Project Spotlight: Thames Tideway Tunnel

Bachy Soletanche, Balfour Beatty, BAM Nuttall, Costain, Ferrovial, Laing O'Rourke, Morgan Sindall, project spotlight, Thames Tideway Tunnel, UK, VINCI,

December 15, 2023

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The 25km Thames Tideway Tunnel is a water infrastructure project designed to reduce sewage overflow into the River Thames and improve London’s wastewater system.

Also known as ‘Super Sewer’, the Thames Tideway Tunnel project is a 25km wastewater and sewage treatment project under the Thames in London, UK. Constructed 70m below ground, the Thames Tideway Tunnel is the largest water infrastructure project in the UK.

The primary aim is to significantly reduce the amount of untreated sewage and stormwater that currently discharges directly into the River Thames each year. The tunnel will protect the Thames from pollution, improve the river water quality, and support the growing needs of London’s population.

Preparatory work for the project began in 2015, and construction is expected to be completed by 2025.

Funding for the Thames Tideway Tunnel project

Total tunnel funding is estimated at £4.5 billion and is being paid by Thames Water’s 15 million wastewater customers through their bills, which will rise by no more than £25 annually. Thames Water is the UK’s largest water and wastewater services company.

Numerous contractors are involved in the Thames Tideway Tunnel project as construction is divided into three main sections. This includes Thames Tideway Tunnel West, Central and the East section.

The BAM Nuttall, Morgan Sindall, and Balfour Beatty consortium are responsible for the West section of the tunnel. Meanwhile, the central section is being constructed by a joint venture comprising Ferrovial Agroman UK and Laing O’Rourke. A consortium of Costain, VINCI Construction Grands Projects, and Bachy Soletanche is building the Thames Tideway Tunnel East section.

The System Integration contract for the Thames Tideway Tunnel has been awarded to Amey, who will oversee process control, communication equipment, and software systems for the tunnel’s operation, maintenance, and reporting.

Why is the Thames Tideway Tunnel required?

Designed by Sir Joseph Bazalgette in the mid-19th century, the current sewer system was a groundbreaking development to address the health crises related to waste and flooding. Bazalgette’s sewer system directed waste eastward through interconnected sewers to treatment facilities, eventually releasing it into the Thames, where tides carried it to sea.

However, it was built to accommodate a population of 4 million people and now struggles to cope with the increased population of 8.9 million people. While the sewer system was innovative for its time, it is not designed to handle the heavy rainfall and increased urban runoff seen today. This network operates at 80% or above even during dry weather, leading to more frequent overflows and environmental concerns for London City.

Redirecting the sewerage overflows through a modern tunnel system will divert sewage from the river to treatment facilities and protect the river for at least the next 100 years.

Thames Tideway Tunnel Construction

As the Thames Tideway Tunnel is divided into three distinct sections, each section has different construction features and specifically different Tunnel Boring Machine (TBM) purposes.

Tunnel Boring Machines (TBMs)

The Thames Tideway Tunnel project utilised six TBMs, each specifically customised and selected to suit the geological conditions of the different segments of the tunnels. These TBMs are crucial for excavating the tunnels and installing precast concrete segments that form the tunnel lining. The design includes strategic shafts for access and maintenance to ensure safety and efficiency and is carefully planned to minimise surface disruption and safeguard existing infrastructure.

Thames Tideway Tunnel central section

The scope of work for the central section of the Thames Tideway Tunnel project involved constructing a 12.7km new sewer tunnel beneath the River Thames between Fulham and Blackfriars.

With an estimated budget of £745m, Ferrovial Construction and Laing O’Rourke Joint Venture crews worked together to develop, design, and construct the new sewer tunnel.

Two custom 8.8m Earth Pressure Balance Tunnel Boring Machines were used and will reach depths of up to 60m between Fulham and Bermondsey. This was a challenge as crews had to pay critical attention to existing infrastructure such as the London Underground. Building eight shafts and pumping stations, managing logistics, and utilising river barges for soil disposal were also involved in the scope of work.

Thames Tideway Tunnel east section

The Tideway East section was completed by the JV comprising Costain, VINCI Construction Grands Projects, and Bachy Soletanche. The contract, valued at £605m, included construction works for building a 5.5km main tunnel and a 4.6km connecting tunnel for combined rainwater and wastewater, situated 45m to 65m underground.

These two tunnels were excavated with slurry pressure balance tunnel boring machines, featuring an interior diameter of 7.2m for the main tunnel and 5m for the connecting tunnel. Works also involved constructing five massive shifts that range from 17m to 25m in diameter to conduct maritime works along the Thames. This was integrated with the existing wastewater system, which completed numerous electromechanical work packages.

Thames Tideway Tunnel west section

The construction for the 7km West section began from Action to Fulham in London, UK. With construction sites stretched across seven sites, BAM Nuttall, Morgan Sindall, and Balfour Beatty crews worked together on the Tideway West contract valued at £416.

Special TBMs suitable only for London’s clay conditions were utilised, and crews excavated the tunnel and installed its lining with precast concrete segments.

A critical aspect of the west section is managing logistics in an urban environment. This included the environmentally conscious decision to transport excavated materials via barges on the River Thames. Moreover, integrating the new tunnel with London’s existing sewer system required meticulous planning to avoid disruptions.

Throughout the construction process, efforts were made to minimise the impact on local communities and the environment.

Benefits of constructing Thames Tideway Tunnel

The Thames Tideway Tunnel will drastically reduce untreated sewage overflow into the River Thames, significantly enhancing the river’s water quality. This improvement will benefit the river’s ecosystem, public health, and recreational activities.

By expanding London’s sewage system capacity, the tunnel will effectively manage increased demands from the city’s growing population. Moreover, it prevents sewage flooding during heavy rains by providing an alternative route for excess water. This will prevent overflow and protect urban areas from flood damage for public safety. 

The project is a significant investment in London’s infrastructure, ensuring resilience and sustainability for future generations. It aligns with the city’s goals for sustainable urban development and environmental responsibility. Moreover, the Thames Tideway Tunnel has created 4,000+ job opportunities throughout its construction phase. Additionally, it is expected to generate 5000+ more indirect jobs across sectors, such as supply chains and support services.

Environmental considerations of Thames Tideway Tunnel

The Thames Tideway Tunnel project has strongly emphasised adopting environmental measures to minimise ecological impact during construction and operation.

Additionally, sustainable river transport reduces the carbon footprint and helps clean the foreshore. Two specialist tugboats with low-emission engines and low noise outputs were used to reduce lorry movements. For the western section, barges were used to carry materials from tunnelling work on the river and kept up to 93 lorries off London’s roads. This also reduced noise and air quality in the already polluted London city. 

Sustainable practices such as electric-powered TBMs and recycling materials were implemented in the Tideway project. Also, special care was taken to protect marine life in the Thames, with effective waste management strategies like utilising river barges to mitigate road traffic and air pollution.

Ultimately, the tunnel will significantly contribute to the health of the River Thames post-construction, enhancing water quality and supporting a thriving ecosystem.

Challenges surrounding the Thames Tideway Tunnel project

Though the Thames Tideway Tunnel project is essential for London, it has faced several challenges and controversies in the past few years.

Environmentalists and local groups have raised concerns about the project’s potential to increase carbon emissions and exacerbate traffic and pollution in already congested areas. There are also fears that the Thames Tideway Tunnel will induce additional vehicle journeys and worsen air quality in pollution-stricken communities.

Financially, the project’s overall substantial costs and impact on increased water bills for consumers in London have been a huge debate. Every customer under the water facilities company, Thames Water pays an extra £25 on top of their water bill annually to contribute to the project. Numerous customers are worried that the amount will add to the financial strain on households in a city with steep living costs.

Additionally, the construction phase has posed logistical challenges in densely populated areas, stirring debate about the project’s overall impact on local communities and the environment.

These issues highlight the complexities of balancing large-scale urban development with environmental and social considerations.

London’s ‘Super Sewer’ is a transformative water infrastructure development that will improve the River Thames’ water quality and address environmental concerns. As of today, main construction works for all sections of the 25km Thames Tideway Tunnel have been completed and is on track for completion in 2025.

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