Surface Water Drainage

All major development is required to use sustainable drainage systems (SuDS) for the management of surface water run-off. Where site specific Flood Risk Assessments are required in association with development proposals, they should be used to design appropriate systems and determine how SuDS can be used on particular sites.

What are sustainable drainage systems?

The main purpose of sustainable drainage systems is to mimic the natural drainage of a site before development.  This is achieved by capturing rainfall and allowing as much of it as possible to evaporate or soak into the ground close to where it fell. The rest is directed through a SuDS management process, which improves water quality, to the nearest watercourse to be released at the same rate and volumes as before development.

There are many different sustainable drainage system features available to suit the constraints of a site. These include green roofs, more natural features such as ponds, wetlands and shallow ditches called swales. Hard engineered elements are often used in high density, commercial and industrial developments.  These include permeable paving, canals, treatment channels, attenuation storage and soakaways.

General SuDS Advice for Developers in Oxfordshire

The demands of each individual development will lead to a wide variety of solutions. Understanding Oxfordshire County Council’s priorities in terms of SuDS will help ensure the solutions are appropriate to our requirements.

It is important that developers establish the geological and hydrological conditions of their site at an early stage through ground investigations, before coming to any conclusions about the suitability of any particular SuDS system.

SuDS incorporate cost-effective techniques that are applicable to a wide range of schemes, from small developments to major residential, leisure, commercial or industrial operations with large areas of hard standing and roof. They can also be successfully retro-fitted into existing developments.

We provide a pre-application advice service for developers and consultants on SuDS and surface water. More information on this can be found here: Pre-application flood advice on major planning applications | Oxfordshire County Council.

Local Standards and Guidance for Surface Water Drainage on Major Development in Oxfordshire

We have published local guidance intended to assist developers in the design of all surface water drainage systems, and to support Local Planning Authorities in considering drainage proposals for new development in Oxfordshire. The guide sets out the standards that we apply in assessing all surface water drainage proposals.

Please download the Local Standards and Guidance for Surface Water Drainage on Major Development in Oxfordshire for more information.

Please note that this guidance is a ‘live’ document which will be continually updated and improved, therefore please ensure you are using the most recent version. The current version is: v1.2 December 2021.

Planning Applications: What OCC would like to see

Detailed guidance relating to the information we would like to see in any Flood Risk Assessment or Drainage Strategy is provided in our Local Standards and Guidance for Surface Water Drainage on Major Development in Oxfordshire.

The Local Planning Authority may have additional requirements for planning submissions so you should contact the relevant District Planning Authority prior to submitting an application.

Under the revised planning guidance, SuDS must be included in any new development unless demonstrated inappropriate. If a traditional (below-ground piped) drainage system is proposed over a sustainable drainage system, the onus is on the applicant to provide evidence to demonstrate that SuDS would be inappropriate for the development. If we are not satisfied with the evidence provided, we may object to the proposal.

Further information

The SusDrain website, an online community for sustainable drainage, contains a whole host of resources relating to the design and management of SuDS, alongside a range of case studies.

SuDS Approval Body and Schedule 3 FWMA 2010

On 10th January 2023, the Defra published “the Review for implementation of Schedule 3 to the Flood & Water Management Act 2010;” this recommended implementation of Schedule 3 and the government has accepted this recommendation. Under Schedule 3, Oxfordshire County Council will take on the role of the SuDS Approval Body (SAB), responsible for approval of sustainable drainage systems (SuDS) then adopting and maintaining features following construction.

It is expected that Schedule 3 will drive a step-change in the design of holistic SuDS systems. SuDS should meet all four pillars of water quantity, water quality, amenity and bio-diversity, being dispersed around a site and not concentrated into single, large attenuation features.

It is anticipated that implementation will be during 2024 with further consultations taking place through 2023 to determine statutory instruments, regulations and technical standards. Some of this is presumed to be undertaken by central government and others parts of process development will be undertaken by OCC in its role as the SAB. OCC Lead Local Flood Authority Team will announce more information as it becomes known.