Yes, Cheltenham has a real flood risk, and most of it does not come from the river. Only a sliver of the town is in the river flood zones. About a quarter of postcodes score high once rainwater is counted. The last recorded river flood came over the top of the defences. A town that got rich on its water has never been very good at keeping it where it belongs.
On the Environment Agency's river-and-sea mapping, about 4% of Cheltenham's postcodes are in flood zone 3, the highest-probability band, and a further 2% are in flood zone 2, the medium-probability fringe outside it. The two bands do not overlap, so the second figure is extra ground beyond the first. The River Chelt rises at Dowdeswell and crosses the whole town on its way to the Severn, and these zones mark where it and the Severn can reach.
Surface water is a separate risk. It is rain that falls faster than the drains can clear it, and it can collect on a street nowhere near a river. The river-and-sea zones leave it out entirely, which is why a house can be outside every zone and still flood.
The Environment Agency's climate-adjusted zone widens to about 8% of postcodes. That is the modelled reach of the same rivers under the extra rainfall allowed for in future, and it is the line to watch for a house being bought for the long term.
Insurers price surface water and river flooding together, at the level of the address, so a flood flag on the postcode tends to appear in the quote as a higher premium, a larger excess or a narrower range of insurers willing to offer cover. Look up the exact address on the Environment Agency's long-term flood risk service, which shows surface water and rivers separately, and ask for an indicative insurance quote while the price is still being negotiated.
The postcode indicators take a wider view, counting a postcode if any one of several measures, surface water included, puts it at a given level. On that basis, about 24% of Cheltenham's postcodes are high on at least one measure, 27% medium and 48% low. The town's name may help explain it. The second half of the old name, Celtan hom, may mean water-meadow, and scholars have not settled the question.
Counting homes is more useful than counting postcodes. In the 320 postcodes that carry any river-and-sea risk at all, the Environment Agency counts 7,265 properties, of which 1,065 are at high risk, 316 at medium, 1,003 at low and 713 at very low. Postcodes with no river-and-sea risk are left out of the count altogether, so these numbers describe the exposed corners and not the town as a whole.
Defences change the map less than buyers hope. About 4% of postcodes are in the high-risk extent with no defence in the model, and about 3% are in it even with a defence included. A defence counted in the model only means a structure exists, not that the houses behind it stay dry. Cheltenham's most recent recorded flood, in July 2007, came from a main river overtopping its defences, and the Environment Agency holds 119 recorded flood events for the area.
The coast is about 7 kilometres from the nearest part of Cheltenham, and the shoreline management plan for the stretches that cover the area is to hold the line over the next 20, 50 and 100 years. That is an intention to keep the existing coastline defended. It depends on money nobody has yet committed, and it tells you nothing about which defences are standing today.
The nearest tide gauge with a long record is at Portsmouth, where sea level rose by about 2 millimetres a year between 1962 and 2023. Portsmouth is a long way off, and the figure is the rate measured there over those years.
The rivers threaten fewer homes than the postcode indicators suggest, but about a quarter of postcodes flagged high and a flood that overtopped its defences make flood one of Cheltenham's weaker points.