With any type of open channel flow measurement device, errors can arise thanks to mistakes in the design. If the design of the monitoring device is off, it can result in either an overestimation or underestimation of flow rates, which most importantly affects water supply delivery. Open channel flow measurement devices include Parshall flumes and other flumes, weirs, and ultrasonic and electromagnetic flow meters.
Utah Water Research Study
Recently, the Utah Water Research Laboratory worked in conjunction with the state of Utah to investigate the accuracy of such flow measurement devices, 71 percent of which were Parshall flumes (common in Western states due to certain mandates). Two-thirds of the devices investigated did not meet design criteria. The study then found that of these devices, 63 percent underestimated the flow rate and 37 percent overestimated the flow rate. Consequently, 2/3 of recipients were receiving excess water and 1/3 weren’t receiving their full allotment.
Common Causes of Open Channel Flow Errors
The assessment criteria used in the Utah Water Research study provides a thorough list of errors that could arise in Parshall flumes and other flow measurement devices. Here are the criteria, listed from most to least commonly found among the inadequate flumes in the Utah study:
- Incorrect or no measurement for secondary point of measurement
- Incorrect or no measurement for primary point of measurement
- Settlement
- Vegetation or debris found in entrance
- Improper approach
- Corrosion, worn concrete or rust
- Incorrect geometry
- Bent, caving in or broken
- Blockage
- Bypassing flow
- Improper parameters or installation
- Cavitation
Solutions to Open Channel Flow Errors
The best solutions to open channel flow errors are preventative; as long as there’s information on what to watch out for, it’s simple to avoid flaws in the design.
For starters, it’s important to go with a manufacturer that specializes in flow measurement. These companies provide products that are much less likely to have an error in dimension or material, e.g. material gauge or thickness. This allows easy avoidance of a number of the above problems, such as corrosion, improper geometry, or bending or caving in.
Additionally, fault criteria—issues that arise due to improper upkeep—can have the largest impact on flow measurement accuracy. These criteria include vegetation or debris, settlement, and blockage. The impact of such criteria can easily be avoided with site maintenance simply once or twice annually.
Finally, never forget to follow installation guidelines—improper installation can be detrimental to accurate flow measurement, in Parshall flumes and other devices. Guidelines should thoroughly cover the upstream and downstream conditions, site selection, and device placement.
Finding Parshall Flumes in Georgia
Tracom, Inc. provides customized solutions for fiberglass products. We specialize in flow measurement devices, producing Parshall flumes, Palmer-Bowlus flumes, Trapezoidal flumes, HS / H / HL-type flumes, Cutthroat flumes, Montana flumes, RBC flumes and SANIIRI flumes. With over 30 years of experience, we can quickly and accurately manufacture fiberglass flumes for any industrial application. Request a quote today to get started.
