I'm afraid I have a particularly squishy position on the historicity of the Great Flood of Genesis 6-8. I'm basically okay with most every proposal, from retroactive interpretation of a particular bad flood in a single valley as God's judgment upon the evils of men all the way up to the full fifteen cubits over the tallest mountain and the waters prevailing upon the earth a hundred and fifty days.
I mean, I wasn't there, was I?
To understand -- or even, astonishing thought, pray -- the Scriptural story, though, we need to take it on its own terms, apart from speculation about the historical basis and textual evolution through which is may have passed.
The question is, what are its own terms?
Answering the question literally, and using the NAB, the terms include (leaving out the engineering and meteorological details):
"no desire that [man's] heart conceived was ever anything but evil"
God said of man, "I am sorry that I made them"
"But Noah found favor with the LORD... Noah, a good man and blameless in that age, ... walked with God...."
the flood would "destroy everywhere all creatures in which there is the breath of life"
Noah "carried out all the commands that God gave him"; he "alone in this age" was "found to be truly just"
And, perhaps most importantly, God's covenant with Noah:
God blessed Noah and his sons and said to them: "... Every creature that is alive shall be yours to eat; I give them all to you as I did the green plants... "For your own lifeblood, too, I will demand an accounting: from every animal I will demand it, and from man in regard to his fellow man I will demand an accounting for human life. If anyone sheds the blood of man, by man shall his blood be shed; For in the image of God has man been made. "Be fertile, then, and multiply; abound on earth and subdue it." God said to Noah and to his sons with him: "See, I am now establishing my covenant with you and your descendants after you and with every living creature that was with you: all the birds, and the various tame and wild animals that were with you and came out of the ark. I will establish my covenant with you, that never again shall all bodily creatures be destroyed by the waters of a flood; there shall not be another flood to devastate the earth."