Thank you very much for the links and suggestions.

I'd read more than a few episodes of River Police: This Time It's Personal, and had tried to made some adjustments before presenting the first draft, but I knew that what I'd come up with was not going to pass muster. It looks as if my dream-self didn't pay as much attention as it could have in Earth Science. I'm going to see what I can do to keep the same general 'shape' of the river-system while being more faithful to reality.