Test: Canal Irrigation & Cross Drainage Works - Civil Engineering (CE) MCQ

Cuiturable area is the cultivable part of the gross command area, and includes all land of GCA on which cultivation is possible. At any given time, all the cultivable land may not be actually, under cultivation.

A contour canal irrigates only on one side because the area on the other sides is higher.

Canal escapes are the safety valves of canal and must be provided at regular intervals depending upon the importance of the canal and availability of suitable drainage. Minimum capacity of escape is generally kept as half of the channel capacity at the point of escape.

The difference in bed level of the canal and drainage is 4 m while the flow depth in drainage is 10 m. Thus HFL of drain at 126 m is higher than the canal bed at 120 m. Therefore syphon aqueduct is most suitable.

If bed level of canal is sufficiently above the HFL of the drain, an aqueduct is the right choice. Sometimes bed level of canal may be little below the HFL of drain so that water flows under syphonic action. This structure is known as aqueduct syphon.If bed level of the drain is sufficiently above the canal FSL, a super passage may be constructed. If the canal FSL is little above bed level of drain to allow syphonic action, the structure is called Canal Syphon. Aqueduct or superpassage type of drainage works are used when high flood discharge is large and continues for a sufficient time.
A level crossing is used when the canal water and drain water are allowed to intermingle with each other. This is adopted when high flood drainage discharge is short lived.

An aqueduct and syphon aqueduct are cross drainage works in which the canal is taken over the natural drain, such that the drainage water runs below the canal either freely or under syphoning pressure. Super passage and syphon are cross drainage works in which the drain is taken over the canal such that the canal water runs below the drain either freely or under syphoning pressure. Level crossing is a cross drainage work in which the canal water and drain water are allowed to intermingle with each other. A level crossing is generally provided when a large canal and a huge drainage (such as a stream or a river) approach each other practically at the same level.

A super passage is just like a bridge in which the natural drain is carried over the canal. A super passage is constructed where the bed of the drain is well above the canal F.S.L.
A syphon serves the same purpose as superpassage and is constructed where the F.S.L.