Important Weir Flow Terminology You Should Know

To get the most out of your weir flow measurements, it’s helpful to know the proper terminology. The process can be quite complicated, and not knowing the vocabulary used can be a significant barrier to learning what you need to know. That’s why we’ve created this easy list of all the most important concepts. Here is the weir flow terminology you need to know.

Components of a Weir

There are quite a few components involved in the functionality of a weir. The primary component of a weir is the notch, which is the area that the water overflows. It’s sometimes also known as the overflow section. Should the notch be thin enough for the water to avoid the downstream face, it’s known as thin-plate or sharp-crested. If you opt for a quality weir, this is likely the kind of notch you’ll be dealing with.

While the notch encompasses virtually the entire flow area, the actual bottom edge of the notch is known as the crest. The crest can take a few different forms, however, depending on the type of weir you have. A rectangular weir, for example, will have a long crest across its bottom, while a V-notch weir’s crest is the singular point of the triangle.

Weir Measurement

When it comes to actually taking flow rate measurements, the most important term you need to know is zero reference elevation. Since weirs always have a bit of water in them, the zero point for the measurement isn’t the floor. Rather, it’s the elevation of the crest, so zero-point elevation and crest elevation are essentially interchangeable terms. 

In order to maintain accurate measurements, the entire flow needs to pass over the notch. For weirs in which the notch doesn’t actually span the full channel, you’ll find a side contraction. Specifically, side contraction refers to the curved flow path implemented by weir designs that create a flow jet that’s narrower than the weir opening.

Weir Installation

There are also two terms you should know that describe certain types of weir installation. Depending on what kind of environment you’re dealing with, knowing the difference between these two terms can be essential. The first is known as a suppressed weir, or a weir in which the sides of the channel function as the weir ends. 

A contracted weir is a bit different. These weirs don’t use the sides of the channel as ends, which leads to a smaller notch opening. This results in head loss, while the head loss of a suppressed weir is negligible. That is the primary difference that the words contracted and suppressed are used to indicate.

Finding Your Own Weir

Now that you’re equipped with the essential weir flow terminology, you can find a weir that best fits your unique needs. At Tracom, we have a wide variety of options and styles on offer, and each is fully customizable. Contact us today to learn more about everything we have to offer and take the first steps toward getting the perfect weir for accurate flow measurement.