Flooding in Venice in 1825 does not mean that today's situation is the same. Today's situation is far more widespread, and it's getting progressively worse. And remember, tidal and local pressure effects ensure that sea levels are never at the same peaks everywhere at the same time, but that does not mean that they never do reach their currently possible limits and that they will not reach progressively higher limits as the ice caps melt.
I watched a docu. on tv recently about the increasing problems that Florida faces due to its foundation of porous limestone. Flooding is now taking place from the ground, not only from the sky. Water is seeping up from sewers and the water plane independently of
local rainfall, but due to pressure from the rise in sea levels. The projection is that most of the beachside palaces will be uninhabitable in a few years. This has led to a drift inland by the wealthy into previously deprived but higher areas, with gentrification slowly taking its toll, just as with cities, but this time due to vanishing real estate rather than the need to increase the existing space.
While mangroves - if reintroduced - may help to a degree, that cannot alter or prevent the effects of the water rising from below the ground.
Apart from the loss of land and second/third/investment/laundering properties, the documentary pointed out the problems that will cause on the fiscal side when the mortgage companies say, hey, your property is not worth the mortgage. In effect, yet another version of the property market collapse. Is Mr Trump's golfing investment on higher gound? Like his morality, for instance?
;-)