Proportional outlet in canal distribution: An outlet is termed “proportional” when its flexibility (ratio of percentage change in outlet discharge to percentage change in parent channel discharge) is

Introduction / Context:
In canal irrigation, outlets connect distributaries to watercourses. Their hydraulic behavior is characterized by sensitivity, efficiency, and flexibility. “Proportional” outlets aim to pass a constant proportion of the parent channel discharge, maintaining equity as supplies vary.

Given Data / Assumptions:

• Flexibility = (% change in outlet discharge) / (% change in distributary discharge).
• Proportionality implies same percentage variation.
• Backwater and submergence effects are negligible for definition.

Concept / Approach:

A flexibility value of one means the outlet flow changes one-to-one with changes in the parent channel discharge, i.e., a fixed fraction is drawn off regardless of supply fluctuations, which is the defining characteristic of proportional outlets.

Step-by-Step Solution:

Verification / Alternative check:

Design texts describe orifice-type proportional modules calibrated to achieve φ ≈ 1 over a range of heads.

Why Other Options Are Wrong:

φ < 1 implies a rigid outlet; φ > 1 implies hyper-sensitive outlet; φ = 0 means insensitive; negative is nonsensical for normal operation.

Common Pitfalls:

Confusing “efficiency” with “flexibility”; overlooking tail-water submergence which can alter actual flexibility in field.

Final Answer:

Exactly one