Options for managed realignment - summary for low-lying coasts

Managed realignment is widely viewed as one of several 'soft' engineering options which may reduce the costs of coastal defence (in this case in low-lying areas), provide a more 'natural' response to the problem of rising sea levels and at the same time deliver environmental, specifically nature conservation, benefits. On the European mainland it is referred to as depoldering.

Caption: Figure showing realignment of the coast, allowing saltmarsh to migrate landwards

Once the decision to undertake a managed realignment is made, several options are available. These are depicted in the Figure opposite and listed below:

• removal of embankment (e.g. Northey Island, Essex);
• removal of a section of the seawall to create a breach (e.g. Orplands and Tollesbury, Essex; Pawlett Hams, Somerset) and build another seawall to landward;
• lower a section of the seawall to produce a spillway;
• reverse fresh water sluices to allow the inflow of seawater (e.g. Abbots Hall, Essex).

A general term for the regulation of tidal movement onto a site is Regulated Tidal Exchange which incorporates the use of spillways and sluices.

Cautions and caveats: This approach may be generally acceptable where the area of land behind the sea wall is already impoverished from a nature conservation point of view. Difficulties will arise where the land has a high value, possibly as lagoonal or more likely traditional coastal grazing marsh. In these circumstances consideration will need to be given to creating new coastal wet grassland from arable or other intensively used agricultural land, if the full sequence of habitats is to be re-created. For a discussion of the issues involved see (Pethick 2002).

Consents and licenses: Any managed realignment schemes will be subject to a number of consents and licenses.

References

DEFRA 2002. Managed Realignment Review - Project Report. Department of the Environment Food and Rural Affairs, London.

Pethick, J.S. 2002. Esturarine and tidal wetland restoration in the United Kingdom: policy versus practice. Restoration Ecology, 10., 431-437. Abstract...