Managed realignment (breach)

Description of measure

Breach Realignment involves deliberately breaching sections of existing seawalls or embankments in order to allow the waters of adjacent coasts or estuaries to inundate the land behind through a defined gap (the ‘breach’).

Application

Implementing the mitigation measure of managed realignment using the technique of breach creation is well suited to schemes where the primary purpose of the works is the rapid creation of a definable new intertidal habitat, particularly saltmarsh habitat, for ecological benefit.

It is a most suitable technique on schemes where a measure of wave protection is needed for the site so that sedimentation can occur more rapidly. Retaining large sections of the original sea wall or embankment provides this shelter and hence both encourages settlement of suspended sediments and reduces potential for re-suspension of recently deposited (and hence unconsolidated) sediments.

Breach Realignment is presently the most widely practiced technique for implementing Managed Realignment within the UK. The Online Managed Realignment Guide (ABPmer, 2009) provides details on 23 schemes within the UK for Breach Realignment which can be used as guidance.

The main constraints specifically to Breach Realignment are related to: potential wider ranging effects due to jetting of egress flows from the breach (e.g. erosion of fronting inter-tidal areas); and potential severing of footpaths (as many run along the crest of sea embankments).

Tidal flows through a managed realignment breach

Benefits for the Water Framework Directive (WFD)

Breach Realignment shares the general benefits for WFD relating to the overall mitigation measure of Managed Realignment.  Additionally, Breach Realignment is more likely to be conducive to:

  • Developing and sustaining intertidal habitat since the retention of sections of the original defences encourages more rapid sedimentation rates in comparison with Bank Realignment;
  • Increasing sedimentation rates and more rapid consolidation encouraging mudflat formation;
  • Establishing saltmarsh vegetation;
  • Rapidly providing suitable habitat for benthic/macro invertebrates, macroalgae and angiosperm Biological Quality Elements (BQEs); and
  • Providing an important nursery area for fish. 

Breach Realignment can be used to optimise sedimentation on the site and, hence, be used to enhance habitat formation and diversity.  A greater diversity of habitats ranging from mudflats on lower levels, through pioneer saltmarsh species to upper shore transitional species promotes enhanced ecological functioning and increases the amenity and aesthetic value of the site.  A greater variety of intertidal habitats can also provide suitable nesting, roosting and feeding areas for water birds.

The optimisation of sediment rates and increased likelihood of developing and sustaining intertidal habitat also has a sea defence function.  Considerable dissipation of wave and tidal energy occurs across wide mud or sand flats.  Vegetated areas, such as salt marshes, provide surface roughness which further dissipates this energy at the upper section of the foreshore profile.  Combined, the mud or sand flat and salt marsh can dissipate almost all of the impinging energy before it reaches the backing high ground or backing defences when a sufficient width is available.

In addition, Breach Realignment is often less expensive compared with Bank Realignment or Regulated Tidal Exchange.

To read more about the effectiveness of the measure within academic literature please click here: Effectiveness for Biological Quality Elements

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