What are SUDS?
Sustainable drainage systems (SuDS) include a range of sustainable methods of dealing with surface water run-off from new and existing developments. They aim to infiltrate as much water as possible back into the ground in order manage flood risk, improve water quality, protect against drought and maintain healthy aquifers.
There are also many other benefits for biodiversity, urban cooling, local amenity and climate change adaptation objectives. SuDS measures, such as green roofs, permeable paving, soakaways, filter strips, swales and ponds, aim to mimic natural processes by managing rainfall close to where it falls, storing runoff and releasing it slowly (attenuation), allowing water to soak into the ground (infiltration), slowly transporting water on the surface (conveyance) and filtering out pollutants.
SuDS should be selected based upon the predicted rainfall, the soil type (geology), the slope (topography), other sources of flood risk and the available space within the development site.
The new SuDS arrangements
The new arrangements for approving and implementing SuDS through the planning system took effect on 6 April 2015 through the implementation of Schedule 3 of the Flood and Water Management Act 2010. While ultimate responsibility for approving and securing the implementation of SuDS measures proposed as part of new developments remains with the local planning authority (LPA), the lead local flood authority (LLFA) is now a statutory consultee on all major planning applications.
As part of these changes, new ‘non-statutory’ national SuDS standards have been introduced and the Government’s National Planning Practice Guidance (NPPG) has been strengthened to make clear that SuDS should be delivered in all new developments.
The Council’s Minimum SUDS Performance Standards
In line with Policies 5.11 and 5.12 of the London Plan, the Mayor’s Supplementary Planning Guidance (SPG) on Sustainable Design and Construction and Policy DM7 of Sutton’s Site Development Policies DPD, all major developments should aim to achieve Greenfield runoff rates and volumes for all storm events up to and including the 1 in 100 yr 6-hr storm event (taking account of climate change) through application of the Mayor’s drainage hierarchy.
Although the volume of storage required to achieve the Greenfield runoff rate is likely to be quite high, this will assist the Borough in adapting to the future impacts of climate change. For more information on the Council’s approach to managing flood risk, visit the Flood risk evidence and information page.
Information Requirements on SuDS
All major planning applications should be supported by a completed Drainage Assessment Form (DAF) in order to demonstrate that the Mayor’s drainage hierarchy has been followed in seeking to deliver Greenfield run-off rates. The DAF provides a template for the run-off calculations and further details that are required alongside site drawings and other relevant drainage information.
Please note that although the DAF requests information on other sources of flood risk (such as fluvial, groundwater and sewer flooding), it does not in itself constitute a site specific Flood Risk Assessment (FRA) which should be prepared for all developments located within Flood Zones 2 and 3, major developments exceeding 1 hectare in Flood Zone 1 and all developments within a critical drainage area (CDA). Where appropriate, both documents should be submitted.
The Council offers a pre-application advice service to enable developers and their agents to acquire clear, impartial professional advice, at an early stage, regarding any key issues. Early LLFA and/or EA input can be secured using this service in order to ensure that flood risk management strategies, including SUDS, are considered from the earliest stages of project planning and design.
Full details of the pre-application services available, costs and timescale can be accessed on the Seek planning advice page.
How will your application be assessed?
There is no need to contact the LLFA separately when applying for planning permission. All supporting documents, including the DAF and site-specific FRA (where required) should be submitted to the LPA as usual who will contact the LLFA as a statutory consultee.