Irrigation control meter (canal structure) features: Identify the correct statements about a properly designed control meter used in canals.

Introduction / Context:
Control meters (e.g., flumes, canal meters) regulate and measure discharge in irrigation canals. Their geometry is tailored to produce critical or supercritical conditions, enabling predictable stage–discharge relations and safe energy transitions.

Given Data / Assumptions:

• Control meter has a converging approach, a throat, and a diverging (expanding) outlet.
• Subcritical to supercritical transitions may occur; hydraulic jump is harnessed downstream for energy dissipation.
• Stable bed and sidewalls (rectangular or trapezoidal) are used for constructability and hydraulics.

Concept / Approach:
A nearly level throat floor preserves critical depth and a stable control section. The expanding outlet requires a suitable slope to recover pressure and accommodate the jump at a designed location, preventing scour and ensuring accurate control.

Step-by-Step Solution:
(a) Canal sections commonly adopt rectangular/trapezoidal forms for the throat.(b) A level throat maintains a well-defined control depth.(c) A steeper slope in the expanding outlet helps manage transitions and velocities.(d) Properly designed, a hydraulic jump forms where energy must be dissipated.

Verification / Alternative check:
Standard designs (Parshall flume variants and similar meters) follow these principles to achieve stable rating curves.

Why Other Options Are Wrong:
Any single statement alone is incomplete; accurate control comes from the combined geometric and hydraulic features.

Common Pitfalls:
Ignoring energy dissipation needs; misplacing the hydraulic jump; providing adverse floor slopes in the control section.

Final Answer:
All the above.