Flood risk and sustainable drainage for planning and development

As the Lead Local Flood Authority (LLFA) we have various duties as set out in the Flood and Water Management Act 2010.  

This includes providing responses to major development planning applications in relation to surface water.  

In this context ‘major development’ means:

• in respect of residential development, the provision of 10 or more dwellings
• in respect of non-residential development, new floorspace of 1,000 square metres or more, or a site of one hectare or more

Surface water management  

As of April 2015 all major planning applications must demonstrate the use of sustainable drainage systems (SuDS) as part of their development.   

As the Lead Local Flood Authority we are a statutory consultee on these planning applications.  

Our sustainable drainage systems supplementary planning document sets out how SuDS should be delivered in South Gloucestershire. It also includes further information about SuDS to inform and supplement any flood risk assessment, surface water drainage strategy and detailed design.   

The West of England sustainable drainage developer guide also has guidance on the delivery of SuDS as part of developments to manage surface water.   

Further information about SuDS can be found on the Susdrain website.

Climate change update  

Since the release of the new climate change guidance it is expected that the updated peak rainfall allowances are used when designing surface water drainage strategies for planning applications. 

As of 1 January 2023 all new planning applications will need to use the May 2022 revised climate change allowance figures.   

To avoid significant delays to planning applications currently validated or well progressed before the 1 January 2023 we will accept for the previous allowances to be used.    

SuDS adoption and sewerage   

The sewerage sector guidance was approved by Ofwat under its Code for Adoption Agreements and has new rules on surface water sewers.  

 Since 1 April 2020 Wessex Water can adopt certain sustainable drainage systems provided they comply with their criteria.    

The decision whether to adopt a sustainable drainage feature will lie with Wessex Water.  

We recommend early consultation with both Wessex Water and ourselves where an application proposes the adoption of sustainable drainage systems by Wessex Water.    

Flood risk  

We need to consider flood risk and drainage issues when deciding on a planning application.   

The National Planning Policy Framework sets out government’s planning policies for England and how these are expected to be applied, including how flood risk and drainage should be considered.   

Our planning document expands on this and sets out our local policy.  

Further guidance on flood risk and applying for planning permission can be found on the GOV.UK website.  

Flood risk assessments 

You can find out more about our Level 1 Strategic Flood Risk Assessment.