Why would the water go there? How? Why didn't such an enormous quantity of water relatively suddenly moving deep underground (using some process never encountered in nature anywhere else) cause massive changes to Earth's ecology? Why didnt the flood itself cause massive changes to Earth's ecology? Why didn't the near-extinction of every race of creatures case massive changes to Earth's ecology? Why didn't the sudden injection of billions of tons of water into the planet's cause enormous mountain ridges or fissures or anything like that? Where did the rain COME from then if it didn't come from in there? Was it always in the atmosphere? If it was, why wasn't it constantly cloudy? Why wasn't the Earth a hothouse like Venus under all that cloud cover? Or did it come from undergound as well? If so, where? How? Why? You clearly haven't thought this through I'm afraid. You're not wrong there.