Yes, Chadwell St Mary carries real flood risk, though the threat is rain and the river has little to do with it. Nine in ten postcodes are rated high on at least one flood measure. Almost none sit in the river-and-sea flood zones. No flooding is on record here. Flood risk is still the weakest part of the place, and it comes down, not in.
In the Environment Agency's river-and-sea flood zones, about 1% of Chadwell St Mary's postcodes fall in Flood Zone 3, the highest-probability band, and none fall in Flood Zone 2, the medium-probability fringe beyond it. The Agency's separate count of properties at risk from rivers and the sea lists 39 across three postcodes, and puts 27 of them at very low risk and none at high, medium or low. On the river-and-sea measure alone, the marshes the church of St Mary looks out over are close to irrelevant.
There is no standalone surface-water figure for Chadwell St Mary on this page. Surface water is one of the indicators folded into the postcode ratings below, and on a hill above the marshes with almost nothing in the river zones, the other indicators are where the high flags have to come from. The Domesday clerks wrote the place down as Celdewella, usually read as "cold spring", so naming the place after its water came first and worrying about it came later.
The Environment Agency's climate-adjusted flood zone, which looks ahead to higher river and sea levels, also covers about 1% of postcodes. On that view the river-and-sea picture barely moves as the climate warms.
Insurers price from the address and the full set of flood indicators, not the river-and-sea zone alone, so a postcode with a high surface-water flag can cost more to cover than its flood-zone status implies. Get an indicative quote early, and put the exact address into the Environment Agency's long-term flood-risk service with the surface-water layer switched on. A house on the slope and a house at the bottom of the same road can come back with quite different answers.
Of Chadwell St Mary's 175 postcodes, 91% are rated high on at least one flood measure, about 62% medium and about 63% low. Each rating counts a postcode if any one of several measures flags it, surface water among them, so a single indicator is enough to set it off. That is why this figure and the river-and-sea zone share can sit so far apart without contradicting each other.
Modelled high-probability flood extents with no defence present cover about 1% of postcodes, and extents where a defence is present in the model cover none. So in this place the question of defences hardly arises. A river wall or embankment, even where one exists, does nothing about rain with nowhere to drain, and that rain is the source of most of the risk here.
The nearest tide gauge with a long record is at Dover, where sea level rose about 2.2 millimetres a year between 1961 and 2010. That is what the gauge measured over that period, a long way from Chadwell St Mary, and on the river-and-sea figures above it has little purchase on the place.
No flooding is recorded for Chadwell St Mary in the Environment Agency's historic flood outlines. That counts for something, though small surface-water events often never reach the official record, so it shows nothing major has been mapped and stops short of proving the streets have always stayed dry.
On flood risk, Chadwell St Mary does poorly, and the reason is surface water on nine postcodes in ten. The river and the sea barely come into it.