If you have a circular headgate, how can you use that as an orifice to measure flow? It’s easy if the gate is fully open – orifice equations from the USBR Water Measurement Manual can be used. The area of a circle is PI*r^2.
Here are the orifice equations for a rectangular headgate – the same equations are used for a circular headgate, or really a headgate of any shape:
A = the area of the orifice g = gravity, 32.2 ft/sec^2 h1 = the upstream depth in feet h2 = the downstream depth in feet
The first equation with the coefficient of 0.61 is for a gate on a wall. The second with the coefficient of 0.70 is for a circular gate at the end of a pipe.
The difference between h1 and h2 can also be measured down from the top of a wall with a level top.
There you go. Based on the change of stem height, you can calculate how much the headgate is open. Convert that to a percentage. For example. A 2.0′ diameter headgate open 0.5′ is 25% open. Then use the table’s 50% row to where it intersects the 2.00 foot diameter column to get an area of 1.913 square feet.
At Don Wright’s WaterWrights news, his July 20 article explains that there is some hope for amendments to bills SB 389, AB 460, AB 1337.
“Legislative committee consultant Alex Dominguez said he has been attending many, many meetings and has seen the opposition to the three big water rights bills: SB 389, AB 460 and AB 1337. He said AB 460’s author Assemblywoman Rebecca Bauer-Kahan or RBK, has dug her heels in and isn’t willing to work with the water community. That’s what I’ve been hearing also. It sounded to me like there is some hope for SB 389 being amended in a way that could actually be helpful. Let’s see what happens with that. Attorney Lauren Layne added there is some indication AB 1337’s author Assemblywoman Buffy Wicks may be willing to amend the bill to make it more palatable.“