Can we be serious for a second. There was no global flood. It never happened. there is no geological evidence for it and there are civillizations that were unbroken across the time period the flood happened. Written Egyptian records exist both before and after this flood and they never experienced it. The dynasty of that time was unbroken. So would people please stop this YEC nonsense.
There is not enough water to cover the entire earth, including the top of Mt. Everest (29, 028 feet above sea level). If the ice caps on Greenland and Antarctica were to melt, it would raise sea levels only a few hundred feet (see calculation). If every cloud worldwide were to rain out all its water, it would still raise the sea levels only another inch. Genesis reports that the "fountains of the deep" spewed forth more water. Until geologists find evidence of these fountains, or discover the underground aquifers that hold 6 miles deep of water worldwide, I cannot honestly accept the idea of a non-miraculous worldwide flood. When evidence for fountains is discovered, I'll be happy to take a look at it.
Calculation: Maximum estimate for raising of ocean levels from melting ice caps.
Greenland and Antarctica contain 97% of the world's glacial ice. The area of Greenland is 840,000 square miles (source: Rand McNally Illustrated Atlas of the World, 1989). The area of Antarctica is 5,400,000 square miles. Since we want a maximum estimate, let's assume that both of those places are solid ice right down to the waterline. The mean elevation of Greenland is 7,000 feet, so Greenland contains 5.88E+9 square-mile-feet of water (like acre-feet). The mean elevation of Antarctica is 6,000 feet, so Antarctica contains 3.24E+10 square-mile-feet of water. So the total amount of glacial ice is 3.828E+10 square-mile-feet.
Let's further assume that the melting water is used only to raise the levels of the major oceans and seas, that the rising sea level does not spill over onto the land (we are estimating the maximum rise). The area of the oceans and seas is 139,100,000 square miles. So if we divide the square-mile-feet of ice by the square miles of the oceans, we obtain (3.828E+10 / 1.391E+8):
Compared to glacial ice, the amount of water in clouds around the world is only a trace amount. "If all of this [water] vapor were to suddenly condense and fall as rain, it would be enough to cover the entire globe with 2.5 centimeters, or 1 inch of water." (from Meteorology Today, by C. Donald Ahrens, 2000, Sixth Edition, Chapter 5, pp. 108-109.) So we are left with the same figure of 275 feet.
Most young earth creationists are aware of the huge disparity between this figure and the height of Mt. Everest. They propose various mechanisms during the Flood year to address the problem (vapor canopy, extremely catastrophic plate tectonics, underground aquifers). I do not find these theories credible on Biblical or scientific grounds.