The flood itself needs to be read against chapter one, because it's deliberately structured as an undoing of creation, not merely a natural disaster. Genesis one separates the waters above from the waters below to make room for dry land and life; the flood collapses that separation — "the fountains of the great deep broken up, and the windows of heaven were opened" — waters above and below rushing back together, the world returning toward the formless deep it began as. This is why Peter, in his second letter, can describe the antediluvian world as being "overflowed with water" and then use that exact memory as his proof that a second, different kind of undoing — this time by fire — is still coming. The flood isn't presented in the New Testament as a strange one-off. It's presented as the first of two comprehensive judgments bracketing all of human history.
And notice the wind — ruach — that God sends to make the waters recede, the same word used for the Spirit hovering over the waters in Genesis one, verse two. Judgment and re-creation are being told with the same vocabulary on purpose. This is a new Genesis one, running in reverse and then forward again, with eight human survivors instead of two, carrying the whole task of filling the earth on their shoulders a second time.
Jesus Himself treats this history as settled fact, not legend, when He warns His disciples in Matthew twenty-four and Luke seventeen: "as the days of Noah were, so shall also the coming of the Son of man be... they knew not until the flood came, and took them all away." Notice what He's actually warning against — not wickedness in some dramatic sense, but ordinary life continuing exactly as normal, eating and drinking and marrying, right up until the door closed. The judgment wasn't sudden in the sense of unwarned; it was sudden in the sense of unheeded, after a century of warning.