ENGINEERING – HYDRAULIC & OPEN CHANNEL FLOW CALCULATOR
Parshall Flume
A precise tool.
What is the Parshall Flume & How does it work?
The Parshall flume is a widely used open‑channel flow measurement device that creates a controlled contraction and acceleration of the water stream. By forcing the flow through a narrow throat, the flume establishes a predictable relationship between the upstream water depth (head) and the discharge, allowing engineers to infer flow rates from simple depth measurements.
The geometry of a Parshall flume is defined primarily by its throat width, denoted as a. This dimension, together with the measured head H at a fixed location upstream of the throat, determines the flow regime—subcritical, critical, or supercritical. In the critical region, the flow rate becomes a function of both a and H, independent of downstream conditions.
For a given throat width, the discharge can be expressed by the empirical formula Q = C·a·H^{1.5}, where C is a dimensionless coefficient that varies slightly with a. This relationship enables rapid field calculations: once a, H, and the appropriate C are known, the volumetric flow rate Q (in m³/s) follows directly.
\( Q = C, a, H^{1.5} \)
Q = discharge (m³/s) C = discharge coefficient (dimensionless) a = throat width (m) H = head (m)
Parameters
Result
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Frequently Asked Questions
What is a Parshall flume used for?
A Parshall flume is used to measure the flow rate of open-channel water by creating a controlled contraction and acceleration.
How does the throat width affect the Parshall flume’s performance?
The throat width (a) of a Parshall flume defines its geometry and directly influences its ability to accurately measure flow rates based on upstream water depth.
Can I use a Parshall flume for any type of liquid?
Parshall flumes are typically designed for water but can be adapted for other liquids with similar properties, such as low viscosity and free-flowing characteristics.
What is the advantage of using a Parshall flume over other flow measurement devices?
The Parshall flume provides a simple method to infer flow rates from depth measurements due to its predictable relationship between head and discharge.
How do I calibrate a Parshall flume?
To calibrate a Parshall flume, you need to establish a relationship between the upstream water depth (head) and the actual flow rate through the device, often done using standard flow meters or by consulting manufacturer-provided calibration charts.
What are the limitations of using a Parshall flume?
Parshall flumes may not be suitable for highly viscous liquids, silt-laden water, or flows with significant turbulence. They also require a certain range of flow depths to function effectively.
How do I maintain the accuracy of a Parshall flume?
Regularly clean the flume to remove debris and sediment that could affect flow measurement. Ensure proper alignment and check for any wear or damage to the throat area.
Results are for informational purposes only and do not constitute professional advice.