Parts of Burnham-on-Crouch are at real risk of flooding, mostly from the river and the sea. About one postcode in five lies in the highest-risk zone. Once climate change is allowed for, that becomes nearer one in three. Most of the low ground relies on defences. The town makes its living from the Crouch, and the river has never agreed to stay in its channel.
On the Environment Agency's river-and-sea flood map, about 20% of the area's postcodes are in Flood Zone 3, the highest-probability band. Only about 1% are in Flood Zone 2, the medium-probability strip just outside zone 3. The two zones don't overlap, so the small zone 2 figure simply means the ground rises quickly at the edge of zone 3. The Agency has 25 flood events on record here, the most recent from the sea in February 1953.
Surface water, the flooding caused by heavy rain that drains can't clear, isn't reported on its own here. It is counted inside the postcode-level measures further down, alongside river and sea risk.
The Environment Agency also has a climate-adjusted version of the zone map, and in it about 30% of the area's postcodes fall in the flood zones. That is the planners' best estimate of where the edge of the risk moves as sea levels rise.
For insurance, a home in the higher-risk postcodes is likely to cost more to cover and to come with stricter terms. Some insurers may decline to quote. Ask for an insurance quote on the exact address while the sale is still at the viewing stage, since the gap between neighbouring streets can be wider here than the town's size suggests.
Postcodes can also be scored against several flood measures at once: river, sea and surface water. On that combined basis, about 11% of Burnham's postcodes rate high on at least one, about 14% rate medium on at least one and about 41% rate low on at least one. A postcode that is fine on one measure can still be flagged on another, so these shares overlap with the zone figures above.
Counting individual properties gives a more concrete picture. The Environment Agency's rivers-and-sea mapping lists 1,411 properties across the 58 local postcodes that carry any risk at all. Of those, 19 are at high risk, one at medium risk, 29 at low risk and 1,038 at very low risk. Fifteen of the high-risk properties are homes. Postcodes with no risk at all don't appear in the count.
What stands between the water and the houses is the part that matters most. If the Environment Agency's model ignores defences, about 20% of postcodes fall inside the high-probability flood extent. With the defences the model includes, that share drops to about half of one per cent. That difference is how much the town relies on its walls and embankments. A defence on the model is one that exists and is mapped. It can still be overtopped, wear out or go without repairs. Being "defended" means something stands in the way of the water, and nothing more.
Burnham lives right on the water. About 38% of postcodes are within 500 metres of the coast, the closest is just 8 metres away, and the middle postcode is about 640 metres from it. The 500-metre line is a single cut-off used across the whole area to measure closeness to the coast. It isn't a safety boundary.
The shoreline management plan for this stretch of coast is to hold the line at every horizon it covers: 20, 50 and 100 years. Holding the line means the stated aim is to keep defences where they are today. It is an intention, and each stage depends on funding that hasn't yet been committed. The plan also tells you nothing about the condition of the defences standing there now.
Flood risk is one of Burnham's weak points. A large share of the town's low ground stays dry only because the defences hold.