Pre-planning Flood Risk Assessment and Preliminary Drainage Strategy to support an outline planning application of up to 250 dwellings at the site of Northumberland College in Ashington.
The Flood Risk Assessment determined that the site was at a low risk of flooding from rivers, surface water and sewers and that development was appropriate and sustainable as set out in the National Planning Policy Framework (NPPF) guidance.
A subsequent drainage strategy was then produced, in accordance with recommendations detailed in the Water Authority Pre-Planning Sewerage Enquiry response (from NWL), North-East Lead Local Flood Authorities Sustainable Drainage Local Standards and Building Regulations Part H, which followed the industry standard hierarchy, in order of surface water drainage priority, as detailed below:
- Use of SUDS
- Watercourse
- Public Sewer
As the planning application is outline only (with layout and design as reserved matters), the principles of the sustainable urban drainage system (SuDS) was key to determine the optimum locations of attenuation basins within the site, to ensure that the layout could accommodate these basins when hopefully progressed to a reserved matters planning application.
When specifying SuDS detention basins to determine the size, depth and volume, the designer has to consider current guidance from the Lead Local Flood Authority (LLFA) and Water Authority to ensure that the correct parameters are adhered to. In this instance the attenuations basins were designed to accommodate all storm events up to and including the 1 in 100-year storm event plus an allowance of 45% to accommodate climate change and an allowance of 10% for urban creep.
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