The airport is a bit away from a city. In fact, it’s across a reasonably long bridge from the island which most people think of as “Venice”. It’s entirely possible for that island to be flooded, but the mainland (including the airport) to be fine. If that’s the case, it would be entirely reasonable for the airport to function normally.

(Note that I have no reliable information on the flooding. I’m just suggesting that you do more research before assuming the airport would be impacted by flooding “in Venice”.)