Flumes
The Rating Curve Tool includes the formula for a Parshall flume which is frequently used in municipal and industrial applications.
Parshall
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Parshall
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The formula for a Parshall flume is: Q =KHn
Where: Q = flow rate
H = head measured at point H
K = constant, dependent upon throat width and units
n = constant power, dependent upon throat width
Discharge Equations for Parshall Flumes with Head in feet are shown in the table below:
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Throat width, W
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CFS
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GPM
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MGD
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1
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Q = 0.3380 H1.550
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Q = 151.7 H1.550
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Q = 0.2184 H1.550
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2
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Q = 0.6760 H1.550
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Q = 303.4 H1.550
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Q = 0.4369 H1.550
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3
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Q = 0.9920 H1.547
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Q = 445.2 H1.547
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Q = 0.6411 H1.547
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6
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Q = 2.060 H1.580
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Q = 924.5 H1.580
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Q = 1.331 H1.580
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9
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Q = 3.070 H1.530
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Q = 1378 H1.530
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Q = 1.984 H1.530
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1
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Q = 4.000 H1.522
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Q = 1795 H1.522
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Q = 2.585 H1.522
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1½
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Q = 6.000 H1.538
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Q = 2693 H1.538
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Q = 3.878 H1.538
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2
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Q = 8.000 H1.550
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Q = 3590 H1.550
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Q = 5.170 H1.550
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3
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Q = 12.00 H1.566
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Q = 5386 H1.566
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Q = 7.756 H1.566
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4
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Q = 16.00 H1.578
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Q = 7181 H1.578
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Q = 10.34 H1.578
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5
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Q = 20.00 H1.587
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Q = 8976 H1.587
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Q = 12.93 H1.587
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6
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Q = 24.00 H1.595
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Q = 10770 H1.595
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Q = 15.51 H1.595
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8
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Q = 32.00 H1.607
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Q = 14360 H1.607
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Q = 20.68 H1.607
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10 to 50 ft.
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Q = (3.688W + 2.5) H1.6
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Q = (1655W +1122) H1.6
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Q = (2.384W +1.616) H1.6
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NOTE: Coefficients for throat widths larger than 10 feet can be found at: https://www.usbr.gov/tsc/techreferences/mands/wmm/chap08_10.html