Environmental Science & Engineering - www.esemag.com - September 2002
Comments? send them to the editor.

Why sustainable drainage is urgently needed

Serious floods are increasing around the globe

AquaCell system being installed beneath the surface of what will become a car park in a housing development.
Photo: Wavin Plastics

The day the Pope left Toronto in August, an intensive storm caused serious flooding in Toronto. Since then we have seen massive floods in Europe, China, Russia and other countries.

Lis Stedman, LPS special correspondent, UK, writes that draining urban areas so that run-off mimics nature instead of providing shock floods is becoming a pressing issue given the increasing frequency of storms throughout the world. But this is a complex issue. Sustainable urban drainage systems - or SUDs for short - can potentially provide a solution for a key climate change effect such as flooding caused by increased rainfall. As SUDs mimic nature in enabling water to sink into the ground rather than running off impermeable surfaces into rivers or drains, they are seen as a way of ameliorating an otherwise intractable problem.

In the United Kingdom, the government has provided impetus in the form of the publication Development and Flood Risks which provides planning guidance that backs the use of SUDs. The government’s recent periodic report TN3, on climate change, also suggests that SUDs should be given greater consideration.

The water industry in England and Wales is keen to get the issues resolved at the outset, in case the government is obliged to step in to say who will clean up pollution. The Water Framework Directive adds another dimension to the complicated picture of responsibility but the water industry is at pains to stress that it views SUDs positively, while stressing that implementation must be thought through carefully.

With SUDs very much a live issue, UK companies are coming up with innovative solutions that are leading the world in providing sustainable drainage solutions. The Construction Industry Research Association (CIRIA) is a major player in research into SUDs. CIRIA’s new SUDs website (www.ciria.org.uk/suds) runs through the different types of SUDs available and gives advice on their use. There is also a glossary of terms and case studies.

One example is Wessex Water’s headquarters in Bath, western England, that uses permeable paving in the car parks, porous blocks that filter through to soakaways and permeable grass paviors through which run-off filters into pipes and a storage tank.

A swale runs down the western edge of the site and this also drains to the main storage tank. Water from the tank is pumped back to soakaways at the top of the site and also feeds an ornamental water feature. Roof run-off and treated grey water are stored in three intermediate tanks and this water is used to flush toilets. CIRIA is providing specific technical guidance in its research project 637 called Source Control Using Constructed Pervious Surfaces - Hydraulic and Structure Performance.

Some manufacturers are producing systems to help house builders who need to reduce run-off so that they can build on sensitive plots of land. Wavin Plastics has introduced a new stormwater system, Garastor, to complement its awardwinning AquaCell stormwater control system. From a concept developed by Bryant Homes, Garastor uses the space under garages as a storage area for excess water during storms. It collects stormwater from roofs and drives in a prefabricated storage facility. A simple control unit regulates the inflow and outflow of water so that run-off is released into the traditional drainage system at a controlled rate.

AquaCell is also intended to aid stormwater control - this consists of 1.0m by 0.5m by 0.4m modules made from recycled polypropylene, in a matrix framework that gives a void to solid ratio of 95 to five per cent. The units clip together in layers to provide a robust infiltration basin that can be wrapped with a permeable geotextile to permit controlled release of water or an impermeable geomembrane so that it becomes a sealed storage unit.

For more information contact CIRIA at www.ciria.org.uk, or Wavin Plastics at www.wavin.co.uk

See our home page on how to order your subscription. We regret we can only accept orders from Canada and the United States.