Swanscombe has a modest flood risk, and most of it comes from rain. None of the town is in the river-and-sea flood zones. About one postcode in nine still rates high once surface water is counted. No flooding is on record. Where risk exists, it is in the dips in the road and the drains that fill up.
On the Environment Agency's mapping, 0% of Swanscombe's postcodes are in flood zone 3, the highest-probability band for rivers and the sea. Another 0% are in flood zone 2, the medium-probability fringe beyond it. The agency's property-by-property assessment of river and sea risk lists 5 properties at very low risk and none at low, medium or high. The Thames estuary has been close by since the Vikings camped along it, and the mapping still keeps it away from the town's postcodes.
Surface water is a different matter. The flood zones only model water coming out of a river or in from the sea. They say nothing about a heavy storm that falls on Swanscombe and has to run somewhere. That is why the town shows any risk at all on the broader postcode measure further down.
The Environment Agency's climate-change version of the flood zones, which allows for higher river flows and sea levels, also puts 0% of postcodes inside it. On the river-and-sea measure, the agency's own forward look leaves Swanscombe where it is today.
Insurers do not price policies from flood zones alone. They price each address on several sources of flooding, surface water included, so two houses in Swanscombe can get different quotes even though both are outside any flood zone. A house with a clear zone check can still pick up a surface-water loading when the quote comes back.
Across the postcodes, counting a postcode if it rates on at least one of several flood measures, surface water among them, about 11% come out high, 16% medium and 31% low. That is a broader measure than the flood zones, which is why it can show risk where the zones show none. Put the exact postcode into the Environment Agency's long-term flood risk service and look at the surface-water layer in particular, because this is where the town's risk varies from one street to the next.
The Environment Agency's modelled flood extents put 0% of postcodes in the high-risk extent, whether undefended or defended, and 0% in the low-risk undefended extent. In this model, "defended" only means a flood defence is present, and it is not a promise that a house stays dry. Here the question doesn't come up, because no part of the town falls in the extent a defence would need to hold back.
The nearest tide gauge with a long record is at Dover, where the sea rose by about 2 millimetres a year between 1961 and 2010. That is the rate the gauge measured over those years, at a gauge some distance down the coast from Swanscombe.
No historic flooding is recorded in the area, and 0% of it falls inside the Environment Agency's record of past floods. That is reassuring, but it only tells you about floods that were recorded. A front garden that held water after a storm would never have made it into that record.
The flood risk in Swanscombe is middling. Rivers and the sea are not a threat, but storm rain can be, depending on the street, and an address check will tell you which kind of street you are buying on.