Allfleet's Marsh (Wallasea)

Year Implemented

2006

Project Type

Managed realignment

Country

United Kingdom

Location

Crouch Estuary (Essex)

Longitude

0.8365

Latitude

51.6163

Habitat(s) Created
  • Mudflat

  • Saltmarsh

  • 5ha borrow dyke and 10 terrestrial grassland landward of seawall

Size

133 Hectares

Why Undertaken
  • Compensation

  • Create a More Natural Shoreline

  • Improve Flood Protection

Project Description Summary

This realignment project was carried out in 2006 by the UK's Department for Environment, Food & Rural Affairs (Defra). It was done to compensate for historic losses of mudflat and saltmarsh habitat at two earlier port developments in the Greater Thames Area (South east England). The project was implemented on the north side of Wallasea Island (Essex, Crouch Estuary). This island had been claimed from estuary centuries previously and had become low-lying farmland that was vulnerable to future flooding. For the realignment a new sea wall was built and six large breaches that were between 60m and 210m wide each (total width of all breaches was 590m) were made in the old, and deteriorating, sea wall. Particular attention was paid to ensuring that the breaches would be stable over time and that the project would not cause major erosion within or outside the realigned area. This was done by carefully designing and numerically modelling the scheme to ensure it did not significantly alter the functioning of the adjacent Crouch estuary and also by ensuring that the breaches had a 'regime' shape which was in-keeping with the tidal hypsometry (i.e. the tidal flow character through them as dictated by the hinterland shape of the site ). A large-scale sediment recharge was undertaken (550,000 m3) at the back of the site to raise the land-form to create saltmarsh ( this was in addition to the mudflat that was created over the low lying areas of the site without any need for land-forming). As part of this scheme the existing field drains & borrow dykes were left in place and one new channel was cut in central area to connect back to sluice/field drain to ensure efficient land drainage was maintained. The habitats within the site matured quickly after it was opened up to the tide in 2006 (there was 5 years of formal post-breach monitoring) and this project also became an important precedent that helped inform the design of even larger and more ambitious realignment work that was carried out across the rest of the island over the 10-13 years that followed. In 2018 this restored habitat (and also the Brandy Hole realignment further upstream) became officially designated when it was included within the Crouch and Roach Estuaries Special Protection Area (SPA) and Ramsar wetland area.

Documents/References uploaded
References
  • ABPmer, 2004. Lappel Bank and Fagbury Flats Compensatory Measures: Phase 2 - Detailed Hydrodynamic Model of Proposed Realignment Scheme on North Bank of Wallasea Island. Southampton, 90p.
  • ABPmer, 2004. Wallasea Island North Bank Realignment: Environmental Statement: Wallasea Farms Ltd. ABP Marine Environmental Research Ltd, Southampton, 220p.
  • ABPmer, 2005. Wallasea Island North Bank Realignment: Proposed Monitoring Programme. ABP Marine Environmental Research Ltd, Southampton, 45p.
  • ABPmer/Jacobs, 2008. Wallasea Wetland Creation Project Monitoring Programme (April 2006 to June 2007) Draft Report to Defra - January 2008 Report Ref RMP2886_B0147800 (3611/03).
  • Defra, 2003. Wallasea Wetlands Restoration Project [leaflet]. Defra, London, 2p.
  • http://www.abpmer.co.uk/experience/habitat-creation-experience/wallasea-wild-coast/
  • https://www.gov.uk/government/news/expansion-of-wildlife-protection-sites-in-essex


ABPmer logo

A free resource maintained by ABPmer

CONTACT US

ABPmer
Quayside Suite
Medina Chambers
Town Quay
Southampton
SO14 2AQ

eZine Signup