Alkborough is situated on the south bank of the Humber estuary on the eastern side of the confluence between the River Humber and the River Trent.
The site is bounded to the south east by the escarpment of the Lincolnshire Heights with the remaining boundaries of the site being formed by a tidal defence approximately 6km in length.
The existing tidal defence comprises a grassed, partially reinforced, earth embankment set back to varying degrees behind saltmarsh with mudflats to seaward. Two thirds of the land within the site is in the ownership of Natural England and the Environment Agency.
The promotion of the Alkborough scheme was driven by strategic requirements and has significant benefits with regard to sustainable estuary management. These are the reduction in tide levels during extreme events deferring the need for raising the level of the tidal defences to cater for future sea level rise, together with the provision of replacement habitat for coastal squeeze losses in the estuary and compensation for losses arising from tidal defence works elsewhere in the estuary.
Halcrow was initially engaged to prepare a project appraisal for the purchase of the remaining land in order to secure funding from Defra for this purpose. The project appraisal for the scheme comprised site and ground investigations, escarpment stability analyses and hydrodynamic modelling and geomorphological analysis to inform the assessment of the external impacts of the development and ensure that these were alleviated by appropriate design. These studies were followed by economic assessment and environment impact assessment.
The key environmental issues with respect to design of the site were the potential impacts outside the site of scour / deposition and tide level reductions on navigation interests and on existing biodiversity interests. Other engineering requirements included the provision of a local tidal defence to both protect Alkborough sewage treatment works and other low lying assets from flooding, and works to ensure appropriate drainage from and maintain the stability of, the escarpment adjoining Alkborough village.
Within the new inter-tidal area a channel was cut to ensure appropriate distribution of tidal waters, together with banks and land forming works within the site to aid creation of various habitats.
The final scheme comprised the managed landward realignment of the 6km of tidal defence, thereby creating 370ha of new inter-tidal habitat and providing flood defence benefits in the inner and middle estuary.