Surface Water Drainage Strategy
When is this required:
A surface water drainage strategy is required for:
- All Major developments
- Minor development within an area liable to flood from all sources of flooding including surface water, ground water or flood zones 2 and 3.
- Minor development that is likely to increase flood risk locally and falls within a Critical Drainage Area
What information is required:
To ensure the Local Planning Authority (LPA) can determine an application in a timely manner, and for the Lead Local Flood Authority (LLFA) to be able to fulfil its role as a statutory consultee, it is necessary for sufficient surface water drainage information to be submitted in support of an application.
Different requirements depending upon whether the application is a major or minor application (as set out in: Article 2(1) of the Town and Country Planning (Development Management Procedure) (England) Order 2010.
Major Planning Applications
In addition to any requirement for a Flood Risk Assessment (FRA), the following information with regard to surface water drainage must be submitted as part of a major planning application in order for the application to be accepted as valid.
Outline Planning Applications
Any outline application for a development falling within the definition of ‘major’ shall be accompanied by a drainage strategy.
Information to include:
- indicative sustainable drainage principles for the development
- topographical survey showing how water naturally flows on the site together with groundwater and land drainage flows
- proposed destination for surface water post-development
- ground investigation results for infiltration (if appropriate)
- existing and/or proposed watercourses
- existing and/or proposed surface water sewers and/or pumping stations
- surface water flows onto the site, flows from the site and flood risk to and from the site
- offsite works which may be required to provide surface water drainage or mitigate against flood risk
- sensitive receptors
- general maintenance principles
Full Planning Applications
Detailed Drainage Strategy (and FRA if appropriate)
To include (in addition to details required for an Outline application above) the following additional information:
- details of compliance with the Defra non-statutory technical standards
- off-site works
- consents required
- flow paths through the development
- surface water storage volumes and locations
- sub-catchment areas
- treatment train components
- proposed landscaping and/or vegetative systems
- design calculations for:
- greenfield run-off
- brownfield run-off if appropriate (including reductions)
- peak flow rates
- surface water volumes
- storage requirements
- drain down times
- multi-use areas
- exceedance routes
- temporary drainage during construction climate change allowances
- future development allowances
- details of how the sustainable drainage system is to be maintained, and by whom, for the lifetime of the development
To ensure the Local Planning Authority (LPA) can determine an application in a timely manner, and for the Lead Local Flood Authority (LLFA) to be able to fulfil its role as a statutory consultee, it is necessary for sufficient surface water drainage information to be submitted in support of an application.
Different requirements depending upon whether the application is a major or minor application (as set out in: Article 2(1) of the Town and Country Planning (Development Management Procedure) (England) Order 2010.
Minor Applications
The Local Planning Authority may consult the Local Lead Flood Authority in respect of minor applications.
If the proposed development meets any of the following criteria, a Drainage Statement may be required, setting out how the development is to be drained:
- inclusion of a proposed adoptable highway
- creating impermeable area over more than 50% of the site
- development in Flood Zones 2 and 3
Further Information:
SuDS guidance - Flood Risk Management (devon.gov.uk)