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UK’s huge new £5bn tunnel finally finished but tourists will never be able to walk down it

The construction of a £5billion tunnel in London has been completed after eight years – but you’ll never be able to walk down it. Thames Tideway Tunnel is a 25km-long super sewer designed to slash the level of sewage pollution along a section of the River Thames through central London.

Tens of millions of tonnes of storm sewage spill into the river annually, but once operational the super sewer should reduce spills entirely, according to its backers. The final piece of the tunnel – a 1,200 tonne concrete lid – was lifted into place on top of a deep shaft at Abbey Mills Pumping Station in Stratford, east London, on Wednesday (March 27).

Tideway has now built the full 15.5 miles (25km) main tunnel, a three mile (4.5km) connection tunnel in south east London and a 1,100m tunnel in south west London.

The company’s Chief Exec Andy Mitchell said in a statement : “This is the moment we’ve all been waiting for. The underground civil engineering on the Tideway project is now complete following eight years of dedicated hard work from all our teams working in the capital. “There is still work to do – we need to finish some above-ground structures and, crucially, test the system – but this nonetheless marks an absolutely critical milestone for the Tideway project and for London.”

Tideway expects expect the sewer to be fully operational in 2025, after testing of the tunnel system. The Abbey Mills shaft is the deepest of the project at 70m and is the point where the super sewer meets up with the Lee Tunnel, completed in 2016. It took five hours to lift the 24m wide lid into position with the use of a purpose-built gantry crane and other manoeuvring equipment.

The manoeuvre represents the heaviest lift on the project, surpassing the lifting of Tideway’s six tunnel boring machines earlier on in the build, according to Tideway.

Robert Ricketts, Tideway’s Project Manager at Abbey Mills Pumping Station, said: “This manoeuvre was a complex operation and required careful collaboration between various teams working on this project. “I’m absolutely delighted the lid is now in place and would like to thank everyone involved in getting us to this stage.”

Storm sewage flows are due to be diverted into the tunnel over the summer, with Tideway continuing building and landscaping work at sites along its route. The eastern stretch of the project is the result of a joint venture between Costain, Vinci Construction Grands Projets and Bachy Soletanche.

News of the tunnel’s construction comes as it emerged storm overflows dumped sewage into rivers and seas across England for more than 3.6 million hours in 2023. The data published by the Environment Agency (EA) reveal there were 464,056 spills in 2023, up 54 percent from 301,091 in 2022, which the organisation said was partly due to England experiencing its sixth-wettest year on record.

Storm overflows dump untreated sewage into rivers and the sea usually during heavy rainfall to stop sewers backing up. The figures have been described as “disappointing”, but “sadly not surprising” by the EA while campaigners said the scale of discharges was a “final indictment of a failing industry”. Sewage spill durations more than doubled from 1,754,921 hours in 2022, to 3,606,170 hours in 2023, the figures show.

Both the frequency and duration of spills were also up on 2020 levels, which saw comparable amounts of rainfall.

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