Tideway reports £100m cost rise on London’s Super Sewer

Tideway has reported a further £100m cost increase on its London Super Sewer project.

Tideway’s overall cost estimate has risen to £4.3bn from its original budget of £3.52bn, announced in 2014.

That is £190m more than was reported in last year’s annual report and higher than the £4.2bn cost estimate announced in Tideway’s interim report, published in November 2021.

The annual report warns of further possible cost increases.

It says: “For our plausible downside scenario, we modelled a 16 per cent increase in the remaining costs to complete taking the total to £4.4bn […] We consider a severe downside case to be a 20 per cent increase in the remaining costs to complete, which equates to a total cost of £4.5bn. The two cost scenarios […] include the impacts to date of the current COVID-19 pandemic, the agreed cost allocation with our stakeholders and assume the current COVID-19 pandemic will not have any significant impact in the future.”

The new sewer is designed to capture more than 95 per cent of the sewage spills entering the river from London’s Victorian sewer system. It will have a significant impact on water quality, making it a much healthier environment for wildlife to survive and flourish in.

Work on the scheme was paused in late March 2020, due to the lockdown, and restarted two months later at a lower level of activity because of social distancing requirements.

Despite the cost increase, the estimated £20-£25 annual expense for Thames Water bill payers remains unchanged.

The report also reveals that construction work was 77 per cent complete at the year-end, with a number of key milestones achieved, including securing a further £300m of green financing to finish the project.

With the tunnelling phase now complete and good progress being made on the secondary lining, the focus is turning towards connecting the super sewer to the existing infrastructure while building the above-ground public spaces.

Tideway chair Sir Neville Simms said: “I am very pleased with the progress we have made on the project this year, not just in achieving the completion of tunnelling but in the way our teams have adjusted to the ‘new normal’ of delivering vital infrastructure in this post-pandemic world.

“Our primary focus continues to be the health, safety and wellbeing of everyone working on and around our sites, highlighting our ambition to do things safely or not at all.

“This year, we also secured the capital to take us to completion of the project in 2025.”

Tideway chief executive Andy Mitchell said: “We have now hit our most significant milestone to date – the completion of tunnelling. The hard work and diligence of the entire Tideway team has been invaluable in getting us to this point.

“I’m pleased to report that, for the first time, our work is as much about what we’re building above ground as it is about the super sewer, deep beneath Londoners’ feet. Our vision has always been to reconnect London with the River Thames, and with new areas of public space beginning to take shape, it’s great to see the visible legacy of the project on the surface.

“Still, we have work to do. Good progress is being made on the secondary lining of the tunnel, and we’re focusing more and more on connecting this infrastructure to Bazalgette’s Victorian network – but the end is truly in sight and a healthier River Thames is closer than ever.”

Tideway delivery partners

West section

Joint venture of BAM Nuttall, Morgan Sindall and Balfour Beatty Group

Central section

Joint venture of Ferrovial Agroman UK and Laing O’Rourke Construction

East section

Joint venture of Costain, Vinci Construction Grands Projets and Bachy Soletanche

Systems integrator

Amey is responsible for providing process control, communication equipment and software systems for operation, maintenance and reporting across the Thames Tideway Tunnel system

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