'Vital' Thames tunnel takes first steps

The Thames Tunnel, a 20-mile sewer deep beneath London to significantly reduce levels of sewage entering the River Thames, has moved a step closer to becoming a reality.

Exploratory works have begun in the riverbed outside the Palace of Westminster, where a borehole has been sunk from a large rig to analyse the ground conditions that engineers digging the proposed tunnel are likely to encounter. This marks the start of a nine-month programme of borehole tests along the river.

The Thames Tunnel, which will broadly follow the route of the river, and the Lee Tunnel, a four-mile sewer to stop sewage overflows into the River Lee, due for completion in 2014, are together known as the London Tideway Tunnels.

About 32M cubic metres of untreated sewage overflows into the river each year during rainfall.

The London Tideway Tunnels will dramatically reduce this, unless, in November when Ofwat sets bill limits for water firms for the next five years, Thames Water receives a deal that leaves the company unable to fund this vital work.

Siân Thomas, project manager for the tunnel, said: "In 1858, parliamentarians vacated the Commons and relocated to Oxford because of the stench coming from the river - then used as an open sewer.

"As a result, Sir Joseph Bazalgette was commissioned to build the Victorian sewer system that still serves London to this day. Though an engineering masterpiece, the system needs extending to ensure it can cope with increasing sewer flows."

The tunnel, which will be seven metres in diameter, is planned to run from West London to Thames Water's Beckton Sewage Treatment Works in Newham.

Although the precise route is not yet finalised, it will need to connect to the 34 most polluting points where sewage currently flows into the river from the original Bazalgette network. These points, were integral to Bazalgette's design, preventing sewage from backing up on to the streets during freak weather.

Modern-day pressures on the sewer system, such as population growth, more intense rainfall linked to climate change and concreting over green spaces are all increasing the urgency of the tunnel solution.

Overflows currently occur more than once a week on average.

Peter Antolik, Thames Water's director of strategy and regulation, said: "Ofwat just make the right decision at this year's price review. A tough deal for Thames, which leaves us unable to fund this crucial project, will simply mean a tough deal for our customers - and, indeed, London and the River Thames.

"The boreholes are key to helping us develop a detailed design for the Thames Tunnel. Ahead of submitting a planning application in 2011, we first need to build up a technical understanding of the potential constraints along the proposed route.

A maximum of three rigs will be in place at one time, for up to three weeks at each location.

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