Sustainable urban drainage


Sustainable urban drainage systems (SUDS) have been developed to improve drainage and reduce the volume of surface runoff in urban areas. The use of green space in the design of SUDS allows water to be controlled using trees and vegetation, green roofs, ponds and wetlands. Green roofs can especially be implemented in order to increase interception, storm water storage and evaporation in highly urbanised areas where the space to introduce green infrastructure is restricted.

Alongside a reduction in the risk of flooding, SUDS in the urban landscape can also provide other environmental and ecological benefits. The inclusion of green space within SUDS can also contribute to noise reduction, air filtering and provide an aesthetically pleasing communal green space. Furthermore, green roofs have been found to support a wide variety of insects and birds, and wetlands can support aquatic species.

Financial incentives are offered for roof greening in European countries such as Germany. Cost analyses have shown that well-designed and maintained SUDS are more cost effective to construct and cost less to maintain than traditional drainage systems. The incorporation of SUDS in urban areas would help reduce the annual cost of flooding in the UK which is currently £54.6 million a year.


SUDS can be more effective than conventional drainage methods because they:

  • Reduce runoff, thereby reducing the risk of flooding
  • Improve water quality
  • Are in keeping with the environment and the needs of the local community
  • Provide a habitat for wildlife.

When used in conjunction with good management of the site, SUDS can prevent flooding and pollution.

SUDS can:

  • Deal with runoff close to the source
  • Manage potential pollution at its source no
  • Protect water resources from point pollution (such as accidental spills) and diffuse sources.

They can also allow new development in highly urbanised areas where existing combined sewerage systems are close to capacity.

Current situation

SUDS can be implemented in different urban settings, including hard-surfaced and soft landscaped areas. There are a variety of design options which allows planners to consider the local land use, future management and the needs of local people so that the drainage system is designed to be sustainable and site specific.

The four general structures for flood and pollution control are:

  • Basins and ponds
  • Filter strips and swales
  • Permeable surfaces and filter drains
  • Infiltration devices.

These structures also provide varying degrees of treatment for surface water runoff, using the natural processes of infiltration, adsorption and degradation.

Prevention – managing the site well can improve quality. Prevention includes design, maintenance and the education of users.

Filter strips and swales - vegetated surfaces that allow water to drain evenly off impermeable areas; swales are long shallow channels, filter strips are gently sloping areas of ground. Both of these features mimic natural drainage patterns by directing runoff through vegetation, slowing and filtering the flow.

Permeable surfaces and filter drains - have a volume of permeable material below ground to store surface water. Runoff flows into this storage area via a permeable surface, such as; Grass, Gravelled areas and Paving blocks.

Infiltration devices - soakaways, infiltration trenches and infiltration basins which drain water directly into the ground. Infiltration devices can easily be integrated into landscaped areas.

Further information

Other resources

Or for further information on good practice guidance for SUDS please refer to CIRIA – Sustainable drainage systems.

To find out about more on SUDS techniques, research, policy and guidance, see the Environment Agency Website.

Benefits of green infrastucture case studies