Weir Flow Vocabulary

weir box
If you’re looking to get a weir for your flow channel, there are a few things you’ll need to know before you can discover which design is the best fit for you. Even before that, however, you’ll need the necessary tools to do the proper research. A lot of uncommon terms are used when describing weirs, and you’ll need to learn them all before you can properly determine which weir is best for your needs. Learn the basics of weir flow vocabulary.

Weir Flow Designs

There are several different designs you can opt for when trying to find the best weir. The most common are rectangular and triangular designs. Rectangular designs are better for high flow rates, while triangular designs, also known as V-notch weirs, are better equipped for low flow rates. Other designs, such as Cipolletti and trapezoidal weirs, may appear in your research as well, and they’re essentially rectangular weirs in which the discharge walls extend out at an angle.


The crest is the part of the weir that is considered to be the bottom edge of the weir plate. It appears differently depending on what kind of weir design you’re working with. For a triangular weir, for example, the crest will be the bottom point of the triangle. For a rectangular weir, on the other hand, the entire flat bottom edge would be the crest.


The notch is often confused with the crest, so make sure you understand the distinction. The notch of a weir is the section of the weir box in which the water overflows. Meanwhile, the crest is the specific bottom point of a weir plate. The crest would be part of the notch, but notch itself refers to the entire overflow section of a weir.


The nappe is also similar in meaning to the crest and the notch. The nappe is in virtually the same location as the crest, but the word specifically refers to the water rather than the point in the weir plate. Specifically, the nappe is the part of the water flow in which the water passes over the crest and enters free flow conditions.

Suppressed and Contracted

When you’re working with a rectangular weir, you’ll find that it’s either suppressed or contracted. A suppressed rectangular weir is one in which the channel itself acts as the walls of the weir. Meanwhile, a contracted rectangular weir has separate walls that leave an opening smaller than the width of the channel itself.

Weir Pool

A weir pool is actually separate from the primary weir box. The weir pool is the body of water that’s created upstream of the weir itself. This must exist because weirs effectively act like dams, causing the upstream flow to stagnate a bit compared to what it would be like under completely open channel conditions.

Find a Weir With Tracom

Now that you know all the relevant weir flow vocabulary, Tracom is happy to help you find the weir that’s best for you. Our team can speak the language and help you design a weir box that perfectly fits your flow channel conditions. Contact us today to take the first step toward a brand-new weir.

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