Soft engineering Case Study Wallasea Island

Soft engineering Case Study Wallasea Island

1. location

   • South East of England
   • South side of the Crouch Estuary, Essex
   • Estuary feeds into the North Sea

2. previous defences

   • areas were protected by a sea wall, land behind the wall was drained by Dutch engineers and used for farming
   • wall on north shore was in poor condition, began to collapse in 2004. This increased the posibilty of fllooding
     • threat of flooding put 2700 properties, 9,500 hectares of land, 168km of flood defences and natural habitats at risk.
     • as sea level rises, intertidal wetlands and salt marshes become eroded

3. The project

   • managing the land in a more sustainable way- modern approach
   • Chose managed realignment - has a number of benefits: reduces cost of hard defences, Recreates river,. creates natural habitats.
   • aimed to create the Uk's largest man made marine wetland using realignment, involving construction of new sea wall, allowing land in front to be inundated by the sea. widens the area of intertidal habitat, also manages flood risk.
   • EA became involved, wanted to make sure that there was no negative impact on the River Crouch or the people that use it
   • stage 1: new sea wall built at the back of th site on the landward line, a new freshwater 'borrow dyke' was built forming a fresh water marsh, in front of the wall there is a salt marsh formed. Robust retaining bund wall built, to hold imported mud for the salt marsh, ensured no silt carried back out to the Crouch. New beach developed in the North East corner
   • stage 2: 700,000 tonnes of mud pumped ashore, build up salt marsh, pumped into a pipeline that ran along the top of the sea wall and into the retaining bud
   • stage 3: old sea walls breached to allow the tide to flood in, wetland started forming
   • completed on 4th july 2006- costing 8 billion- when a 300m section of the old sea wall was bulldozed to allow the sea to flood into the area at high tide. wetland area covers about 115 hectares.
   • RSPB wild coast project
     • add a series of mudflats, salt marshes and lagoons south of the original project.
     • 6 phased approach

4. Effectiveness

   • restoration has been successful in developing salt marsh, saline lagoons and mudflats
   • enormous environmental benefit; increase of wader birds and overwintering water birds.
   • project has provided an area 115ha of natural flood defences that wasn't previously available.
   • improved biodiversity
   • through the creation of a visitors centre and recreation opportunities they have ensured a future income stream