Sustainable drainage systems (SuDS) are the preferred approach for managing rainfall from developed surfaces and can be used on any site. The aim of SuDS is to bring together benefits for flood risk, water quality, biodiversity and amenity when implementing surface water drainage.
This is achieved by capturing rainfall and allowing as much as possible to evaporate, be absorbed by plants or soak into the ground as close as possible to where it fell. The rest is directed to the nearest watercourse (preferably) or sewer to be released at the same rate and volumes as before development.
Between falling to the ground and entering the nearest watercourse or sewer, any pollutants, including hydrocarbons, heavy metals and silts, are reduced by natural processes, helping to protect the environment.
By providing open and vegetated drainage systems, SuDS can also provide green open spaces in the urban environment so new developments are more pleasant places to be for those living, working and visiting them.
SuDS replace traditional piped drainage systems which direct runoff from paved surfaces quickly below ground and to the nearest watercourse. SuDS aim to return to a more naturalistic runoff from new developments by reducing peaks in surface water runoff.
SuDS can take many different forms depending on the site in question and the opportunities and constraints posed on the site. Examples have been published online by Susdrain, a community and resource base for those involved in delivering SuDS. A collection of SuDS case studies can be found by visiting the Susdrain website.
Broadly speaking, a SuDS design for any given site may include may include:
Information, including the advantages, disadvantages, constraints and maintenance requirements of these features can again be found on the Susdrain website, in the ‘The SuDS Manual’ (CIRIA C697) or in the our SuDS Design and Adoption Guidance.
In line with existing government planning policy, we expect that SuDS are utilised on all new development sites wherever this is appropriate.
According to the national planning policy contained within the House of Commons: Written Statement (HCWS161), SuDS will be required on the following developments unless demonstrated to be inappropriate:
It is recognised that new developments only form a very small part of the existing urban environment. The capacity of many traditional piped drainage systems built over many years has not kept up with the rate of development. As such, many surface water and sewer flooding issues exist partly as a legacy of traditional drainage techniques.
SuDS can be installed into existing developed areas, termed retrofitting, to take pressure off existing piped drainage systems and to make improvements to the rate and quality of runoff from urban areas. Retrofitted SuDS can also significantly improve the urban environment for people, directly affecting their quality of life.
In managing flood risk in Derby, we will always seek opportunities to retrofit SuDS to improve flood resilience and relieve pressure on existing drainage systems. We are currently seeking to retrofit SuDS in a number of locations in the city where opportunities have been identified for multiple benefits.