157/10 Environment Secretary Caroline Spelman today gave her support to Thames Water’s plans for a tunnel to reduce the amount of raw sewage discharged into the River Thames.
The core of London’s sewage network was designed in the late 19th Century and was designed to overflow at times of heavy rainfall to ensure that sewage did not back up into houses and streets. Combined Sewer Overflows (CSOs) were intended to discharge the raw sewage into the Thames in the event of extremely heavy rain.
Increasing populations and changes to land use in London have lead to this occurring around 50 times per year. With further population growth and projected climate change, this figure is expected to increase in coming decades and spills could occur when there is very little rain. This also creates problems for the UK’s continued compliance with EU waste water treatment regulations.
On 22 March 2007, the then Minister for Climate Change and the Environment announced his support for a tunnel based solution to the problems in the Thames and asked Thames Water to take forward the design process for the Thames Tideway Project. This included the Lee Tunnel (a smaller tunnel on which construction work has begun), upgrades to sewage treatment works and the larger Thames Tunnel. In the intervening years Thames Water, the Environment Agency and Ofwat have worked together researching and analysing different options. Thames Water estimates that the proposed Tunnel will cost £3.6bn which could result in bill increases of around £60-65 per year for Thames Water customers.
Caroline Spelman said:
‘A tunnel continues to offer by far the most cost effective solution to the unacceptable problem of raw sewage being regularly discharged into the Thames. This is a large and complex project and I recognise that it comes at a significant cost. I will ensure that Defra and Ofwat continue to scrutinise the costs and options to ensure that Thames Water’s proposals represent proper value for money.’
Thames Water will shortly launch a consultation exercise on the need for the tunnel, the route and the sites needed to construct and operate the project. Defra carried out an Impact Assessment in 2007 and will update this before publishing the revised version of the document on the Defra website.
Notes to editors
1. A Written Ministerial Statement can be found on the Defra website here:
2. Sewage collection and treatment in the UK is largely determined by the requirements of the Urban Waste Water Treatment Directive (91/271/EEC) transposed into domestic law by the Urban Waste Water Treatment (England and Wales) Regulations 1994.
3. The controlled use of CSOs is a necessary part of combined sewer systems that collect both rainwater and sewage. Without them, sewer flooding of premises and roads and overloading of sewage treatment works could occur following heavy rainfall.
4. Recent investigations have shown that around 39 million cubic metres of storm water are discharged annually from the tideway CSOs with six of those 57 CSOs discharging on a weekly basis (50 – 60 times annually).
5. Currently under construction is the Lee Tunnel which runs from Abbey Mills pumping station to Beckton STW and will be completed in 2014. The Lee Tunnel and Beckton STW upgrade will reduce the total volume of discharges to the tideway by around two thirds. The Thames Tunnel is expected to be completed in 2020.
6. A separate consultation on the route of the Thames Tunnel is being carried out by Thames Water during September 2010.
7. Further information on the Tunnel can be found on the Defra website at:
Phone: For enquiries please contact the above department