The construction of a sewer tunnel in London that is intended to reduce pollution getting into the River Thames is now complete.
A 1,200-tonne concrete lid was set in place on top of a deep shaft of the Thames Tideway Tunnel recently, marking completion of the 25-km long sewer.
The tunnel, which measures 7.2 metres in diameter, will become fully operational in 2025 following a commissioning phase, which is set to begin shortly. It runs from Acton in West London to Stratford in East London, which is where the concrete lid was put in place at the Abbey Mills Pumping Station.
It has taken several years for the project to reach this point, with chief executive officer of Tideway Andy Mitchell saying: “[This] marks an absolutely critical milestone for the Tideway project and for London.”
Once it is up and running, it is hoped it will have a big impact on the amount of waste that travels through the capital. Currently, tens of millions of storm sewage enters into the River Thames, causing serious water pollution.
Water surveys of the Thames revealed 92 per cent of samples had a “significant presence of coliform bacteria”, according to the London Assembly.
This can result in stomach complaints for those who ingest the water, including diarrhoea and gastroenteritis.
What’s more, the Environment Agency gave Thames Water a score of two out of four for its Environmental Performance in 2021. This was due to 12 pollution incidents it deemed to be serious.
The 24m-wide concrete lid is now in place, thanks to the help of a purpose-built gantry crane, which lifted it in position over five hours. The lift was heavier and more complex than when Tideway’s six tunnel boring machines were lifted at the beginning of the project.
Robert Ricketts, Tideway’s project manager at Abbey Mills Pumping Station where the shaft is located, said: “This manoeuvre was a complex operation, and required careful collaboration between various teams working on this project.”
Despite now being securely in place, it will take a while before the sewer tunnel is functional.
This is because it is essential to ensure the infrastructure is working properly. Live storm sewage flows will be directed into the tunnel, allowing engineers to see how effective it is at protecting the River Thames from the overflow.
It has taken ten years for the tunnel to get from the planning stage to completion, with construction beginning in 2016. Tunnelling commenced in 2018, with the help of boring machines and conveyor belt vulcanising, and came to an end in 2022.
First estimations on the cost of the tunnel were £4.2 billion but the expenses have now reached around £5 billion. This will be paid for by Thames Water customers, who will see their bills rise by about £25 a year. This additional fee will take several decades to repay.
