Policy information sourced from Wandsworth Development Planning Management Policies Document
DMS 6 Sustainable Drainage Systems
As outlined in Policy DMS3, all new developments should seek to incorporate Sustainable Drainage Systems SuDS) or demonstrate alternative sustainable approaches to the management of surface water. Applications for developments located within flood zones 2, 3a and 3b, 1ha in size or greater, or where flooding in a 1 in 30 event is predicted to result in flood depths exceeding 300mm in flood zone 1 must be accompanied by a Flood Risk Assessment which addresses the criteria listed below. All other developments should have regard to the following criteria:
- application of a site wide sequential approach to development by locating buildings within the areas of lowest flood risk on a site in accordance with the areas set out within the LFRMS as areas with increased risk of surface water flooding;
- determination of potential overland flow paths and proposals for appropriate solutions to minimise the impact of development on surface water flooding. Road and building configuration should be considered to preserve existing flow paths and improve flood routing, whilst ensuring that flows are not diverted towards other properties elsewhere;
- application of SuDS measures to achieve at least 50% attenuation, aiming for 100% attenuation of the undeveloped (existing) sites’ surface water run off at peak times, in accordance with the preferred standard in the Mayor’s Sustainable Design and Construction SPG. Applications for development in sites located within Critical Drainage Areas set out in the Surface Water Management Plan/LFRMS should provide a drainage strategy outlining how surface water will be managed to demonstrate the safe attenuation of surface water utilising SuDS where possible, for rainfall events up to the 1 in 100 year plus climate change level;
- in areas with increased risk of surface water flooding within Critical Drainage Areas, a FRA should contain measures to mitigate off site surface water flooding by aiming to achieve greenfield runoff rates (8 litres per second per hectare) or better. SuDS techniques should be applied with regard to the London Plan Sustainable Drainage Hierarchy outlined in Policy 5.13, or such guidance as supersedes it. Demonstrable justification should be provided on the extent to which each measure is being proposed;
- incorporation of soft landscaping and permeable surfaces into all new residential and non-residential developments. Retention of soft landscaping and permeable surfaces in front gardens and other means of reducing, or at least not increasing, the amount of hard standing associated with existing homes is encouraged. New driveways or parking areas associated with non-residential developments and those located in front gardens should be made of permeable material; consideration of the vulnerability and importance of local ecological resources (such as water quality and biodiversity) when determining the suitability of drainage strategies/SuDS;
- demonstration of the maintenance and long term management of SuDS through a SuDS Management Plan which should outline the on-going maintenance responsibilities and the measures to be put in place to undertake these. A Section 106 agreement or planning condition may be required to agree the long term management responsibilities of SuDS.
Where appropriate in new developments, the Council will seek contributions towards flood protection measures and SuDS, in accordance with Core Strategy Policy IS7, the Planning Obligations SPD and the CIL Regulations.
For more information please see the Development Planning Management Policies Document