Major construction work on the 25km Thames Tideway tunnel was finished last month after a 1,200-tonne concrete ‘lid’ was lifted into place to cap the project’s deepest shaft at Abbey Mills Pumping Station in east London.

Now, the teams are preparing to bring the tunnel into service by making a connection to the 6.9km Lee Tunnel, which has been in operation since 2016. 

The work involves breaking down and removing a thick wall separating the Lee Tunnel from the Thames Tideway Tunnel, to create a single system which will protect the entire tidal Thames. 

Built from concrete and steel, the wall is 1.5m thick and around 8m2 – and sits 66m below ground. 

The connection of the two tunnels needs to be completed to enable flows captured by the Thames Tideway Tunnel when in operation, to be transported to Beckton Sewage Treatment works for treatment. 

At the same time, another team will be working on the construction of a new weir wall at the Beckton works.  

To ensure the teams can work safely during these works, the Lee Tunnel must be taken out of service for a period of approximately two weeks. The works have been carefully sequenced to keep the work period to a minimum. 

Once the super sewer and the Lee Tunnel have been joined together, the team will switch to the final commissioning phase on the mega-project.

This is expected to take several months. The system will be tested in different weather conditions at half capacity and then full capacity, ahead of full operation, which is due in 2025.