Differences Between Long Throated and Short Throated Flumes

parshall flume

While there are plenty of different types of flumes you can use, they all tend to fall into two primary categories. You can either get long throated flumes or short throated flumes. They both have their advantages and disadvantages, but you can only choose one for your flow rate measurement efforts. Discover the most important differences between long throated and short throated flumes, and discover which would best fit your flow channel conditions.

The Central Difference

As the name suggests, the central difference between these flume types is the length of the throat. A short throated flume is designed to produce a curvilinear effect in which flow is controlled in a specific region of the flume. This is the most common type of flume, as it’s the category that Parshall flumes fit in. Meanwhile, a long throated flume creates parallel flow lines in the flow control section. You’ll find this effect in RBC flumes, for example.

Measurement Point

Measurement points differ depending on how long the throat is in a flume. If you’re working with a short-throated flume, you’ll have a single measurement point that you must abide by. If you measure upstream of this point, the flow rate will come across as too high while measuring downstream will have the flow rate read too low compared to what it actually is. If you have a long throated flume, however, you can measure at virtually any point upstream of the throat drawdown. That grants a bit more flexibility.


Equations can be much more complicated when you’re working with long throated flumes. The reason for this is twofold. First, most meters don’t actually support measurements for long throated flumes. You’ll likely need additional devices to gather batch downloads to work in a longer form equation. That complexity may not be a problem for big organizations, but it can cause undue stress on a smaller-sized effort. Additionally, long throated flumes aren’t standardized, so operators will have to take special care that they’re using the right equations. This leaves much more room for error.


While standardization makes the application of equations easier, it doesn’t make installation any easier. In fact, it can have the opposite effect. The standardization of short throated flumes can make it difficult to fit these flumes into unique flow channel configurations. When you opt for a long throated flume, on the other hand, it’s much easier to customize as needed to fit with the flow channel conditions.


Submergence can be a major problem for a lot of flumes depending on the flow channel conditions. If you’re worried about submergence, a long throated flume gives you a bit more leeway on them. Submergence transitions for long throated flumes are up to 90%. Meanwhile, short throated flumes tend to vary from 50% to 80%. If your downstream conditions are prone to submergence, a long throated flume is going to be your best defense.

Flumes from Tracom

Now that you know the differences between long throated and short throated flumes, it’s time to get one of your own. No matter which side you’re leaning towards, Tracom is happy to help. Contact us to find the perfect flume for your needs today!

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