Thanks for the confidence you put in me.

I do not only have modelling as a hobby, but also sports fishing. I have quite often fished in Brooks and small rivers. So have quite some knowledge about them... I also can say that the stones of the ford's might get rather slippery from algae. Of course the amount of muck thrown up by the carriers as partly based on how frequently the ford is used.
To reproduce the whirling will be quite a challenge, since it must be done in a very controlled way. Upstream from the carriers, the water must be clear, yet down stream the swirl will be present in a very particular way. It obviously will start at the bottom, where the intensity will be at its summit, gradually decreasing as it, in the same time, will fan up and out.
If you want to put the first carrier mid stream, the area before it will be clear too, but if it will be across the brook, then the swirl will be fading behind it already, in a sweeping way. I hope you understand what I mean...
Not sure how to represent this...