Outlet performance terminology: The ratio of head recovered to head put in for a device or system is termed as what?

Introduction / Context:
In irrigation outlet and hydraulic device evaluation, several indices are used. “Efficiency” specifically quantifies how much input head (or energy) is converted into useful output head or work. It is a foundational metric used across hydraulic machines and control structures.

Given Data / Assumptions:

• Head put in H_in and recovered head H_out are measurable.
• Losses due to friction, turbulence, and separation are present.

Concept / Approach:
Efficiency η is defined as beneficial output over input. For head-based systems, η = H_out / H_in. This succinctly captures how effectively a device converts or transmits energy without loss.

Step-by-Step Solution:
1) Define η = output / input.2) For head: η = head recovered / head put in.3) Choose the corresponding term: efficiency.

Verification / Alternative check:
Equivalent definitions exist for power and energy. In all cases, efficiency is a ratio less than or equal to 1 (or 100%).

Why Other Options Are Wrong:

• Sensitivity: relates change in outlet discharge to canal discharge changes.
• Flexibility: relates outlet discharge change to head change in parent channel.
• Modular limit: relates to range over which an outlet behaves as a module.

Common Pitfalls:

• Mixing up head-based efficiency with discharge-based flexibility or sensitivity metrics used for outlets.

Final Answer:
Efficiency.