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Ridge canal is designed in a command when the high contours join in a straight
alignment can distribute water on both sides of the canal. On the contrary, a
contour canal follows in parallel a contour line and as a result water can be
distributed only one side of the canal. In practice, both the types have field
problems and in a ridge canal, it could be necessary to keep the alignment
straight because the water shed or high contours may turn in a loop abruptly. In
such cases, economics of the canal construction is considered so that major
part of the command area can be covered. Side slope canals runs at right angles
to the contours and roughly parallel to the natural drainage of the country.
Design of Irrigation channels is a special subject dealt by the Irrigation
Engineers. The design aspects take into account the required discharge through
the canals, the area of cross-sections, the silt factor and the required slope, the
soil characteristics, seepage from the canals. Seepage losses constitutes a
major portion of losses from the canals and excessive losses may lead to
water logging. The Central Water Power Commission recommends the
following values of losses :
Soil type
Transmission loss (cumec/
million sq.m. of wetted perimeter)
Rock 0.91
Black cotton soil
1.83
Alluvial soil
2.74
Weather rock or gravel
3.00
Sometimes losses are expressesed as
percentage of total discharge :
Main canal and branches
15% to 20%
Distribution and minors
6% to 7%
Water courses
17% to 22%
Lining of canal
With a view to prevent excessive losses the canals are lined with
cement-concrete or materials which prevent seepage. Most common types of
lining are :
1) Cement concrete lining
2) Brick lining
