The accuracy of the depth-discharge relations for Palmer-Bowlus flumes in not considered to be constant over the full range of flows.
- For large values of H/L (Ha point of measurement head / throat ramp top length) the estimated accuracy is +/- 3%
- For small values of H/L the estimated accuracy is +/- 5-6%
The decrease in accuracy reflects the increased importance (and uncertainty) of the Coefficient of Discharge (Cd) at low flows.
Also, smaller Palmer-Bowlus flume sizes tend to be less accurate in general than larger Palmer-Bowlus flumes sizes.
Source: Recommended Practice for the Use of Parshall and Palmer-Bowlus Flumes in Wastewater Treatment Plants
