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This set of Irrigation Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Advantages of Lining”.

1. A lined canal costs about 2 to 2.5 times as much as the unlined canal.
a) True
b) False

Explanation: The construction of larger reservoirs and bigger dams will be necessary if there is heavy seepage loss in canals. Lining the canals reduces their impounding capacity and hence lower the construction costs of these works.

2. Which of the following is not an advantage of the lining of the canal?
a) Seepage control
b) Prevention of water-logging
c) Increase in channel capacity
d) Increased maintenance costs

Explanation: Huge expenditure is spent on annual repair and maintenance of the unlined canal. The provision of lining reduces expenditure required for removal of silt, minor repairs like plugging of cracks, cuts, and removal of weeds and water plants.

3. The capacity of the channel is a function of velocity.
a) True
b) False

Explanation: The vegetation on the sides and bottom of the canal retards the flow of water in unlined canals. The higher the velocity, the greater is the capacity of the channel and hence, capacity is a function of velocity.

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4. What is the range of value of Manning’s coefficient for straight alignment for cast in-situ concrete lining?
a) 0.012 – 0.015
b) 0.015 – 0.018
c) 0.018 – 0.020
d) 0.020 – 0.025

Explanation: In absolutely straight reaches and with relatively higher discharges lower values of Manning’s constant may be attained. For cast in-situ concrete lining, the value of n varies from 0.015–0.018 and for cement plastered masonry the value varies from 0.012-0.015.

5. Lining decreases the channel capacity and consequently reduces the required channel section.
a) True
b) False

Explanation: The lining causes less resistance to the flow of water as it provides a smooth surface and consequently velocity is more. The capacity can be considerably increased by lining the canal section. A lined channel will require fewer dimensions and less earthwork.
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6. Removal of silt considerably reduces the annual expenditure required on unlined channels for desilting.
a) True
b) False

Explanation: Lining protects the canal section against breaches and bank erosion. On account of the high velocities in lined-channels silts are readily carried away. This reduces the annual expenditure for desilting.

7. Which of the following statement is wrong?
a) A lined canal is not susceptible to erosion
b) The provision of adequate lining reduces the danger of breaches of channel
c) The lining does not reduce the money spent in removing weeds
d) Lining eliminates flood dangers

Explanation: The plants flow down the canal due to higher flow velocities in lined-canals due to which expenditure is reduced considerably. A strong concrete lining eliminates the dangers from flood and minor repairs like plugging of cracks, cuts and uneven settlements of banks (which results in breaches of the channel).

8. Which of the following statement is wrong?
a) The velocity varies inversely with the Manning’s coefficient
b) For unlined channels in good condition, the value of Manning’s coefficient is 0.015 for concrete
c) Flatter slopes can be provided without silting on a lined channel
d) The lining does not help to bring high areas under the command

Explanation: The longitudinal slope of a lined canal is flatter than the corresponding unlined canal. Flat slope raises the F.S.L of the lined canal and it brings high patches of the land under command.

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