Grade aqueducts (drainage carried over a canal): which barrel section is most commonly adopted in practice?

Introduction / Context:
In cross-drainage works, a grade aqueduct conveys a drainage channel over a canal. The structural and hydraulic design of the drainage barrels must pass design discharges efficiently and economically while fitting within construction constraints.

Given Data / Assumptions:

• Masonry or reinforced concrete construction is used for drainage barrels.
• Headroom, ease of formwork, and flow capacity are key considerations.

Concept / Approach:
Rectangular barrels are widely used because they are straightforward to design and build with standard formwork, they stack well for multi-cell arrangements, and they offer predictable hydraulic performance (with smooth transitions and wing walls). Specialized shapes like horse-shoe are common in tunnels, while parabolic or triangular are rare for closed conduits.

Step-by-Step Solution:

Verification / Alternative check:
Typical irrigation engineering texts illustrate grade aqueducts with rectangular RCC multi-cell barrels.

Why Other Options Are Wrong:

• Circular (a) is common for pressure flow or culverts, not the most common for grade aqueduct multi-cells.
• Parabolic (c) and triangular (e) are seldom used as closed conduit sections here.
• Horse-shoe (d) is more typical for tunnels.

Common Pitfalls:
Confusing culverts under roadways (often circular) with large multi-cell over-canal aqueducts where rectangular proves practical.

Final Answer:
Rectangular section