London’s sewage system is well beyond capacity. Originally designed in the Victorian era (a detailed history of the sewers can be found here) some 150 years ago, it was designed to handle all the sewage for a city of some four million people.


Built in the 1830s, this is one of London’s oldest still-working sewer lines. This tunnel is also the remnant of the Walbrook Stream or River, so called because it was once the only significant watercourse to flow through London’s fortified walls. The river began to disappear as early as the Roman era, and it was already used as an open sewer long before that.

London reached, and then surpassed, the two million population mark around 1920, and the existing system has been struggling ever since. With the city’s population in excess of 8 million today, we’ve clearly gone well beyond capacity, and in fact, are now in violation of the European Union’s directives for wastewater treatment and management. With the city still growing briskly, and expected to reach a population of 16 million by 2160, it is clear that something needs to be done, and quickly. That’s why the Thames Tideway Tunnel project was commissioned, and now, it’s about to become reality.

Annually, the overflow is equivalent to 8 billion toilets flushing straight into the river.

What Happens Now?

Sadly, because the sewage system is so overwhelmed, it simply cannot handle the volume, and regularly overflows when it rains. When it does so, the waste flows straight into the Thames. Annually, the overflow is equivalent to 8 billion (yes, billion, with a “B”) toilets flushing straight into the river.

The Plan

The Thames Tideway Tunnel is the product of more than a decade spent studying the problem of London’s sewage overflows and what to do about it. The project is expected to take a full seven years to complete, and when finished, will see a massive new tunnel running under the Thames, intercepting the overflow from the existing system and pumping it to the Abbey Mills Pumping station, which is located near Stratford.

From there, it will connect to the Lee Tunnel, which will transfer the sewage to the Beckton Treatment Works for proper handling. At 2011 prices, the project is expected to cost the city £4.2 billion, but the finished product will enable the city’s sewer system to handle the expected increase in population growth for the next hundred years. All told, the tunnel is expected to be 25 kilometres long and more than seven metres in diameter, running 65 metres deep. It is the largest infrastructure project ever to be undertaken by the UK water industry.

The Project Timeline

As mentioned, this project has been in the planning phase for more than a decade, and has now been approved. Beginning in 2015, the project’s director will begin laying proper groundwork for the project, including diverting utilities as needed in order to facilitate construction. Actual construction is set to begin in 2016, and will take the six remaining of the seven years scheduled, which should see the project completed by 2022.

Benefits Of The Project

The project is expected to benefit London, and indeed, the whole of England in a variety of ways. Of course, there are the obvious things like the improved environment. The Thames is one of the world’s great rivers, and it’s a shame to see the condition it is presently in. This plan will help to clean the river and improve the local ecosystem.

The health benefits for all Londoners are obvious as well. In addition to those things, however, there are enormous economic benefits to be had. This is a project of immense scale that will bring engineering and construction jobs to the city. Additionally, a cleaner Thames will help contribute to the rejuvenation of London’s river economy, which will only enhance economic growth.

Note: If you’d like to keep up-to-date on the ongoing progress of the project, the official Tunnel website is here along with a very entertaining video on the system.

thames tunnel boring machine

Fraser Ruthven is the Growth and Strategy Manager for the Capitals leading drainage companies – London Drainage Facilities. Fraser and the team fully support the project and believe it will improve London on a vast scale.