Most efficient channel section is

Explanation:

Half hexagon in the form of trapezoid

• Represents a well-proportioned trapezoidal section commonly used in canal design.

• Provides an optimal balance between flow efficiency, stability of slopes, and ease of construction.

• Considered the most efficient channel shape in practical applications.

Additional InformationSemicircular

• Theoretically most hydraulically efficient due to minimum wetted perimeter.

• Difficult to construct and maintain, especially in large-scale field works.

• Rarely used except in small-scale or prefabricated systems.

Rectangular

• Simple and commonly used in lined drainage and urban water systems.

• Not hydraulically efficient because of high wetted perimeter and energy loss at corners.

• Preferred where formwork and modular construction is involved.

Triangular

• Least efficient hydraulically due to highest wetted perimeter for a given area.

• Used in specific cases such as roadside drains or where space is limited.

• Not suitable for large-scale or high-discharge channels.