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19 January 2009

Environment Agency - Home

Sustainable Drainage Systems

Find out about SUDS techniques, research, our policy and guidance.

This section:

  • explains the problems with traditional drainage practices
  • outlines why SUDS offer a more sustainable option for drainage
  • provides links to sources of further information.

Harmful effects of traditional drainage

Traditional drainage is designed to move rainwater as rapidly as possible from the point at which it has fallen to a discharge point, either a watercourse or soakaway.

This approach has a number of harmful effects:

  • Run-off from hard paving and roofing can increase the risk of flooding downstream, as well as causing sudden rises in water levels and flow rates in watercourses.
  • Surface water run-off can contain contaminants such as oil, organic matter and toxic metals. Although often at low levels, cumulatively they can result in poor water quality in rivers and groundwater, affecting biodiversity, amenity value and potential water abstraction. After heavy rain, the first flush is often highly polluting.
  • By diverting rainfall to piped systems, water is stopped from soaking into the ground, depleting ground water and reducing flows in watercourses in dry weather.

As a result, many urban watercourses are lifeless and unattractive, and are often hidden in culverts under the ground.