Flood Risk Assessment in Canterbury

Unda prepares flood risk assessments in Canterbury for development across the city, the coastal towns of Whitstable and Herne Bay, and the villages of the Nailbourne and Little Stour valleys. A flood risk assessment in Canterbury shows your local planning authority that a development will stay safe from flooding for its whole lifetime, without pushing flood risk onto anyone else.

Canterbury is one of the more varied flood-risk districts in Kent. The River Great Stour bisects the district from west to east and runs through the heart of the city, the north faces 21 kilometres of coast at Whitstable and Herne Bay, and the chalk valleys to the south feed winterbournes that flood from below ground. We assess every source that matters here — the Stour and its floodplain, the tidal coast, the surface water that overwhelms the older towns' drains, and the groundwater that rises through the chalk — then deal directly with the Environment Agency and Kent County Council, the Lead Local Flood Authority, on your behalf. We guide architects, planning consultants, developers, landowners, home buyers and businesses through to a decision, whether the report is needed for planning, a property purchase, a mortgage or insurance, BREEAM, or a surface-water drainage strategy.

If you need a quote or want to talk a site through, contact one of our experienced flood risk consultants on 01293 214444.

About 15% of the Canterbury district lies low, with roughly 46 square kilometres falling inside the Environment Agency's highest-probability river and sea flood zone — and the River Stour runs straight through the middle of the city.

Flood risk assessment in Canterbury at a glance

Canterbury City Council determines planning applications and applies national flood risk policy through its Strategic Flood Risk Assessment; Kent County Council is the Lead Local Flood Authority for surface water, groundwater and ordinary watercourses. A flood risk assessment in Canterbury has to satisfy both.

• Every source assessed. The Great Stour and its city-centre floodplain, tidal flooding along the 21 km coast, surface water and surcharged sewers, and groundwater emergence from the chalk.
• Two authorities to satisfy. Canterbury City Council as the planning authority, and Kent County Council as the Lead Local Flood Authority on surface-water drainage for major development.
• Reports for every reason. Flood risk assessments for planning, property purchase, mortgage and insurance, and BREEAM, alongside sequential and exception tests and surface-water drainage strategies (SuDS).
• A response within 60 minutes. Send us the site address and one of our experienced flood risk consultants will get back to you with a free, no-obligation quote within the hour.

Check flood risk anywhere in Canterbury

Canterbury is outlined below. Screen any postcode in the district against Environment Agency data for rivers and sea, surface water and the planning flood zones, with a climate outlook to 2125. It is an indicative first pass, not a substitute for a site-specific assessment.

Flood risk in Canterbury: the Stour, the coast and chalk groundwater

A flood risk assessment in Canterbury has to weigh river, tidal, surface-water and groundwater risk together, because most of the district sits where at least two of them overlap. The Canterbury Strategic Flood Risk Assessment records roughly 46 square kilometres of the district within Flood Zone 3a, the Environment Agency's highest-probability zone for rivers and the sea.

The River Great Stour and the city centre

The Great Stour is the main hydrological feature of the district, running west to east and passing directly through Canterbury city centre, where it splits into several channels around the historic core. Environment Agency mapping places a large part of the central area within Flood Zones 2 and 3, and parts of the city centre fall within the functional floodplain (Flood Zone 3b), where development is tightly restricted. Major flows on the Stour are influenced by storage reservoirs upstream of Ashford; in November 2000, flows equating to a 1-in-50-year event were recorded in the river. Any scheme near the Stour corridor needs a site-specific assessment of flood levels, finished floor levels and safe access for the lifetime of the development.

Whitstable, Herne Bay and the coast

Canterbury's northern coast runs for 21 kilometres from Graveney Marshes in the west to the Northern Seawall east of Reculver, with around 10.1 kilometres of low-lying frontage defended by a seawall and shingle beach. The coastal towns — Whitstable, Tankerton, Swalecliffe, Hampton, Studd Hill and Herne Bay — sit largely within Flood Zone 3 and rely on those defences. Protection is not uniform: some frontages benefit from a high standard while others are defended to a much lower return period, and the failure of the Reculver seawall in the 1996 storm is a reminder that defended land carries residual flood risk. A coastal assessment has to look behind the headline flood zone at the actual standard of protection and what happens in a breach or overtopping event.

The Nailbourne, the Little Stour and chalk groundwater

South of Canterbury the ground rises into the chalk of the North Downs, a principal aquifer cut by dry valleys and ephemeral streams. The Nailbourne is a winterbourne that is usually dry downstream of Lyminge but reactivates when groundwater levels climb, flowing on into the Little Stour. Groundwater emergence has driven the Nailbourne and Little Stour in 2000/01, 2003, 2010, 2012, 2013/14, 2014/15 and 2015/16, flooding the villages of Barham, Kingston, Bishopsbourne, Bridge, Patrixbourne and Littlebourne. Groundwater appears on no national flood map, rises slowly from below according to geology, can persist for weeks, and breaks the assumptions behind soakaway drainage — so it is assessed directly within the flood risk assessment for any site on or near the chalk.

Surface water and sewers

Surface water is now the most widespread source of flood risk in England, and Canterbury is no exception. The district has a history of flooding from small watercourses, overland flow off saturated farmland, and surcharging surface-water and combined sewers, particularly in the older coastal towns. Kent County Council's Canterbury Surface Water Management Plan and the Strategic Flood Risk Assessment together identify where these risks concentrate. A site in or near one of these areas, or within a critical drainage area, can need a flood risk assessment or a drainage strategy even when it sits in Flood Zone 1.

A history of flooding in Canterbury

Canterbury's flood history reads as a record of every source at once, which is why local knowledge matters so much when an assessment is reviewed. The dated events below are drawn from the Canterbury Strategic Flood Risk Assessment and local flood records.

• 1953 and 1978 — coastal. Major sea flooding along the north Kent coast, including Whitstable and Herne Bay, which led to substantial improvement of the sea defences.
• April 2000 — surface water. Fifty millimetres of rain in twelve hours on saturated ground flooded properties across the district; the Plenty Brook flooded 18 properties at Eddington near Herne Bay.
• Winter 2000/01 — widespread. The wettest winter since records began, with more than twice average rainfall; in what was estimated as a 1-in-100-year event, around 290 houses were flooded internally across the district, and homes at Bishopsbourne and Patrixbourne stayed flooded for months.
• August 2007 — Whitstable flash flood. Fifty millimetres of rain fell on Whitstable in two hours, flooding 30 to 50 houses through surcharging combined sewers and the Gorrell Tank outfall.
• Winter 2013/14 — river and groundwater. England's wettest January since 1766, with the South East receiving 258% of its average January rainfall; the Nailbourne reactivated and peaked at 2.08 m at Bekesbourne on 15 February 2014, the rare Petham Bourne flowed and closed the Canterbury West–Ashford railway at Shalmsford Street, and the December 2013 storm surge — the biggest since 1953 — prompted the precautionary evacuation of homes at Seasalter.

Planning and drainage policy for development in Canterbury

For a development in Canterbury, two authorities shape the flood risk and drainage requirements. The Environment Agency advises on main-river and tidal risk as a statutory consultee, while Kent County Council, the Lead Local Flood Authority, reviews surface-water drainage for major development. Canterbury City Council determines the application. Getting all of them satisfied early is what keeps a scheme moving.

• Strategic Flood Risk Assessment. The Canterbury SFRA (first prepared 2011, updated 2019 and 2024) maps flood zones, the functional floodplain and climate-change allowances across the district, and is the evidence base for applying the Sequential Test.
• Surface-water drainage. Kent County Council expects schemes to follow the drainage hierarchy and the 2025 national standards for SuDS, with infiltration tested to BRE Digest 365 where it is relied on.
• Local Plan. The emerging Canterbury District Local Plan to 2045 carries the flood risk and drainage policies a development must satisfy, including the requirement to incorporate SuDS on major development unless it is shown to be inappropriate.
• All sources of flooding. Since the September 2025 Planning Practice Guidance update, the sequential, risk-based approach formally applies to all sources of flooding, including surface water and groundwater — which matters greatly in a district with so much chalk groundwater risk. The NPPF and its guidance set the framework an assessment must meet.

What flood risk means for development across the district

Development in Canterbury covers a wide range, and each type tends to raise its own flood and drainage questions. City-centre regeneration and infill near the Stour runs up against the functional floodplain and tight finished-floor-level requirements. Coastal regeneration at Herne Bay and Whitstable has to address tidal defences, residual breach risk and surface-water drainage on flat, low-lying ground. Rural and village schemes in the chalk valleys face groundwater emergence and the limits it places on infiltration drainage. Large parts of the district's flood-risk land also coincide with internationally designated habitats — The Swale, the Thanet Coast and Stodmarsh — so the surface-water and water-quality side of a scheme often carries as much weight as the flood risk itself. An assessment built around the specific site, rather than a template, is what turns these constraints into an approvable scheme.

How Unda helps with flood risk in Canterbury

We are experts on Canterbury's flood risk, and what gets a difficult Kent site approved is an assessment that reads the Environment Agency and Kent County Council data correctly for the specific location and translates it into a scheme that satisfies policy. We have prepared flood risk assessments and drainage strategies across Kent, dealt directly with the Environment Agency and the Lead Local Flood Authority, and stayed involved past the report to answer objections. A Senior Flood Risk Consultant oversees and signs off every report, and Unda has completed more than 5,000 flood risk assessments since 2014. You can read more about Unda and our flood risk consultants.

Flood risk assessments for every situation in Canterbury

People need flood risk work in Canterbury for very different reasons. A flood risk assessment, a sequential or exception test and a drainage strategy are three distinct reports. They often travel together in a planning submission, but they answer different questions: is the site safe, should the development be here, and where does the surface water go.

• Flood risk assessment for planning. A site-specific report submitted with a planning application to show the development is safe for its lifetime and does not increase risk elsewhere. Flood risk assessment for planning.
• Flood risk survey for property purchase. An independent assessment for home buyers when a search or lender flags flood risk on a Canterbury property. Flood risk survey for property purchase, and how flooding can affect house prices.
• Flood risk assessment for insurance. Property-specific evidence where premiums have risen, cover has been restricted, or risk needs clarifying after a flood event. Flood risk assessment for insurance.
• Flood risk assessment for BREEAM. Structured around the BREEAM Pol 03 flood and surface-water criteria for schemes pursuing certification. Flood risk assessment for BREEAM.
• Sequential and exception tests. The locational justification that steers development to lower-risk land, prepared alongside the flood risk assessment. Sequential and exception tests.
• Drainage strategy and SuDS design. Surface-water engineering that keeps discharge within limits, built on the four pillars of SuDS, with discharge of conditions and preliminary drainage design as the later and earlier stages. Surface-water drainage strategy.
• Groundwater and flood modelling. Groundwater is assessed within every flood risk assessment we prepare in Canterbury, and 1D/2D flood modelling is brought in where national mapping cannot describe the site accurately.

Canterbury sits within our wider flood risk assessment work across Kent, and all of it draws on Unda's flood risk assessment service. Before commissioning a report, you can screen a site for free with our flood risk map, check current river conditions on the live river levels map, test infiltration potential with the geology and ground conditions checker and the BRE 365 infiltration rate calculator, or size a scheme with our drainage calculators.

Flood risk management and emergency contacts in Canterbury

If you need to report flooding or prepare for it, the responsible body depends on the source. The table below sets out who does what across the Canterbury district.

Flood risk assessment in Canterbury: frequently asked questions