ALIGNMENT OF CANAL AND
G. Krishna Reddy
S. Gopinath Reddy
Canals are open channels that transport water from a
source to distribution and delivery locations.
Canals may be either lined or unlined depending on
earth and rock materials encountered.
If the R.L of formation of canal bed is below the R.L
of ground cutting is done and vice versa.
Classification of canals on the basis of their
functions are given below:
These are the canals which carry water to the
These are the canals which are used to
provide transport and voyage facility from one
city to the other or from one country to the other.
Main canal is navigation canal.
The canals which are constructed to supply
water with very high force to the hydro electric
power station for the purpose of moving turbine
to generate electric power is known as power
The canal that is from river to river is known as
link canal. which are constructed to transfer water to
the other conveyance structure which contains insufficient quantity of water.
A feeder canal is constructed with the idea of
feeding two or more canals. When main canal is
divided into two canals then it is called as feeder
Alignment of canals
irrigation canals can be aligned in any of the
following three ways:
1. As watershed canal or ridge canal.
2. As contour canal.
3. As side slope canal.
Watershed canal or ridge canal
The dividing ridge line between the catchment areas
of two streams is called the watershed. Thus, between two
major streams, there is the main watershed, which divides
the drainage area of the two streams. Similarly , between
a main stream and any of its tributary, there are subsidary
watersheds dividing the drainage between the two streams
on either side. It is suitable for plain areas, where slopes
are relatively flat and uniform. The canal which is aligned
along any natural watershed is called watershed canal.
This type alignment ensures gravity irrigation on both
sides of the canal. However , the main canal has to take
off from the river and it must mount the watershed in as
short a distance as possible . Once the canal has reached
the watershed , it is generally kept on the watershed
Localities are settled on the watershed.
II. Where the canal is looping and not running straight .
If the watershed passing through villages or
towns, the canal may have to leave the watershed for
This is widely used method for alignment of canals.
The ridge line method is not found economical in hill
areas. In hills, the river flows in the valley well below
the watershed. Infact, the ridge line may be hundreds of
meters above the river, so it is impossible to take the
canal on top of such a higher ridge line. In such
conditions contour canals are usually constructed.
Contour channels follow a contour except for giving the
required longitudinal slope to the canal.
A contour canal irrigates only on one side because the
area on the other side is higher. As the drainage flow is
always at right angles to the ground contour. Such a
channel would definitely have to cross natural drains and
streams, necessiating construction of cross drainage
Side slope canal
It is a canal which is aligned at right angles to the
contours. Since such canal runs parallel to the natural
drainage flow, it usually doesn’t intercept drainage
channels. Thus, avoiding the construction of cross
Approved alignment plan showing all structures along the
Longitudinal section of the canal preferably to the scale H
– 1cm:100m & V – 1cm:10m
Cut off diagram for the project / canal
Full supply depth
Width of land acquired
Following statements in the prescribed form for each set
of works viz. sluices, railway bridges, road bridges, foot
bridges, regulator, C.D. works and drops etc.