As Parshall Flumes get larger there are fewer applications that they fit beyond measuring surface waters and treatment plant flows.  Even then, the 84-inch Parshall Flume is not frequently used - the flow rates for these applications are usually smaller or larger than the 84-inch Parshall Flume's operating range.  Due to its size, the 84-inch Parshall Flume ships in two pieces for field assembly.   

Applications

The 84-inch Parshall Flume is normally only used to measure:

• Surface waters
  • Rivers / streams
  • Catchments
  • Watersheds
• Water rights
  • Canals
• Wastewater treatment plants​

Configurations

Due to its size, the 84-inch Parshall Flume is only offered in two different configurations:

• Plain
  • Requiring field formed transitions
• Wing Walls
  • Inlet or outlet walls to span rectangular channels

Regardless of which configuration is selected, the 72-inch Parshall Flume usually ships in two-pieces for ease of handling.

Flume Accuracy

With proper upstream flows, a good installation, and a flume that is in dimension, an 84-inch Parshall Flume can be as accurate as +/-5% (ASTM D1941).

In the unlikely even that the flume settle or possibly submerges, corrections can be made to the flow equation.

Flume Dimensions

While similar in layout, Parshall Flumes are not scale models of each other.  The flumes differ in section lengths and convergence / divergence angles.  

Free-Flow Equation

The general, free flow equation for a Parshall Flume is:

Substituting for the 84-inch Parshall Flume:

Minimum Head (ft)	0.25	Minimum Head (m)	0.0762
Minimum Flow Rate (cfs)	3.043	Minimum Flow Rate (l/s)	86.17
Maximum Head (ft)	2.50	Maximum Head (m)	0.7620
Maximum Flow Rate (cfs)	121.4	Maximum Flow Rate (l/s)	3438
Equation (cfs, ft)	28*H1.601	Equation (l/s, m)	5318*H1.601

Discharge Table

A flow table is available for download for the 84-inch Parshall Flume. 

The table provides:

• Plan view of the flume showing the point of measurement (H_a) 
• Discharge equations (cfs, gpm, mgd, l/s, m3/hr)
• Flume accuracy (per ASTM D1941)
• Submergence transition (S_t)
• Source of the tables data 

Materials

Openchannelflow offers the 84-inch Parshall Flume in two different materials:

• Fiberglass (FRP)
  • Lightweight / customizable
• Galvanized steel
  • Good for areas where cattle are present

Submergence Transition

Submergence occurs when the downstream restrict the flow out of a flume.  As submergence increases, a point is reached where the difference between the indicated and actual flow rates is large enough that a correction needs to be made.  

This point is termed the submergence transition (S_t).

70% is the submergence transition (S_t) for the 84-inch Parshall Flume.  At or above this point and the indicated discharge needs to be corrected to reflect the actual discharge rate.