Some of Stroud floods, and most of it does not. The river risk runs in a narrow line along the valley floor. About one postcode in ten carries a high risk on at least one measure. The homes up the hillsides have mostly hills to worry about. Which slope you buy on matters more than which town.
In the Environment Agency's river-and-sea flood zones, about 7% of Stroud's postcodes are in Zone 3, the highest-probability band, and another 1% are in Zone 2, the medium-probability fringe around it. Zone 2 comes out smaller because so much of the valley floor is already inside Zone 3, with steep ground rising straight behind it. The town takes its name from the marshy ground where the Slad Brook meets the River Frome, so the risk was written into the name before anyone built a mill.
Surface water is the other half of it. In a town spread down the sides of five valleys, heavy rain runs downhill fast and collects in roads, lanes and low gardens long before any river overtops. The Environment Agency's rivers-and-sea zones miss that entirely, so surface water turns up only in the wider postcode measure further down.
With the Environment Agency's climate-change allowance applied, about 6% of postcodes fall in the climate-adjusted flood zone. That is the agency's modelled look ahead, built on assumptions about future rainfall and river flows, and it moves the line very little in a town where the valley sides do most of the containing.
For insurance, the valley floor and the hillside are different propositions. A house in Zone 3 by the Frome will be quoted on its own flood history and position, and premiums and excesses there can look nothing like the figure for a house fifty metres up the slope. Put the exact postcode into the Environment Agency's long-term flood-risk checker and get an insurance quote while the house is still only a viewing.
Taking every measure together, surface water included, about 10% of Stroud's postcodes rate high on at least one of them, 12% medium and 27% low. Any postcode only has to trip one of several measures to count, which is why those shares run higher than the river-and-sea zones on their own.
Counted as properties, the Environment Agency's rivers-and-sea mapping lists 874 in the 42 postcodes that carry some risk, and only those at-risk postcodes appear in it. Of those properties, 192 are at high risk, 120 of them homes, with 109 at medium risk, 36 at low and 21 at very low. The agency has 18 recorded flood events here, the latest in July 2007, when a main river ran over because the channel could not carry the water and there were no raised defences.
On defences, about 2% of postcodes are in the high-risk river extent with no defence in the model, and about 7% are in it with one. "Defended" means only that the Environment Agency's model includes a defence nearby. It does not tell you how high the defence is, how old it is, or whether it holds against a July like 2007.
The nearest coast is at least 8 kilometres away, but about 37% of postcodes still fall under a shoreline management plan, and the policy there is to hold the line over the next 20, 50 and 100 years. Hold the line is the stated plan to keep defences where they are today. That plan relies on money nobody has yet committed, and it tells you nothing about the defences standing there now. The tidal Severn is the reason the plan reaches this far inland.
The nearest tide gauge in the national record is at Portsmouth, where the sea rose by about 2 millimetres a year between 1962 and 2023. That gauge is a long way from Stroud's valleys, and the figure is the rate it measured over those years.
Stroud's flood risk is middling: real and well mapped along the valley bottoms, and mostly irrelevant to anyone buying on the hill.