Project part-financed by the European Union (European Regional Development Fund)

The Interreg IVB North Sea Region Programme

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Alkborough Managed Realignment

Crux of the matter

The “crux of the matter“ refers to the basic, central or critical point of an issue. For example, in this context, the main issues relating to the development and progression of the specific measure detailed within this FAS Repost represent the crux of the matter.

The main purpose of the measure is to provide flood storage during extreme events with an additional objective of providing compensatory habitat for coastal squeeze.

The majority of the site act as a sediment sink and accretes. The initial rapid siltation from 2006 to 2008 (0.6m) has not continued and the average rates of accretion between 2008 and 2012 ranges between 0.03m and 0.09m per year. A linear extrapolation of the accretion rates show that siltation will reach the present day MHWS level within the majority of the site in 13 to 35 years after site opening.

The flooding and sedimentation regime within the realignment site have resulted in the formation of a mosaic of habitats which is considerably more diverse than that on the natural mudflats outside the site. Habitats present include mudflat, standing water, wet grassland and reed beds and fulfil the habitat requirements of a wide range of species or fish and birds. In contrast, the benthic communities are impoverished (throughout this region of the estuary) and do not yet represent those on the mudflats outside the site and are largely composed of freshwater and terrestrial species. Overall the Alkborough site does not necessarily compensate for habitat loss and coastal squeeze in terms of mudflat creation and infaunal community development. It does however appear to be acting as a nursery area for fish and a significant feeding and roosting area for birds. In this respect, the development of the site appears to have been beneficial to this region of the estuary which is otherwise largely characterised by narrow mudflats with species poor communities and, in most areas, little vegetation.

Over time it is anticipated that the site will become well vegetated and cease to be fully inundated by high tides. This will mean that the site will not provide the 'like for like' direct habitat compensation. Over time the site will continue to accrete and thus reduces the space available for water storage and reduce the effectiveness of the site to provide flood protection. The Environment Agency is currently investigating options for changing the breach configuration and altering the scheme to a regulated tidal exchange scheme.

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Reports / Measures / Tools

Report: Management measures analysis and comparison