How to Measure With a Parshall Flume

parshall flume

While there are plenty of different flume styles available, the Parshall flume is among the most common for a wide variety of applications. This is in large part because Parshall flumes are easy to read. Even so, you’ll want to make sure you’re doing everything right to ensure that you’re getting the accurate measurements you need. It isn’t just a matter of going up to the flume and checking the gauge. Learn how to measure with a Parshall flume and ensure that the measurements are accurate.

Investigate the Site

Before you take your reading, you’ll want to investigate the site itself. Quite a few conditions can be present that will throw off the results of any displayed measurements. First, you’ll want to see if there are any upstream obstructions. Trash, vegetation and debris are examples of this. Then you’ll want to do the same for the downstream. Both need to be clear and uniform for a flume to function properly. Additionally, you’ll need to see whether the flume is centered in the stream to ensure that the flow has a uniform velocity profile.

Examine the Flow

Once the site has been examined, you’ll need to look at the flow itself. The most important factor to keep an eye out for is tranquility. The flow needs to be uniform and calm without any surface turbulence. Upon verifying this, take a look at the downstream flow. Make sure it’s all exiting the flume properly without backing up into the flume itself. This is to verify that the flume isn’t suffering from submergence.

Inspect the Flume Itself

Now you can move on to the flume itself. One of the most important factors here is ensuring that the flume is level from front to back and side to side. The sidewalls and the floor need to be straight without any distortions. The head and staff gauge also need to be verified. Once all that’s complete, you can move forward to finding the point of measurement. In most cases, the point of measurement is two-thirds of the distance between the throat and the back of the flume. If it’s larger than 96 inches in size, however, the point will be closer to the throat.

Take the Measurement

The final step is to take the measurement. There are two primary ways of doing this. If the staff gauge is in good condition, you can simply look at where the water level is at the staff gauge. That’s going to be the measurement you need for the equation. If the staff gauge is in poor condition, however, you’ll have to measure it manually. That means measuring the distance from the bottom of the approach section to the surface and applying that to the equation appropriately.

Parshall Flumes From Tracom

Now that you know how to measure with a Parshall flume, you can install one of your own. At Tracom, we’ll help you find the right Parshall flume for your unique flow channel conditions, even if we have to custom design it ourselves. Contact our team today to get started!

Andrew Helbling

Andrew Helbling is the Product Specialist at Tracom, where he works with engineers, contractors, and product owners alike to assess and select the best open channel flow and general-purpose fiberglass products for their application. Andrew is passionate about clean water and helping operators and engineers provide the cleanest water possible.

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