Flood Risk Policy in Royal Borough of Kensington and Chelsea

“All development, regardless of size, should ensure that there is a net reduction in flows to the combined sewer network.”

In July 2024, the Royal Borough of Kensington and Chelsea (RBKC) adopted a new Local Plan which has superseded the previous Local Plan (2019).

Within the 2019 Local Plan, Policy CE2 Flooding was the sole policy that focused on reducing the impacts of flood risk, and the implementation of SuDS across the Borough. Now, within the 2024 Local Plan, the flood risk and SuDS requirements have been split across two policies, into Policy GB11: Flood Risk, and Policy GB12: Sustainable Drainage.

Below, we explore the key differences between the 2019 and 2024 Local Plan flood risk and SuDS requirements, and the impacts this will have on development across the Borough. 

When is a Flood Risk Assessment required?

Previously under Policy CE2 of the 2019 Local Plan, a site-specific Flood Risk Assessment, including an ‘Exception Test’, was required for for all development in Flood Zones 2 and 3, for sites in Critical Drainage Areas, and for all sites greater than one hectare. Policy GB12 of the 2024 Local Plan reiterates this but extends the requirement for an FRA, and thus now, all basement development should submit a Flood Risk Assessment with the associated planning application.

Sleeping Accommodation

Previously, Policy CE2 stated that the Council will resist “vulnerable development”, including self-contained basement dwellings, in Flood Risk Zone 3 and Critical Drainage Areas – thus it specified only that they would resist certain types of development including self-contained basement dwellings, in these areas. Whereas, Policy GB11 of the 2024 Local Plan states that in addition to the above, no sleeping accommodation will be permitted below ground floor level in Flood Zone 3. For context, the extent of Flood Zone 3 within the Borough is provided below. 

Development within proximity of the River Thames

Policy CE2 of the 2019 Local Plan stated that the council would require development adjacent to the Thames to be “set back” from the Thames flood defence to enable the sustainable and cost effective upgrade of flood defences and to implement any other recommendations of the Thames Estuary 2100 plan (TE2100); however it offered no specific requirement for what that set back distance needed to be. Generally the EA would seek to maintain a 16m buffer from tidal Main Rivers and their defences anyway, but this is now formalised in the 2024 Local Plan with GB11 stating “New development adjacent to the River Thames and Chelsea Creek must be set back by 16m from the Thames flood defence, including tie rods and support structures, to enable the sustainable and cost-effective upgrade of flood defences in line with the requirements of the Thames Estuary 2100 Plan”. 

Sustainable Drainage Systems (SuDS)

As discussed above, previously flood risk and SuDS were considered under one Policy – CE2. However, GB12 of the 2024 Local Plan sets out the local SuDS requirements separately, with some key differences from CE2. 

Policy CE2 stated that the council required major development to achieve greenfield run-off rates and minor development to achieve a reduction of 50% of existing rates. This 50% reduction of rates was applied to the site as a whole, rather than just the footprint or proposed development area, meaning developers were required to provide runoff attenuation for an entire site boundary even if only providing a small rear extension.

Within GB12, this requirement has been relaxed slightly, with the policy wording now stating “Development proposals must aim to achieve greenfield run-off rates. Householder applications must reduce the rate of runoff from the site in a way that is proportionate to the scale of development and reflects the site constraints.” Therefore the updated Local Plan appears to appreciate that on smaller scale developments and compact sites, significant attenuation may not be possible so this allows for more flexibility with the type of SuDS available for minor developments and removes the need to provide 50% reduction in runoff rates for the whole site. 

However the 2024 Local Plan still reiterates that all development needs to play its part in reducing flood risk to the Borough – “All development, regardless of size, should ensure that there is a net reduction in flows to the combined sewer network” – and thus SuDS should still be considered for all development, albeit appropriate to the scale, nature, and constraints of the proposed development. 

Flood risk planning in RBKC? Aegaea are here to help!

Aegaea have extensive experience working across the RBKC region and are more than happy to help you out with your project. Please do get in touch and one of our dedicated consultants will be on hand to answer any questions.

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About the Author

Nick Darling-Drewett
BSc MCIWEM AMIEnvSC
Principal Flood Risk Consultant
I’m a Principal Flood Risk Consultant at Aegaea with extensive experience in producing FRAs and drainage strategies. Specialist Subject: FRAs
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