Pre-Application & Outline Planning Drainage Strategy

The National Planning Policy Framework of 2019 introduced the use of SuDS as a requirement unless it is deemed to be inappropriate for the development.

When determining any planning applications, local planning authorities should ensure that flood risk is not increased elsewhere. Where appropriate, applications should be supported by a site-specific flood-risk assessments. Development should only be allowed in areas at risk of flooding where, in the light of this assessment (and the sequential and exception tests, as applicable) it can be demonstrated that:

a) within the site, the most vulnerable development is located in areas of lowest flood risk, unless there are overriding reasons to prefer a different location;

b) the development is appropriately flood resistant and resilient such that, in the event of a flood, it could be quickly brought back into use without significant refurbishment;

c) it incorporates sustainable drainage systems, unless there is clear evidence that this would be inappropriate;

d) any residual risk can be safely managed; and

e) safe access and escape routes are included where appropriate, as part of an agreed emergency plan.

This new policy means it’s highly encouraged to use sustainable drainage systems, however, there are limited exemptions.

A common exemption would be an extension atop the existing built footprint. If it doesn’t exceed the existing building footprint and will connect into former/existing roof drainage, it can be exempt from needing a new SuDS strategy.

Each application is unique and although this is a common exemption, we would strongly recommend liaison with your Local Planning Authority and Lead Local Flood Authority before proceeding with similar projects.

The main difference between outline planning and full planning is the level of detail that’s required. You need significantly more data and information in a full planning application than an outline plan. Outline planning could also be viewed as a well thought out conceptual plan.

Outline Planning is focused to the concept and principles of drainage. How will the runoff be mitigated post development? Where could the sustainable urban drainage systems be located on the site? How will water be discharged from the site? Planning Authorities will expect these questions to be answered, with surface water drainage calculations and a plan demonstrating the potential future arrangement.

Outline planning may not be as detailed as full planning or pre-construction, but it still has to be implementable and detailed enough to justify the selection and specific sizing of the chosen SuDS (such as tank size, etc).

Due to it being more conceptual, it can lead to more information being requested as planning consent is being issued before permission to start the works can go forward.

Each Surface Water Drainage Strategy is unique, however, typically our expert team can produce a surface water drainage strategy within 10 to 20 working days from receiving all necessary data. Much of this time-frame depends greatly on the size of the project, complexity of the site (brownfield, existing connections), environmental constraints (geology, topography, ground water etc.) and the amount of data that is already available. Review of all of these elements is required to allow our experts to cross review and interrogate each element and piece of data in order to provide you with a national planning policy compliant report for planning.

It is the responsibility of the client/applicant to source the majority of the datasets and necessary pieces of information. However, our experts are able to support in sourcing information and supporting you through the project. We have a network of specialists who can provide additional services as and when required.

If you’re looking for a much shorter time frame, our team can provide reports in an accelerated time-frame at an additional cost to meet your requirements. We’re able to provide this rapid service due to our teams experience of supporting our clients and the tried and tested methodologies and approaches.

Ideally, before. A pre-application or outline drainage strategy establishes whether the scale and type of development you are proposing is acceptable in drainage terms before you commit to a detailed design. Finding out at full planning that the layout cannot accommodate the required attenuation usually means reworking the scheme.

Where a site is constrained, early drainage input often shapes the developable area, so it is worth having before the masterplan is fixed rather than after.