Genesis 7:20 - Ellicott's Commentary On The Whole Bible

Fifteen cubits upward. — This apparently was the draught of the ark, computed after it had settled. in the region of Ararat. Fifteen cubits would be about twenty-two feet, and as the ark floated onward without interruption until it finally grounded, there must have been this depth of water even on the highest summit in its course. Continuous rains for forty days and nights would scarcely produce so vast a mass of water, unless we suppose that the adâmâh was some low-lying spot of ground whither the waters from many regions flowed together; but this is negatived by the ark having travelled into Armenia. In England the whole average mean rainfall in a year is not more than twenty-eight or thirty inches in depth. If we suppose this amount to have fallen in every twenty-four hours, the total quantity would be about 100 feet. Such a rain would denude the mountains of all soil, uproot all trees, sweep away all buildings, dig out new courses for the rivers, completely alter the whole surface of the ground, and cover the lower lands with débris. Wherever there was any obstacle in their way, the waters would deepen in volume, and quickly burst a passage through it. But as they would be seeking the lower grounds during the whole forty days, it is difficult to understand how they could cover any of the heights to the depth of twenty-two feet, unless there were some cosmic convulsion (see Note on Genesis 7:11), by which the waters from the equator were carried towards the poles, and in this way there would be no difficulty in the ark being carried against the current of the Tigris and Euphrates up to the high lands of Armenia.