Streamflow velocity measurement – best instrument for discharge gauging For measuring the point velocity profile in natural streams to compute discharge accurately, which instrument is considered the best standard practice?

Introduction / Context:Accurate discharge measurements in rivers and canals require reliable velocity observations at multiple depths and laterals. The choice of instrument affects measurement accuracy, repeatability, and suitability across a range of velocities and depths.

Given Data / Assumptions:

• Wading or boat-mounted discharge measurements using standard mid-section or mean-section methods.
• Velocities typically range from slow to moderate (roughly 0.1 to 3 m/s).
• Field conditions may include suspended sediment and debris.

Concept / Approach:Price’s current meter (cup or rotor type) is a well-established, calibrated instrument designed to measure point velocity at selected depths (e.g., 0.2 and 0.8 of depth) to estimate mean velocity. It is rugged, field-proven, and supported by rating procedures. In contrast, floats provide only surface or near-surface velocities and require empirical correction factors, while pitot tubes are sensitive to alignment and debris in natural channels.

Step-by-Step Solution:Identify the instrument that measures point velocity reliably at depth → current meter.Among current meters, Price’s meter is the classic benchmark for stream gauging.Therefore choose option (b).

Verification / Alternative check:Hydrometry standards recommend current meters (including electromagnetic/ADCP for advanced surveys). Historical datasets commonly rely on Price’s meters for rating curves.

Why Other Options Are Wrong:

• (a) Pitot tubes are practical in clean pipelines or labs; field use in rivers is cumbersome.
• (c) Surface floats measure only surface velocity and require uncertain correction to mean velocity.
• (d) Sub-surface floats are less precise and harder to control than meters.

Common Pitfalls:Relying on float methods for precise discharge studies; for robust hydrographs and rating development, point-velocity methods are preferred.

Final Answer:Price’s current meter