No, it wasn't God who wrote Genesis, some say it was Moses putting to paper what had long been an oral tradition in pakistani/hebrew culture. A true story of survival at sea during a hurricane was turned into a myth/fish story that gets bigger with each telling. It's really no different than other myths : greek gods, aryan superiority, the list goes on and on; even today we have the myth of OBL living in a cave, sending out his assassins, a medieval arabic myth. Don't underestimate the POWER of myth, it is MYTHS that underpin religions. It was a MYTH that impelled the 9/11 hijackers to kill so many.....As to Jesus and floods : his main clue : "and the lightning flashed from the east even unto the west". Put that(counter EMF force) together with the GREAT earthquake and HUGE hailstones...and you've got what I figured out in 1979.
Why must the Noahic flood be myth? Not to be facetious, but I hardly expect that anyone who could raise Jesus from the dead would have trouble creating a worldwide flood. As I said before, Jesus had no trouble either with the idea of a worldwide flood or with Mosaic authorship of the Pentateuch, so why should we?