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Alkborough Flats Managed Realignment
Alkborough, North Lincolnshire, England, United Kingdom
Alkborough Flats is the location of an Environment Agency of England (EA) coastal-managed realignment (or restoration) scheme, completed in 2006, in the Humber Estuary. The scheme was constructed by Volker and Stevin and is one of the largest managed realignment sites and one of the largest flood storage schemes in Europe. It is located on the south bank of the inner Humber Estuary at the confluence of the River Ouse and the River Trent.
Inundation of the Alkborough Flats provides a massive flood storage area that is sufficient, according to EA predictions at the time of the site design, to reduce high-tide levels over a large part of the upper estuary by up to 150 millimeters. At a projected annual sea level rise of 4 millimeters per year until 2025, and then 8.5 millimeters per year until 2055, the analysis at the time of construction indicated that the Alkborough Flats scheme would modify the regime to account for 25 years of climate change impact.
Producing Efficiencies
Providing flood storage at Alkborough makes it possible to defer improvements to other flood defenses in the tidal rivers upstream of the site. These upstream defenses would likely have otherwise been needed sooner to counter the effects of sea level rise.
Using Natural Processes
An approach was developed to create a relatively small breach to permit inundation of the site by normal tides, together with an adjoining overspill weir, to make flood storage within the site easier during extreme events. The use of a twenty-meter-wide breach was the preferred arrangement because it met one of the primary project objectives of creating intertidal habitat while limiting the impacts of the scheme on other uses of the estuary—in particular, navigation and environmental interests.
Broadening Benefits
Ten years since site creation, the project has achieved numerous benefits. The scheme has increased flood protection over an area extending along both the River Ouse (from the Humber Bridge to Goole) and the River Trent (as far as Keadby Bridge).
New intertidal bird and fish habitat has been developing at the inundation zone; the new habitat includes reed beds, saltmarsh, and mudflats—these areas will help replace comparable areas lost in other sections of the estuary due to rising sea levels.
The scheme has also provided the public with a system of footpaths and nature-viewing opportunities.
Promoting Collaboration
Designed by Halcrow and constructed by Volker Stevin, the scheme was created through a partnership involving the EA, Natural England, Associated British Ports and Lincolnshire County Council. Most of the site area was purchased by the EA and Natural England (at the time known as English Nature) in 2003, using external funding made available by HM Treasury, the United Kingdom’s finance ministry, and the Regional Development Agency.
