Wotton-under-Edge has more flood risk than a hill town should, and almost none of it comes from a river. The river and sea flood zones barely reach the town. Water running off the slopes after heavy rain affects far more of it. About one postcode in six rates high on at least one flood measure. The danger here is downhill runoff, not a river bursting its banks.
On the Environment Agency's river-and-sea mapping, about 1% of the area's postcodes are in Flood Zone 3, the highest-probability band. Another 1% are in Flood Zone 2, the medium-probability band just outside it. The two zones don't overlap, so a postcode is counted in one or the other, never both. By the river measure alone, the town is close to dry. "Not in a flood zone" will be true for almost every listing in Wotton, and it is the least useful thing a seller can tell you about a house under the Cotswold Edge.
The Environment Agency doesn't publish a separate surface-water share for the town, but it counts surface water in the broader postcode measure below. The geography explains why that measure matters more here. The town is built against an escarpment, with the Ozleworth and Kilcott brooks in the valleys nearby. Heavy rain runs down the slope through gardens, lanes and back doors on its way to the lower ground.
If the river zones are redrawn with a climate-change allowance, about 2% of postcodes fall inside them. That keeps river flooding small on the Environment Agency's forward look. It does not change the slope.
For insurance, a house in one of the few river-zone postcodes, or on a street that rates high for surface water, can expect insurers to ask more questions and some to charge more. A house higher up the hill is usually quoted like any other. While the survey and mortgage are going through, get an insurance quote for the exact address, because insurers price individual addresses, not whole towns.
The broadest count looks at every postcode against several measures together, surface water included, and records the worst rating each one gets. On that basis about 16% of postcodes rate high on at least one measure, 17% medium and 28% low. The large gap between this measure and the river zones is the runoff showing up in the figures.
Counting properties tells you more than counting postcodes. The Environment Agency's rivers-and-sea register lists 260 properties across nine postcodes, the only postcodes in the town with any river or sea risk at all. Of those properties, 14 are at high risk, 12 of them homes, with 18 at medium and 27 at low. These counts are small. The 14 households at high risk get no comfort from that.
On the Environment Agency's modelling, about 1% of postcodes fall in the high-risk river extent whether or not defences are included, so the modelled defences make no measurable difference. The only flood the Environment Agency has on record here happened in July 1968, when the river overtopped its channel with no raised defences in the way. The model counts a defence if one exists there, but that doesn't mean a house behind it is safe, and here there is very little for the model to count.
The nearest tide gauge is at Portsmouth, where sea level rose by about 2 millimetres a year between 1962 and 2023. That is the rate measured over those years, at a gauge a long way from an inland Cotswold town. Of Wotton-under-Edge's flood problems, the sea is the smallest.
Flood risk is a real weakness for Wotton-under-Edge. The river barely matters here, but the slope does, and about one postcode in six is at high risk on at least one flood measure.