If the R.L. of canal bed level and high flood level of drainage are 212.0 m and 210 m respectively, then the cross-drainage work will be
aqueduct
Understanding Cross-Drainage Works
Cross-drainage works are crucial structures built when a canal and a natural drainage channel (like a river or stream) intersect. Their purpose is to allow one path of flow (either the canal or the drainage) to pass over or under the other, preventing the mixing of waters and ensuring the continuous operation of the canal.
Classifying Cross-Drainage Works by Water Levels
The type of cross-drainage structure is determined by comparing the canal's relevant levels with the drainage channel's levels, particularly the High Flood Level (HFL).
Key Levels Involved:
- Canal Bed Level (CBL): This is the level of the bottom surface of the canal.
- High Flood Level (HFL) of Drainage: This represents the maximum water level expected in the natural drainage channel during periods of heavy flow or floods.
Types of Cross-Drainage Works:
The primary types are classified based on whether the canal flows over or under the drainage:
- Aqueduct: Used when the canal flows over the drainage. This occurs when the Canal Bed Level (CBL) is higher than the High Flood Level (HFL) of the drainage.
- Syphon: Used when the drainage flows under the canal. This happens when the drainage's High Flood Level (HFL) is higher than the Canal Bed Level (CBL).
- Super Passage: Used when the drainage flows over the canal. This occurs when the drainage's HFL is below the canal's components, and the canal water flows freely without pressure, typically having the drainage bed level below the canal bed level.
- Syphon Aqueduct: A specific type of aqueduct where the canal passes over the drainage, but the drainage structure (barrel) is designed such that the water flows through it under pressure (like a syphon). This usually happens when the drainage HFL is below the canal's soffit (underside of the arch).
| Condition Comparison | Structure Type | Flow Arrangement |
|---|---|---|
| CBL > HFL of Drainage | Aqueduct | Canal over Drainage |
| HFL of Drainage > CBL | Syphon | Drainage under Canal |
| HFL of Drainage < CBL | Super Passage | Drainage over Canal |
Applying the Levels to the Problem
We are given the following levels:
- Canal Bed Level (CBL) = 212.0 m
- High Flood Level (HFL) of Drainage = 210 m
Now, let's compare these values:
$CBL = 212.0 \, m$
$HFL_{drainage} = 210 \, m$
We can see that $CBL > HFL_{drainage}$, as $212.0 \, m$ is greater than $210 \, m$.
Conclusion on the Cross-Drainage Work Type
Since the Canal Bed Level ($212.0 \, m$) is higher than the High Flood Level of the drainage ($210 \, m$), the canal must pass over the drainage channel.
Based on the classification criteria, when the canal flows over the drainage because its bed level is above the drainage's flood level, the structure is identified as an Aqueduct.
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
When the drain is over the canal, and FSL of canal is below the bed level of drain the structure provided is known as
