What calibrated device developed for measuring flow in an open channel consists of a contracting length, a throat with a sill, and an expanding length?

What calibrated device developed for measuring flow in an open channel consists of a contracting length, a throat with a sill, and an expanding length?

• A. Parshall flume
• B. Venturi meter
• C. Weir
• D. Flume gauge

Answer: (A)

Measuring open-channel flow with a device that creates a controlled constriction is the idea here. The Parshall flume does exactly that: it has a contracting inlet, a throat that includes a sill, and an expanding downstream section. As water enters the narrow throat, it must rise upstream to a higher depth. The relationship between that upstream water depth (head) and the discharge is fixed by calibration for that specific flume geometry. The expanding section helps stabilize the flow and reduce oscillations, so the head measurement remains reproducible. This setup—constriction, a sill at the throat, and subsequent expansion—is characteristic of the Parshall flume and is why it’s widely used for open-channel flow in wastewater settings. The other options don’t fit this configuration: a Venturi meter is designed for closed pipes and uses a differential pressure across a converging-diverging nozzle; a weir measures flow by the height of water over its edge; and “flume gauge” isn’t the standard device with this contracting-throat-sill-expanding design.

Measuring open-channel flow with a device that creates a controlled constriction is the idea here. The Parshall flume does exactly that: it has a contracting inlet, a throat that includes a sill, and an expanding downstream section. As water enters the narrow throat, it must rise upstream to a higher depth. The relationship between that upstream water depth (head) and the discharge is fixed by calibration for that specific flume geometry. The expanding section helps stabilize the flow and reduce oscillations, so the head measurement remains reproducible. This setup—constriction, a sill at the throat, and subsequent expansion—is characteristic of the Parshall flume and is why it’s widely used for open-channel flow in wastewater settings. The other options don’t fit this configuration: a Venturi meter is designed for closed pipes and uses a differential pressure across a converging-diverging nozzle; a weir measures flow by the height of water over its edge; and “flume gauge” isn’t the standard device with this contracting-throat-sill-expanding design.