How to direct erosion on a rising terrain?

hi there,

I got a little bit of a problem, may somebody like to help:

I got a pre-made terrain (heightmap) and I need to erode it a bit.
However, the mostly flat ground needs to stay untouched - the problem is, the terrain rises up from south to the north.

[attach id=3498]MTNER.png[/attach]

Now, as you can see on the image, if I would use erosion without any selection or masking, WM would erode everything, including the ground (see light-green lines)

I need a way, to direct erosion in a “diagonal line” across the terrain (see blue, dotted line).

Now - how can I get there?

Kind Regards!

I guess the image was lost during the upgrade/change to a different forum platform.

On a general note, what I’d do is erode everything, then use a combiner to combine the original and the erosion, with a mask to select where the eroded landscape is visible.