River flow induced nonlinear modulation of M4 overtide in large estuaries
River flow induced nonlinear modulation of M4 overtide in large estuaries
River discharge is known to enhance tidal damping and tidal wave deformation in estuaries. While the damping effect on astronomical tides has been well documented, river impact on tidal wave deformation and associated overtide generation (shallow water harmonics of one or more astronomical constituents, such as M
4) remains insufficiently understood. Overtides affect tidal asymmetry, extreme water levels, and subsequent sediment transport and flooding management, thus meriting in-depth examination. Being inspired by unusual overtide changes in the landward and seaward parts of the Changjiang Estuary under low and high river discharges, in this work, we use a schematized tidal estuary model to systematically explore overtide variations under different river discharges. Model results show enhanced overtide generation in the case with river discharge compared with that without river impact. The M
4 amplitude decreases in the landward parts of the estuary, but increases in the seaward parts under increasing river discharges. The potential energy of M
4 integrated throughout the estuary shows nonlinear variations and reaches a transitional maximum when the river discharge to tidal mean discharge (R2T) ratio at the mouth is close to unity. Similar nonlinear behaviors are observed for compound tides like MS
4 when more astronomical constituents are prescribed and triad tidal interactions are enabled. The space-dependent overtide variability is more profound in large estuaries with high river discharges like the Amazon and Changjiang estuaries. It is ascribed to the inherently nonlinear river-tide interactions, specifically the twofold effects of river discharge in enhancing bottom stress, which simultaneously enhances dissipation of astronomical constituents and reinforces the energy transfer to overtides. These findings highlight the profound nonlinear impact of river discharge on overtides, and inform the study of tidal asymmetry and compound flood risk in large estuaries and deltas.
Bottom stress, Estuary, Overtide, River discharge
925-940
Guo, Leicheng
713f7dde-d88a-4f2c-9c66-7f9c6978ceb0
Zhu, Chunyan
3b539a8b-319a-4662-aa39-7b4eab164acb
Cai, Huayang
1cb6d8e3-58d5-4d01-b825-fbe920a4f219
Wang, Zheng Bing
0bf73ba6-eed4-4ebe-8175-929d35912e3d
Townend, Ian
f72e5186-cae8-41fd-8712-d5746f78328e
He, Qing
94baedd4-45f0-436e-83d4-4e2ebcd1bec3
June 2023
Guo, Leicheng
713f7dde-d88a-4f2c-9c66-7f9c6978ceb0
Zhu, Chunyan
3b539a8b-319a-4662-aa39-7b4eab164acb
Cai, Huayang
1cb6d8e3-58d5-4d01-b825-fbe920a4f219
Wang, Zheng Bing
0bf73ba6-eed4-4ebe-8175-929d35912e3d
Townend, Ian
f72e5186-cae8-41fd-8712-d5746f78328e
He, Qing
94baedd4-45f0-436e-83d4-4e2ebcd1bec3
Guo, Leicheng, Zhu, Chunyan, Cai, Huayang, Wang, Zheng Bing, Townend, Ian and He, Qing
(2023)
River flow induced nonlinear modulation of M4 overtide in large estuaries.
Estuaries and Coasts, 46 (4), .
(doi:10.1007/s12237-023-01183-0).
Abstract
River discharge is known to enhance tidal damping and tidal wave deformation in estuaries. While the damping effect on astronomical tides has been well documented, river impact on tidal wave deformation and associated overtide generation (shallow water harmonics of one or more astronomical constituents, such as M
4) remains insufficiently understood. Overtides affect tidal asymmetry, extreme water levels, and subsequent sediment transport and flooding management, thus meriting in-depth examination. Being inspired by unusual overtide changes in the landward and seaward parts of the Changjiang Estuary under low and high river discharges, in this work, we use a schematized tidal estuary model to systematically explore overtide variations under different river discharges. Model results show enhanced overtide generation in the case with river discharge compared with that without river impact. The M
4 amplitude decreases in the landward parts of the estuary, but increases in the seaward parts under increasing river discharges. The potential energy of M
4 integrated throughout the estuary shows nonlinear variations and reaches a transitional maximum when the river discharge to tidal mean discharge (R2T) ratio at the mouth is close to unity. Similar nonlinear behaviors are observed for compound tides like MS
4 when more astronomical constituents are prescribed and triad tidal interactions are enabled. The space-dependent overtide variability is more profound in large estuaries with high river discharges like the Amazon and Changjiang estuaries. It is ascribed to the inherently nonlinear river-tide interactions, specifically the twofold effects of river discharge in enhancing bottom stress, which simultaneously enhances dissipation of astronomical constituents and reinforces the energy transfer to overtides. These findings highlight the profound nonlinear impact of river discharge on overtides, and inform the study of tidal asymmetry and compound flood risk in large estuaries and deltas.
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Accepted/In Press date: 1 February 2023
Published date: June 2023
Additional Information:
Funding Information:
This work is supported by National Natural Science Foundation of China (Nos. U2040216; 41876091), and partially sponsored by the project “Coping with deltas in transition” within the Programme of Strategic Scientific Alliance between China and The Netherlands (PSA), financed by the Ministry of Science and Technology, P.R. China (MOST) (No. 2016YFE0133700) and Royal Netherlands Academy of Arts and Sciences (KNAW) (No. PSA-SA-E-02).
Publisher Copyright:
© 2023, The Author(s), under exclusive licence to Coastal and Estuarine Research Federation.
Keywords:
Bottom stress, Estuary, Overtide, River discharge
Identifiers
Local EPrints ID: 476209
URI: http://eprints.soton.ac.uk/id/eprint/476209
ISSN: 1559-2723
PURE UUID: 298c727e-68fe-4d7c-ba02-8d9ca9b8e9de
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Date deposited: 14 Apr 2023 16:33
Last modified: 17 Mar 2024 07:43
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Contributors
Author:
Leicheng Guo
Author:
Chunyan Zhu
Author:
Huayang Cai
Author:
Zheng Bing Wang
Author:
Qing He
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