Select the correct statements about circular sewer sections and hydraulic equivalence.

Introduction / Context:
Choosing sewer cross-sections involves hydraulic efficiency, constructability, and operation at part-full conditions. Understanding key properties of circular sections and the concept of hydraulic equivalence helps make informed design decisions.

Given Data / Assumptions:

• Gravity flow, turbulent regime is typical.
• Standard Manning/Chézy design practices.
• Comparative statements on shape efficiency and equivalence.

Concept / Approach:

(a) For a given perimeter, the circle maximizes area and thus hydraulic mean depth R = A/P; it is highly efficient hydraulically. (b) In separate systems (only sewage), circular pipes are ubiquitous due to ease of manufacture and laying. (c) For part-full operation, circular pipes perform well above about half depth, ensuring adequate velocities for self-cleansing. (d) Hydraulic equivalence means that if two different shapes, running full, have the same discharge under the same slope and roughness, they can be considered equivalent in capacity for that condition.

Step-by-Step Solution:

Verification / Alternative check:

Design manuals and standard texts endorse circular pipes for separate systems; they also define hydraulic equivalence and the advantages of circular geometry for R and capacity.

Why Other Options Are Wrong:

Selecting any one item would ignore the broader truth of the others; there is no contradiction among the statements.

Common Pitfalls:

Confusing “running full” capacity with “part-full” performance; overlooking that egg-shaped sections can outperform circular at very low flows but are costlier.

Final Answer:

All the above