The production of aggregate minerals, which include sand and gravel, is the largest extractive industry in Britain.
Sand and gravel, which accounts for about 90 million tonnes (40%) of national aggregate production, is used primarily for construction. Nottinghamshire is the largest producer of sand and gravel in the East Midlands and one of the largest in Britain. The gravel component here is normally a quartzitic, high strength material often used to manufacture concrete. This factor can give Nottinghamshire's deposits a premium above those found elsewhere.
The richest and most extensive deposits occur along the River Trent, where yields can exceed 100,000 tonnes per hectare, although 60-80,000 tonnes is more typical. The ratio of sand to gravel also varies, from near equal proportions in Trent Vale upstream of Girton to a third gravel or less elsewhere. In general high gravel yields are normally more economically attractive, thus Trent Vale sites are valuable.
Extraction and impact on the landscape
After stripping soils and overburden, the exposed mineral can easily be excavated by dragline or hydraulic excavators, which either load direct onto dumptrucks or feed conveyors for transporting the raw mineral to the processing plant. At the plant a series of screening and washing operations grade and sort the mineral into the required sizes of sand and gravel. Waste 'fines' (i.e. fine sand or silt, clay) which on average make up between 5-10% of the deposit are pumped into silt ponds. Silt ponds are normally allowed to dry out to permit reclamation, although once full they can be re-excavated to provide extra capacity.
The high water table level at most sand and gravel quarries means that active workings have to be pumped, to enable dry extraction. Wet extraction is possible, but is less efficient and the increased risk of pollution means that this is rarely practised.
Once pumping ceases following extraction, the void soon floods to form a lagoon. Whilst most sand and gravel is transported by road, Trent Vale quarries can barge large quantities of mineral to receiving wharves in Yorkshire and Humberside.
In terms of land take, sand and gravel extraction is voracious being the largest surface mineral working in the area. This gives concerns over visual impact, noise and traffic. In addition to this, the Trent Vale is very rich in archaeological remains which may be lost.
Restoration for wildlife
In Nottinghamshire about 50 hectares a year are worked for sand and gravel, a significant proportion of which is eventually restored to wetland. The high water table level and lack of suitable fill means that for most sand and gravel workings a water after-use is the only feasible option. Well designed water areas can be very beneficial by creating valuable new habitats that can promote biodiversity, encouraging birds such as little ringed plover, avocet and sand martin. Sports and other amenity facilities can also be developed.
If properly planned, restoration with a high proportion of wetland can have a positive impact. Today careful consideration is given to ensure that future restoration provides an improved landscape for wildlife and people. Through close working between companies, local communities and organisations like the Wildlife Trusts and RSPB, restoration plans are developed which provide a positive mix of agricultural land, wetland areas and lakes.