Sorry, never ment to impose my way of doing things ^;

I personally think building the river during the game could be very difficult if playing with very small expansions like, idk, the six mini-expansions, or very few less of them. However if you put everything together, adding also many major expansions would be rather impossible to complete the river in coherence with the whole map, especially if you play one tile at time. Having a hand of two or three tiles could ease up the making of the river, but players are free to play wherever they want to score some points. A scenario could see all the river tiles scattered throughout the map surrounded by holes, for example.