Parshall Flume Flow Calculator
Calculate free flow through a Parshall flume from the head measured at the upstream gauging point.
- n = 1.522 × W0.026 = 1.5220
- Q = 4 × W × Han = 4 × 1 × 0.98431.522 = 3.9045 ft³/s
Parshall Flume Equation
Valid for free flow in flumes with throat widths of 1 to 8 ft. Ha is measured in the converging section at two thirds of its length upstream of the crest.
Worked example
A 1 ft flume with 0.3 m (0.984 ft) head: n = 1.522, Q = 4 × 0.9841.522 = 3.90 ft³/s = 398 m³/h.
Frequently Asked Questions
Why use a flume instead of a weir?
Flumes have low head loss and are self cleaning, so they suit wastewater and channels carrying solids.
Where is the head measured in a Parshall flume?
At the Ha gauging point in the converging section, two thirds of the converging wall length upstream of the throat.
What sizes does this cover?
Throat widths from 1 to 8 ft. Smaller and larger flumes use different coefficients.
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