I have always maintained that the Flood myth in the bible is dependent upon the earlier Mesopotamian Gilgamesh as a source. Tablet XI (http://www.ancienttexts.org/library/mesopotamian/gilgamesh/tab11.htm) shows clearly that the two stories are so similar as to be beyond chance. This explicitly illustrates how the biblical narrative cannot, in any realistic sense, be anything like the truth. This quote from Cyrus Gordon sums it up (Cyrus H. Gordon and Gary A. Rendsburg, The Bible and the Ancient Near East, 50.):


Here we need to say a special word about the relationship between the flood accounts as preserved in the Bible and in the Gilgamesh Epic. It is obvious that the two versions are strikingly similar and must be related in some way. The consensus of scholars is that the Babylonian version influenced the Israelite version. The reasons for this are manifold. First, all things being equal, a greater society is more likely to influence a lesser society than vice versa. Babylonia was the dominant culture of the Asiatic near East and Israel represented a backwater of sorts. Secondly, the manner of destruction, i.e., by flood, is typical of Mesopotamia, where the great Tigris and Euphrates Rivers regularly flooded their banks and cause havoc and destruction. Israel, by contrast, is very arid; it is unlikely that anyone in that part of the Near East would conceive of a divine destruction of the people through flooding. Third, the geography of the biblical accounts points to a Mesopotamian origin. Noah’s ark lands on the mountains of Aratat, at the headwaters of the Tigris and the Euphrates; if the story had originated in Canaan we would expect Mount Hermon (c 7,500 feet high), for example, as the locale of the ark’s resting place. Fourth, as we have seen, the Gilgamesh Epic was the literary masterpiece of antiquity, and one fragment even has been found in the land of Israel (at Megiddo). Fifth, the earliest Hebrews come from Mesopotamia, and it is unlikely that Abraham and his entourage would have been unfamiliar with the story.