Super-Sewer Debate: A Step Too Far for SuDS?

Written By: Market Development Director, Hydro International.

Aerial Photo of the River Thames

The extent and passion of the debate over the proposed £4.1 billion Thames Tunnel “super sewer” has highlighted the mountain still to climb in reaching a vision for integrated urban water management in the UK which can be shared and owned by all stakeholders including planners, designers, the water companies and the general public.

Thames Water plans to build the 15.5mile long tunnel to solve the problem of 39 million cubic metres of raw sewage polluting the Thames from Combined Sewer Overflows (CSOs) during peak rainfall every year.   

A detailed report by Lord Selborne’s Thames Tunnel Commission (sponsored by the London boroughs most critical of the proposals) was published on 31st October, just days before Phase 2 consultation for the tunnel began. The report proposes an alternative solution based on a shorter tunnel combined with a mix of green infrastructure and Sustainable Drainage (SuDS) solutions.

Then, a CIWEM debate in December proposed by Prof Richard Ashley and Lord Selborne on the motion: “This house considers that the Thames Tunnel would be worse value than controlling rainwater near source” was roundly defeated.

Richard Aylard Thames Water’s external affairs and sustainability director, who argued against the motion, is reported to have commented after the debate: that “the overwhelming view from the floor was that it’s not a question of having either the Thames Tunnel or SuDS, we need both.”

As a relative bystander in this process, and in my role as convenor of the British Water SuDS focus group, what strikes me most about this whole affair is two things:  Firstly, the strength of feeling of respected professionals on both sides.  Secondly a temptation to polarise the debate into a “text book” battle between traditional ‘end-of pipe’ approaches and arguably more sustainable source control solutions on the other.  

Understandably what drives the debate is the urgency of relieving pollution in the Thames as quickly as possible and environmental groups have argued strongly in favour of the tunnel proposal. Richard Aylard himself famously warned the comedian David Walliams not to complete the last leg of his charity Thames Swim into central London.   

Yet, it is also true that many other modern Western cities have now moved away from large tunnel schemes in favour of more “water sensitive” solutions incorporating green infrastructure and SuDS. I must say, the Selborne report argues eloquently enough in favour of Green Infrastructure solutions and of the multiple benefits of urban stormwater management based on the principles of Water Sensitive Urban Design (WSUD). These, I understand to be fundamental to the Government’s vision outlined in the Natural Environment White Paper.

The vision of Water Sensitive Urban Design is promising a future for our cities in which stormwater is considered more of a resource within the context of an integrated solution to water management, which goes much further than simply conveying excess flows or holding back surface water flooding. Instead of being a waste product to be swept quickly away underground, stormwater can help deliver multiple values for local communities from water recycling and reuse, improved ecology and more attractive urban environments.

A blog is neither the time nor place for detailed arguments of the pros and cons of the Tunnel proposals, and far greater experts than I have spent a long time preparing detailed analyses. Nevertheless, for a true believer in SuDS such as myself, I live in hope that we can still bring water sensitive solutions, including retrofit SuDs into our capital city. I hope we will be bold enough to encourage disconnection of stormwater runoff from roofs, roads and developments from the sewer network and deal with it instead through more localised source-control, addressing quality, quantity and amenity requirements.  

I think most of us in the industry who have been working for many years to promote SuDS would agree that we have made substantial progress in countering those who suggest SuDS are not up to the task.  The result, I’m pleased to say is, a much more positive acceptance to SuDS in general, including by Government and policymakers, and an understanding of the need for retrofit solutions.

But there is still a long way to go.  It seems unlikely that the super-sewer project is going to change direction completely to a WSUD alternative at this late stage in the project’s evolution. It would certainly take an unprecedented leap in faith, courage, commitment and public education to achieve the goals of the alternative proposals.     

Twenty years ago, Hydro International (then HRD Ltd.), first published “Urban Drainage – the Natural Way” and argued for a change in paradigm from urban solutions which conveyed stormwater through combined sewer networks to end-of pipe wastewater treatment works, to at-source attenuation and infiltration with treatment of pollutants and sediments.  Looking back, those early arguments in favour of SuDS still seem prophetic.    

As we look forward with optimism to the year ahead, we hope to see some important steps forward in the adoption and implementation of SuDS in the UK.   The Thames Tunnel affair should, at the very least, spur us on to future progress, without dwelling too much on what might have been…

Phase two of Thames Water’s Consultation on the Tunnel project runs from the 4 November 2011 to the 10 February 2012.  Visit the website.

Read the Selborne Commission report.

Read Thames Water’s Response to the Selborne Commission.

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