How do you choose a weir?

• A. By the cost
• B. Without calculations, it is better to go with a bigger weir
• C. By the material used
• D. Without calculations, it is better to go with a smaller weir

Answer: (B)

Sizing a weir means making sure its capacity matches the amount of water you expect to pass, which normally requires calculating the discharge for the weir type and head available. If you don’t have the calculations at hand, going with a larger weir is the safer default. A bigger crest provides a margin for higher-than-expected flows and reduces the risk that the weir will under-serve the system, causing flow restrictions, upstream water buildup, or inaccurate measurements. Cost and material are secondary concerns to ensuring reliable flow control, and choosing a smaller weir without calculations can create a bottleneck and more problems down the line.