One of the advantages of the Parshall Flume is how easy it is to use!  Unlike Palmer-Bowlus  or RBC Flumes, there are no zero height offsets to worry about.  Just inspect the flume, find the point of measurement, and stick / gauge to the bottom of the flume.  Under free-flow condtions you only have to measure the level at one point in the flume.

As a fixed device, there is no need to calibrate a Parshall flume once it has been installed.  With a properly sized and installed flume, once the placement is complete, flow readings can be taken immediately.  

• Inspect the Site
  • Are there any obstructions upstream of the flume?
  • Is there trash, debris, vegetative grown, upstream, downstream, or in the flume?
  • Is upstream undermining / downstream scour visible?
  • Is the flume centered in the flow stream?
• Watch the Flow
  • Watch the flow entering the flume. Is it well distributed, tranquil, laminar?
  • All are necessary for a Parshall flume to operate correctly.
  • Watch the flow exiting the flume. Does the flow back-up into the flume? Is it restricted? If so, verify the flume is not operating under submerged conditions.
• Inspect the Flume
  • Is the flume level from front-to-back and from side-to-side?
  • Are the sidewalls and floor of the flume sound and not visibly distorted?
  • Inspect the head / level / staff gauge (if present)? Is it in good condition? Located at the point of measurement (see below)?
• Find the Point of Measurement
  • For Parshall flumes from 1-Inch to 96-Inches in size, the correct point of measurement is 2/3 of the distance along the sidewall as measured BACK from the throat, in the approach section of the flume.
  • For Parshall flumes larger than 96-Inches, the point of measurement is closer to the throat, refer to a Parshall flume dimensional drawing for the exact dimension in the approach section of the flume.
• Read the Water Level
  • If a head / level / staff gauge is present and in good condition, visually read the indicated level.
  • If a head / level / staff gauge is not present, not in good condition, or is otherwise suspect, manually gauge the water level to the bottom of the approach section. The distance from the bottom of the approach section to the surface of the water is the correct level.    

With the water level you can now either apply the free-flow discharge equation or look up the flow rate on the discharge table. 

 

 

Image:  Wikipedia