Thames Tideway 'super sewer' cost holds steady at £4.5bn

Tideway, the company building London’s new super sewer Thames Tideway, has released its latest annual report, confirming the capital cost of the project remains £4.5bn, as reported in April.

Tideway confirmed the figure in its financial results for the year ending March 2023, detailing a year in which almost all underground works were completed.

The Thames Tideway super sewer tunnel will run from the Acton Storm Tanks in West London to the Lee Tunnel at Abbey Mills in East London, mostly under the River Thames. 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.

Construciton of the east section of the scheme will be delivered by a joint venture between Costain, Vinci Construction Grands Projets and Bachy Soletanche. In the central section, Flo, a joint venture between Ferrovial and Laing O’Rourke, is carrying out the work. The western section is overseen by BMB, a joint venture between Bam Nuttall, Morgan Sindall and Balfour Beatty.

Tideway is set to commission the new infrastructure in 2024, with the system due to be fully operational in 2025 when an estimated 95 per cent of sewage overflows will be prevented from spilling into the tidal Thames.

The project was initially costed at £3.52bn in 2014, but the sum has gradually risen over the course of its construction. The £4.5bn reported in April represented a 2% rise in cost since the previous report at the end of the 2021/22 financial year.

This week’s report confirms several milestones were achieved during the year including the completion of primary tunnelling works; completion of secondary lining of the west and central sections of the tunnel; and completion of shaft cover slabs at five sites. The removal of temporary river structures also got underway and worksite testing was carried out at three sites in preparation for system commissioning.

The year saw a number of above ground works undertaken including bronze ventilation columns, the first artworks forming part of Tideway’s art programme and ‘floodable’, intertidal terracing at Chelsea and Victoria Embankments which will encourage a range of habitats.

Tideway has also published its latest Sustainability Report, which details the progress and impact of the project’s legacy programme.

The Sustainability Report includes Tideway’s response to the Task Force on Climate-Related Financial Disclosures (TCFD) as well as analysis from Tideway’s first social impact analysis to quantify the social value of the project beyond legally binding baseline targets.

Ratings agency S&P increased its ESG evaluation of the company during the year to a score of 77 reflecting the focus on sustainability and strong corporate governance.

The report said a clear carbon target had been set and embedded into contracts and reporting processes of Tideway contractors, with quarterly data monitoring and reporting process in place. The report confirmed that with construction almost 90% complete, “we do not expect to exceed our anticipated carbon footprint of ~770,000tCO2e.”

Tideway CEO Andy Mitchell said: “We’ve worked for eight years deep underground, but it’s wonderful to see our works beginning to take shape on the surface.

“Next year is all about switching the system on and diverting pollution away from the Thames for the first time – this is what we’re focussed on, and we’re all looking forward to a healthier future for London.”

Tideway Chair Sir Neville Simms said: “The past 12 months on the Tideway project have seen the most significant change in focus since we started work – with the construction phase nearing completion and attention turning to testing this new and vital infrastructure.

“As we look forward to bringing the system on-line next year, our delivery model – which encourages long-term private investment in infrastructure – is showing its worth in delivering value for all stakeholders.”

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