An Inside Look At Tideway: London's Super Sewer

Harry Rosehill
By Harry Rosehill Last edited 47 months ago
An Inside Look At Tideway: London's Super Sewer
A tunnel inside the new super-sewer Tideway

London is full of shit. In fact, it's overflowing with shit.

No I'm not talking about the character of its citizens — that's a discussion for another time — but about physical excrement. And urine for that matter. Us Londoners are creating rather a lot of the stuff, and the sewers that Joseph Bazalgette built can't handle our crap.

London's Victorian sewers

When Bazalgette designed his sewers in the 1850s there were fewer than three million people in London, so they were built to handle the waste of roughly that many people. The current population of London is estimated to be hovering around the nine million mark. Hence, the sewers are struggling.

Population isn't the only thing that's changed since the Victorian era. We've now paved over plenty of the city. This means that when it rains, the ground doesn't absorb the water — instead, much of this also heads into the sewers. All in all, there's plenty of waste heading down there and not much space.

So what happens when there's too much sewage and the sewers can't cope? Well, there's a failsafe. When the sewers can't transport everything down to a sewage treatment works, the sewage is simply launched out into the Thames, via a CSO (combined sewer overflow). Yes, we know — that doesn't sound like a particularly 'safe' failsafe. And it isn't. Roughly 39 million tonnes of sewage flowing into the Thames annually, is environmentally ruinous. And that's where Tideway comes in.

Meet the 'super-sewer'

I'm in a snug boat cruising east down the Thames from London Bridge. Every couple of minutes the boat pulls alongside a massive construction site on the banks of the river. Well, I say 'banks' — not so long ago, these worksites were in the river. But the water was pumped out, and corrugated iron placed to keep it out, to allow for the building of the solution to the Thames' sewage problem.

Tideway is that solution. It has been dubbed a 'super-sewer' and aims to divert the sewage overflow out of the river and into a 25km long tunnel, 30 metres beneath the surface. I say 'aims', because it's believed that Tideway will have a 94% success rate at keeping sewage out of the Thames. And I say 'tunnel' but more accurately its 'tunnels'. The major tunnel stretches from Acton to Abbey Mills, but there are also two smaller tunnels forming part of the project too.

One is called the Frogmore Connection Tunnel (1.1km long) the other is the Greenwich Connection Tunnel (4.6km long). Perhaps not the catchiest names, but these tunnels aren't meant to be glitzy. They are merely two smaller sewers funnelling into the main Tideway tunnel.

Inside the Frogmore Connection Tunnel

New public spaces

Back on the river, I quickly realise how much Tideway has already impacted London while I wasn't looking. Construction hoardings every kilometre or so is an obvious change, as are the huge metal shed structures that have sprung up at the drive sites in Bermondsey, Battersea and Fulham. There are however some slightly more subtle alterations to the city, like Blackfriars Pier moving to the other side of the bridge, to allow for the interception of the point where the Fleet sewer runs into the river.

When Tideway is up and running, there will be an even more obvious (and probably talked about) effect on the city, at sites such as Blackfriars. Much like Bazalgette's original sewers led to the creation of the Embankment, the super-sewer will create new public foreshore spaces alongside the Thames. Seven of them to be precise, which brings a sense of continuity to the project.

The new public spaces aren't identikit — each has its own personality dependent on its location. The standout is the Chelsea Embankment Foreshore. When Bazalgette's sewers were built, it was intended that the Chelsea Pensioners in the Royal London Hospital would be able to see the river from the building. But the engineers fudged the measurements, the river wall was built too high, and the view obstructed. This new foreshore will right that wrong roughly 150 years later.

A barge taking soil out to Rainham

The land that's been dug up in the creation of these new public spaces, along with that in the tunnel down below, isn't being wasted. A barge collects it and takes it down to Rainham, where it's being used for a nature reserve. Extremely un-wasteful for a project that's ultimately devoted to waste.

That's not the only piece of ingenuity accompanying Tideway. There's no pumping involved within the main part of the sewer. That's because the entire thing is sloped on a very slight gradient, so the sewage naturally flows towards its end point.

An inside look at Tideway

Our boat follows that downward gradient from Chelsea to Battersea, so we can get a look inside one of the aforementioned giant metal sheds. Inside is a drive site, where tunnel boring machines began their journeys to create the sewer. It's enveloped by a shed so people can work on the site 24/7, without noise bothering neighbours.

We arrive and are kitted out with neon orange PPE gear, so we can go out and get a proper look at the shaft connecting the surface world to the sewer beneath. Just before I head inside the worksite proper, someone casually asks me, "You're not afraid of heights, are you?", a question which only helps to generate excitement for what I'm about to see.

Peering into a shaft in Battersea built for Tideway
The epic and slight sci-fi shaft

They weren't joking about heights. The shaft is epic. I stand there for a few minutes staring at the scale of it. Then I shift my gaze: up instead of down. There's a man operating a crane attached to the ceiling delivering large curved concretes slabs, that form the wall of the sewer below.

There's something distinctly sci-fi about the whole experience. Staring into a massive hole in the ground, pipes climbing up the walls, and the workers below looking like ants. By pushing my nose up against the barrier, I can just about make out railway tracks leading into the sewer. Of course these tracks — and the trains running on them — are only temporary, used for the transportation of workers and equipment. A full time train running through an in-use sewer doesn't sound like a pleasant experience.

Speaking of a railway, there are inevitable comparisons between Tideway and Crossrail. Both are massive feats of engineering, happening beneath the city. Both have also had their estimated costs spiral upwards over time. When I ask the press team at Tideway whether the project could bear another similarity to Crossrail — massive delays — they are pragmatic. While they don't commit to anything, they point out that once tunnelling is done, it's a lot simpler to get a sewer up and running than a railway. There are no stations as such, no track that needs to be laid, no signalling to sort. Just some coating to the walls. And even though costs of the project have risen to an estimated £4.2 billion, the price rise that Thames Water customers has had to face has fallen to £20-£25 from original figures that were as high as £80.

On the edge of Tideway's shaft
"You're not afraid of heights, are you?"

As I walk away from the shaft, I can't help but feel like it's a tad wasteful to use these tunnels for... well, waste. They're so awesome and brutal, part of my mind wants to see them preserved as they are, like a subterranean playground. Oh well. That definitely isn't worth paying the price of having sewage pumped into the Thames every time it rains.

Last Updated 11 November 2019