What do weirs measure in wastewater channels?

• A. Flow Rate
• B. Color
• C. Water Temperature
• D. Dissolved Oxygen

Answer: (A)

Weirs are used to measure flow rate (discharge) in open wastewater channels. They work by presenting a known crest and geometry, so the water depth upstream—the head—relates in a predictable way to how much water is passing over the crest. By measuring that head, you can calculate the discharge with standard stage–discharge relationships for the specific weir shape. This flow information is essential for process control, balancing inflows and plant capacity, and meeting regulatory requirements. Color, water temperature, and dissolved oxygen are determined with separate instruments or tests and are not what a weir directly measures.