Surface water drainage scheme, sustainable urban drainages (SuDS)
Used to ensure a satisfactory standard of surface water drainage for development and to minimise the risk of flooding.
All major applications and applications in areas at risk from flooding (Flood Zone 2 or 3) or adjacent to areas at risk of flooding and applications where development adjoins a highway.
The Lead Local Flood Authority is Cumbria County Council. We will consult them on planning applications that include the provision of Sustainable urban drainages (SuDS).
SuDS are an approach to managing rainwater falling on roofs and other surfaces through a sequence of actions. The key objectives are to manage the flow rate and volume of surface runoff to reduce the risk of flooding and water pollution. SuDS also reduce pressure on the sewage network and can improve biodiversity and local amenity.
SuDS is a departure from the traditional approach to draining sites. There are some key principles that influence the planning and design process enabling SuDS to mimic natural drainage by:
- storing runoff and releasing it slowly (attenuation)
- allowing water to soak into the ground (infiltration)
- slowly transporting (conveying) water on the surface
- filtering out pollutants
- allowing sediments to settle out by controlling the flow of the water
A surface water drainage scheme should include the following information:
- a metric scaled plan of the existing site
- a metric scaled topographical level survey of the area to metres above ordnance datum
- metric scaled plans and drawings of the proposed site layout identifying the footprint of the area being drained (including all buildings, access roads and car parks)
- the existing and proposed controlled discharge rate for a 1 in 1 year event and a 1 in 100 year event (with an allowance for climate change), this should be based on the estimated greenfield runoff rate
- the proposed storage volume (attenuation)
- information on proposed SuDS measures with a design statement describing how the proposed measures manage surface water as close to its source as possible
- geological information including borehole logs, depth to water table and/or infiltration test results
- details of overland flow routes for exceedance events
- a management plan for future maintenance and adoption of drainage system for the lifetime of the development