Yes, along the Thames, and much less once you walk away from it. About one in eight postcodes are in the highest river flood zone. A couple of hundred properties carry a high river risk. Only one flood has ever been recorded. The river gives Twickenham its best addresses and nearly all of its flood risk.
The Environment Agency's river-and-sea mapping puts about 12% of Twickenham's postcodes in flood zone 3, the high-probability band. Another 11% are in flood zone 2, the medium-probability fringe outside it. The two bands don't overlap, so between them they cover the postcodes nearest the water. The town is bounded by the Thames to the south and east, with the River Crane to the north, and the land is fairly flat, rising gently west toward Whitton. The postcodes in the zones are the ones lining the river from Strawberry Hill round to Marble Hill.
Surface water has no separate share of its own here. It is folded into the postcode indicators further down, alongside rivers and sea, so any figure quoted for it on its own would be a different measure from the zones above.
Allow for climate change and the picture widens. About 36% of Twickenham's postcodes fall inside the Environment Agency's climate-adjusted flood zone. That is a modelled view of where the water could reach under future conditions. It describes what the model can see coming, and nobody has scheduled it.
Insurers price the individual address, and a riverside postcode in Twickenham can quote very differently from a street a few hundred metres inland. Ask for an indicative buildings-insurance quote on the exact address early on, while it is still cheap to walk away. The premium is the market's own reading of the risk on that house.
On a broader measure that includes surface water, 9% of Twickenham's postcodes rate high on at least one flood indicator, 15% medium and 40% low. These bands overlap with the river zones above and measure something wider, so they cannot be added to them. Much of the low band is rain with nowhere to go, the sort of thing that troubles drains and cellars more than ground floors.
Counting homes is more useful than counting postcodes. The Environment Agency's rivers-and-sea mapping covers 4,836 properties in the 202 Twickenham postcodes that carry any risk at all. Of those, 194 are at high risk, 139 of them homes, 424 are at medium risk, 2,211 at low risk and 255 at very low risk. Postcodes with no river or sea risk are left off the list entirely, and that is why the total looks smaller than the town.
The modelled flood extents separate defended ground from undefended ground. About 5% of postcodes are in the high-probability extent with no defence in the model, and about 3% are in it with a defence present. "Defended" only means the model includes a barrier of some kind. It says nothing about whether the barrier will hold on the night it matters. The one flood the Environment Agency has on record came in December 1965, when the main river overran its channel where there were no raised defences. Eel Pie Island had no bridge until 1957, and before that the crossing was a hand-hauled ferry on a chain. People living on that island have never needed reminding where the river is.
The nearest tide gauge in the record is at Portsmouth. There the sea rose at about 2 millimetres a year between 1962 and 2023. That gauge is a long way down the coast from the tidal Thames at Richmond Bridge, so the figure describes what was measured there over those years and nothing more.
Flood risk in Twickenham is middling. It is real and mapped along the riverbank, and most of the town inland of it has little to worry about.