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January 13, 2015updated 29 Jul 2021 1:27pm

What's a super sewer, and why does London need one?

By City Monitor Staff

For a few years now, plans have been on the table for a massive extension to London’s sewer system. And last September, ministers finally gave Thames Water the go-ahead to start construction in 2016. The project’s official name is the Thames Tideway Tunnel; but more likely you’ve heard it referred to by another name: the “super sewer”.

But what is a “super sewer”? What’s so super about it? And why does London supposedly need one?

1. It’s big.

In fact, it looks like London actually coined the phrase “super sewer” for no other reason than that the word “sewer” didn’t really convey the enormity of Thames Water’s plans. As infrastructure projects go, the super sewer has more in common with the Channel Tunnel than it does with a standard sewer pipe.

If built, the tunnel will be 15 miles long, and building it will require round-the-clock drilling from large boring machines of the kind used to construct underground railways lines. Once completed, the network would be the largest sewerage system in the UK.

The main tunnel would start at Acton and then move under Fulham, through central London to Tower Hamlets. Then, it would connect to the existing Nothern Outfall Sewer, which transports sewage to a treatment plant at Beckton. For most of its length it would run under existing watercourses: the Thames, then the Limehouse Cut canal.

Here’s a map of the route – the solid orange line represents the main new tunnel:

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2. Lots of people think the plans aren’t super at all.

Of course, as the map shows, the plan will require an awful lot of invasive construction work at an awful lot of sites in central London. The aforementioned 24-hour drilling by giant machines at Battersea, Fulham and Chambers Wharf would, as Hammersmith & Fulham Council has noted, subject residents to “24/7 noise, dust and air pollution”. There are eight primary schools within a mile of the Fulham drilling site, and residents living within ten yards. Not ideal.

Even angrier than Hammersmith & Fulham is Southwark Council, which has stood against the choice of Chambers Wharf as a drilling site since the plans were first proposed. Here’s a view of Chamber’s Wharf from above:

The proposed drilling site is technically defined as a derelict, industrial “brownfield” one – but surrounding it are houses, local businesses and a school. In a statement last year, Peter John, the leader of Southwark council, called the decision to approve the plans “ludicrous and evil”. (That’s right: “evil”.)

3. It’s expensive

The new network will cost £4.2bn. This would be bad enough if it was all public spending, but it looks like some of the cost will be borne by Thames Water customers in London and the southeast, through a levy added to their waste water bill.

The Telegraph has estimated that this could add £40 to bills over the next few years, climaxing in an £80 charge by the 2020s – one which would continue indefinitely. 

4. It should help clean up the Thames.

The overriding argument for why London needs a super sewer is simple. In 2013, as a result of heavy rainfall flooding the existing sewer system, 55m tonnes of sewage flowed into the river. The year before, it was 36m tonnes.

You can see why even a £4.2bn plan for a giant new sewer won out against the horrifying reality of millions of tonnes of… that. As Phil Stride from Thames Water told the BBC last year, “It is absolutely not consistent for a world-leading city to be using its river as an open sewer.” Quite.

London’s original sewer system was actually built as a response to a similar problem. The 20,000 mile network owned by Thames Water was installed in the 1860s to prevent raw sewage being flushed into the Thames. Outbreaks of cholera earlier in the century had killed around 40,000 people, and led to the system’s installation – though officials were convinced a “miasma” rising from sewage was to blame, rather than water contamination.

The Thames: London’s sewer system until the mid-19th century.

5. It’ll take ages to build.

If local councils’ objections are dodged, and the green light holds, construction on the sewer should be underway by 2016, but won’t be completed until 2023.

In the meantime, millions of tonnes of sewage will continue to flow into the Thames and out to sea. Really diminishes the appeal of urban beaches, doesn’t it? Or, in fact, all beaches.  

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