Wife disguised as sister, and the parting of waters

LH pointed out that there were three parallel narratives in the Bible of miraculous crossing of bodies of water, once with Moses, leading Joshua and the Israelite nation, parting the Red Sea, once with Joshua crossing the dry Jordan, and finally with Elijah and Elisha also crossing the dry Jordan.
The Jordan miracles are certainly less well known than the Red Sea parting. I suppose that the reason is that the Jordan was never mighty, like the Mississippi, and that its parting is a less impressive feat than parting the Red Sea.
The parallel narratives reminded me of the three parallel narratives of “wife disguised as sister” in Genesis (http://en.wikipedia.org/wiki/Wife%E2%80%93sister_narratives_in_Genesis). A patriach arrived with his wife in a strange land. To save his own skin, he lied that his wife was his sister, so that the local chief could take her for himself, without killing the patriach. The story is told thrice, twice of Abraham and once of Issac.
The non-religious explanation of this is that the motif (theme) of “wife disguised as sister” had been popular in the oral transmission of the Jewish tribal myths. Different story tellers at different times had attached the same motif to different stories. When the oral stories came to be written and compiled, without any single editor being in the position to exercise editorial control to ensure plausibility and consistency, we get the strange and implausible parallel narratives.
The same process of a popular “miraculous parting of the sea/river” motif being orally attached to multiple stories also accounts for the three similar miracles of parting of waters.