Work starts to connect Tideway to London sewer system at Lee Tunnel

Tideway said the material from the wall would be separated and sent away for reuse or recycling.

The tunnels need to be connected to allow sewage flows to reach Beckton Sewage Treatment works.

At the same time as the tunnel wall is being broken through, another team will be building a new weir wall at the Beckton works.

The Lee Tunnel must be taken out of service for approximately two weeks to ensure the safety of the workers on these two projects, which have been sequenced to keep the work period short.

A Tideway spokesperson said: "Because the Lee Tunnel is required to be out of service for the duration of the works, any flows that would have travelled through the Lee Tunnel would be discharged via the Abbey Mills CSO (combined sewer overflow).

"Steps have been taken to reduce the risk of this happening, for example, Thames Water will be actively managing its network to utilise capacity in the system."

After Tideway and the Lee Tunnel are linked, the process to switch the system on will begin, with CSO points along the Thames being connected in a sequence.

Connecting the CSOs with Tideway represents the commissioning phase, which is expected to begin soon and will take several months. At this point, the new infrastructure will begin to protect the Thames River from pollution.

The tunnel will be operated at half capacity until late summer 2024 ahead of full operation which is due in 2025.

Tideway chief technical officer Roger Bailey said: "This is another important step that gets us closer to protecting the River Thames from the harmful effects of sewage pollution.

"Teams are working around the clock to connect the new infrastructure to the Lee Tunnel so that we can start commissioning and testing this essential new asset for London."

Tideway

The £4.5bn Tideway project completed underground construction in March 2024

Heavy civil engineering works associated with the project have included the construction of a 25km tunnel, two connection tunnels, 21 shafts and a host of valves and vortex generators.

The tunnel reaches up to 67m underground and stretches from Acton in the west to the Abbey Mills Pumping Station in Stratford in the east.

The flow from over 30 combined sewer overflows (CSOs) will be diverted from the sewerage network into the main tunnel. From there it will run to the Tideway Pumping Station, to be pumped to Beckton sewage treatment works.

The main tunnel construction used tunnel boring machines (TBMs) in four drives from three main sites, with primary tunnelling having concluded in April 2022.

Lee Tunnel

The Lee Tunnel, which was finished in 2016, is said to be the deepest ever beneath London at between 75m and 80m below ground.

It was costed at £635M when it was commissioned in 2010. This included all the consultancy and preparation costs, as well as construction, but, as Thames Water's then asset director Lawrence Gosden explained to NCE that construction costs increased after Morgan Sindall, Vinci Construction Grand Projects and Bachy Soletanche joint venture won a £425M contract to build the scheme.

Gosden said: "It has gone up in value because we've incorporated some reasonably significant elements of the Thames [Tideway] Tunnel scope."

These included installing pumps for Tideway, an extra flow transfer system at Beckton and an extra shaft and a short section of tunnel at Abbey Mills so that, when it was constructed, the Thames Tideway Tunnel could break through into a dry shaft, as is being done soon.

"We had a good bit of support from the regulator [Ofwat], and it enabled us to make some good, longer-term strategic decisions rather than dealing with one thing at a time," said Gosden.

Like what you've read? To receive New Civil Engineer's daily and weekly newsletters click here.