Final destination for London’s deepest tunnel

Feb 17, 2014

A giant sewer will collect waste water currently discharging from London’s overwhelmed Victorian sewers into the River Lee. This project is part of Thames Water’s urgently needed programme to prevent tens of millions of tonnes of raw sewage entering River Thames every year. At 75 metres below ground, the four-mile long Lee Tunnel is London’s deepest and the width of three buses.

The mighty machine digging a four-mile long giant sewer the width of three double-decker buses under east London has reached its final destination. Thames Water’s tunnel boring machine "Busy Lizzie", as named by a local schoolboy after winning a competition involving hundreds of pupils across the London Borough of Newham, has been burrowing its way from Beckton to Abbey Mills since February 2012.

It reached the end of tunnelling, on time and on budget, this month after cutting through layers of chalk and flint at extreme groundwater pressures. At its peak the 120 metre long machine tunnelled through an astonishing 54 metres of London earth a day, creating the capital’s deepest tunnel.

When in full working action in 2015 the £635 million Lee Tunnel will help prevent millions of tonnes of raw sewage entering the River Lee every year when heavy rainfall overloads the Victorian sewers that London has outgrown. The tunnel will act as a storage tank before transferring the flows to Beckton sewage works, Europe’s biggest, which is being expanded by a further 60 per cent to deal with the increased volumes.

Martin Baggs, chief executive of Thames Water, said: "It is unacceptable in modern-day London to have raw sewage entering the River Lee. The completion of this tunnelling work is an important milestone within our long-term plans to improve London’s sewer system. We’re immensely proud of this project, delivered on time and on budget, to clean up the River Lee. As well as the clear environmental benefits, the project has provided jobs for both local people and engineering experts from across the world, allowing London to show it is a leader in engineering technology."

London has seen its population quadruple in the last two hundred years and it urgently needs a new sewer system to cope. The Lee Tunnel is the first of two tunnels, along with the Thames Tideway Tunnel which is currently being examined by the Planning Inspectorate, designed to combat the tens of millions of tonnes of sewage that spill into the River Thames every year.

Howard Davidson, regional director of the Environment Agency, said: "By tackling sewage discharges from London’s largest combined sewer outfall at Abbey Mills pumping station, the successful completion of the Lee Tunnel will protect ecology, tackle aesthetic pollution and minimise the health risk to people using rivers in the Lower Lee. All of which can only be a good thing for both the river and its local communities."

Debbie Leach, chief executive of leading waterways charity Thames21, said: "It is fantastic news that this vital step in tackling sewage overflows into the River Lee is completed – fantastic news for the people who live by, use and appreciate the river, and for the wildlife that depends upon it. The River Lee faces many environmental challenges – and completion of the Lee Tunnel is a real reason to celebrate."

Programme management firm CH2MHill, along with tunnelling contractors MVB, (a joint venture of three leading civil engineering contractors, Morgan Sindall, VINCI Construction Grands Projets and Bachy Soletanche), completed the tunnelling work on Sunday 26 January.

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