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Sustainable drainage is a concept that includes long term environmental and social factors in decisions about drainage. It takes account of the quantity and quality of runoff, and the amenity value of surface water in the urban environment. Many existing urban drainage systems can cause problems of flooding, pollution or damage to the environment and are not proving to be sustainable.
Sustainable development and Local Agenda 21 was introduced to manage the balance between social, economic and environmental requirements minimising the conflict that can exist between economic development and the protection of the environment.
Sustainable development was the central theme of the UN Earth Summit at Rio de Janeiro in 1992, which called on governments to produce their own strategies for sustainable development. In the UK, the Government updated its national strategy in May 1999. Parallel to this the Local Government Management Board has published Local Agenda 21 - A framework for local sustainability. Local authorities have their own Agenda 21 strategies.
Cities, towns and villages create demands on the environment by using resources and producing waste. The built environment is therefore one area where the strategies of sustainable development should be put into practice.
Built-up areas need to be drained to remove surface water. Traditionally this has been done using underground pipe systems designed for quantity, to prevent flooding locally by conveying the water away as quickly as possible. The alteration of natural flow patterns can lead to problems elsewhere in the catchment. Water quality issues have become increasingly important, due to pollutants from urban areas being washed into rivers or the groundwater. Once polluted, groundwater is extremely difficult to clean up. Conventional drainage systems cannot easily control poor runoff quality and may contribute to the problem. The amenity aspects, such as water resources, community facilities, landscaping potential and provision of varied wildlife habitats have largely been ignored. Conventional drainage systems are not designed with these wider considerations in mind. Continuing to drain built up areas with limited objectives and ignoring wider issues is not a sustainable long-term option causing an impact on the terrestrial and aquatic environments.
Drainage systems can be developed in line with the ideals of sustainable development, by balancing the different issues that should be influencing the design. Surface water drainage methods that take account of quantity, quality and amenity issues are collectively referred to as Sustainable Drainage Systems (SUDS). These systems are more sustainable than conventional drainage methods because they:
They may also allow new development in areas where existing sewerage systems are close to full capacity, thereby enabling development within existing urban areas.
Urban drainage is moving away from the conventional thinking of designing for flooding to balancing the impact of urban drainage on flood control, quality management and amenity.
(July 2005)