Marcham has some flood risk, and most of it comes from rain landing on the area, not from rivers. The river zones barely reach it. Surface water reaches further. About one postcode in nine rates high on at least one flood measure. The risk is concentrated, which is good news for most houses and bad news for a few.
The Environment Agency's river-and-sea mapping puts about 1% of the Marcham area's postcodes in Flood Zone 3, the highest-probability band. Another 2% are in Flood Zone 2, the medium-probability band just beyond it. The two zones don't overlap, so together they cover only a sliver of the area. The agency has three recorded flood events here. The most recent was in July 2007, when a main river overflowed its channel at a point with no raised defences.
Surface water is the part the flood zones leave out. It's rain that falls faster than the ground and drains can take it, and it collects in dips and low roads whatever any river is doing. That's why the wider postcode measures further down come out higher than the zone shares. The zones are about rivers, and surface water floods places no river ever reaches.
Looking ahead, about 6% of the area's postcodes fall inside the flood zone once the Environment Agency adds its allowance for climate change. That's still small, but it's several times today's Flood Zone 3 share, and it shows which way the agency expects the line to move.
For insurance, the risk matters house by house. Most homes in Marcham should get ordinary cover on ordinary terms. A home in one of the few mapped flood areas, or one that has flooded before, can expect more questions, a higher premium or a larger excess. Insurers price individual properties, so a quote is more useful than any share of postcodes.
The broader postcode picture combines several measures, with surface water counted alongside rivers and sea. On that basis, about 11% of the area's postcodes rate high on at least one measure, about 15% medium and about 31% low. A postcode only has to fail one measure to count. That makes these shares much larger than the zone figures, and it's why they shouldn't be read as the same thing.
Counted in homes, the picture is more specific. The Environment Agency's rivers-and-sea mapping lists ten postcodes in the area with some risk, covering 217 properties. Of those, 29 are rated high risk, 4 medium and 16 low, and 23 of the high-risk ones are homes. Postcodes with no river or sea risk aren't listed at all. The agency's long-term flood risk check works by address, and it settles in minutes whether a house you're viewing is one of the 29.
The question of defences has an awkward answer. About 2% of postcodes fall inside the high-risk extent when defences are left out of the model, and the share is still about 2% when they're included. Whatever defences the model accounts for, they don't shrink the high-risk area at all. A defence counted in a model is a line on a map. Nobody should take it as a promise that the water stays out.
The nearest tide gauge is at Portsmouth. Between 1962 and 2023 it recorded sea level rising by about 2mm a year. That's a past rate measured on the coast. Marcham is a long way inland, so the risks that matter here are rivers and rain.
Marcham's flood risk is middling. It's light across most of the village, but a small number of homes carry real risk, and the defences don't change that.