Venturi head flume geometry checks: Which of the following statements about side-wall splay and width recovery is incorrect?

Introduction / Context:

A venturi head flume (venturi regulator) uses a contracted throat to create a measurable head–discharge relation. The geometry of the contraction and expansion transitions is critical to avoid separation, undue head loss, and poor rating stability.

Given Data / Assumptions:

• Standard practice uses gentle divergence after the throat (e.g., ~1:10 initially) and a shorter, steeper recovery (e.g., ~1:3) near the end.
• Intermediate recovery often targets ~2/3 of the distributary bed width before the final widening.
• Smooth transitions are assumed to keep flow attached.

Concept / Approach:

The sequence—initial mild splay, intermediate width recovery, and final steeper splay—is a widely cited guideline for distributary head regulators/venturi flumes. Each listed statement in options (a) through (c) aligns with this guidance; therefore there is no incorrect statement among them.

Step-by-Step Solution:

Verification / Alternative check:

Field drawings and manuals show gradual expansion followed by a shorter final flare; the exact distances may vary with discharge, but the pattern remains similar.

Why Other Options Are Wrong:

• Option (e) suggests parallel walls after the throat without splay changes; that would prolong contraction effects and increase losses—contrary to best practice. It is not among the options to choose as incorrect under the given set since (d) is the called-out answer.

Common Pitfalls:

• Using too steep an initial divergence which induces separation and distorts the rating curve.
• Ignoring downstream tailwater effects on submergence during calibration.

Final Answer:

None of these.