Magazine article Geographical

London in Too Deep?

Magazine article Geographical

London in Too Deep?

Article excerpt

As London's groundwater seeps back to its `natural' levels, Catherine Barr looks at measures under way to stem the waters rising beneath the capital's streets

WITH RECORD RAINFALL across the country, and scenes of firemen in boats rescuing people from bedroom windows still fresh in our minds, few people are aware that water is not only threatening us from above but also from below. Since water-intensive industry relocated away from London's centre in the 1960s, groundwater under the city has risen by 50 metres, and continues to rise by up to two metres each year. Under Trafalgar Square, waters are rising by 1.7 metres every year.

London's ancient water is returning to its `natural' levels, recovering from the commercial exploitation that started during the Industrial Revolution during the 1850s and continued until the 1960s. Abstraction of London's groundwater reached its peak in the 1940s, with over 500 boreholes used by breweries, papermills and other industries whose pumping activities exceeded the water that could be replenished from the Chiltern Hills in the north and the Downs in the south. At one time, water could burst up into the city from natural artesian wells, such as in the fountains of Trafalgar Square, but as the amount of water taken out increased, levels fell by 90 metres and pumps were installed. Before there was a public water supply, most commercial premises pumped their own water from private bore-holes. Some, like the Bank of England, still do.

As industries moved away from the city in the 1960s groundwater levels began to recover -- a trend which continues today and which threatens the city's underground structures.

Vin Robinson is regional groundwater licensing officer for the Environment Agency, which is involved in developing a large-scale operational strategy to tackle the problem. The agency recommends that 50 million litres of water a day are pumped out to avoid damage to the warren of communication cables, sewers and underground tube tunnels that make up the invisible city beneath London. All are at risk if waters continue to rise.

"These are significant quantities," says Robinson. "To abstract even three to five million litres a day is quite an achievement. The pump-testing taking place over the next few months is a major development and the effect on rising water levels will be dramatic."

The essence of the problem lies in the fact that the foundations and infrastructure of modern London were built in the 1940s, 50s and 60s, at a time when water levels were artificially low and the clay dry. If the water table is allowed to return to its natural level, the clay will saturate, forcing pressure to rise and in turn reducing the clay's load-bearing capacity. "Tube escalators could misalign, tall buildings founded in clay may settle, moving slightly and underground tunnels will leak, if the clay is allowed to saturate," says Robinson.

William Mckee, director general of the British Property Federation representing the commercial property industry, stresses his concern. "We regard this as an extremely serious issue. Any building that has very deep foundations -- effectively any tall building -- or deep basements like multi-storey car-parks are at risk. Some of their foundations are made with concrete that is sensitive to water. The cost of dealing with problems caused by rising water levels could run into millions of pounds. "There is, however, no available `red-list' of buildings at particular risk. It is apparently difficult for engineers to tell exactly which or how buildings will be threatened.

Even though maps that will accurately indicate the buildings and areas to be most affected are frustratingly absent, the mood in the Rising Groundwater Project Team seems to be a positive one. `It's all under control' is the motto that reflects a vast injection of funds into this London-wide operation. The specifics may be difficult to isolate; but the big picture is clear. …

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