Recent estimates indicate that of all the concrete currently being used in construction projects across Greater London, 50% uses sand and gravel sourced from marine aggregate reserves in UK waters. But how do aggregate companies go about defining a viable source of material and what controls the extraction process that then allows them to supply the construction industry with a quality product?
In the same way that oil and gas companies use geologists to investigate the seabed and identify fossil fuel reserves for exploitation, aggregate companies also employ marine geologists to prospect for marine sand and gravel within areas of the UK territorial waters. In identifying a viable reserve, workability is one of the key considerations. It’s of little use to find a high-quality aggregate source in the middle of an offshore windfarm; equally, reserves in too deep or too shallow water might be outside of the workable water depth of commercial aggregate dredging vessels.
Knowing where to look is also a key skill, requiring an underlying knowledge of the geological history of the deposits. Where they came from? How were they were deposited? And when?, then relating this to the recent geological history of the UK, since the end of the last ice age around 10,000 years ago. This type of knowledge also helps when considering the potential quality of the mineral reserve. Is it likely to be clean sand or gravel, or might it be mixed with high concentrations of fine material? Is it only likely to be a thin veneer of gravel over underlying bedrock, or could the reserve be thicker, making it more commercially viable? All these considerations can help with planning prospecting surveys, the data from which will then enable the geologists to confirm and quantify the aggregate resource.
But once a viable resource has been identified, UK law dictates that a number of licences are then required before commercial dredging can be permitted.
Companies and individuals are unable to buy land at sea (unlike on land), so firstly an agreement on mineral rights to the area of seabed in question is required. The Crown Estates owns over 99% of the seabed within UK territorial waters so, in most cases, negotiations on a Production Agreement are required, and royalties need to be agreed.
Operations at sea are governed by UK law, in particular the Marine and Coastal Access Act 2009 (with amendments), which requires that a Marine Licence be sought for a range of activities, including ‘the depositing or removal of any substance or object, either in the sea, on or under the seabed’. Aggregate extraction falls into this category, so a Marine Licence Application will need to be made to the relevant regulator (the Marine Management Organisation in England and Natural Resources Wales, in Wales). Such Applications will require supporting documents, including and Environmental Impact Assessment, which considers the proposed extraction activities, and assesses the potential effects on receptors such as physical processes, benthic ecology, water quality, fisheries, navigation etc. This allows the regulator, through consultation with relevant stakeholders, to determine whether or not to allow the aggregate extraction proposed.
Finally, a positive consent decision will include conditions on the licence, requiring aggregate companies to continue to monitor their licence areas, focussing their dredging activity into Active Dredge Zones, and ensure that a capping layer of sediment is maintained for recolonization once the aggregate resource is no longer viable.
This overview was recently presented at a Crown Estate workshop for aggregate professionals entitled Resource Area Application and Management, in respect of marine sources of sand and gravel.
Prepared by Adam Fulford, Physical Processes specialist
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