Yes, in parts, and the parts are easy to find on a map. About one postcode in eleven is in the highest-risk river-and-sea zone. Around 190 properties are rated at high risk from rivers or the sea. The long-term plan for the shoreline is to leave it alone. Most of the town is on safer ground, so the risk is moderate overall and very uneven.
In the Environment Agency's river-and-sea flood zones, 9% of Lydney's postcodes are in zone 3, the highest-probability band. Another 5% are in zone 2, the medium-probability band just outside it. The two don't overlap, so zone 2 is the extra ring around zone 3. The geology explains where they fall. The lower parts of town are on estuarine alluvium laid down by the Lyd, Plummer's Brook and the Severn, and the town climbs from there towards Allaston and Brockhollands.
There is no separate surface-water figure for Lydney here. Surface water is counted in the wider postcode measure further down. The ground that collects river water is also where heavy rain tends to settle.
With the Environment Agency's allowance for climate change, about 9% of postcodes would be in the highest zone. That is almost the same as now, so the zone boundaries in Lydney don't move much in the long-range modelling.
Insurers price individual addresses, and a house inside zone 3 can cost noticeably more to cover, or need a specialist policy, while a house a few streets uphill may not. Put the exact address into the Environment Agency's long-term flood risk service, and get an insurance quote early in the purchase, while walking away is still cheap.
Counting every measure, surface water included, about 11% of Lydney's postcodes are high risk on at least one, 11% are medium and 28% are low. A postcode only has to fail one test to land in a band, so this is a broader net than the river-and-sea zones and will always catch more of the town.
The Environment Agency's rivers-and-sea mapping lists 38 Lydney postcodes with some risk. Postcodes with no risk are left off the list entirely. Those 38 postcodes hold 835 properties: 191 rated high risk, 89 medium, 206 low and 15 very low. Of the high-risk properties, 76 are homes. That count is more useful to a buyer than any percentage, because the only question is whether the house you are viewing is one of the 191.
About 4% of postcodes are inside the high-probability flood extent with no defence in the Agency's model, and about 5% are inside it with a defence modelled. "Defended" means a defence appears in the model. It says nothing about how high the defence is, what state it is in, or whether it holds. A listing that leads with the word is selling a reassurance the Environment Agency never gave.
The Severn is close. The nearest postcode is about 370 metres from the shoreline, and the typical postcode is about 1,850 metres away. Only about 1% of postcodes fall within 500 metres, the distance this site uses as its coastal threshold. The town was once built for the water. Docks went in in 1810, and in 1851 the South Wales Railway's embankment stopped the sea flooding the Lydney Level. Lydney's best-known sea defence began as a railway line.
The shoreline management plan for Lydney's frontage says no active intervention at all three horizons: 20, 50 and 100 years. That is a statement of what the authorities intend, made without committed money behind it, and it says nothing about what defences are standing today. In plain terms, nobody has planned to build anything new along this stretch of shore.
The nearest tide gauge with a long record is at Portsmouth, a long way from the Severn. It measured sea level rising about 2 millimetres a year between 1962 and 2023. That is what that gauge recorded over that period, nothing more.
Flood risk in Lydney is middling. It is mapped tightly enough that a buyer who checks the exact address knows where they stand, and a buyer on the low ground near the brooks and the estuary should expect to pay for it.