In accordance with the National Planning Policy Framework a Surface Water Drainage Strategy is required when:
A development comprises 10 or more dwellings
A development site has a total area greater than 1 ha
The floor space to be created by a development is over 1000m2
A development comprises less than 10 dwellings but is located within :
an area identified at risk of flooding (including surface water) and / or
an area identified as having a critical drainage problem
A development proposes to increase the impermeable area at a site and the Local Planning Authority are concerned about the cumulative impacts of development in the area.
However, as a general trend, it is becoming increasingly common for Local Planning Authorities and Lead Local Flood Authorities to request surface water drainage strategies to accompany smaller applications where there is a change or increase in impermeable surfacing (eg. built footprint or paved area) at a site. Therefore, it is always worth checking whether a drainage strategy will be required before submitting your application.
Many Local Authorities have their own Local Policy Guidance which outline when a drainage strategy is required. These include:
The aim of a surface water drainage strategy is to assess how surface water runoff generated by a proposed development can be managed for the lifetime of said development (in the case of residential housing this is 100 years) so that future site users and third party land will not be at an increased risk of flooding as a result of your proposals. Factors such as Climate Change and the possibility of additional impermeable surfaced areas being created in the future (eg. a patio area or a driveway constructed at a later date by future owner/occupier), known as Urban Creep, need to be considered within the drainage calculations and accounted for within the sizing of the proposed SuDS system.
If you need any more information or assistance with a specific project please see our Surface Water Drainage Strategy product page here or get in touch at info@geoson.co.uk / 0117 441 4993.