Knowledge Framework
Use Cases
- Detect and report sewage overflows — Identify when combined sewer overflows (CSOs) discharge untreated sewage into rivers or coastal w...
- Collect real-time system data — Gather continuous readings from sensors across the water network — pressure, flow, quality, and e...
- Detect pollution events in waterways — Identify contamination of rivers, lakes, or coastal waters from sewage, industrial discharge, agr...
Decision Patterns
- Deep storage tunnels — Store excess wastewater underground
- Continuous monitoring networks — Track system events continuously
- Water quality monitoring networks — Monitor environmental conditions
System Models
Leakage & loss models
Tool: InfoWorks ICM — Simulates sewer flows, CSO events, and storage capacity
Water quality models
Tool: Thames water quality models — Tracks dissolved oxygen recovery from reduced CSO discharges
Overview
The Thames Tideway Tunnel is a 25 km storage and transfer tunnel running beneath the River Thames through central London. It is designed to intercept the most polluting combined sewer overflows (CSOs) that currently discharge a mixture of raw sewage and rainwater directly into the tidal Thames.
London’s sewer system, largely designed by Sir Joseph Bazalgette in the 1860s, was built for a population of around 4 million. With London’s population now exceeding 9 million, the combined sewers overflow into the Thames around 60 times a year, discharging approximately 39 million tonnes of untreated sewage annually. The Tideway Tunnel captures these overflows and transfers them to Beckton Sewage Treatment Works for treatment.
The tunnel runs at depths of up to 65 metres below ground, with an internal diameter of 7.2 metres, and connects to the existing Lee Tunnel (completed 2016) at Abbey Mills Pumping Station.
Timeline & Location
2001: Thames Tideway Strategic Study commissioned. 2007: Tunnel solution selected as the preferred approach. 2014: Development Consent Order granted. 2015: Bazalgette Tunnel Limited (Tideway) established as a separately regulated infrastructure provider. 2016: Construction begins with three main drive sites. 2024: Tunnelling completed. 2025: System commissioning and handover to Thames Water for operation.
The project involved construction at 24 sites along the Thames, with three main tunnel boring machine launch sites at Fulham, Battersea, and Bermondsey.
Stakeholders
The tunnel is owned by Bazalgette Tunnel Limited (Tideway), a separately licensed infrastructure provider regulated by Ofwat. Once commissioned, it is operated as part of the Thames Water sewer network.
The project was delivered by three joint venture contractors: BMB (west section), FLO (central section), and CVB (east section). Financing was provided through a bespoke regulatory framework with government support, attracting investment from pension funds and sovereign wealth funds.
Key stakeholders include the Environment Agency, Greater London Authority, Port of London Authority, and local London boroughs along the route.
Digitalisation & Data
The Tideway project employed advanced digital technologies throughout construction and will support ongoing operations:
Building Information Modelling (BIM)
Full BIM Level 2 implementation across all three construction joint ventures, enabling coordination of complex underground works beneath an active river and dense urban environment.
Real-Time Monitoring
SCADA systems monitor tunnel flows, water levels, and CSO interception. The system integrates with Thames Water’s existing telemetry network for operational decision-making.
Environmental Monitoring
Continuous water quality monitoring in the Thames tracks the impact of reduced CSO discharges on dissolved oxygen levels and aquatic ecology.
Hazards
Exogenous Hazards
Increasing rainfall intensity due to climate change places greater pressure on combined sewers and increases CSO frequency. Population growth in London continues to add demand beyond original sewer design capacity.
Endogenous Hazards
Ageing Victorian sewer infrastructure with limited capacity. Complexity of tunnelling beneath an active tidal river through varied London geology including chalk, clay, and gravel.
Cost & Benefit
Cost: Approximately £4.3 billion (2014 prices), funded through Thames Water customer bills with a bespoke regulatory model. The average household bill impact is around £20–25 per year.
Key Benefits: Captures 94% of the sewage that currently overflows into the Thames. Reduces annual CSO discharges from approximately 39 million tonnes to around 2.4 million tonnes. Significantly improves dissolved oxygen levels and ecological health of the tidal Thames. Helps the UK meet the EU Urban Waste Water Treatment Directive requirements.
Resilience Principles Assessment
Assessment of meeting Principles of Resilient Infrastructure
Proactively Protected (P2)
The tunnel provides a major capacity uplift to London’s sewer system, designed to handle growth and climate change projections to 2100. The 7.2 m diameter and 25 km length provide significant storage volume during storm events.
Environmentally Integrated (P3)
The primary purpose is environmental restoration of the River Thames. Construction included creation of new riverside public spaces and foreshore ecology enhancements at several sites along the route.
Shared Responsibility (P5)
Innovative financing model with a separately regulated infrastructure provider (Tideway), government contingent financial support, and costs shared across Thames Water’s 15 million customers.
Socially Engaged (P4)
Extensive public consultation during planning, with legacy commitments including new public riverside walkways, improved foreshore access, and community investment programmes along the route.
Continuously Learning (P1) To Do
Details pending — operational monitoring data will inform future CSO management strategies.
Adaptively Transforming (P6) To Do
Details pending.
Futures
The Tideway Tunnel is expected to transform the ecological health of the tidal Thames. Post-commissioning monitoring will track water quality improvements and the recovery of aquatic ecosystems. The tunnel also provides a platform for future sustainable drainage strategy integration as London adapts to climate change.