i'll add a few finds and thoughts if i may which i offer purely for circumspection with no real concrete view, as of yet, what they actually mean, if anything.
i once read of steiners view on the flood...in it he cites the name manu as the noah and prtoclaims him to be an inititiate...which i take to mean as an awakened or enlightened being. the reason given for the flood is that during the time of atlantis the air was filled with mist and one could barely see the sun. when the earth changed and the mist condensed we had the flood..it was then he states that the first rainbow was seen because of the change in atmosphere. much of this is from memory so bits maybe different. they eventually landed in india where they started a new agricultural based society.
Steiner points out that the ratio of the dimensions of Noah's Ark as given by God in the Bible, exactly corresponds to the ratio of dimensions of the human physical form: 30:5:3 in length, width and depth. this from here
http://www.doyletics.com/_arj1/occsigns.htm
i thought it interesting to read the aboriginal story of the the rainbow snake and see simlarities::
Then one day after a huge rainstorm his huge coloured body was arched up from the waterhole, over the tree-tops, up through the clouds and across the plain to another waterhole.
To this day, aboriginals are careful not to disturb the Rainbow Snake as they see him going across the sky from one waterhole to another. from here :
http://www.dreamtime.auz.net/default.asp?PageID=71
and this:
Thus the divine leader who lead the migrations eastward from Atlantis was the Manu of our Fifth Great Epoch, working with the below-embodied Noah or Mani. During this time, in addition to a select group of human beings, animals representing the seven principal animal group souls were likewise saved, for there was to be continued work within the animal kingdom. It goes without saying that in various other areas of the world, isolated groups of human beings, plants and animals, would have survived the final cataclysms, but Manu's work was directed toward the appropriate forms for the future, toward the new epoch and the true evolution of earth and humanity.
from here :
http://tcpubs.com/brunnen/articles/
which seems to state that manu was more a spiritual being and noah the physical part--two beings in one.
i do disagree with some of steiners hypothesis in general but i have not researched this deep enough to knowe my mind on it...i shall do though at some point.