By Rowe, Mark
Geographical , Vol. 80, No. 3
Concrete, an alien might reasonably conclude, is as indispensable to life on Earth as oxygen and water. In the UK alone, our annual demand for aggregates, which are a vital ingredient for the production of concrete, adds up to 272 million tonnes, the equivalent of four tonnes per person. To meet this mind-boggling demand, the construction industry turns to three sources of aggregate: land quarries; secondary, or recycled aggregate; and, increasingly, the offshore sand and gravel resources that lie beneath our seas.
Last year, 24.8 million tonnes of coarse gravel and fine sand were removed from the seabed off England and Wales, providing around 17 per cent of the sand and gravel needs of the two nations, and six per cent of Britain's total primary aggregate needs.
Although the annual turnover of the marine aggregate industry is a modest 250million [pounds sterling], the scale of demand--augmented by huge projects such as the Thames Gateway development and the London Olympics--is causing disquiet among environmentalists, who argue that understanding the impacts of extracting aggregates is vital if our marine environment is to be protected from long-term or irreversible damage.
Marinet, a marine arm of Friends of the Earth (FOE), argues that aggregate dredging imperils sensitive coastal habitats such as salt marshes, sand dune systems and sand cliffs, and even inland habitats that are vulnerable to coastal erosion. 'Sandbanks are major players in the wave regime', says Marinet's Stephen Eades.' The height of the sandbank can determine the height and strength of waves. The wave regime starts far out to sea, and sandbanks acts as a buffer. If the sandbanks are disappearing, then the wave regime intensifies and erosion around the coast becomes greater.'
Critics say the erosion and emaciation of sandbanks off the Norfolk and Suffolk coasts are linked to dredging, and that the industry is wasteful in its approach. According to Mariner, just over half of the dredged material is rejected because it's silt or the wrong size. Of the 24.8 million tonnes landed last year, 13.4 million tonnes was landed in UK ports and went on to supply the construction industry. A further 4.2 million tonnes was placed on the shoreline to replenish holiday beaches damaged by erosion--often, says Marinet, caused by dredging--and 6.7 million tonnes was taken to Dutch and Belgian North Sea ports. 'This is an astonishing practice,' says Eades. 'The Netherlands and Belgium don't allow the commercial exploitation of the offshore seabed for aggregate materials within 25 kilometres of their shoreline, so why should the UK?'
But despite FoE's concerns, the environmental impacts of dredging remain uncertain. 'We don't really know quite what's going to happen; says Jolyon Chesworth, conservation manager of the South East Marine Programme for the Wildlife Trusts. 'One of our biggest issues is recovery. Sandy environments appear to recover within three to four years--because they are mobile and dynamic--but in the gravel environments, the pits and furrows left by the dredgers can remain for 20 years or even be permanent.'
The long-term impact is evident at Formby on Merseyside, where dredging 100 years ago has led to an incremental loss of 400 metres of coastline. During the early 20th century, new'training walls'--barriers to create a deeper channel for larger ships moving along the Mersey - were dredged up. While natural sand movement north of Formby continued, this was no longer replenished from the south. According to Andrew Brockbank, property manager for the National Trust, which owns 220 hectares of Formby, four metres of coastline are reclaimed by the sea there each year. 'Formby Point was once truly a point--now it's more flattened,' he says.
The sand dunes of Merseyside's Sefton Coast are the fourth largest in the British Isles and are part of a wider Site of Special Scientific Interest and a Special Area of Conservation, a nationally important habitat for the natterjack toad and sand lizards, which live in the edge of the dune system. …