Look at the photos of the great ancient Sumerian city of Ur, specifically the terrain around it, parched land where only five inches of rain falls per year, yet when the city flourished, they had to build flood control structures because the Euphrates river flowed much wider and deeper, even distributaries overflowing from its banks, which sometimes swelled even more, hence the flood control structures during the Ice Age when perhaps thirty inches of rain per year fell.
