Question

Why do we need to do the lining of the canal?
(A) To minimize seepage losses in canal
(B) To prevent erosion of bed and sides due to high velocities
(C) To decrease the discharge in the canal section by increasing the velocity

• A. Only A
• B. Only A and B
• C. Only C
• D. All A, B and C

Answer 1

The correct option is B Only A and B

$\text{Lining of irrigation channels}$
$\text{1. Advantage of the lining of irrigation channels.}$

• The lining of channels reduces the seepage loss thus resulting in a saving of water which can be utilised for irrigating additional areas. The cost of irrigation per unit area is therefore reduced.
• The lining of channels is an important anti-water logging measure as it reduces the percolation of water to the groundwater reservoir and thus prevents the rising of the water table.
• The lining provides a smooth surface having a low value of rugosity coefficient. Hence a lined channel has a higher velocity of flow.
• Due to higher velocity of flow in a lined channel greater discharge can pass through a small area of cross-section of the channel.
• The higher velocity of flow in a lined channel helps in providing a flatter hydraulic gradient or belt slope and hence better command can be obtained. Further, this is an important advantage in the case of channels that are utilised for power generation because a smaller slope results in a larger available head at the powerhouse.
• The higher velocity of flow in a lined channel results in reducing the evaporation loss.
• The problem of silting is reduced in a lined channel due to a higher velocity of flow.
• Due to the smaller cross-section of a lined channel there is a saving is the cost of earthwork, land width, and various structures.
• Lining reduced maintenance cost.
• Lining provided a stable channel section which is easier to operate.

$\text{2. Disadvantage of Lining of Irrigation channels}$

• The lining of the irrigation channel involves a high initial investment.
• It is difficult to repair the damaged lining.
• The lining being permanent, it is difficult to shift the outlets if necessary.
• A lined channel is without a berm. As such the additional safety provided by the beams for vehicular and pedestrian traffic is absent in the case of lined channels.