Irrigation System in Pakistan

Irrigation System in Pakistan Points : Irrigation System in Pakistan, Different Methods of Irrigation, Uncontrolled or Wild Flooding, Free Flooding, Contour Laterals, Border Strip Method, The Zigzag Method, Furrow Method, Advantages of Furrow Irrigation, Corrugation Methods, Contour Framings, Sub-Surface Irrigation, Sprinkler Irrigation, Advantages of Sprinkler Irrigations, Advantages of Drip Irrigation System, Disadvantages of Drip Irrigation System, Important Barrages of Pakistan Different Methods of Irrigation Different Methods of Irrigation Irrigation water may be applied to the crops by three basic methods: (1) Surface irrigation method, (2) Sprinkler irrigation method, and (3) Sub-surface irrigation method. The surface irrigation method can further be sub-divided into various methods as indicated below:

Irrigation water may be applied to the crops by three basic methods: (1) Surface irrigation method, (2) Sprinkler irrigation method, and (3) Sub-surface irrigation method. The surface irrigation method can further be sub-divided into various methods as indicated below: Every irrigation method has both advantages and disadvantages. Before selecting a particular method, the irrigation engineer (or agricultural engineer) must evaluate all the factors, and choose that method which is best suited to the local conditions.

The basic requirements for adaptation of any irrigation method or mode of application of water are as follows:
1. The method should be such that uniform water distribution with as small as 6 cm water depth applications can be made for light irrigations.
2. At the same time, it should afford heavy uniform application of 15 to 20cm water depth.
3. It should allow the use of large concentrated water flows for reduction of conveyance losses, and labour cost
4. It should be sui1able for use with economic conveyance structure.
5. It should be such that mechanised farming is facilitated.

Good irrigation method results in increased yield and conservation of resources with soil productivity maintained and water utilized economically. Over irrigation results in soil erosion, leached fertilizers, drainage troubles and salt accumulation. Uncontrolled or Wild Flooding In this method, water 18 spread or flooded on a rather smooth flat land, without much control or prior preparation. This method is generally used in the inundation irrigation system in which water is forced to spread over wast tracts during the season of high stream flow. It is wasteful use of water, and is practised largely where irrigation water is abundant and inexpensive. Free Flooding In the controlled flooding, water is spread over the land, with proper methods to control the depth of application. Controlled flooding can be achieved by free flooding, contour laterals, border strips or by checks or levees

Free flooding method, also known as irrigation by plots, is commonly used in Pakistan. The field is divided into a number of small sized plots which are practically level. Water is admitted to these plots at the higher end and the supply is cut off as soon as the lower part of the plot has received the sufficient depth of water. Oblong plots are preferred to the square ones. The size of plots depend on the porosity of the soil.

Contour Laterals This method is applicable for steeper terrain. The field is cut by relatively dense network of small contour laterals, the spacing of which depends upon the prominent grade of the field between two adjacent ditches or laterals, the uniformity of slope and the soil type.

Border Strip Method In the border strip flooding method, the farm is divided into a series of strips 10 to 20 metres wide and 100 to 300 metres long. These strips are separated by low levees or borders (low flat dikes) and run down the predominant or any other desired slope, To irrigate, water (discharge varying from 0.014 to 0.028 cumecs) is turned from the supply ditch onto the head of the border. Water advances-confined and guided by two borders-in a thin sheet towards the lower end of the strip. The surface is essentially level between two borders so that the advancing sheet of water covers the entire width of the strip. The lengthwise slope varies from 0.5 to 1.5 %.

This method is especially suited to forage crops, its advantage being that for a relatively low investment a system can be developed which can afford the highest irrigation efficiency and lowest labour requirements. With highly mechanised farming, large area can be irrigated within a short time by border strip method. The length of border strip depends upon how quickly it can be wetted over its entire length. This, however, depends upon:

The following lengths are suggested for moderate conditions
	Types of Soil	Length of Order Strip
1.	Infiltration rate of the soil,	60 to 90 m
2.	Longitudinal slope of the land and	90 to 150 m
3.	Size of irrigation stream available	150 to 300 m

The first 6 to 12 m length of the strip should be made level to ensure uniform spreading of water.

(b) Under-ground concrete pipes through risers: In this method, water is let into the strips by concrete risers, as shown in Fig. (b). Analysis of time to cover a strip area

Size of irrigation stream applied to unit area of land be varied according to the rate of infiltration of water into the soil. When a large stream is applied to unit area of the soil of low infiltration rate, excessive surface runoff occurs. However, when a small stream is applied to a unit area of soil of high infiltration rate, excessive depths of water are lost by deep percolation. The relation between size of stream and time rate of water application over a given area of land can be most easily stated by means of a rational equation derived below:

The Zigzag Method It is special method of flooding where water takes circuitous route before reaching the dead end of each plot. The whole area is divided into a number of square or rectangular plots; each plot is then subdivided with the help of low bunds or levees. This method is suitable for relatively level plots. It is, however, highly unsuitable for farming operations with modem farm machinery.

Furrow Method The furrow method of irrigation is very much used for row crops like maize, jowar, sugarcane, cotton, tobacco, groundnut, potatoes etc. in the other irrigation methods described so far, almost the entire land surface is wetted, but in this method only one half to one fifth of the surface Ii wetted, and thus evaporation losses are very much reduced. A furrow consists of. narrow ditch between rows of plants. The length of furrows vanes from 3.0 m or less for gardens to as much as 500 in for field crops, the common length being 100 to 200 m. If the furrows are of excessive length, deep percolation losses and soil erosion near the upper end of the field may result, The general slopes provided for furrows may from 0.2 to 5 %

Furrow spacing for com, potatoes sugarcane and other row crops is determined by the proper spacing of the plant rows, one irrigation furrow being provided for each row. The spacing of furrows ii kept from I to 2 m in orchard irrigation. If the spacing is kept more, it is essential to check the distribution of moisture after each watering by ager boring. For soil of low permeability the depth of furrows may vary from 20 to 30 cm. It is essential in irrigating the root crops (such as sugarcane etc.) to have furrows deep enough, and the stream in each small enough so that water cannot come in contact with the plant. The common size of furrow for row crops such as cotton, tobacco and potatoes is about 25 cm wide and 8 to 10 cm deep. Furrows arc sometimes made before planting, at the time of planting or after plants have grown large enough not to be covered up. Often young plants are irrigated by small furrows until a good root 8ystem is developed. Thereafter the furrow is made larger.

Advantages of Furrow Irrigation Furrow irrigation method has the following advantages:
(i) In the furrow irrigation, water contacts only 1f5 to I: of the land surface, thereby reducing pudding and crusting of the soil. Evaporation losses are also reduced.
(ii) Earlier cultivation Is possible in heavy soil and may he adapted to use without erosion on a wide tinge of natural slope by carrying furrows across a sloping field rather than down the slope.
(iii) It Is specially suitable for those crops (like maize etc.) that are injured by contact with water.
(iv) Labour requirements in land preparation and irrigation are very much reduced.
(v) There is no wastage of land in field ditches Corrugation Methods Furrows and corruptions are essentially similar in both the cases water is convoyed to the plant through long small capacity channels dug at regular Intervals While furrows are channelets of a comparatively large cross section and are used on flat slop corrugations are chennelats of smaller cross sections and run down the predominant slope Thus, corrugations are small furrows and are used for grain and other forage crops such as alfalfa. The corrugations are advantageous when the available Irrigation streams are small and also for land of uneven topography. Contour Framings Contour farming is practiced in hilly areas having steep slopes with quickly falling contour Contour farming is the practice of conducting field operation such as ploIughing, planting and cultivating land, across the slope rather than up and downhill. The area Is divided into longitudinal curved plots the bend. of the plots following the contours The Irrigation water stored In some deproesloti higher up, flows between the bunds. Before starling contour forming an land which Is not terraced or bunded, contour guide line, are established first On average hill sides the first contour should ordinarily be laid about 1.2 to 1.5 m vertically below the top of the hill. Additional contour lines are located with the same spacing as the first. The design of contour bunds involves the selection of the vertical and horizontal Interval end determining dimensions of the bund cross section Table 2.1 gives Gadkalys recommendations for the spacing of contour bunds on different land slopes. Table 22 gives Ghumar’e recommendation for the dimensions of contour bundi of various types of soil.

Sub-Surface Irrigation The sub-surface irrigation method consists of supplying water directly to the root zone of the crop- The favourable conditions for the sub-surface irrigation practice are.
1. Impervious sub-soil at reasonable depth (say 2 to 3 m) or high water table
2. Permeable soil such as loam or sandy loam in the root zone of the soil.
3. Uniform topographic condition
4. Moderate slopes.
5. Good quality irrigation water

If all these favorurable conditions are filled and if proper precautions are taken to prevent alkali accumulation or excess water logging, the method results in economical use of water, high crop yield and low labour cost in preparing the irrigation plots. Water is supplied to a series of ditches half to one meter deep and 25 to 100 cm having vertical sides. These ditches are spaced from 50 to 100 cm apart. Water flows at a slow rate and seeps into the ground to maintain the water table at a height such that water from the capillary fringe is available to the crops. Proper drainage of excess water is permitted, either naturally or with the other drainage works to prevent water logging of the fields. Sometimes the upward capillary water flow from shallow water table may produce saline and alkali conditions and may make the land less productive. Under such circumstances, the sub-surface irrigation method had to be discontinued and irrigation has to be resorted by sprinkling method.

Spacing of contour bunds
	Slope of land (%)	Vertical interval (m)	Horizontal distance (m)
1.	0 to 1	1.05	105
2.	1 to	1.20	98
3.	13 to 3	1.35	70
4.	2 to 4	1.50	60
5.	3 to 4	1.65	52

Specfication of bound cross section
	Depth of soil	Base width (m)	Top width (m)	Height (m)
1.	Shallow soils (7.5 to 22.5cm)	2.67	0.38	0.75
2.	Medium soil (22.5 to 45 cm)	3.12	0.60	0.85
3.	Medium deep soil (45 to 90 cm)	4.25	0.90	0.90

Sprinkler Irrigation The sprinkler method consists of applying the water in the form of a spray, somewhat as in ordinary rein, as is done in the garden lawn sprinkling. The greatest advantage of sprinkler irrigation is its adaptabilities to use under conditions where surface irrigation methods are not efficient. This method is more useful where:
(i) The land cannot be prepared for surface methods
(ii) Slopes are excessive
(iii) Topography is irregular
(iv) Soil is erosive
(v) Soil is excessively permeable or impermeable
(vi) Depth of soil is shallow over gravel or sand.

In this system, the cost of land preparation and permanent water delivery system of channels or conduits is less. However, there is large initial investment in the purchase of the pumping and sprinkling equipment.

Sprinkler system can be classified under three heads
(i) Permanent system,
(ii) Semi-permanent system, and
(iii) Portable system.

Earlier, stationary over-head perforated pipe installations were used. However, with the introduction of light weight steel pipes and quick couplers, portable sprinkler system were developed. In the permanent system, pipes are permanently buried in such a way that they do not interfere with tillage operations. In the semi-permanent system, the main lines are buried while the laterals are portable. Portable system have both portable mains lines and laterals. These systems are designed to be moved from around the farm from field tc, field. A pump usually lifts the water from the source, pushes it through the distribution system and through the sprinkler nozzel on the sprinkler heads mounted on rising pipes attached to the laterals. Turbine and horizontal centrifugal pumps are used Sprinkler system usually is composed of perforated pipes or revolving head sprinklers and may be high pressure’ (2.1 kg/cm2) or “low pressure” (1.4 kg/cm2) system. Generally, a perforated pipe system operates on the low pressure where as the revolving head sprinklers operate in both ranges depending on the type of rotary head used. Advantages of Sprinkler Irrigations (i) Erosion can be controlled
(ii) Uniform application for water is possible.
(iii) Irrigation is better controlled; light irrigation is possible seedling and plants which are young.
(iv) Land preparation is not required. Labour cost Is reduced. More land is available for cropping, as borders and ditches are not required. Surface run off is eliminated.
(v) Small streams of irrigation water can be used efficiently.
(vi) Time and amount of fertilizers can he controlled for application.
(vii) Crop damage from frost can be reduced
(viii) It is a stand by drainage pumping plant.
(i) Wind may distort sprinkling pattern.
(ii) A constant water supply ii needed for commercial use of equipment.
(iii) Water must be clean and free from sand etc.
(iv) The power requirements is high
(v) Heavy soil with poor Intake cannot be irrigated efficiently Efficiency If no water application efficiency of the plum, W, Is the Irrigation water stored in root tone and 7water pumped into the system, then

h= ws/wf x 100

About 80 % Irrigation efficiency is possible with sprinkler Irrigation particularly In semiarid and humid areas The efficiency decreases by 5 % tor each 7.5 km per hour of wind. Drip Irrigation In drip Irrigation, also known u trickle irrigation, water is applied in the form of drops directly near the base of the plant. Water Is conveyed through a system of flexible pipe lines, operating at low pressure, and is applied to the plants through drip nozzles. This technique is also known as “feeding bottle’ technique where by the soil is maintained. In the most congenital form by keeping the soil proportions in the optimum rang. Drip Irrigation limits the water supplied consumptive use of the plant by maintaining a minimum soil moisture, equal to the field capacity thereby maximizing the saving. The system permits the fin, control on the application of moisture and nutrients at stated frequencies.

The method of drip irrigation was first introduced in Israel, but is now practiced in many countries of the World. Along with irrigation water, nutrients (fertilizer solution) are also fed to the system. Water is first filtered so that the impurities may not clog the fine holes of the drippers. The whole arrangement consists of the following components
(i) a pump to lift water.
(ii) a head tank to store the water and to maintain a pressure head of 5 to 7 m.
(iii) Central distribution system which filters the water, adds nutrients (or fertilizer solution) and regulates the pressure and amount of water to be applied.
(iv) Mains and Secondary lines made of polyethylene, polyvinyle chloride or a alkathyelene material. The diameter of the piping may vary from 20 mm to 40 mm. A water meter may be fixed at the beginning of the mains.
(v) Trickle lines consisting of 10 to 20 mm dia PVC pipes with perforations at a distance equal to the spacing of the crops. The trickle lines are fined to the secondary lines at a distance equal to the row to row spacing of the crops, which may vary between 60 cm to 90 cm, a more common value being 75 cm for the most of the crops. The spacing of the nozzles, to be fitted in the perforations of the trickle lines, depends upon the planting distance along a row, and this distance may vary between 30 cm to 50 cm.
(vi) Plastic Nozzle Having perforations attached to the trickle line The perforations are so designed that water leaves the nozzle at a very slow rate. Usually ranging between 2 to 10 litres per hour, depending upon the irrigation requirements of the crop,

The whole field is divided into suitable plots. A secondary line is provided for each such plot, and a number of trickle lines are connected to each secondary line. A discharge regulator is provided at the beginning of each secondary line, and its capacity is fixed in accordance with the size and number of nozzles used. The automatic valve at the head is so adjusted to deliver the desired quantity of water and the irrigation terminates automatically after this amount is discharged. The drip irrigation system is suitable to practically all types of crops, except paddy which requires standing water It is also suitable to all climatic conditions and to all types of soils. However, it is most suited to coarse sandy formations.

Advantages of Drip Irrigation System 1. Less requirement of irrigation water The evaporation and percolation losses, commonly associated with surface irrigation method are reduced. 2. Water supply at optimum level An optimum water level, equal to the field capacity can always be maintained, by the water flow controls available in this method. Soil is maintained in most congenial form. 3. Water logging avoided Because of check over deep percolation losses, the chances of water logging are all together removed. 4. High yield Because of proper control over the factors governing soil water-crop relationships, higher yield is obtained. 5. Cultivation of cash crops The method is specially suited to cash crops such as vegetables, cotton, tabbacco and orchard products. 6. Moreover-irrigation In surface methods of water application, over-irrigation is sometimes done to provide sufficient moisture at deficient area. This is avoided in this method since water is supplied to the root zone directly for each crop. 7. Variation In application rate It is possible vary the application rate, throughout the crop period. When the crop is infant, application rates can be easily increased. 8. Weed control The nuisance of weeds commonly associated with surface application methods, is avoided. This will, in turn, result in increase in crop production, and saving in farm application. 9. Increase in net irrigable area In surface application, a lot of area is wasted in the construction of field channels etc. As water is an-is carried through small diameter pipes, there is considerable saving in land. 10. Nutrients preservation Soil nutrients are preserved because of. reduction in deep percolation losses. Moreover, feeding of water enriched with fertilizers results in proper maintenance and preservation of nutrients at optimum level. 11. Effective pest control Insect and pest combating chemicals can be directly conducted into the root zone. 12. Reduced labour cost The labour cost, otherwise associated with the maintenance of field channels furrows etc., is reduced. 13. No soil erosion The problems of surface soil erosion, associated with surface application methods, are practically absent in this method. 14. Suitability for saline soils The saline, alkaline or brakish soils otherwise unsuitable, can be utilized by cultivation by the drip irrigation method. 15. Maintenance of high surface temperature In surface application method, soil temperature is lowered because of water spread over the entire area. However, in this method, entire soil surface is not wetted. Hence high soil temperature is maintained which will be useful in hastening the ripening or maturity of the crop. 16. Suitable for any topography No land leveling is required, and is suitable even for sloping and undulating terrain. Disadvantages of Drip Irrigation System (i) High initial cost. The initial cost of various components such as pumping unit, filter units, pipelines, nozzles etc. is very high.
(ii) Danger of blockade of nozzles. The nozzle holes are very small in size (0.5 to 1 mm dia.). Hence they are very frequently clogged. if the water has high degree of total dissolved salts which cannot be removed by filtration.
(iii) Change in spacing of nozzles due to change in the crops may result in frequent replacement of trickle lines.
(iv) Shallow root depth of the crops, specially for fruit trees etc., may result in instability of the crop or tree which may topple during high winds. Important Barrages of Pakistan These are 17 main barrages in Pakistan listed below:
1. Jinnah Barrage over river Indus.
2. Marala Barrage over river jhlum.
3. Rasul Barrage over river Chenab
4. Khanki Barrage over rive Chenab
5. Qadirabad Barrage river Indus
6. Chashnia Barrage over river Indus
7. Trimmu Barrage over river Indus
8. Baloki Barrage over river Indus
9. Sulaimanki Barrage over river Indus
10. Sidhnai Barrage over river Indus
11. Taunsa Barrage over river Indus
12. Islam Barrage over river Satluj
13. Punjab Barrage over river Satluj
14. Prinad Barrage over river Indus
15. Guddu Barrage over river Indus
16. Sukur Barrage over river Indus
17. Kotri Barrage over river Indus.