October 2024

Thames Rivers Trust – Briefing: An Overview of the Thames Tideway Tunnel Project

October 2024  

The Thames Tideway Tunnel, also known as the ‘super sewer,’ is a critical infrastructure project addressing untreated sewage overflows into London’s River Thames. Built to capture excess waste that overflows into the river during rain, the tunnel spans 25 kilometres under the Thames, from Acton to Abbey Mills, connecting with the Lee Tunnel to transport sewage for treatment at the Beckton Sewage Treatment Works. 

  • Dimensions: 7.2 meters in diameter and up to 67 metres deep. 
  • Expected Completion: 2025, with Bazalgette Tunnel Ltd managing construction and operation under regulatory oversight by Ofwat. 

 

Why the Thames Tideway Tunnel Is Necessary 

  1. Aging Infrastructure: London’s sewer system, designed in the Victorian era, cannot handle modern demands. The system overflows frequently—up to 39 million tonnes of sewage annually—into the river, risking health and harming the ecosystem. 
  1. Environmental Impact: Sewage spills reduce dissolved oxygen, kill fish, and impact the entire Thames ecosystem. Pollution harms recreational users and affects the visual appearance of the river, with sewage waste moving up and down the tidal river. 
  1. Legal Compliance: The UK must comply with the EU’s Urban Waste Water Treatment Directive (UWWTD) and Water Framework Directive (WFD). In 2012, the EU Court of Justice found the UK in violation of UWWTD. The Thames Tideway Tunnel is essential to comply with these directives and avoid potential fines. 

 

Benefits of the Thames Tideway Tunnel 

  • Environmental Restoration: The tunnel will capture 15.5 million tonnes of untreated waste that would otherwise flow into the river, improving dissolved oxygen levels and restoring the Thames as a functioning ecosystem. 
  • Public Health and Recreation: Cleaner water reduces health risks for recreational users and improves the river’s visual appeal. 
  • Legal and Financial Compliance: Ensures the UK meets its legal obligations, reducing the risk of substantial fines. 

 

Economic Impact and Public Support 

  1. Public Support: Surveys show strong support for the tunnel, with an estimated willingness to pay valued between £7.4 and £12.7 billion, covering environmental improvements and reduced health risks. 
  1. Economic Benefits: 
  • Job Creation: Around 4,250 direct jobs will be created during construction, with an additional 5,100 indirect jobs across related sectors. 
  • Housing and Development: The project will reduce infrastructure constraints, allowing for expanded riverside development. 
  • Long-term Growth: By improving London’s infrastructure, the tunnel enhances the city’s global appeal, supporting tourism and business. 

 

Alternatives and Their Limitations 

  • Other Solutions Considered: Options like converting combined sewer systems to separate systems, implementing Sustainable Drainage Systems (SuDS), or localized treatment facilities were evaluated but were found to be more costly, disruptive, and less effective in meeting environmental standards. 
  • Chosen Solution: The tunnel-based solution was chosen for its effectiveness, lower cost relative to other options, and faster implementation to achieve regulatory compliance. 

 

Project Financing and Costs 

  • Funding Model: Costs will be spread across Thames Water’s customer base, with an estimated annual increase of £20-£25 in customer bills. The project financing structure has reduced anticipated costs, and Thames Water’s affordability programs aim to minimize the impact on low-income households. 
  • Cost-Benefit Summary: The tunnel is estimated to cost £4.5 billion, justified by a projected economic benefit worth at least £7.4 billion, as well as the avoidance of fines. 

 

Updated Project Timeline and Key Stages 

  1. Approval and Planning (2014-2016): The project was approved in 2014, and site preparation took place across 24 sites from Acton to Abbey Mills. 
  2. Construction Start (2016): Full-scale construction began in 2016, with tunnelling and excavation using tunnel boring machines. 
  3. Completion of Major Tunnelling (2020): Tunnelling work was largely completed by 2020, with integration work ongoing. 
  4. Initial Operations (2023): In 2023, the first four sites began operation. During heavy rain on September 23, over 589,000 cubic meters of wastewater were captured. 
  5. Full Operational Capacity (Expected 2025): The system will be fully operational by 2025, reducing storm sewage spills by approximately 95% and supporting aquatic life in the Thames. 

 

Key Takeaways for Media 

  1. Essential Infrastructure: The Thames Tideway Tunnel is vital for preventing millions of tonnes of sewage from polluting the Thames each year, safeguarding public health and the river’s ecosystem.
  2. Economic and Social Benefits: Beyond environmental improvements, the project offers public health benefits, thousands of jobs, and supports London’s development. 
  3. Public and Legal Backing: With broad public support and necessity for regulatory compliance, the project’s benefits outweigh its costs.

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