Getting technical, the 0.5% Annual (1 in 200) Exceedance Probability of that address is 0.15 - 0.5 metres,
page 46, where you can also find most of the flood risks for Dover town.
According to my best efforts with Google maps and an Ordnance Survey map the property is about 230 metres from the seafront - all info that his conveyancing solicitor and insurers should have known.