Policy information sourced from the Islington Development Management Policies

DM6.6 Flood prevention

A) Applications for major developments creating new floorspace and major Changes of Use that are likely to result in an intensification of water use are required to include details to demonstrate that Sustainable Urban Drainage Systems (SUDS) have been incorporated and meet the following design standards:

  • Quantity: schemes must be designed to reduce flows to a ‘greenfield rate’ of run-off (8 litres/second/hectare for Islington), where feasible. The volume of run-off that must be stored on site should be calculated based on the nationally agreed return period value of a 1 in 100 years flood plus a 30% allowance for climate change for the worst storm duration. Where it is demonstrated that a greenfield run-off rate is not feasible, runoff rates should be minimised as far as possible. The maximum permitted runoff rate will be 50 litres/second/hectare.
  • Quality: the design must follow the SUDS ‘management train’, maximise source control, provide the relevant number of ‘treatment stages’ and identify how the ‘first flush’ will be dealt with.
  • Amenity and biodiversity: the design must maximise amenity and biodiversity benefits, while ensuring flow and volumes of run-off entering open space are predictable and water at the surface is clean and safe. Schemes should maximise areas of landscaping and/or other permeable surfaces to support this.

B) Sites located in Local Flood Risk Zones (LFRZs) will be required to submit a Flood Risk Assessment (FRA) to assess the risk of flooding, particularly surface water flooding, taking climate change projections into account. Where the FRA indicates that an additional volume of run-off must be stored above and beyond the amount calculated based on the method above, this must be provided on site.

C) All minor new build developments of one unit or more are required to reduce existing run-off levels as far as possible, and as a minimum maintain existing run-off levels, including through the incorporation of SUDS.

D) Developments may be required to make contributions to addressing surface water flood risk, particularly where they are located in areas considered at high risk of surface water flooding and in exceptional cases where the SUDS quantity standards cannot be achieved on site.

See also Chapter 7 (Energy and environmental standards).

For more information please see the Islington Development Management Policies