Coming back to this, one other question I'm left with is: "Can the river pass through mountains?" That is to say: if I get lucky with the initial layout and can route the river right around the edge of the board, can I run water from one mountain directly through the other, or do I have to leave a channel around it?
Also it would be nice if the game eliminated layouts where villages spawned directly beside mountains. Aiming to beat my personal best, I find it's possible to hit a Minesweeper-style run of bad starts where at least one village is doomed from the very beginning. It doesn't prevent a win, but it seriously hampers your chances of a top score.
As before, though: really nice little game. I'm looking forward to seeing how it develops, but even in its current state it's hugely enjoyable once you pick up the basic rules.