Sustainable Drainage Systems

Proposed developments in Wales of more than one dwelling, or where the construction area is more than 100m2, must implement Sustainable Drainage Systems (SuDs). The national SuDs standards in Wales are mandatory and all designs need to be approved by the local SuDs Approval Body (SAB). The standards promote the use of above ground SuDs features, which may have a major influence on drainage strategies and development masterplans.

Due to the implementation of Schedule 3 of the Flood and Water Management Act 2010, the SuDs design standards are expected as part of the pre-application stage of the planning process. A SAB and formal application is made to the SAB approving officer at a similar time as the planning application is made. The determination period is seven weeks and no engagement is allowed to take place during the vetting period with the SAB officer.  It is advised to engage with the Council prior to a formal submission to avoid any time delays for the project.

The proposed drainage strategy for a project must be compliant with the 6 standards (S1 – S6) as set out by Welsh Government SuDs guidance:

Standard S1 – Surface Water Runoff Destination

This Standard addresses the use of surface water by the development and where it should be discharged. The aim is to ensure that runoff is treated as a resource and managed in a way that minimises negative impact of the development on flood risk, the morphology and water quality of receiving waters and the associated ecology. This will ensure that early consideration is given to the use of rainwater harvesting systems to both manage runoff and deliver a source of non-potable water for the site where practical. Where it is not, prioritisation should be given to infiltration. Discharges to sewerage systems must be limited where possible.

Priority Level 1 – Surface water is collected for use

Priority Level 2  – Infiltrate to Ground

Priority Level 3 – Discharge to a surface water body

Priority Level 4 – Discharge to surface water sewer or highway sewer

Priority Level 5  – Discharge to a combined sewer

Standard S2 – Surface Water Runoff Hydraulic Control

The aim of Standard S2 is to manage the surface water runoff from and on a site to protect people on the site from flooding from the drainage system for events up to a suitable return period, to mitigate any increased flood risk to people and property downstream of the site as a result of the development, and to protect the receiving water body from morphological damage.

Standard S3 – Water Quality

Standard S3 addresses the drainage design requirements to minimise the potential pollution risk posed by the surface water runoff to the receiving water body.

Standard S4 – Amenity

Standard S4 addresses the design of SuDS components to ensure that, where possible, they enhance the provision of high quality, attractive public space which can help provide health and wellbeing benefits, they improve liveability for local communities, and they contribute to improving the climate resilience of new developments.

Standard S5 – Biodiversity

Standard S5 addresses the design of SuDS to ensure, where possible, they create ecologically rich green and blue corridors in developments and enrich biodiversity value by linking networks of habitats and ecosystems together. Biodiversity should be considered at the early design stage of a development to ensure the potential benefits are maximised.

Standard S6 – Design of drainage for Construction, Operation and Maintenance and Structural Integrity

Standard S6 deals with designing robust surface water drainage systems so they can be easily and safely constructed, maintained and operated, taking account of the need to minimise negative impacts on the environment and natural resources.