Yes, and in parts of Tonbridge it's the first thing to check. About one in ten postcodes sits in the highest-risk river zone. Nearly a quarter show a high reading once surface water is counted. Hundreds of homes are mapped at high risk from the river. The risk is real, and it changes from one street to the next.
The Environment Agency's river-and-sea flood zones put about 10% of the area's postcodes in Flood Zone 3, the highest-probability band, and about 3% in Flood Zone 2. The two zones don't overlap. Zone 2 is the medium-probability fringe outside Zone 3, which is why it's the smaller figure here. The Medway sets the shape of it. For most of its history the town stayed north of the river because the land to the south flooded every season, and the flood zones still show that.
Rain does its own damage away from the river. About 11% of postcodes have a recorded history of flooding, and the flood records list 270 events. The most recent, on 27 December 2013, was put down to local drainage and surface water rather than the river. Water that falls on the town and has nowhere to drain doesn't need a riverbank to reach a kitchen.
The mapping also looks ahead. With a climate allowance built in, the share of postcodes inside the river-and-sea flood zones goes up to about 16%. That's a planning scenario, not a forecast for any one house, but a 25-year mortgage runs into the period it describes.
In practice, cover is likely to be available on most Tonbridge homes, but a property inside a flood zone or with a flood history can cost more to insure, carry a larger excess, or need specialist cover. Get a quote on the exact address before you instruct a solicitor, not after. Once the offer is accepted, the insurer's answer comes too late to change your mind. About 11% of postcodes also fall within the Upper Medway Internal Drainage Board's area, which manages water levels on the low ground.
This site's postcode-level measure is broader. It flags a postcode if at least one flood indicator, including surface water, rates it at that level. On that basis about 23% of postcodes rate high on at least one measure, about 25% medium and about 39% low. Those bands overlap with the flood-zone figures above and aren't added to them. They answer a wider question: does any kind of water pose a mapped risk to this postcode?
Counting homes makes the risk easier to picture than postcode shares do. The Environment Agency's rivers-and-sea mapping lists 3,542 properties in Tonbridge postcodes that carry some risk: 440 at high risk, 1,159 at medium, 723 at low and 95 at very low. Of the high-risk properties, 280 are homes. Postcodes with no mapped river risk don't appear in these counts at all, so the 3,542 is the at-risk slice of the town, not the whole town.
Whether anything holds the water back varies. About 10% of postcodes fall inside the high-risk flood extent modelled without defences, and about 9% inside the high-risk extent modelled with defences in place. "Defended" means a defence exists in the model. It doesn't mean the house stays dry, and a listing that treats the word as a guarantee is telling you more than the map does. Defences can be overtopped, and surface water goes round them.
Sea level matters less here than the river, since Tonbridge is well inland. The nearest tide gauge, at Dover, recorded sea level rising by about 2 millimetres a year over its record from 1961 to 2010. That's a measured historical rate, not a prediction. The river flooding described above is what Tonbridge buyers should focus on.
Flood risk is Tonbridge's weak spot, and it's worse than average. Most streets are clear, but on the wrong one the river decides the terms.