Witham has a small river flood problem and a larger rainwater one. Barely any of the town sits in the river flood zones. About one postcode in eight rates high on at least one flood measure. Around two dozen properties face high risk from the river. The River Brain gets the blame in conversation, while rain with nowhere to drain does more of the damage on the maps.
The River Brain runs through Witham and joins the Blackwater on the outskirts. In the Environment Agency's river-and-sea flood zones, about 1% of the town's postcodes are in zone 3, the highest-probability band, and fewer than 1% fall in zone 2, the medium-probability fringe beyond it. The Environment Agency holds four recorded flood events for the town. The latest, in October 2001, came from the main river when the water outgrew the channel, at a spot with no raised defences.
Surface water is a different and bigger question in Witham. It comes from heavy rain landing on roofs, roads and back gardens faster than drains and ground can take it away, and it can reach streets nowhere near the Brain. The Environment Agency's long-term flood risk service shows the surface-water layer separately for any exact address, and it is the layer to look at here, because the river layer will look reassuring for almost every home in town.
The Environment Agency's climate-adjusted flood zone, which allows for heavier future river flows, takes in about 1% of postcodes. Witham's river zone barely grows under that scenario, so the forward look for river flooding stays modest.
For most Witham homes, insurance should be unremarkable. Policies are priced on the specific property, and a home in the river zone, or on a street with a surface-water record, can expect more questions and a higher premium. A previous claim on the house will matter more to an insurer than which side of town it is on.
On the broader postcode picture, which counts a postcode against any of several measures including surface water, rivers and the sea, about 12% of Witham's postcodes rate high on at least one, 17% medium and 38% low. That high share is far bigger than the 1% in the river zone. Rain falls on everyone, and the river only floods its banks.
The Environment Agency's rivers-and-sea mapping counts 558 properties in Witham postcodes carrying some risk, and only postcodes with risk appear in that list at all. Of those properties, 25 are at high risk, 176 at medium and 56 at low. Six of the 25 high-risk properties are homes. The rest of the town does not appear in the river count at all.
About 1% of Witham's postcodes fall inside the Environment Agency's high-probability river extent when the model leaves defences out, and about 1% when defences present in the model are included. The two figures match, so at this scale the modelled defences do not shrink the high-risk area. Either way, "defended" only records that a defence appears in the model. It says nothing about whether a particular house stays dry.
Witham is about 6.6 kilometres from the coast on average, and the shoreline management plan for that stretch sets "hold the line" as the policy for the next 20, 50 and 100 years. A shoreline management plan states what the authorities intend to do. The money for it has not been committed, and the plan says nothing about which defences stand on the estuary today. At this distance it matters far less to a Witham buyer than the drains on their own street.
Witham's flood risk is middling. The river troubles a few dozen properties, and surface water is the risk most buyers here will actually need to check.