Yes, in parts, and the Thames decides which. About one postcode in twenty is in the highest river flood zone. More than a quarter lie inside the outlines of past floods. The modelled defences barely change the picture. Most of Walton stays dry, and the part that doesn't is mostly the part that sells itself on being near the water.
The Environment Agency's river-and-sea flood zones put about 5% of Walton's postcodes in Zone 3, the highest-probability band, and about 11% in Zone 2. The two zones don't overlap. Zone 2 is the medium-probability fringe beyond Zone 3, so the larger number describes the outer ring of the risk, and the core is the smaller one. In 1864 a brick viaduct was built to carry the road across the flood plain south of the river, and it's still standing. The Victorians knew exactly where the water went.
Surface water from heavy rain isn't counted in those zones, and here the Agency doesn't publish it separately. It is folded into the postcode indicators further down this page. The town's past is clearer. About 28% of postcodes fall inside the Agency's outlines of recorded flooding, and it holds 187 recorded flood events for the area. The latest was in January 2003, when a main river overtopped a channel with no raised defences.
Looking ahead, about 4% of postcodes fall inside the Agency's climate-change flood zone, its modelled extent once a future allowance for heavier flows is added.
Insurance is where this turns into money. In the higher zones, buyers can expect insurers to ask more questions, quote higher premiums or set a larger flood excess, and a mortgage lender will want cover in place. Ask the seller for their current buildings-insurance schedule and look at the flood excess. It's the most honest price tag the house has.
Counting every measure the Agency publishes, rivers, sea and surface water together, about 7% of Walton's postcodes rate high on at least one, 19% medium and 44% low. These bands overlap with the flood zones above and measure something wider, so the two sets of numbers shouldn't be added together.
Counted by property, the Agency's rivers-and-sea mapping lists 3,539 properties across 145 postcodes that carry some risk. Postcodes with none aren't listed at all. Of those properties, 9 are at high risk, 1,138 at medium and 1,105 at low, and only 4 of the high-risk ones are homes. The medium band is the one to watch here. It is where most of Walton's exposure lives, and it's large enough to include the house on your shortlist.
The Agency also models the high-risk flood extent twice, once with defences and once without. Both versions put it at about 6% of postcodes. That doesn't mean the defences fail. It means that in the model, whatever stands in the way doesn't shrink the area at the highest risk. Without defences, about 19% of postcodes fall inside the low-risk extent.
The nearest tide gauge is at Portsmouth, where the sea rose by about 2 millimetres a year between 1962 and 2023. That gauge is a very long way downstream from Walton, and the risk here comes down the Thames from upriver.
Flood risk is Walton's weak spot, small in its high-risk core and wide at the edges. Most addresses will never notice it, and the ones in the medium band will find out from their insurer first.