Colindale's main flood risk comes from rain, and the river matters less. Very little of it is in a river flood zone. About a quarter of its postcodes are rated high on at least one flood measure. A few hundred properties are rated high for river flooding. Measured by the rivers alone, the place looks safer than it is.
On the Environment Agency's river-and-sea mapping, about 2% of the area's postcodes are in Flood Zone 3, the highest-probability band. Another 2% are in Flood Zone 2, the medium-probability band just outside it. The two zones don't overlap, so Zone 2 adds to Zone 3 rather than containing it. The Silk Stream, a tributary of the River Brent, runs north to south through the district, and that narrow corridor is where these zones lie.
Surface water is a bigger part of the risk. The wider postcode ratings below include surface water alongside rivers, and they cover a much larger share of the area than the river zones do. Most of the difference comes from the measures that do not depend on a river. Colindale is mostly flats, roads and paving, so heavy rain has to drain away through gutters and drains, because very little of the ground can soak it up.
Under the Environment Agency's climate-change allowance, the share of postcodes inside the flood zones rises to about 5%. That figure comes from a modelled future scenario, not from any flood that has happened.
Insurers price each property, not the area as a whole. A ground-floor flat on a low street and a fourth-floor flat in the next block can get very different quotes, even though they share a postcode. Ask the insurer for an actual quote on the specific flat, ground floor or not, early in the purchase.
Across all the measures combined, about 26% of postcodes are rated high on at least one of them, 23% medium and 40% low. These ratings are a postcode's worst result across several separate measures, surface water included, so they overlap with the river zones above and should not be added to them.
Counting homes instead of postcodes, the Environment Agency's rivers-and-sea mapping lists 1,923 properties in the area, but only in the 77 postcodes that carry some risk. Of those, 312 are rated high, 290 medium, 641 low and 39 very low. The mapping identifies 291 of the high-risk properties as homes. The Environment Agency has 17 recorded flood events here. The latest was in August 2015, when a main river overtopped its channel at a spot with no raised defences.
About 2% of postcodes are inside the high-risk extent with no defence in the model, and about 2% are inside it with a defence present. "Defended" means only that the model includes a wall or bank somewhere along the water. It does not mean the defence would hold, or that it protects any particular house.
The nearest tide gauge with a long record is at Portsmouth, where sea level rose about 2 millimetres a year between 1962 and 2023. Colindale is a long way inland, so the sea has little bearing on its flood risk.
Flood risk is one of Colindale's weaker points. The river zones are small, but rain that cannot drain affects a large part of the area.