Marduk

"But the more simple explanation, which doesn't require that these people keep an oral tradition for a few thousand years until they write it down, is that they live in a area that is prone to flooding"

True, but the Nile was prone to flooding and the Egyptians have no Noah type flood mythology. They were used to the Nile flooding, no big deal, as would those living near the Tigris I would think.

Pitman & Ryan claim that when the waters started pouring over the strait it would have been quite spectacular, making Niagra falls look like a creek overflowing, something to tell your grandkids about.
Don't forget the pottery and an influx of newcommers to the area at this time as well. Also the original Sumerians were not semites and had a non semetic language, they had to have come from somewhere.
My guess is they already had a reasonable civilization going near the Black Sea before they moved, making it appear as if civilization sprung up out of 'nowhere' in the fertile crescent.