Thames Tideway Tunnel

Thames Tideway Tunnel
Overview
LocationInner London
StatusCompleted
StartActon
EndLee Tunnel, Abbey Mills, near Stratford
Operation
Work begun2016[1]
ConstructedVarious (see article)
Opens2025[2]
Owner
  • Bazalgette Tunnel Ltd
  • (trading as Tideway)
OperatorBazalgette Tunnel Ltd
CharacterCombined sewer
Technical
Design engineerVarious (see article)
Length25 km (16 mi)
Highest elevation−30 m (−98 ft) at Acton
Lowest elevation−70 m (−230 ft) at Abbey Mills
Width7.2 m (24 ft)
CSOs intercepted34
Cost£5 billion (2024 estimate)
Proposed route. Black arrows show direction of boring machine movement, not flow of sewage

The Thames Tideway Tunnel is a deep-level sewer along the tidal section of the River Thames in London, running 25 kilometres (16 miles) from Acton in the west to Abbey Mills in the east, where it joins the Lee Tunnel which connects to Beckton Sewage Treatment Works. The tunnel is designed to capture almost all the raw sewage and rainwater from combined sewers which would otherwise overflow into the river during heavy rain. The sewage can be stored in the tunnel until it can be treated at Beckton.

Construction of the Tideway Tunnel began in 2016 and the first sewage flowed into the tunnel in September 2024.[3] It is expected to be fully operational in 2025 at a cost of £5bn.[4]

The main tunnel has an internal diameter of 7.2 m (24 ft) and runs at a depth of between 30 m (98 ft) at the western end, and 70 m (230 ft) in the east. The tunnel will drain 34 of the most polluting combined sewer overflows and is expected to lead to the overflows operating for 3.7% of the time on a maximum of four days per year at the time of commissioning.

Bazalgette Tunnel Limited (BTL) is the licensed infrastructure provider for its finance, building, maintenance and operation. It has as investors: Allianz, Amber Infrastructure, Dalmore Capital and DIF. Since the licence award, it also trades as Tideway. On 3 November 2015, the award was made by Ofwat, ensuring the start of the project.[5]

Started in 2016, the project was due to be completed by 2024.[1][6][7] The COVID-19 pandemic delayed this to early 2025.[2]

The estimated capital cost – excluding financing, operations and maintenance  – was £3.8bn with an additional £1.1bn for preparatory works.[8] Due to the COVID-19 pandemic, additional costs of £233m were incurred.[2] The 2021-22 annual report gave an updated cost of £4.3bn.[9] The final cost was £5bn.[4]

  1. ^ a b "Timeline". Tideway London. Archived from the original on 12 February 2019. Retrieved 10 November 2019.
  2. ^ a b c Cite error: The named reference TCI-25Aug2020 was invoked but never defined (see the help page).
  3. ^ "Thames Tideway Tunnel: Gates open on super sewer". BBC News. 14 October 2024. Retrieved 14 October 2024.
  4. ^ a b Cite error: The named reference BBC-27Mar2024 was invoked but never defined (see the help page).
  5. ^ "Green light for £4.2bn London 'super sewer'". Thames Tideway Forum. 3 November 2015. Archived from the original on 17 November 2015. Retrieved 15 November 2015.
  6. ^ "Green Light for examination of Thames Tideway Tunnel Proposal". Thames Water. 27 March 2013. Archived from the original on 7 June 2013.
  7. ^ "Timeline". Tideway. Retrieved 16 September 2019.
  8. ^ "Who will pay for the Thames Tideway Tunnel?". Thames Water. Archived from the original on 1 April 2019. Retrieved 10 November 2019.
  9. ^ "Tideway Annual Report 2021-22" (PDF). Bazalgette Tunnel Ltd. p. 6.