Which statement best describes the flow at the throat of a weir?

• A. Slow and Deep
• B. Turbulent and Deep
• C. Fast Moving and Shallow
• D. Laminar and Shallow

Answer: (C)

At the throat of a weir, the flow has to pass through the narrowest cross-section. To keep the same discharge, the velocity must increase as the area decreases, so the water speeds up as it moves through the throat. This acceleration comes with a drop in depth, since continuity and energy exchange favor a shallower flow when velocity rises. So the defining picture is a fast-moving, shallow flow right at the throat.

The other descriptions don’t fit because they imply either slower speeds or greater depths, which contradict the constriction effect at the throat. While high speeds can induce turbulence, the key characteristics here are the rapid velocity and reduced depth.