title /
/ DEFRA
project code
Department for Environment, Food and Rural Affairs CSG 15
Research and Development
Final Project Report
(Not to be used for LINK projects)
Two hard copies of this form should be returned to:Research Policy and International Division, Final Reports Unit
DEFRA, Area 301
Cromwell House, Dean Stanley Street, London, SW1P 3JH.
An electronic version should be e-mailed to
Project title / Coastal and Estuarine Managed Realignment - Design issues
DEFRA project code / FD2413/TR
Contractor organisation and location / CIRIA, Classic House, 174-180 Old Street, London, EC1V 9BP
Total DEFRA project costs / £ 50000
Project start date / 01/03/03 / Project end date / 30/04/04
Executive summary (maximum 2 sides A4)
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CSG 15 (Rev. 6/02) 3
Projecttitle /
/ DEFRA
project code
Managed Realignment is the deliberate process of altering flood defences to allow flooding of a previously defended area as part of a wider shoreline or estuary management strategy. Its precise form depends on the reasons for undertaking it and the techniques that are applied.
This is a developing area of flood management and no comprehensive guidance was available on the design and construction aspects of Managed Realignment schemes, although a number of reports had been produced on saltmarsh and habitat creation. Current practice draws upon traditional techniques as well as using new approaches. Careful design and implementation is needed for any managed realignment in order to maximise its benefits and help to avoid uncertain outcomes or negative impacts.
An earlier Managed Realignment Review (carried out by Halcrow under Policy Theme) concluded that it would be beneficial to improve the guidance available to practitioners. Defra and the Environment Agency contracted CIRIA to carry out this project (FD2413) to provide guidance on the design issues surrounding coastal and estuarine Managed Realignment schemes.
The exact scope of the guidance was determined through discussion with over 70 professionals who provided direct knowledge and experience of Managed Realignment. Published literature and un-published reports from a range of organisations were also reviews. The new guide aims to:
· Improve the design and implementation of coastal and estuarine Managed Realignment projects.
· Facilitate the wider and correct use of Managed Realignment.
· Increase stakeholder confidence in Managed Realignment as an option for flood management.
· Encourage more sustainable design and construction for flood management.
· Help conserve and enhance natural coastal environments.
The circumstances where realignment may take place are diverse, and the guidance identifies matters to consider in developing an appropriate approach. This includes the level of risk associated with realignment and the appropriate detail of investigations needed for planning any Managed Realignment project.
The new guide addresses realignment in both low-lying estuarine and coastal situations. It considers coastal erosion in relation to intertidal areas and coastal features such as beach ridges or dunes, however processes such as controlled retreat of a cliffed coastline are outside the scope of this report.
The guide is divided into 3 parts.
PART I explains the objectives of Managed Realignment schemes. This is intended primarily for use by Coastal and Estuarine Managers who would consider Managed Realignment as a policy option within a management strategy. It gives a general background to Managed Realignment, and considers success and failure criteria for different stakeholders and how these will have a bearing on site design issues.
PART II considers whether Managed Realignment is appropriate for a particular site, and discusses how it might be delivered. This section has a more diverse audience, including geomorphologists, managers, planning authorities, environmental advisors and the informed public. Part II explains the decision process that leads to a preferred approach.
PART III provides technical guidance on designing and implementing Managed Realignment schemes. This part is primarily aimed at modellers, engineers, environmental scientists and geomorphologists. The guidance covers the design, implementation, construction and monitoring phases.
CSG 15 (Rev. 6/02) 3
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Scientific report (maximum 20 sides A4)
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CSG 15 (Rev. 6/02) 3
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The above output will be available under the Flood and Coastal Defence section (Engineering Theme) on the Defra website (www2.defra.gov.uk/research/Project_Data ). It is also available to download for free from the CIRIA website at www.ciria.org/downloads. Copies will be held by Environment Agency Information Centres and can be purchased through CIRIA’s Bookshop on www.ciriabooks.com
The information below includes a contents list of the publication and some key ‘conclusions’ from each of the three main parts of the book.
Contents list of publication
Summary 2
CRYNODEB 3
Acknowledgements 3
Introduction and preambles 14
GLOSSARY 18
GLOSSARY OF ORGANISATIONS 23
PART I : WHY MANAGED REALIGNMENT 25
1.0 What is Managed Realignment? 26
1.1 Aim and Purpose of Managed Realignment 30
1.2 Drivers Leading to Managed Realignment 31
1.2.1 Coastal and Flood Management 31
1.2.2 Environmental Benefit 31
1.2.3 Funding 33
1.2.4 Legislation 34
1.2.5 Navigation 36
1.3 potential Constraints Limiting Managed Realignment opportunities 36
1.3.1 Consents and Legislation 36
1.3.2 Environmental issues 37
1.3.3 Funding and financial compensation 39
1.3.4 Opposition from the community 39
1.4 Mechanisms that Support Managed Realignment 40
1.4.1 Strategic Managed Realignment 40
1.4.2 Opportunistic Managed Realignment 43
1.4.3 Legislative Requirements 43
1.5 Stakeholder Participation 44
1.5.1 Introduction to stakeholder participation 44
1.5.2 Involvement throughout the design process 44
1.6 Success and Failure Criteria 47
1.6.1 Multiple Objectives 50
1.6.2 Communicating the Lessons Learnt 51
PART II: HOW AND WHERE CAN MANAGED REALIGNMENT BE ACHIEVED 54
2.0 Identifying options for Managed Realignment 55
2.1 Introduction to planning and design process 55
2.2 Site Selection Criteria 57
2.3 Baseline Geomorphology and Hydrodynamics 59
2.4 Baseline Engineering Characteristics 60
2.4.1 Performance of Existing Defence 60
2.4.2 Contaminated Land 62
2.4.3 Geotechnical Assessments 63
2.4.4 Site Access 63
2.5 Environmental Characteristics and Assessment 64
2.5.1 Environmental Impact Assessment 64
2.5.2 Existing Environmental Assets 65
2.5.3 Target Habitats 71
2.5.4 Infrastructure and land ownership 73
2.6 Economic Viability 74
2.7 Consents, permissions and Licences 74
2.7.1 Planning permission under the Town and Country Planning Act 1990 75
2.7.2 Habitats Regulations 76
2.7.3 Wildlife and Countryside Act 1981 (as amended by the Countryside and Rights of Way Act (CRoW) 2000) 76
2.7.4 Coast Protection Act (1949) 76
2.7.5 Food & Environment Protection Act (1985) 77
2.7.6 Environment Agency and Scottish Environment Protection Agency 77
2.7.7 The Crown Estate 77
2.7.8 Port Authorities 78
2.8 Methods of Managed Realignment 78
2.8.1 Breach Managed Realignment 78
2.8.2 Bank Managed Realignment 79
2.8.3 Tidal Exchange Systems 80
2.9 Timing and Timing Constraints 82
3.0 Information to support evaluation 84
3.1 Proportionality 84
3.2 National R&D and other supporting studies 84
3.2.1 Habitat R&D 84
3.2.2 Futurecoast 85
3.2.3 Estuary Research Programme Phase 1 86
3.2.4 Shoreline Management Plans and Coastal Defence Strategies 87
3.2.5 Coastal Habitat Management Plans 87
3.2.6 Living with the Sea 87
3.2.7 Local and Regional Studies 87
3.2.8 International Navigation Association (PIANC) Working Groups 88
3.2.9 A Guide to the Understanding and Management of Saltmarshes 89
3.2.10 A Guide to Managing Coastal Erosion in Beach/Dune Systems 89
3.2.11 A Guide to the Management and Restoration of Coastal Vegetated Shingle 90
4.0 Communication 91
PART III: DESIGNING AND IMPLEMENTING MANAGED REALIGNMENT 94
5.0 Designing and Implementing Managed Realignment 95
5.1 Physical Processes And Morphology 95
5.2 General Approaches To Assessesing Physical Processes 98
5.2.1 Desk-based reviews 99
5.2.2 Direct field-based measurements 99
5.2.3 Numerical model based assessments 99
5.3 Specific Assessment Techniques 101
5.3.1 Tidal levels and range 101
5.3.2 Tidal prism and discharges 102
5.3.3 Tidal current velocities 110
5.3.4 Tidal asymmetry 111
5.3.5 Waves 114
5.3.6 Sediment dynamics and morphological response 124
5.4 Assessment Procedure 130
5.4.1 Appropriate level of Technical Assessment 130
5.4.2 Applying proportionality 133
5.5 Engineering Requirements 138
5.5.1 Site Boundaries 138
5.5.2 Realigned Defence 139
5.5.3 Creation of New Shoreline 141
5.5.4 Treatment of New Intertidal Area 142
5.5.5 Establishment of Vegetation 146
5.5.6 Design of Breaches 150
5.5.7 Tidal Exchange Design 153
5.5.8 Land Drainage Considerations 154
5.5.9 Dealing with Services 155
5.5.10 Decommissioning of Existing Defence 155
5.5.11 Health and Safety 156
6.0 Monitoring 158
6.1 Reasons for monitoring 158
6.1.1 Outline Monitoring Requirements 158
6.1.2 Outline approaches to monitoring 159
6.2 Principal Monitoring Techniques 161
6.2.1 Outline programme for post-project monitoring 162
6.3 Maximising the use of monitoring data and information 164
7.0 Bibliography 168
Websites 181
Appendix 1 - Monitoring Techniques 185
A1.1 Topographical survey 185
A1.1.1 Land-based methods 185
A1.1.2 Aerial methods 185
A1.1.3 Benefits and disbenefits of different topographic approaches 186
A1.2 Monitoring hydrodynamics 186
A1.2.1 Monitoring flow 187
A1.2.2 Monitoring waves 189
A1.3 Monitoring intertidal accretion and erosion 190
A1.3.1 Monitoring intertidal accretion 190
A1.3.2 Monitoring intertidal erodibility 192
A1.4 Ground and flood defence investigations 192
A1.4.1 Ground investigation analytical techniques 193
A1.4.2 Scour and erosion monitoring 193
A1.5 Ecological monitoring 194
A1.6 Summary of environmental monitoring techniques 195
Appendix 2: Understanding specific landform processes and habitat (re) creation 199
A2.1 Saltmarshes 199
A2.1.1 Saltmarsh elevation and tidal inundation 200
A2.1.2 Site gradient 203
A2.1.3 Wave conditions 203
A2.1.4 Soil type 207
A2.1.5 Water quality 207
A2.1.6 Biological factors 208
A2.2 Intertidal flats 208
A2.3 Sand Dunes 209
A2.3.1 Sand Dunes and Managed Realignment 210
A2.3.2 Formation and development 210
A2.3.3 Erosion of Sand Dunes 211
A2.4 Shingle Ridges 214
A2.4.1 Evolution of Shingle Ridges 214
A2.4.2 Shingle Ridge landforms 215
A2.4.3 Managing Shingle Ridge profiles 215
A2.4.4 Shingle Ridges and Managed Realignment 216
A2.4.5 Shingle habitats 217
A2.5 Saline Lagoons 218
A2.6 Intertidal Reedbeds 219
A2.6.1 Creating Reedbed 219
Appendix 3: Physical Processes and their Influence on Design 221
Appendix 4: Review of scheme implementation, including assessment of physical processes 227
A4.1 Review of schemes implemented/not implemented 227
A4.1.1 Managed Realignment schemes that have been implemented 227
A4.1.2 Managed Realignment schemes that have not been implemented 231
A4.2 Case study experience in assessing physical processes 232
A4.2.1 Case Study 1 – Managed Realignment of flood embankment within an estuary 232
A4.2.2 Case Study 2 – Managed Realignment of a gravel embankment along the open coast 235
A4.2.3 Case Study 3 – Managed Realignment of a flood embankment within a large tidal embayment 237
Summary
Benefits of Managed realignment include:
· Can offer innovative, long term, sustainable flood management solution
· Reduces coastal squeeze (ie loss of intertidal habitat seawards of flood defences) and thus reduces the loss of natural habitats
· Can offer potential for habitat (re-)creation
· Potential to use less resources than hard defences in construction and can re-use materials extracted from sites,
· Cost savings can be considerable – a recent Environment Agency study indicated that it can reduce costs of coastal defence construction by as much as £4,600 per metre
However, despite the clear benefits, relatively few schemes have been operationally adopted, even though a number of the early Shoreline Management Plans included MR as a strategy policy option. Schemes are often rejected because:
· Cost savings or benefits are often not clearly defined in initial designs
· Limited experience amongst coastal engineers in comparison to more traditional coastal defence options has meant some over compensation and design.
· Some poor past examples have needed remedial works or have not provided adequate protection over their design life.
The objectives of this project were to:
· Share lessons learned and provide guidance
· Improve the design and implementation of MR projects
· Facilitate wider and correct use of MR
· Increase stakeholder confidence in MR as an option for flood management
· Encourage more sustainable design and construction for flood management
· Help conserve and enhance natural coastal environments
The guide addresses low-lying estuarine and coastal situations.
Structure and content of the book
Part 1 explains the objectives of MR schemes. This section is intended primarily for use by coastal and estuarine managers and it explains managed realignment as an option. It gives a general background to Managed Realignment and considers success and failure criteria for different stakeholders and how these may have a bearing on site design issues.
Part 2 discusses whether Managed Realignment is appropriate (once it has been selected as an option) for a particular site, and explains how it may be delivered. This section has a more diverse audience; including Coastal Managers, Geomorphologists, Consenting Authorities, and Environmental Advisors. Part 2 explains the decision process that leads to a preferred approach.
Part 3 covers technical issues associated with designing and implementing managed realignment. This chapter is targeted at design disciplines, particularly geomorphologists, modellers and engineers, to assist them in the design, construction and monitoring phases.
Conclusions from PART 1 – Why managed realignment?
Managed Realignment may be undertaken for different purposes including flood management, habitat creation, or in association with new development. The reasons for Managed Realignment as well as the characteristics of the particular location will help determine the preferred approach.
§ Managed Realignment may have one or more drivers. This provides an opportunity to meet a variety of stakeholder needs, but requires careful management to ensure the drivers have complementary objectives.
§ The need for Managed Realignment may arise from strategic management plans objectives, ad-hoc opportunities or may be compelled by legislation.
Community opposition to Managed Realignment can occur for a variety of reasons, for example emotional ties to assets or economic loss for the individual or change to rights of access (particularly footpaths). These issues need to be addressed through public involvement and/or participation from an early stage and for some years following the scheme implementation.