"Uniform" means it has no small scale structures as I explained in my first post. Also I think what @gadget271 said hits the mark. What I call "uniform" and gadget "flat floor" and "straight up" walls makes your stream look a bit like a man-made channel, not a natural stream made by natural erosion. In the picture you took for inspiration you can see al the irregular rocks and many different inclinations of the cliffs.
A problem is size of your new project. I said you should make is more narrow and you did that but you also made it much smaller in general. If you would have higher cliffs you could add more small details like side (lateral) ravines.
I still think you should make vegetation, stencils are essential part of voxel. Also adding stuff like moss covering the ground with plants like grass and moss (wall creeping moss from Gondor rp would be cool) using overlay and splatter overlay brush are important voxel skills.

I don't exactly know what @BWOT want's to see for voxel badge. I'm just giving feedback on terraforming
But I really think it should not matter for what purpose you plan to use a badge. The required skills should be the same for everyone.
Btw you wrote in your application that you want to use it for terraforming in general and Belfalas/Mordor in special

I believe your ravine is a good example to show skills needed for Mordor. All of my points will apply there.

I mean: Make that ravine with all the details I suggested.
Or if you prefere make something else, try this:
[QUOTE="The Return of the King - The Stairs of Cirith Ungol]Still on and up the stairway bent and crawled, until at last with a final flight, short and straight, it climbed out again onto another level. The path had veered away from the main pass in the great ravine, and it now followed its own perilous course at the bottom of a lesser cleft among the higher regions of the Ephel Dúath. Dimly the hobbits could discern tall piers and jagged pinnacles of stone on either side, between which were great crevices and fissures blacker than the night, where forgotten winters had gnawed and carved the sunless stone. [/QUOTE]