As it nears completion, how is the Thames Tideway Tunnel impacting London’s river health?

April’s university Boat Race was tainted when campaign group River Action claimed tests showed unsafe levels of the bacterium E. coli in the Thames. Although the claim was disputed by Thames Water, the spat highlighted ongoing problems with the health of the river – and the standard of infrastructure supporting sewage treatment.

One bright spot has been the fully operational Thames Tideway Tunnel – a project we covered in the autumn 2024 edition of Project journal.

Since then, the scheme has won Major Project of the Year at the International Tunnelling Association Awards; unveiled completed surface works – most notably at Blackfriars and King Edward Memorial Park in Wapping; and was able to boast of diverting 850,000 tonnes of sewage in one 24-hour period of heavy storms in December.

Praying for rain

In fact, by the start of March, over six million tonnes of sewage had been prevented from entering the river by the new system – with all 21 connections with the existing sewer system completed in February. “Everything is operating as expected,” says Programme Director James Smith. But there is one problem.

“A lack of rain recently means we haven’t been able to hit the parameters for our storm tests,” he explains. “We have to put it through its paces now every site is connected with some decent – that is to say, ‘bad’ – weather.” A small storm in west London in the middle of April helped prove the case – 400,000m2 of sewage did get processed through Tideway – but the project team really needs two decent storm days to validate the structures.

Even those won’t be at full capacity. “We don’t want to damage the tunnel before we go ‘hands off’ on the project,” says Smith. But they would test the crucial interconnections with the legacy sewage system, as well as discharge protocols and the air circulation system.

What does this mean for the project team, then?

“We’ve just gone through the business plan, and we still need to have plenty of the project managers and contractors on-site – not least to generate the handover documentation,” Smith says. That’s going to run to thousands of documents – all of which are vital, given the multi-generational lifespan of the Tideway Tunnel.

Ebb and flow

There are other snagging tasks for the project. “We’re aiming to hand back all the land to the third-party stewards before Christmas this year, so we need to make sure all the legacy sites are in tip-top condition,” Smith stresses. “There’s lots of architectural work and landscaping still on the project plan.” And there is a raft of consents to close out.

“Working under a DCO [development consent order] really doesn’t give you much guidance, just a starting point, so there’s lots of work there, too,” he adds. “And while the construction and handover are done, there’s a period of monitoring for 15 to 18 months – a systems acceptance period – giving us the opportunity to test in every circumstance.”

Smith’s programme management office, then, has plenty still to do. But winding up the office is also part of the plan now.

“We look at each site individually,” he says. “We have three main works contracts, an area delivery manager in each, with a team of project managers; each of them has a site. They’re tied to that site until the paperwork’s all be completed, so we have an idea of when they’ll wind up based on the monthly updates.”
The team then works with a central HR function to start helping project managers and others find new roles about three months out from their own site’s close-out.

“Obviously lots of people have moved on already,” says Smith. “HS2 has taken a lot of people on – as have other water projects.”

Neat and Tideway

Smith himself is likely to be on the job until December, but he will be involved in a more modest capacity with a small Jacobs team assigned to those optimisation efforts into 2026.

“I get lots of phone calls and requests, but I’m not really looking at the moment,” he admits. “That might change over the summer, but for now I’m just looking at what we’ve won here!”

And if you’ve read the Project feature from last year, you’ll know that Thames Tideway delivered far more than just a super-sewer solution to a polluted river. To many involved, it was a model way to run a big public infrastructure project.

“Tideway set their stall out from day one – they were very open and honest,” Smith says. “On contracts, of course there were challenges, but they always had an open-door policy and sought to understand everyone’s side of things. It all starts with the client – Andy [Alder, Tideway CEO] and his team really showed how it could be done.”