Flood Risk Assessment in Twickenham

A flood risk assessment in Twickenham deals with a stretch of the Thames that is tidal but behaves like a river. The tide reaches Teddington Weir, just upstream, yet the level a riverside building has to be protected against can be set by flood flows coming down from upstream, and the River Crane and the Duke of Northumberland's River add their own floodplain inland. Our consultants assess sites in Twickenham for planning applications, property purchases, lenders and insurers, and prepare sequential and exception tests and surface water drainage strategies for the London Borough of Richmond upon Thames.

Twickenham here means the four wards that carry its name, in the TW1 and TW2 postcode districts: the town centre and Twickenham Riverside with Eel Pie Island, St Margarets and East Twickenham, Strawberry Hill and South Twickenham, and West Twickenham out to the Stadium. The council's Local Plan groups the same ground as Twickenham, Strawberry Hill and St Margarets. Whitton is planned separately and lies outside the outline on this page, as do Fulwell and Teddington Lock.

In Twickenham the river flood is higher than the tide: the council's own riverside scheme was set a 1% annual chance river level, with climate change, of 6.94 m above Ordnance Datum (AOD), above the 6.90 m AOD the tidal defences are planned to reach by 2100.

To talk through a site with one of our flood risk consultants, call 01293 214444 or email enquiries@unda.co.uk.

Why does Twickenham's riverside flood when the tide is in?

Below Teddington Lock the Thames rises and falls twice a day, and on the biggest spring tides the Environment Agency warns that the riverside road can flood. On 9 October 2026 the Environment Agency issued a flood alert naming Riverside and The Embankment at Twickenham and Ranelagh Drive in TW1, with a high tide of 4.70 m AOD forecast at Richmond in the early hours of 10 October. It issued the same kind of alert on 30 March 2026, and on both occasions said it did not expect properties to flood.

• The walls belong to riverside owners. The tidal defences along this reach are raised, privately owned walls and embankments. The Environment Agency told the council's Twickenham Riverside team that owners must keep them at the statutory defence level of 6.02 m AOD, and it inspects them twice a year.
• River flow sets the design level. The flood risk assessment for Twickenham Riverside, prepared by Webb Yates Engineers in July 2021, records a present-day tidal level of 5.8 m AOD at the nearest Environment Agency model point, rising to 6.42 m AOD by 2100. The 1% annual chance river flood with a 35% climate change allowance reached 6.94 m AOD, so the river, not the tide, governed the floor levels; our note on climate change allowances explains where the 35% comes from.
• The Thames Barrier helps the river as well. The Environment Agency closes the barrier against storm tides and also uses closures to make room for high river flows. Under the Twickenham policy unit of the Thames Estuary 2100 plan, the way the barrier is operated changes in 2035, and before then the agency is working with Richmond and Hounslow councils on alternative protection against smaller river floods of up to 600 cubic metres a second at mean high water springs.
• The policies run in two directions. The unit, which runs along the north bank from Teddington Lock to Brentford, is under policy P5 for tidal flooding, meaning defences will be raised for sea level rise, and policy P3 for river flooding, meaning river defences stay as they are while the risk grows. Riverside owners are expected to adapt and raise their walls by 2050, and the councils to agree a riverside strategy by 2030. Our piece on the Thames Barrier covers the wider system.

Is Twickenham in a flood zone? It depends which side of the railway you are on

Much of Twickenham sits on higher ground in Flood Zone 1, with Flood Zones 2 and 3 confined to the Thames frontage, the islands and the Crane corridor. Zone 1 land still floods here. The council's Strategic Flood Risk Assessment lists Twickenham, St Margarets and Strawberry Hill as three of the borough's seven critical drainage areas, and three of its four groundwater throughflow zones lie on Twickenham's slopes.

Land behind the walls still counts as Flood Zone 3 on the national map, because flood zones ignore defences, so the assessment has to show what happens if a wall is breached or overtopped. Our guides to residual flood risk and the functional floodplain cover both ideas in more depth.

Check a postcode in Twickenham, St Margarets or Strawberry Hill

Enter a postcode below to screen a site against Environment Agency data for rivers and the sea, surface water and reservoirs, or open our full flood risk map for anywhere in England. The coral line follows the four Twickenham wards, so the tidal Crane at Isleworth, Whitton and the towpath below Teddington Lock lie just beyond it.

Flood alerts and recorded flooding in Twickenham

Twickenham's recent record, in the council's and the Environment Agency's own documents, is one of repeated tidal alerts on the riverside and sudden surface water flooding in storms, not one large river flood.

1. 12 July 2021. A storm of between a 1 in 10 and more than a 1 in 100 year intensity fell across the borough. Richmond's Section 19 report records internal flooding on Chestnut Road in West Twickenham, where residents said the drains back up quickly in heavy rain, and highway flooding on Strawberry Vale.
2. 30 March 2026. The Environment Agency's alert for the tidal Thames from Putney Bridge to Teddington Weir forecast 4.60 m AOD at Richmond and named the Twickenham riverside among the places at risk.
3. 9 and 10 October 2026. A further alert for the same reach forecast a 4.70 m AOD high tide, again listing Riverside and The Embankment at Twickenham and Ranelagh Drive.

The Environment Agency's gauges at Richmond, Teddington Lock and the River Crane at Marsh Farm all appear on our live river levels map, which shows every station in England on one screen. At Richmond the agency treats 4.60 m as the level at which low-lying land can flood.

Richmond Local Plan Policy 8: the tests a Twickenham site has to pass

Richmond upon Thames council is both the planning authority and the Lead Local Flood Authority for Twickenham. It adopted the Richmond upon Thames Local Plan 2024 to 2039 on 7 October 2025, replacing the 2013 Twickenham Area Action Plan, and Policy 8, Flood Risk and Sustainable Drainage, sets the local tests. The Environment Agency advises on the Thames, the Crane and the Duke of Northumberland's River.

• Zone by zone. Highly vulnerable uses are refused in Flood Zone 3a and in areas at 1 in 100 year surface water risk, and self-contained basement flats and basement bedrooms are refused in Flood Zones 2 and 3. In Flood Zone 3b only water-compatible uses and essential utility infrastructure are allowed on undeveloped land.
• Islands count as floodplain. Where the way on and off an island starts in the functional floodplain, the island is treated as Flood Zone 3b for new development, even if parts of it sit higher. That covers Eel Pie Island, which is reached only by a footbridge from the Twickenham bank.
• Floor levels. Finished floors should sit at least 300 mm above the 1 in 100 year river level or the 1 in 200 year tidal level, whichever is higher, with climate change. Where defended tidal flooding applies, sleeping accommodation goes above the Thames tidal breach level for 2100.
• Room for the walls. New building is set back at least 16 m from the landward side of a tidal defence and 8 m from other main rivers, culverted stretches included, so that the defences can be maintained and raised. Riverside schemes must show how their walls could reach the TE2100 level, and any site that relies on an active, demountable defence should replace it with a permanent one.
• A local sequential test. Twickenham is a district centre and St Margarets and East Twickenham are local centres. The Local Plan waives the sequential test for development inside a centre, for housing or mixed use within the 800 m buffer around one, for allocations already tested, for replacing a single house and for conversions or changes of use.
• Flood emergency plans. Schemes of 10 or more homes or 1,000 m² of other floorspace in Flood Zones 2 or 3, at 1 in 100 year surface water risk or in a surface water hotspot, and any site without safe access, must submit a flood emergency plan.
• Runoff. Every scheme uses SuDS and aims for greenfield runoff. Where that is not feasible, the minimum is 2 l/s, and failing that at least 50% attenuation of the existing peak runoff, and written confirmation of capacity before any discharge to a public sewer.

The evidence behind Policy 8 is the Level 1 Strategic Flood Risk Assessment, prepared by Metis Consultants in 2020 with minor updates in March 2021; our explainer covers what an SFRA is for. Across London, the 2021 London Plan's policies SI 12 on flood risk and SI 13 on sustainable drainage still apply: the Mayor's draft replacement plan finished its consultation on 15 October 2026 and is not expected to be adopted before 2028.

Nationally, flood risk sits in chapter 18 of the August 2026 NPPF. Policy F4 says when a site-specific assessment is needed, F5 and F6 cover the sequential and exception tests, and F8 expects all development to follow the 2025 National Standards for sustainable drainage. Our summary of the August 2026 NPPF changes sets out what moved.

Basements in Strawberry Hill, Marble Hill and St Margarets West

Rain that soaks into permeable ground on the slopes moves downhill over the London Clay beneath, and the council calls this throughflow. Three of the four throughflow and groundwater policy zones in Policy 8 are in Twickenham, and a basement or cellar inside one needs extra evidence before the council will decide the application. The council's flood strategy also reports a feasibility study for a scheme in the Strawberry Hill critical drainage area.

• A screening assessment first. Every basement or cellar proposal in a zone needs one, covering the ground below the site, land stability and flood risk and drainage, including throughflow, groundwater and surface water.
• Then a basement impact assessment where needed. If screening finds a possible effect, a basement impact assessment by a chartered professional follows, with at least two borehole readings taken over a period of at least 12 months to catch seasonal change.
• Limits on size. Basements in these zones stay within the site's curtilage and take no more than half of each garden or open space on the plot.
• Near the river, breach hazard decides. In Flood Zone 3a where the SFRA maps extreme, significant or moderate breach hazard, new basements are limited to less vulnerable uses unless an assessment shows the risk to life can be managed, and basement bedrooms are refused.

Our articles on basement conversions in a flood zone and on groundwater evidence for planning explain how the monitoring and screening usually run.

From Twickenham Riverside to the Stadium: allocated sites and their flood constraints

The Local Plan allocates eight sites inside the Twickenham wards, and its site sheets record the flood constraints on each. Every one has a flood or drainage constraint, and only Twickenham Riverside reaches Flood Zone 3.

The riverside allocation is being built now. Approved by the council's planning committee on 24 November 2022, it brings 45 homes, half of them affordable, with shops, offices and new public gardens; Kier began main construction in July 2026, a new river defence wall was going up by August, and completion is planned for 2027. Its published flood risk assessment and SuDS report sets the ground floor at 7.4 m AOD, half a metre above the TE2100 defence level, and limits runoff to the public sewer to 10 l/s.

Does my project need a flood risk assessment in Twickenham?

Any planning application in Flood Zones 2 or 3 needs one, and in Twickenham so do many Zone 1 sites inside the critical drainage areas or the throughflow zones. The table sets out the usual cases; the site's levels and the proposed use decide the rest.

Homes in Flood Zones 2 or 3 beyond the centres and their buffers also face the sequential test, with the exception test where more vulnerable use is proposed in Zone 3a. The council's critical drainage areas are explained in our separate guide.

Reports we prepare for Twickenham sites, from Eel Pie Island to the Crane

Which report a Twickenham site needs depends on whether it faces the Thames, the Crane or a hillside above the clay, and on who is asking. Our consultants are chartered, Unda is a CIWEM Business Partner, and every Twickenham report is checked and signed by a senior consultant.

• Riverside and Crane applications. Schemes in Flood Zones 2 and 3 along the Thames or the Crane need a flood risk assessment for planning that answers Policy 8 and the SFRA.
• Tide, river, rain and ground together. Here a flood risk assessment weighs the defended tide, the higher river level, the critical drainage areas and the throughflow zones for the plot in question.
• Before exchange. Riverside flats, Eel Pie Island homes and houses near Cole Park raise lender questions that a flood risk survey for property purchase can settle.
• Homes outside the centres. Housing in Flood Zones 2 or 3 beyond the 800 m buffers around Twickenham, St Margarets and East Twickenham goes through the sequential and exception test.
• Major schemes. Ten or more homes or 1,000 m² of floorspace bring a drainage strategy for the council to review as Lead Local Flood Authority.
• Clay ground and limited discharge. Soakaways rarely work on the London Clay, so a surface water drainage strategy here stores water in green roofs, permeable paving or tanks and releases it at greenfield rate, or the 2 l/s minimum, to a Thames Water sewer.
• After permission. Where the council attaches a drainage condition, we prepare the information needed for the discharge of drainage conditions.
• Levels the maps do not give. Where a riverside or Crane site needs a level that published data does not provide, flood modelling can set it, as the river level did for Twickenham Riverside.
• Getting people out. Policy 8 asks larger schemes in the flood zones, the surface water hotspots or without safe access for a flood emergency plan, which a flood warning and evacuation plan provides.
• Throughflow below Strawberry Hill. Basements in the three Twickenham throughflow zones need borehole evidence, and a groundwater flood risk assessment brings the monitoring and screening together.
• Cover for a flooded street. After internal flooding on Chestnut Road in 2021, and with three critical drainage areas in the town, a flood risk assessment for insurance gives an underwriter evidence about the building rather than the postcode.
• Trading on the riverside. Businesses on The Embankment and Riverside sit on the road the Environment Agency names in its tidal alerts, and a business continuity flood assessment helps them plan around high water.
• Commercial floorspace. The riverside allocation adds shops, offices and restaurants, and the Stadium allocation supports growth in its sporting role, where a BREEAM flood risk assessment supports the Pol 03 credit.

Who looks after Twickenham's rivers, drains and flood warnings?

If a flood puts anyone's life at risk, call 999, and call 105 for a power cut. Below that threshold, several bodies share the work in Twickenham.

Four Environment Agency areas cover the town: the Tidal Thames from the River Crane to Teddington Weir warning area, taking in St Margarets, Eel Pie Island and Strawberry Hill; the River Crane at Twickenham warning area around Cole Park; the Tidal River Crane alert area; and the riverside alert from Putney Bridge to Teddington Weir. The Richmond gauge shows the tide as it arrives.

The whole borough is covered on our Richmond upon Thames page, and the river on our River Thames page. Upstream, Molesey and Thames Ditton sit above Teddington Weir, where the Thames is not tidal, while Brentford closes the same TE2100 policy unit downstream and the riverside at Chiswick is named in the same tidal alert. Twickenham also falls within the historic county covered by our Middlesex page, and the full list of areas covers the rest of the country.

Twickenham flood risk: questions from owners, buyers and developers

From Eel Pie Island to Crane Park, Unda Consulting Limited prepares flood risk assessments, sequential and exception tests and drainage strategies for homes, businesses and development land. To discuss a site in Twickenham, St Margarets or Strawberry Hill, call 01293 214444 or email enquiries@unda.co.uk.