Ok, any tips and tricks in how to measure easy and accurate the water flow?

we have what are apparently, 2 first magnitude springs, and would like to measure but is not that easy...

the second one at one point the flow splits in 2, apparently, going to a second hole (not explored yet, need a bit more mental preparation -read balls- to go in that kind of strong downstream) the question here, should we measure at this point where it splits? or do it at the sinkhole? well maybe at both?...

ok, any advise?