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Marine Aggregate Dredging - Abbreviated Version
Offshore Marine Aggregate Dredging
This Briefing deals with the dredging of sand and gravel, known as marine aggregate, from the seabed for commercial use, mainly by the construction industry. It is a concise edition of a more extended Briefing on the same subject published by MARINET in January 2004. This present Briefing is focused on the licensing procedure and environmental issues which surround this activity. It forms part of a national campaign being run by MARINET which calls for a reassessment of marine aggregate dredging and, over a phased period of time, a major reduction in its licensed activity.
Marine aggregate dredging is a major industry which supplies raw materials to the UK construction industry. The marine aggregate industry is thus of strategic importance to the UK economy. However this strategic importance must not blind us to a proper assessment of the consequences of obtaining these raw materials from the seabed. To damage the marine biological community when so little is yet known about it, and to damage the ability of the commercial fishing industry to regenerate itself, whilst also damaging beaches and coastlines which are part of our heritage and essential to the safeguarding of coastal communities and the tourist industry, would all be an enormous mistake.
There is clear evidence that this is exactly what is happening.
What is Marine Aggregate Dredging?
Marine aggregate dredging is a form of strip mining. Sand and gravel is removed from the seabed to a depth of approximately two metres. The dredging sites are normally located between two to ten kilometres offshore, with each generally covering an area of around 1km by 2km . The aggregate extraction is carried out by large vessels with a capacity of 5000 tonnes or greater by means of suction. The material stripped from the seabed is screened onboard the vessel, with half or more of the dredged material being returned to the sea as unsuitable (i.e. mud, silt, shells and unwanted sand and gravel of a non-commercial size).
Marine life at the site of extraction experiences a severe rate of mortality, and over an even greater area of seabed marine life is smothered by the fine rejected material returned overboard from the dredger. At sites where sand is extracted the physical character of the seabed may be restored by natural means in a relatively short period of time (usually months, depending on the onshore/offshore and longshore currents) should sand be available from the surrounding locality, such as the shoreline, but in areas where gravel is extracted the change in the physical character of the seabed is more permanent due to the lower mobility of marine gravel deposits.
Having said this, physical restoration is also governed by the number of times which the dredgers visit the site. Each return visit removes surface sand and gravel to a depth of around 30 centimetres, and a site may be visited six times or more during the lifetime of the licence. Consequently, each visit complicates the potential for physical restoration.
What Lives on the Seabed?
Both sand and gravel seabeds support rich and varied biological communities, mostly animals rather than plants due to the absence of sunlight at these depths. The nature of these animal communities varies. On a sandy seabed, where the sand is generally mobile, the habitat tends to favour, although not exclusively, burrowing animals. In contrast, in a gravelled area the seabed largely remains fixed and creatures can attach themselves to the seabed and inhabit secure and sheltered spaces between the pebbles.
Both sand and gravel areas are important to fish, not just in terms of their habitat and food supply, but also as spawning and nursery areas for their juveniles. Gravel areas tend to be richer than sandy areas in terms of biodiversity, this being due in part to the fact that the physical habitat is more stable and has been largely undisturbed since the last Ice Age. Thus gravel areas are pristine environments as they have evolved without interference from mankind over a period of 12,000 years. Seabed biological communities will also differ due to variables such as depth, light intensity, temperature and the strength of currents.
How is Aggregate Dredging Licensed?
All offshore marine aggregate dredging in the UK takes place within the 12 nautical mile limit. It therefore occurs on the seabed owned by the Crown Estate which issues the licence and receives the financial benefit arising from the licence. However, in practice, the actual licensing authority is the UK central government which administers a licensing system set out in Marine Mineral Guidance Note 1 (MMG1).
This licensing procedure requires the applicant to undertake an Environmental Impact Assessment (the terms of which are specified in MMG1) and to submit this EIA to public scrutiny by interested parties. Following this, the applicant is required to seek consent for the licence from central government, a procedure known as the "Government View". Succeeding in this, the applicant will then be permitted by central government to obtain a licence from the Crown Estate, the terms of which will specify the volume of extraction, the period of the licence and other various requirements including environmental monitoring. The current central government department handling the "Government View" procedure is the Office of the Deputy Prime Minister.
Which Coastal Waters are being Dredged?
There currently exist around 75 licences held by eleven different marine aggregate companies permitting the exploitation of sand and gravel from 1,413 square kilometres of the seabed in all UK coastal waters, but particularly along the east coast from the Humber to the Thames estuary, along the south coast from Southampton to Hastings, and in the Bristol Channel along the south Wales coast.
Between 1989 and 2002, a fraction short of 185 million tonnes of sand and gravel were taken from the east coast sites, mainly offshore from Norfolk, with 13.8 million tonnes in 2002 alone. However many of these east coast licences are now approaching "commercial exhaustion" and the industry is looking to move its operations into the eastern English Channel, midway between France and England. These English Channel licences are expected to yield 8.5 million tonnes per annum, but could eventually rise to 15 million tonnes per annum.
Currently, total UK marine aggregate production stands at around 22 million tonnes per annum (2002 figures), and around 30% of this material is exported to Holland, Belgium and France who, generally speaking, do not permit offshore aggregate dredging within their coastal waters. Most of the UK marine aggregate that is supplied to UK markets goes to the construction industry, and in the south east of England around 35% of all construction aggregate is supplied from marine sources.
What are the Issues of Concern?
Extraction of aggregate from marine sources is growing, and the volume extracted has increased considerably over the last 15 years. The main reasons for this are the increased demand for concrete as a building material, and the fact that it is a more involved and complicated matter to obtain a new licence for a land-based quarry than it is for a marine dredging site.
Increased extraction of sand and gravel from the seabed raises a number of important issues, the answers to which are often uncertain and short on facts. The principal concerns are as follows:
- Can removing sand and gravel from the seabed be a sustainable practice?
Marine sand and gravel deposits were formed during the last Ice Age, and the size and extent of these deposits is finite. Therefore if a particular locality is heavily dredged, it is possible to overwork the deposit and this can lead to fundamental changes in the physical character of the seabed. If this occurs the ability of the site to support marine life also changes and this, in turn, can result in serious economic consequences for commercial fishing in the area. - Does dredging damage the biodiversity of marine life?
Dredging, and in particular repeated dredging, changes the physical character of the seabed. Sandy areas can eventually be restored by natural processes provided the integrity of the total reservoir of sand in the locality is not damaged, but areas of gravel on the seabed are far more susceptible to fundamental physical alteration because gravel deposits are largely immobile and incapable of physical restoration. Therefore where intensive dredging occurs there is a danger that the natural biodiversity of the marine environment and the varied physical habitats which support this biodiversity will be damaged on a long-term basis, and particularly so in areas where gravel predominates. - How extensive is the research into the biodiversity of life on the seabed?
The seabed and its biodiversity are, unlike the terrestrial environment, largely unmapped and unexplored. This means that many areas of importance to marine life are, from an ecological perspective, still largely unknown. Limited marine aggregate dredging may be tolerable because the damage it causes is, by definition, limited. However extensive aggregate dredging runs a serious risk of destroying valuable biological resources and, consequently, commercial resources as well before we have ever had the chance to assess their value. This short-term approach is akin to the destruction of forests and their biodiversity in tropical areas of the world. - To what extent is the fishing industry affected by dredging?
Commercial fisheries are in decline throughout UK coastal waters and, in the case of some commercial species, the fishery is facing commercial extinction. Many aggregate dredging sites are located in the heart of the spawning and nursery grounds of commercial fish species. The impact of dredging is not confined to the extraction site itself, but also extends further afield due to the smothering of the seabed by rejected material from the dredger. This material can be particularly damaging to the eggs and juveniles of fish as well as other sedentary creatures in the marine food chain. Thus intensive dredging in an area, both by repeated dredging of the same site and through the placing of several dredging sites in close proximity to one another, can have a long-term damaging effect on commercial fish species. - What is the connection between sand and shingle on beaches and sand and gravel deposits offshore?
During winter months storms tend to draw down sand and shingle from beaches to offshore, whilst during the calmer weather of summer months these materials accumulate onshore and beaches regenerate. Dredging of offshore sand and gravel deposits can disturb this dynamic relationship. Moreover if beaches become severely eroded due to offshore dredging then coastal defences, and particularly sand cliffs, sand dunes, salt marshes and shingle beaches, can be progressively damaged so producing coastal erosion. This process is well understood and well documented, and is currently occurring in Norfolk and on the Gower peninsula. - Can applications for dredging licences be refused?
Damage to coastal defences and marine biological systems are grounds for the refusal of a dredging licence. Such potential damage should be revealed in the environmental impact assessment (EIA) which precedes the decision on whether to grant a licence. However there is evidence that these EIAs, whilst being an improvement on the old licensing system which did not require EIAs, are not fulfilling their purpose. Independent studies of the EIAs prepared for recent aggregate dredging licences (see MARINET Briefing No. 1) confirm this, and it is believed that some of the organisations carrying out the EIAs have become too financially dependant upon the income from the aggregate companies. - Is the impact of dredging licences monitored?
Aggregate dredging licences generally run for a period of ten years or more, and are open to further renewal upon submission of a new EIA. However little monitoring of the impact of the dredging upon fisheries and marine biological communities, or upon shorelines and coastal defences, takes place during the lifetime or after the expiry of the licence. Thus the nature of the impact, which it is essential to record in order to provide meaningful information to EIAs for future licence applications, remains unrecognised. Further, the absence of continuous monitoring of the ongoing, cumulative impact of dredging makes it very difficult to know whether to suspend a licence mid-term due to the lack of knowledge about the damage that is being caused. - Is it possible to meet the demand for aggregate without dredging the seabed?
Currently the demand for marine aggregate is growing and the number of new marine licences is being increased in order to meet this. However, it is possible to meet part of this demand by increasing the amount of recycled construction and demolition waste as a substitute for marine aggregate. Clearly, quality aggregate will have to be met from marine and land-based quarries but many infill projects, road building and lower grade concrete construction projects could be adequately served by recycled aggregate. The important requirement is that recycled aggregate is properly collected, sorted and graded, and then subjected to a quality assurance process. This does not happen in any meaningful manner at the present time. The development of quality assured recycled aggregate is essential in order to relieve the demand on marine aggregate. - Is it true that marine aggregate is exported?
In order to protect their coastline and fisheries, Holland and Belgium do not allow dredging of sand and gravel deposits within 25km of their shoreline or in coastal waters whose depth is less than 20 metres. In contrast, the UK permits dredging within these limits. Consequently, the UK exports around 30% of its dredged marine aggregate to these countries and France. This is justified on the grounds that aggregate dredging operates within a free market, and that this principle of economics should not be interfered with. However, free markets which cause damage to the environment should be restrained. Thus there is a clear basis for implementing such restraint on the operation of the UK aggregate dredgers.
MARINET's View of the Future.
We are rapidly developing an industry of strategic importance to the UK economy without properly evaluating the terms on which it should develop or the consequences of its development. Accordingly, MARINET is calling for a fundamental reassessment of marine aggregate dredging.
- MARINET wants to see a strengthening of the quality of Environmental Impact Assessments which accompany licence applications, and an expanded system of environmental monitoring during the lifetime and aftermath of existing licences so that EIAs which accompany future licence applications are properly informed.
- MARINET wants to see a full and proper development of the recycled aggregate industry with the UK government taking the lead to develop a robust system of quality assurance. By this means, pressure of demand on marine aggregate reserves can be reduced.
- As this reassessment is undertaken and new facts emerge and new systems of meeting aggregate demand are developed, MARINET wants to see a phased and deliberate reduction of marine aggregate dredging licences so that we can be confident that the industry is operating on a sustainable basis.
We need to conserve this finite resource not only for future generations, but also to protect sea defences and coastal communities from the consequences of erosion due to over-extraction at a time when sea levels are rising. Furthermore, and just as importantly, we need to protect the marine biological community. We need to do this not just because of an obligation to protect marine biodiversity, but also because we need to demonstrate that we know what we are doing and that the future of the sea is safe in our hands.
