From rivers and the sea, barely. From heavy rain, a little. The river-and-sea flood zones hardly touch the town. Adding the climate allowance changes nothing. The exposure that remains is rain with nowhere to drain. So look at the street, not the nearest river.
The Environment Agency's river-and-sea flood zones cover almost none of Corsham. None of the area's postcodes sit in zone 3, the highest-probability band. Under 1% sit in zone 2, the medium-probability fringe that lies beyond zone 3. The two zones are separate bands, so the zone 2 figure is extra to zone 3, not a slice of it. On this measure, Corsham is about as dry as an inland Wiltshire town gets.
Surface water is a different story, told by a different measure. That's rain falling faster than the ground and drains can take it. Corsham's only entry in the Environment Agency's register of recorded floods is a local drainage and surface-water event on 6 March 1978. Nobody sells a house by mentioning the drains. They're still where the risk here sits.
Looking ahead, the Environment Agency's climate-adjusted flood zone covers 0% of Corsham's postcodes. Even with an allowance for wetter decades, the river-and-sea map stays clear.
For insurance, river and sea risk this low should keep most homes away from the flood questions that push premiums up. The exception is a property in one of the pockets that score for surface water. Those homes can still draw questions or a higher quote, and it's better to find that out before exchanging contracts than at renewal.
At postcode level, about 7% of Corsham's postcodes rate high on at least one flood measure, about 16% medium and about 28% low. These bands include surface water alongside rivers and sea, and they overlap with the zone figures above. Don't add them together or treat them as the same thing. They explain why a town with almost no river-and-sea flood zone still carries some flood risk on paper: the high ratings come from water that never reached a river in the first place.
Counting homes rather than postcodes is more useful. The Environment Agency's rivers-and-sea risk mapping lists 250 properties across the 9 postcodes that carry any risk at all. Postcodes with none don't appear. Of those 250 properties, 10 are rated high risk, 9 of them homes, none medium and 30 low. That's a handful of properties, not a district, and the listing tells you which postcodes they're in.
On defences, Corsham's postcodes sit 0% inside the high-risk flood extent undefended and 0% inside it defended. With no high-risk extent to speak of, there's nothing to defend. Note that "defended" in this modelling only means a defence is present in the model. It never means a property is safe.
The nearest tide gauge in the records is at Portsmouth, where the sea rose by about 2 millimetres a year over its measured record from 1962 to 2023. That's a historic rate at a gauge a long way from Corsham, not a forecast for the town, and it matters here about as much as the tide tables do.
The Environment Agency's historic flood outlines cover none of the area. No recorded river or sea flooding is a reassuring fact, but it's a statement about records, not a promise that water has never come through.
Corsham's flood risk is middling rather than alarming. The rivers and sea leave it almost untouched, and a scattering of rain-driven hotspots is enough to stop it being a clean bill of health.