Medmerry

Year Implemented

2013

Project Type

Managed realignment

Country

United Kingdom

Location

Sussex Coast (Sussex)

Longitude

-0.8244

Latitude

50.751

Habitat(s) Created
  • Lagoon

  • Mudflat

  • Reedbed

  • Saltmarsh

  • Transitional Grassland

  • Extra habitat landward of seawall (including 6km of new water vole ditch to landward)

Size

302 Hectares

Why Undertaken
  • Compensation

  • Flood Risk Management

  • Reduce Flood Protection Costs

  • Create a More Natural Shoreline

  • Provide a Recreational Facility

Project Description Summary

The Medmerry Realignment is an innovative and large-scale coastal management project. It is the only open-coast managed realignment in the UK and remains (as of January 2020) the only such project to involve deliberately creating a breach through a mobile shingle barrier. This project was carried out by the Environment Agency (England) in 2012 and 2013 to provide coastal flood protection and to create a large expanse of coastal habitat. The design included the following: 1) A new 7 km long embankment at the back of the site (up to 2.5 km from the seafront); 2) A network of ponds and ditches behind the embankment to provide a flood storage and drainage function as well as to create valuable freshwater wetlands (including mitigation areas for protected water vole and reptiles); 3) A 300 hectare (ha) area of new coastal habitat and farmland in front of the embankment (i.e. on seaward facing side) which was designed to include: 3a) Around 183 ha of lower lying intertidal habitat that is regularly inundated by the tide; 3b) Around 117 ha of higher elevation land that does not get inundated by the tide and includes a mix of transitional grassland and areas used for grazing and agriculture; 4) Four sluice structures within the embankment to allow freshwater to drain into the main site and out to coastal waters when required; and 5) Preparatory landscaping and channel excavations in front of the embankment to facilitate freshwater drainage and ensure tidal waters efficiently flood and ebb over the new intertidal areas (which also helps to maximise the amount of intertidal habitat created). As one of the final key stages of the project’s implementation, the shingle barrier fronting the site was breached on 9 September 2013. This allowed tidal waters to inundate the lower lying areas within the site and create large expanses of new intertidal habitat in front of the new flood embankment. The shingle barrier had previously been mobile and required regular (typically annual) reshaping to minimise the risk of coastal flooding. The breach in this barrier was 110 m wide and included a 30 m wide deeper central inlet channel (at a depth equivalent Mean Low Water Neap (MLWN) tide level). This project has provided valuable lessons about working with nature and about engaging with and involving local communities in coastal management decisions.

Documents/References uploaded
References
  • Environment Agency, (2008). Medmerry Managed Realignment: Environmental Statement. Environment Agency, Worthing, 545p.
  • Environment Agency (2016) Monitoring Report http://www.cdas.info/PDF/Medmerry%20monitoring%202016%20report%20final.pdf
  • Environment Agency (2019) Medmerry Managed Realignment - Five-Year Review ENVIMSE1000291 August 2019
  • RSPB Website https://www.rspb.org.uk/reserves-and-events/reserves-a-z/medmerry/
  • RSPB Information sheet http://ww2.rspb.org.uk/Images/medmerry_tcm9-405348.pdf
  • Sussex IFCA, 2019. Medmerry Small Fish 2018 and 2014-2018 Review. Sussex IFCA, Shoreham-by-Sea, 12p.
  • Maplesden, C., Gilham, A., and Callaway, T., 2016. No Access Medmerry Managed Realignment; Changing the Minds and Coast of Sussex – a Case Study. ICE Conference. Available at: https://www.icevirtuallibrary.com/doi/abs/10.1680/cm.61149.283.
  • Willing, M.J., 2018. Brackish & Marine Molluscan Survey of the Medmerry Managed Retreat Area: August-October 2018. Report prepared on behalf of the RSPB. 41p.
  • CCO, 2019. Medmerry Summary of monitoring August 2013 to January 2019. CCO report no. TR98. CCO, 117p.
  • Dale, J., Burgess, H.M., Nash, D.J., and Cundy, A.B., 2018. Hydrodynamics and sedimentary processes in the main drainage channel of a large open coast managed realignment site, Estuarine, Coastal and Shelf Science, 215, p.100-111.


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