Sustainable Urban Drainage Systems

Sustainable drainage systems (SuDS) are designed to manage stormwater locally (as close its source as possible), to mimic natural drainage and encourage its infiltration, attenuation and passive treatment.

SuDS are designed to both manage the flood and pollution risks resulting from urban runoff and to contribute wherever possible to environmental enhancement and place making. With this in mind, the multi-functionality and multiple benefits of SuDS should always be considered.

SuDS essentially operate through infiltration where possible and attenuation combined with slow conveyance. Many SuDS solutions employ a combination of infiltration and attenuation. Situations where infiltration is not an option, for example because of the soil type or contamination, tend to favour attenuation type SuDS.

Good SuDS design should follow the SuDS philosophy, which calls for the inclusion of a number of key principles:

1. A management train – using a number of SuDS components in series and characterising areas into land use and drainage type
2. Source control – managing runoff as close as possible to where it falls as rain
3. Managing water on the surface – wherever possible, runoff should be managed on the surface
4. Early and effective engagement – consider the use of SuDS at the earliest stages of site selection and design. 

Good practice with attenuation and slow conveyance type SuDS is to use ‘soft engineered' surface features rather than underground storage and to align the conveyance train with exceedence flood routing.

When SuDS are used in new developments with highways or retrofitted in existing developed areas where there is also highway drainage, the highway drainage arrangements will generally be a key theme which shapes the form of the SuDS. This is because highway run-off often forms a high percentage of the total run-off from developed areas and is also the surface water element that contains the highest level of pollutants.

Sustainable drainage systems (SuDS) mimic natural drainage processes to reduce the effect on the quality and quantity of run-off from developments and provide amenity and biodiversity benefits. When specifying SuDS, early consideration of potential benefits and opportunities will help deliver the best results.

• flood risk management – reducing the risk of flooding from development
• water quality management – reducing the impact of diffuse pollution
• improving amenity and biodiversity – the integration of green infrastructure with SuDS solutions can help to create habitat, recreational and biodiversity areas
• water resources – SuDS can help to recharge groundwater supplies and capture rainwater for re-use purposes
• community benefits – attractive, well designed public open space that incorporate SuDS can help to create better communities through social cohesion and quality of life improvements
• recreation – multi-purpose SuDS components can not only manage surface water, but also act as sports/play areas
• education – SuDS in schools provide a fantastic learning opportunity whilst also providing additional recreational space
• enabling development – SuDS can help to free up capacity in already established drainage networks, and the provision of SuDS can often be a prerequisite of planning permission.