Doesn't really matter.
Waters from under the earth's crust broke through, waters from the heavens came down, regardless of the earth's surface being flat or spherical.
What matters is that Adam's flat Earth was totally destroyed in the flood as the following verse confirms:
2Pe 3:6 Whereby the world (Greek-kosmos)
that THEN WAS, being overflowed with water, perished: (destroyed totally utterly)
This agrees with what God told Noah:
Gen 6:13 And God said unto Noah, The end of all flesh is come before Me; for the earth is filled with violence through them; and, behold, I will destroy them with the earth.
This agrees with this verse:
Isa 24:19 The earth is utterly broken down, the earth is clean dissolved, the earth is moved exceedingly.
This agrees with this verse:
2Pe 2:5 And spared NOT the old world, but saved Noah the eighth person, a preacher of righteousness, bringing in the flood upon the world (Greek-kosmos) of the ungodly;
Adam's firmament, which God called "Heaven" was made on the
2nd Day. Gen 1:6-8 God made other 'HeavenS" on the
3rd Day, the SAME Day Adam's Earth was made. Gen 2:4 That is the world that
THEN WAS, which was totally destroyed in the Flood. Adam's flat Earth was "
clean dissolved" in the flood but that could NEVER happen to our Earth since our Earth is a Rock with a molten core. God identifies our 2nd Heaven here:
2Pe 3:7 But the heavens and the earth, WHICH ARE NOW, by the same word are kept in store, reserved unto fire
He also tells us of another Heaven, the New Heaven and New Earth of Rev. 21:1. Paul was taken to that
THIRD Heaven:
2Co 12:2 I knew a man in Christ above fourteen years ago, (whether in the body, I cannot tell; or whether out of the body, I cannot tell: God knoweth) such an one caught up to the third heaven.
The firmament, which surrounded Adam's Earth and kept it from being destroyed by the water which surrounded it is STILL in Lake Van, Turkey where it sank, releasing the 450 ft Ark into the Lake. HISTORY also confirms this event since Human farming, on our Earth, and ALL other modern Human traits began just 10-11k years ago EXACTLY where God tells us the Ark arrived. Here is a map of the Fertile Crescent where Noah arrived.
http://www.fsmitha.com/h1/map00-fc.html
Lake Van is in the mountains of Ararat AND in the center of the Fertile Crescent at the top of the Map. There are many more confirmations of this event, but the above is PROOF of the Literal flood which totally destroyed Adam's world and all of it's people and left the Ark safe in the 75 mile wide 1500 ft deep Lake Van.
The Scoffers/Unbelievers of the last days before Jesus returns will NOT believe that Adam's entire world was totally destroyed in the flood nor that the present Cosmos will be burned. ll Peter 3:3-7 Amen?