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Flooding 8: Managed realignment

expanse of river water around trees on floodplain

Suitable for GCSE and A level

Mudflats and saltmarsh are intertidal environments that are important natural habitats that provide a source of food and shelter for a wide range of wading birds. These environments provide other key services such as carbon sequestration and regulation of water quality. Perhaps the most significant key service is their ability to absorb wave energy and flood water during coastal flooding events. By absorbing wave energy, a salt marsh can reduce the cost of flood defences that are built behind the intertidal zone.

In the UK many intertidal habitats have been managed for hundreds of years to provide additional agricultural land or land suitable for port development or heavy industry. In the last 20 years this trend has begun to be reversed, with the restoration of some intertidal environments through the process of managed realignment. Managed realignment is an example of Natural Flood Management (NFM) and is defined as:

‘the removal of part (breach) or all of existing coastal structures. Where there is no naturally occurring high ground, new flood protection structures are created further inland, creating a new or “setback” line of protection.’ Source: Natural Flood Management Handbook (SEPA 2015).

This resource explores managed realignment and explains the significance of the intertidal zone. It uses Medmerry, West Sussex, as a case study. Medmerry is the largest managed realignment on the open coast in Europe. It is a multi-objective scheme, providing cost effective flood risk management for 348 properties as well as restoring 183 hectares of intertidal habitat. In the A level resource, this scheme is compared with the Alkborough Flood Storage Area in north Lincolnshire.

Specification requirements

Coastal management is the focus of several GCSE specifications while some require understanding of managed realignment. Download the GCSE Specification audit.

An understanding of coastal management strategies is a requirement of all A level specifications. Download the A level Specification audit.

Learning objectives

This resource can be used to meet one or more of the following objectives:

  • create a case study of managed realignment
  • evaluate the impacts of managed realignment on people and wildlife
  • assess the economic costs and benefits of managed realignment.

Download the Assessment Objectives.

Activities for GCSE

You might use this three-minute video, which uses time lapse photography to record the breach in the coastal embankment, as a starter to your lesson.

  • What is happening here?
  • Why might people deliberately make a hole in coastal defences?

A basic understanding of the importance of the intertidal zone is needed if students are going to understand how managed realignment provides long-term protection. This short animation is a useful teaching tool.

  • Why are sea levels rising?
  • What effect does this have on the intertidal zone? Why is the inter-tidal zone important for wildlife and people?

An overview of the Medmerry scheme is given in this six-minute video. The scale of the scheme is described and some of its benefits examined.

Students can investigate change over time by comparing the 1183-1913 six inch map with a recent satellite image of the area affected by the Medmerry scheme.

Activities for A level

This Environment Agency document provides evidence of the effectiveness of working with natural processes as an intervention strategy. Students should go to Figure 1.1 on page 12 of the pdf and follow the hyperlink to read section 5.2 Saltmarsh and mudflat management and restoration.

  • How do salt marshes help reduce flood risk?
  • What are the environmental benefits of managed realignment?
  • Where do saltmarshes occur in the UK?
  • What processes occur in the intertidal zones that make it dynamic?
  • What are the potential strengths and limitations of managed realignment?

Having read the general information, students could compare the Medmerry and Alkborough schemes. The Environment Agency describes the Alkborough Flats Flood Alleviation Scheme in this case study. The Institution of Civil Engineers has case studies of the Medmerry realignment and Alkborough realignment schemes on its website.

  • What are the key similarities and differences between the Medmerry and Alkborough schemes?

Further resources

The RSPB report that, since the Second World War, the UK has lost 15% of its saltmarsh; 18% of its sand dunes and 46% of its shingle habitat. The full report can be downloaded from the RSPB website.


Other lessons in this series:

Flood risk and flood management: Introduction
Flooding 1: Causes of river floods
Flooding 2: Investigating the effects of river floods
Flooding 3: Response to floods: Oxford Case Study
Flooding 4: Managing the upper drainage basin
Flooding 5: Sustainable Drainage Systems (SuDS)
Flooding 6: Managing river floods – exploring the role of the Environment Agency
Flooding 7: Coastal flooding at Chiswell
Flooding 9: The role of the Environment Agency in coastal management and the development of shoreline management plans

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