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CANAL IRRIGATION
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IRRIGATION AND WATER RESOURCES ENGINEERING
An irrigation canal system consists of canals of different sizes and capacities (Fig. 5.1).
Accordingly, the canals are also classified as: (i) main canal, (ii) branch canal, (iii) major
distributary, (iv) minor distributary, and (v) watercourse.
IRRIGATION AND WATER RESOURCES ENGINEERING
An irrigation canal system consists of canals of different sizes and capacities (Fig. 5.1).
Accordingly, the canals are also classified as: (i) main canal, (ii) branch canal, (iii) major
distributary, (iv) minor distributary, and (v) watercourse.
Layout of an irrigation canal network
The main canal takes its supplies directly from the river through the head regulator
and acts as a feeder canal supplying water to branch canals and major distributaries. Usually,
direct irrigation is not carried out from the main canal.
Branch canals (also called ‘branches’) take their supplies from the main canal. Branch
canals generally carry a discharge higher than 5 m3/s and act as feeder canals for major and
minor distributaries. Large branches are rarely used for direct irrigation. However, outlets
are provided on smaller branches for direct irrigation.
COMMAND AREAS
Gross command area (or GCA) is the total area which can be economically irrigated from an
irrigation system without considering the limitation on the quantity of available water. It
includes the area which is, otherwise, uncultivable. For example, ponds and residential areas
are uncultivable areas of gross command area. An irrigation canal system lies in a doab (i.e.,
the area between two drainages), and can economically irrigate the doab. It is, obviously,
uneconomical to use the irrigation system to irrigate across the two drainages. Thus, the
boundaries of the gross command of an irrigation canal system is fixed by the drainages on
either side of the irrigation canal system.
PLANNING OF AN IRRIGATION CANAL SYSTEM
Planning of an irrigation canal project includes the determination of: (i) canal alignment, and
(ii) the water demand. The first step in the planning of an irrigation canal project is to carry
out a preliminary survey to establish the feasibility or otherwise of a proposal.
ALIGNMENT OF IRRIGATION CANALS
Desirable locations for irrigation canals on any gravity project, their cross-sectional designs
and construction costs are governed mainly by topographic and geologic conditions along
different routes of the cultivable lands. Main canals must convey water to the higher elevations
of the cultivable area. Branch canals and distributaries convey water to different parts of the
irrigable areas.