Flood Risk Assessment in Richmond upon Thames

Few places in London live as closely with the river as Richmond upon Thames. It is the only borough to sit on both banks of the Thames, and the water that gives the borough its parks, towpaths and riverside its character is also the reason so many sites here need careful flood risk work. Below Teddington Lock the Thames is tidal, so a site can be threatened by a high spring tide pushing up from the estuary as readily as by heavy winter rainfall. A flood risk assessment in Richmond upon Thames sets out how a development can be made safe for its lifetime, allowing for climate change, without increasing flood risk anywhere else.

We prepare flood risk assessments in Richmond upon Thames for planning, property purchase, mortgage and insurance, and BREEAM — alongside sequential and exception tests and surface-water drainage strategies. Our flood risk consultants know the borough's tidal reaches, its tributaries and the Council's planning policy well, and turn that knowledge into reports that satisfy the Environment Agency and the local planning authority first time.

Richmond upon Thames sits on both banks of the tidal Thames, so here it is a high spring tide as much as heavy rain that can put a low-lying site under water — and that shapes how every flood risk assessment in the borough is written.

Speak to one of our experienced flood risk consultants on 01293 214444 or email enquiries@unda.co.uk for a no-obligation quote.

• Both banks of the Thames. Richmond upon Thames is the only London borough spanning both sides of the river, so a large number of properties sit near the Thames and its tributaries.
• Tidal below Teddington Lock. Downstream of the lock the Thames rises and falls with the tide; upstream it is non-tidal. Tidal flooding can occur on extreme high tides and storm surges.
• Several sources at once. The borough faces flooding from rivers, the tide, surface water, groundwater and sewers — often interacting.
• Defended, but not risk-free. The Thames Barrier and a system of tidal walls and embankments protect the borough, yet parks, towpaths and low-lying roads still flood on the highest tides.

Why flood risk in Richmond upon Thames is different

Most of the borough's flood risk comes from the River Thames — both as a tidal river below Teddington Lock and as a fluvial (rainfall-fed) river. Because Richmond upon Thames sits on both banks, a large number of properties are potentially at risk from the Thames and its tributaries, with surface water and groundwater adding to the picture. Alongside the main river run a set of smaller watercourses that each behave differently, which is why a site-specific assessment matters here rather than a broad, borough-wide statement of risk.

The groundwater and surface-water picture is shaped by the borough's geology and its heavily urbanised catchments. The River Crane, for example, drains a clay catchment that responds rapidly to rainfall, an effect made sharper over the last century by urbanisation and hard standing. You can see the broad pattern of risk across the borough on our free Flood Risk Map and track the state of the river on our Live River Levels Map.

Which flood zones is Richmond upon Thames in?

Large parts of the riverside sit in Flood Zone 3 (the highest-probability zone) and Flood Zone 2, particularly the tidal frontage at Richmond, Twickenham, Ham, Petersham, Mortlake and Kew, while much of the higher ground away from the river falls in Flood Zone 1. The Environment Agency's Flood Map for Planning shows the zones ignoring defences, so a site can appear in Zone 3 yet benefit from tidal walls in practice — a distinction a proper assessment has to explain rather than gloss over.

The tidal limit is Teddington Lock: below it the Thames is tidal, above it non-tidal. The Thames Barrier protects the borough by holding back storm tides travelling up the estuary, and a network of flood walls and embankments forms part of the Environment Agency's tidal defence system along the Thames, the lower Brent and the Crane. Defences change how a site should be assessed, but they do not remove the need for an assessment where the underlying zone is 2 or 3.

• When an assessment is required. A flood risk assessment is expected for development in Flood Zone 2 or 3, on sites of one hectare or more in Flood Zone 1, in a Critical Drainage Area, or where surface water risk is shown on the Flood Map for Planning.
• Record tide. The Thames Tideway at Richmond usually ranges between -0.93m and 4.67m; the highest level recorded is 5.30m, on 11 December 2018.
• Check the frontage, not just the zone. Threshold levels, ground levels and flood defences on the specific site often matter more than the headline zone.

A history of flooding in Richmond upon Thames

The borough's flood history is dominated by the tidal Thames. The most severe event in living memory was the 1928 Thames flood, when the river broke its banks along riverside London from Woolwich up to Richmond; St Margarets, just across the river, was among the areas inundated on 7 January 1928 after snowmelt, heavy rain and a North Sea storm surge coincided. That disaster, with the 1953 east-coast floods, led directly to the building of the Thames Barrier.

More telling for developers than the rare catastrophe is the routine: the towpath through Ham and Petersham and the riverside at Twickenham flood on the higher spring tides several times a year, for an hour or two either side of high water.

These regular tidal inundations rarely reach homes, but they define how riverside sites must be designed — finished floor levels, safe access and escape, and flood-resilient construction all follow from them. Spring tides are a frequent trigger for Environment Agency flood alerts covering the Thames from Richmond Bridge to Teddington Weir, and you can check the current state of the river against those levels on the Environment Agency's Richmond river gauge.

• 1928. The last great flood of riverside London reached Richmond; fourteen people died across the capital and thousands were made homeless.
• December 2018. The Thames Tideway at Richmond reached its recorded high of 5.30m.
• Every year. High spring tides regularly close low-lying towpaths and roads at Ham, Petersham and Twickenham riverside for short periods around high water.

Planning and drainage policy for development in Richmond upon Thames

The London Borough of Richmond upon Thames is the Lead Local Flood Authority, responsible for managing flood risk from surface water, groundwater and ordinary watercourses, while the Environment Agency covers the main-river Thames and the tide. Development proposals are judged against national policy in the NPPF and against the Council's own Local Plan. The controlling flood policy is Local Plan Policy LP21 (Flood Risk and Sustainable Drainage), and the Council's Strategic Flood Risk Assessment, updated in September 2020, is the evidence base a site-specific assessment should be read against.

On the drainage side, sustainable drainage has been a material planning consideration since April 2015, and proposals that change surface-water run-off must follow the London Plan drainage hierarchy. Since 1 April 2019 the Council has required a completed London Sustainable Drainage Proforma for all planning applications, setting out how run-off is managed as close to source as possible. A sequential test may also be needed where a more vulnerable use is proposed in a higher-risk zone.

Longer term, the borough's tidal defences are governed by the Environment Agency's Thames Estuary 2100 plan. Richmond falls within the plan's P3 policy area, and updated climate modelling means the defences upstream of the Thames Barrier are now due to be raised by 2050 — around fifteen years earlier than first planned. New riverside development is expected to work with that trajectory, safeguarding land for future defence improvements and building in the freeboard that rising levels will demand.

• Lead Local Flood Authority. Richmond upon Thames Council manages surface water, groundwater and ordinary watercourses; the Environment Agency manages the Thames and the tide.
• Local Plan Policy LP21. Flood Risk and Sustainable Drainage — the policy a development must satisfy.
• London Sustainable Drainage Proforma. Required for every planning application since 1 April 2019.
• Thames Estuary 2100 (P3). Tidal defences upstream of the Barrier are to be raised by 2050, shaping riverside schemes now.

What kind of developments need a flood risk assessment in Richmond upon Thames?

Demand for assessments here spans the borough's largest regeneration schemes down to single riverside dwellings. The former Stag Brewery at Mortlake, the borough's biggest redevelopment site at around 22 acres and consented in 2025 for over a thousand homes, includes a new flood protection barrier and an elevated riverside walkway that stays usable when the towpath floods. At Twickenham the Council's own Twickenham Riverside scheme sits in Flood Zones 2 and 3, in an area benefiting from defences but at high tidal and fluvial risk. These headline projects show the level of flood detail the borough expects.

Most instructions, though, are smaller: a riverside apartment conversion, a basement, an extension over a threshold near the towpath, or a change of use that raises the vulnerability of a site. Each still has to demonstrate safe access and escape, appropriate floor levels and no worsening of risk elsewhere. Where national mapping is not detailed enough, as is common on tidal frontages and beside the tributaries, we bring in hydraulic flood modelling to derive accurate levels for the specific site.

• Riverside regeneration. Large mixed-use schemes on the tidal frontage, where flood barriers, walkway levels and safe refuge are central to consent.
• Basements and conversions. Below-ground and change-of-use projects near the river, where groundwater and tidal levels drive the design.
• Householder work. Extensions and outbuildings in Flood Zone 2 or 3 that still need a proportionate assessment.
• Commercial and mixed use. Sites where surface-water drainage and discharge rates must be resolved alongside flood safety.

How Unda helps with flood risk assessment in Richmond upon Thames

Unda are experts in flood risk assessment in Richmond upon Thames. We have prepared assessments and drainage strategies for tidal-frontage sites across London and the Thames valley, and we deal directly with the Environment Agency and lead local flood authorities on behalf of developers, architects, planning consultants and homeowners. Our flood risk consultants understand how a Richmond upon Thames site behaves on a spring tide, how LP21 and the Strategic Flood Risk Assessment will be applied, and how to present a case that gets approved without avoidable rounds of comment.

We work to a clear, fixed quote and aim to get a first draft to you quickly, with the reporting and modelling scaled to what the site and the application actually need. If you would like to see how we present our work, our recent projects and coverage are collected on our about page, and you can begin any instruction through Start a Quote.

Flood risk assessments for every situation in Richmond upon Thames

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. We prepare each of them for sites across the borough.

• Flood risk assessment for planning. The site-specific report submitted with an application to satisfy the NPPF and the Environment Agency, covering every source of flooding.
• Property purchase and homebuyer surveys. For conveyancing, where a search flags risk or a lender needs the actual building assessed rather than broad datasets.
• Flood risk assessment for insurance. Where premiums have risen, cover has been restricted, or a policy needs supporting after a flood event.
• BREEAM flood risk assessment. Structured around BREEAM Pol 03 for surface water and flood management, which a planning assessment alone will not satisfy.
• Sequential and exception tests. The locational case that a site is the most appropriate available, applied where higher-risk land is proposed.
• Drainage strategies and SuDS. Surface-water design to the drainage hierarchy, sizing storage and discharge to meet the required run-off rate.
• Groundwater assessment. The below-ground source assessed within the wider report, important on the borough's clay and low-lying sites.
• Flood modelling. Hydraulic 1D/2D modelling where national mapping is insufficient, feeding accurate levels into the assessment.

For help sizing soakaways and drainage on a specific site, our free Geology and Ground Conditions map and BRE 365 infiltration rate calculator are a useful starting point, and you can read how national policy applies in our NPPF guidance.

Local flood risk management and emergency contacts

Flood risk in the borough is shared between several bodies. The table below sets out who to contact for advice, to report flooding, or in an emergency. For planning enquiries, the Lead Local Flood Authority and the Environment Agency are the key consultees on most Richmond upon Thames applications.

• Report flooding. Contact the Council for surface-water and highway flooding, and Thames Water on 0800 316 9800 for sewer flooding.
• Check your risk and sign up for warnings. Use the Environment Agency's check-for-flooding service and register for free flood warnings via Floodline on 0345 988 1188.
• In a flood emergency. Call 999 if life is in danger, and 105 to report or check power cuts.

Flood risk assessment in Richmond upon Thames — frequently asked questions

We prepare flood risk assessments and drainage strategies across neighbouring areas too, including Surrey, Middlesex, Thames Ditton, Molesey, Walton-on-Thames and Staines. See every location we cover on our flood risk assessment areas page.