In conjunction with the State of Utah, the Utah Water Research Laboratory conducted a statewide study to determine the accuracy of flow measurement devices in Utah. Their investigations showed that 2/3rd of the devices (flumes, weirs, electromagnetic and ultrasonic flow meters) did not meet the device's design criteria.
Of these devices, 37% overestimated the flow rate, while 63% underestimated the flow rate. Where water rights are an issue, almost 1/3rd were not being supplied their full water rights, while almost 2/3rd were receiving more than their allotment of water.
Of the sites investigated, 71% of the devices measured were Parshall flumes. The prevalence of Parshall flumes in the study is unsurprising as, in some Western states, the use of the Parshall flume is mandated for the measuring of water right allotments.
| Assessment Criteria | Devices* |
| Acceptable Condition | 20 |
| Bent, broken, or caving in | 13 |
| Blockage | 6 |
| Bypassing flow | 5 |
| Cavitation | 2 |
| Corrosion, rust, or worn concrete | 25 |
| Improper approach | 26 |
| Improper installation or parameters | 5 |
| Incorrect geometry | 20 |
| Incorrect or no Ha measurement | 35 |
| Incorrect or no Hb measurement | 52 |
| Settlement | 34 |
| Vegitation or debris in entrance | 28 |
| *Devices can exhibit more than one criteria | |
A number of problems listed above (bent / corrosion / geometery) can be easily avoided by utilzing a device that is suitable to the applicaiton. Suitable in this context refers to a device that is manufactured by a company specializing in flow measurement. Devices from companies such as this are considerably less likely to be out of dimension or of thin gauge / thickness materials.
Once or twice annual site maintenance can also help to avoid or minizmie the imapact of blockage / bypassing flow / settlement / vegitation. Left unattended, these fault criteria can have the largest impact on accurate flow meeausrement of all the criteria.
Improper approach and installation can be avoided by installation guidelines.
These guidelines should cover:
In the even that a device does settle out of position, corrections to the flow equations can be appliled in some cases.
By designing for free flow, the need to measure Hb (the secondary point of measurement) can be eliminated. In those instances where the device cannot be set for free flow under all conditions, corrections to the flow equation can be made for some flumes.
