Policy 5.13 Sustainable drainage
A Development should utilise sustainable urban drainage systems (SUDS) unless there are practical reasons for not doing so, and should aim to achieve greenfield run-off rates and ensure that surface water run-off is managed as close to its source as possible in line with the following drainage hierarchy:
1 store rainwater for later use
2 use infiltration techniques, such as porous surfaces in non-clay areas
3 attenuate rainwater in ponds or open water features for gradual release
4 attenuate rainwater by storing in tanks or sealed water features for gradual release
5 discharge rainwater direct to a watercourse
6 discharge rainwater to a surface water sewer/drain
7 discharge rainwater to the combined sewer.
Drainage should be designed and implemented in ways that deliver other policy objectives of this Plan, including water use efficiency and quality, biodiversity, amenity and recreation.
B Within LDFs boroughs should, in line with the Flood and Water Management Act 2010, utilise Surface Water Management Plans to identify areas where there are particular surface water management issues and develop actions and policy approaches aimed at reducing these risks.
5.57 There will also be increased surface water flood risk, with the likelihood of more intense storms. The Flood and Water Management Act 2010 gives London boroughs clearer responsibilities related to surface water flood risk. Implementation mechanisms including the national Sustainable Drainage Systems Standards are emerging. Moreover, the Drain London Forum brings together the key agencies involved in managing London’s drainage system and has delivered draft Surface Water Management Plans for every London borough. As the RFRA illustrates, it has also made significant progress in the understanding of surface water flood risk. In the meantime, the now well established sustainable drainage hierarchy contained within Policy 5.13 will lead to a steady reduction in the overall amount of rainfall being discharged to the drainage system. The sustainable drainage hierarchy in policy 5.13A is intended to ensure that all practical and reasonable measures are taken to manage surface water higher up the hierarchy (1 being the highest) and that the amount of surface water managed at the bottom of the hierarchy, is minimised. The hierarchy is designed to apply across the whole of London. In addition, green roofs (see Policy 5.11) can also make a contribution to sustainable urban drainage by absorbing a proportion of surface water and therefore reducing rates of water flow. Implementing such measures will not only reduce run-off but provide multiple benefits to London amenity, biodiversity and better water quality to name but three. Changes to the General Permitted Development Order 2008 restricting permitted development rights for impermeable surfaces within the curtilage of dwelling houses should also contribute to a reduction of surface water run-off.