When the drain is over the canal, and FSL of canal is below the bed level of drain the structure provided is known as
super-passage
Understanding Cross-Drainage Structures: Super-passage
Cross-drainage structures are essential components of irrigation and drainage networks. They are built where a canal and a natural drain (like a river or stream) cross each other. The type of structure depends on the relative levels of the canal and the drain, specifically their full supply levels (FSL) and bed levels.
Analyzing the Given Scenario
The question describes a specific situation:
- The drain is over the canal.
- The Full Supply Level (FSL) of the canal is below the bed level of the drain.
We need to identify the structure that fits these conditions.
Exploring Cross-Drainage Structure Types
Let's look at the common types of structures used at crossings and how they relate to the given conditions:
1. Aqueduct
- In an aqueduct, the canal is carried over the drain.
- The Full Supply Level (FSL) of the canal is above the bed level of the drain.
- This configuration does not match the first condition (drain over canal).
2. Canal Syphon
- In a canal syphon, the canal is carried under the drain.
- The Full Supply Level (FSL) of the canal is above the bed level of the drain. The canal flows under pressure like a siphon.
- This configuration does not match the first condition (drain over canal).
3. Super-passage
- In a super-passage, the drain is carried over the canal.
- The Full Supply Level (FSL) of the canal is below the bed level of the drain.
- In this structure, the canal water flows freely below the drain.
- This configuration matches both conditions provided in the question.
4. Syphon Aqueduct
- A syphon aqueduct is a type of aqueduct where the canal is carried over the drain.
- The Full Supply Level (FSL) of the canal is above the underside of the drain trough, causing the canal water to flow under pressure like a siphon.
- While it involves a drain and a canal, the canal is over the drain in this case, which doesn't match the first condition (drain over canal).
Comparison Table of Cross-Drainage Structures
Here is a summary of the key characteristics of these structures:
| Structure Type | Relative Position | Relative Levels (Canal FSL vs. Drain Bed/Trough) | Canal Flow |
|---|---|---|---|
| Aqueduct | Canal over Drain | Canal FSL > Drain Bed | Free flow |
| Super-passage | Drain over Canal | Canal FSL < Drain Bed | Free flow |
| Canal Syphon | Canal under Drain | Canal FSL > Drain Bed | Under pressure (Syphonic) |
| Syphon Aqueduct | Canal over Drain | Canal FSL > Underside of Drain Trough | Under pressure (Syphonic) |
Conclusion
Based on the analysis and the conditions given (drain over canal, canal FSL below drain bed), the structure that fits this description is a super-passage. The canal flows freely beneath the elevated drain structure because its water level is well below the drain bed.
Revision Table: Cross-Drainage Structures at a Glance
| Structure | Key Feature | Canal Level vs. Drain Level |
|---|---|---|
| Aqueduct | Canal over Drain | Canal FSL is higher than Drain Bed |
| Super-passage | Drain over Canal | Canal FSL is lower than Drain Bed |
| Canal Syphon | Canal under Drain | Canal FSL is higher than Drain Bed (flows under pressure) |
Additional Information: Importance of Crossings
Properly designed cross-drainage works are crucial for the efficient functioning of both irrigation canals and natural drainage systems. They prevent the mixing of canal water and drainage water, which can affect water quality and lead to waterlogging. They also ensure uninterrupted flow in both systems, preventing damage from flooding or erosion. The choice of structure depends on topography, hydrology, and economic considerations.
Important Questions from Cross Drainage Works
A cross drainage work in which a canal is provided over the natural drainage is called:
Which of the following is not a cross-drainage work?
The cross drainage structure in which the canal bed level is kept much higher than the high flood level (HFL) of a stream is called
In an aqueduct, natural drainage is kept at the following of a canal
Select the correct option for the given statements.
Statement 1: When the crossing site is such that the canal FSL is well above the stream HFL, the choice between aqueduct and siphon aqueduct is made depending on the stream discharge.
Statement 2: For larger stream discharges (i.e. when the stream bed is much wider), an aqueduct is more suitable than a siphon aqueduct which requires lowering of the stream bed by a drop.
