Tideway Tunnel

The Tideway Tunnel is a major deep-level sewer tunnel running beneath the River Thames in London, designed to capture combined sewer overflows that currently discharge untreated storm-sewage into the river. It is widely called the 'Super Sewer' because of its massive diameter—around 7 meters—and its roughly 25-kilometer length.

Construction has been underway for several years, with main tunneling completed in the early 2020s and full commissioning expected around 2025. Once operational, it will transfer intercepted overflow to treatment works operated by Thames Water rather than releasing it into the Thames.

London's existing Victorian-era sewer system, originally designed by Joseph Bazalgette, combines storm water and sewage in the same pipes and overflows into the Thames during heavy rain. The Tideway Tunnel is designed to intercept tens of millions of tonnes of these combined sewer overflows each year.

The project is being delivered by Tideway, an infrastructure company set up specifically for the project, with construction undertaken by major joint ventures including companies such as Bam Nuttall, Ferrovial, and Laing O'Rourke. Thames Water will operate the tunnel once it is commissioned.