For this reason God is going to wipe them out and he chose a worldwide flood to take out mankind.
We know God's reasoning for taking out the human race with a flood. The human race at that time was evil and wicked. So God chooses to create a flood that in the Biblical narrative says that it was a flood that covered the whole globe, "The waters rose greatly on the earth, and all the high mountains under the entire heavens were covered" (Gen. 7:19). According to this passage, you can see the Bible clearly states the flood covered the whole earth. The debate that has gone on forever about whether this was a worldwide flood or a localized flood that wiped out all of humankind in the particular area. There are good arguments for both and I think one who is going to be a biblical scholar should know both sides of the argument and try to come to a conclusion for themselves.
It seems there must have been a big catastrophic event that caused something significant to happen because when going through history of the early civilizations you find most of them have some sort of devastating deluge in their history. The most well recognized story outside the biblical account is the Gilgamesh epic. There are striking similarities in this story as to the one in the biblical account . One cannot help but wonder where these accounts of a worldwide flood originated. There has to have been an event that lead to an oral tradition because most of all the early civilizations have a story that includes a worldwide flood.
With things such as this one then must wonder if the biblical account was written first and the other accounts learned from this, or if the biblical account was written after people knew of the other traditions. Whatever or whenever the account was written you need to understand why it was written. If one is to take a literal approach to the Bible then you would agree that the flood covered the whole earth and the only things that survived would be what was in the ark.