River basins by triangle slope

Doodled around a bit with the river basin algorithm to see if there was a way of embedding both mountain chains and river basins as never-touching trees. Somehow it warped into rivers passing through the side of a triangle while the vertex defined the mountain.

From the doodles it looked like there would always be only one exit from each triangle (almost 100% in real life too) so I hacked up some diagrams in Office to then check out if we can use the slope of the triangle to represent implicitly the exit points. Seems like it works, but certain initial heights will preclude different configurations from forming. Not sure whether it's terminal or not yet ...