Irrigation engineering

Irrigation engineering : in agriculture, artificial watering of the land. Although used chiefly in regions with annual rainfall of less than 20 in. (51 cm), it is also used in wetter areas to grow certain crops, e.g., rice. Estimates of total irrigated land in the world range from 543 to 618 million acres (220 to 250 million hectares), almost half of them in India, Pakistan, and China. The United States had almost 60 million acres (23.8 million hectares) of irrigated farmland in 1991.

In Irrigation engineering Methods of applying water include free-flooding of entire areas from canals and ditches; check-flooding, in which water flows over strips or checks of land between levees, or ridges; the furrow method, in which water runs between crop or tree rows, penetrating laterally to the roots; the surface-pipe method, in which water flows in movable slip-joint pipes; sprinklers, including large-scale center-pivot and other self-propelled systems; and a variety of water-conserving drip and trickle systems. In many cases irrigation is correlated with drainage

 to avoid soil salinity, leaching, and waterlogging. Irrigation may also involve preliminary clearing, smoothing, and grading of land. Especially in areas of high evaporation rates, intensive irrigation can result in excessive quantities of salts accumulating in the upper layers of the soil as water evaporates from the surface, rendering the soil unfit for crop production.

Since prehistoric times water has been diverted from waterways to fields by ditching. Early improvements for raising water included counterbalanced poles with attached water vessels, and adaptations of the wheel and of a pump called the Archimedes’ screw. The use of canals, dams, weirs, and reservoirs for the distribution, control, and storage of water was probably initiated in ancient Egypt. A system of gently sloping underground tunnels (qanats) to deliver water from a subterranean source to distant areas where it is accessed through shafts was developed in ancient Persia and has been widely used elsewhere. In modern times pumps have facilitated the use of underground as well as surface water, but overuse of water in aquifers can exhaust their usable water. Large-scale 20th-century irrigation projects commonly also include water supply, hydroelectric power, and flood control.

 

Classification and Alignment of Canal

BEST QUESTIONS Give various classifications of canals, with a brief description of each classification. What points should be consider while choosing the alignment of a canal? What do you understand by inundation canal? Under what circumstances they are construct? (a) Enumerate the design considerations of an inundation canal. (b) What points should be consider while choosing off taking point for an inundation canal? What is meant by Bandhara? Describe its working. Enumerate advantages and disadvantages of Bandhara irrigation scheme. 10. Write short notes on: (i) Ridge canal (ii) Side slope canal (iii) Distributory (iv) Lined canal (v) Main canal    

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Design of inundation canals

DESIGN CONSIDERATION OF INUNDATION CANALS The head regulator should be installed a few kilometers D/S of the off-take point. This measure would eliminate the risk of the head regulator being washed away. As escape should be located D/S of the head regulator and escape channel should be joined to the river D/S. If more water enters the canal at the off-take point it can be taken out through the escape. In order to reduce the chances of silting of the canal. The flood regulator should be provided with vertical lift gates that could be lifted in stages. The full supply level of the canal should be fixed at a level at which the river water is more or less steady for a period of 40—50 days. which the canal can be run full to irrigate the lands. This steady level of water in the river is called fair irrigation level.…

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Characteristics of inundation canals
CHARACTERISTICS OF INUNDATION CANALS

Characteristics of inundation canals

CHARACTERISTICS OF INUNDATION CANALS Inundation canals are mostly used in deltic and alluvial regions of the river. As river course here is generally at a higher level and the course is maintained between dykes or embankments. The section of the canal is not regular. The banks are not very strong and may breach if not properly looked after. These canals have longitudinal, slopes varying from 25 cm to as much as 1 m per kilometer length. Depth of the canal maybe 1.5 m to 3.5 m. Like regular canal system inundation canal system may also have the main canal and then smaller canals. The bed level of these canals should be kept at the most at the level of minimum water level in the river. Lower the bed level of the canal, more will be the time for which water will remain available. An inundation canal may be provided with…

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Inundation canal

INUNDATION CANALS Inundation canals are made under the following circumstances.  If river water level during floods remains high for a considerable length of time. If sufficient floodwater reaches the river in March or April, the flood water may be use to submerge the land, so that the Kharif crop could be sown. If flood water remains available say up to late September, the Kharif crops can irrigate up to this time and, even, areas may be submerg to sow early Rabi crops in October. Areas to be irrigate when in the vicinity of the river banks the inundation canals may serve the purpose of irrigation. When soil has good stabilizing power so the bed and banks of the canal remain stable. Inundation canals are more or less similar to permanent canals. The major difference is that, in the case of permanent canals, permanent masonry or concrete works. Like weirs, barrage,…

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Alignment of water courses

ALIGNMENT OF WATER COURSES Though the responsibility of maintenance of the water courses is that of farmers, still in new irrigation works. The alignment, of the water courses is fixed by the government. This work is being done these days by canal area development (C.A.D.) department or collonisation department. Following points should however be considered while fixing the alignment of water courses. Separate water courses should be provided for high lands and low lands of the same village. They should not cross through field but should be laid along the boundries of the fields. Sufficient water should be available to fields lying at the farthest point from the outlet. The water courses should be aligned along the ridges of the area of the village. If low lying area is near the outlet and high land is at the further end of the village. The water course which has to carry…

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Best questions of diversion head works

Draw a neat sketch of a diversion head work and name its various parts. Give brief explanation of each part. Explain the terms weir, barrage and dam. Point out the points of difference among, them. Enumerate various causes of failure of the weirs. Discuss each cause and suggest the remedies. Explain the various stages of river. Discuss the suitability of each stage in regard to the location of a diversion headworks. What are the points which should be considered while selecting the site for diversion headworks? Explain the Bligh’s creep theory for the design of impervious aprons on permeable foundations. What are limitations of this theory?  Expalin the Khosla’s findings which he conducts on the weirs that were designed according to Bligh’s theory but failed. Why some of the works designed according to Bligh’s theory did not fail while others failed? Explain Khosla’s method of independent variables. Explain the method…

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Classification of canals
CLASSIFICATION OF CANALS

Classification of canals

CANAL The canal is an artificial channel, usually trapezoidal in section. It is construct on the surface of the ground. It is use to convey water from the river, lake, reservoir, etc., to fields for irrigation, for water supply schemes, for power generating units, etc. They always flow under gravity. The canal may be Kucha or Pucca. Pucca canals are known as lined canals. CLASSIFICATION OF CANALS The canals can be classified in several ways. All the possible classifications are given as follows: 1. Classification based on financial output. Under this classification canals may be divided into two types: (i) Protective canal. (ii) Productive canal. (i) Protective canal. The purpose of a protective canal is to protect the areas most prone to famines. The canals are construct having all the permanent works required for their regulation. No discharge of water is left in them under normal conditions. But whenever famine…

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Considered during canal alignment

POINTS TO BE CONSIDERED WHILE FIXING CANAL ALIGNMENT The following points should be considered while fixing the alignment of a canal: The canal should be straight. Such a canal would be minimum in length. Length being minimum losses due to percolation and evaporation are bound to be minimum. The canal should follow the ridge as far as possible. This will cause irritation of the areas lying on both sides of the canal. If somewhere a canal leaves the ridge, our effort should be to catch the ridge again as soon as possible. Cross-drainage works should be minimum, as such works are very costly. The canal should not pass through a village or town, but by the side of it. Canal taking off from a river is a contour canal for some length. Every effort should be made to mount if the main watershed, as soon as possible. Alignment should avoid…

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Effect of Diversion headwork

EFFECTS OF CONSTRUCTION OF DIVERSION HEADWORKS ON THE BEHAVIOUR OF RIVERS Following are the changes that take place in the behavior of the river after the construction of a diversion headworks. The silt carrying capacity of river is decreased because heading up of water causes flattening of the surface slope on the U/S side of the weir. Because of reduction in silt carrying capacity, the pond formed on U/S side starts silting. Because of silting on U/S side, the water passing D/S of the weir contains less amount of silt. To make up for the deficiency of the silt, the D/S flowing water starts scouring the bed and banks. The scouring may lead to undermining the stability of the weir. Because of silting of the pond, the afflux goes on increasing and thus more and more areas on U/S are submerged. At last, a stage is reached when no more…

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Silt control at head regulator

SILT CONTROL AT HEAD REGULATOR Excess silt entering into the main canal has to be prevented by all the possible means. If excess silt gets to enter the main canal, it will cause silting of the whole canal system and ultimately. The capacity of the canal will be reduce. The silt entry into the main canal from a river can be controlled by the following measures. Divide wall in the river creates a quiet pocket behind the head regulator. The quiet pocket renders top layers of water silt free and only top layers of water are admitt into the canal. Provid raised crest for the head regulator. This measure automatically eliminates lower silt-laden layers of water. Providing a wide head regulator also causes less entry of silt into the canal. The entry of water into the canal should be smooth. Smooth entry does not cause any disturbance and as such…

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