What is coastal squeeze? Project FRS17187 We are the Environment Agency. We protect and improve the environment. Acting to reduce the impacts of a changing climate on people and wildlife is at the heart of everything we do. We reduce the risks to people, properties and businesses from flooding and coastal erosion. We protect and improve the quality of water, making sure there is enough for people, businesses, agriculture and the environment. Our work helps to ensure people can enjoy the water environment through angling and navigation. We look after land quality, promote sustainable land management and help protect and enhance wildlife habitats. And we work closely with businesses to help them comply with environmental regulations. We can’t do this alone. We work with government, local councils, businesses, civil society groups and communities to make our environment a better place for people and wildlife. Published by: Author(s): Environment Agency, Horizon House, Deanery Road, Nigel Pontee Bristol, BS1 5AH Ken Pye James Tempest http://www.gov.uk/government/organisations/ Simon Blott environment-agency Dissemination status: ISBN: 978-1-84911-473-8 Publicly available © Environment Agency – January 2021 Keywords: Flood and coastal erosion risk management, coast, coastal squeeze All rights reserved. This document may be reproduced with prior permission of the Environment Agency. Research contractor: Jacobs, Burderop Park, Email: [email protected] Swindon Further copies of this report are available from our Environment Agency’s Project Manager: publications catalogue: Christabel Mitchell http://www.gov.uk/government/publications Theme Manager: Hayley Bowman or our National Customer Contact Centre: T: 03708 506506 Collaborator: Kenneth Pye Associates Ltd Email: [email protected] Project number: FRS17187 What is coastal squeeze? ii Evidence at the Environment Agency Scientific research and analysis underpins everything the Environment Agency does. It helps us to understand and manage the environment effectively. Our own experts work with leading scientific organisations, universities and other parts of the Defra group to bring the best knowledge to bear on the environmental problems that we face now and in the future. Our scientific work is published as summaries and reports, freely available to all. This report is the result of research commissioned and funded by the Joint Flood and Coastal Erosion Risk Management Research and Development Programme. The Joint Programme is jointly overseen by Defra, the Environment Agency, Natural Resources Wales and the Welsh Government on behalf of all risk management authorities in England and Wales: http://evidence.environment-agency.gov.uk/FCERM/en/Default/FCRM.aspx. You can find out more about our current science programmes at: https://www.gov.uk/government/organisations/environment-agency/about/research. If you have any comments or questions about this report or the Environment Agency’s other scientific work, please contact [email protected]. Professor Doug Wilson Director, Research, Analysis and Evaluation What is coastal squeeze? iii Acknowledgments We wish to thank a large number of individuals who although remain unnamed, had an important role in the development of this project via the workshop (Appendix B). The Project Steering Group provided considerable support, guidance and direction to the work, resulting in the outputs presented here. The technical expertise within Jacobs and supported via Kenneth Pye Associates Ltd has been instrumental to the assessment and production of this report. Project Steering Group (core members, representing organisations as listed) Phillip Winn, Environment Agency Nick Hardiman, Environment Agency Dr Chrissy Mitchell, Environment Agency Dr Sue Manson, Environment Agency Representation provided, Defra Tim Collins, Natural England Sue Rees, Natural England Nick Williams, Natural England Kat Ball, Scottish Environment Protection Agency Dr Christopher Sweeting, Marine Management Organisation Nicola Rimmington, Natural Resources Wales James Morris, Welsh Government Lowri.Norrington-Davies, Welsh Government Contractor Project Team Jacobs Prof. Nigel Pontee Dr James Tempest Richard Ashby Crane Emma Allan Claire Andrassy Toby Wilson KPAL Prof. Kenneth Pye Dr Simon Blott What is coastal squeeze? iv Executive summary The purpose of this project is to better understand what causes ‘coastal squeeze’. This is particularly relevant where there is a legal obligation to compensate for the impacts of maintaining coastal flood management infrastructure or management activities that could lead to coastal squeeze. Compensation in these cases has normally involved creating new habitat, which can be costly.1 Accordingly, there is a strong economic impetus to improve the understanding of coastal squeeze impacts, including a need to consistently define, measure and better appreciate the uncertainty of habitat losses due to coastal squeeze. There are, nevertheless, other policy and legislative influences for positively managing, enhancing and creating coastal priority habitats (for example, as set out in national biodiversity strategies and climate change national adaptation programmes). It is anticipated that aspects of this ‘What is coastal squeeze?’ report will also be helpful in improving our understanding of the likely rate and scale of the impacts of accelerating sea level rise on coastal habitats and promoting the need to periodically review the evidence available. A number of studies carried out for the Environment Agency around England have highlighted inconsistencies in the definition of ‘coastal squeeze’, and demonstrated several problems in quantifying it. This project aims to improve understanding of what coastal squeeze is, and also to set out best practices for assessing the historic and future impacts of coastal squeeze at different scales. The main outputs from the work are: a new definition of coastal squeeze that clarifies the habitats that can be affected and the causes of habitat loss not caused by coastal squeeze a standard method and guidance for consistently assessing coastal squeeze four case studies that demonstrate how the method can be applied to mudflats, saltmarshes and sand/shingle beaches The revised definition we have produced is as follows: “Coastal squeeze is the loss of natural habitats or deterioration of their quality arising from anthropogenic structures, or actions, preventing the landward transgression of those habitats that would otherwise naturally occur in response to sea level rise (SLR) in conjunction with other coastal processes. Coastal squeeze affects habitat on the seaward side of existing structures.” The definition must be read together with the points of clarification in section 5.1 - Definition and points of clarification. The method has been summarised in 2 flow diagrams: past changes (Figure 6.1) and future changes (Figure 6.2). An initial scoping stage defines the study area, the habitats to be included and the period of interest. A subsequent screening stage allows a rapid assessment of whether or not coastal squeeze is likely to be a potential cause of habitat change. The method outlines how to quantify these changes, the relevant data sources and causes of uncertainty that apply to each step of the method. The final stage of the assessment requires expert judgement to assess whether the observed/predicted changes actually represent coastal squeeze. The method outlines 1 Providing the 11,500 compensatory habitat hectares identified by Shoreline Management Plan (SMP) policies over the next 44 years will cost at least £575 million in present day terms (Pontee, 2017). What is coastal squeeze? v how an assessment of confidence in the findings - ‘high’, ‘medium’, or ‘low’ - should be made. Where there is low confidence, 2 approaches can be taken: adopt the ‘precautionary principle’, assuming that habitat losses are, in fact, the result of coastal squeeze, and review the assessment in the future carry out further studies to increase confidence in the findings The main conclusions from the work are: To identify whether coastal squeeze is happening, an assessment must be made of the effect structures or management actions have in preventing habitat from moving landwards (transgress) or slowing its progress in response to sea level rise. This project has demonstrated that even under natural baselines (in other words, without defences), the area (extent) of habitat (for example, saltmarshes) may decrease over time if steeply rising land means there is not enough room for habitat to migrate landwards. If this happens, any resulting habitat losses would be a form of natural change (accepting that accelerated sea level rise is not really ‘natural’). Previous assessments of coastal squeeze have often lacked basic data to scientifically assess the causes of habitat loss. The limitations of past studies include the failure to scientifically demonstrate that: (i) habitat losses have been due to sea level rise (ii) habitat losses have not been due to other causes (for example, increases in wind waves, lateral channel movements) Increasing the level of confidence is vital, using the best available data from scientific studies and other sources. In some cases, additional data sets and/or analysis already exist to improve scientific understanding. The case studies suggest that historic coastal squeeze losses could be smaller than previous assessments have suggested.