What is the most common triangular weir notch used for open-channel flow measurement?

• A. 60-notch triangular
• B. 90-notch triangular
• C. 60- and 90-notch (triangular) combined
• D. V-notch

Answer: (A)

In open-channel flow measurement, the notch shape on a weir controls how discharge relates to the water depth over the notch. The 60-degree triangular notch is the standard choice because it provides a stable, predictable relationship between head over the notch and flow across a wide range of discharges. It’s easy to calibrate, easy to construct in the field, and tends to give accurate readings under typical wastewater conditions.

A V-notch is better suited for very low flows and can be more sensitive to disturbances, while a 90-degree triangular notch offers a different, narrower measurement range that’s not as versatile for general use. For these reasons, the 60-degree triangular notch remains the most common option.