APSC AE WRD 2019 Questions: Cross-Drainage Structures: Super Passage and More

Cross-Drainage Structures: Super Passage and More

Question: When the drain is over the canal, the structure provided is known as:
(A) Aqueduct
(B) Super passage
(C) Canal siphon
(D) Siphon aqueduct

Answer: (B) Super passage

In a super passage, the drain or natural stream passes over the canal through a bridge-like structure, allowing both to flow without obstruction. This structure is used when the drain is at a higher elevation than the canal, specifically when the Full Supply Level (FSL) of the canal is below the Bed Level (BL) of the drain.

Types of Cross-Drainage Structures

Cross-drainage structures are designed to allow a canal and a drain (or natural stream) to cross each other without mixing their flows. Below is a detailed comparison of the relevant structures:

Structure	Definition	When Used	Key Feature
Super Passage	The drain passes over the canal through a bridge-like structure.	When the FSL of the canal is below the BL of the drain.	Both canal and drain maintain open channel flow.
Aqueduct	The canal passes over the drain through a bridge or trough-like structure.	When the HFL of the drain is below the BL of the canal.	Both canal and drain flow as open channels; no pressure flow.
Canal Siphon	The canal passes below the drain, flowing under pressure through a closed conduit.	When the drain is higher and cannot be diverted, and the canal bed is lower.	Canal flows under pressure (siphonic action).
Siphon Aqueduct	The canal passes over the drain, but the drain flows under pressure through a siphon.	When the HFL of the drain is above the BL but below the FSL of the canal.	Canal flows as open channel; drain flows in siphon.
Siphon Super Passage	The drain passes over the canal, but the canal flows under pressure through a siphon.	When the FSL of the canal is above the BL but below the HFL of the drain.	Drain flows as open channel; canal flows under pressure.
Level Crossing	The canal and drain intersect at nearly the same level, with regulators controlling flow.	When elevation separation is not feasible due to cost or site conditions.	Both flows intersect freely with regulators.

Key Notes

• FSL (Full Supply Level): The maximum water level in the canal during normal operation.
• BL (Bed Level): The elevation of the bottom of the canal or drain.
• HFL (Highest Flood Level): The maximum water level in the drain during flood conditions.
• Cross-drainage structures are critical in irrigation and drainage systems to ensure uninterrupted flow of both canal and drain.
• The choice of structure depends on relative elevations, flow conditions, and site constraints.

Note: Proper design of cross-drainage structures ensures efficient water management and prevents flooding or flow obstruction in irrigation systems.

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