Most of Melbourn is at low risk of flooding, and a small part of it is at real risk. Only a few postcodes fall in the highest river-and-sea flood zone. About one in ten is rated high risk once rain with nowhere to drain is counted. Nothing in the area is on record as having flooded. For most of the village the risk is low, but the minority who are at risk need to know it.
The Environment Agency's river-and-sea mapping puts about 3% of the Melbourn area's postcodes in Flood Zone 3, the highest-probability zone, and less than 1% in Flood Zone 2. The two zones don't overlap. Zone 2 is the medium-probability strip outside zone 3, which is why it can be the smaller of the two numbers. Neither figure says anything about rainwater pooling in the street.
That rainwater is surface-water flooding: rain falling faster than the ground and the drains can take it away. It has nothing to do with being near a river, and the river-and-sea zones leave it out completely. In this area surface water is counted in the postcode ratings further down, which is why those ratings come out higher than the zone figures.
The Environment Agency's climate-adjusted mapping, which models how the flood zones grow under a changing climate, still puts about 3% of postcodes in the area at risk. It is a modelled projection of future risk, with no date attached to any flood.
For insurance, a home in the highest zone or with a high surface-water rating can expect fewer insurers willing to quote and higher premiums from the ones that do. Most of the village shouldn't see a difference. Get an indicative quote on the specific address early on, because an insurer's answer for one house is worth more than any village-wide map.
Across 232 postcodes in the Melbourn area, about 9% are rated high risk on at least one flood measure, about 11% medium and about 43% low. These ratings combine several measures, including rivers, sea and surface water, and a postcode only has to reach a level on one of them to be counted at it. That is how a village with so little river risk ends up with nearly half its postcodes rated low or worse.
Counting buildings instead of postcodes, the Environment Agency's rivers-and-sea mapping lists 22 postcodes in the area with any risk at all, holding 558 properties. Of those, 79 are rated high risk, 57 of them homes, one is medium and 18 are low. Postcodes with no river or sea risk aren't in this count at all. Seventy-nine is a small number for the village, but for the people living in those 79 buildings it is what matters most.
The modelled high-risk area covers about 3% of postcodes without flood defences and still about 3% with them. In the Environment Agency's model, then, whatever defences exist do not shrink the high-risk area around these homes. "Defended" only means a defence appears in the model, and it never meant a house was safe. Here the model shows it makes no difference to the high-risk area. An estate agent who uses the word "defended" about a Melbourn house is relying on a word the model gives no support to.
The Environment Agency has no recorded flood outlines anywhere in the Melbourn area. That is reassuring, and it is also only as complete as the records: it means no flood was mapped, which is not the same as no flood ever happening.
Flood risk in Melbourn is middling. Most addresses face little or none, while a small, defined group of homes faces high risk, and the defences make no difference to it.