Denham carries some flood risk, and very little of it comes from the river. Hardly any homes are in the river flood zones. None are in the highest one. More of the village shows up once rain and drains are counted too. The bigger risk is surface water from heavy rain, not the River Colne.
The Environment Agency's river-and-sea flood zones cover about 2% of Denham's postcodes in zone 2, the medium-probability band, and none in zone 3, the highest. The two zones are separate bands, with zone 2 being the extra fringe outside zone 3, so here the whole of the river risk falls in that outer fringe. Counted by property, the Environment Agency puts 2 homes at medium risk from rivers and the sea, 3 at low risk and none at high. The River Colne runs past the village under a listed footbridge north of Denham Court. Most of the time it causes Denham less trouble than its weather does.
The Environment Agency's river zones leave out surface water: rain falling faster than the ground and drains can take it away. That is the part of the risk that turns up in the broader postcode measures below, and it explains why those measures flag far more of Denham than the river zones do. Surface water also pays no attention to the river's floodplain. A street with no river nearby can still collect water if it sits low and the drains are struggling.
On the Environment Agency's climate-adjusted mapping, which allows for heavier future rainfall and higher rivers, about 2% of postcodes are in the flood zones, the same share as today. As modelled, climate change doesn't widen Denham's river risk.
That small river footprint should make buildings insurance straightforward for most homes. The few properties near the Colne, and any on low ground where surface water collects, are the ones where an insurer may ask more questions or quote a higher premium. Ask for an indicative quote on the exact address early, before paying for surveys and searches. An insurer's answer is the quickest way to tell whether a particular house is one of the handful that matter.
A wider measure scores each postcode on several types of flooding, surface water included, and records the worst rating it gets on any of them. On that basis about 7% of Denham's postcodes rate high on at least one measure, about 27% medium and about 37% low. These shares overlap with the river zones above, and they are higher because surface water is included. Buyers who stop at "not in a flood zone" have only checked the river.
The Environment Agency's model shows no Denham postcodes inside the high-probability flood extent, either with defences or without them. About 2% fall in the low-probability extent with no defences modelled. In other words, the model shows no high-risk river ground here at all, defended or otherwise. "Defended" would only mean a defence appears in the model, which is a long way from saying a house is safe.
The nearest tide gauge to Denham is at Portsmouth, where sea level rose by about 2 millimetres a year between 1962 and 2023. That is the rate recorded on the south coast, and Denham is a long way inland from it. Rising seas do not drive this village's flood risk.
There is no recorded flooding in the area around Denham. That is genuinely reassuring, but the absence of a record isn't proof that water has never come up a garden path. It is best read as no recorded floods yet.
Flood risk in Denham is middling. River flooding is minor, and surface water from heavy rain is the thing to check, one address at a time.