Gravesend has a moderate flood risk, concentrated along the river and the marshes. Most of the town is on rising ground. A narrow riverside strip is in the highest-risk zone. Surface water adds patches further inland. Which side of Windmill Hill the house is on decides most of the answer.
On the Environment Agency's river-and-sea flood map, about 7% of Gravesend's postcodes are in Flood Zone 3, the highest-probability band, and under 1% are in Zone 2, the medium-probability fringe beyond it. Zone 2 being the smaller of the two is unusual and says something about the shape of the land. The town grew as a landing place under the shelter of Windmill Hill, with the Shorne Marshes to the east and the Swanscombe Marshes to the west, so the ground drops straight from dry to wet with very little in between.
Surface water is a separate problem, and the river zones do not show it. It shows up in the Environment Agency's postcode indicators, which are covered further down, and it is the reason some homes well away from the Thames still carry a flood flag.
With the Environment Agency's climate allowance added, the share of postcodes in the flood zones goes up to about 10%. That is the modelled look ahead. It moves the edge of the zone outwards and leaves the hill as it is.
For a home in Zone 3 by the river, expect insurers to ask more questions and charge more, and expect some of them to decline. A house on the slope above the old town is a different conversation with the same insurer. Get an indicative buildings quote on the exact address early, and check whether the property also pays a rate to the North Kent Marshes Internal Drainage Board, which covers about 11% of Gravesend's postcodes.
The Environment Agency's postcode indicators count a postcode if it scores on any one of several measures, surface water included. On that basis about 14% of Gravesend's postcodes are at high risk on at least one measure, about 17% at medium and about 36% at low. These figures overlap with the zones above, because a riverside postcode can show up on both.
Counted as properties, the Environment Agency's rivers-and-sea mapping lists 2,706 in Gravesend, and only postcodes with some risk appear on it at all. Of those, 97 are rated high risk, 142 medium, 181 low and 1,421 very low. At most addresses on that list the risk is very low.
About 6% of postcodes fall inside the high-risk extent with no defence in the model, and about 1% inside it with a defence modelled. Modelled means a wall or embankment appears in the Environment Agency's calculation. It says nothing about the condition of that wall on the night it matters. The Environment Agency has seven recorded flood events in Gravesend, the latest on 14 September 1968, when the sea came over the defences. A defence was in place that night too.
The shoreline management plan for this stretch of coast is to hold the line, meaning keep the existing defences where they are, for the next 20, 50 and 100 years. That is the plan's stated intention for each period. The money for it has not been committed, and the plan tells a buyer nothing about what stands at the end of the street today.
The nearest long-running tide gauge is at Dover, where sea level rose by about 2 millimetres a year over its record from 1961 to 2010. That is what the gauge measured over those years. Gravesend is upriver on the Thames, so the figure comes from a different stretch of water.
Gravesend's flood risk is about average: serious on the riverside and the marsh edges, and modest on the hill where most of the town lives. Find out which of the two the house is on early in the process.