London Borough of Kensington and Chelsea Flood Risk Assessments

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London Borough of Kensington and Chelsea is affected by a range of flood risk sources including surface water, sewer surcharge and tidal influences from the River Thames.

Whether you are a homeowner planning an extension, an architect preparing a development scheme or a planning consultant managing a complex application, flood risk and drainage requirements must be addressed clearly and robustly to secure planning permission.

Speak to a Chartered Flood Risk Consultant today for advice or a free quote

Call 01174 414993 or email info@geoson.co.uk

Flooding in Kensington and Chelsea

The Royal Borough of Kensington and Chelsea has experienced several notable flood incidents, primarily attributed to surface water accumulation and sewer surcharge.

Significant surface water flooding occurred across parts of London, including within Kensington and Chelsea, during intense rainfall events in July 2007 which led to drainage systems being overwhelmed.

More recently, heavy rainfall events in summer 2016 and summer 2021 caused localised flooding of roads and properties, highlighting the vulnerability of dense urban areas to short duration, high intensity storms.

There have been no major flood events attributed to the River Thames within the borough since the 1930 Flood Act when, following the 1928 flood event, the level of the flood defences along the River Thames were raised. In addition to the raised defences, tidal flood risk across London is managed by the Thames Barrier. Despite this, the south of the borough remains within an area that is at residual risk of tidal flooding, particularly when considering climate change and a potential breach of the defence infrastructure.

Key Planning Policies and Documents

Flood risk planning in Kensington and Chelsea is guided by a combination of national, London-wide and borough specific policy.

The Kensington and Chelsea Local Plan (2024) sets out the council’s specific planning policies in relation to flood risk management. The two main policies relating to flood risk management are:

Policy GB11: Flood Risk
Policy GB12: Sustainable Drainage

Supplementary Planning Documents (SPDs) have been created to support these policies.

The London Plan (2021) also includes Policy SI 12 and Policy Sl 13 which cover flood risk management and sustainable drainage, respectively.

When undertaking a Flood Risk Assessment in Kensington and Chelsea, the following documents should be used to assess flood risk at a site:

Royal Borough of Kensington and Chelsea Level 1 Strategic Flood Risk Assessment
Kensington and Chelsea Local Plan
Local Flood Risk Management Strategy
Royal Borough of Kensington and Chelsea Surface Water Management Plan
Thames Flood Risk Management Plan
Section 19 Flood Investigation Reports

When is a Flood Risk Assessment Required in Kensington and Chelsea?

In Kensington and Chelsea, Flood Risk Assessments are commonly required due to surface water flood risk, the location of a site within a Critical Drainage Area (CDA) or the proximity of a development to the River Thames.

In accordance with local and national guidance a Flood Risk Assessment is required to accompany a planning proposal in the following situations:

When a site is located within Flood Zone 2 or Flood Zone 3 (land in the south of the borough is located within Flood Zone 2 and 3)
When a site is 1 hectare or greater (even if located in Flood Zone 1)
When the application area is identified to be at risk of surface water flooding or is located within a Critical Drainage Area (CDA). More information on Critical Drainage Areas is provided below.
There is a known history of flooding at or near the site

Critical Drainage Areas

A large proportion of the borough is located within a Critical Drainage Area (CDA) which will trigger the requirement for a Flood Risk Assessment to accompany a planning application.

Kensington and Chelsea's Surface Water Management Plan defines a Critical Drainage Area as:

A discrete geographic area (usually a hydrological catchment) where multiple and interlinked sources of flood risk (surface water, groundwater, sewer, main river and/or tidal) cause flooding in one or more Local Flood Risk Zones during severe weather thereby affecting people, property or local infrastructure.

The links below show the four Critical Drainage Areas located within the Royal Borough of Kensington and Chelsea:

Surface Water Drainage Requirements

The 2024 Local Plan includes Policy GB12 (Sustainable Drainage) which sets out the requirements for the management of surface water runoff through development proposals and replaces the former Local Plan Policy CE2.

Policy GB12 states that development must contribute towards a reduction in the rate and volume of surface water run-off into the sewer network through measures that promote multifunctional benefits.

Householder applications must aim to reduce the rate of run-off from a site in a way that is proportionate to the scale of development and reflects the site constraints.

Only where it can be clearly demonstrated that the on-site reduction in surface water run-off to greenfield rates is not feasible may financial contributions be provided by the developer towards the delivery of SuDS in the locality.

How Policy GB12 May Affect Your Development

Householder or small-scale developments

SuDS are required for basement developments, lower ground / ground floor extensions, construction of outbuildings, landscaping requiring planning permission, and new or replacement hardstanding.
Development currently exempt from the SuDS requirements include Changes of Use with no external works, fenestration changes, and upper-floor or roof extensions.
For householder developments Policy GB12 can be met through an increase in the permeable surfaces at a site, increase in greening and/or rainwater storage to control the amount and speed that surface water run-off leaves the site.
Typical measures include installation of water butts and/or SuDS planters, incorporation of green roofs, promotion of infiltration to ground (where possible), and the replacement of hardstanding with permeable materials.
A drainage statement must be submitted with planning applications, showing existing and proposed impermeable surfaces, SuDS features, drainage hierarchy compliance, and maintenance responsibilities.

One+ new residential units or equivalent

SuDS should be considered from the master planning stage so that they are fully integrated with the topography, landscaping and conditions of the site.
A drainage strategy should be submitted to support the application.
The SuDS strategy should show how the development will comply with policy GB12 and aim to achieve greenfield run-off for all events.
The drainage strategy should include details of pre/post development run-off rates, SuDS design, exceedance flows, foul drainage plan, maintenance plan, SuDS pro-forma and records of relevant consultations.
A verification condition on the application will ensure SuDS are built and maintained as approved.
In some circumstances off-site SuDS contributions may be required if on-site greenfield rates cannot be achieved.

Paving Front Gardens

The council encourages removal of paving and use of permeable materials.
Planning permission is required for hard paving over 5m² unless permeable materials are used or run-off is directed to a permeable area within your property boundary.
Non-permeable paving is generally resisted under policy GB12.

Speak to a consultant today for a free, no-obligation quotation

How We Can Help

At GeoSon we have undertaken many Flood Risk Assessments and Surface Water Drainage Strategies to support developments within Kensington and Chelsea. With this we are well placed to advise on the local policy requirements that need to be considered in order to enable your application to gain planning approval.

Early consideration of flood risk and drainage can reduce planning delays, improve design outcomes and ensure compliance with Kensington and Chelsea’s local guidance.

If you have a project in Kensington and Chelsea and would like some advice on how best to address the flood risk or drainage contact GeoSon today. One of our consultants would be happy to discuss your project in more detail and support your application through the planning process.

Areas that we cover include, but are not limited to: Abingdon, Brompton and Hans Town, Campden, Chelsea Riverside, Colville, Courtfield, Dalgarno, Earl's Court, Golborne, Holland, Norland, Notting Dale, Pembridge, Queen's Gate, Redcliffe, St Helen's and Stanley.