Chinnor's flood risk is mostly about rainwater, and the rivers and the sea barely come into it. No part of the village falls in the river-and-sea flood zones. A small minority of postcodes still register high risk on at least one measure. About a third register low risk. Rain running off the hills is the threat, and it doesn't need a river nearby to reach a house.
The Environment Agency's river-and-sea mapping puts 0% of Chinnor's postcodes in Flood Zone 3, the highest-probability band, and 0% in Flood Zone 2, the medium-probability band just outside it. In that sense the village is about as far from a main river problem as a place can be. That measure covers rivers and the sea only, and surface water uses a different indicator.
Surface water is the part that counts here. Chinnor is a spring-line settlement under the Chiltern escarpment, built where water comes out of the chalk, and its neighbour Crowell, also covered on this page, grew up at the source of a stream called the Pleck. After heavy rain the water comes off the hill and runs downhill through lanes, gardens and the occasional driveway built in the wrong place.
The Environment Agency's climate-adjusted flood zones also show 0% of Chinnor's postcodes, so the forward-looking river-and-sea picture matches today's. That covers the zones only. It adds nothing to the surface-water picture.
For insurance, a home outside the river-and-sea zones usually gets a straightforward quote. A property on one of the surface-water flow paths can still get asked questions, and the answer depends on the individual house more than on the village. The Environment Agency's long-term flood risk service lets you enter the exact address and see its surface-water rating separately from the river rating, and that single result tells a buyer more than any village average can.
Combining every measure the Environment Agency publishes, surface water included, about 7% of Chinnor's postcodes rate high on at least one of them, 8% medium and 33% low. A postcode only needs one measure to qualify, so these shares overlap with each other and with the zone figures, and the high-risk ones are scattered among the rest of the village.
The modelled high-probability flood extents cover 0% of Chinnor's postcodes, both where a defence appears in the model and where none does. So the question of whether a wall stands between a river and the houses never arises here. Surface water is not held back by defences of that kind in any case.
The nearest tide gauge to Chinnor is at Portsmouth, which recorded sea levels rising by about 2 millimetres a year between 1962 and 2023. That is the rate measured at that gauge over those years. Portsmouth being the nearest gauge says about all there is to say about Chinnor's exposure to the sea.
The Environment Agency has no recorded historic flooding in Chinnor, which is reassuring. The record covers floods someone mapped and kept, so an unrecorded wet lane at the foot of the hill would not appear in it.
Overall, Chinnor's flood risk is middling. Rivers and the sea pose none, but a minority of homes sit in the path of water coming off the Chilterns, and the address you buy decides which group you are in.