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Alkborough Tidal Defence Scheme

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Project Team: Environment Agency (client), Jacobs (project management), Halcrow (design), Volker Stevin (construction)

Award presentation for the Alkborough Tidal Defence Scheme

Project background

Alkborough Flats are on the south bank of the Humber Estuary, on the eastern side of the confluence between the River Trent and the River Humber. The site is around 440 hectares of agricultural land, of which approximately 375 hectares are protected by a flood embankment constructed in the late 1950s.

The Alkborough tidal defence scheme cost £10.2 million and is a fundamental part of the Environment Agency’s long-term strategy for managing flood risk on the Humber Estuary.

More than 90,000 hectares of land and 300,000 properties around the Humber are below high tide levels and rely on the system of flood defences around the estuary.

Details of the scheme

The Alkborough tidal defence scheme increases the level of flood protection to an area stretching from the Humber Bridge to Goole up the tidal River Ouse and as far as Keadby Bridge on the tidal River Trent.

The scheme features include a 20-metre-wide breach of the existing flood bank, a 1,500-metre length of lowered embankment or spillway and a new section of floodbank to protect assets at the edge of the site.

The scheme has been designed to:

• reduce the impact of sea level rise;
• safeguard the internationally-important nature conservation interest of the Humber by creating new wetland habitat;
• provide a focus for education and access opportunities for local communities.

The scheme was developed by a partnership of the Environment Agency, Natural England, Associated British Ports and North Lincolnshire Council.

For a flood event with a 0.5 per cent chance of happening in any year (1 in 200) the scheme at Alkborough will reduce extreme water levels by more than 150 mm.

Providing flood storage at Alkborough has made it possible to defer improvements to other flood defences in the tidal rivers upstream of the site that would otherwise be needed to counter the effects of sea level rise.

Habitat at Alkborough

Studies we carried out on the Humber Estuary show that valuable saltmarsh and wetland – known as inter-tidal habitat – will be lost over the next 100 years as a result of sea level rise.

The scheme at Alkborough assists in replacing these losses and recreates more than 150 hectares of wetland and increase the biodiversity of the area. Other smaller managed realignment projects are being developed in other parts of the estuary to help address this problem.

The new wetland habitats at Alkborough meets all national Biodiversity Action Plan targets for saltmarsh and mudflat habitat creation for 2006–2007. Part of the site has been developed as freshwater reedbeds to support a different range of species from the main inter-tidal area. As well as providing this new habitat the higher parts of the site will be used for grazing. This will add to the range of plants and animals that the site will support.

The total area of wildlife habitat created by the scheme is approximately 370 hectares, of which 170 hectares are inter-tidal areas. This contributes to habitat creation responsibilities under the EU Habitats and Wild Birds Directives set out in the Humber Estuary Coastal Habitat Management Plan.

Recreation and access at Alkborough

Alkborough tidal defence scheme is part of several larger projects being promoted along the South Humber bank. This includes a variety of access, education and interpretation projects funded by the Heritage Lottery Fund and a range of new visitor and tourism opportunities along the Humber from Barton to Alkborough, led by North Lincolnshire Council and funded by Yorkshire Forward.

Respect for the local community

The contractor, Volker Stevin, placed particular emphasis on maintaining a good relationship with the local community throughout the entire duration of the project.

The site manager kept neighbours informed, including the Parish Council and local farmers. A traffic plan was drafted to avoid overloading local roads with heavy vehicles. The contractor also sponsored a village show and several local building projects. The construction programme was adapted to suit farming cycles.

As a result of these particular efforts the project also won a Bronze Award through the Considerate Constructors Scheme in March 2007.