Foreshore or intertidal recharge

Effectiveness for Biological Quality Elements

At Maldon, Essex, sediment recharge was used to manage erosion of a saltmarsh and raise foreshore levels.  Monitoring surveys following implementation at this site found no further signs of erosion and recharged areas developed algal mats and a saltmarsh vegetation comparable with that of the surrounding marsh (Nottage & Robertson, 2005).  However, this scheme involved ongoing placements of material and therefore does not represent a permanent solution to the underlying erosion problem.  If removal of recharge material occurs relatively rapidly at a site, this may prevent benthic invertebrates, macroalgae and/or vegetation (angiosperms) from colonising the surface successfully, hence reducing the effectiveness of this technique for WFD.

Several authors have studied the effects of the placement of dredged material on some of the WFD BQEs.  Koel and Stevenson (2002) found macro-invertebrate taxa densities to be highest at sites that have never received dredged material, suggesting the need for its strategic placement and specifically avoiding islands or other areas where invertebrate diversity would naturally be relatively high.  In contrast, Bolam & Wormsley (2003) reported a rapid recolonisation of the fauna typical of surrounding saltmarsh channels (within 3 months) following fine grained sediment recharge at a site in southeast England.  However, community structure did not progress towards those of reference sites.  In Delaware Bay, USA, Weinstein & Weishar (2002) reported that intertidal recharge improved the geomorphology of the saltmarsh platform, providing high marsh refugia for species that depend on this habitat type for survival and stabilised shorelines to reduce erosion rates.

At Horsey Island, Essex, recharge of the foreshore was first carried out in the early 1990s and a volume of 18,000 m3 of coarse dredged material was sprayed onto the mid intertidal area by rainbow discharge from a vessel at high spring tide.  The scheme resulted in increased abundances of the ragworm Nereis and the formation of a new saltmarsh habitat behind the recharged material.

For at least the last decade there have been beneficial use schemes undertaken and planned by UK ports and harbours, mostly providing uses for coarse dredged material such as gravels and sands for construction or coastal defences purchases, such as beach replenishment schemes. The use of maintenance dredged material for environmental enhancement, such as habitat creation, restoration and enhancement, has increased considerably in recent years, particularly intertidal sediment recharge (foreshore nourishment) schemes which provide a means of combating the erosion of saltmarsh and intertidal habitats. Intertidal recharge schemes have been undertaken on a largely small-scale experimental basis in over 20 locations in Essex and Suffolk using dredged material from the Blackwater Estuary and Harwich Harbour. In particular, Harwich Harbour has been responsible for more beneficial use schemes than any other port in the UK. Dredged sands and gravels from channel deepening works have been used in a number of varied schemes, including intertidal recharge for coastal defence in the Stour, Orwell and Blackwater Estuaries and Horsey Island, construction of low water berms for foreshore stabilisation, and the creation of shellfish and crustacea habitat.

A number of experimental intertidal recharge schemes were undertaken in 1993 and 1994 with the objective of using the coarse dredged sediments to protect eroding saltmarshes and the infrastructure behind them. At Parkeston Marshes Copperas Bay on the north bank of the Stour Estuary, with funding from the Environment Agency, 250,000 cubic metres of dredged sands from Harwich Harbour were sprayed onto the intertidal mudflats using rainbowing techniques. Post-scheme monitoring of the shore profile, sediments and faunal communities has indicated that erosion of the foreshore has reduced and the wetland is naturally being restored.

Harwich Harbour also carred out two experimental intertidal recharge trials, each using maintenance dredged muds (Posford Duvivier Environment, 1998). In the North Shotley scheme in the lower Orwell Estuary, maintenance material was pumped via a pipeline into a gravel bunded area to protect sea wall and the internationally important freshwater wetlands behind. In the Horsey North and Horsey Beach scheme, silt has been placed on a degraded marsh at Island Point to protect and regenerate saltmarsh.

Academic references

Blankenship, K.  (1996)  From Shipping Lanes to Shorelines: ‘Beneficial Use’ Projects give new life to Dredged Materials.  Bay Journal 6(7), October 1996.

Carpenter, K.E. and Brampton, A.H. (1996) Maintenance and Enhancement of Saltmarshes. Environment Agency R&D Note 473.

Colenutt, A. (2001) Saltmarsh Management Techniques: A Review. New Forest District Council Coast Protection Group

Nottage, A.S. and Robertson, P.A. (2005) The saltmarsh creation handbook: a project manager's guide to the creation of saltmarsh and intertidal mudflats. The RSPB, Sandy and CIWEM, London.

Simm, J.D., Brampton, A.H., Beech, N.W. and Brooke, J.S. (1996) Beach Management Manual, CIRIA Report 153, London.