The canals are classified according to:

[1] Their alignment as

[a] Contour canal.

[b] Ridge canal.

[c] Side slope canal.

[2] Their origin and capacity as

[a] Main canal

[b] Branch canal

[c] Major dis-tributary

[d] Minor dis-tributary or minors, sub minors

[e] Water courses or field channels.

Contour canal. (Fig. 6.2)

• In this alignment, the canal generally follows a contour except for necessary longitudinal slope. Main canal is run as contour canal in the head reach. It can irrigate on one side only. i.e. the lower side. In contour canal, one of its sides is high, so bank is required only on the other side. It runs the risk of breaching or silting. The contour canal need not follow the same contour all along. To enable the water to flow by gravity, some surface slope has to be given.

• Points to be considered while fixing alignment of canal.

• The drawbacks of contour alignment:

1. Extra cost on C.D. works.

2. Irrigates on one side only.

3. Drainage enters the canal and hence runs a risk of breaching or slitting.

Contour canal: Advantages:

a] Suitable in hilly areas.

b] In contour canals longitudinal slope is given to enable water to flow by gravity.

Limitations:

a] Large number of cross drainage works.

b] Can irrigate only one side.

Ridge canal (Fig. 6.3)

• The canal is aligned along a natural watershed known as ridge. These canals usually take off from the contour canal. It irrigates on both sides. C.D. works can be avoided and hence it is more economical.

Ridge canal: Advantages:

a] It can irrigate on both sides.

b] Economical

c] No cross drainage is required.

Limitations :

a] Velocity of water needs to be controlled.

b] Scouring of bed due to higher velocities.