I also really really really do not think that even the most primitive human being couldn't tell the difference between a serious one-time local flood and a flood that covered everything in sight, NOTHING visible but water, and required being on a boat to survive.
this shows you know next to nothing about how these stories develop.
lets say you lived were it was common for your area to flood, now think about how little people know about the world and fear most of it.
the flood stories came about because of fear of water - namely the wiping out of their lives by floods natural or unatural
as because they had examples of this, from what the evidence shows us near the black sea
and they wanted to show the power and control gods had over humanity and to teach children to fear the gods, who for a reason might destroy them
most people who live near the sea have more water based myths, because they live near water and they live by fishing
people would tell the differnece, but do you understand that not one of them is about current events? they all take place in some time before the tellers peoples existed
by the way not all of the flood myths were about boats