Most of Keynsham stays dry, and the numbers sit on the reassuring side of ordinary. Under one in a hundred postcodes fall inside the highest river flood zone. Around three in a hundred sit in the wider zone that floods less often. The town grew up where the River Chew runs into the River Avon, so the risk is real but it clusters on the low ground near the water. This is not a flood town. It is a river town with a handful of streets that keep an eye on the forecast.
The river flooding is the headline risk, and it is a narrow one. Roughly three in a hundred addresses sit within the medium river flood zone, the band that carries a moderate long-run chance of water. Fewer than one in a hundred fall into the highest zone, the ground closest to the two rivers where flooding is most likely. That the town has form here is not a secret. Memorial Park, which runs alongside the River Chew, was extended after the floods of 1968, which tells you the water has come up before and that the low ground remembers it.
Surface water is the broader story, the kind of flooding that has nothing to do with a river bursting and everything to do with rain arriving faster than the drains can clear it. About seven in a hundred postcodes carry a high surface-water risk, and something closer to one in eight sit at medium. Add in the lower band and roughly three in ten have some level of surface-water exposure on paper. Most of that is the kind of once-in-a-blue-moon puddling that never troubles a floor, but the higher-risk pockets are worth checking street by street rather than trusting the town average.
Look forward and the picture holds broadly steady. The flood zone drawn with a climate allowance built in, the map that tries to price in wetter decades ahead, still covers well under one in a hundred postcodes. The rising-water problem here is a known, bounded one rather than a slow creep that swallows the town. The streets at risk in thirty years are mostly the streets at risk now.
For insurance, that split matters more than the town-wide figure. For most Keynsham addresses, flood risk is a non-event and cover prices itself accordingly. For a home in one of the river or high surface-water pockets, expect the questions to get sharper, the premium to reflect it, and the sensible move to be checking the specific address history before you commit rather than after. The difference between a dry street and a flagged one is a few hundred metres and a real number on the renewal.
Keynsham carries a middling flood risk, and middling is the honest word for it. The bulk of the town has little to worry about, a thin band near the two rivers has genuine exposure, and which one you are buying comes down to the exact address rather than the name on the sign.