Sophie Campbell



The biggest bores in London

April 26, 2023
Pristine tunnel some 200 feet below Bermondsey @SCC

For the past eight years, barely noticed by many of us on the surface, the Thames Tideway Tunnel (aka the ‘Super Sewer’) has been burrowing through the capital’s subsoil. Between 80 ft/23 m and 200 ft/60 m underground, six Tunnel Boring Machines of different sizes, all named after women, have been grinding their way from Acton, in west London, to Abbey Mills Pumping Station in east London. When the tunnel opens for business in 2025, the River Thames will never be the same again.


Map of the 15.5 mile/25 km Thames Tideway Tunnel ©Tideway

When the great sewer engineer, Sir Joseph Bazalgette, designed London’s intercepting sewers in the nineteenth century (thereby creating the riverside highway we know as the Embankment), he allowed for what seemed at the time colossal growth in the population. His radical combined sewers carried not only human waste but ‘grey’ or dirty water and rainwater, too. When the level in the conduits reached a certain point, they were designed to release the overflow into the Thames .

Bazalgette's sewers under construction, 1860/70s.

Around 150 years on, not only is London’s population on a steady trajectory to 9 million, but we have unprecedented numbers of bathrooms and showers. Add to that eccentric weather patterns, and any torrential rain in the Thames catchment area, some 215 miles/346 km upstream in the Cotswolds, causes the overflow to run into the river, undoing decades of environmental work. Hence the building of this immense, 15.5 mile/25 km tunnel from west to east, to keep effluent and river separate.

Concrete clad tunnels, up to 29 ft/8.84 m in diameter. © SCC

Last month, just two years from completion, the gleaming, £4.4 bn tunnel opened up to the friends and family (including me) of the 400 Tideway staff and hundreds of workers from four contractor companies, so they could see what their relatives and mates had been up to for much of the past decade. What a chance. Especially, as a couple of wags noted, it would never look this clean again.

Families wait to descend the shaft. © SCC

Londoners have certainly noticed – and sometimes complained about – the building sites on land and in huge coffer dams on the edge of the river. Most of these conceal the shafts that allowed the TBMs to be lowered into position, as well as access for construction workers. Like the latter, we friends and relatives descended in a metal cage lift, emerging to wonder at the immaculately clean, newly bored and concrete clad tunnels and the sheer scale of the engineering – a new world below the ground.

Bottom of the shaft @ SCC
View to the surface @ SCC

The tunnels are roughly 11 ft/3.4 m to 28 ft/8.8 m in diameter, depending on location and function, and are now neatly lined in concrete. Worker access is via small trains, one of which was still in situ when my group went down the shaft at Chambers Wharf, Bermondsey, one of the busiest ‘drive sites’ (tunnelling start points) and a junction where three tunnels meet.


Underground train @ SCC
TTT staff guide visiting families @ SCC

The last TBM to be lowered down here – it took 12 hours – was Selina (below), all 1500 tonnes of her. She was named after Dr Selina Fox, who founded the eight-bed Bermondsey Medical Mission in 1904 (it’s still a local charity today) and her job was to take the tunnel the final 3.4 miles/5.5 km under the river to the pumping site at Abbey Mills, just south of the Queen Elizabeth Olympic Park. This she completed in the spring of 2022, only a few months over schedule, despite Covid delays.

TBM Selina (1,500 tonnes). @ Tideway

This is where the Thames Tideway Tunnel comes to an end. The sewage overflow goes on to be pumped over 196 ft/60 m to the surface at Abbey Mills and sent on its way via the existing Lee Tunnel to the sewage treatment plant in marshy Beckton, on the far side of the Borough of Newham.


We temporary visitors, meanwhile, had to surface. While picking our way through the remaining equipment (much of which has been dismantled, recycled or taken to the surface), carefully guided by staff who had volunteered for the day, I saw a small effigy of Saint Barbara on the wall, topped by a cross, that would have been more at home in a Catholic country that in largely secular Britain.

Shrine to St Barbara @ SCC

I’ve long been slightly suspicious of the fact that all the really big bores in London (Thames Tideway Tunnel and Crossrail, most recently) are named after women. But Barbara, it turns out, imprisoned by her pagan father for her Christian conversion and miraculously released through solid rock, is the patron saint of tunnellers. As a result, a prayer is always said to her before tunnelling work begins and boring machines and other subterranean equipment across the world usually have female names.

Saint Barbara escapes her rock © Wikimedia Commons

As for the ‘Tideway Six’ – Rachel, Millicent, Ursula, Selina, Charlotte and Annie – their work is done. From 2025, the River Thames in central London will be a cleaner, healthier river and Londoners will be able to use new parks, housing and amenities built on the old construction sites. Tree planting is well underway and 50 artworks have been commissioned. Soon we won’t remember what was there.

And in a busy, densely-populated, modern city, that’s quite an achievement, ladies.

Thames Tideway Tunnel

Artwork on Blackfriars Bridge foreshore @ M J Chapman

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