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.
- ABoth statement 1 and statement 2 are true, but statement 2 is not the correct explanation of statement 1
- BStatement 1 is true and statement 2 is false
- CBoth statement 1 and statement 2 are true, and statement 2 is the correct explanation of statement 1Correct
- DStatement 1 is false and statement 2 is true
Solution
Concept
When canal FSL is well above stream HFL, stream discharge (stream width) decides aqueduct or siphon aqueduct.
Step-by-step solution
1. Canal FSL well above stream HFL means the canal must pass over the stream, so the choice is aqueduct or siphon aqueduct. 2. A siphon aqueduct needs the stream bed lowered by a drop, so the stream flows under pressure through barrels. 3. For a large stream with a wide bed, lowering the bed and pressure flow are costly and give silting and scour problems. 4. So for large stream discharge an aqueduct is better, and for small discharge a siphon aqueduct can be used. 5. Statement 2 gives the reason why discharge decides the choice in Statement 1. Answer: C.
Explanation
Both statements are true. The choice between aqueduct and siphon aqueduct depends on stream discharge. Statement 2 explains why: a large, wide stream suits an aqueduct, while a siphon aqueduct needs a drop in the stream bed.
Why the other options are wrong
A: Statement 2 is the direct reason for Statement 1. B: Statement 2 is true. D: Statement 1 is true.
Shortcut
Large stream discharge → aqueduct. Small stream discharge with bed drop → siphon aqueduct.
Common mistake
Students think the choice depends only on levels (FSL, HFL) and forget that stream discharge also matters.
Correct answer: C) Both statement 1 and statement 2 are true, and statement 2 is the correct explanation of statement 1