This set of Irrigation Engineering Assessment Questions and Answers focuses on “Cross Drainage – Aqueducts and Syphon Aqueducts Types”.
1. The canal alignment is finalized only after finalizing the CD works.
Explanation: The canal alignment may be changed so that the crossing is shifted to the d/s where drainage bed is low if the conditions are not suitable for the construction of a siphon-aqueduct. Thus, sufficient headway becomes available for constructing an aqueduct. The CD works are finalized before the canal alignment.
2. The relative bed levels of the canal and the drainage may be changed and manipulated by _________________
a) changing the alignment
b) changing the positions of the water table
c) altering the head level
d) use of dewatering equipment
Explanation: The point of crossing is shifted upstream or downstream of the drainage by suitably changing the canal alignment. It manipulates the bed levels of the canal and the drainage.
3. The selection of the CD works depends on?
i. Selecting canal alignment
ii. Position of water-table and availability of dewatering equipment
iii. Suitability of soil for embankment
iv. Availability of funds
a) i and ii
b) i, ii and iv
c) i, ii and iii
d) i, ii, iii and iv
Explanation: The choice of selection of the suitable type of CD works depends upon many factors such as suitable canal alignment, nature of available foundation, the suitability of the soil for embankment, availability of funds, permissible head loss. The position of water table and availability of dewatering equipment also affects the choice of site selection.
4. Inlets and Outlets are inferior to aqueduct or super-passage type of work.
Explanation: Inlets though cheaper are not preferred nowadays since their performance has not been very satisfactory. They are used when the high flood drainage discharge is small. Similarly, a super-passage is inferior compared to an aqueduct and should be avoided whenever possible.
5. In order to reduce the CD works, the artificial canals are generally aligned along the ridgeline.
Explanation: Canal drainage works are generally not required when the canal reaches the watershed line unless the canal alignment deviates from the watershed line. The canal which takes off from the river has to cross a number of drains which move from the watershed towards the river before the watershed is reached.
6. The type of canal alignment which involves maximum CD works is a ______________
a) ridge canal
b) contour canal
c) side slope canal
d) both ridge and contour canal
Explanation: A watershed line or ridgeline crosses the minimum number of drains and contour canal crosses the maximum number of drains. When a canal is aligned as contour canal it requires more CD works. It is a costly construction and should be avoided as far as possible.
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