Well, I suppose that should these things prove to be what they appear to be it goes without saying either that the sea level has risen much more than 300 feet or that there has been subsidence to a great degree or both.
Humans are primarily adapted for aquatic or semi-aquatic life (see Elaine Morgans "Aquatic Ape") and have always lived near water. The basic answer to the evos refrain ("where did the waters of the flood GO?") is NOWHERE. The waters of the flood are still here; the continental shelves are in all likelihood the pre-flood ocean boundaries and we are living on areas which were regarded as plateaus before the flood. There's simply more water on Earth now than there was then.
There is reason to believe that the missing oceans of Mars may been been dumped on this planet at the time of the flood but that's a longish story.
Most of the antediluvian cities figure to be below the waves as this site is, and I assume other such sites will be found as well.