Direction: The item consists of two statements, one labelled as the 'Statement (I) and the other as 'Statement (II)'. You are to examine these two statements carefully and select the answers to these items using the codes given below:
Statement (1) : Cross drainage structure, aqueduct is constructed to negotiate an aligned channel over, below or at the same level of a stream.
Statement (II) : Aqueduct is constructed, when full supply level (FSL) of canal is much higher than high flood level (HFL) of a stream

Explanation:

• Purpose of Cross Drainage Works (CDWs):
  Cross drainage works are constructed where an irrigation canal and a natural stream intersect. Their primary goal is to safely convey both canal water and stream flow without allowing one to interfere with the function of the other.

• Function of an Aqueduct:
  An aqueduct carries the canal water over a drainage stream using a masonry or concrete trough supported by piers and abutments. It ensures uninterrupted canal supply even during high flood events in the underlying stream.

• Aqueduct vs. Other CDWs:
  While an aqueduct carries the canal over the drainage, other CDWs like superpassages or syphons allow the stream to pass over or under the canal. Each is selected based on the relative elevations of the canal’s FSL and the stream’s HFL.

• Design Basis of Aqueducts:
  Aqueducts are constructed when the canal’s Full Supply Level (FSL) is sufficiently higher than the stream’s High Flood Level (HFL), allowing gravity flow without pressure conditions in the canal.

• Importance of FSL and HFL Relationship:
  The FSL of a canal is the designed maximum water level in the canal, while HFL of a stream is the highest water level expected during floods. Their relative positions dictate the type of CDW needed.

 Additional Information

• False Understanding of Aqueducts Crossing at Same Level:
  An aqueduct never involves the canal and stream crossing at the same level; that condition is handled by a level crossing, which incorporates regulators to manage flow interaction.

• Selection Criteria for CDW Type:
  Key factors in choosing the type of cross drainage structure include: relative FSL and HFL levels, topography, canal discharge, stream discharge, economic feasibility, and maintenance requirements.

• Flow Regulation in Level Crossings (not Aqueducts):
  In level crossings, special regulators are provided to manage flow interference. Such systems are complex and not typically used unless FSL and HFL are close to the same level.

• Importance of Freeboard in Aqueduct Design:
  Adequate freeboard (space between water surface and top of canal wall) must be provided in aqueducts to prevent overtopping during sudden rise in canal flow or wave action.

• Canal Trough Design in Aqueducts:
  The canal trough in aqueducts must be designed to carry the full canal discharge and withstand static and dynamic forces. Materials used include reinforced concrete or stone masonry.