There was only one body of dry land with no known elevation above sea level.
Since the sediment at the Grand Canyon is over 5,000 ft and the Grand Staircase another 5,000 ft of sediment, the water had to be over 10,000 ft deep. So the water would have to rise 250 ft per day during the flood.
The Bay of Fundy is a very extreme example of tides. The normal range of tides is more like 3 ft IIRC. The range varies according to orientation and subsurface geography.