Falmouth dredging trial: What happens next?

Falmouth dredging trial: What happens next?

Falmouth dredging trial: What happens next?

First published in News by

As experts gear up to start the dredging trial in Falmouth Bay, The Packet lays out the players involved, detail of the trial itself, and concerns from those opposed that the trial will not show the full potential impact.

The trial is part of gathering vital scientific evidence on the impact of Falmouth Harbour Commissioners multi-million pound plan to dredge the harbour to encourage more cruise ship visits. Those supporting the plan say this is vital to ensure the future of the town as a working port, bring jobs to the area and that the increased ship traffic will have a positive knock on effect for local businesses across Falmouth and further afield.

Environmentalists and fishermen say they are concerned fishing beds and a rare algae, maerl, important as a nursery for marine species and commercial fish stocks, would be damaged, and that the trial will not be a true reflection of the dredging’s impact. Some have raised concerns that taxpayers will be funding the dredging, which they claim will mainly benefit a private company.

The six-month trial, due to start later this month, will see maerl taken from the seafloor in areas “the size of a badminton court”, resettled and then the impact judged. This will be part of the jigsaw of information that would inform any decision to give the dredging the green light.

Concerns have been raised that the trial will not show the true effects of the full dredge, however Martin Attrill, Professor of Marine Ecology at the University Of Plymouth, said: “It’s the equivalent of a person being examined in an area of about two-and-a-half times the size of a football pitch.

“It will give us a good understanding of how the organism will react to this, and then we can extrapolate up to the bigger picture. You could make the areas bigger and bigger again, but you're not going to learn anything more.”

 

The groups involved

Falmouth Harbour, including the Carrick Roads, is reputed to be the third largest natural harbour in the world.

Falmouth Harbour Commissioners is a statutory port authority created by an act of parliament in 1870 with responsibility for the Inner Harbour at Falmouth (excluding Falmouth Docks), the Penryn River up as far as Boyers Cellars, the southern part of the Carrick Roads and a large part of Falmouth Bay.  It operates as a trust port and has a board of eight commissioners who act as trustees. 

  • The Port of Falmouth Masterplan , is a vision for the future marine use of Falmouth and its role in the community. The proposals centre around Falmouth Docks and set out projects for the next five years, as well as for the longer term, up to 2026. These include modernising ship repair facilities, upgrading wharves at the Docks, improving bunkering services, a new state-of-the-art 290 berth marina and providing new super yacht workshops and offices.
  • Professor Martin Attrill , BSc, PhD, FLS. Professor Martin Attrill is a marine ecologist. He has published over 100 papers, primarily on fish and benthic systems such as seagrass, and has also current projects investigating the roles of Marine Protected Areas, such as the new Defra designation in Lyme Bay. Since May 2009, Prof Attrill has been Director of the Marine Institute at Plymouth University, a multidisciplinary organisation comprising over 150 academic staff working in marine and maritime areas, 250 researchers and PhD students and 2600 students enrolled on marine and maritime courses.
  • Marine Management Organisation (MMO): The Marine Management Organisation (MMO) is an executive non-departmental public body given powers under the Marine and Coastal Access Act 2009. Its mission is to enable the sustainable development of English seas.
  • Independent Scientific Advisory Panel (ISAP): The MMO has established an Independent Scientific Advisory Panel to provide independent scientific knowledge, advice and judgement to assist the MMO in assessing whether the methodology and conclusions of the proposed trial are scientifically robust. The ISAP consists of five independent scientists with significant and recognised expertise in maerl ecology, experimental design, and the wider impacts of dredging operations.

 

The scientific trial

The experimental trial will assess the impact of removing and replacing the top 30cm of maerl habitat within the Fal Estuary planned dredge area and is designed to address specific concerns raised regarding the predicted rates of recovery.
 

The trial’s results will not determine whether the full scale dredging goes ahead, rather it will form a vital part of a jigsaw of information that will inform the final decision.


The trial methodology, which has been designed by Plymouth University Marine Institute, constitutes four phases – extraction, storage, relaying and monitoring. Each phase is designed to replicate what is likely to occur during the full scale dredge.

  • Extraction – The dead maerl is to be extracted to ensure the top 30cm of habitat is dredged and stored. A backhoe operating from a barge will skim the top 30cm of an area 10m x 5m at each of the six sites. The backhoe will have sensors in the dredge end to assess depth of penetration. The dredged material will be discharged into suitable watertight containers. The location of each of the six extraction sites will be marked and accurately recorded using state-of-the-art software.
  • Storage – The containers will be filled to the required depth with the dredged material, topped up with sea water and then either kept on the barge or lifted ashore. The maerl containers will be stored for 12 hours. Temperate and dissolved oxygen will be monitored. Storage depth will be a maximum of 1m for dead maerl and 30cm for dead maerl with live maerl covering.
  • Re-laying – The backhoe will recover material from the storage container and relay the dead maerl back into the previous excavation site and spread to a layer as close as possible to the original depth. The centre of each site will be marked by a small clump weight with a sub-surface float to give a visual reference for divers undertaking future samples.
  • Monitoring – Each of the six locations will be sampled before translocation, five weeks and 25 weeks after the maerl has been relayed. The variables tested will be species richness, total abundance, biomass, species composition and maerl size, proportion of live maerl, mean particle size and organic matter.
  • Conclusion – At the end of the trial the results will be interpreted by Plymouth University’s Marine Institute and reviewed by the Independent Scientific Advisory Panel (ISAP).

 

Concerns

While those worried about the environmental impacts of the dredge say they are reassured that the dredging trial is now being presented as  "just one small part of the jigsaw" – and that it would not be the critical deciding factor, they still have clear concerns.


Here Dr Miles Hoskin, an independent marine biological consultant based in Falmouth speaks on behalf of the Falmouth Bay and Harbour Action Group, a group of environmentalists, commercial fishermen and others who are opposed to aspects of the dredge.


Their main concern is the impact of dredging on the marine environment and fisheries within the Fal estuary, the impact of the connected plan to dump one million tonnes of dredge-spoil in Falmouth Bay, and the plan by Cornwall Council to pay for the dredging with £23 million of local taxpayers' money, when the “principal beneficiary is a private company with an extremely wealthy owner”, The Peel Group.
 

Dr Hoskin said that almost the entire inshore commercial fishing fleet operating out of the Fal and Helford estuaries - some 40 fishing vessels - have signed a statement expressing concern about damage to fishing grounds from the dredging and spoil disposal. Signatories include Fal oyster dredgermen, who he said are concerned about silt and pollution stirred up by the dredging settling out on their oyster beds.

He has expressed concern that the trial will test whether maerl habitats can recover from the disturbance of dredging and re-laying “under ideal conditions, saying that in the full-scale dredge conditions for recovery would be “very far from ideal”.
 

Dr Hoskin said the three “key differences” between the trial and the full-dredge are: 

  • The extent of disturbance in the full dredge is more than 6,000x larger than the scale of disturbance in the trial (330,000 versus 50 m sq).
  • The duration of the disturbance in the full dredge is more than 400x longer than the disturbance in the trial (seven months versus 12 hours).
  • That in the trial there will be no dense sediment plume to settle out and smother the maerl after it has been re-layed on the seabed and that in the full dredge, the re-layed maerl will experience six to seven months of heavy silt smothering.


Dr Hoskin said the group feared that the trial had been designed to produce a positive result that could be used to provide scientific cover for a political decision that had already been made. However he said that they were reassured by an “unambiguous statement” from the MMO that the trial would provide "just one small part of the jigsaw" – and that it would not be the critical deciding factor.

He was also “greatly reassured” to hear that the impact of silt-smothering of the seabed, both in the channel and in adjacent areas, was an important issue of concern needing much more work.
 

He added: “It now seems clear that we were right to think that the trial could not possibly be the deciding factor for the full-scale dredge and that the impact of sediment-resuspension and silt-smothering was too important to ignore. The ISAP has fully backed us up on both of these points.


“It is very difficult to see how the dredging proponents could practically and affordably satisfy the ISAP's requirement that the dredging mustn't cause deposition of fine silt in surrounding areas. The current estimate of £23 million for the dredging takes no account of either the maerl mitigation now being trialled, or silt containment.


“These new factors are likely to add significantly to the cost of the dredging. If the proponents were planning to spend their own money on the dredging that would be one thing, but they're not - they expect local taxpayers to pick up the bill. If they've bitten off more than they can chew, that's their problem - they can't expect the people of Cornwall to fund their hubris regardless of cost.”

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