From what I hear there is actually evidence for two great floods taking place (well moreover, massive waves that left floods in their wake).

It is speculated that the crashing waters came from a large object from space colliding somewhere in the Earth's oceans, thereby creating two huge cataclysmic waves (with the first being more powerful than the second). I think the physics behind this is supposed to be similar to what would happen if you throw a small stone straight down into some shallow waters.

The Bible isnt the only book that has references to global flood(s). I think there are also some other "myths" found around the world as well.

The fact that similar stories are found around the world doesnt mean its true necessarily though, it just means that we should further use our current technology to figure out if it really did happen.