Thames Tideway

Year:2023-4 (planned completion)

Duration:7 - 8 years


Country: London, UK

What did this project achieve?

Increase the ability for London to deal with its own sewage

London’s sewage system was designed in the 1860s for a city of around 4 million. There are now around 8 million people living in the capital. Although the system still works well it’s struggling to cope in terms of capacity. The result is that millions of tonnes of sewage pour into the river Thames every year.

The Thames Tideway Tunnel is part of a 3-stage project to cut river pollution and clean up the Thames.

Stage 1 upgraded the main sewage treatment works in London – plants including Mogden, Crossness and Beckton can now treat more sewage every year.

Stage 2 built the Lee Tunnel. Operational since 2015, the 6.9km tunnel reduces sewage overflowing into the river Lee.

Stage 3 is the Thames Tideway Tunnel. The 25km tunnel will stretch from Acton in west London to Abbey Mills pumping station in Newham, where it will connect to the Lee Tunnel.

Tideway will connect with 34 of the most polluting overflow points along the river - collecting sewage that currently overflows into the Thames and transfer it to Beckton for treatment.

Difference the project will make

The Tideway Tunnel – nicknamed the super sewer – aims to make the river Thames cleaner for both Londoners and river wildlife.

Currently, even a moderate amount of rainfall can mean sewage and other social excreta overflows into the Thames and floats past the House of Commons.

High levels of sewage also affects wildlife. When a large amount overflows into the river, the bacteria that breaks it down sucks oxygen out of the water – suffocating and killing fish.

When the tunnel is finished, the system should only overflow in severe weather conditions such as 3 days of solid rain.

How the work is being done

The Thames Tideway Tunnel will be 25km long, 66m deep and 7m in diameter.

It will follow the route of the river Thames and go through ground conditions including chalk and clay.

Engineers will use 3 main ‘drive sites’. This is where the tunnel boring machines (TBMs) will be lowered into the ground via vertical shafts. They’ll dig the tunnel in 3 sections – east, central and west.

Each TBM uses a rotating cutterhead to dig. At the same time, the machine creates a tunnel wall behind it using concrete segments. Waste material is removed using a conveyor belt or pump, depending on the ground. In some areas the waste is solid, in others it will be more liquid – known as slurry.

The TBMs will be transported along the river by barge to where they’re needed. The first TBM arrived in November 2017.

Tunneling starts in 2018 it will go on for 24 hours a day.


The Thames Tideway Tunnel will… dramatically improve the environment by reducing the amount of sewage overflowing into the river.

Shirley Rodrigues

Deputy Mayor for Environment and Energy

Fascinating facts

The Thames Tideway Tunnel is the UK water industry’s biggest-ever infrastructure project.

Engineers will use 6 tunnel boring machine (TBMs) to dig the tunnel. Each TBM weighs 1,350 tonnes and is 147m long – the same length as 12.5 double decker buses. The first TBM arrived in November 2017 and is called Rachel after engineer Rachel Parsons, who started the UK’s first women-only engineering company.

The project will create 3 acres of public space along the Thames – including at Blackfriars (near the City) and Victoria Embankment (near Downing Street). All the new spaces aim to let people get closer to the river.

People who made it happen

The tunnel is being built by 3 different consortia.

  • West section (Acton to Fulham): Balfour Beatty, Morgan Sindall and BAM Nuttall
  • Central section (Fulham to Bermondsey): Ferrovial and Laing O’Rourke
  • East section (Bermondsey to Newham): Costain, Vinci Construction and Bachy Soletanche

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