IIRC, there is some evidence of a very large flood in...western Asia, I think?...caused by a highland sea breaking through a natural dam and emptying into a lowland area, right around the time that humans were starting to keep histories. It was big enough to affect multiple distinct cultures at the time. There's a theory that that's the origin of the ubiquitous Great Flood stories.

Also the Missoula Floods[0], though it's possible nobody was really around, and if there was, probably not many ( assuming humans started migrating ~18,000 years ago, it's possible some were there)

[0]-http://en.wikipedia.org/wiki/Missoula_Floods

He might mean this, since the time period is a bit more correct : http://en.wikipedia.org/wiki/Black_Sea_deluge_hypothesis