Botany Bay has little to fear from rivers or the sea, and quite a lot more from heavy rain. Hardly any postcodes fall in a river flood zone. About one in five carries a high reading once surface water is counted. Only one home is listed at high river risk. The danger here comes down from the sky, not up from a riverbank.
The river-and-sea picture is close to clean. In the Environment Agency's flood zones, under 1% of postcodes across the EN2 district are in Flood Zone 3, the highest-probability band, and under 1% are in Flood Zone 2, the medium-probability fringe beyond it. The two bands do not overlap, so each figure counts different postcodes. On this measure the area barely registers.
Surface water is a separate matter, and the flood zones ignore it entirely. There is no surface-water share on its own for this area. What shows its weight is the gap between the near-empty river zones and the much larger postcode figures further down. Heavy rain on clay and lane drains does its own damage, without any river to cause it.
The Environment Agency also models the flood zones with an allowance for climate change. On that measure, under 1% of the district's postcodes fall inside the zone. The river picture stays small even when it is projected forward.
Insurers will see this the same way. For most homes here the river question is quickly settled, so what goes into the quote is the surface-water rating for the individual property. Two houses on the same lane can come back with different premiums depending on where the water collects.
The postcode-level picture includes rain. Counting a postcode as high risk if it scores high on at least one of several measures, surface water included, about 22% of postcodes in the district rate high, about 26% medium and about 43% low. A postcode can appear in more than one band, because each measure is scored separately. Put the exact address into the Environment Agency's long-term flood risk service and read the surface-water result as carefully as the river one, because that is where this area's risk shows up.
Counting homes in place of postcodes makes the river risk look smaller still. The Environment Agency's rivers-and-sea mapping lists 275 properties across the 16 postcodes in the district that carry any river or sea risk at all. Of those, 8 are at high risk, 16 medium, 23 low and 20 very low, and only one high-risk property is a home. Postcodes with no river risk are left out of the list completely.
On whether anything holds the water back, about 0.4% of postcodes sit inside the high-risk extent with no defence in the model, and about 0.1% sit inside it with a defence present. A defence in the model means a structure has been mapped, not that the house behind it stays dry. The district's recorded flood history runs to two events, the latest on 12 December 1947, when a main river overflowed its channel with no raised defences in the way.
The nearest tide gauge is at Portsmouth, where the sea rose at about 2 millimetres a year between 1962 and 2023. That is a measured rate for the south coast over those years. For a hamlet called Botany Bay, the sea plays almost no part in its flood risk.
Flood risk is below average for Botany Bay. The rivers leave it alone, and the rain is the risk a buyer needs to check, one property at a time.