Royston has no river problem and a modest rain problem. None of the town is in a river or sea flood zone. About one postcode in eleven carries a high flood indicator anyway. More than a third carry at least a low one. The water to think about here is the rain that falls on the town, since no river runs through it.
The Environment Agency's river and sea mapping puts none of Royston's postcodes in Flood Zone 3, the highest-probability band, and none in Flood Zone 2, the medium-probability fringe beyond it. Royston grew up where Ermine Street crossed the Icknield Way on the slopes of the chalk downs, and the Romans had no reason to build their roads beside a river. Neither does the flood map.
Surface water is a different matter. It is rain that collects where the ground or the drains cannot take it fast enough, and it has nothing to do with a river. Every flood indicator that touches Royston comes from surface water or another measure outside the river and sea mapping, because the river and sea zones are empty. That makes the risk local and patchy, sometimes down to one dip in one road.
The Environment Agency's climate-adjusted mapping, which redraws the zones with allowances for heavier future rainfall and higher rivers, still puts none of Royston's postcodes inside them. Even with a worse climate built in, the river map stays empty.
For insurance, a home outside any river or sea zone generally starts from a stronger position. Insurers also price surface-water risk, though, and some of them look at it street by street. On a house in one of the town's lower-lying roads, the quickest way to see where it stands is to get an indicative quote on the exact address early. A surveyor's report seldom says much about where the rain goes after it leaves the gutter.
Across Royston's postcodes, on at least one of several measures, including surface water alongside rivers and sea, about 9% rate high, about 14% medium and about 36% low. Those shares count any one measure, and here almost all of it is surface water. "Not in a flood zone" is true of every house in town, but it says nothing about rain.
The Environment Agency's modelled flood extents put none of the area's postcodes in the high-risk outline, whether undefended or behind a modelled defence. The model has no flood channel to defend against, so the question of a defence never comes up. Whatever protection a house has from surface water comes down to drains, gradients and gutters.
Royston has no recorded flood history, with none of the area's postcodes inside the Environment Agency's historic flood outlines. That is reassuring for a town with no river to overflow. But the outlines record the floods someone mapped, and surface water usually comes and goes before anyone surveys it.
Flood risk in Royston is middling. The river and sea picture is clean, but the surface water in some postcodes keeps it from being a non-issue.