Yes, Bushey has a flood problem, and it mostly comes from rain. The river maps hardly touch the town. Broader measures flag nearly a quarter of its postcodes as high risk. The hill keeps the sea well away. The water to worry about is the kind that runs off roads and gardens after a heavy storm, and the zone maps were never drawn to show it.
On the Environment Agency's river-and-sea mapping, about 1% of Bushey's postcodes are in Flood Zone 3, the highest-probability band, and about another 1% are in Flood Zone 2, the medium-probability fringe outside it. The two bands don't overlap, so each one counts different postcodes. The agency has recorded four flood events affecting the area, the most recent in February 2014, when a main river ran over the top of a channel that had no raised defences. About 1% of postcodes have a recorded flood in their history.
Surface water is the risk that the river zones leave out. It comes from rain landing faster than the ground and the drains can take it, and it can reach streets nowhere near a watercourse. Bushey has no separate published surface-water share. That risk is folded into the postcode measure further down, and it is the main reason that measure reads so much higher than the zone figures.
The Environment Agency's climate-adjusted mapping, which models how far the river zones could spread in future, puts about 3% of postcodes inside them. That is a modelled scenario for the zones, and it leaves surface water out.
Insurers look at the individual address, and they price surface-water risk alongside river risk. A house on one of the flagged postcodes can carry a higher premium or a higher excess even with no river in sight. The Environment Agency's long-term flood risk service rates a single address for surface water as well as rivers and the sea, and that rating is the one an insurer will see.
Postcode by postcode, the wider picture is less comfortable. About 23% of Bushey's postcodes carry a high rating on at least one of several flood measures, surface water included, about 24% have a medium rating on at least one, and about 40% a low one. A postcode only needs one measure against it to count, and in Bushey that one measure is usually the rain.
Counted as properties, the Environment Agency's rivers-and-sea mapping lists 952 properties in Bushey postcodes that carry some river or sea risk. Of those, 153 are rated high, 91 medium and 149 low. Postcodes with no river or sea risk don't appear in that list, so the count describes the at-risk corner of the town and leaves the rest out.
Defences make no difference here. About 1% of postcodes are inside the high-probability flood extent with no defences in the model, and the share is the same, about 1%, with defences included. In this context "defended" only means a defence appears in the model, and Bushey's figures change by nothing when it does.
The nearest tide gauge is at Portsmouth, where sea level rose by about 2 millimetres a year across its record from 1962 to 2023. Bushey Heath once held the highest point in Middlesex, so the sea is the least of the town's flood worries.
Flood risk is Bushey's weak point. A small share of the town sits near a river, but nearly a quarter of its postcodes are high risk on some measure, and in most cases that means rainwater on the road outside.