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Montana Flume Accuracy

Properly installed and under free-flow conditions, the Montana flume should have laboratory accuracy of +/-2%. However, practical considerations such as approach flow, installation, and dimensional tolerances mean that it's free-flow discharge precision is likely to be closer to +/-5% (per ASTM D1941).  

Should a Montana flume become submerged the indicated flow rates will be substantially different from the actual flow through the flume.  While some studies have been conducted to develop corrections for submerged flows, Openchannelflow always recommends designing Montana flume installations in particular for free-flow discharge.

Montana Flow Equations

Montana flumes use the same free-flow equations as Parshall flumes.  The level-to-flow equation can be expressed as:

Free flow discharge equation for Montana flume

Per ASTM D1941

Throat Width

C (Imperial)

C (SI)

n

1”

0.338

0.0479

1.55

2”

0.676

0.0959

1.55

3”

0.992

0.141

1.55

6”

2.06

0.264

1.58

9”

3.07

0.393

1.53

1’

4

0.624

1.522

1’-6”

6

0.887

1.538

2’

8

1.135

1.55

3’

12

1.612

1.566

4’

16

2.062

1.578

5’

20

2.5

1.587

6’

24

2.919

1.595

7’

28

3.337

1.601

8’

32

3.736

1.607

10’

39.38

4.709

1.6

12’

46.75

5.590

1.6

15’

57.81

6.912

1.6

20’

76.25

9.117

1.6

25’

94.69

11.32

1.6

30’

113.13

13.53

1.6

40’

150

17.94

1.6

50’

186.88

22.35

1.6

Montana Flume Flow Tables

Free-flow discharge tables for Montana flumes can be found in the Discharge Tables section.