Solution for Irrigation Engineering December 2015 Index Q.1) a). 2-3 b).3-5 c).5-6 d).6-8 e).9-10 Q.2) a).10-11 b). 12-14 c). 14-15 Q.3) a). 15-16 b). 17 c). 18 Q.4) a). N.A b). N.A c). N.A Q.5) a).20-22 b).22-24 c). 25 d). 26-27 Q.6) a). N.A b). 28-19 1 www.brainheaters.in
Q1) (a) Define irrigation and irrigation engineering and explain the necessity of irrigation in India. (5 mks ) Irrigation: The process of irrigation can be defined as, It is the process of supplying water to the land by using artificial equipment, for the purpose of cultivation. The basic aim of irrigation is to supplement the natural supply of water ie. rainfall, to get maximum yields of the crops grown on that field. Irrigation Engineering: The technology adopted by an Irrigation Engineer, to develop a total irrigation system is called as Irrigation Engineering. 2 www.brainheaters.in
Defination: (b) Define hydrology and explain with neat sketch hydrological cycle. (5 mks) 3 www.brainheaters.in
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Solution: (c) Explain the terms : aquifer, aquiclude and aquifuge. (5 mks) 5 www.brainheaters.in
Solution: (d) What are the various forces that acts on gravity dam, explain each of them. (5 mks) 6 www.brainheaters.in
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Solution: (e) What do you understand by canal lining state its advantages. (5 mks) 9 www.brainheaters.in
Q2) Solution: (a) Derive relation between duty, delta. (5 mks) 10 www.brainheaters.in
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Ans: (b) An irrigation canal has gross command are of 80,000 hectares out of which 85% is cultivate command area.the intensity of irrigation for Kharif crop is 30% and for rabi crop is 60%.Find the discharge required at the head of the canal if the duty at its head is 800 hectares/cumec for kharif and for rabi is 1700 hectares / cumec.(8 mks) 12 www.brainheaters.in
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(c) Describe the drip irrigation also state what are the favourable conditions to use irrigation and sprinkler irrigation. (7 mks) AnS: Drip irrigation is a form of irrigation that saves water and fertilizer by allowing water to drip slowly to the roots of many different plants, either onto the soil surface or directly onto the root zone, through a network of valves, pipes, tubing, and emitters. It is done through narrow tubes that deliver water directly to the base of the plant. It is chosen instead of surface irrigation for various reasons, often including concern about minimizing evaporation. Components used in drip irrigation (listed in order from water source) include: Pump or pressurized water source Water filter(s) or filtration systems: sand separator, Fertigation systems (Venturi injector) and chemigation equipment (optional) Backwash controller (Backflow prevention device) Pressure Control Valve (pressure regulator) Distribution lines (main larger diameter pipe, maybe secondary smaller, pipe fittings) Hand-operated, electronic, or hydraulic control valves and safety valves Smaller diameter polytube (often referred to as "laterals") Poly fittings and accessories (to make connections) Emitting devices at plants (emitter or dripper, micro spray head, inline dripper or inline driptube) Favourable conditions for using drip irrigation and Sprinkle irrigation 1 Suitable crops Drip irrigation is most suitable for row crops (vegetables, soft fruit), tree and vine crops where one or more emitters can be provided for each plant. Generally only high value crops are considered because of the high capital costs of installing a drip system. 14 www.brainheaters.in
2 Suitable slopes Drip irrigation is adaptable to any farmable slope. Normally the crop would be planted along contour lines and the water supply pipes (laterals) would be laid along the contour also. This is done to minimize changes in emitter discharge as a result of land elevation changes. 3 Suitable soils Drip irrigation is suitable for most soils. On clay soils water must be applied slowly to avoid surface water ponding and runoff. On sandy soils higher emitter discharge rates will be needed t o ensure adequate lateral wetting of the soil. 4 Suitable irrigation water One of the main problems with drip irrigation is blockage of the emitters. All emitters have very small waterways ranging from 0.2-2.0 mm in diameter and these can become blocked if the water is not clean. Thus it is essential for irrigation water to be free of sediments. If this is not so then filtration of the irrigation water will be needed. Blockage may also occur if the water contains algae, fertilizer deposits and dissolved chemicals which precipitate such as calcium and iron. Filtration may remove some of the materials but the problem may be complex to solve and requires an experienced engineer or consultation with the equipment dealer. Drip irrigation is particularly suitable for water of poor quality (saline water). Dripping water to individual plants also means that the method can be very efficient in water use. For this reason it is most suitable when water is scarce Q3) Solution: (a) State methods of computing average rainfall over the basin and explain any one of them. (5 mks ) 15 www.brainheaters.in
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Solution: (b) What is unit hydrograph and S hydrograph.state significance of each one. (6 mks) 17 www.brainheaters.in
(c) The ordinates of a 4 hr unit hydrograph are given below.determine the ordinates of 12 be unit hydrograph (9 mks). Time (hour) Ordinate in m 3 /sec 0 4 8 12 16 20 24 28 32 36 40 44 0 24 84 159 184 151 103 64 36 17 6 0 Solution: Similar sum 18 www.brainheaters.in
Q4) Ans: N.A (a) Derive an equation for discharge from well in an unconfined aquifer.(6 mks ) (b) A 40 cm diameter well fully penetrates and unconfined aquifer whose bottom is 75 m below the undistributed ground water table.when pumped at a steady rate of 1.40 m 3 /min. The draw downs observed in observation wells at radial distance of 4 m and 14 m are 4m and 2m respectively.determine the draw down in the well. (9 mks) Ans: N.A Ans: N.A (c) Explain recuperation test. (5 mks) 19 www.brainheaters.in
Q5) (a) What do you mean by reservoir sedimentation.state methods to control sedimentation. (5 mks) 20 www.brainheaters.in
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(b) Distinguish with neat sketches between. (5 mks ) (i) Low gravity dams and high gravity dams. 22 www.brainheaters.in
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(ii) Theoretical and practical profile of gravity dams. 24 www.brainheaters.in
Solution: (c) Explain causes of failure of earth dam. (6 mks) 25 www.brainheaters.in
(d) Describe usefulness of arch dam and buttress dam. (4 mks) Ans: 26 www.brainheaters.in
Q6) Ans: N.A (a) Design an irrigation channel to carry a discharge of 40 cumec Take N= 0.0225 and critical velocity ratio as 1.The channel bed slope is 0.20 meters per kilometres. (11mks) 27 www.brainheaters.in
(b) Write short note on diversion head works with sketch (9 mks) Ans: It was stated earlier that the main permanent canal, forming the primary part of a direct irrigation scheme, takes off from a diversion weir. or a barrage. In fact, these permanent canals take off from rivers and the arrangements are so well made-at their heads, that a constant and a continuous water supply is ensured into- the canal, even during the periods of low flow. The works, are constructed at the head of the canal, in order to divert the river water towards the canal,. so as to ensure a regulated.. Continuous supply of silt-free water with a certain minimum -head into the canal, are known as Diversion Head Works. The Diversion Weir and its Types.: Alignment. As stated earlier, a soon weir or an any cut _or an intake weir is a raised pucca structure with or without shuttle and laid across the river width. It is, essentially, of a height-say up to 9 metres or so. The height of shutters over the weir crest seldom exceeds 1.2 metres or so. The entire length.er the weir is divided into a number of bays by means of divide piers so as to avoid crossflower in floods. As far as possible, the weirs should be aligned at right angle to the direction the main river current. This ensures lesser length of the weir, better discharging capacity and lesser cost. This right-angled alignment is better and, therefore, common, especially~ when the river bed is silty or sandy. Sometimes, the weir may be aligned at an oblique to the direction of the river current, and thereby, obtaining more safe and better foundation In such a case, the weir will be of greater length, will have less discharging power and will be costlier. Moreover, due to non-axial flow, cross-currents may be developed, which undermine the weir foundation. An oblique alignment may sometimes become necessary, when the river bed consists of gravel and shingle, which could otherwise enter the head regulator of the main canal and get deposited into the head reach of the main canal. Types of Weirs. The weirs may be divided into the following three classes: (i) Masonry weirs with vertical drop (ii) Rock-fill weirs with sloping aprons and (iii) Concrete weirs with sloping glacis. 28 www.brainheaters.in
Layout of a Diversion Head Works and its components A typical layout of a canal head-works is shown in figure below. Such a headworks consists of: Weir proper Under-sluices Divide wall River Training works Fish Ladder Canal Head Regulator River Training Works e.g. Guide bank, Marginal bunds, spur and groyne etc. Shutters and Gates Silt Regulation Works 29 www.brainheaters.in