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London to build £4.2 billion super sewer
is it the best value for money?

Ian Byatt, a previous director general of water regulator Ofwat, accused the government of failing to investigate cheaper alternatives to the Thames Tideway super sewer.

River Thames from Westminster Bridge, looking west, (photo Tom Arthur),_London-17Aug2009.jpg
River Thames from Westminster Bridge, looking west, (photo Tom Arthur)
London has a combined system of surface water and sewerage drainage. Normally the system works well, with tertiary treatment of sewage before it goes into the River Thames, but the system dates back to Victorian times. After heavy rain, greater than 6 mm per hour, the system overloads and raw sewage is  discharged into the River Thames. At really high rainfall there can be localised flooding and this can happen weekly. 

With a rising population, increasing densification and unusual weather patterns associated with global warming there is increasing pressure on the existing system. In 2013  55m tonnes of sewage polluted the tidal River Thames, far higher than the average 39m tonnes that discharges in a typical year. There are over sixty incidents of sewage discharge each year.

One response has been to propose a Thames Tideway scheme with a wide 7.2m+ diameter storage-and-transfer tunnel built on the bed of the Thames from Acton in the west for 25km to Abbey Mills in the east. This £4.2 billion scheme was given the go ahead by central government on 12 September 2014.

Critics says that city-wide sustainable drainage (SUDS) and green roofs would be a more sustainable, and cheaper response to increased flooding.

Christian Sarrasin, from the environmental group, Clean Thames Now and Always has commented "We've concreted over all the cities and that's why we've got this issue with the Thames Tunnel," He said there were cheaper, greener alternatives to it that involved preventing stormwater flooding into the sewers in the first place, such as green roofs and porous asphalt roads that soaked up or stored water. 

Ian Byatt, a previous Director General of government water regulator Ofwat, accused the government of failing to investigate cheaper alternatives. He said: "What matters is not a particular project, but dealing with the problem.‘All the developments in sustainable urban drainage, which are being looked at and developed and used in America, more work should be done on that."

In 2013 Landscape Institute president Sue Illman, managing director, Illman Young said "I don’t doubt the super sewer will do what they say it will do, but I’m not convinced we need it."..."One of the problems with the design is that it has finite capacity and Thames Water admits there will still be some floodings of sewage into the Thames each year anyway. So we are building something we know is not going to deal with today’s problem completely and will cope even less well if the rainwater situation gets worse."..."The solution has to be a grey-green infrastructure initiative that utilises the sustainable drainage techniques we have at the moment – green roofs, rainwater gardens that slow the run-off into the sewers and improving our green spaces. Public buildings and office buildings could all be retrofitted. Lots of interventions locally can start to make a difference very quickly, while with the tunnel we’ve got 20 years of upheaval before we see any benefits."

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15. Sep 2014
Reported by Robert Holden, London



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