Parts of it, and the parts matter more than the town. The river zones are narrow. Surface water is the bigger story here, and it does not care where the river is. Most of Westbury sits well clear of anything, while a minority of postcodes carry a high rating on at least one measure. This is a street-by-street question with a town-level answer that would mislead you.
Start with rivers. The Environment Agency's river-and-sea flood zones cover about 2% of the town's postcodes in zone 3 and about 2% in zone 2. Those two are exclusive bands rather than nested ones: zone 3 is the higher-probability core and zone 2 is the additional medium-probability fringe sitting outside it, so the two numbers add up to the affected strip rather than one containing the other. The Biss Brook, which becomes the River Biss as it heads north towards Trowbridge, runs along most of the western boundary of the parish, and that is where the strip mostly is.
Surface water is the measure that catches people out, because it does not follow a watercourse and it does not appear in the postcard view of a property. It is folded into the wider postcode-level indicator below rather than published here as a separate share, but it is the reason the broader risk picture looks worse than the river zones alone suggest. Drainage in a town built across several eras of housing does not perform uniformly, and the water finds the low points regardless of who owns them.
Once climate projections are applied, the share of postcodes falling inside a flood zone rises to about 8%. That is a forward look built into the mapping rather than an observation of what has happened, and it is the figure a buyer planning to be in the house for twenty years should be reading rather than the current one.
For insurance, the practical consequence is that the address decides the quote, not the town. Two houses a few streets apart in Westbury can produce very different premiums, and a high-risk address can attract an excess large enough to change the economics of a purchase. Get an indicative quote before you instruct a solicitor, not after.
Across all measures combined, around 14% of the town's postcodes carry a high rating on at least one flood indicator, around 21% a medium rating and around 44% a low one. Those bands fold surface water in alongside rivers and sea, which is why they run so much wider than the river-zone shares. They overlap with the zone figures rather than sitting alongside them, so they are not something to add together.
Counted as homes rather than postcodes, the Environment Agency's rivers-and-sea mapping puts 62 properties at high risk, 75 at medium and 153 at low, out of 1,088 properties in the postcodes that carry any risk at all. Fifty-eight of the high-risk properties are residential. Only postcodes with some measured risk appear in that dataset in the first place, so the total is not the town.
On whether anything stands in the way, the modelling puts about 2% of postcodes inside a high-risk extent with a defence present, and about 2% inside a high-risk extent with none. Defended means a defence exists in the model. It does not mean the property is safe, it does not tell you the standard the defence was built to, and it does not tell you who maintains it.
Sea level is a background fact here rather than a live one. The nearest tide gauge, at Portsmouth, recorded a rise averaging about 2 millimetres a year across its 1962 to 2023 record. That is a measured historic rate over six decades, not a prediction, and Westbury sits inland under Salisbury Plain.
There are no recorded historic flood events on record for the town's postcodes. Three flood events appear in the wider records, the most recent in March 1978 from an ordinary watercourse. An absence of recorded flooding is genuinely worth something, but recording has been patchy over the decades and it is not proof that nothing has ever happened.
Flood risk is the middling part of Westbury's picture and the one thing here worth a specific check rather than a general impression. Put the exact address into the Environment Agency's long-term flood-risk service before you offer, because the answer changes within a few hundred metres and the town-wide version of it will not tell you what you need to know.