Inside London’s £5 billion super sewer
For too long the Thames has acted as an open sewer – but not any more. Nick Harding reports
If you found yourself faced with some fiendishly tricky flat-pack furniture this weekend, spare a thought for the engineers working on London’s new super sewer. One of the biggest engineering projects in British history, workers have thus far successfully lowered two partially assembled 850-ton excavators down a 53 metre (174ft) shaft, and are now tasked with bolting together the remaining 450 tons of components to get the 100metre-long machines fully functional. This latest phase of the monumental £5billion, nine-year project is self-assembly on steroids.
The two giant subterranean diggers, known as tunnel boring machines (TBMS), are currently at the bottom of a huge shaft near Battersea Power Station. They were custom made for the super sewer project, or Thames Tideway Tunnel to give it its official name: once ready, they will be sent off in opposite directions to eat their way through the capital’s substratum like giant mechanised worms, cutting through rocks that have lain undisturbed for 50 million years.
Millicent, named after Millicent Fawcett, an English suffragist, will tunnel 5km (3 miles) to Fulham. Meanwhile, Ursula, named after Audrey Ursula Smith, a British cryobiologist at King’s College hospital, will tunnel 9km to Bermondsey. As is tradition, both were blessed by a priest, which is done whenever a new tunnel is dug, and over the course of three years, they will chomp their way through miles of clay, sand, gravel and chalk, and displace around four million tons of spoil, which will be conveyed to the surface and on to barges, where it will be sent downstream, sorted and reused.
Despite the size of the machines, their progress will be invisible to Londoners on the surface as they will be operating between 30 and 60 metres below ground, and their course runs mainly under the Thames. Chris Darton, delivery manager for the central section of the Thames Tideway Tunnel, explains: “At ground level, it will be imperceptible that tunnelling is going on below because we are so deep. Also, we have invested in noise enclosures with damping for noise and vibrations, so even though our operations will go on 24/7, our neighbours shouldn’t feel or hear any of our activity.”
The super sewer is being developed to save London from a particularly unpleasant problem. The city’s Victorian pipes were designed and built in the 1860s by Sir Joseph Bazalgette to service a population of two million, but, today, nine million people live in the capital, and the system is struggling to cope with the amount of waste they generate. When it rains, the sewers flood. To stop the system backing up into the homes of the people above, the excess effluent is flushed into the Thames via a network of 50 overflow pipes. Nearly 40million tons of raw, untreated sewage gushes into the river each year, creating a health hazard for river users, fish, birds and aquatic mammals.
“London has forgotten the Thames,” opines Andy Mitchell, the Tideway Tunnel chief executive. “Personally, I think it is unacceptable for our capital city river to be treated as an open sewer. That needs to change.”
It is feared that as the population continues to grow, London, without intervention, could face conditions similar to those of the Great Stink of 1858, during which the pong of sewage in the river became so unbearable that disinfectant-soaked sheets were draped over the windows of the Houses of Parliament to stifle the stench reaching MPS.
It is hoped that the super sewer will save London from this malodorous threat and reduce the amount of sewage that flows into the Thames by some 95 per cent. To undertake such a feat, the scheme involves an army of 4,000 workers using machinery straight out of a Thunderbirds episode to create a 25km tunnel network under the Thames that will be wide enough to hold three double-decker buses full of London’s ordure: the main tunnel will stretch from Acton in the west, to Abbey Mills Pumping Station near Stratford in the east. Along the way, it will connect to the existing sewer network via 15 access shafts.
At Abbey Mills, the main tunnel will be linked via a 72metre-deep shaft to the now-completed, 6.9km (4.3mile) Lea Tunnel, which will then take the overspill sewage to Europe’s biggest sewage treatment plant, in Beckton. Gravity will move the waste eastwards because the super sewer is built on a gradient that starts at 30 metres and finishes at a depth of 60 metres.
The project involves 24 sites across the city, and much of the work will be done on the foreshore of the Thames, with several riverfront public spaces being added along the route. It is, in all aspects, a gargantuan job – the progress of which has been followed by a fascinating three-part BBC Two documentary series, The Five Billion Pound Super Sewer.
Despite the scale of the project, Darton says that one of the biggest challenges was getting agreement from all the stakeholders involved. “The programme isn’t so much about building a tunnel, it’s about getting the consent, signoffs, approvals and agreements of all the authorities involved,” he says. “It’s taken a lot of work and effort over the past two and half years to get those.”
When Millicent and Ursula are in full operation later in the year, each will be maintained by an on-board gang of 10 to 15 workers, plus a support team at the base of the shaft from which they “launch”. As they progress under the city, the holes they create will be shored with prefabricated concrete panels. Darton explains that conditions for the workers below ground will be luxurious compared with those endured by labourers on Bazalgette’s original sewers.
“They will have areas where they can rest, and there will be sufficient space, toilet facilities and running water,” he says. “The machines also isolate the personnel from the exposed face of the tunnel, and any water or pressure.”
The TBMS were built by a French company that sourced components from across Europe. Some of the specialist cutting heads were manufactured in Sheffield and are made of coated steel – when the tunnelling ends in 2021, Millicent and Ursula may then be refitted for other projects.
Globally, engineers are increasingly looking to the spaces beneath congested cities to solve the surface problems. In Los Angeles, for example, Tesla billionaire Elon Musk has invested in his own tunnelling company and hopes to dig a subterranean network of road tunnels that will convey drivers and their cars around the city on moving platforms.
Meanwhile, in the UK, the third runway scheme at Heathrow that MPS endorsed last month involves the massive task of re-routing the M25 in a tunnel under the proposed runway.
“The Thames Tideway Tunnel is not proof of concept for what Elon Musk is proposing,” admits Darton, “but it will provide information for the market into how things can be done more efficiently and costeffectively.” Some of the sites already in operation along the super sewer’s route have provided a fascinating glimpse into the past.
As Darton explains: “At Albert Embankment, we found some Mesolithic timbers in the foreshore, and, in Battersea, we went through an old timber dry dock and found lots of old oil drums, one of which was dated 1830.”
As the past and the future intersect along the length of the Thames, the mammoth TBMS will most likely uncover even more secrets of the capital’s buried history. It is proving anything but boring.
‘It is hoped it will reduce the amount of sewage in the river by some 95 per cent’