I read Flood as transform into an Ocean at first, which would be cool - although you'd have to add "unoccupied".
I'm not sure about flooding a mountain, either - although I guess Baeru does.
It's possibly stepping on green's ... turf .
I guess the intended use is to give aquatic creatures access. That does seem strategic in a way, although it's quite a gamble having a card like that in your deck.
Tsunami is yet more "random unexpected damage" - one more thing to worry about. IMHO the game already has a bit too much random damage - so much that you can't really try and counter it all, you've just gotta cross your fingers.
So, i'd give it a 5 or 6 land cost (so that you get a good warning) and drop the price - that way it becomes strategic. I'm also thinking it doesn't need the "flying or aquatic" qualifier from a gameplay perspective (as those are very color-specific - and fish do get owned by tsunamis).
I guess increasing the land-cost would put it into mid/late game, which means there's already lots of land. Balancing it would be tricky then.
But the core mechanic is quite a good idea.