Thames Water is thought to be considering ditching a significant section of the £2bn London Tideway Tunnels scheme to save costs, sources close to the project told NCE this week.
It is understood the utility company is considering cutting the length of the 32km long Thames Tunnel section by diverting it to connect with the Lee Tunnel at Abbey Mills Pumping Station.
The original plan was to take it all the way to Beckton Sewage Treatment Works.
The Thames Tideway project comprises two tunnels, The Thames Tunnel between Hammersmith and Beckton and the Lee Tunnel from Abbey Mills to Beckton.
“The diameter [of the Lee Tunnel] will probably be bigger.”
The move to scale back the project is being considered as the firm comes under pressure from industry regulator Ofwat to find cost savings in the next regulatory period that begins in April next year.
If the Thames Tunnel was diverted, the 7km long Lee Tunnel would be also have to be adapted to take the diverted sewage to Beckton for treatment. Construction was due to begin in the New Year, with a contract award expected by the end of the year.
“Although the Lee Tunnel contract award was thought to be imminent, nothing will move until the cost of the main [Thames] Tunnel has been looked at,” said one source close to the scheme. “And we have been told that Thames Water is looking at making the Thames Tunnel end at Abbey Mills.”
The Lee Tunnel is currently planned to run from a depth of 55m below Abbey Mills down to 75m below Beckton with a 7.2m diameter. But the diameter would have to be increased if the tunnel had to handle extra flows from the Thames Tunnel.
“The diameter [of the Lee Tunnel] will probably be bigger,” said the source. “To offset the cost of a larger diameter tunnel, you might find the Lee Tunnel is less deep [saving on deep shaft work].”
But this could bring added complications, other geotechnical experts warned.
“We expect to announce the winning bidder before the end of the year.”
Thames Water spokesman
“The most obvious thing is if you bring the tunnel up, you would be much nearer all the other service tunnels, which has other complications,” said one.
Thames Water confirmed that it was considering a change in scope, but said that work on the Lee Tunnel would begin as planned. “The exact route of the Thames Tunnel has not been decided and we are considering all options,” said a spokesman.
“But we expect to announce the winning bidder before the end of the year, and work will start on site in the New Year.”
Murphy/Hochtief and Morgan Est/Vinci/Bachy Soletanche joint ventures are currently vying for the £430M Lee Tunnel contract. Water companies expect to tighten their budgets after Ofwat’s final water price determination on 26 November.
Thames Water has proposed the largest capital programme.