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As a long-throated flume, the Palmer-Bowlus is best when used within a defined band of levels. 

  • The minimum head at the point of measurement should be no less than the larger of 0.1 L (L = throat ramp top length) or 0.2-feet (0.06 m).
  • The maximum head should not exceed 0.6 L.

For Openchannefllow Palmer-Bowlus flumes, the throat ramp top length (L) is equal to the flume width (D – also the flume size).

Substituting and consolidating, the recommended head should be between:

0.1 D < H < 0.6 D

Remeber that H is measured at the same level (although upstream) as the top of the throat ramp (which is itself D/6 above the floor of channel in the upstream portion of the flume).

Therefore, if an operator is measuring from the water's surface to the bottom of the flume, the total reading should be:

0.27 D < H < 0.77 D