Woolwich has a real flood risk, and most of it is on the low ground by the Thames. About one postcode in five rates high on at least one flood measure. About one in ten is in the river's highest-risk zone. The last time the sea came in, it came through a broken defence. The streets climbing towards Shooter's Hill are where the risk thins out.
On the Environment Agency's river-and-sea mapping, about 11% of Woolwich's postcodes are in Flood Zone 3, the highest-probability band. Another 1% are in Flood Zone 2, the medium-probability fringe just beyond it. The town has a long river frontage and rises steeply behind it, so the boundary between the two zones is tight. The river's big tidal barrier is just upstream, and it closes against surges coming up from the estuary. Woolwich is on the estuary side.
There is no separate surface-water figure for Woolwich in the Environment Agency's river-and-sea zones, and the slope matters for that reason. Rain that falls on the high ground runs downhill towards the river, so a house can be outside every river zone and still have a reason to think about a heavy downpour.
The Environment Agency also publishes a version of its zones that allows for climate change, and on that version about 8% of Woolwich's postcodes fall in the high-probability area. It is a modelled look forward, and it still puts the risk on the same riverside ground.
For cover, this mostly comes down to where the house is. A home on the flat ground near the river is likely to need specialist cover or carry a higher premium, while one up the hill should look much like any other London house to an insurer. Check the exact address on the Environment Agency's long-term flood risk service and get an indicative insurance quote early, because two homes a few streets apart can come back with very different answers.
A wider measure counts a postcode if it rates high, medium or low on any one of several flood indicators, surface water included. By that count, about 21% of Woolwich's postcodes rate high on at least one indicator, about 25% medium and about 41% low. A single bad reading on any one measure is enough to count, which explains why these shares are larger than the zone figures.
Counting homes gives a more concrete picture. The Environment Agency's rivers-and-sea assessment lists 166 postcodes that carry some risk, covering 5,633 properties. Of those, 983 are at high risk, 804 of them homes, along with 185 at medium risk, 143 at low risk and 2,610 at very low risk. Postcodes with no risk at all do not appear in the list.
The defences are the part buyers usually ask about least. About 10% of postcodes are inside the high-probability flood extent with a defence present in the Environment Agency's model, and about 6% are inside it with none. A defence in the model means a wall or embankment is there, and says nothing about whether it will hold. Two floods are on record in Woolwich, and the latest, in February 1953, came from the sea after a defence breached. A flood in 1236 killed many people in medieval Woolwich. Both times the river did what the walls were meant to stop.
The nearest tide gauge with a long record is at Dover, where sea level rose by about 2.2 millimetres a year between 1961 and 2010. That is what the gauge measured over those years, and it describes the coast further out, not the river at Woolwich.
Woolwich's flood risk is worse than most buyers will want, and it is concentrated by the river. The hill behind the town is a different matter, but anything near the water comes with history and a defence that has failed before.