The £70m Wallasea Island Wild Coast Project is a landmark conservation project using waste from Crossrail to create flood protection and a wetland habitat.
Project details
Location: Wallasea Island, Essex
Value: £70m
Date of completion: August 2015
Duration: 3½ years
Employer: Crossrail
Client: RSPB
Contractor: BAM Nuttall
Consulting Engineer: ABPMer & AECOM
Project manager: Dave Bugden, BAM Nuttall
Introduction
The Wallasea Island Wild Coast Project located on the Essex coast, is a landmark conservation and engineering scheme for the 21st century on a scale never before attempted in the UK and the largest of its type in Europe; combining ecological research and environmental vision with commerce and innovative industrial engineering for the benefit of future generations.
The project is a flagship site for the Royal Society for the Protection of Birds (RSPB), and an example of how waste material from large-scale infrastructure projects can be put to beneficial reuse in a sustainable manner while also providing flood protection for the local area through managed coastal realignment.
Sustainable re-use as an alternative to landfill
The early partnership between the RSPB and Crossrail provided a sustainable solution for the disposal of excavated material: creating replacement wetland habitats and constructing new flood protection. BAM Nuttall was contracted by Crossrail in 2012 to accept material in London and transport it by ship to Wallasea Island.
Transportation from London to Wallasea Island: Docklands Transfer Station (DTS) and Northfleet
Movement of material from London on this scale by water had never been attempted before. We refined and improved the process, proving that this could be a viable commercial option.
BAM Nuttall constructed loading equipment at two locations in London: at Docklands Transfer Station (DTS), and at Northfleet, to ship the Crossrail waste material. At DTS, vehicle loads were accepted, processed and managed within a 3 minute period.
We achieved:
- Marine transportation of 3million tonnes of excavated material
- Duration: 2½ years
- 24/7 operations
- 1,500 container ship return voyages
- Prevention of 150,000 lorry journeys, or 12 million road miles.
Typically this material would be used for low-grade landfill.
An 800m long conveyor system and temporary pontoon was constructed at Wallasea, threaded across narrow land corridors and protected RSPB breeding grounds, to a radial stacker. The unloading system was modified with improved access, guarding, lighting and lock out systems. Lessons learnt were fed back across Crossrail and the tunnelling industry.
Material challenges: Solutions & innovations
The variable consistency of the tunnelled material arriving from Crossrail provided the site team with a technical challenge to overcome. The Wallasea Material Handling Equipment (MHE) would periodically become clogged and blocked at each intersection.
Many different innovations were attempted, of which one idea was to load each vessel with half dry, granular material and half heavy clay material, resulting in a consistent material characteristic.
In addition, modifications to the MHE were carried out during 2013. These innovative solutions worked with an increase in productivity and cost effectiveness, and at reduced risk.
Ecology, environment & engineering
In advance of the construction works, 30 ecologists trapped and relocated 8,200 protected reptiles to purpose-built hibernaculae and habitats on site. The project ensured the site population of 206 water voles was saved and allowed to flourish in new enhanced habitats on the island.
The environmental sustainability of the project has been carried through to the earthworks. The introduction and trial of hybrid diesel/electric construction plant at Wallasea Island helped to reduce the on-site diesel consumption and environmental noise emissions. Sustained efforts were made with our supply chain to secure the latest traditionally powered plant to reduce emissions of particulates, oxides of nitrogen (NOx) and fuel overall.
Sculpting the landform of Jubilee Marsh
Placed across Phase 1 - 162 hectares of the entire 670 hectare site - the excavated material was designed to an innovative hydraulic model by ABPMer to allow 1.1 million m3 of tidal flow, creating pools, lagoons and channels to offer varied habitats for various breeds of migratory birds. The average land raised height was 1.8m, with maximum 5m fill and 3m deep channels all within a 3.5 km long earthwork flood embankment. Existing land was at a level below the adjacent mean tidal level. From the radial stacker, traditional earthworks plant transported the material up to two miles. GPS-controlled plant was used to form the earthworks profile with its many creeks, islands, embankments and lagoons. Three concrete structures were also constructed along the embankment to regulate tidal flow.
Triple Seawall Breach
The completion of the works at Wallasea involved the simultaneous triple breaching of the existing seawall to allow tidal waters to flow across the newly-formed wetland. This was planned 12 months in advance to utilise specific tidal conditions on certain days during the summer of 2015. 4D modelling was used to identify operational issues, tidal effects, and potential risk elements. Breach Day, 11 July 2015, was a success due to good communication, a strong team buy-in, and risk planning.
Completion and benefits
Commended by Crossrail for achieving a safety record of 700+ days without a Lost Time Incident, the Wallasea Island Wild Coast Project is an innovative scheme, demonstrating that large quantities of material can be transported by water from London. Phase 1, latterly named ‘Jubilee Marsh’ by the RSPB, opened to the public earlier than anticipated in September 2015, 12 months ahead of original programme. The tidal flows are accreting silt across the intertidal habitats which will increase bird food source and the RSPB reported a successful first breeding season one year on.
Further material is required to be sourced for Cells 2 and 4. When completed in 2025, the Project will reinstate a total of 670 hectares of wetland.
