Thames Tideway Tunnel West

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Our role
Client challenges
Our approach
Key successes
Next steps and project legacy

Our role
Client challenges
Our approach
Key successes
Next steps and project legacy

Markets

Water
Location

London, UK
Client

BMBJV (Balfour Beatty, Morgan Sindall, Bam Nuttal Joint Venture)
Collaborators

Arup-Atkins Joint Venture (AAJV)
Completion date

Scheduled for completion in 2025

During the 1850s, when the London sewer system was built, London had a population of 2.5 million people. The Victorian architects who built the sewer, had the foresight to ensure the system could accommodate the waste of up to 4 million people. However, since then the population of London has exploded, and is now approaching 9 million people. It is no surprise that the sewer system could no longer cope under the strain of double the waste it was built to transport – untreated sewage would often leak into the Thames river when it rained.

That’s why the Thames Tideway tunnel, completed in 2025, was built. The tunnel forms part of the new London ‘super sewer’ improvement works aimed at making the River Thames cleaner and healthier by reducing the volume of untreated sewage overflowing into the river. The overall Thames Tideway Tunnel will connect to thirty-four of the most polluting overflows to capture sewage and transfer it to the Beckton sewage works, making it the biggest combined sewer project in the world.

Our role

AtkinsRéalis, as part of a joint venture with Arup, was appointed as a designer for the Thames Tideway West Tunnelling project under the Design and Build contract. Since the project began in 2015, AtkinsRéalis has supported both the contractor (BMBJV) and client by developing detailed construction designs and providing on-site support.

The Western section includes a 7km long tunnel with a 7.2m internal diameter, running along the River Thames from Acton Storm Tanks to Carnwath Road. It also features a 1.5km connection tunnel with a 3.2m diameter. Across seven worksites, the system intercepts combined sewage overflows, with each site including a drop shaft, tunnel connection, and underground chambers.

Client challenges

The key challenges faced by Tideway for Tideway WEST, were:

Designing a sewer system with a 120-year life span
Delivering the project within their available budget to strict timelines and planning constraints
Minimising impacts on adjacent structures and communities
Providing a lasting legacy of new urban spaces to reconnect London and its inhabitants to the River Thames.

Our approach

The AtkinsRéalis design team, as part of a joint venture with Arup, worked closely with BMBJV and Tideway to create practical, cost-effective solutions for building deep and complex structures next to active Thames water pumping stations and sewers. Their collaboration ensured the designs were strong and efficient, reducing the impact on nearby buildings, infrastructure, and utilities, while meeting the project's 120-year lifespan requirement.

To limit disruption to local communities along the route, the team carefully considered design constraints. They also invested significant effort into the landscape architecture at each site to create welcoming public spaces and help reconnect Londoners with the River Thames.

Throughout the design process, AtkinsRéalis partnered closely with Tideway and BMBJV to encourage collaborative working. This approach was supported by a structured and step-by-step design assurance process, from early planning through to final construction. The team used a shared 3D CAD/BIM platform to work together, making it easier to communicate and share design progress with stakeholders and third parties.

Thames Tideway Tunnel in numbers

1.6 Million M³

Capacity - equivalent to 600 Olympic swimming pools

33-66 M

Depth (a high-rise building is 35M)

95 %

Reduction in untreated sewage entering the Thames

9.4 M³

Sewage diverted from River Thames

Key successes

Established strong collaboration with Tideway and BMBJV from the outset of design services, fostering a unified approach that delivered optimal project outcomes.
Engaged proactively with key stakeholders and third parties to ensure alignment and transparency throughout the project lifecycle.
Advanced the design through a structured technical assurance process, integrating value engineering opportunities to enhance efficiency and cost-effectiveness.
Delivered design development and assurance within the parameters of DCO planning approvals, maintaining compliance and programme integrity.
Successfully minimised disruption to surrounding buildings, infrastructure, utilities, and local communities through thoughtful design and planning.
Leveraged 3D BIM technology to drive seamless collaboration, coordination, and communication across all project partners and stakeholders.
Designed and delivered high-quality urban realm improvements at each worksite, creating lasting public spaces that reconnect communities with the River Thames.

Next steps and project legacy

The project has reduced untreated sewage leaks into the river Thames by 95% and the sewers are currently undergoing storm testing.

As well as providing significant environmental benefits to the city of London, the project has created new public spaces, which will benefit local communities and leave a lasting legacy for London.