When viewed from the top, the Parshall Flume has an hourglass shape and, like the Venturi Flume upon which it is based, is composed of three distinct sections:  

• Uniformly converging inlet
• Short and narrow throat section
• Uniformly diverging discharge  

The floor of the Parshall Flume is: 

• Flat in the converging section (where the primary point of measurement is)
• Drops through the throat (creating supercritical flow and one of Dr. Parshall's more radical inventions)
• and then rises in the diverging section.  

The diverging section's outlet is always lower than the converging section's floor - the floor dips in at the beginning of the throat and only partly recovers at the end of the throat. 

A flat floor in the converging section (where the free flow point of measurement is) means that all that is necessary to determine the flow rate is to simply gauge or “stick” the water level at the point of measurement - measuring the depth of water from the surface to the flume floor.  Unlike Palmer Bowlus or RBC Flumes, there is no ramp level to deduct from the reading. 

Unlike Palmer Bowlus or Trapezoidal Flumes, the sidewalls of the Parshall flume are vertical.  Vertical walls mean that when a staff gauge is used, there is no need to check that the gauge has been calibrated to read true vertical depth. 

The flat converging section floor and the straight vertical sidewalls make the Parshall Flume one of the easiest flumes to use accurately.