Flood accounts do not equate to a worldwide deluge where even the mountains are submerged and an ark is needed to save a selection of people and animals in order to repopulate the earth......It did not happen, the story is impossible.
The story was probably embellished from a localized flood event/hero legend what a family saved their themselves and their livestock under difficult conditions, to the amazement of the surrounding tribes.
The Flood did happen. The story is possible because it did happen. Because you don't believe it and maybe even read others don't believe it makes no never mind to the facts.
The issue is not whether I believe in a world wide deluge, or not, the issue is not that you do, you can believe whatever floats your boat, this is just about the evidence for such an event. The problem being, there is no evidence for a world inundating flood. There is evidence for localized flooding.
