Very interesting! For just (semi-)randomly picking directions, this generates some nice results. I am also watching this thread to see how far you can take this!

There's no concept of elevation involved...
I would hesitantly disagree, and say that your hydrological divides could be an abstraction of elevation data (ridge lines?). I am now wondering if there is some way of processing elevation data so that this can read it as just a set of ridge lines/break lines/divides.