You’re all too kind. The effect is very simple to produce as, in many respects, it’s just an illusion. I make my terrain on 6mm thick 30cm sq MDF tiles so (other than Belgium, which is raised on plinths for the building basements) there is no real depth. The lack of depth means the technique could also be used for sectioned rivers, though snake-like strips of MDF would probably warp so the base might need to be something more stable (hmmm, not sure what).
Anyways, the bank is raised up using slivers of foam board and plaster:
Then a base texture for the ground level using sifted ‘sharp sand’ onto the aforementioned glue:
Painting (the Afghan river was clear and shallow, so had texture to its bed, whereas The North river is tinted and deep, so the bed is left smooth):
Then the pour:
The pour will overlap and have some shrinkage, which is actually a good thing, as it allows the adding of extra layers including waves and turbulence. For the Afghan river, protruding rocks were repainted as ‘dry’ after the river had cured.
I haven’t got a suitable finished image of the WIP section above but the following is just downstream. In the foreground is a ford and in the shot you can just about make out the texture of the shallower river bed.
In this Afghan/Arizona/Sicily shot you can see the rocks etc underwater:
So, though a long post I’m not advocating anyone doing it this way (horses for courses, each to their own, etc, etc), I just wanted to show that what works for me is the result of what is actually a pretty simple process.