Flood Risk Assessment in Twickenham

Unda prepares flood risk assessments and drainage strategies for developers, homeowners, architects and planning consultants working across Twickenham, and we deal directly with the Environment Agency and the London Borough of Richmond upon Thames on your behalf. A flood risk assessment in Twickenham has to account for a place caught between the tidal River Thames and a tangle of smaller rivers, so a Flood Zone map alone rarely settles what a site needs.

Twickenham sits on the north bank of the Thames between Richmond and Teddington Weir — the point where the river stops being tidal. That geography matters: the same streets can be exposed to tidal flooding off the Thames, fluvial flooding from the River Crane and its neighbours, and surface water that overwhelms the drains in a heavy storm. Getting a report accepted here means understanding which of those risks applies to your plot, and how they interact.

When Twickenham Stadium was built in 1908, its pitch was deliberately raised above ground level and drained to keep the nearby River Crane out. Flood risk has shaped how this corner of the Thames valley is built for well over a century — and it still governs what planners will accept today.

If you want a quote or need to talk a site through, you can call one of our experienced flood risk consultants on 01293 214444 or email enquiries@unda.co.uk, and we will reply quickly with a fixed fee.

Flood risk assessment in Twickenham at a glance

Most people who reach us need a report to unlock a planning application, a property purchase, an insurance renewal or a drainage condition. Whatever the reason, the work is the same in principle: assess every source of flooding that can reach the site, then show the council and the Environment Agency that the development will stay safe for its lifetime without pushing risk onto anyone else.

• Planning applications. A flood risk assessment for planning is the report most Twickenham sites need — for a new home, an extension, a change of use or a larger scheme in Flood Zone 2 or 3, or on sites flagged for surface water risk.
• Buying or selling. A flood risk survey for a property purchase gives a buyer, lender or solicitor a clear read on a riverside or low-lying Twickenham property before exchange.
• Insurance. An insurance flood risk assessment can challenge an inflated premium or a blanket decline where the mapped risk overstates the real exposure at the property.
• Drainage and SuDS. A surface water drainage strategy shows how the scheme will manage rainfall on heavy London Clay, using sustainable drainage where the ground allows.
• BREEAM. A flood risk assessment for BREEAM supports the Pol 03 credits on commercial schemes.

Not sure which of these your site needs? Send us the address and a sketch of what you are proposing, and we will tell you plainly — often at no cost.

Flood risk in Twickenham: the tidal Thames, the River Crane and the hidden rivers

Twickenham does not have one flood problem, it has several, and they can arrive together. The most significant recent event, in January 2014, saw surface water, river and sewer flooding combine across the borough after sustained heavy rainfall. A good assessment starts by naming every source that can reach your plot rather than reading a single map.

You can get an early read on any of these before you commission a report. Our free flood risk map screens a postcode for rivers, sea, surface water and reservoirs; the live river levels map shows how the Crane and the Thames are behaving right now; and the geology and ground conditions checker gives an indicative view of whether infiltration drainage is likely to work on your plot.

A history of flooding in Twickenham

Twickenham has a long, well-documented flood record, which is exactly why the Environment Agency and the council scrutinise development here. Real events, not just modelled maps, tell you what a report has to defend against.

• January 2014. The borough's most significant recent flood, when surface water, rivers and sewers combined after weeks of rain and damaged properties across Richmond upon Thames.
• February 2014, Eel Pie Island. The Thames rose over the footbridge and around twenty-five residents were cut off, with police wading through water to reach them.
• Spring tides on the embankment. High tides routinely flood Twickenham's riverside and car parks along the embankment — a recurring, visible reminder that this reach is tidal.
• Surface-water hotspots. Environment Agency mapping identifies North Twickenham and South Twickenham among the borough's areas most susceptible to surface-water flooding.

Climate change is expected to make this worse: analysis in Aviva's 2025 report found the number of properties at risk in the Twickenham area could rise by around a third by 2050.

Your Lead Local Flood Authority and planning policy in Twickenham

Twickenham falls within the London Borough of Richmond upon Thames, which is both your Lead Local Flood Authority and the Local Planning Authority. The council leads on surface water, groundwater and ordinary watercourses, while the Environment Agency covers the main rivers and the tidal Thames. A report that speaks to both, in the terms they use, is far more likely to be accepted first time.

• Richmond's evidence base. The borough's Local Flood Risk Management Strategy, Strategic Flood Risk Assessment and Surface Water Management Plan set the local expectations your report should reflect.
• The tidal Thames and TE2100. Twickenham sits in the Environment Agency's Twickenham policy unit under Thames Estuary 2100, which plans how tidal risk is managed as the climate changes.
• The Thames Barrier. Tidal London, including Twickenham, is protected by the raised Thames Tidal Defences and the Thames Barrier downstream — but planning policy increasingly asks new development not to lean on defences that have to be adapted over time.
• National policy. Every report is judged against the NPPF and its planning practice guidance, and against the Environment Agency's flood risk assessment requirements for planning applications.
• Drainage sign-off. Where a scheme increases impermeable area, the council and Thames Water will expect a drainage strategy and, often, discharge of a planning condition before you can build.

The wider tidal picture is moving, too. Delays to the River Thames Scheme upstream and the long-term adaptation of the barrier are a reminder that no site should be justified on defences that are not yet in place — a point Richmond's planners and the Environment Agency take seriously.

What your flood risk assessment in Twickenham must show

Whether the trigger is a planning condition or an Environment Agency objection, the assessment has to answer the same questions convincingly. On a tidal Twickenham site that usually means proving the development is safe against a modelled tidal level, with a suitable allowance for climate change, and that it does not make flooding worse anywhere else.

1. Every source, screened. Tidal, fluvial, surface water, groundwater and sewer risk assessed for the specific plot, not just the headline Flood Zone.
2. The right design levels. Finished floor levels and safe access and egress set against the relevant flood level plus climate change allowance.
3. The sequential approach. Where required, a sequential test and, if needed, an exception test to show the development is steered to the lowest-risk land available.
4. No worse for the neighbours. Compensatory flood storage and a drainage design so the scheme does not raise flood levels or run-off elsewhere.
5. Modelling where the maps fall short. Site-specific flood modelling or a groundwater assessment where the published data does not resolve the risk.

Getting any of this wrong is a common reason applications are invalidated or refused — so it is worth doing properly the first time.

Development and flood risk on the Thames at Twickenham

Building on the tidal Thames is done all the time in Twickenham, but it takes careful design. A good example of the approach is a riverside scheme in a tidal Flood Zone 3 location: the buildings are raised so that finished floor levels sit above the modelled one-in-a-thousand-year flood with a climate change allowance, water-compatible uses are placed at the lowest levels, and the whole thing is worked up in close dialogue with the Environment Agency. That is the template we follow — turning a high-risk riverside plot into a scheme planners can support.

Flood risk assessments for every situation in Twickenham

Twickenham sends us every kind of enquiry, and each has a home in our service range. Whichever applies to you, the report is prepared to the same standard and signed off by a senior consultant.

• Planning. Flood risk assessments for planning across new build, extensions, conversions and change of use.
• Property purchase. Flood risk surveys for buyers, sellers and lenders on riverside and low-lying homes.
• Insurance. Insurance-focused assessments to challenge premiums and declines.
• BREEAM. BREEAM flood risk assessments for commercial schemes.
• Sequential and exception tests. Sequential and exception tests where policy requires them.
• Drainage and SuDS. Surface water drainage strategies, preliminary drainage design and discharge of drainage conditions.
• Free tools. Our drainage calculators and BRE 365 infiltration rate calculator help you get a first pass before commissioning a design.

Twickenham is part of the historic county of Middlesex, and you can see our wider coverage on the Middlesex flood risk assessment page or across our other areas we cover, including nearby Thames-side towns such as Molesey and Thames Ditton.

How Unda helps with flood risk assessment in Twickenham

We are a chartered flood risk and drainage consultancy that has completed more than 5,000 assessments across England and Wales since 2014. We know this stretch of the Thames, we know how Richmond upon Thames and the Environment Agency assess a scheme, and a senior flood risk consultant signs off every report. You can read more about us or explore what a flood risk consultant does before you commit.

Frequently asked questions