David says that he measured with GPS that the dam has moved a few centimetres. But GPS accuracy does not allow that.
As the water is rushing through the city, you can tell that the water is animated. In some shots the water does not look real.
When they are both drowning in the room at the beginning of the movie and the boy swims back up to the top there is a hand under his armpit helping him up. His father is on the other side.