Dredging, and the disposal of dredged material, are activities essential to the maintenance of navigable waterways and to the construction and operating of ports and harbours. The activities must comply with the OSPAR Convention, relating to north-western Europe, and the global London Protocol of 1972. The disposal of dredged material at sea is subject to strict regulation under licences granted under the Food & Environmental Protection Act 1985, the Coast Protection Act 1949 (CPA) and/or the Marine Works (Environmental Impact Assessment) Regulations 2007. These controls cover maintenance (relocation of settled material from channels and berths) and capital (creation of new harbour facilities or deeper channels) dredging. The Rame Head dredged material disposal site, located in Whitsand Bay, off the SE coast of Cornwall, receives dredgings from the Tamar Estuary, including the channel, Dockyard and marina areas of Plymouth. The disposal site has been in use for over a century and has received materials from before present controls were implemented. Compared to many UK disposal sites, this site is not only very close to the coast but also to an area significantly dependent on tourism to support the local economy. Local stakeholders have raised concerns over the environmental impacts of the disposal activity and the impact on the local economy. Most significantly, the death of two divers on HMS Scylla was alleged to be due to poor water clarity and reduced visibility resulting from siltation within the vessel. Accordingly, these concerns have led to multidisciplinary monitoring of sediment transport, sediment contamination, particle size distribution and marine ecology carried out by Cefas (Centre for Fisheries and Aquacultural Sciences) since 2001. While this monitoring has cost an estimated £850-900k, and been accompanied by other studies from the University of Plymouth, the Marine Biological Association and the Plymouth Marine Laboratory, local stakeholders have concerns regarding the validity, objectivity and adequacy of this work. These concerns are sufficiently serious to have attracted the attention of the media and local Government. Although any marine activity has the potential for environmental consequences, the economic importance of maintaining ports, harbours and navigable waterways is acknowledged, together with the importance of waterside developments in Plymouth which lead to the requirement for dredging. Such activities provide business, employment and tourism opportunities to the city. Applications for the renewal of dredging and disposal licenses are currently under consideration but due to the importance of the socio-economic and environmental issues which have been raised, the Marine Management Organisation (MMO) has requested an independent and objective review of the scientific data generated through monitoring and academic studies, together with information and views provided by local stakeholders. The purpose of this review was to determine whether the original conditions under which licenses for disposal were granted remain valid and that the environmental effects remain tolerable. The review, carried out by Professor Mike Elliott and Dr Krysia Mazik of the Institute of Estuarine & Coastal Studies at the University of Hull, has focussed on the adequacy of the monitoring and the validity of the concerns. Concerns raised and an assessment of their significance 1. Increased siltation and turbidity at the HMS Scylla dive site is believed to have resulted in poor visibility and associated problems with safety and quality of the diving experience: As would be expected, silt has accumulated in areas of the vessel where there is little water movement. No evidence of increased turbidity at the disposal site or at the HMS Scylla site, in relation to disposal activities, has been found. Hydrographic and sediment transport modelling studies indicate that significant deposition of sediments originating from the disposal site is unlikely to occur on or around the vessel and that scour around the vessel may be a source of silt. HMS Scylla has been colonised by a mature invertebrate and algal community which is not indicative of excessive levels of silt in the water column. The number of comments from divers visiting the wrecks in the area does not indicate that they are deterred from diving in Whitsand Bay. 2. Siltation of the beach and rocky reefs at the eastern side of Whitsand Bay (Polhawn Cove) is reported to have significantly impacted the reef communities: Comparative photographs were provided to demonstrate the difference between the biological quality of the reefs in Heybrook Bay (east of Plymouth Sound) and Polhawn Cove (west of Plymouth Sound). Modelling studies indicate the potential for the onshore transport of sediments but also indicate that significant accumulation is unlikely in the long term. Furthermore, the reefs to the west of Plymouth Sound are naturally less diverse than those in the east due to residual current direction which is generally to the west. As a result, reduced salinity water and sediments are transported to the west and modelling studies indicate a potential for the deposition of sediment and contaminants within Whitsand Bay, particularly the eastern side (Polhawn Cove) where the degraded reefs have been reported. Therefore, silt is likely to accumulate in Polhawn Cove to some extent, regardless of the disposal activity. Scientific studies specifically investigating reef quality have not been carried out. 3. Sediment contamination is believed to be a problem, particularly in the Polhawn Cove area in the east of Whitsand Bay: Spatial comparison of contaminant data does indicate elevated concentrations (of some contaminants) in this area and Cefas acknowledge this. However, analysis (of metals) is carried out on the fine fraction of the sediments only and this represents a small proportion of the sediment fabric. Therefore, metal concentrations should be considered an overestimate. Elevated concentrations of polycyclic aromatic hydrocarbons (PAH) were recorded in Polhawn Cove and although close to guideline values, these are not exceeded. The source of this contamination needs to be identified but, based on hydrodynamic models, the natural transport of sediments from Plymouth Sound into Polhawn Cove should be considered as a potential source. Furthermore, the natural inputs of contaminants (particularly metals) must be acknowledged. 4. Widespread concerns over the amount of litter on the seabed and on the beaches of Whitsand Bay: There is no doubt that litter accumulates on the beaches in this area. Whilst this has not been specifically studied by Cefas, evidence has been often presented by those who visit Whitsand Bay. Various litter items have been collected or noted which relate directly to the Naval Dockyard and these may have entered Whitsand Bay as a result of dredge disposal operations. However, large quantities of other types of litter have been recorded. There are no detectable ecological impacts of the litter and, although possible, there are no specific records of harm to marine life. However, the aesthetic impacts of litter are unacceptable even though there is no simple way of removing it from beaches other than by hand. It is recommended that the dredging companies continue to be rigorous about screening for litter prior to disposal. 5. Widespread concern over the impacts of dredged material disposal on marine life: Reduced species diversity and abundance of organisms have been reported from within the disposal site and within the immediate vicinity but no impacts have been reported farther afield. Therefore, any impacts are low level and isolated. However, the variable nature of the sea bed makes difficult the detection of impacts directly associated with dredged material disposal. Despite this, the characteristic species of a degraded seabed, which would include pollution and disturbance tolerant species, are not present. The observation of the sulphur-reducing bacteria Beggiatoa, indicative of organic enrichment on the seabed, cannot be attributed to the disposal and may be a feature of natural subsea peat deposits. The rocky areas support predatory echinoderms, cup corals, the pink sea fan (Eunicella verrucosa) and various mobile crustaceans and fish but there is insufficient evidence to indicate whether fish and crabs have declined in the area as a result of the disposal activity. Similarly, there is insufficient evidence to link any decline in the populations of commercial fish to the disposal activity. It is of note that there have been large scale changes in fish stocks due to overfishing and that southerly species are now being recorded in Cornish waters as a result of climate change. 6. Concerns regarding the adequacy of the monitoring: The extensive monitoring has been at a high cost but justified using priorities based on the need for environmental protection and public concern. Approximately 20% of the Cefas total budget available for monitoring the impacts of dredge disposal has been assigned to the Rame Head site. Overall, the science has been adequate and proportionate to the issues being addressed. In addition to routine monitoring, further, detailed studies have been carried out by Cefas and other institutions. These have focussed on sediment transport modelling, turbidity monitoring, contaminants monitoring and studies on the impacts of pollutants. These studies have used accepted procedures and protocols. None of these studies has identified any adverse impacts outside the disposal area directly attributable to the disposal activities at Rame Head. Cefas staff have engaged with the stakeholders when requested and fulfilled their duties as government advisors although they have not always fully communicated their results, or explained the licensing process or the constraints of detecting effects. This has exacerbated local concern. Cefas have attempted to summarise their findings and have their work examined in peer-review scientific publications although this needs improvement. Certain stakeholders should be congratulated for raising concerns about the disposal activity but they appear to be selective in their use of the available science and do not always appreciate the interpretation and the value of the evidence. Those concerned need to question the provenance of the available information while realising the limitations of the science. However, communication between the various institutions was inadequate and the reports produced by Cefas are brief and may not have enabled the public to fully understand the research outcomes. Furthermore, the use of a standard approach can be criticised for not being sufficiently site-specific in formulating and addressing testable hypotheses for the area. 7. Socio-economic concerns: Several issues relating to the potential for loss of income if current dredging and disposal practices were allowed to continue were highlighted. Similarly, significant changes or removal of the dredging license may also have negative economic consequences in a region reliant on the maintenance of its waterways to support regeneration and development work. Drawing attention to the issue, through campaigning for changes in dredging and disposal practise is also thought to negatively impact upon local businesses. The disposal activity is largely restricted to the winter months and the licence conditions adopt best-practice to minimise the environmental impacts. There may be the case for a minor adjustment to the disposal site by moving it slightly further offshore over a rocky reef into slightly deeper water. Some stakeholders consider that it is unfortunate that the local media are more willing to report perceived problems rather than carry out objective reporting. 8. Public health: No Serious public health issues were identified although the source of the PAH contamination in Polhawn Cove may need to be identified even if it appears to be unrelated to the disposal operation. Silt accumulation on HMS Scylla was just one of several health and safety concerns associated with diving on the wreck. It is alleged to have caused the death of 2 divers who became disorientated as a result of poor visibility caused by the resuspension of fine sediments. However, there is no direct evidence to suggest that this silt has accumulated as a result of the disposal operation. Furthermore, numerous other hazards have been documented which pose an equal or more significant risk than poor visibility. Conclusions and recommendations. The impacts of dredge disposal are evident at the Rame Head site but are low level and not widespread. Based on the general nature of marine impacts due to human activities, the changes observed at Rame Head due to dredged material disposal are regarded as acceptable. However, it is recommended that screening for litter prior to disposal continues as rigorously as possible and that quayside practices are monitored to reduce waste. The source of the PAH contamination should be investigated and studies to determine the fate of sediments and contaminants transported out of Plymouth Sound would be beneficial. Whilst there may be impacts associated with current disposal practices, it is thought that much of the contamination (litter and chemical) may be the result of historical disposal activity. With the exception of small scale changes in the benthic ecology within and adjacent to the disposal site, there is no evidence to directly attribute any other impacts to the disposal activity. Therefore, the licence conditions are considered valid and there is little economic or environmental justification for moving the disposal site further offshore or for considering on shore disposal options. A slight adjustment to the boundary of the licence area, enabling disposal in a rocky area with greater potential for offshore dispersal may be beneficial. The conclusions of the review can be summarised as follows: The disposal site shows limited evidence of the impact of disposal, via contamination and ecological change and is rightly regarded as a dispersing site. The present licensing regime is designed to ensure that contaminated dredged materials are not disposed of to sea and that the dredged material does not have a toxic component. The scientific studies carried out in the area by Cefas and others have produced a large amount of information, data and understanding and the surveys (their components and funding) have been proportionate to the environmental issues being addressed; they have followed the accepted international guidelines for monitoring dredged-material disposal grounds. There have been failings in the way the findings and background to the dredging and disposal operations have been communicated to stakeholders. The concerns regarding litter at the disposal site and in adjacent areas are warranted and based on good evidence of the type of litter encountered although much of this appears historical and from before controls were in place. The beach litter is from all sources irrespective of the disposal of dredging and is thus part of a wider problem. It is considered more environmentally sustainable to keep licensing the existing site than choose another site. Despite perceptions of environmental problems, moving the site further offshore would have adverse environmental and economic repercussions and there are no beneficial onshore uses of the dredged material. Recommendations for Further Work The rigorous scientific assessments of the hydrography and sedimentology of the Rame Head-Whitsand Bay area have concentrated on the disposal ground and the inshore area but there needs to be a wide scale assessment of silt dispersed over the wider offshore area. Research into sediment dynamics and the fate of suspended sediments coming from the estuarine areas would give valuable information for future studies of disposal grounds here and elsewhere. Remote grab and core sampling and seabed acoustic techniques have been used to good effect but more targeted and precise sampling, including diver surveys accompanied by surveys to obtain more video footage, would be of benefit. Cefas have placed little emphasis on understanding the ecological quality of the rocky areas, and hence they have been unable to counter comments from the stakeholders with concerns regarding the quality of the reef areas. The local diving fraternity could be used to obtain more rigorous scientific information. The dredging company should ensure that its controls on litter entering the dredging barge hopper should be as effective as possible. However, it is acknowledged that screening does occur and that smaller grids cannot be used without an economic and logistical cost. There should also be checks on quay-based practices to minimise waste entering the system, following IMO guidelines. The litter appears to have an aesthetic impact rather than an ecological one such that a code of practice asking the large number of divers to retrieve dangerous pieces of litter would be of benefit and may allow them to feel they are contributing to the solution. The HMS Scylla as a dive site and artificial reef can be regarded as a success and does not show signs of being affected by turbid conditions. However, its interior will scavenge silts and divers must be made aware of the hazards of this, together with the hazards associated with deterioration of the vessel. The disposal monitoring has benefitted from the high number of marine scientists in the Plymouth area and it has provided education opportunities but the university supervisors have a duty to present a balanced view to their students and ensure that external lecturers are also giving a balanced view. The projects must have an open and objective rigour. The Tamar Estuaries Consultative Forum is to be congratulated in taking the initiative to devise a dredging protocol but they are encouraged to include repercussions for the wider Rame Head area, disposal site and Whitsand Bay. A detailed research project would be valuable to provide further support for the environmental and economic costs and benefits of the different disposal options.
Mazik, K., & Elliott, M. (2011). Rame Head Environmental Impact study: Review of Evidence. DEFRA