress (BSS) from river, tide and waves based on the numerical model output was used to infer the respective contribution to the evolution of the subaqueous delta. Our examination did not however extend to modeling the sediment transport or the morphological bed changes. The results suggest that (i) the dominance of river discharge is limited to an area inside the mouth, while outside, the mouth-bar is tide-wave dominant; (ii) considering just the tide, the currents on the shallow shoals are flood dominant and deep channels are ebb dominant, which induces continued accretion over the shallows and erodes the deeper parts of the mouth-bar until the tidal currents become too weak to transport sediment; (iii) whereas waves are very efficient at reshaping the shallow shoals, with the effect being subtly dependent on the depth distribution over the mouth-bar; (iv) the stability of shallow shoal morphology is highly dependent on the presence of seasonal wind-waves and characterized as “summer storing and winter erosion”, while deep channels perform like corridors of water and sediment, exporting sediment all year round. The nature of the mouth-bar response has important implications for coastal management, such as the ongoing deep water channel maintenance, reclamations and coastal defense measures.
0278-4343
30-49
Zhang, Min
b05c2fb3-97e7-49a1-9a42-ca8a7c0cc4f0
Townend, Ian
f72e5186-cae8-41fd-8712-d5746f78328e
Cai, Huayang
1cb6d8e3-58d5-4d01-b825-fbe920a4f219
He, Jiawei
5d7c2e59-ecc4-455b-a591-a7a141d1240d
Mei, Xuefei
f4a2184d-4208-4b22-8eb9-8d19880f54aa
Zhang, Min
b05c2fb3-97e7-49a1-9a42-ca8a7c0cc4f0
Townend, Ian
f72e5186-cae8-41fd-8712-d5746f78328e
Cai, Huayang
1cb6d8e3-58d5-4d01-b825-fbe920a4f219
He, Jiawei
5d7c2e59-ecc4-455b-a591-a7a141d1240d
Mei, Xuefei
f4a2184d-4208-4b22-8eb9-8d19880f54aa

Zhang, Min, Townend, Ian, Cai, Huayang, He, Jiawei and Mei, Xuefei (2018) The influence of seasonal climate on the morphology of the mouth-bar in the Yangtze Estuary, China. Continental Shelf Research, 153, 30-49. (doi:10.1016/j.csr.2017.12.004).

Record type: Article

Abstract

The geomorphology of the Yangtze Estuary in the Changjiang River Delta in Eastern China has been the subject of extensive research. This study extends previous work to examine the influence of wind-waves on the mouth-bar, where about half of the river-borne material settles to the bed. The site is located just outside of Changjiang River mouth, which is meso-tidal and subject to seasonally varying river flows and wind-wave conditions. Modeling was performed with a coupled wave-current hydrodynamic model using TELEMAC and TOMAWAC and validated against observed data. Bottom Shear Stress (BSS) from river, tide and waves based on the numerical model output was used to infer the respective contribution to the evolution of the subaqueous delta. Our examination did not however extend to modeling the sediment transport or the morphological bed changes. The results suggest that (i) the dominance of river discharge is limited to an area inside the mouth, while outside, the mouth-bar is tide-wave dominant; (ii) considering just the tide, the currents on the shallow shoals are flood dominant and deep channels are ebb dominant, which induces continued accretion over the shallows and erodes the deeper parts of the mouth-bar until the tidal currents become too weak to transport sediment; (iii) whereas waves are very efficient at reshaping the shallow shoals, with the effect being subtly dependent on the depth distribution over the mouth-bar; (iv) the stability of shallow shoal morphology is highly dependent on the presence of seasonal wind-waves and characterized as “summer storing and winter erosion”, while deep channels perform like corridors of water and sediment, exporting sediment all year round. The nature of the mouth-bar response has important implications for coastal management, such as the ongoing deep water channel maintenance, reclamations and coastal defense measures.

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Accepted/In Press date: 8 December 2017
e-pub ahead of print date: 18 December 2017
Published date: 1 February 2018

Identifiers

Local EPrints ID: 417069
URI: http://eprints.soton.ac.uk/id/eprint/417069
ISSN: 0278-4343
PURE UUID: 3f88a106-5aff-4b92-a721-f5e55a5fc8a9
ORCID for Ian Townend: ORCID iD orcid.org/0000-0003-2101-3858

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Date deposited: 18 Jan 2018 17:30
Last modified: 28 Apr 2022 05:43

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Contributors

Author: Min Zhang
Author: Ian Townend ORCID iD
Author: Huayang Cai
Author: Jiawei He
Author: Xuefei Mei

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