Some of Chessington is, and the threat comes more from the sky than from the stream. The river maps barely notice the place. Nearly one postcode in five rates high on at least one flood measure. A small tributary runs through the middle of it. Chessington's water problem mostly falls out of the sky.
The Environment Agency's river-and-sea mapping puts about 10% of Chessington's postcodes in Flood Zone 2 and about 1% in Flood Zone 3. The two zones are separate bands. Zone 3 is the highest-probability core, and Zone 2 is the medium-probability fringe outside it, which is why the fringe can be the bigger number. For a town with no river of any size and no coast, the sea-and-river map is almost blank.
The Bonesgate Stream, a tributary of the Hogsmill, runs through Chessington, and it is the main reason the water has any history here. The Environment Agency holds 44 recorded flood events for the area, the latest in September 1968, when an ordinary watercourse overflowed a channel with no raised defences. About 11% of postcodes lie inside a recorded historic flood outline. For a stream that rarely makes the local news, that is a long file.
The Environment Agency's climate-adjusted mapping, which redraws the river-and-sea zones with an allowance for wetter decades ahead, puts about 11% of postcodes inside them. That is barely wider than the outline today. The stream is not expected to grow much. The rain is the variable.
Insurers price from their own address-level flood models, and a house near the Bonesgate Stream or in a low dip can be quoted very differently from one up the road. Get an indicative buildings-insurance quote on the exact address early, alongside the survey, because a hard-to-insure house costs more to own and to sell on.
Counted by postcode, with surface water included alongside rivers and sea, about 18% of Chessington's postcodes rate high on at least one flood measure, 15% medium and 35% low. These shares overlap with the flood zones above and measure something wider, so they should never be added together. The gap between the river map and this one is a measure of how often the problem is rain with nowhere to drain. The mention of the stream on the sales particulars is not the risk to worry about.
The Environment Agency's rivers-and-sea property count lists only postcodes carrying some risk, and in Chessington just three appear, holding 74 properties. Of those, 8 are rated high, 3 medium and 10 low, and all eight high-risk properties are homes. Eight houses carry the river risk for a whole town, and their owners know exactly who they are.
The modelled high-probability flood extent covers about 2% of postcodes with no defences assumed, and about 2% with the defences in the model included. Whatever defences the model knows about make no difference to that outline. A defence on a map is a line in a model, and it was never a promise to any one front room.
The nearest tide gauge is at Portsmouth, where the sea rose about 2 millimetres a year across its record from 1962 to 2023. That is a measured past rate on the south coast. Chessington's buyers can leave the tide tables to Portsmouth.
Flood risk is the weak point in an otherwise dry suburb. The river threat touches a few homes by the stream, while surface water reaches far more postcodes than any buyer looking at the river map would expect.