Manage foreshore / intertidal erosion

Description of measure

The management of intertidal and/or foreshore erosion can encompass a wide variety of soft- and hard-engineered approaches.  A number of techniques may used in isolation or combination to manage intertidal erosion.  There are essentially two main approaches to managing intertidal and/or foreshore erosion: (i) retaining existing sediment on the foreshore/intertidal and (ii) restoring sediment to the foreshore/intertidal.

Techniques to retain existing sediment on the foreshore/intertidal include:

  • Offshore or shore-attached structures such as breakwaters and artificial reefs.
  • Cross-shore structures, such as groynes, to retain sediment that is transported along the coast.
  • Beach drainage systems.
  • Artificial headlands.
  • Increasing sediment roughness, for example by using artificial seaweed or seeding mudflats with mussel sprat

Techniques to restore sediment to the foreshore/intertidal include:

  • Sediment recharge (see separate technique sheet ‘Foreshore or Intertidal Recharge’.
  • Trapping material moving along the coast (groynes).
  • Sedimentation fences.
  • Vegetation planting.

Application

The application of any one technique will be subject to the management aims and the conditions at the site. No one technique is applicable to all environments and therefore care must be exercised in choosing the correct technique.  Whether a technique is applicable to a specific environment is dependant upon a number of external parameters such as wave and tidal regime, whether the site is of high or low energy, topography and availability of accommodation space.

The use of cross-shore structures (groynes), wavebreak structures (breakwaters and artificial reefs), artificial headlands and beach drainage systems are effective in coarser, non-cohesive sediment (sand and gravel) environments to retain sediments moving along the open coast. In estuarine environments, where finer cohesive sediments dominate, increasing sediment roughness or techniques to deflect nearshore currents and/or restore sediment may be more applicable. 

Benefits for the Water Framework Directive (WFD)

Techniques to manage erosion can help deliver objectives of the Water Framework Directive by:

  • Stabilising intertidal/foreshore sediments providing benefits to macro/benthic invertebrates and, in saltmarsh areas, angiosperms and juvenile fish
  • Providing additional subtidal and/or intertidal habitat where artificial reefs, breakwaters and artificial headlands are employed, allowing colonisation by macroalgae and providing nursery areas for fish.
  • Reducing the levels of suspended sediment locally, increasing sunlight provision and plant growth, and reducing pollutants such as phosphorous.
  • Sustaining the functioning of the water body.

Other benefits of the management of erosion are dependant upon the technique implemented and the characteristics of the site.  However, generally, management of the foreshore/intertidal will provide the following additional benefits:

  • Reduced flood/erosion risk of backing land (such as dunes, gravel barriers, cliffs or low-lying hinterland).
  • Reduced risk of overtopping of defences by waves as more energy is dissipated across the foreshore, and reduced risk of undermining of defences as higher beach levels are retained.
  • Reduced risk of irreversible erosion of the underlying strata (and any associated features of ecological / geological interest) since superficial sediments provides protection.
  • Maintenance or enhancement of the amenity/recreational value of the intertidal/foreshore area.

 

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