Water

4A.14 Sustainable drainage

The Mayor will, and boroughs should, seek to ensure that surface water run-off is managed as close to its source as possible in line with the following drainage hierarchy:

• store rainwater for later use
• use infiltration techniques, such as porous surfaces in non-clay areas
• attenuate rainwater in ponds or open water features for gradual release to a watercourse
• attenuate rainwater by storing in tanks or sealed water features for gradual release to a watercourse
• discharge rainwater direct to a watercourse
• discharge rainwater to a surface water drain
• discharge rainwater to the combined sewer.

The use of sustainable urban drainage systems should be promoted for development unless there are practical reasons for not doing so. Such reasons may include the local ground conditions or density of development. In such cases, the developer should seek to manage as much run-off as possible on site and explore sustainable methods of managing the remainder as close as possible to the site.

The Mayor will encourage multi agency collaboration (GLA Group, Environment Agency, Thames Water) to identify sustainable solutions to strategic surface water and combined sewer drainage flooding/overflows.

Developers should aim to achieve greenfield run off from their site through incorporating rainwater harvesting and sustainable drainage. Boroughs should encourage the retention of soft landscaping in front gardens and other means of reducing or at least not increasing the amount of hard standing associated with existing homes.