Surface water drainage

As of April 2015, all major planning applications (those for 10 or more homes and over 1,000m2 of commercial/industrial floorspace) must demonstrate the use of sustainable drainage as part of their development. West Northamptonshire Lead Local Flood Authority (LLFA) are a statutory consultee on these planning applications. This page sets out how sustainable drainage should be delivered in West Northamptonshire.

What are Sustainable Drainage Systems?

Sustainable drainage is a way of mimicking natural drainage in the built environment. Instead of surface water being piped underground and released fast into the sewer system, water remains at the surface, where it is cleaned and stored. This reduces flood risk, and improves water quality before it soaks into the ground or discharges to a watercourse or surface water sewer. This can also support biodiversity and amenity.

SusDrain, an online community for sustainable drainage, have developed a video overview of what Sustainable Drainage Systems (SuDS) are. Case studies of example SuDS schemes can also be found on the SusDrain website.

We encourage all new development and redevelopment that requires planning permission to use SuDS to reduce flood risk, improve water quality and present options for biodiversity and public amenity. This is consistent with existing national guidance and local planning policy.

General SuDS advice for developers

The demands of each individual development will lead to a wide variety of solutions. Understanding West Northamptonshire 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 retrofitted into existing developments.

Local Standards and Guidance for Surface water drainage in West Northamptonshire

We have published local guidance intended to assist developers in the design of all surface water drainage systems, and to support us in considering drainage proposals for new development in West Northamptonshire.  

The guide sets out the standards that we apply in assessing all surface water drainage proposals. 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.  

Flood data and information requests

WNC can provide the following information to support and supplement any flood risk/drainage assessment, regardless of the size or nature of the development:

• a review of surface water drainage constraints from national mapping
• a review of site-specific flood risk issues
• a summary of any historic flood incidents that have occurred on the site or within the locality
• a review of flood related assets that are within the locality
• a statement of any flood related issues to be considered further
• advice on the type and nature of surface water drainage that could be designed into the relevant development
• information about flood risk consenting that may be required for your proposed development

This service can provide a written email response and a charge of £250 per site may apply, up to and including 5Ha, for greater than 5Ha the charge may be £750 exclusive of VAT. Please be aware this cost is to cover the time taken to investigate the area in question and to prepare a full response. Where no historic flooding information is available, or where there is no risk identified on the site, this charge will still apply.

For more information about these data requests please contact the Surface Water Drainage Team at: [email protected].

Technical flood advice service

We can provide technical advice on the surface water drainage design and other local sources of flood risk, for any proposed development in the county. 

We also advocate the use of pre-application discussions to ensure SuDS can be incorporated into developments at the early stage of design, and to streamline the planning approval process. 

We can also provide technical surface water drainage pre-application advise for strategic major sites which are submitted to the Local Planning Authority.

We may provide advice on documents and plans you submit, advice on aligning planning and consenting requirements, and other specific tasks we agree. 

Furthermore, we may carry out desk-based analysis, arrange meetings and make site visits as set out in our agreement with you. For this service, we may charge £84 per hour, exclusive of VAT.

Please get in contact with the Surface Water Drainage Team by emailing [email protected] if you would like to use this service, or would like further information. 

We will then provide you with a unique reference number with which you will be able to make the required online payment.  

Planning applications

Find detailed guidance relating to the information we would like to see in any Flood Risk Assessment or Drainage Strategy.

We may have additional requirements for planning submissions so you should contact the planning and building control team prior to submitting an application.

We encourage SuDS in any new development. 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. 

Green, more sustainable SuDS should be prioritised. If we are not satisfied with the evidence provided, we may object to the proposal.

Last updated 08 March 2024