3 July 2009

The Thames Tunnel, a 20-mile sewer deep beneath London to significantly reduce levels of sewage entering the River Thames, today 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 Thames, 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 32 million cubic metres of untreated sewage - enough to fill the 02 Arena 15 times - currently overflows into the river each year during rainfall.

The London Tideway Tunnels will dramatically reduce this - unless, in November this year 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 Thames Tunnel, said:

"In 1858, parliamentarians had to vacate the House of Commons and relocate to Oxford because of the foul stench coming from the nearby River Thames - then used as an open sewer.

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

"Today, over 150 years on from the ‘Great Stink’, Thames Water can be seen on the same stretch of river, planning what will be the next chapter in Bazalgette's legacy."

The Thames Tunnel, which will be seven metres in diameter - big enough to drive three London buses down side by side - is planned to run from West London to Thames Water's Beckton Sewage Treatment Works in Newham, broadly following the course of the river. 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 Bazagette network. These points, known as "Combined Sewer Overflows", were integral to Bazalgette's design, preventing sewage from backing up on to the streets of London 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 Thames Tunnel solution. Overflows currently occur more than once a week on average.

Peter Antolik, Thames Water's Director of Strategy and Regulation, said:

"Ofwat must make the right decision at the 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 in the river 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 thorough technical understanding of the potential constraints along the proposed route.

"Prior to setting up the borehole rigs in the river, we have been liaising closely with the Port of London Authority and local councils to ensure we minimise noise and disruption."

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

Ground data obtained, from previously unexplored depths under London, will be added to a national library of samples, which is held by the British Geological Survey, after construction.