Helston has a flood problem, and it is a small, specific, addressable one. Most of the town is nowhere near the water. A narrow band along the river is, and always has been. The whole place sits behind a shingle bar that blocked the river's way to the sea thousands of years ago and turned it into a pool. That is the arrangement Helston has been living with since before anyone started drawing maps of it, and the risk here is a question about which street you buy on rather than about the town.
On the Environment Agency's river-and-sea flood zones, about 4% of the area's postcodes fall in zone 3, the higher-probability band, and about 2% fall in zone 2, the medium-probability fringe that sits outside zone 3 rather than around it. Zone 2 being the smaller figure is not a mistake. It is what happens when the floodplain is a river corridor with steep ground either side, which is exactly what the Cober gives you as it comes down through the town towards Loe Pool.
Surface water is the risk that estate agents never mention and insurers never forget, and it is measured separately from those zones. This site's postcode indicators fold surface water in alongside rivers and sea, which is why the indicator shares further down are considerably larger than the zone shares above. The two are not the same measure and must never be added together. Historic flood outlines cover about 5% of postcodes, and the Environment Agency's records list 20 recorded flood events here, the most recent in June 1993 from the main river.
Looking forward, the zone that carries a climate change allowance covers about 1% of postcodes. That is the modelled future extent rather than a prediction of any particular winter.
For insurance, the practical point is that a general area figure is worthless to you. Underwriters price the address, not the town, and the gap between a quote inside that river corridor and one three streets up the hill can be the difference between a routine policy and a large excess with conditions attached. Get an indicative quote on the specific property before you instruct a solicitor, because finding out at the mortgage-offer stage is an expensive way to learn geography.
Taking every measure together, about 13% of the area's postcodes rate high on at least one flood indicator, about 19% medium and about 36% low. Those bands overlap with the zone figures above rather than adding to them, and they are shares of postcodes rather than counts of homes.
The property counts are more useful. Across the 31 postcodes that carry any risk at all from the Environment Agency's rivers-and-sea mapping, and only those postcodes appear, 611 properties are covered: 17 at high risk, 148 at medium and 155 at low. Of the high-risk ones, 11 are residential. Eleven homes is a number you could walk past in five minutes, which is a very different thing from a town at risk.
On whether anything stands between the water and the door, about 3% of postcodes sit inside a high-risk extent with no defence present in the model, against about 1% where a defence is present. Note what that second figure means. The model records that a defence exists, not that it will hold, not that it is maintained, and not that your floor stays dry. Defended is a mapping category, not a promise.
Every postcode here is covered by a shoreline management plan, and the stated policy is to hold the line over the twenty, fifty and hundred-year horizons. That is an intention to maintain defences, not a defence, and not a commitment anybody has signed in blood. It matters less here than it would on the coast proper, since the town centre sits about 2,850 metres from the sea at its nearest point and about 3,670 metres at the median.
At the nearest long-record tide gauge, Devonport, sea level rose by about 2.35 millimetres a year across the 1962 to 2015 record. That is measured history rather than forecast, and it is the baseline anything about the future gets built on.
Flooding here is middling: not a town-wide problem, but not a box you can tick without looking. Find out which side of the Cober corridor your address sits on before you fall in love with the kitchen.