How can there be a great flood but no photosynthesis below 13,200ft (2.5 miles)?

I believe in the "Great flood" of Noah's time, but I feel it was only regional. There's no way the entire Earth was flooded. The Bible says a dove brought an olive leaf back to Noah. If everything was flooded, where would the waters have receded back to in order for the dove to bring back plant life? And I agree, all plant life not on high peeks would have died...well, except for aquatic plant life. :)