I'm not aware of a single secular, Biblical scholar who does not believe that the flood story is composed of two stories from two completely different traditions, containing contradictory information.
The "single" story appearing in Genesis 6-9 was created by taking one passage from an author who called the deity "God," and the next passage from an author who called the deity "LORD," then the next from the "God" author, and so on for five or six interleavings.
Readers may confirm this for themselves. All they have to do is copy and paste the flood story from an online Bible, then take out all of those passages which speak of "God." Miraculously, those "God" passages together tell a complete story of the flood, while the passages left behind, attributed to the "LORD" author, also tell a complete--but different--story of the flood.
One also finds, for example, that one of the authors refers repeatedly to Noah's "sons," while the other other never does, referring instead only to Noah's "family" or "those with him." One author mentions "convenant" nine times; the other never uses the word.
One of the authors seemed to be obsessed with the divine number "seven," so he used it repeatedly; the other author didn't. The former author is the one who wrote that Noah was instructed to put seven of each kind of animal on board, while the other other wrote that Noah was to put two of each kind of animal on the ark.
There are five other correspondences like this which remove any doubt about there being two different authors and two different--and conflicting--stories.
If one doesn't wish to do the work I've mentioned above, it's already been done at the site below
* http://sol.sci.uop.edu/~jfalward/Two_Flood_Stories.htm
In that article, one will see how one may unravel the "single" flood story into two different, and complete, flood stories.
If, after reading this article, anyone still believes that Genesis 6-9 was not a composite of two different and contradictory flood stories, I would invite them to present their counter-argument to this forum.
Joseph F. Alward
"Skeptical Views of Christianity and the Bible"
http://members.aol.com/jalw/joseph_alward.html