I can't thank you enough for spending time to explain and give out your inputs. (You should be a professor in hydrology or maybe you are). From your information I think I understand somewhat in regard to the water flow not only from the surfaces from the tributaries but also from the underground. From the latest diagram I have noticed the deceleration of the water level drop, in fact, a little reverse direction at the end (from 1.75m to 1.76m) does give me hope.
But let just say if there is no rain between now and then and the river water level continue to drop, what is the minimum number that you think is the cut line? for instant if it drops to 1m by Oct 21 is it still ok for the ship to depart?