@Stevehill

To indundate the planet the water would have to be about 8.85km higher than sea level, to cover Mt Everest.

Who said Mt Everest existed before the flood? You make an assumption. The flood covered the existing mountains, how high were they? who is to know? but if you were to level the earth to equal level the surface water on this planet would be over 2km deep!

When the flood subsided, 4.5 bn cubic miles of water had to go back to "somewhere" other than on this planet. To reach escape velocity requires 7.89 kilowatt hours of energy per kilogramme of mass. The energy expenditure to shift such a volume of water would be colossal: the planet would not survive.

In similar manner as scientists believe the moon was formed? Supposedly the earth survived that event!

Maybe you could think about it without an evolutionary bias, you would be surprised how the evidence tells a different story.