Watermasters, technicians, diverters, and anyone who needs to regulate diversions in the field uses the U.S. Bureau of Reclamation Water Measurement Manual. I used this as a watermaster, and I still take it with me on some visits to clients. The manual answers a lot of questions:
What kind of measurement device should I install?
How do I get the flow from my measurement device?
How accurate is my device, and how can I figure that out?
You can buy a hardback version like I have by starting at the webpage https://www.usbr.gov/tsc/techreferences/mands/wmm.html . You can download a PDF version from https://www.usbr.gov/tsc/techreferences/mands/wmm/WMM_3rd_2001.pdf . I put a link to the PDF on the left sidebar here, too.
I should have posted this years ago. Better late than never….