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Footprint: The Thames 'Super Sewer'

As London prepares to radically change its water systems, architects can seize an opportunity, writes Richard Ashley

Around the world, the water that runs off streets in cities and towns is being managed in new and exciting ways.

In the Netherlands, the ‘Room for the River’ programme is creating new space for water in urban areas, recognising the futility of building new flood defences and ever larger sewers to cope with increasing rainfall due to climate change. This approach is taking hold in Europe, America, Australia and Asia in recognition that water is a resource not to be wasted.

By contrast, in the UK we put water into drains and sewers and evacuate it as quickly as possible. This approach was followed by Joseph Bazalgette’s re-sewering of London in the late nineteenth century. Large sewers were constructed parallel with the river Thames to convey both sanitary sewage and stormwater runoff to east London for treatment. This practice continues today.

Almost 60 combined sewer overflows stretch along the Thames from Hounslow to Woolwich and discharge virtually every time it rains in London, causing pollution and nuisance in the Thames.

In 1991, the European Commission published a directive on urban wastewater treatment that mandates the elimination of pollution from combined sewer overflows. Over the last decade, Thames Water has devised a £3.6 billion plan to clean up London’s overflows by constructing the Thames Tunnel, a 7.2-metre diameter tunnel along the bed of the Thames, into which discharges from the major polluting overflows can be directed during times of rainfall. The inflow will then be held until the rain abates, when it will be pumped out to treatment works at Beckton and Crossness, east of London. The current plan proposes connecting the 16 most polluting overflows to a 22-kilometre long tunnel.

Led by the London Borough of Hammersmith and Fulham, a commission of five boroughs was established in June to review the evidence for the tunnel. The commission will report its findings on 31 October prior to public consultation by Thames Water, which will begin in November.

There is considerable debate about the overall scale of the project and the value for money of some of the 16 overflows. An alternative approach would be to deal with excess water at or near source, prior to it entering drainage or sewer networks. This would not eliminate the need for a tunnel, but could significantly reduce its scope. Such an approach requires joined-up thinking between land use planners, urban designers, architects, landscape architects and engineers.

Looking abroad again, Philadelphia has opted for a small tunnel for the most intractable sewer overflows, while some 50 per cent of stormwater is handled by green infrastructure. The city’s surface water management has been directly linked to improving the public realm, green jobs, climate change mitigation and even crime reduction. The mayor has estimated that the added-value benefits to the community are some $3 billion (£1.9 billion) compared with a tunnel-only solution.

Thames Water is proposing a ‘big infrastructure’ approach. Despite promoting London as ‘the greenest city’, mayor Boris Johnson supports Thames Water’s position. Part of the challenge is that in England local authorities share only limited responsibilities for water, through planning for flood risk and the development planning process. Because drainage and water supply function is vested in private water companies, local authorities’ ability to integrate the full range of services is restricted.

Nevertheless, there are signs that green infrastructure is gaining momentum in the UK. The design of the Olympic Park is underpinned by a thorough water management strategy. Earlier this month, Defra launched the Green Infrastructure Partnership. This level of thinking needs to be applied to the Thames Tunnel project.

So what can architects do? You are in a pivotal position to ensure that services and infrastructure are considered holistically. This entails:

• Seeing stormwater as an opportunity to enhance the public realm rather than as a threat;

• Using stormwater close to its source in buildings;

• Using green roofs for slowing down runoff and improving water quality; 

• Ensuring that SUDS are the preferred option for draining
new developments;

• Addressing drainage considerations at the outset of a project.

All of the above are positive steps that can be taken now. But London must take heed of global exemplars and seize the opportunity of the Thames Tunnel to initiate a joined-up approach to urban water management.

A public debate on the Thames Tunnel will take place on 14 December at the Society of Chemical Industries, London. Visit www.ciwem.org for details 

Richard Ashley is professor of urban water and researcher at the Department of Civil and Structural Engineering, University of Sheffield

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