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. 

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  1. Both statement 1 and statement 2 are true, and statement 2 is the correct explanation of statement 1
  2. Statement 1 is false and statement 2 is true
  3. Both statement 1 and statement 2 are true, but statement 2 is not the correct explanation of statement 1
  4. Statement 1 is true and statement 2 is false

Answer (Detailed Solution Below)

Option 1 : Both statement 1 and statement 2 are true, and statement 2 is the correct explanation of statement 1
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Detailed Solution

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Explanation:

Cross-drainage structures are essential in canal systems. They help water flow smoothly while allowing rivers or natural drains to go under or over the canal. These structures ensure that canal and drainage water don't mix, keeping both types of water separate and maintaining their quality and quantity.

Types of Cross Drainage Works:

Based on the relative bed levels, water levels of the canal and the drain and their relative discharge, the Cross Drainage works are of the following types:

(1) Cross-drainage works carrying the Canal over the Natural Drain:

  1. Aqueduct
    • In these works, the canal is taken over the natural drain, such that the drainage water runs below the canal either freely or under siphoning pressure.
    • When the HFL of the drain is sufficiently below the bottom of the canal so that the drainage water flows freely under gravity, the structure is known as Aqueduct.
    • An aqueduct is more suitable for larger stream discharges than a siphon aqueduct, which requires lowering the stream bed by a drop. 

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  1. Syphon Aqueduct
    • If the HFL of the drain is higher than the canal bed and water passes through the aqueduct barrel under symphonic action, the structure is known as the Syphon Aqueduct.

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Additional Information(2) Cross drainage works carrying the natural drain over the canal:

  1. Superpassage:

    • Analogous to a bridge, a superpassage carries the natural drain over the canal.​

    • This structure operates as the inverse of an aqueduct, where the canal flows beneath the drain.

    • Due to the canal's location under the drain, providing an inspection road alongside the canal becomes impractical.
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  2. Syphon:
    • This structure shares similarities with a siphon aqueduct, utilizing barrels to transport water.
    • However, in a siphon, the water flowing under pressure through the barrels is the canal water, not the drain water.
    • Siphons are employed where the canal's FSL is higher than the drain's bed.

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(3) Intermixing Canal and Drain Water

When allowing canal and drain water to mix, two types of cross-drainage works are used:

  1. Level Crossing:
    • This simple structure allows the drain water to flow into the canal directly at the same level.
    • While straightforward, this approach lacks control and may not be suitable for all situations.
  2. Inlet and Outlet:
    • This design involves a controlled inlet for drain water to enter the canal and an outlet for excess water discharge.
    • This method offers better control over the mixing process than a level crossing.
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