Flood Risk Assessment in the Royal Borough of Kingston upon Thames

The Royal Borough of Kingston upon Thames is both the local planning authority and the Lead Local Flood Authority for its area, so the same council decides your planning application and reviews the surface water drainage behind it. A development here usually needs a flood risk assessment, a drainage strategy, or both, and Kingston applies a local surface water rule that catches sites the national flood map treats as low risk.

We prepare flood risk assessments and drainage strategies for schemes across the borough — for planning, property purchase, mortgage and insurance, and BREEAM — alongside sequential and exception tests and sustainable drainage design. If you want to know exactly what Kingston will ask for on a specific site, call 01293 214444 or email enquiries@unda.co.uk and one of our experienced flood risk consultants will talk it through.

Kingston is unusual in treating the 1-in-100-year surface water flood extent as Flood Zone 3a, so a site that reads as Flood Zone 1 on the national map can still trigger the council's highest flood risk requirements.

Flood risk and drainage in Kingston at a glance

The essentials an applicant needs before designing a scheme or submitting an application in the Royal Borough of Kingston upon Thames:

• Decision-maker. The Royal Borough of Kingston upon Thames is a unitary London borough — it is the local planning authority and the Lead Local Flood Authority in one.
• What is usually required. A site-specific flood risk assessment where national or local flood risk is flagged, and a drainage strategy for all major development.
• Adopted policy. Core Strategy Policy DM4 (Water Management and Flood Risk), adopted April 2012, read together with the London Plan (2021) policies on flood risk and drainage.
• Evidence base. The borough's Strategic Flood Risk Assessment, prepared by Metis Consultants and published in 2021, with a Level 2 assessment of site allocations.
• Drainage benchmark. Surface water runoff restricted towards greenfield rates using the sustainable drainage hierarchy, evidenced on the council's drainage assessment form.
• Main rivers. The River Thames, the River Hogsmill, the Surbiton Stream and the Beverley Brook are all Environment Agency main rivers affecting the borough.

Who decides flood risk and drainage in Kingston?

Three bodies shape what a Kingston application must prove on flooding and drainage. The council carries two of the three roles itself, which is why its drainage team and its planning officers both have a say on the same scheme.

• The local planning authority. The Royal Borough of Kingston upon Thames determines the application and applies national policy, the London Plan and its own Core Strategy. It runs the sequential and exception tests where they apply.
• The Lead Local Flood Authority. The borough is also the Lead Local Flood Authority, a statutory consultee on surface water drainage for all major applications. It manages flood risk from surface water, groundwater and ordinary watercourses and can object to a scheme whose drainage is not properly evidenced.
• The Environment Agency. The Agency manages the main rivers — the Thames, the Hogsmill, the Surbiton Stream and the Beverley Brook — and advises the council on development in Flood Zones 2 and 3. Thames Water is the sewerage undertaker for the area.

Because the council wears both the planning and the drainage hat, a scheme can satisfy the planning case on flood zones yet still stall on drainage detail. Our guide to LPA flood and SuDS roles explains how the two functions interact, and it is worth designing for both from the start rather than treating drainage as an afterthought.

Does a Kingston application need a flood risk assessment or a drainage strategy?

A flood risk assessment and a drainage strategy answer different questions, and a Kingston scheme often needs both. The assessment shows the development is safe and does not raise flood risk elsewhere; the drainage strategy shows where the surface water goes and how runoff is controlled. The table below sets out the common triggers in the borough.

If you are unsure which reports a site needs, our explainer on flood zones and the vulnerability classification guide set out the national tests, and our free flood risk map gives a first read on where a Kingston site sits. A quick call will confirm the position before you commit to a design.

Kingston's drainage and SuDS requirements

Drainage is where Kingston applications most often come unstuck, because the council reviews surface water design in its Lead Local Flood Authority role and expects it evidenced to a set standard. For all major development you must complete the borough's drainage assessment form, submit detailed drainage design plans, and show that runoff will be managed so it does not increase flood risk on or off the site.

• Restrict runoff towards greenfield rates. Surface water discharge should be reduced in line with the sustainable drainage hierarchy, restricting off-site runoff rates towards greenfield conditions, particularly within critical drainage areas.
• Follow the SuDS hierarchy. Manage water as close to source as possible, prioritising infiltration and green measures over a straight connection to the sewer, in line with the four pillars of SuDS — water quantity, water quality, amenity and biodiversity.
• Prove infiltration properly. Where infiltration is proposed, back it with BRE 365 soakaway testing; Kingston's London Clay geology often limits infiltration, so this needs checking early.
• Design to 1-in-100 plus climate change. Systems should accommodate the 1-in-100-year storm with an allowance for climate change, without flooding to property.
• Plan for adoption and maintenance. You must agree a plan setting out adoption and maintenance of the SuDS over the lifetime of the development.

The council's approach reflects the London Plan drainage hierarchy and the London Sustainable Drainage Action Plan, so a scheme that simply proposes to connect to the Thames Water sewer will usually be sent back. Our surface water drainage strategy and discharge of drainage conditions services produce exactly this evidence, and our free drainage calculators and BRE 365 infiltration calculator help at concept stage. For outline schemes, a preliminary drainage design flags problems before they reach the officer.

Kingston's Local Plan flood and drainage policies

The development plan for the borough combines the Royal Borough of Kingston upon Thames Core Strategy (adopted April 2012) with the London Plan (2021), which applies to every London borough. A new Local Plan is being prepared and was progressing towards submission in 2026, but until it is adopted these are the policies that govern flood risk and drainage on a Kingston application. The table names the ones that matter.

Policy DM4 — water management and flood risk

Policy DM4 in the Kingston Core Strategy requires development to avoid areas at higher risk of flooding and, where a site is susceptible to flooding, to be designed so buildings are flood compatible or incorporate flood resilient measures. In practice this means your flood risk assessment must show the layout, floor levels and resilience of the scheme respond to the site's flood risk, not just describe it. The policy sits within the borough's wider climate and water management approach.

London Plan Policy SI 13 — sustainable drainage

Policy SI 13 of the London Plan requires development to aim to achieve greenfield runoff rates and to manage surface water in line with the drainage hierarchy, keeping water on the surface and close to source wherever possible. For a Kingston scheme this is the policy the Lead Local Flood Authority will hold your drainage strategy against, so the evidence needs to show each step of the hierarchy was considered before any discharge to a sewer.

London Plan Policy SI 12 — flood risk management

Policy SI 12 requires development to ensure it is safe for its lifetime, to reduce flood risk overall, and to apply a sequential, risk-based approach to the location and design of the scheme. Read alongside the national sequential and exception tests, it is the backbone of the flood risk case for a borough with as much watercourse frontage as Kingston.

The borough's Strategic Flood Risk Assessment

Kingston's Strategic Flood Risk Assessment, prepared by Metis Consultants and published in 2021 with a later Level 2 assessment of site allocations, is the borough-wide evidence base for flood risk. It maps flood risk from every source and defines how the flood zones are applied locally — and this is where Kingston departs from the national picture.

• A local surface water Flood Zone 3a. The SFRA defines the 1-in-100-year surface water extent as Flood Zone 3a, in addition to the Environment Agency's fluvial flood zones, so surface water is treated as a Flood Zone 3 constraint in its own right.
• Functional floodplain to 1-in-30. Flood Zone 3b (functional floodplain) is defined as land flooding in events up to and including the 1-in-30-year return period, allowing for defences.
• Who assesses what. Fluvial Flood Zone 3a and 3b are assessed with the Environment Agency; the borough's surface water Flood Zone 3a is assessed by the council alone.
• Use it for the sequential test. The SFRA provides the basis for applying the sequential test and should be your starting point before designing a scheme.

The practical consequence is that a site reading as low risk on the national flood map for planning can still fall within Kingston's surface water Flood Zone 3a and attract the highest level of requirement. We check the borough's own mapping, not just the national dataset, on every Kingston assessment.

What must accompany a Kingston application?

A flood risk and drainage submission that is incomplete is one of the most common reasons an application is delayed or invalidated. For the Royal Borough of Kingston upon Thames, make sure the following are in place before you submit.

• A site-specific flood risk assessment where the site is in Flood Zone 2 or 3, in the borough's surface water Flood Zone 3a, or where surface water risk is otherwise flagged.
• The council's drainage assessment form, completed with runoff rates, required storage volumes, the discharge destination and the proposed SuDS features, for every major application.
• Detailed drainage design plans showing the drainage layout, not just a written strategy.
• A sequential test where a more vulnerable use is proposed in a higher flood zone, with an exception test if required.
• An adoption and maintenance plan for the SuDS covering the lifetime of the development.

How national policy applies in Kingston

National policy sets the framework the borough works within. The National Planning Policy Framework and its Planning Practice Guidance require flood risk to be managed from all sources, steer development to lower-risk land through the sequential test, and expect major development to include sustainable drainage. The September 2025 PPG update broadened the sequential test to consider surface water, groundwater and sewers, which matters in a borough where surface water is a defining risk. The 2025 national SuDS standards and the NPPF flood risk provisions shape what a compliant drainage scheme looks like. Kingston layers the London Plan and its own surface water flood zone approach on top, so a scheme designed to national policy alone can still miss the local requirements.

Flood risk in the Kingston area

Kingston's flood risk is driven by the Thames and its tributaries plus a strong surface water and sewer component in the urban centre. The River Thames runs along the north-western boundary as a non-tidal main river, and the River Hogsmill, its tributary the Surbiton Stream, and the Beverley Brook all pose fluvial risk. The metropolitan centre of Kingston is particularly exposed where the Thames and the Hogsmill meet.

• Flashier tributaries. The Hogsmill, Surbiton Stream and Beverley Brook respond faster to rainfall than the Thames, giving shorter warning times and a sharper flood response.
• Surface water and sewers. Densely built, largely impermeable areas concentrate surface water and sewer flooding; the borough records repeated sewer flooding in parts of Surbiton, Kingston, Chessington, New Malden and Worcester Park.
• Clay geology. The borough sits on the Thames Group (London Clay) with variable superficial sands and gravels, which limits infiltration on many sites and pushes drainage design towards storage and attenuation.
• Residual risk behind defences. Defences exist on the Hogsmill, Surbiton Stream and Beverley Brook, but Kingston expects an assessment of residual risk where a site relies on them.

For the full picture of how the borough floods, the neighbouring Richmond upon Thames area page covers the same stretch of the tidal and non-tidal Thames, and our guide to ordinary watercourse consent is worth reading where works affect a smaller channel. The opening of the Thames Tideway Tunnel has changed the wider London sewer picture downstream.

How Unda helps with Kingston applications

We are experts on the Royal Borough of Kingston upon Thames and how it assesses flood risk and drainage, and we have prepared assessments and drainage strategies across this part of south-west London. We know the borough's surface water Flood Zone 3a approach, the drainage assessment form the Lead Local Flood Authority expects, and the London Clay that shapes drainage design here — so we produce evidence the council can accept first time rather than reworking it after an objection.

• Flood risk assessments for planning. Clear, technically robust FRA reports that satisfy the council and the Environment Agency.
• Drainage and SuDS. Surface water drainage strategies and detailed design built to the London Plan hierarchy and the borough's standards.
• Sequential and exception tests. The policy evidence to place development correctly against flood risk.
• Fast, responsive service. A reply to every quote within 60 minutes, and reports built to keep applications moving.

Flood risk and drainage services for every situation in Kingston

Beyond planning, we prepare flood risk assessments and drainage work for the full range of reasons a Kingston property or scheme needs them. Each is a distinct piece of work answering a different question.

• Property purchase. An independent flood risk survey for buyers where a search flags a Kingston property.
• Insurance. A property-level flood risk assessment for insurance to clarify risk for underwriting.
• BREEAM. A BREEAM flood risk assessment structured for Pol 03 credits.
• Groundwater. A specialist groundwater flood risk assessment where the water table is a credible issue.
• Flood modelling. Site-specific flood modelling where national mapping does not reflect local conditions.
• Ground conditions. Our free geology and soakaway map helps gauge infiltration potential before testing.

Frequently asked questions

Speak to a flood risk consultant about your Kingston scheme

Whether you are testing a site, responding to a drainage objection, or assembling a planning submission for the Royal Borough of Kingston upon Thames, we can prepare the flood risk assessment and drainage strategy the council needs. Useful borough references include the council's Strategic Flood Risk Assessment, its drainage requirements for major developments, the emerging Local Plan, the London Plan, the national flood risk planning guidance, the NPPF and the Environment Agency's check for flooding service.