Effective design of managed realignment schemes can reduce coastal flood risks

Joshua Kiesel; Mark Schuerch; Elizabeth K. Christie; Iris Möller; Tom Spencer; Athanasios T. Vafeidis

doi:10.1016/j.ecss.2020.106844

Effective design of managed realignment schemes can reduce coastal flood risks

Joshua Kiesel^*
, Mark Schuerch
, Elizabeth K. Christie
, Iris Möller
, Tom Spencer
, Athanasios T. Vafeidis

^*Corresponding author for this work

Research output: Contribution to Journal › Article › Academic › peer-review

Abstract

Managed realignment (MR) constitutes a form of nature-based adaptation to coastal hazards, including sea level rise and storm surges. The implementation of MR aims at the (re)creation of intertidal habitats, such as saltmarshes, for mitigating flood and erosion risks and for creating more natural shorelines. However, some evidence suggests that the desired coastal protection function of MR schemes (in terms of high water level (HWL) attenuation) may be limited and it was hypothesized that this was due to the configuration of the remaining seawalls, which we refer to as scheme design. Here we present the results of a hydrodynamic model application, which we used to analyse the effects of scheme design on within-site HWL attenuation by applying six scheme designs that differ in terms of breach characteristics and water storage capacity. In specific, we vary the configuration of the seaward defence line (including the seawall breaches) and the position of the landward dike by modifying the digital elevation model of the site. Our results show that changes in scheme design, particularly storage area and number and width of breaches, had significant effects on the site's HWL attenuation capacity. Decreasing the tidal prism by changing the number and size of breaches, with the site area kept constant, leads to increased modelled HWL attenuation rates. However, average HWL attenuation rates of >10 cm km⁻¹ are only achieved when site size increases. The mean high water depth of each scheme design scenario, calculated by dividing tidal prism by MR area, explains most of the variation in average HWL attenuation between all scenarios. Attention to potential within-site hydrodynamics at the design stage will aid the construction of more effective MR schemes with respect to coastal protection in the future.

Original language	English
Article number	106844
Journal	Estuarine, Coastal and Shelf Science
Volume	242
DOIs	https://doi.org/10.1016/j.ecss.2020.106844
Publication status	Published - 5 Sept 2020
Externally published	Yes

Bibliographical note

Funding Information:
The work presented in this paper is based on field data obtained during JK's research stay at the Department of Geography's Visiting Scholar programme of the University of Cambridge. JK particularly thanks B. Evans (Cambridge Coastal Research Unit) for technical and field assistance. Furthermore, JK thanks Pushpa Dissanayake for his helpful introduction to the Delft3D modelling environment and the Integrated School of Ocean Science as part of the Future Ocean Excellence Cluster (University of Kiel) for funding the original field campaign. The authors thank the UK Environment Agency, for the supply of vertical aerial photography, LiDAR data and for their fast and helpful responses to our requests regarding the data. Furthermore, the authors would like to thank Deltares Delft Hydraulics for providing the Delft3D-FLOW model. This is a contribution towards UKRI NERC BLUECoast project (NE/N015878/1).

Funding Information:
The work presented in this paper is based on field data obtained during JK's research stay at the Department of Geography's Visiting Scholar programme of the University of Cambridge. JK particularly thanks B. Evans (Cambridge Coastal Research Unit) for technical and field assistance. Furthermore, JK thanks Pushpa Dissanayake for his helpful introduction to the Delft3D modelling environment and the Integrated School of Ocean Science as part of the Future Ocean Excellence Cluster (University of Kiel) for funding the original field campaign.

Publisher Copyright:
© 2020 Elsevier Ltd

Funding

The work presented in this paper is based on field data obtained during JK's research stay at the Department of Geography's Visiting Scholar programme of the University of Cambridge. JK particularly thanks B. Evans (Cambridge Coastal Research Unit) for technical and field assistance. Furthermore, JK thanks Pushpa Dissanayake for his helpful introduction to the Delft3D modelling environment and the Integrated School of Ocean Science as part of the Future Ocean Excellence Cluster (University of Kiel) for funding the original field campaign. The work presented in this paper is based on field data obtained during JK's research stay at the Department of Geography's Visiting Scholar programme of the University of Cambridge. JK particularly thanks B. Evans (Cambridge Coastal Research Unit) for technical and field assistance. Furthermore, JK thanks Pushpa Dissanayake for his helpful introduction to the Delft3D modelling environment and the Integrated School of Ocean Science as part of the Future Ocean Excellence Cluster (University of Kiel) for funding the original field campaign. The authors thank the UK Environment Agency, for the supply of vertical aerial photography, LiDAR data and for their fast and helpful responses to our requests regarding the data. Furthermore, the authors would like to thank Deltares Delft Hydraulics for providing the Delft3D-FLOW model. This is a contribution towards UKRI NERC BLUECoast project (NE/N015878/1).

Funders	Funder number
University of Kiel
University of Cambridge
Environment Agency
UK Research and Innovation
Natural Environment Research Council	NE/N015878/1

Keywords

Coastal protection
Coastal restoration
Coastal wetland
de-embankment
High water level attenuation
Managed realignment

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10.1016/j.ecss.2020.106844

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Cite this

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title = "Effective design of managed realignment schemes can reduce coastal flood risks",

abstract = "Managed realignment (MR) constitutes a form of nature-based adaptation to coastal hazards, including sea level rise and storm surges. The implementation of MR aims at the (re)creation of intertidal habitats, such as saltmarshes, for mitigating flood and erosion risks and for creating more natural shorelines. However, some evidence suggests that the desired coastal protection function of MR schemes (in terms of high water level (HWL) attenuation) may be limited and it was hypothesized that this was due to the configuration of the remaining seawalls, which we refer to as scheme design. Here we present the results of a hydrodynamic model application, which we used to analyse the effects of scheme design on within-site HWL attenuation by applying six scheme designs that differ in terms of breach characteristics and water storage capacity. In specific, we vary the configuration of the seaward defence line (including the seawall breaches) and the position of the landward dike by modifying the digital elevation model of the site. Our results show that changes in scheme design, particularly storage area and number and width of breaches, had significant effects on the site's HWL attenuation capacity. Decreasing the tidal prism by changing the number and size of breaches, with the site area kept constant, leads to increased modelled HWL attenuation rates. However, average HWL attenuation rates of >10 cm km−1 are only achieved when site size increases. The mean high water depth of each scheme design scenario, calculated by dividing tidal prism by MR area, explains most of the variation in average HWL attenuation between all scenarios. Attention to potential within-site hydrodynamics at the design stage will aid the construction of more effective MR schemes with respect to coastal protection in the future.",

keywords = "Coastal protection, Coastal restoration, Coastal wetland, de-embankment, High water level attenuation, Managed realignment",

author = "Joshua Kiesel and Mark Schuerch and Christie, \{Elizabeth K.\} and Iris M{\"o}ller and Tom Spencer and Vafeidis, \{Athanasios T.\}",

note = "Funding Information: The work presented in this paper is based on field data obtained during JK's research stay at the Department of Geography's Visiting Scholar programme of the University of Cambridge. JK particularly thanks B. Evans (Cambridge Coastal Research Unit) for technical and field assistance. Furthermore, JK thanks Pushpa Dissanayake for his helpful introduction to the Delft3D modelling environment and the Integrated School of Ocean Science as part of the Future Ocean Excellence Cluster (University of Kiel) for funding the original field campaign. The authors thank the UK Environment Agency, for the supply of vertical aerial photography, LiDAR data and for their fast and helpful responses to our requests regarding the data. Furthermore, the authors would like to thank Deltares Delft Hydraulics for providing the Delft3D-FLOW model. This is a contribution towards UKRI NERC BLUECoast project (NE/N015878/1). Funding Information: The work presented in this paper is based on field data obtained during JK's research stay at the Department of Geography's Visiting Scholar programme of the University of Cambridge. JK particularly thanks B. Evans (Cambridge Coastal Research Unit) for technical and field assistance. Furthermore, JK thanks Pushpa Dissanayake for his helpful introduction to the Delft3D modelling environment and the Integrated School of Ocean Science as part of the Future Ocean Excellence Cluster (University of Kiel) for funding the original field campaign. Publisher Copyright: {\textcopyright} 2020 Elsevier Ltd",

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AU - Schuerch, Mark

AU - Christie, Elizabeth K.

AU - Möller, Iris

AU - Spencer, Tom

AU - Vafeidis, Athanasios T.

N1 - Funding Information: The work presented in this paper is based on field data obtained during JK's research stay at the Department of Geography's Visiting Scholar programme of the University of Cambridge. JK particularly thanks B. Evans (Cambridge Coastal Research Unit) for technical and field assistance. Furthermore, JK thanks Pushpa Dissanayake for his helpful introduction to the Delft3D modelling environment and the Integrated School of Ocean Science as part of the Future Ocean Excellence Cluster (University of Kiel) for funding the original field campaign. The authors thank the UK Environment Agency, for the supply of vertical aerial photography, LiDAR data and for their fast and helpful responses to our requests regarding the data. Furthermore, the authors would like to thank Deltares Delft Hydraulics for providing the Delft3D-FLOW model. This is a contribution towards UKRI NERC BLUECoast project (NE/N015878/1). Funding Information: The work presented in this paper is based on field data obtained during JK's research stay at the Department of Geography's Visiting Scholar programme of the University of Cambridge. JK particularly thanks B. Evans (Cambridge Coastal Research Unit) for technical and field assistance. Furthermore, JK thanks Pushpa Dissanayake for his helpful introduction to the Delft3D modelling environment and the Integrated School of Ocean Science as part of the Future Ocean Excellence Cluster (University of Kiel) for funding the original field campaign. Publisher Copyright: © 2020 Elsevier Ltd

PY - 2020/9/5

Y1 - 2020/9/5

N2 - Managed realignment (MR) constitutes a form of nature-based adaptation to coastal hazards, including sea level rise and storm surges. The implementation of MR aims at the (re)creation of intertidal habitats, such as saltmarshes, for mitigating flood and erosion risks and for creating more natural shorelines. However, some evidence suggests that the desired coastal protection function of MR schemes (in terms of high water level (HWL) attenuation) may be limited and it was hypothesized that this was due to the configuration of the remaining seawalls, which we refer to as scheme design. Here we present the results of a hydrodynamic model application, which we used to analyse the effects of scheme design on within-site HWL attenuation by applying six scheme designs that differ in terms of breach characteristics and water storage capacity. In specific, we vary the configuration of the seaward defence line (including the seawall breaches) and the position of the landward dike by modifying the digital elevation model of the site. Our results show that changes in scheme design, particularly storage area and number and width of breaches, had significant effects on the site's HWL attenuation capacity. Decreasing the tidal prism by changing the number and size of breaches, with the site area kept constant, leads to increased modelled HWL attenuation rates. However, average HWL attenuation rates of >10 cm km−1 are only achieved when site size increases. The mean high water depth of each scheme design scenario, calculated by dividing tidal prism by MR area, explains most of the variation in average HWL attenuation between all scenarios. Attention to potential within-site hydrodynamics at the design stage will aid the construction of more effective MR schemes with respect to coastal protection in the future.

AB - Managed realignment (MR) constitutes a form of nature-based adaptation to coastal hazards, including sea level rise and storm surges. The implementation of MR aims at the (re)creation of intertidal habitats, such as saltmarshes, for mitigating flood and erosion risks and for creating more natural shorelines. However, some evidence suggests that the desired coastal protection function of MR schemes (in terms of high water level (HWL) attenuation) may be limited and it was hypothesized that this was due to the configuration of the remaining seawalls, which we refer to as scheme design. Here we present the results of a hydrodynamic model application, which we used to analyse the effects of scheme design on within-site HWL attenuation by applying six scheme designs that differ in terms of breach characteristics and water storage capacity. In specific, we vary the configuration of the seaward defence line (including the seawall breaches) and the position of the landward dike by modifying the digital elevation model of the site. Our results show that changes in scheme design, particularly storage area and number and width of breaches, had significant effects on the site's HWL attenuation capacity. Decreasing the tidal prism by changing the number and size of breaches, with the site area kept constant, leads to increased modelled HWL attenuation rates. However, average HWL attenuation rates of >10 cm km−1 are only achieved when site size increases. The mean high water depth of each scheme design scenario, calculated by dividing tidal prism by MR area, explains most of the variation in average HWL attenuation between all scenarios. Attention to potential within-site hydrodynamics at the design stage will aid the construction of more effective MR schemes with respect to coastal protection in the future.

KW - Coastal protection

KW - Coastal restoration

KW - Coastal wetland

KW - de-embankment

KW - High water level attenuation

KW - Managed realignment

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ER -

Effective design of managed realignment schemes can reduce coastal flood risks

Abstract

Bibliographical note

Funding

Keywords

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