Actually from my understanding as a geologist and anthropologist, you are somewhat incoreect. There is ample evidence for a worldwide flood. Granted it didn't occur anything like the story in the Bible.

Let me begin with the anthropolgical evidence for a worldwide flood incident. Worldwide there are multiple cultures that maintain a story in there mythologies and beliefs that make reference to a ", great flood" event. They are surprisingly similar in their description. Too many for accidental coincidence to explain.

Geologically, again there is evidence worldwide for a extendive flooding episode. Sediments lain down in an inundation depositional environment exist all around the world. In fact, using radiometric dating methods, it appears that they all date roughly to the same age.

Here is the logic. At the time of this prurported event, most civilizations were living adjacent continental coastlines, and along the base of major rivers. These environments were a good source of readily exploitable resources and able to support larger populations. Coincidently, these areas tend to be low lying in elevation, being on or near sea level. Around the time of the purported event, a major eustatic sea level changed. And it appears that this hapoened rather quickly.

Thus said, the major consequence was that the major low lying civilizations were flooded out and there cities were inundated and destroyed. Large bodies of people were forced to flee inland worldwide. Again, this resulted in a worldwide mythology of a great flood. Therefore, the mythologirs are subsequently based on a real event. As I ssid before. It did not happen as described in the Bible, and the continents were not totally inundated as suggested, just the continental coastlines, but the home of most civilizations of the time. Many mythologies are based on a peoples attempt to explain natural events that were beyond their worldview to make sense of at the time.