Seabed Recovery following Dredging

You will recall that the spokesman for BMAPA originally denied any damaging impact to the sea bed as a result of dredging. Following our provision of evidence disproving this claim in our objections to licence applications, this was later amended by a claim that full recovery resulted within a year of the termination of dredging operations.

A year later, following the findings published by CEFAS and HR Wallingford that no recovery was evident even after three years (see "Assessment of the rehabilitation of the seabed following marine aggregate dredging" at www.marinet.org.uk/mad/scientificstudies.html#cfn) BMAPA amended the claimed recovery period to be within 'two to three years' (see the interview with their spokesman Dr. Andrew Bellamy on our MARINET video film).

But we know that this myth has long been disputed by fisherman, who have discovered from first hand knowledge and practical experience that dredged out areas do not recover even after eighteen years. (See the findings by Rodney and Graham Burns of the Aldeburgh Fishing Guild under 'The Losses Account' in our Briefing Paper No.1 on this website and also on our MARINET video film).

Now some good news is at hand with possible remediation in sight as it was announced that CEFAS are instituting an experimental project that might just bring about recovery to dredged out areas.

This encouraging move was revealed at the the April 2009 meeting of the East Coast Dredging Liaison Committee which is made up of representatives from the MFA, The Crown Estate, Hanson Aggregates Marine Ltd, Westminster Gravels Ltd, BMAPA, ERM Cemex, UK Marine Ltd, United Marine Dredging, Britannia Aggregates Ltd, Southend Fishermen's Association, Environment Agency, DEME Building Materials, VDL Sea Aggregates and Kent and Essex SFC NFFO. (MARINET has been excluded from this committee)

The purpose of the experimental project is to set up a field trial to investigate the potential for gravel seeding as a means of restoring sediment composition in areas where dredging has resulted in an overburden of fine sediments. Specific objectives are to determine whether:

1. … it is practically feasible to perform gravel seeding' at a relinquished aggregate extraction site, and …
2. … whether the technique results in sediments more physically similar to that of non-impacted gravelly habitats in the wider environment, and …
3. … whether the technique results in the return of more gravelly fauna.

An initial attempt took place in Zone 2 within aggregate extraction Area 408 (offshore to the Humber) this chosen as the experimental site as there was some evidence for persistence of sand which may have resulted from screening operations at this site. Two 4000 tonne cargoes were dredged, using a commercial suction hopper trailer dredger, from within an active zone of Area 408 and deposited within the treatment box.

Prior to deposition, a baseline survey, using a combination of acoustic tools and grab sampling was undertaken. This survey was followed up, post deposition, by a further three surveys. Results showed that a commercial dredger, typical of those operating at extraction Area 408, could be used to undertake gravel seeding. Results also indicated that the technique was successful in increasing the proportion of gravel exposed at the seabed surface. The increase in gravel led to the establishment of a faunal community more similar to that of local gravel dominated reference sites. Although results suggest gravel seeding could be used for restoration, further work is required to assess the long-term success of the technique".