Tideway Tunnel connection ushers cleaner future for the Thames

Mott MacDonald is proud to see the activation of London’s Tideway Tunnel, a generational infrastructure project that it has been heavily involved in from the start.

Tideway announced the successful connection of the new super sewer, signalling a healthier future for London’s iconic river.

After 10 years of construction, the last of 21 connections was made between the original Victorian sewers and the new 25km Thames Tideway Tunnel, bringing the entire system online, protecting the tidal Thames from sewage pollution.

Divided into three main regions for the purposes of delivery, Mott MacDonald was involved in the east region that was delivered by a joint venture of Costain, Vinci Construction Grands Projets and Bachy Soletanche.

The 25km-long super sewer connects to the 6.9km-long existing Lee Tunnel, a Thames Water asset – forming the ‘London Tideway Tunnel’ (LTT) system.

The work of bringing the full system online began in the autumn of 2024, when Tideway announced that the first four connections had led to 589,000 tonnes of storm sewage being captured by the LTT in a single, rainy 24-hour period.

Tideway then revealed that 848,365 tonnes had been captured during heavy rainfall in another 24-hour period in late November.

Work, including Mott MacDonald’s involvement on the project, began in 2016 – with activity taking place at two dozen construction sites from Acton in west London to Abbey Mills Pumping Station in Stratford, east London.

More than 20 deep shafts – some as wide as the dome of St Paul’s Cathedral – were constructed across London to divert sewage flows and to lower tunnelling machines into the ground.

Discover more about this incredible project and Mott MacDonald’s role.