CANAL LININGS
What is canal lining?
An impermeable layer is provided at the bed and sides
of canal to improve the life and discharge capacity of canal known as canal
lining. Generally seepage can result in losses of 30 – 40 % of irrigation water
in canals, so we can reduce the effect of seepage by providing lining to the
canal.
Advantages
of Canal Lining:
An important reason for lining a canal can be the
reduction in water losses, as water losses in unlined irrigation canals can be
high. Canals that carry from 30 to 150 liters/sec can lose 10 to 15% of this
flow by seepage and water consumption by weeds. Lining a canal will not
completely eliminate these losses, but roughly 60 to 80% of the water that is
lost in unlined irrigation canals can be saved by a hard-surface lining. 42
Canal lining Minimizing water losses is very important, and especially so in
schemes where irrigation water is pumped. Reduced water losses means less water
to pump and thus a reduction in pumping costs.
Seepage
reduction:
If canal banks are highly permeable, the seepage of
water will cause very wet or waterlogged conditions, or even standing water on
adjacent fields or roads. Lining of such a canal can solve this problem, since
the permeability of a lined canal bank is far less than that of an unlined
bank, or may even be zero, depending on the lining material.
Reduced
canal dimensions:
The roughness – resistance to flow – of a lined canal
is less than that of an unlined canal, and thus the flow velocity will be
higher in the lined canal when the canal bed slope is the same. Moreover, the
hard surface of the lining material allows a higher velocity compared to an
earthen canal surface as it is not so easily eroded. As discussed earlier,
canal discharge is the product of the cross-section of a canal and the velocity
of the flow. Therefore, with the higher velocity allowable and obtainable in
lined canals, the canal cross-section for a lined canal can be smaller than
that of an unlined canal.
Reduced
maintenance:
A surface lining, such as concrete, brick or plastic,
on the canal prevents the growth of plants and discourages hole-making by rats
or termites, and so the maintenance of a lined canal can be easier and quicker
than that of an unlined canal. Moreover, the higher velocity that can safely be
allowed in the lined canal prevents the small particles of soil carried in the
water from settling out, accumulating and causing siltation.
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