## 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.

meter and non meter fall

## Meter and non meter fall

METER AND NON-METER FALLS The falls may be divided into following two types: 1. Meter falls 2. Non-meter falls. 1. Meter Falls. The falls which can be used to measure the discharge flowing over them, are known as meter falls. Such falls must have broad crest so that the discharge coefficient remains constant under variable head. Glacis type falls are most suitable as meter falls. If section of the channel at the site of the fall has to be flumed. From economic considerations, smooth U/S transition. Should be provided to avoid turbulences and also to maintain accurate stage-discharge relationship. 2. Non-meter Falls. The falls which cannot be use to measure the discharge passing through them, are known as non-meter falls. Vertical drop falls cannot be used as meter falls. Some vacuum is developed under the nappe of falling water, which causes non-uniform flow conditions.

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Canal Regulation Works

## Canal Regulation Works

INTRODUCTION To exercise control on discharge, full supply level, velocity of flow, silting etc. various masonry or concrete structures have to be constructed over the canals. All these structures are know Canal Regulation Works. Main Regulation works may be listed as follows: 1. Canal falls 2. Head regulator 3. Cross regulator 4. Metres and Flumes 5. Canal escapes. Canal outlets, also come under the category of regulation works, but they have been discussed separately.

CANAL FALLS

## CANAL FALLS

CANAL FALLS Why Falls are Provided When natural slope of the country is steeper than the designed longitudinal slope of the irrigation canal. The falls have to be provided. If falls are not provided, the canals run so much in filling. That it will be almost impossible to even construct the canals. If canal is constructed very much in filling. It will be a constant danger to the adjoining people, and also it will be impossible to mantain it. For example, let slope of a particular canal be say 1 in 5000 and general slope of the ground say 1 in 2500. If canal bed at the start i.e. zero distance, is say 1 m in cutting. The bed of canal will just coincide with ground level at a distance of 5000 m and thereafter. The bed of the canal will come in filling. The fill of the canal will…

Classification of falls

## Classification of falls

CLASSIFICATION OF FALLS The falls can be classified into the following four categories according to the approach conditions. 1. Falls which maintain relation between depth and discharge. 2. Falls which maintain level of U/S water constant. 3. Combination of fall and regulator. 4. Miscellaneous falls. 1. Falls in which D-Q relationship is maintained. In such falls there is neither drawdown nor heading up of water on U/S side. The Depth-discharge relationship for the channel is maintained. Trapezoidal notch falls and low crested rectangular notch falls, fall under this category. 2. Falls which maintain fixed F.S.L. on the U/S side of the fall. Siphon fall or Siphon spillway high crested weir fall are the falls which fulfil this condition. Such falls cause silting on U/S side. Such falls are necessary under following circumstances. (i) When a sub-channel has to take off at some distance U/S of the fall. (ii) When Hydro-electricity…

## Type Membrane Lining

Buried and Protected type Membrane Lining These linings are such lining in which a waterproof thin membrane is place on the prepare subgrade. Thereafter it is covered by a protective layer of earth or gravel. The protective layer provides protection to the lining against damage due to outside effects. Membrane itself provides imperviousness. The commonly used buried membranes may be: 1. Sprayed asphaltic lining. In this hot asphalt is sprayed on the subgrade which acts as water proofing barrier. 2. Prefabricated asphaltic membrane lining. In this, asphalt lined papers, clothes, mats etc. are used to put a barrier against seepage. All these fabrications are available in marked in form of rolls. The membrane is laid on smooth well prepared subgrade and covered with a fine soil or earth. 3. Plastic or rubber membrane lining. In this case, plastic or synthetic rubber membrane is used as water proofing membrane. Out of…

Lined Canals and Their Design

## Lined Canals and Their Design

INTRODUCTION Canal lining is a treatment given to the canal bed and banks, so as to render the canal section impervious. Since imperviousness of the canal section is achieved mostly by making canal section pucca. Either by cement concrete or bricks, the lined canals are also sometimes know pucca canals. Lined canals are mostly referred to as pucca canals. It has been estimated that seepage losses in irrigation canals. May amount from 30% to 50% of the water admitted in the canals at diversion headworks. This much loss of water in unlined channels cannot be afforded. As resources of water in India are limited in relation to irrigable area available. Hence in order to reduce or rather eliminate the seepage losses, lining of canals is the need of the hour. Advantages of Lining Following are the benefits of lined canals: Seepage losses are practically eliminated or reduced to minimum. Maintenance…

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ESSENTIAL PROPERTIES OF A GOOD LINING

## Essential properties of a good lining

ESSENTIAL PROPERTIES OF A GOOD LINING Following are the essential properties of a good lining: The lining should be completely water tight. The rugosity coefficient of the lining material should be low, so as to make the section more efficient, hydraulically. The lining should be strong and durable. Initial cost of lining and its subsequent maintenance cost should be low. The lining should not get damaged by tramping of cattles. It should resist growth of weeds and attack of burrowing animals. Lining should not get damaged when flow in the canal is stopped. TYPES OF LINING The linings may be classified under the following four heads: Hard surface lining Buried and protected type membrane lining Earth lining Porous type lining, Each class of lining is discussed in details one by one. Hard Surface Lining The following types of linings come under this category: Cement concrete lining Shot-crete lining Precast concrete…

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DESIGN OF LINED CANAL

## Design of lined canal

DESIGN OF LINED CANAL The design of line canals is always done by Kennedy’s Theory.. Following equations given by Kennedy are used in the design. $V0= 0.54mD^{0.64}$ $V= \frac{R^{2/3}S^{1/2}}{N}$ The value of N for protected type of linings is taken same as for natural soil. The value of N of natural soil varies from 0.02 to 0.025. In order to obtain the most economical section, it is necessary to adopt the best discharging section. The flow will be greater when the friction is least. This happens when wetted perimeter is least for any particular given area of the channel. In other words, the discharge will be maximum when Hydraulic mean depth (H.M.D.) is maximum. A semi-circular section of channel is considered as the best theoretical section. But Trapezoidal channel section is mostly adopted on practical grounds. In order to increase the H.M.D., the angle subtended at the corners at bottom…

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STANDARDS OF CANAL CROSS-SECTION

## Standards of canal cross section

STANDARDS OF CANAL CROSS-SECTION Usual dimensions of canal cross-section elements have been given here and there inappropriate articles. The standards as suggest by CWPC are given as follows.   1. General. A trapezoidal section is recommended for the canal. The longitudinal slope of the canal is determined depending upon the average slope. The natural ground along the proposed alignment. This is the maximum average slope that can be provided on the canal. 2. Side Slopes. These are dependent on the local soil characteristics and are designed to withstand. The following conditions during the operation of the canal. (a) The sudden drawdown condition for inner slopes. (b) The canal running full with banks saturated due to rainfall. Canal in the filling will generally have side slopes of 1.5: 1. For canals in cutting, the side slope should be between 1: 1 and 1.5: 1 depending upon the type of soil. 3.…

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