It's impossible to read the text reasonably as a global flood.
* Such a cataclysm doesn't fit the ancient cosmological view of the earth as a flat plate surrounded by and under washed with cosmic waters.
* The earth doesn't have that amount of water.
* The sky doesn't have that much rain.
* For water, even if there were that much, to rise that fast would have created currents that would have destroyed the ark.
* That much water would throw the earth off its orbit.
* The ancients didn't have the technology to make a wooden boat that size. I'm not sure we even have the technology to make a wooden boat that size. It's never been done.
* Our science tells us it's impossible on SO many different levels.
But what in the text tells us it's hyperbole?
When read plainly, the text speaks of a global flood. As I've said several times (maybe to you, maybe to others), the author uses the language of universality to get his theological point across. But there's more to the text than "reading plainly."
* The Earth was not destroyed (6.13)
* A wooden boat of that size (6.15) is impossible, and they knew it.
* "All" (6.17) in Genesis is used elsewhere for a particular population (Gn. 41.57). It is used in Exodus where "all" is not what happened (the plagues). It is used in Deuteronomy for local populations (2.25). These books are all from the same authorial source.
* "The great deep" and "the floodgates of the heavens" in Gn. 7.11 refers to an ancient cosmological perspective where the subterranean waters below the surface of the earth were joined with the waters of the firmament above. This is obviously figurative language, and the extent of their scope of hyperbole.
* The vast upheaval described (6.11) would have overturned any boat.
* Rain for 40 days and nights is impossible (6.12). "40" is always (as far as we know) a symbolic number in the Bible.
* Neither ravens nor doves can fly at the altitudes required for the text to be "read plainly."