If my neighborhood was hit by a 14m high wall of water, a hermetically sealed cellar with its own air supply where I could keep all my stuff actually sounds pretty good.
I’d want to make sure the entrance couldn’t be blocked by falling buildings. And I’d try not to rent “Downfall”, “The Bunker” or half a dozen other movies set in claustrophobic conditions. Otherwise this sounds pretty decent.
“We’ve got provisions, and lots of beer...”