Early civilisations inhabited the flood plains of rivers. There is a clue in that name that may answer why many civilisations have flood myths.
I'm guessing you mean Mesopotamia (middle of the river).
Yes, rivers would be a sure bet to establish irrigation for community farming.
It's an interesting anomaly that the Nile was gentler in its seasonal floods, so the Egyptian artifacts don't speak of this chaos and disaster and the wrath of the gods. Yet in Mesopotamia the floods could be devastating, so they are inclined to think the gods have a grudge. If Western religions had developed out of Egyptian lore, I suspect they might have produced a rosier outlook. All the trials and tribulations probably would have been replaced by a sunnier kind of positive reinforcement.