Yes, l know a number of places that they have gauges at certain points for that.
I am often asked by the clients How fast is that water moving, MPH, and as you rightly stated that changes as you move down the river.
I used to know a simple formula for that and l have for got how to do It, l do not know how accurate it was, but it amounted to something like counting in seconds, for a given distance a floating object.
Say it took 10 seconds for the object to travel 20 yards. You may well know the answer to that one or a alternative way to calculate it. If not, no problem.
I think that a USA mile may be different from UK, 1760 yards. I know that gallons are.
Sorry to get you going here but you got my brain in gear with this one
I can catch fish ok, but l am no mathmatical genius !!!
Thanks again Davy