Wallasea - Scheme Background

Scheme Background

Location

Wallasea Island lies at the junction of the Crouch and Roach Estuaries and the proposed realignment will involved the construction of a new seawall set back from the north and northeast fringes of this island.

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Promoters and Objectives

Promoted by the UK’s Department for Environment Food and Rural Affairs European Wildlife Division (DEFRA European Wildlife Division) the aim was to create new mudflat and saltmarsh to compensate for losses of these habitats (and associated impacts seabird species that used them) which occurred following past port developments at Lappel Bank (in the Medway Estuary) and Fagbury Flats (in the Orwell Estuary). It was also designed to enhance the coastal protection afforded to the island the north bank of which was at risk of natural and unmanaged seawall breaching.

Funding

Funded mainly by DEFRA-EWD (at a cost of around £8m) who commissioned an extensive site investigation/selection programme as well as all the legal, public consultation and scheme build elements of the project. They are also funding the post realignment monitoring programme. The landowner, Wallasea Farms Ltd, has assisted throughout and was responsible for the submission of the Planning Application and, post-construction, is responsible for site maintenance.

Design

For this scheme a new secondary wall was constructed on the site in 2005 by the UK’s Department for Environment Food and Rural Affairs (DEFRA) and was set about 400m back from existing sea defences. This new wall was an extension to one that had been constructed three years previously by the landowner (Wallasea Farms Ltd.). The majority of the site fronting these two walls is at an elevation half way between Mean Low Water (MLW) and Mean High Water Neap (MHWN) and thus was be suitable for mudflat development. To also create an area of saltmarsh, maintenance dredge arisings (from the Port of Harwich) were placed on the seaward side of the walls. This was deposited in a 45m-wide strip to raised the topography to a level that was just below the MHWS level. In addition, several ‘island’ features were created in the realignment site and a new borrow dyke (soke dyke) was excavated on the landward side of the new counterwall. In summer 2006, six breaches will be made through the existing seawall to flood this 108ha site. The total width of the breaches was 590m wide with one large breach being 210m wide while the other five were either 60m or 100m. The site as a whole will be separated in three discrete areas with no exchange of water flow between them so that it will act lie three individual but contiguous realignment sites.

Date of realignment