Modules and outlets in canal irrigation: Identify the correct statements about flexibility, proportionality setting, and rigidity for canal outlets (modules).

Introduction / Context:

Irrigation outlets (also called modules) connect a distributary canal to a watercourse. Their hydraulic behaviour is described using flexibility, which measures the ratio of proportionality between fluctuations in discharge delivered to the watercourse and changes in the parent canal discharge. Understanding hyper-, sub- and rigid behaviour is critical for equitable and stable water distribution across a canal network.

Given Data / Assumptions:

• Outlet flexibility f is defined as (percentage change of outlet discharge)/(percentage change of parent canal discharge).
• Perfect proportionality implies f = 1.
• Outlet sill setting relative to canal full supply level (FSL) influences head and therefore discharge sensitivity.

Concept / Approach:

Classification follows directly from f. If f > 1, the outlet magnifies parent fluctuations (hyper-proportional). If 0 < f < 1, it damps fluctuations (sub-proportional). If f = 0, discharge is essentially independent of parent changes (rigid). Sill (or throat) elevation controls the head across the outlet: raising the sill reduces submergence and makes discharge more sensitive, while lowering the sill increases submergence and reduces sensitivity.

Step-by-Step Solution:

Verification / Alternative check:

Textbook module types (e.g., orifice semi-modules, pipe outlets, proportional modules) are catalogued by their f value and by how setting shifts the head–discharge curve. Each option matches those standard definitions.

Why Other Options Are Wrong:

• Each of the first four options is individually correct; hence the comprehensive correct choice is All the above.

Common Pitfalls:

• Confusing rigidity (f = 0) with constant-head devices; true rigidity means outlet discharge is independent of parent fluctuations within its operating range.
• Assuming sill changes always improve equity; improper settings can create over-sensitivity (hyper behaviour) and inequity.

Final Answer:

All the above.