A really bad flood that was basically permanent because it wiped out coastal civilizations and created a new sea, would be a very big deal to early civilization.
For them, it wasn’t local; it was global. It was their known universe.
The best explanation for the story is not rainfall, but a cataclysmic inundation of coastal communities in the Mediterranean, either at Gibralter or at the Bosporus.
Such an explanation is heresy to those who believe that animals lined up two by two or seven by seven to enter Noah’s ark. But the burden on those who believe in a truly global flood like that is to explain how that happened, why there is no evidence of it globally, or really how it makes any sense at all.
How many chapters later in Genesis were they making the Tower of Babel? If God was “cleansing the earth”, it didn’t work out so well. Care to explain why He goofed up? What was accomplished by Noah’s Flood?
It did NOT happen.