UNIT 4 CANAL IRRIGATION

DEFINITION canal usually draw their supplies from rivers.they are not provided with any headwork for diverson of river water to the canal.they are however provide with a canal headregulators.and finally water from the canal is directly supplied to main ditch and then to the secondary ditch

ALIGNMENT OF CANAL Watershed Canal or Ridge Canal Contour Canal Side-slope Canal

WATERSHED CANAL The dividing ridge line between the catchment areas of two streams (drains) is called the watershed or ridge canal. Thus between two major streams, there is the main watershed (ridge line), which divides the drainage area of the two streams, as shown in figure below. Similarly, between a main stream and any of its tributary, there are subsidiary watersheds (ridge lines), dividing the drainage between the two streams on either side.

The canal which is aligned along any natural watershed (ridge line) is called a watershed canal, or a ridge canal. Aligning a canal (main canal or branch canal or distributary) on the ridge ensures gravity irrigation on both sides of the canal. Since the drainage flows away from the ridge, no drainage can cross a canal aligned on the ridge. Thus, a canal aligned on the watershed saves the cost of construction of cross-drainage works.

CONTOUR CANAL Contour channels follow a contour, except for giving the required longitudinal slope to the canal. Since the river slope is much steeper than the canal bed slope, the canal encompasses more and more area between itself and the river. A contour canal irrigates only on one side because the area on the other side is higher

SIDE-SLOPE CANAL It is a canal which is aligned roughly at right angle to contours of the country but not on watershed or valley. The canal thus runs roughly parallel to the natural drainage of the country cross drainage works are avoided. The side slope channel has the advantage of not intercepting cross drainage works but its course must follow the shortest route the nearest valley and such channelshall be along a line of steepest possible slope except in very flat areas

CANAL DROPS A drop has been defined to be a work designed to secure lowering of water surface in a channel and safe destruction of surplus energy so liberated. The velocity in channel is a function of slope and there is a limiting velocity which can be allowed in a channel depending upon the nature of soil through which it passes without causing it to scour

CANAL HEAD WORKS Any hydraulic structure which supplies water to the off taking canal. Diversion head-work provides an obstruction across a river, so that the water level is raised and water is diverted to the channel at required level. The increase water level helps the flow of water by gravity and results in increasing the commanded area.

CANAL REGULATORS Structure at the head of canal taking off from a reservoir may consist of nu ber of spans separated by piers and operated by gates. Regulators are normally aligned at 90° to the weir. upto 10" are considered preferable for smooth entry into canal. These are used for diversion of flow. Silt reduces carriage capacity of flow.

TYPES Types of regulators in canals Still pond regulation Open flow regulation Silt control devices

RIVER TRAINING WORKS The object of river training/protection works is to prevent the river from damaging railway formation, bridges and other structures. The training/protection works will have to be decided depending on the reach in which the river is situated

TYPES OF RIVER TRAINING WORKS Upper reaches (Mountainous) Submontane reaches (Foot hills) Quasi-alluvial reaches (Trough) Alluvial reaches, and Tidal reaches