Siphon aqueduct floor level estimation: How is the floor level of a siphon aqueduct obtained relative to the canal bed level?

Introduction / Context:
In a siphon aqueduct, the drainage passes through barrels below the canal prism; the canal is carried on a structure and the drainage flows under pressure. Determining the structural floor level is a layout step for vertical alignment and hydraulic capacity.

Given Data / Assumptions:

• Known canal bed level (CBL).
• Required culvert (barrel) depth and floor/roof thicknesses.

Concept / Approach:
The floor level beneath the canal has to accommodate the total structural depth of the barrel (its internal waterway depth) plus the structural thickness (roof/floor). Therefore, the finished floor level is obtained by lowering from the canal bed level by the sum of the culvert depth and its structural thickness.

Step-by-Step Solution:
Start with CBL (canal bed level).Subtract the structural thickness + barrel (waterway) depth.Floor level = CBL − (thickness + depth).

Verification / Alternative check:
Check freeboard and head losses to ensure the hydraulic gradient for drainage remains acceptable and that the canal waterway clearances are maintained above.

Why Other Options Are Wrong:
Subtracting only the culvert depth ignores the required structural thickness; resulting level would be too high.“Both (a) and (b)” is incorrect because (a) is incomplete.

Common Pitfalls:

• Neglecting the slab or roof thickness in vertical alignment.
• Forgetting allowances for wearing courses or protection layers if provided.

Final Answer:
By subtracting the thickness of the culvert plus the depth of the culvert from the canal bed level