Open channel flow measuring methods include velocity versus area calculations, weirs, and which type of flume?

• A. Parshall
• B. Venturi
• C. Orifice plate
• D. Pitot tube

Answer: (A)

In open-channel flow measurement, a reliable way to convert depth into discharge is using a flume designed for open channels. The Parshall flume is specifically built for this purpose: its contracted throat creates a predictable relationship between the water depth at a measuring point and the flow rate, producing a stable, well-calibrated stage-discharge curve. It handles debris and typical wastewater conditions well and gives accurate discharge readings from the upstream water depth without moving parts.

In contrast, a Venturi or an orifice plate are constrictions used in closed conduits to infer flow from a pressure drop, which isn’t ideal for open-channel conditions. A Pitot tube measures velocity at a point and would still require combining with cross-sectional area to estimate discharge, not providing a direct, robust open-channel discharge measurement on its own.