Foreshore or intertidal recharge

Description of measure

Intertidal recharge aims to mitigate a sediment deficit by restoring the functioning of the intertidal/foreshore through the introduction of sediment to directly or indirectly feed intertidal areas.  Schemes may utilise sediment derived from the navigational dredging of ports and harbours and, in doing so, provide a ‘beneficial’ use for this material, may use material ‘recycled’ from areas of accretion along the foreshore (e.g. accumulated along beaches against harbour arms), or may use material dredged from offshore sand banks. 

Application

Intertidal recharge may be used to either manage erosion or promote accretion.  It is appropriate to both open coast and estuarine environments but application of this technique requires consideration of the availability of a suitable source of recharge material. 

The purpose of foreshore or intertidal recharge can be to:

  • Transform low and eroding foreshores into elevated and accreting shores;
  • Reduce or reverse the rate of retreat of managed coastal habitats;
  • Reduce wave energy, control tidal velocities and to encourage sediment deposition;
  • Protect backing assets, including dunes, gravel barriers and cliffs, from erosion and/or flooding; or
  • Cover underlying geological strata with a veneer of protective material.

The technique aims to mitigate deficits in sediment by restoring the functioning of mudflats, saltmarshes or sandy foreshores through the introduction of sediment onto, or adjacent to, intertidal areas. In most cases this is considered to be a sacrificial sediment supply but can be an important response to critical conditions. It can provide a sustainable solution in some circumstances and provide additional time to investigate the sustainable options in others. Placement of materials is often technically difficult on soft shorelines, and this technique may have significant ecological consequences in terms of habitat alteration.

Whilst immediately restoring intertidal volumes, these will in most cases progressively diminish over time and there may be a need for periodic ‘top-up’ recharges to maintain the restored sediment as the site will still be subjected to the shoreline processes which caused the original problem.

Introduction of large volumes of sediment to the intertidal has the potential to cause various ecological effects in terms of habitat alteration associated with smothering of infauna and habitat loss.  An additional constraint associated with the application of sediment recharge is the potential for recharge material to contain toxic contaminants and the impact on macro/benthic invertebrates and fish at the point of sediment origin through direct removal and dredging effects.

Foreshore or intertidal recharge can provide the following additional benefits:

  • Maintenance or enhancement of intertidal and/or subtidal habitat helping to increase the conservation value of a site.
  • Benefits for flood and coastal erosion risk management – e.g. 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.
  • Beneficial use of dredged sediment which would otherwise be disposed of elsewhere.
  • Reduced risk of irreversible erosion of the underlying strata (and any associated features of ecological / geological interest) since the sediment veneer provides protection.
  • Maintenance or enhancement of the amenity/recreational value of the intertidal/foreshore area.

Benefits for the Water Framework Directive (WFD)

Sediment recharge can be effective at maintaining or increasing the area and stability of intertidal and/or subtidal sedimentary habitat available for colonisation by macroalgae, benthic/macro invertebrates and angiosperms and, hence, lead to improvements in these Biological Quality Elements.

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

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