Naming the cross-drainage work: A canal is carried below a natural drainage such that the canal’s full supply level (FSL) does not touch the underside of the supporting structure. What is this structure called?

Introduction / Context:

Cross-drainage works (CDWs) are categorized by the relative positions of the canal water surface and the drainage water surface. Correct naming is crucial because it implies different hydraulic design assumptions (open channel versus pressure flow).

Given Data / Assumptions:

• The canal passes below a natural drainage course.
• The canal’s FSL does not touch the soffit (underside) of the crossing structure; thus the canal remains an open channel within the structure.
• Pressure-flow in the canal barrel is not intended here.

Concept / Approach:

When the drainage is carried over the canal, the arrangement is a super passage. The canal remains open-channel flow, with clearance to the soffit. In contrast, an inverted syphon/syphon-aqueduct indicates pressure flow in the canal conduit beneath the drainage (FSL effectively pressed against the soffit). An aqueduct carries a canal over a drainage.

Step-by-Step Solution:

Verification / Alternative check:

Standard CDW selection charts confirm: drainage over canal with open channel in canal = super passage; drainage over canal with canal in pressure flow = syphon-aqueduct.

Why Other Options Are Wrong:

• Aqueduct: Canal over drainage (opposite).
• Syphon / Syphon-aqueduct: Canal under drainage in pressure flow, which contradicts “FSL does not touch soffit”.
• Level crossing: Rare arrangements where both flows interact; not applicable.

Common Pitfalls:

• Mislabeling any canal-below arrangement as “syphon” without checking whether pressure flow is intended.

Final Answer:

Super passage