But it's not too hard at all; just a painted (Photoshop) mask for the stream (which could have been warped SSS, but it had to be exact), then a compute normal, then a lateral offset from a surface shader masked by that same stream mask (but a bit whiter [color adjust], to effect only the stream area), then some snow colors (look for old snow and ice clip), masked by a PF for some areas of less snow. Offset the snow a bit and add some soft displacements upward only, so from a color PF. That way the grasses sitting on the node before that would stay below the snow 'layer' where it thickens.
The local rough areas where the vertebrates are masked by soft SSS's (piled in line), added some downward voronoi billow holes, and some fake stone clumps (and the blood spatters), masked by that line. Because the sides of those clumps would have lost their snow color when using slope constraints, I didn't use that.
