Red to green
Designed to clean up the River Thames, the multi-billion pound Tideway project has been delivered on time and on budget. In the past few weeks, it has even received the royal seal of approval from King Charles. Utility Week caught up with the team behind the tunnel, to discover the impact on combined sewer overflows and the anxious wait for storm clouds to gather.
By Ruth Williams, water correspondent
Red to green
Designed to clean up the River Thames, the multi-billion pound Tideway project has been delivered on time and on budget. In the past few weeks, it has even received the royal seal of approval from King Charles. Utility Week caught up with the team behind the tunnel, to discover the impact on combined sewer overflows and the anxious wait for storm clouds to gather.
By Ruth Williams, water correspondent
All photos: Tideway London
When Thames Water published the sector’s first live storm overflow discharge map, the company knew it was opening itself up to criticism.
It was the first time members of the public could see where storm overflows occurred and if they had been active recently. Unfortunately for Thames, the map went live towards the end of 2022 and by December it was awash with red markers as event duration monitors (EDMs) were triggered across its region.
While it unsurprisingly attracted a lot of negative attention at the time, it offers a stark comparison to the map of today. As John Sullivan, head of the Tideway integrations group at Thames Water, explains the picture is now very different two-and-a-half years on from the launch of the map.
“The EDM map shows green ticks up and down the river!” Sullivan exclaims, adding that since the Tideway project was fully connected in February, the tunnel has caught everything emitted from storm overflows that would have previously gone straight into the river. “Nothing on the map is red, it is all green – it is like the dog that doesn’t bark,” Sullivan adds.
“Nothing on the map is red, it is all green – it is like the dog that doesn’t bark.”
John Sullivan, head of the Tideway integrations group, Thames Water
All photos: Tideway London
Back to life
Tideway was only officially opened last month, with King Charles providing the obligatory pomp and ceremony that all major infrastructure projects command. However, the benefits of the self-proclaimed “Super Sewer” have been felt since it was connected in February.
Sullivan, however, explains that the River Thames clean up actually begun a decade ago with the creation of the Lee Tunnel. Often badged as the first phase of the Super Sewer project, the 6.9km Lee Tunnel was connected to Thames’ existing network as long ago as 2016.
It runs from Abbey Mills pumping station to the Beckton sewage treatment plan in east London, and Sullivan explains that it had an almost instant impact on the River Thames’ health.
During surveys in 2023 species were recorded in the waters at parts of the river that had been declared biologically dead. Sullivan said there were 12 species and 714 specimens found, including a whopper of a seabass, who was christened Harry. “He was found where nothing had lived in the upper reaches of the River Lea,” Sullivan says.
The 10-pound fish in the Channelsea part of the river became a totem for the team’s efforts – keep working to protect Harry. Seeing the real-world benefits of the Lee Tunnel brought home the potential impact that the Tideway project could also have. Sullivan adds: “The Lee Tunnel has had a fantastic impact on that part of the river, that’s the same effect we are hoping that Tideway will have for aquatic biodiversity, marine life and people who want to use the river.”
Given the Lee Tunnel stops 100 tonnes of plastic from entering the waterway annually, Sullivan believes the 25km Tideway tunnel will capture 250 tonnes each year that would have been released through CSOs discharging. The two tunnels are now linked, having connected in May last year ahead of Tideway’s full completion.
King Charles officiated at the tunnel's official opening last month
Many years in the making
The successes are many years in the making. A strategic plan was first published in 2005 after Thames Water, the Environment Agency, Ofwat and the Mayor’s Office knocked heads together and agreed something had to be done to help the river. Back then, CSOs did not make the headlines they do today and the project was subject to opposition that customers would be lumbered with higher bills.
Fast-forward and the project, remarkably for one of its scale, has been delivered not only on schedule but also to budget. Around £20 a year has been added to the bills of Thames Water customers to fund the Super Sewer via a novel regulatory model through a separate company established solely to build the tunnels.
After the commissioning is completed, ownership of the finished tunnels will be split. Sullivan describes this division as Thames Water retaining ownership of the surface, the land that you can see and stand on, as well as sub-surface mechanical assets, which will also be operated by the water company. Meanwhile, Tideway will retain ownership and maintenance responsibility of the shafts and tunnels themselves.
The company established specifically for this project will earn a return on investment on the value of these into the future. That division makes Thames the first system operator in the water industry that does not own the assets.
Rainy days ahead
While construction is long complete, work is still ongoing as part of Tideway’s commissioning phase.
Since construction completed earlier this year on connecting the final parts of the tunnel, Tideway has been operating in “half tunnel mode”. Sullivan says this means it will only fill to 800,000 tonnes at any one time, so automation systems can be checked before going to full tunnel mode. Testing must be run at a variety of conditions – wet and dry, measuring the time it takes for sluice gates to open and close and understand the impacts on pumping stations.
Then comes storm testing, but that cannot be reliably scheduled. “We’re taking the brakes off and allowing the tunnel to fill, but we keep looking out of the window and there’s no rain,” Sullivan bemoans.
The team is anxiously waiting for the weather to change to test the tunnel in its full glory. But it has been the driest spring for decades and the team has been forced to patiently wait for storm conditions to carry out the requisite testing. With the dry spell shifting to unsettled, the Tideway crew are hoping June will bring a change of fortune. “We’ll learn from that (the tunnel filling) and then we leave the system alone for 30 days with no fiddling or adjustments to the software or code and allow it to operate. If there’s a problem we will stop, fix it and then go again.”
Last year, Sullivan says there was an equally anxious weather watch for a two-week stretch that was sufficiently dry for testing, but months of repeated named storms meant the opposite challenge of this year’s wait.
Feel the force
The volume of wastewater and force of the water entering the tunnel is enormous, Sullivan explains. Up to 1.6 million tonnes of sewage can be held in the tunnel and managing the flow safely is as impressive a feat as any part of the bespoke engineering.
The impact of the system working at capacity could see a force of stormwater hitting the bottom of a 50 metre tunnel at 40 tonnes per second. The engineering teams had to design this to spin around, similar to a plug hole, to take the energy out of it at Hammersmith. At Abbey Mills a cascade, like a staircase, has been designed to break the energy. Without these measures Sullivan says quite simply the force of it will break the shafts.
Similarly, trapped air in the system could be destructive, which has been guarded against in the design. Along the river from Putney to the end of the tunnel, lines of a poem are inscribed into the brass vent columns that allow air to escape. This whimsical detail might capture the imagination of passersby, but doesn’t tell the whole story of the design.
Sullivan explains that the vents have been engineered to spiral air from the tunnels and out via carbon filters – for any unpleasant smells – to release air safely when the tunnel fills. Without these, if the system were to fill at 200 to 300 tonnes every second in a downpour, the build-up of air would be enough to blow manhole covers out of sight.
Blueprint for future projects?
The water industry, especially wastewater, has had to field criticisms about its performance with a laser-sharp focus on pollution and river health. A project completed at this scale that is already delivering tangible improvements is a point of celebration.
But can those successes be replicated? Sullivan simply says, yes of course.
Regulations were created with Ofwat for Tideway that can be used for other major infrastructure schemes. Already United Utilities is exploring a solution at the scale to have similar impacts to improve how sewer systems in Liverpool operate. As the face of water and sewerage infrastructure is set to drastically change and upgrade, in some instances from Victorian designs, something already proven to turn the EDM map from red to green, and encourages fish back to dead rivers can only be welcomed.
Against the backdrop of Thames’ wider financial turmoil, the successes of the new sewer cannot come soon enough. Sullivan is confident that despite the maelstrom, Tideway will, like the rest of the organisation’s day-to-day activities, carry on delivering for nature, for customers and for Harry the seabass.
