Surface water

Surface water

Key points for surface water, in accordance with chapter 5 of the PPS25 Practice Guide, are:

• Surface water runoff should not increase flood risk to the development or third parties. This should be achieved by using Sustainable Drainage Systems (SuDS) to attenuate to at least Greenfield runoff or where possible achieving betterment in the surface water runoff regime. (The applicant should contact Local Authority Drainage Departments and/or the Lead Local Flood Authority where relevant for information on surface water flooding.)
• An allowance for climate change needs to be incorporated, which means adding an extra amount to flow calculations. 
• The residual risk of flooding needs to be addressed should any drainage features fail or if they are subjected to an extreme flood event. Overland flow routes should not put people and property at unacceptable risk. This could include measures to manage residual risk such as raising ground or floor levels where appropriate.
• An assessment of flood risk associated with ordinary watercourses may also be necessary as the Environment Agency’s Flood Zone Maps primarily show flooding from main rivers not ordinary watercourses.