The rivers leave Chipping Ongar mostly alone, but the rain doesn't always. Almost no postcodes fall in the river flood zones. One river flood is on record, and it was a long time ago. About one postcode in ten still rates high risk on at least one flood measure. That risk comes from surface water, the kind that runs off a field and into the road.
On the Environment Agency's river-and-sea flood zones, fewer than 1% of the area's postcodes fall in Flood Zone 2, the medium-probability band, and none fall in Flood Zone 3, the high-probability band. The two zones don't overlap, so the zone 2 figure is the whole of the river risk here. The Environment Agency has one recorded flood for the area, in December 1993, when a main river overflowed its channel at a spot with no raised defences. Fewer than 1% of postcodes fall inside the area it mapped as flooded.
Surface water is a different matter, and the ground explains a lot of it. The subsoil around Ongar is heavy clay, wet enough in winter that the surrounding farms found it too soggy for sheep. Clay drains slowly, so heavy rain sits on top and finds the nearest low point, whether that's a ditch or someone's drive. A survey that says "Flood Zone 1" has answered the river question and left the rain question open.
Looking ahead, the Environment Agency's climate-adjusted mapping, which adds an allowance for heavier future rainfall to its river and sea modelling, still puts fewer than 1% of postcodes in the flood zones. Climate change makes little difference to Ongar's rivers on this measure. It says nothing about the clay.
Insurance follows the same split. A home well clear of the river zones should be quoted without much fuss for river flooding, but insurers look at surface water as well, so the rate depends on the exact property more than the town. The most useful check here is the Environment Agency's long-term flood risk service for the exact address, with the surface-water result read as carefully as the river one.
On the postcode-level indicators, which count a postcode as at risk if any one of several measures flags it, surface water included, about 10% of the area's postcodes rate high, 9% medium and 30% low. A postcode only needs one measure against it to count, so these shares run well ahead of the river zones without contradicting them.
Counted in homes, the river picture shrinks even further. The Environment Agency's rivers-and-sea mapping lists only the postcodes that carry some risk, and around Ongar that is 8 postcodes covering 362 properties. Of those, 1 property is at high risk, 1 at medium and 8 at low. The single high-risk property isn't a home.
No postcode in the area falls within the Environment Agency's high-probability river flood extent, with or without a defence in the model, so for river flooding the question of what protects a house hardly comes up. "Defended" in that modelling only means a defence is drawn on the map, and it would never mean a house was safe from the water. Here there is nothing on the map to protect.
Chipping Ongar's flood risk sits in the middle: the rivers are close to a non-issue, but the clay and the rain keep the town from being a safe bet.