Weir Calibration — Bazin’s Observation on Coefficient of Discharge According to Bazin's experiments on sharp-crested weirs, does the coefficient of discharge (Cd) vary with the height of water (head) over the sill/crest?

Introduction:
Weir coefficients account for non-idealities such as viscosity, surface tension, and approach velocity. Historical calibrations by researchers like Bazin demonstrated how coefficients depend on head and geometry for sharp-crested weirs.

Given Data / Assumptions:

• Sharp-crested weir under free overflow (fully aerated nappe).
• Measured head H above crest.
• Standard laboratory conditions and careful head measurement.

Concept / Approach:
The discharge relation Q = Cd * (2/3) * b * sqrt(2*g) * H^(3/2) shows Cd as an empirical factor. Experiments indicate Cd is not strictly constant; it varies with H, crest condition, approach velocity, and Reynolds effects. Bazin reported such dependence with head over sill.

Step-by-Step Solution:
Recognize Q depends on both H and Cd.Empirical data sets show Cd changes with H, especially at small heads where surface tension and approach influence are significant.Thus Bazin’s statement that Cd varies with head is correct.

Verification / Alternative check:
Modern standards provide tables/curves of Cd vs. H for different crest conditions and end contractions, confirming non-constancy.

Why Other Options Are Wrong:
Restricting variation only to submerged flow or triangular weirs ignores evidence for rectangular sharp-crested weirs; calling it incorrect contradicts experimental results.

Common Pitfalls:
Using a single Cd across a wide H range; neglecting velocity-of-approach corrections; ignoring submergence thresholds where different formulas apply.

Final Answer:
Correct