London’s super-sewer: is there light at the end of the tunnel?

Beneath London lies an engineering marvel few of the city’s inhabitants stop to consider despite relying on it whenever they flush their toilets. Fewer still have ever seen it.

The city’s sewerage system, designed by civil engineer Joseph Bazalgette around 150 years ago, was built to last and still works as smoothly as it ever did, despite being so unappreciated. Effectively a network of press-ganged culverted rivers draining into the centre of the great conurbation, Bazalgette’s sewers are unexpectedly beautiful. They boast inch-perfect brickwork more worthy of a temple than a channel for urine and faeces. It’s strangely peaceful down there too, sheltered from all the noise of the metropolis.

One legacy of Bazalgette’s project that Londoners might be familiar with is the way he also beautified the city above. Aside from the obvious aesthetic advantages of consigning overflowing cesspits to the dustbin of history, the great man left behind a network of verdant embankments, along which Victorian families loved to promenade. 

His visionary scheme, ordered by then Prime Minister Benjamin Disraeli, is often credited with having done more for public health than the foundation of the National Health Service by helping vanquish cholera in the city. Today, his sewers remain an otherworldly repository of the hopes and dreams Londoners flush away along with their waste. Wedding rings are sometimes found down there amid the effluent, as (predictably perhaps) are shoals of dead goldfish. There are bullet casings and coins dating back to the reign of Queen Victoria.

E&T recently joined Thames Water workers for a special behind-the-scenes tour of one of the oldest parts of the sewerage network. We witnessed the notorious lumps of kitchen fat and conglomerations of wet wipes (remember not to flush those) and heard tales of super-sized rats living off discarded junk food that finds its way into the sewers of the West End.

Bazalgette’s network, including his suitably grand pumping stations, was built to serve a city of four million inhabitants. Its population is now double that, and the fact that the old sewers act as a drainage system for rainwater as well as carrying away all the dirty water from the capital’s homes and workplaces means a total of 20 million tonnes of raw sewage ends up being dumped into the tidal section of the Thames every year. That lowers oxygen levels, suffocating fish – an environmental scandal.

Just as MPs were prompted to act in Bazalgette’s day because they could not bear the stink from the river permeating Parliament, so politicians decided sullying one of the most iconic waterways in the world with millions of tonnes of raw sewage annually was no longer defensible. Thus, three years ago they rubber-stamped construction of what will be the equivalent of a motorway for sewage and excess surface water runoff.

The ‘super-sewer’, as it is known in the media, will be London’s biggest sewerage upgrade since Bazalgette’s time. The project will consist of a 16-mile-long tunnel, running from Acton in the west to an expanded sewage treatment works at Beckton in the east. It will get progressively deeper, going from about 30m at its westernmost point to a maximum depth of around 75m, enabling gravity to carry the contents to its destination, where it will be pumped up into the treatment works.

One part of the ‘super-sewer’, the Lee Tunnel, has already been built and is said to be London’s deepest tunnel. Whenever it rains and the old sewers overfill, the Thames Tideway Tunnel, as the mammoth project is officially known, will swing into action and pick up the slack.

The work is predicted to cost around £4.2bn, with water bills likely to rise as a result. Critics claim the scheme is overly expensive and say potentially cheaper techniques for dealing with river pollution by limiting surface water run-off were not sufficiently explored. Some have also queried the somewhat opaque funding structure put in place to make the project feasible. Tideway is owned by a consortium of investors that comprises Allianz, Amber Infrastructure, Dalmore Capital and DIF. More than two million UK pensioners have an indirect investment in Tideway through pension funds managed by the investors.

Supporters stress the ‘super-sewer’ will make this vital part of London’s infrastructure fit for purpose for the next 120 years. Perhaps surprisingly for such a modern project, it uses age-old tunnelling techniques essentially unchanged – aside from the introduction of some types of new technology – since Marc and Isambard Kingdom Brunel built the first tunnel under the Thames in 1843. Integral to the workings of the Thames Tideway Tunnel are the old Victorian sewers that still serve London so dependably after all these years.

“Our tunnel doesn’t replace Bazalgette’s sewage system,” stresses Geoff Loader, head of stakeholder engagement at Tideway, the organisation building the new tunnel, as he guides a party of sewer enthusiasts on a boat tour along the Thames. “We simply back that system up and stop it from using the river.”

Construction and testing of the tunnel is expected to be complete in around a decade’s time. The scheme has been timed so as to use part of the workforce that built Crossrail. Four enormous tunnel-boring machines are shortly to be transported to London by sea and river from continental Europe to start this new chapter in the city’s engineering history.

“The tunnelling machines we use are bigger than those used for Crossrail,” says Loader. “They’re not going to tunnel quite as far, though. If you talk to Tideway engineers, size really matters. Talk to Crossrail engineers and they’ll tell you the length is much more important.”

As was the case with Bazalgette’s scheme, the Thames Tideway Tunnel will also lead to changes along the river at road level.

“In total, three and a half acres [1.4ha] of new public realm and foreshore will be created and left behind as a result of this project,” Loader explains. That includes a piazza type lookout point at Blackfriars and a similar space reclaimed from the river opposite the London Eye.

His colleague Hannah Shroot expects the improvements above ground will help “reconnect people with the river”.

That is a theme Tideway is eager to stress. The company is aiming to transport as much material as possible by river during construction, resulting in an overall increase of 60 per cent in freight traffic on the Thames, and 600 river-based jobs will be created. Many hope this will act as a catalyst for transporting more material, and perhaps increasing numbers of commuters, using the so-called ‘blue infrastructure’, thereby helping cut pollution from roads.

“It’s not just about planning for the future, it’s about how we can use the river now and maximise its potential,” says Shroot.

The Thames Tideway Tunnel has received markedly less media attention than, say, the Channel Tunnel or Crossrail – perhaps because sewers are inherently unglamorous. However, Shroot says anyone who loves the Thames should see its significance. “The river is one of the most iconic assets our city has, and I think sometimes people don’t realise how much sewage goes into it and that we all have a duty to look after it. It’s just really important we look after it and protect it for future generations.”

The Thames has already come a long way since it was declared biologically dead in the 1950s. Seals and even porpoises are a not uncommon sight, particularly downriver. In decades to come, Londoners might take delight in a rejuvenated aquatic ecosystem featuring salmon, eel and otters. Who knows, visitors to the IET’s Savoy Place venue, located next to Bazalgette’s Thames Embankment, might even be allowed to venture into the newly cleansed water for a quick dip before drying off and hurrying in through the front door.