The water is easy to explain. Before the flood, the mountains were much lower. So, then it would not have taken as much water to cover the highest mountains at that time. Not sure if Everest was the highest mountain at that time. After the end f the flood, God raised the mountains and lowered the ocean depths so that the water level returned to today's levels.
Why is there shells at the top of Mount Everest and on top of most mountains?
The shells on the top of Mt Everest are evidence of the collision of the Indo-Australian plate with the Eurasian plate resulting in the formation of Mt Everest about 50 million years ago. And the plate is still moving northwards at the rate of ~70mm/year, which is why the Himalayan range is still rising at the rate 0f ~5mm/year.
So what is your evidence that Mt Everest was not about 8848 metres above sea level when Noah rounded up and herded millions of animals onto his tardis-boat less than 4000 years ago?
And what happened to the dinosaurs and megafauna after they left Noah's tardis boat?
Have you ever had a face to discussion with a god about your hypothesis like Abraham and his god did when they shared a meal together (Gen 18)?
Or is your hypothesis just an imaginary fantasy with not a skerrick of evidence to support it?