Let us elaborate the question. There is a separate problem about the Noah story that does not depend upon it being derivative: if, as seems to be the case (see questions about Gen 6 and 7), the story is inconsistent with science, then does that not indicate more strongly that it is merely borrowed from some common pagan source? Does that not indicate that the Noah story, and thus the Bible generally, has very questionable sources and thus lacks any credibility? As far as I am concerned, this is certainly one of the hardest problems for any Bible believer who does not accept a Young Earth theory. One way through, of course, is simply to take one horn of the dilemma and espouse the Young Earth theory, attempting to defend the claims made. There are ways to do that that are more plausible than might appear at first glance, but I have not learned about how creationists attempt to shift scientific paradigms. Another way is to deny that there is anything terribly wrong, theologically, with a Bible the first eleven chapters of which contain legendary or mythic elements shared with other traditions. Those traditions were recast in terms of a true theology, which is why those old stories did not completely sink into the mists of time but gained a lease on life by being dignified by association with Moses and those who followed after him. But this strikes me as unsatisfactory for the simple reason that so much of the rest of the Bible takes Gen 1-11 for granted as literal truth.