Background
London has a 'combined' sewerage system, which was masterminded by Victorian engineer Sir Joseph Bazalgette following the 'Great Stink' of London of 1858. At that time, the River Thames was effectively 'dead', but is now very much alive after many decades of clean up.
Learn more about the 'Great Stink'
Sewer overflows
The system was designed to overflow into the River Thames during periods of heavy rainfall to prevent sewage from backing up and flooding streets and buildings.
Today the overflows are happening much more frequently - on average more than once a week.
Annually 32 million cubic metres of diluted sewage is discharged, enough to fill the O2 (Millennium Dome) almost 15 times.
21st Century challenges
London's population has grown dramatically since Bazalgette's day and continues to rise.
An increase in paved areas means there is less space available to soak up rainfall, which has also increased the amount of rainwater run-off entering the sewers.
Climate change too is predicted to bring more frequent intense storms.
This all means that we have to take action now.
Background study
In 2000, the Thames Tideway Strategic Study (TTSS) was set up to consider the environmental impact of storm discharges to the tidal River Thames and to propose potential solutions that would comply with the EC Urban Wastewater Treatment Directive.
Thames Water, the Environment Agency, the Greater London Authority, Defra and Ofwat (as an observer), all contributed to the study, chaired independently by Engineering Consultant, Professor Chris Binnie.
The final report produced by the group in February 2005 can be downloaded in sections below.
TTSS: Executive Summary (0.25Mb)
TTSS: Steering Group Report (2.5Mb)
TTSS: Objectives Report - Volume 1 (0.42Mb)
TTSS: Objectives Report - Volume 2 (0.61Mb)
TTSS: Solutions Report - Volume 1 (0.64Mb)
TTSS: Solutions Report - Volume 2 (0.39Mb)
TTSS: Cost Benfit Report (1.0Mb)
After reviewing the report, Ofwat asked for further information. We produced a supplementary report and a summary of the findings in November 2005. These documents can be downloaded below.
Supplementary Report Summary (0.5Mb)
Government Regulator's Independent Review
In view of the scale of the project and the significant cost for our customers, Ofwat commissioned Jacobs Engineering Group Inc to carry out an independent review of the potential for less expensive and partial solutions to the problem. The final report published in February 2006 can be downloaded below.
Report submitted to Government
On the basis of the TTSS report and the independent review, the Government asked us to work up two options which we did. In December 2006, we submitted a report, detailing both options for tunnels to capture storm sewage discharges.
The various sections and a summary of this report are available to download below.
Tackling London's Sewer Overflows - Summary Report (0.56Mb)
Working Group: Objectives Report - Volume 1 (0.42Mb)
Working Group: Objectives Report - Volume 2 (0.61Mb)
Working Group: Solutions Report - Volume 1 (0.64Mb)
Working Group: Solutions Report - Volume 2 (0.39Mb)
Working Group: Planning and Environment Report (0.76Mb)
Working Group: Cost Benefit Report (0.43Mb)
Government decision
In March 2007, the Environment Minister at the time, Ian Pearson MP, asked us to proceed with the Thames Tunnel and Lee Tunnel urgently. The Defra report containing the Government decision can be downloaded below.
Defra Regulatory Impact Assessment (0.4Mb)
