Policy information sourced from the Guildford Local Plan: Develpment Managment Policies
P11: Sustainable Surface Water Management
All development proposals
Drainage schemes are required to intercept as much rainwater and runoff as possible, including runoff from outside the site.
Greenfield sites are required to achieve runoff rates and volumes consistent with greenfield conditions. Previously developed sites are required to achieve runoff rates and volumes as close as reasonably practicable to greenfield runoff rates. In any case, runoff rates and volumes must be no greater than the conditions of the site prior to the development.
Development proposals are required to maximise the use of permeable surfaces across the development site.
Drainage schemes are expected to avoid the use of boreholes or other deep structures for the discharge of surface water to ground, except for clean roof water.
Major developments and developments in areas at risk of flooding
Development proposals are required to follow the discharge hierarchy and prioritise the use of Natural Flood Management (NFM) and Sustainable Drainage Systems (SuDS) for all surface water that is not captured for later use. Alternative drainage systems may be used only if there is clear evidence that SuDS would be inappropriate.
SuDS are required to be considered from the earliest stage of site design to ensure they are fully integrated into the development and that the greatest multifunctional benefits are realised.
When designing SuDS, development proposals are required to:
- follow the SuDS sustainability hierarchy;
- comply with the technical standards and design requirements set out in Defra’s nonstatutory technical standards for sustainable drainage systems;
- comply with guidance produced by the Lead Local Flood Authority;
- ensure that surface water runoff is managed as close to its source as possible;
- maximise biodiversity and amenity value, taking full advantage of opportunities for habitat creation and enhancement and improvements to water quality;
- incorporate a management treatment train to minimise risk of pollution to ground and surface waterbodies; and
- ensure that runoff from all hard surfaces receives an appropriate level of treatment.
Proposals for infiltration SuDS are required to:
- provide evidence showing that there is at least 1 metre of vertical distance between the base of the infiltration system and the maximum likely groundwater level.
- if located within Source Protection Zone 1, an area of known land contamination and/or an area with high seasonal groundwater, undertake a hydrogeological risk assessment where anything other than clean roof drainage is to be received.
For more information please see the Local Plan