Tidal-flat reclamation aggravates potential risk from storm impacts
Tidal-flat reclamation aggravates potential risk from storm impacts
A better understanding of how tidal-flat reclamation changes the flood hazard is critical for climate-proofing coastal flood defense design of heavily urbanized areas. Since the 1950s, large-scale reclamation has been performed along the Shanghai coast, China, to fulfill the land demands of city expansion. We now show that the loss of tidal flats may have resulted in harmful impacts of coastal storm flooding. Using the foreshore profiles measured before and after reclamation (i.e., wide vs. narrow tidal flat), we determined the long-term changes in flood risk using a numerical model that combines extreme tidal level and wave overtopping analysis. Results show that wide tidal flats in front of a seawall provide efficient wave damping even during extreme water levels. Reclamation of these tidal flats substantially increased wave heights and correspondingly reduced the return period of a specific storm. As a result, estimates of overtopping are aggravated by more than 80% for the varying return periods examined. It is concluded that the disasters of coastal flooding after the 1997 tidal-flat reclamation in Hangzhou Bay, China are a consequence of both anthropogenic and natural activities. Moreover, our model calculations provide an equation describing the equivalent dike height needed to compensate for the loss of every km tidal flat of a certain elevation, and vice versa. For example, for every km of tidal flat ranging from high marsh to bare tidal flat that is being regained, the dike can be lowered by 0.84 m–0.67 m, when designing for a 1 in 200 years storm event. Overall, we suggest that wide tidal flats are ideally restored in front of dikes, and that when tidal areas are reclaimed, the seawall height is raised as part of the intertidal reclamation procedure. Using such an equivalent protection standard is relevant to designing hybrid flood defense system worldwide.
Equivalent protection standard, Extreme value analysis, Joint probability analysis, Reclamations, Storm flooding
Zhang, Min
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Dai, Zhijun
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Bouma, Tjeerd J.
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Bricker, Jeremy
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Townend, Ian
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Wen, Jiahong
e05ad632-eeea-4d00-863f-30be3d9881c5
Zhao, Tongtiegang
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Cai, Huayang
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1 June 2021
Zhang, Min
a7325ff1-529e-4010-9877-36b486325e6a
Dai, Zhijun
518bc4ef-716d-461d-a781-a3e5b4d04ba7
Bouma, Tjeerd J.
0f64a6ad-e198-462e-9d30-d6a1f43e25e9
Bricker, Jeremy
ebcf337f-34bc-4aff-b70d-71d6f39ed97a
Townend, Ian
f72e5186-cae8-41fd-8712-d5746f78328e
Wen, Jiahong
e05ad632-eeea-4d00-863f-30be3d9881c5
Zhao, Tongtiegang
35f9e812-e30b-440f-982c-9fa7a565090b
Cai, Huayang
1cb6d8e3-58d5-4d01-b825-fbe920a4f219
Zhang, Min, Dai, Zhijun, Bouma, Tjeerd J., Bricker, Jeremy, Townend, Ian, Wen, Jiahong, Zhao, Tongtiegang and Cai, Huayang
(2021)
Tidal-flat reclamation aggravates potential risk from storm impacts.
Coastal Engineering, 166, [103868].
(doi:10.1016/j.coastaleng.2021.103868).
Abstract
A better understanding of how tidal-flat reclamation changes the flood hazard is critical for climate-proofing coastal flood defense design of heavily urbanized areas. Since the 1950s, large-scale reclamation has been performed along the Shanghai coast, China, to fulfill the land demands of city expansion. We now show that the loss of tidal flats may have resulted in harmful impacts of coastal storm flooding. Using the foreshore profiles measured before and after reclamation (i.e., wide vs. narrow tidal flat), we determined the long-term changes in flood risk using a numerical model that combines extreme tidal level and wave overtopping analysis. Results show that wide tidal flats in front of a seawall provide efficient wave damping even during extreme water levels. Reclamation of these tidal flats substantially increased wave heights and correspondingly reduced the return period of a specific storm. As a result, estimates of overtopping are aggravated by more than 80% for the varying return periods examined. It is concluded that the disasters of coastal flooding after the 1997 tidal-flat reclamation in Hangzhou Bay, China are a consequence of both anthropogenic and natural activities. Moreover, our model calculations provide an equation describing the equivalent dike height needed to compensate for the loss of every km tidal flat of a certain elevation, and vice versa. For example, for every km of tidal flat ranging from high marsh to bare tidal flat that is being regained, the dike can be lowered by 0.84 m–0.67 m, when designing for a 1 in 200 years storm event. Overall, we suggest that wide tidal flats are ideally restored in front of dikes, and that when tidal areas are reclaimed, the seawall height is raised as part of the intertidal reclamation procedure. Using such an equivalent protection standard is relevant to designing hybrid flood defense system worldwide.
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Accepted/In Press date: 13 February 2021
e-pub ahead of print date: 19 February 2021
Published date: 1 June 2021
Additional Information:
Funding Information:
This research is supported by the National Natural Science Foundation of China (Project no.: 41701001 , 2018YFE0109900 , 51761135024 ), China Postdoctoral Science Foundation (Project no.: 2018M630414 ) and Guangdong Provincial Department of Science and Technology ( 2019ZT08G090 ). The authors would like to thank Dr. Elisa Ragno and Prof. Oswaldo Morales Napoles from Delft University of Technology for their helps on non-stationary Copulas. Great thanks are due to the reviewers for a number of very constructive comments and suggestions that have helped the substantial improvement of the manuscript.
Funding Information:
This research is supported by the National Natural Science Foundation of China (Project no.: 41701001, 2018YFE0109900, 51761135024), China Postdoctoral Science Foundation (Project no.: 2018M630414) and Guangdong Provincial Department of Science and Technology (2019ZT08G090). The authors would like to thank Dr. Elisa Ragno and Prof. Oswaldo Morales Napoles from Delft University of Technology for their helps on non-stationary Copulas. Great thanks are due to the reviewers for a number of very constructive comments and suggestions that have helped the substantial improvement of the manuscript.
Publisher Copyright:
© 2021 Elsevier B.V.
Copyright:
Copyright 2021 Elsevier B.V., All rights reserved.
Keywords:
Equivalent protection standard, Extreme value analysis, Joint probability analysis, Reclamations, Storm flooding
Identifiers
Local EPrints ID: 449940
URI: http://eprints.soton.ac.uk/id/eprint/449940
ISSN: 0378-3839
PURE UUID: 060beb08-5256-41e9-972f-15da73098c10
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Date deposited: 28 Jun 2021 16:32
Last modified: 17 Mar 2024 06:28
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Contributors
Author:
Min Zhang
Author:
Zhijun Dai
Author:
Tjeerd J. Bouma
Author:
Jeremy Bricker
Author:
Jiahong Wen
Author:
Tongtiegang Zhao
Author:
Huayang Cai
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