It's a short story, and you can read it for free on Orson Scott Card's website at <a href="http://hatrack.com" target="x">http://hatrack.com</a>.
Basically, it's an earlier version of the story of Kemal and his discovery of the original inspirations of both Atlantis and Noah (and Utnapishtim from the Gilgamesh legend, etc. - amazingly, Card gives all of these disparate legends a common, and actually plausible, origin) as told in Chapter 3 (if I remember right) of Pastwatch: The Redemption of Christopher Columbus. The youth and adult names of the Noah character are drastically and slightly different, respectively, from the condensed version told only in summary form in the novel. The relationship is similar to that of the short stories in the back of The Worthing Saga and the main story in that compilation, which was formerly published separately as the novel The Worthing Chronicle. Those stories in the back appear in the novel in condensed and refined form. So it is with Pastwatch: The Flood and Chapter 3 of Pastwatch: The Redemption of Christopher Columbus.
I recommend reading the short story only if you've read and enjoyed the novel. The novel is one of Card's most profound works, though flawed by some minor plot contradictions.