Here is a term paper on ‘Sprinkler Irrigation’ for class 7, 8, 9, 10, 11 and 12. Find paragraphs, long and short term papers on ‘Sprinkler Irrigation’ especially written for school and college students.
Term Paper on Sprinkler Irrigation
Term Paper Contents:
- Term Paper on the Introduction to Sprinkler Irrigation
- Term Paper on the Components of Sprinkler System
- Term Paper on the Fertilizer Applicators of Sprinkler System
- Term Paper on the Types of Sprinkler System
- Term Paper on the Design Data for Sprinkler Irrigation System
- Term Paper on the Design Criteria for Sprinkler Irrigation System Layout
- Term Paper on the Operation and Maintenance of Sprinkler System
Term Paper # 1. Introduction to Sprinkler Irrigation:
The sprinkler irrigation system is in use since 1920 A.D. in some advanced countries. In India this method has come into use since 1950. Till recently it was mostly adopted in tea and coffee gardens. But the situation has compelled the experts to explore the possibilities of using this method on a large scale.
The experiments conducted on this aspect at various research centres in the country have shown that there is great scope for wide application of this method. This system is becoming popular in our country in the regions where water is scarce.
Broadly following conditions favour introduction of sprinkler irrigation:
(a) Water supply is just sufficient for crop growth.
(b) Soil is too porous for good distribution of water by surface irrigation.
(c) Soil is easily erodable.
(d) There are fields with uneven surfaces.
Term Paper # 2. Components of Sprinkler System:
The basic objective of sprinkler irrigation is to develop water spray comparable to rainfall. Since this condition is artificially created, for achieving maximum irrigation efficiency, the system is designed to achieve uniform water application. In principle parts of all sprinkler systems are similar Fig. 11.1.
They mainly consist of:
(a) Pressure generating unit (pumps and booster pumps).
(b) Water carrier unit (main and lateral pipe lines).
(c) Water delivery unit (risers and sprinkler heads or perforated pipes).
i. Pumping Set:
A pump lifts water from the source and pushes it through a carrier or distribution system and the sprinklers.
Capacity of the pump should be such that it can lift the required amount of water from the source of water supply to the highest point in the command and maintain adequate operating pressure. Generally volute centrifugal pumps and turbine pumps are used to operate sprinkler systems.
When the source of supply is an open well or shallow surface water source centrifugal pump is more suitable. The turbine pump is installed to pump water from deep tube wells. Centrifugal pumps are more popular because unlike turbine pumps it can be used as a portable as well as permanent installation.
The pumps are driven by electric motors or internal combustion engines. For fixed installations electric motors are very useful because they have low initial cost. Also their running cost is less and maintenance is easy. On the other hand for portable pumping sets oil (diesel) engines are to be used. At places where supply of electricity has not reached, oil engines have to be necessarily used to drive the pumps.
Booster Pumps:
Booster pumps are used when sprinkler irrigation system is installed on the existing pumping system which draws water from a well and where the pump capacity is insufficient to force the water through the sprinklers at the desired pressure.
Booster pumps are almost exclusively of the centrifugal type. Booster pump can be very profitably used to provide adequate additional pressure to bring small patches of land under irrigation that lie at considerably high elevations in the command area. With the use of booster pump it does not become obligatory to carry whole water discharge at high pressure from the main pumping plant.
ii. Desilting Basin:
(i) A source of water supply for sprinkler irrigation could be either a surface water source or an open well or a tube well. That water to be delivered through the nozzles must be clean and free of sand and debris. Such a water source is always not available in practice.
Desilting basin may be required to trap sand or suspended silt when water comes from streams and open ditches. Sometimes if well water has silt, desilting basin is essentially required. Desilting basin should be large enough not to allow settled silt particles to get agitated due to pumping. While larger capacities are desirable, desilting basin should be capable of providing water supply at least for one day.
(ii) Debris screens are usually needed when surface water source is tapped for sprinkler irrigation. Debris screen keeps the system free of trash that might clog the sprinkler nozzles. Screens should be of fine mesh to arrest small particles like weed seeds.
Debris screens are also required to prevent large sized debris like sticks, plant stalks and other things from entering the pipe line. More than one screen is used with mesh becoming finer progressively in the direction of flow as the water enters the system. It is necessary to occasionally clean the screens. Sometimes desilting basin and debris screen are built as a combined structure.
iii. Water Pipe Lines:
Main lines of a sprinkler system may be fixed or portable while laterals are usually portable. On a farm with fixed boundaries and for crops which require full season irrigation, permanently fixed mains are found desirable. When sprinkler system is to be shifted from field to field portable mains are more economical.
Permanent lines are generally kept buried so as to be out of the way of farming operations. Similarly in orchards and tree nurseries permanently buried laterals are used. Movable mains generally have lower initial cost and they do not provide obstruction to field operations.
Mostly steel pipe is used for permanent main and lateral lines. Quick coupled aluminium pipes are used for most portable main and lateral lines. The lateral pipes are usually available in small lengths. The maximum length is 12 metres but pipe in 5 or 6 metre lengths are also manufactured. Each length is provided with quick coupling. In the coupling rubber gasket is provided which makes the joint watertight due to sealing under water pressure.
When the flow in pipe stops water pressure falls, seal is broken and water drains out from the pipe making it easier to uncouple the pipes. The lateral takes water from the main either through a valve placed at its junction point or through a L and T section which replaces the coupling on the main to enable joining of the lateral.
iv. Sprinkler Heads:
Sprinkler head is a most important part of a sprinkler system because through its operation that a spray is developed. The mechanism has a revolving head and may have one, two or more nozzles. (Fig. 11.2 and 11.3). The nozzles are attached on riser pipes fixed at uniform intervals along the length of the laterals. Height of riser depends upon height of the crop.
For rotating sprinkler a small hammer is provided in the assembly. It gets activated by force of water and it strikes a small vane connected to it. The vane taps the sprinkler head and the head rotates under its force. Mostly slow rotation sprinklers are used for irrigating field crops.
The jet of water is thrown to a considerable distance due to combination of pressure and slow rotation. It enables to keep wide spacing between adjacent sprinklers. Further it permits use of nozzles having large orifices and minimizes problems of clogging.
The number of nozzles preferred depends upon the diameter of the wetted circle. Single nozzle sprinkler is used when water is to be applied at low rates.
Twin nozzle sprinkler head is one which is most commonly used. In this type one nozzle sprays water at a considerable distance while other nozzle covers the area near the sprinkler centre (Fig. 11.2). This type cannot apply water at as low a rate as single nozzle sprinkler system can. Twin nozzle sprinkler, however, is capable of applying water uniformly at low pressures.
Giant multiple nozzles sprinkler operates under high pressures. They are rotated by water-activated gear device. They usually have one large nozzle with smaller supplementary nozzles which fill the gaps in the spray pattern.
As a result they are best suited for close growing high plants, like sugarcane, where closer spacing of sprinklers is difficult. Generally giant sprinklers are limited to soils which have high infiltration rate. They are not suitable in regions having appreciable wind. They have low water distribution efficiency.
There is one more type of sprinkler called pop-up sprinkler. It is used for irrigating lawns (Fig. 11.4).
The sprinkler head is housed in a casing which is provided with a cover at the top. With cover closed the sprinkler is fixed on the lateral with the cover almost at the land surface. The cover opens by means of a retract spring when the sprinkler is in operation. The cover remains closed when the sprinkler is shut off.
Selection of Sprinkler Head:
Revolving head sprinklers are classified according to pressure range and their location in relation to irrigated crops. It is important that proper pressure is developed for sprinkler heads to be used. Too low or too high pressure for a particular type of sprinkler results in poor water distribution.
v. Perforated Pipes:
It is another method of developing spray. It consists of light weight, quick coupling portable pipes with small perforations in the upper third perimeter of the pipe. This assembly is capable of development of spray irrigation at quite low pressures. The rate of spray irrigation depends on the spacing of the perforations. It, however, gives a rate of 15 mm/hour.
The points in favour and against the use of this type are the following:
Points in Favour:
(i) It develops spray at low pressures.
(ii) Other conditions being favourable this system is preferred for under-tree application in orchards of coconut and other plantations.
Limitations:
(i) Due to high rate of application this system is suitable only on permeable sandy soils or for supplemental irrigation where depth of application per setting is not high.
(ii) Perforated pipes are not suitable in areas with high wind because it badly distorts the jets. purchase
(iii) It is suitable only on flat lands.
(iv) Small perforations get clogged quickly. It, therefore, requires frequent cleaning.
vi. Valves:
Take-off valves and Flow control valves. Take-off valves control the pressures in the laterals. With their use it becomes possible to maintain appropriate pressure in the laterals even though there is significantly high pressure in the main line. In multiple lateral systems they permit shifting of individual laterals without shutting down the sprinkler system completely.
Flow control valves regulate pressure and discharge of individual sprinkler. They are useful when undulating fields are likely to create unequal pressure distribution along the laterals. Normally they are not needed on level farms or fields with smooth slopes.
Term Paper # 3. Fertilizer Applicators of Sprinkler System:
In sprinkler system it is possible to do irrigation and fertilization simultaneously. To achieve this objective solution of chemical fertilizer is injected into the sprinkler system. By using fertilizer in solution with sprinkler irrigation water there is no danger of the fertiliser getting leached away.
This method enables fertiliser to reach desired depth in a soluble and readily available form to plants. The equipment used for injecting fertiliser is called fertiliser applicator.
When it is attached to sprinkler system the method of operation is as follows:
The sprinkler system is operated without turning on fertiliser injector valve till the soil and plant foliage is fully drenched. The fertiliser solution is then injected through the system. The strength of fertiliser solution is 30 : 1 parts by weight (i.e., in 30 kg of water 1 kg of fertiliser is dissolved).
The concentration of solution is so selected that fertiliser injection is completed in about 30 minutes. In the end injecting valve is closed again and system operated for about 20 minutes to flush it with clean water to protect sprinkler pipes from toxic effect of the fertiliser.
Fertiliser applicators used are simple in operation as well as fabrication. Two types of fertiliser applicators are used depending upon location where fertiliser solution is proposed to be injected.
i. Applicator Combined with Suction:
In this equipment an auxiliary suction pipe joins the main suction pipe, Fig. 11.5. Controlled by a valve the auxiliary suction pipe dips into a fertiliser solution tanks.
The fertiliser solution tank is fed with clean water by a lateral as shown in Fig. 11.5. Operation of this system is already explained. To prevent corrosion of impellers they are made of corrosion resistant material.
ii. Applicator Combined with Venturi:
This equipment comprises of a sealed tank, feeder pipe for feeding the tank with clean water, injector pipe, a venturi fixed in the main pipe and flow control valves (Fig. 11.6).
A venturi fixed in the main line Fig. 11.7 creates differential head and allows fertiliser solution to flow in the main pipe line from the sealed fertiliser tank.
Term Paper # 4. Types of Sprinkler System:
The sprinkler systems can be classified according to:
(a) Arrangement for spraying water, and
(b) Portability of the equipment.
That there are two systems for developing water spray namely, rotating head system and perforated pipe system.
i. Rotating Head System:
In this system either laterals are mounted on the posts above crop height or laid on the ground. Riser pipes are fixed at uniform intervals on the lateral pipes and nozzle heads are attached to the top end of riser pipes. The sprinkler heads are rotated due to impact given by a hammer and vane assembly. The hammer gets activated due to thrust of water which in turn strikes against a vane which rotates the head through occasional pushes.
ii. Perforated Pipe System:
In this system perforations are made in the lateral pipes to develop the spray. The system works on low operating pressures ranging from 0.5 kg /sq cm to 2.5 kg/sq cm. Due to workability of such low pressures it is possible to connect the system to an overhead tank to obtain necessary pressure head.
In this system since irrigation water is applied at a relatively high rate it is suitable for soils having moderately high infiltration rates. The perforated pipe sprays water on both sides and covers 6 to 15 metre sprip. This system is suitable for irrigating crops whose height does not exceed 40 to 60 cm. It is quite efficient in irrigating lawns, gardens and small vegetable fields.
On the criteria of portability, following types of sprinkler system are recognised:
iii. Permanent System:
It consists of permanently laid mains, susbmains and laterals. Also, the pumping unit is stationary since water source is also single. All pipe lines including laterals are buried sufficiently below in the ground so that they do not get damaged while ploughing. Sprinkles are permanently kept fixed on each riser. This system is generally adopted in orchards. It is expensive as compared to other types because it is used only on one farm.
Sometimes laterals are not kept buried but laid in the farm at the beginning of the crop season and is retained in position till the crop matures. This system is used for crops requiring short and frequent watering. It is called solid-set system to distinguish it from permanent system.
iv. Portable System:
It consists of main line, laterals and pumping unit which are all portable. The equipment is moved from field to field or from place to place in the same field to different water points. The pumping set is moved on a trolley. The mains and laterals can be moved either manually or by using mechanical power.
When moved manually it is moved pipe by pipe. Therefore although initial investment is less operation cost is high. The advantage of moving the pipe lines by mechanical power is that whole system can be moved as a unit on wheels. The cost of wheel move system adds to initial investment, however, labour requirement is less than hand move system.
v. Semi-Portable System:
It is similar to portable system except that the pumping plant is fixed on one water source permanently. Irrigation can be done by this system on more than one farm by extending the main line. It may also become necessary to use additional booster pumping set. As another category in some cases alongwith stationary pumping set main line and submains may also be permanently fixed. They are then kept buried. Only laterals are portable on which risers are located at suitable intervals for fixing the nozzles. It is called semi-permanent system.
Term Paper # 5. Design Data for Sprinkler Irrigation System:
In order to achieve high efficiency and economy it is necessary to plan and design the sprinkler irrigation system taking into consideration all relevant information.
The steps involved are as given below:
(i) A detailed map of the fields or farm area is a basic requirement. Once an accurate contour map is prepared it is possible to draw layout of the sprinkler irrigation system showing locations of water source, pumping unit and pipe lines. From the map difference of elevation from water source to highest point can be calculated which together with friction losses in pipe lines and pressure requirement of the sprinklers determines the pressure that must be developed by the pump.
(ii) A dependable source of water supply is absolutely essential. Sprinkler system can work on a well, tube well or surface source. It is necessary to ascertain availability of water to meet the seasonal as well as maximum crop needs of irrigated area. Water quality analysis is very important. Water should be chemically suitable, should not corrode the equipment and should be free from suspended impurities.
(iii) Sprinkler irrigation system is designed for daily peak rate of consumptive use of crops to be irrigated. To calculate consumptive use it is necessary to compile information about climatic parameters like temperature, humidity, wind velocity and radiation. Knowing the peak demand of crops in mm depth in the field its equivalent in terms of continuous flow in litres/sec/ha is calculated for design of pipe line.
(iv) Depth of irrigation is calculated on the basis of available moisture holding capacity of the soil and soil moisture consumption pattern of the crop. Procedure to work out irrigation water requirement. Irrigation interval in sprinkler irrigation system can be varied reducing or increasing the spraying time of one setting. For example 50 mm depth can be applied in 20 hours spraying time over a field and process repeated after interval of 20 days or alternatively 25 mm depth can be applied in 10 hours spraying time and then irrigation interval can be kept 10 days.
(v) That in sprinkler irrigation water application is limited by the infiltration capacity of the soil. Any amount of water applied in excess goes waste as run-off.
(vi) For ensuring uniform distribution of water by the sprinklers it is necessary to keep spacing between two adjacent sprinklers in such a way that their area of influence overlap appropriately. The amount of overlap depends on the prevailing wind velocity. More the velocity of wind more is overlap kept.
Term Paper # 6. Design Criteria for Sprinkler Irrigation System Layout:
In determination of location of pumping unit, orientation of mains and laterals following points should be given due consideration:
(a) When the source of water supply is a well it may be located at a high corner or preferably in the centre of the area to be irrigated to minimize the distance over which the water is to be pumped.
(b) When a field channel runs along one edge of a farm possibility may be explored to combine the farm on the other side in one setting of the sprinkler system. It helps in achieving efficiency and to cover more area with smaller length of laterals.
(c) For the well it is advantageous to select such a pump to be permanently installed at source, which has adequate capacity to lift the water, to provide necessary pressure to overcome friction loss in the pipes and to operate the sprinklers.
(d) In situations when field channel forms a source and it runs either on one edge or through the centre of the area to be irrigated, a portable pumping set and sprinkler unit with the lateral extending on one side of the channels may be used.
(e) Sometimes for underground main pipe lines it may be advantageous to use portable pumping plant with suction attached to the hydrants mounted on the pipe outlets.
(f) Layout of the mains depends on the location of a water source. The mains should be located in the general direction of the steepest slope.
(g) The laterals should normally be laid on level ground. The laterals should be laid at right angles to the alignment of the mains and should be as close as possible to the contour. If laterals are laid on the upgrade water pressure is lost in overcoming the potential head and water cannot be taken over reasonably long distances.
(h) In a system where laterals are moved, their movement should be planned in strictly sequential rotation from one end to the other downward on one side and then from far end to near end upward on the other side of a main pipeline or a field channel.
(i) There could be various alternative layouts possible but main consideration should be minimal investment in pipes, low labour requirement and working efficiency in spraying total area in the required period of time.
(j) Based on pressure limitation, application rates, sprinkler discharge, diameter of coverage and crop water requirement, type of sprinkler system is determined. Table 11.1 gives the characteristics and adaptability of different type of rotating head sprinkler.
(k) On the lateral, numbers of sprinklers are fixed at equals spacing. At the entrance end discharge is the maximum which goes on reducing towards farther end as each sprinkler successively takes away its share of flow. Friction loss in the lateral will be much less if it carries full discharge through its entire length.
This fact may call for tapering the diameter of the pipe towards far end. But in practice since same laterals are used on different farms under variable conditions the pipe diameter is kept uniform. The size of the lateral is so selected that total pressure variation between two ends is not more than 20% of the higher pressure.
(l) The main line is required to convey required quantity of water at desired pressure to all lateral lines under maximum pressure condition. The selection should be done on economic considerations. In practice main line friction loss of about 3 metres for small systems and 12 metres for large systems is allowed.
Term Paper # 7. Operation and Maintenance of Sprinkler System:
i. Principles of Operation:
For success of sprinkler irrigation proper operation of the system is essential.
Sound operation practice requires attention to following points:
(i) It should be ensured that prime mover and pump are in alignment. In case of tractor-driven pumps particularly the drive shaft and pump shaft should lie at nearly same height. It avoids formation of steep angle on the universal shaft.
(ii) Laying of mains and lateral should begin from pump site. It helps in quick and correct coupling of all pipes. Dismantling of installation for shifting should be done in reverse order, starting from far end.
(iii) Before starting the motor or the engine it should be ensured that all valves are closed. After pump attains designated pressure delivery valve should be opened slowly. When with valves closed the pump does not attain full pressure, it shows that there is a fault in suction line. After completing irrigation the delivery valve is closed first and then the power unit is switched off.
ii. Maintenance of Equipment:
a. Pipes and Fittings:
The pipes and fittings there-on constitute bulk of the hardware used in sprinkler system. They are stationary and sturdy components and virtually need no maintenance except for cleanliness and proper storage on racks. Rubber sealing rings on the couplings need to be removed and stored in a cool dark place.
b. Sprinkler Heads:
Heads are delicate type of equipment and care should be taken to make sure that while moving the pipe lines sprinklers are not damaged or dragged over the soil. The sprinklers are lubricated by water itself and oil, grease or any other lubricant should never be used. Washers of the sprinkler head are subject to wear and tear. They need replacement once in a season. In general at the end of the season the sprinklers are removed, thoroughly cleaned, all components checked for their good condition before they are stored in a cool dry place.
c. Pump:
At the end of the season, suction and delivery pipes are disconnected from the pump and small quantity of medium grade oil is applied. The pump is then rotated for a few minutes. The suction and delivery branches are then blanked off. On the shaft grease is applied. This prevents rusting of pump. Similarly electric motor is protected against ingress of dust, dampness and rodents.