Here's an analogy to describe how to redo a global flood. Gravity affects the Earth's sphericity somewhat like gravity affects a weighted seesaw. Place the weight in the middle of the seesaw and it will be balanced. Make the Earth completely spherical and it's water will cover every point to a similar depth. Move the weight on the seesaw and the beam will tip in that direction. The analogous action to the Earth is a little difficult to understand, but it is essentially the same thing. Move some weight from one side of the Earth and it will not tip - rather the Earth's gravity will work to reform the Earth into a sphere. Spherical Earth = balanced seesaw. The two situations are not the same, but the 2 dimensional seesaw example is a helpful tool to understand how the Earth could be flooded. Back to the seesaw - imagine a waterline drawn a short distance above the beam. When the weight is in the middle, all the beam is below the waterline. But with the weight a little offset, the end of the beam opposite the weight will poke above the waterline. Move the weight further and more of the opposite end will rise above the waterline. Now if we suddenly move the weight, the seesaw will rock back and forth a few times before reaching equilibrium. This will put each end alternatively above and below the waterline. If we look at today's Earth, it is like a seesaw tilted so that 2/3 of one side is above the waterline. The way to regenerate a global flood is to move the weight on the beam to the same position on the opposite side. In reality, that would mean removing a great deal of rock from somewhere. Maybe if we teleported Australia to deep space. Gravity would force the Earth into a more spherical shape and, during that process the "beam" would spend time entirely below the waterline. Its not a magical process, just very difficult to achieve. A meteor strike of extreme size might achieve it. A vast chain of volcanoes, perhaps. But the actual flood (rather than trying to replicate it today) had a very different mechanism for removing mass from the Earth.