The four mile Lee Tunnel will prevent more than 16 million tonnes of sewage annually entering River Lee, a tributary of the River Thames. At certain points the 7.2 metre diameter tunnel will be as deep as 75 metres.

The Lee Tunnel will capture sewage mixed with rainwater that would otherwise flow into the River Lee and transfer the flows to Beckton Sewage Treatment Works, which is being expanded to deal with the increased volumes.

The contract was awarded to MVB, which is a joint venture between Morgan Est, VINCI Construction Grands Projets and Bachy Soletanche. The contract is the biggest single construction contract to be awarded in the United Kingdom water industry since privatisation.

Works on the project will commence in April 2010 and is expected to be completed by 2014.

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Thames Water’s CEO Steve Shine said “The Lee Tunnel, which is the first of two huge tunnels planned over the next ten years, is the biggest engineering project to be carried out in the UK water industry since privatisation 20 years ago,”

“The Lee Tunnel will cut in half the 32 million tonnes of storm sewage that currently overflows into London’s rivers each year. This is an essential part of providing the capital with a 21st century sewer system, resulting in a cleaner and healthier river that we can all be proud of.”

London’s Victorian sewer system was originally designed to overflow into the River Thames and its tributaries in exceptional circumstances to prevent sewage backing up into homes, streets and gardens. However, London’s population growth, the concreting over of green spaces and more torrential downpours caused by climate change mean that overflows occur much more regularly than they did 150 years ago.

The Lee Tunnel is the first of the two London Tideway Tunnels, which will collectively catch an estimated 32 million tonnes of sewage overflows each year.

The proposed Thames Tunnel will be bigger and more complex than the Lee Tunnel and will run 20 miles from west London to east London. A planning application is expected to be submitted in 2011 and it is hoped the tunnel will be completed in 2020. Extensive investigation works are currently under way to identify the most suitable route for the tunnel and the ground conditions engineers will encounter during tunnelling.