Test: Irrigation - 1

Culturable Cultivated Area is the area in which crop is grown at a particular time or crop season.

Solution: (b) 

Ridge/Watershed Canal: The dividing ridge line between the catchment areas of two streams (drains) is called the watershed or ridge canal. It is suitable for plain areas, where slopes are relatively flat and uniform. This type of alignment ensures gravity irrigation on both sides of the canal.

Contour Canal: Canal aligned nearly parallel to the contour line is called contour canal. They are aligned generally when canals take off from a river. Culturable area lies on one side of it as one of the banks is on the higher side.

Side Slope Canal- A side slope canal is that which is aligned at right angles to contours i.e. along the side slopes. It is a canal which is aligned roughly at right angle to contours of the country but not on the watershed of the valley. The canal thus, runs parallel to the natural drainage of the country and as such cross drainage works are avoided.

It is the structure required to dispose of surplus or excess water from canal from time to time. Thus, a canal escape serves as safety valve for canal system. It provides protection to the canal from possible damage due to excess supply which may be due to mistake in releasing water at head regulator or heavy rainfall that makes sudden regular demand of water.

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 symphonic action. This structure is known as aqueduct siphon. 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 symphonic action, the structure is called Canal Siphon. Aqueduct or super-passage 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.

Canal lining is the process of reducing seepage loss of irrigation water by adding an impermeable layer to the edges of the trench. Seepage can result in losses of 30 to 50 percent of irrigation water from canals, so adding lining can make irrigation systems more efficient so there is increase in command area.

Advantages of Canal Lining:

An important reason for lining a canal can be the reduction in water losses, as water losses in unlined irrigation canals can be high. Canals that carry from 30 to 150 liters/sec can lose 10 to 15% of this flow by seepage and water consumption by weeds. Lining a canal will not completely eliminate these losses, but roughly 60 to 80% of the water that is lost in unlined irrigation canals can be saved by a hard-surface lining.

Explanation: The various factors that contribute to the rise in water table i.e. water-logging are –
• Over and intensive irrigation
• Seepage of water through canals and adjoining high lands
• Inadequate natural drainage and surface drainage
• Excessive rains and submergence due to floods
• Impervious obstruction.

Leaching is a process of extracting a substance from a solid material that is dissolved in a liquid. Thisprocess is commonly referred to as extraction, particularly in the chemical industry. Three basic steps are involved in the leaching process: contact, separation, and extraction.