Here, we will look at one issue and one issue only. According to the local flood hypothesis, an area perhaps the size of California was flooded. If it was more the size of Europe, it would make no difference.
Genesis 7:20 “Fifteen cubits upward did the waters prevail; and the mountains were covered.” KJV. The context is clear. The highest mountains were covered approximately 20ft or just over 6 meters.
The flood is recorded at being at its highest stage for several months. Now, try to imagine a local flood of any land mass where the highest points were exceeded by 6 meters. Do you know what would happen? The complete perimeter of the flood area would be flooding over the hilltops by at least 20 feet!
Now you have a situation where you would have at least a perimeter of 2,000km gushing over at a rate that is so incomprehensible that it actually would flood the whole world. Let us now consider Niagara Falls.
Before Niagara Falls water was diverted for power generation, the depth at the rim before flowing over could be about 3 meters or about 9 feet. Even today, with the thunderous flow, the depth is
approximately 2 feet.
The intensity of Niagara at its original peak is something the none of us have seen. Yet, if the flood was local, the spillover from such an imaginary flood would be 10 times the current rate of Niagara and several thousand times as wide. It would take little time for such a local flood to become global.
Try to imagine if you can a wall of water gushing 15 cubits over the rim of a local flood mountain rim. Now try to imagine this for several months non-stop. Quite a mess, isn't it?
Another issue comes up. It is evident that the height of the global flood over the mountains is a revelation from God. Not a soul would be aware of the depth under the flood crest of 15 cubits over the top of the mountains.
Of course one could just spiritualize all the texts that we don't like, but then why bother studying the scriptures at all?
Let us rightly divide the word of truth.