What device is used to measure flow in an open channel that narrows to a throat and then expands?

What device is used to measure flow in an open channel that narrows to a throat and then expands?

• A. Partial Flume
• B. Orifice plate
• C. Venturi meter
• D. Pitot tube

Answer: (A)

Open-channel flow is measured with a device that combines a converging section to a throat and a expanding section downstream, which is a Parshall flume (often called a partial flume). The narrowing causes the flow to accelerate and the pressure to drop, while the channel remains open. The important part is that the relationship between the upstream water depth (the head) and the discharge is standardized, so you can convert a measured head difference into a flow rate using established rating tables. This setup provides a reliable, noncontact way to measure open-channel discharge without needing to insert sensors into a closed pipe. The other options aren’t suited for this open-channel, throat-design measurement. An orifice plate or Venturi meter are used in closed conduits and rely on pressure differences across a restriction to infer flow, which isn’t ideal or standard for open-channel setups. A Pitot tube measures velocity at a point via stagnation pressure and doesn’t directly give the total discharge in an open channel.

Open-channel flow is measured with a device that combines a converging section to a throat and a expanding section downstream, which is a Parshall flume (often called a partial flume). The narrowing causes the flow to accelerate and the pressure to drop, while the channel remains open. The important part is that the relationship between the upstream water depth (the head) and the discharge is standardized, so you can convert a measured head difference into a flow rate using established rating tables. This setup provides a reliable, noncontact way to measure open-channel discharge without needing to insert sensors into a closed pipe.

The other options aren’t suited for this open-channel, throat-design measurement. An orifice plate or Venturi meter are used in closed conduits and rely on pressure differences across a restriction to infer flow, which isn’t ideal or standard for open-channel setups. A Pitot tube measures velocity at a point via stagnation pressure and doesn’t directly give the total discharge in an open channel.