Reptilian survival

A rather rough look into the begging story of Anunaki, reptilians, Nephilim or fallen Angels.
It’s said the were around before and after the flood of Noah’s time.
I grapple with the thought. Wouldn’t the tunnels flood too? It seems if a tunnel curves upwards. Then back down. The water would have a choke point. Rendering air to be below.
This video may not spell things out to well. But it surly is food for thought.
I find the thought and questions worthy of looking into. Hopefully you do as well. As it could help confirm or debunk some stories.