What is ‘Managed Realignment’ and ‘Regulated Tidal Exchange’?
This web-site seeks to include project-specific information about completed Managed Realignment and Regulated Tidal Exchange projects in North West Europe and, in so doing, to communicate the lessons learned in the past and thus, to improve the quality of similar projects in the future.
This is believed to be the first site to provide such a comprehensive source of project-specific information although a number of very useful products already exist to describe selected managed realignment projects and to discuss in general terms what Managed Realignment is and why it is undertaken (as distinct from this site which concentrates on specific project lessons). A bibliography of reports and web-site links is included in this web site under the ‘Sources of Information’ section. Of these, the following two are particularly useful products that are worth highlighting: -
- The ComCoast Web-Site at http://www.comcoast.org/ - ComCoast is a European project which develops and demonstrates innovative solutions for flood protection in coastal areas across the North Sea Interreg IIIb region. It is a rich source of information on coastal defence strategies in current and future sites. It includes, among other contents, animations and videos of flood management measures; details of the multifunctional values of such measures from an economical and social point of view and guidance on best practice for communicating these measures to technical and non-technical communities
- The UK Environment Agency’s Managed Realignment Electronic Platform at http://www.intertidalmanagement.co.uk/. This site provides an easy to use, portable source of reference information. It introduces the principles of Managed Realignment and provides information of the diverse range of policy, legislation, and issues that relate to Managed Realignment in the UK.
To assist users of this web-site, the text below provides a summary description of Managed Realignment and Regulated Tidal Exchange.
The term Managed Realignment (also called ‘De-Embankment’ in mainland Europe) is most commonly understood to involve a deliberate breaching, or removal, of existing seawalls, embankments or dikes in order to allow the waters of adjacent coasts, estuaries or rivers to inundate the land behind.
Depending upon the height and shape of land behind the breached wall, there may or may not be a need to build a new line of defences behind the site. In most instances the newly flooded land is low-lying coastal flood plain and therefore a new seawall (or ‘counterwall’) is needed to clearly define the inundated area and protect the hinterland behind. However, on areas with rising ground (such as at Abbotts Hall in the Blackwater Estuary) either no new line of defences or only a partial counterwall is required.
This landward movement of the primary sea defence line is used as a defining characteristic of Managed Realignment in this web-site. However, it is recognised that the term ‘managed realignment’ can be applied to other coastal habitat creation methods that extend intertidal habitats in a seaward direction. For example, the new Shoreline Management Plan guidance for England and Wales (issued in 2006) defines managed realignment as ‘the process of allowing the coast line to move backwards or forwards with management to control or limit that movement’. This definition would additionally apply to activities such as sediment recharge which can be used extend the width of existing intertidal habitats (e.g. at Horsey Island as described in the ComCoast web-site at http://www.comcoast.org/).
Often considered together under the umbrella term of Managed Realignment (MR), Regulated Tidal Exchange (RTE) is considered in this web-site as a distinct category of coastal intervention. RTE essentially encompasses a range of techniques for intertidal habitat creation other than full breaching of the existing sea wall. These include the use of sluice gates, spillways, culverts, or pipes to control regular tidal inundation. It has been argued that these mechanisms can be interpreted as MR where the active defence line is actually moved to landward. However, it is distinct from MR because a high degree of control is retained, the tidal range is restricted and the old defence line tends to require continued maintenance. Regulated tidal exchange has also been discussed as a precursor to bank or breach-managed realignment in order to allow the ground behind seawalls to rise through sedimentation in controlled circumstances (as practised at Abbotts Hall).
Burd, F., 1995. Managed Retreat: a Practical Guide. Peterborough: English Nature, 26p.
CCPEM study (undertaken by S. Rupp-Armstrong, Southampton University – email address: sarmstrong{at}ABPmer.co.uk) (unpublished data)
ComCoast, 2007. http://www.comcoast.org/