Design rules for a venturi flume (venturi head regulator) on a canal: Which of the following sizing guidelines are appropriate?

Introduction / Context:

A venturi flume or venturi head regulator is widely used for discharge measurement and control in canals. Its geometry—throat width, length, and sill level relative to FSL—determines the head–discharge relationship and whether critical flow can be established. Empirical sizing rules are used for safe, accurate performance and to avoid undue head loss.

Given Data / Assumptions:

• Discharge Q and difference in levels d (FSL – sill) are known or prescribed.
• Throat section must avoid submergence and flow separation.
• Standard empirical proportions are acceptable for preliminary design.

Concept / Approach:

To maintain a measurable control, the throat must be wide enough to pass Q with the available head d while not being so narrow that it induces excessive losses or submergence. Minimum geometric limits (like 0.60 m throat) ensure constructability and debris passage. A throat length of ~2.5 times the approach depth helps develop uniform velocity and suppresses abrupt transitions.

Step-by-Step Solution:

Verification / Alternative check:

Prototype designs use gradual converging/diverging transitions (~1:3 to 1:6) to minimize losses—consistent with the above throat rules for a well-behaved control section.

Why Other Options Are Wrong:

• Each individual guideline is part of standard preliminary design; therefore the most complete choice is All the above.

Common Pitfalls:

• Ignoring submergence at downstream levels; submergence corrections may be needed for calibration.
• Using too short a throat or too sharp transitions, causing separation and unreliable rating.

Final Answer:

All the above.