Managed Realignment

Managed realignment, sometimes referred to as managed retreat, is one of several 'soft' engineering options available to coastal planners. In most cases it involves breaching an existing coastal defence, such as a sea wall or an embankment, and allowing the land behind to be flooded by the incoming tide. This land is then left to be colonised by saltmarsh vegetation. When established, the vegetation disperses wave energy during storm events, reduces erosion rates and provides an important habitat for coastal flora and fauna. If the newly breached area is backed by low-lying land, a new embankment is usually constructed beforehand on the landward side of the site to reduce the risk of flooding. Although a relatively new idea, it is widely recognised that managed realignment can reduce the costs of coastal defence whilst offering numerous environmental benefits.

Example of a 'hard' flood defence option:

Example of managed realignment:

The advantages

• Flood Defence: the inter-tidal region is able to dissipate wave energy and protect property and land. Managed realignment schemes have reduced capital and maintenance costs compared to fixed defence schemes.
• Habitat Creation: inter-tidal habitats support a wide variety of specialised plants, invertebrates, molluscs, birds and fish. The new habitats created by such schemes may offset the loss of natural intertidal habitats from development pressures, pollution and land reclamation.
• Recreational opportunities: some inter-tidal habitats created by realignment schemes produce areas which are suitable for recreation.

The limitations?

• Only suited to areas with low-lying, low-grade agricultural land.
• Potential opposition from landowners and developers, even if compensation is offered.
• In-built political and institutional preference for 'hard' engineering schemes.

Managed realignment in the UK

A small number of realignment schemes have been undertaken in the UK, mainly along the Essex coastline. The first deliberate attempt at managed realignment in the UK was on a small island located in the Blackwater Estuary in Essex. The Northey Island scheme, organised by the National Trust (the landowners of the site), the Environment Agency and English Nature involved breaching and lowering a seawall to encourage saltmarsh development on its landward side. Aided by high sedimentation rates the scheme has been successful, with a viable saltmarsh community now established at the site.

Similar schemes have been undertaken elsewhere on the Essex coast at Abbotts Hall, Orplands and Tollesbury, and in other coastal areas, for example at Pawlett Hams in Somerset. Although existing schemes are small in scale and number they do highlight the potential for managed realignment to play a role in future flood development programmes.