An end to the sequential test for sites affected by surface water flooding

The flood risk sequential test is a strategic tool used in both the preparation of local plans and decision-making for planning applications. It aims to steer new development away from areas of highest flood risk through demonstrating that there are no sites at a lower risk of flooding which could accommodate the proposed development. 

Previous approach to surface water flooding

Prior to 2022 the sequential test was generally considered to apply to sites at risk of flooding from rivers and seas.  Surface water flooding, which occurs when excessive waterfall means drainage systems (natural or man-made) are overwhelmed, was dealt with differently, through drainage strategies submitted with planning applications.  This was logical as development inevitably changes how existing drainage systems work through the introduction of impermeable surfaces, changes to run off rates to watercourses and alterations to ground levels.

However in 2022 the Government updated the National Planning Practice Guidance (NPPG) to require sequential tests to consider all types of flooding. Suddenly surface water flooding, no matter how local or minor, was being dealt with in the same manner as flooding from rivers and seas. Therefore a planning application on land which was subject to surface water flooding also needed to provide a sequential test.

Impact of updated flood maps

The Environment Agency’s (EA) mapping shows where surface water flooding is likely to occur. Whilst the maps are only indications of likely areas of flooding they are used definitely by Local Authorities. In December 2024 the EA updated their surface water flood maps and this dramatically increased the areas at risk from rainfall. Suddenly many more sites were affected by surface water flooding and therefore caught by the requirement to provide a sequential test.

When the National Planning Policy Framework was also published in December 2024 it was hoped some clarity would be provided to overcome this. However paragraph 173 continued to identify that a sequential risk-based approach should be taken to individual areas known to be at risk now or in the future from any form of flooding. Paragraph 175 did provide an exception from providing a sequential test when there would be no development on an area that would be at risk from flooding from any source, now or in the future.  But other than that there was no way round, a sequential test was required, even if the risk of flooding could be mitigated through the development.

On this basis we received a single matter refusal on surface water flooding for a site in London which comprised the redevelopment of some former garages to provide two dwellings. It was impossible to design the scheme to avoid the area which was subject to surface water flooding (despite this area being very small) and it was impossible to provide a sequential test, as there are many sites in the borough where two dwellings could be delivered. Policy restricted planning being granted despite the scheme not increasing flood risk and also facilitating development of brownfield land.

It is understood that due to the binary and inflexible policy the issue of sequential tests had become a significant barrier to development. Perhaps in light of the most recent statistics on dropping numbers of planning applications, it is of no surprise that the NPPG on flood risk and coastal change has been updated in respect of the sequential test and specifically in relation to surface water flooding. 

The 2025 update: a proportionate approach

Paragraph 027 now states “In applying paragraph 175 a proportionate approach should be taken. Where a site-specific flood risk assessment demonstrates clearly that the proposed layout, design, and mitigation measures would ensure that occupiers and users would remain safe from current and future surface water flood risk for the lifetime of the development (therefore addressing the risks identified e.g. by Environment Agency flood risk mapping), without increasing flood risk elsewhere, then the sequential test need not be applied”.