Syphon aqueduct is a cross drainage work provided to carry canal over a natural drain when
- ACanal bed is well above the H.F.L. of the natural drain
- BCanal bed is below the HFL of the natural drainCorrect
- CCanal bed is at the same level as the bed of the natural drain
- DNone of the above
Solution
Concept
Conditions for constructing syphon aqueduct
Formula
NONE
Step-by-step solution
1. An aqueduct or syphon aqueduct carries a canal over a natural drainage channel. 2. In a syphon aqueduct, the high flood level (H.F.L.) of the drain is above the canal bed level, forcing water through the drain under siphonic pressure. 3. Therefore, it is provided when the canal bed is below the H.F.L. of the natural drain. Answer: B
Explanation
A syphon aqueduct is constructed when the canal passes over a natural drainage channel, but the canal bed level lies below the high flood level of the drain. In this setup, the drain water flows under siphonic pressure beneath the canal trough.
Why the other options are wrong
A) A normal aqueduct is provided when the canal bed level is well above the high flood level of the drain. C) Level crossings or inlets and outlets are used when canal and drain beds are at the same level. D) Option B is correct because the drain flows under pressure beneath the canal in a syphon aqueduct.
Shortcut
Canal over drain: Aqueduct if Canal bed > Drain HFL; Syphon Aqueduct if Canal bed < Drain HFL.
Common mistake
Confusing a syphon aqueduct with a standard aqueduct where the canal bed remains well above the HFL.
Correct answer: B) Canal bed is below the HFL of the natural drain