15. Drainage Assessment
What is it?
Policy ENV4 of the Plan Strategy states that in all circumstances the Council will adopt a precautionary approach in assessing proposals in areas that may be liable to flood risk presently or in the future.
Policy ENV5 of the Plan Strategy states that all built development should include, where appropriate, SuDS measures to manage surface water effectively on site, to reduce surface runoff and to ensure flooding is not increased elsewhere.
A Drainage Assessment is a statement of the drainage issues relevant to a development proposal and the measures to provide the appropriate standard of drainage. The detail of the assessment will be proportionate to the nature of the proposal. (It may also be called a Drainage Impact Assessment).
When is it required?
In accordance with the Planning and Flood Risk Supplementary Planning Guidance, a Drainage Assessment should be provided for all development proposals that meet or exceed any of the following thresholds:
- new residential development comprising of 10 or more residential units; or
- a development site in excess of 1 hectare; or
- change of use involving new buildings and/or hardstanding surface exceeding 1,000 sqm in area.
A Drainage Assessment should also be provided for any development proposal, except for minor development, where:
- the proposed development is located in an area where there is evidence of a history of surface water flooding; or
- surface water run-off from the development may adversely impact upon other development or features of importance to nature conservation, archaeology or the built heritage.
What should be included?
Guidance on the information that should be contained in a Drainage Assessment is provided in Annex E of the Planning and Flood Risk Supplementary Planning Guidance.
