The “fountains of the deep” are referred too outside of genesis as well. Many scholars identify them with aquifers. Which the ancients knew quite well because of…wells. Mesopotamia (where Genesis 2 – 9 seems to take place) is indeed situated on-top of a large aquifer. When it rains or there is significant nearby snowmelt, aquifers can and do overflow causing floods. (Google: Aquifer floods)