RSPB Wallasea Island wild coast project - Lessons for designing managed realignment sites

Wright, A. and Townend, I. and Scott, C. (2009) RSPB Wallasea Island wild coast project - Lessons for designing managed realignment sites. In: 44th Defra Flood and Coastal Management Conference, 30th June - 2nd July 2009, Telford, UK.

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Abstract

On the 23rd April 2009, planning consent was obtained for the Royal Society for the Protection of Birds’ (RSPB’s) Wallasea Island Wild Coast Project. This project represents one of the largest coastal wetland schemes of its type in Europe and the application area covers 677ha of Wallasea Island which lies at the confluence of the Crouch and Roach Estuaries in Essex (Figure 1). The design for this scheme includes both Managed Realignment (MR) and Regulated Tidal Exchange (RTE) areas as well as an area set aside for the creation of mitigation habitats and visitor access facilities. Central to the whole design will be the importation of a large amount (7.5 Million m3) of inert recovered fill material which will be obtained predominantly from the Crossrail link tunnelling. These materials will be used raise the land levels, which have sunk greatly since the island was claimed, and to landscape the site in a way that manages the volumes and direction of the tidal exchanges from the site. The final design is one that not only delivers large amounts of intertidal habitat in contribution to Biodiversity Action Plan (BAP) targets but also performs a critical flood protection need at a location where, if there is no intervention, there is an imminent risk of a damaging unmanaged breach in the near future (Halcrow 2006). Once the island has been landscaped and the sea walls are breached (a process that will take place in a phased way) the volumes of tidal water that it will exchange with the Roach Estuary will be around 2.1 Million m3 on a spring tide. This is a substantial reduction when compared against an unmanaged breach scenario which, given the low elevations and flat topography throughout the island, would exchange around 11 million m3. The mechanism for designing this scheme, understanding how it would function and assessing its hydrodynamic effects on the estuary system was pursued as an integrated and iterative process. This ensured that the key issues, constraints and stakeholder requirements were foreseen and addressed as required. For this design and assessment work, the lessons learned from previous intertidal habitat creation projects (especially those from the Defra MR on the north bank of the island) were taken on board alongside available guidance and new modelling techniques. This iterative process, and the principles and tools that were applied, are outlined here as a guide for implementing future projects although it is recognised that the work required for all future schemes will need to be evaluated on a case-by-case basis.

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