It might be if you are trying to debate with a young earth creationist but that fact isn’t nearly as important when you consider how the tale probably started. Civilization as we understand it started around the end of the last ice age (see the amazing and rather recent discovery of the 12,000 year old Gobekli Tepe temple discovered in roughly the same area where the flood myth is based for reference).
Much of the world’s fresh water was locked up in glaciers around that time. If you live in say, Connecticut, your house today would have been under about 1 mile of ice back then. Most of the Northern hemisphere was like that and the glaciers extended fairly far south in Europe close to today’s Middle East and its bodies of water.That is a mindboggling amount of water that was released as the glaciers melted. Some of the existing reservoirs of water like the Black Sea saw an incredible amount of water flow in a short time (some estimates say it was the equivalent of 20 Niagara Falls in places where the water breached banks).
It was an incredible time and place to witness something that civilization hasn’t experienced since. There is a reason why the flood myth is so widespread all over the world. It is because versions of it really happened in places where modern civilization was already taking root and that got passed down and spread as a myth to this day. The people experiencing it didn’t have the perspective to understand what they were seeing or the full scope of it on a global scale but it was very real to them and everything they knew. Much of the land that they knew probably did get flooded resulting in mass evacuations and water levels that rose to the tops of the highest hills that they could see. Whole settlements got covered in water by the Black Sea and are probably still there to this day.
That is correct but I think it is much less interesting to dismiss the Great Flood myth as a completely made up story rather than acknowledge that such a thing could (and probably did) happen either in a single geographical area where human civilization was just developing or in several places around the world. The fact remains most cultures, even those thousands of miles apart, have a Great Flood story passed down through countless generations. It is also true that the end of the last Ice Age did cause events that could be interpreted as a world-wide flood to people that didn’t have the means to move out of their immediate area very quickly. In some areas, it would certainly seem to them that the whole world was flooding with an endless amount of water. It is quite possible that there was an eccentric person of means named Noah who built a boat to face the encroaching flood waters and loaded up examples of all the animals in the area (not all that many species). The Old Testament is quite specific about the details of his boat and that is a big tip-off that it was based on a real event. Ancient legends with specific details tend to have a basic in reality even if the details get distorted or misinterpreted over time.
Being a skeptic with hard numbers is one thing but I have learned over time that ancient texts and legends are passed down for a reason. It all makes sense once you know how the legend developed. The Old Testament is full of stories like this and biblical archaeologists have discovered over time that there is real evidence that such events took place even if the details got distorted over time. Those range the Great Flood myths to lost cities like Ur and Jericho (whose ancient walls really did collapse).
If you are invoking a supernatural explanation for where it came from and where it went, why not do the same for the throughput? God don’t need no physics laws that restrict throughput!