The water on the surface of the earth is not the whole story. There is MUCH MORE water within the mantle of the earth — perhaps 5 times more within than on the surface.
So that water was pushed to the surface for 40 days and all the while the subterranean cavities where the water resides were empty. Again, 13,000 feet of water in addition to the current ocean depths would be a stretch. I believe that there was a historic event that became the great flood story that has been around since before the Bible but not one that covered the entire surface with 13,000 feet of water. The 13,000 ft. depth is almost as deep as the depth of the Titanic. But then, interpret it any way you like; all of those men who have written/compiled the Bible over the many centuries certainly have.