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IRRIGATION ENGINEERING

IRRIGATION ENGINEERING. IRRIGATED AGGRICULTURE. WATER REQUIREMENTS OF CROPS. For its full and successful growth, every crop requires proper warmth, proper amount of water, proper agricultural soil, air and proper methods of cultivation.

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IRRIGATION ENGINEERING

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  1. IRRIGATION ENGINEERING IRRIGATED AGGRICULTURE

  2. WATER REQUIREMENTS OF CROPS • For its full and successful growth, every crop requires proper warmth, proper amount of water, proper agricultural soil, air and proper methods of cultivation. • The main crops growing in Pakistan are wheat, cotton, rice, maize, barley, cane etc. • The water requirement is different for different crops and also the different type of land is required for various crops. From agricultural point of view the soil is classified as, • Light soil • Medium or normal soil (10 - 20% clay contents) • heavy soil • This classification of soil depends on the clay content. If the clay contents are more, the more will be the water retentive power and vice-versa.

  3. WATER REQUIREMENTS OF CROPS • Heavy and retentive soil is suitable for crops like cane, rice etc. requiring more water, whereas light or sandy soil is suitable crops like wheat grain etc requiring less water. Normal and medium soil i.e. the one having 10 - 20% day content is suitable for crops like cotton, maize etc. • Some terminology used for the water requirements of the crops are following:

  4. WATER REQUIREMENTS OF CROPS • Base Period: It is defined as the time period between the First watering of a crop at the time of its sowing and the last watering, before its harvesting. • Crop Period: It is the time period between the sowing of a crop and its harvesting. Theoretically the crop period is more than the base period but practically we take it same.

  5. WATER REQUIREMENTS OF CROPS • Gross Commanded area of a Canal: It is the total area in the charge of a canal which may be cultivated by it. Gross Command Area of a Water Course (G.C.A.) It is the total area in the charge of a water course which may be cultivated by it. Cultivable Commanded Area (C.C.A.) It is the difference between the G.C.A and uncultureable area which is occupied by villages, roads, buildings and other uncultureable area which is occupied by villages, roads, buildings and other uncultureable land like alkaline water logged and barren lands. This is the area which can be cultivated.

  6. WATER REQUIREMENTS OF CROPS • Intensity of Irrigation It is the percentage of CCA proposed to be irrigated annually. As irrigation is done according to the crop season viz.,Rabi or Kharif, the precise definition of Intensity of Irrigation is the percentage of CCA irrigated at a time in one crop season.

  7. DUTY AND DELTA: • The water requirements of crops is on the basis of duty and delta concept. Each crop requires certain amount of water after fixed interval of time throughout its period of growth. As the amount of each watering and the interval of watering and hence the number of watering are fixed for each crop, the total quantity of water required by each crop is also fixed and is different for different crops. The depth of each watering is usually from 2 ½’ to 4’ depending on the kind of the crop. • The total depth of water in inches required by a crop to come to maturity is called Delta of the crop.

  8. DUTY AND DELTA • e.g. the depth of each watering for Rice =4” • Interval between each watering =10 days • Crop Period = 120 days •  Total No. of watering = 120=12 10 •  Total water required = 12 x 4 =48 •  = 48 = 4 ft. •  Total water required for “A” acres of land (on which Rice is cultivated = A = 4A acre - ft. • [ 1 Acre - ft = 43560 ft2 ]

  9. DUTY AND DELTA • The number of acres irrigated by the constant flow of one cusec (1 Cfs.) is called Duty of irrigation water during crop period. • Water supplied during the crop period of rice at the rate of 1 Cfs. = 120 crop period (24 x 60 x 60) x 1 = 10368000 ft3 •  Area of rice land irrigated by this water will be, • A = 10368000=2592000 ft2[1 acre = 4840 Yards2] • 4 • = 59.5 acres [1 acre = 43560 ft2] =60 Cfs. • This is the maturing capacity of this 1 Cfs. flow. Therefore the duty of irrigation water for rice is 60 acres/cusec on the field, the period being 120 days.

  10. DUTY AND DELTA • Duty of water at the head of water course is less than that on the field due to transit losses of water flowing from the head of water course and reaching the field. In order to supply net 1 cusec on the field, therefore, more than 1 Cfs. say 1.1 Cfs. must be admitted at the head of water course. This duty is called as outlet duty.

  11. Relation Between Duty and Delta: The relation between duty and delta is Delta= 1.98 B/D Where = delta for crop in feet B = Base period of crop in days D = Duty of irrigation water for crop in acres/Cfs.

  12. TABLE

  13. Factors affecting Duty 1. Soil Characteristics: If the soil of the canal bed is porous and coarse grained, it leads to more seepage loss and consequently low duty. If it consists of alluvial soil, the percolation loss will be less and the soil retains the moisture for longer period and consequently the duty will be high. 2. Climatic Condition: When the temperature of the command area is high the evaporation loss is more and the duty becomes low and vice versa.

  14. 3. Rainfall: If rainfall is sufficient during the crop period, the duty will be more and vice versa. 4. Base Period: When the base period is longer, the water requirement will be more and the duty will be low and vice versa. 5. Type of Crop: The water requirement for various crops is different. So the duty varies from crop to crop. 6. Topography of Agricultural Land: If the land is uneven the duty will be low. As the ground slope increases the duty decreases because there is wastage of water.

  15. 7. Method of Ploughing: Proper deep ploughing which is done by tractors requires overall less quantity of water and hence the duty is high. 8. Methods of Irrigation: The duty of water is high in case of perennial irrigation system as compared to that in inundation irrigation system. 9. Water Tax: If some tax is imposed the farmer will use the water economically thus increasing the duty. Various methods of improving duty are:

  16. (1) Proper Ploughing: Ploughing should be done properly and deeply so that the moisture retaining capacity of soil is increased. (2) Methods of supplying water: The method of supplying water to the agriculture land should be decided according to the field and soil conditions. For example, • Furrow method For crops sown ion rows • Contour method For hilly areas • Basin For orchards • Flooding For plain lands

  17. (3) Canal Lining: It is provided to reduce percolation loss and evaporation loss due to high velocity. (4) Minimum idle length of irrigation Canals: The canal should be nearest to the command area so that idle length of the canal is minimum and hence reduced transmission losses. (5) Quality of water: Good quality of water should be used for irrigation. Pollution en route the canal should be avoided. (6) Crop rotation: The principle of crop rotation should be adopted to increase the moisture retaining capacity and fertility of the soil.

  18. (7) Method of Assessment of water: Particularly, the volumetric assessment would encourage the farmer to use the water carefully. (8) Implementation of Tax: The water tax should be imposed on the basis of volume of water consumption.

  19. PROBLEM1 • The gross command area for a distributary is 15000 acre, 80% of which is cultivable. The intensity of irrigation for Kharif season is 25% and that for Rabi season is 50%. If the average duty at head of distributary is 50 acres/Cfs. for Kharif season and 120 acres/Cfs. for Rabi season. Find the discharge required at the head of distributary.

  20. PROBLEM1 • SOLUTION: • G.C.A = 15000acres • C.I.A = 15000*0.8 = 12000acres • Area to be irrigated during kharif season= 25%= 0.25*12000=3000acers • Area to be irrigated during rabi season = 50%=0.5*12000 = 600acres • Discharge for kharif = 3000/50 = 60cfs • Discharge during rabbi = 6000/120=50 cfs • Design discharge for distributry= 60cfs

  21. PROBLEM 2 • Some crops are irrigated from the water of a reservoir by means of the canal system. The necessary data about these crops is given below: Assuming 30% of losses of water in the entire canal system and 15% losses in the reservoir find the necessary live storage of the reservoir in acre-ft.

  22. PROBLEM 2 • Q = area/duty • And volume = Q*crop period • Total vol= 76100 • Total volume to be irrigated= 76100cfs-day • = 76100*24*60*60= 6.75*109 ft3 • 6.75*109 ft3 / 43560 = 150942.15 acre-ft • Losses in canal systems = 30% • Total volume in canals = 150942.15 * 100/70=215631.646 acre-ft • And volume of live storage = 100*2151631.64/85= 253684.24 acre-ft

  23. Problem3 • The C.I.A. of a water course is 300 acres. Intensities of sugarcane and wheat crops are 15% and 45% respectively. The duties for these crops at the head of water course are 50 acres/Cfs. and 130 acres/Cfs. respectively. Find the discharge required at the head of water course.

  24. Problem3 • Solution: • C.I.A = 300 acres • FOR SUGAR CANE: • Intensity = 15% • Therefore; • Area = 0.15 x 300 = 45 acres • Duty = 50 acres/cfs • Therefore; • Discharge = 45/50 = 0.9 cfs • FOR WHEAT: • Intensity = 35% • Therefore; • Area = 0.35 x 300 = 105 acres • Duty = 130 acres/cfs • Therefore; • Discharge = 105/130 = 0.81 cfs • Thus; • Total discharge required = 0.9 + 0.81 = 1.71 cfs

  25. Problem 4 • In a certain area, the transportation of rice crops tabs 15 days and the total depth of irrigation water required by the crop is 23” on the field. During this transplantation period the useful rain falling on the land is 3”. Find the duty of irrigation water for this crop on the field during the transplantation period. Also assume 25% losses of water in the water course. Find the duty at the head of water course.

  26. Problem 4 • Solution: • Total depth of water required by crop = 23” • Rainfall on the land = 3” • Therefore; • Net Depth of water required = 23 – 3 = 20” • Transplantation (Crop period) of rice = 15 days • Therefore; • Water supplied during crop period of 15 days @ 1cfs = 1 x 15 x 24 x 60 x 60 = 1296000 ft3 • This is the maturing capacity i.e Duty of this 1 cfs flow • Therefore; • Duty of water = 18 acres/cfs • Now assuming 25% losses at the head of water course • Therefore; • Water supplied @ 1cfs during 15 days • = 1 x 15 x 20 x 3000 x 0.75 = 972000 ft3 • Therefore;

  27. Problem 5 • Establish or find relation between duty and delta and hence find the delta for a crop when the field duty for it is 60 acres/cfs. The base period is 120 days. • Solution: • The relation between duty & delta is • Here; • B = 120 days & • D = 60 acres/cfs • Therefore;

  28. FORMULAS FOR CONSUMPTIVE USE: • Consumptive use = Evaporation + Transpiration • Evaporation and Transpiration are measured in terms of depth of water. The sum of these is the consumptive use of irrigated area to which it is supplied. • Effective need of water for crop is the water needed by the crop + evaporation + transpiration. Therefore we apply excessive water than that of water required by that crop, so that the effect of evaporation and transpiration may be compensated.

  29. Methods of Irrigation: • Sub Surface • Surface

  30. Sub-Surface Methods: • In this method water is supplied directly to root zone of plants, by a system of underground pipes laid below the land with their joints open. Water running through these pipes comes out through the open joints and keeps the root zone moist. • In this method loss of water due to absorption and evaporation is less but as it is expensive and gives less yield of crops, it is quite uncommon.

  31. Drip Irrigation:

  32. Drip Irrigation:

  33. Surface Methods: In surface irrigation systems, water moves over and across the land by simple gravity flow in order to wet it and to infiltrate into the soil. Surface irrigation can be subdivided into: • Free Flooding • Border Flooding • Furrow Method • Basin Method

  34. 1. Free Flooding: • The land is divided into suitable size plots by ridging. Each plot is practically levelled. Water is admitted at the higher or upstream end of the plot and when water reaches its downstream or the lower end of plot, the supply of water is cut off. • If the water is made to flow over the surface too quickly, an insufficient amount will percolate into the soil and if water is kept on surface too long, waste will result from persecution beyond the root zone. It is therefore difficult to apply water efficiently by flooding method.

  35. 2. Border Flooding: • Land is levelled and divided by about 1 high lunds into a number of 30 to 60 feet wide and 330 to 1320 feet long strips. Water is allowed at the head or upper end of each strip and it flows down along the strip in the form of a thin 2 inch to 3 inch sheet of water to the lower end of the strip.

  36. 3. Furrow Method: • The furrow method is usually useful for crops which are planted in rows, like onions chillies etc. and also for those crops which need open dry land for proper growth. In this method a number of furrows are laid out on the land with a plot between every two furrow. The water is the two neighbouring furrows percolates from their beds and sides and this saturates the root zone of the plants between two furrows. This method necessitates 1/2 to 1/5th of the surface being wetted with water thus reducing the evaporation losses.

  37. 4. Basin Method: • In this method a basin is excavated around a plant (e.g. a tree). the basin is filled with water which percolated gradually to the root zone.

  38. SPRINKLER IRRIGATION: • Sprinkler Irrigation is a method of applying irrigation water which is similar to rainfall. • Water is distributed through a system of pipes usually by pumping. It is then sprayed into the air and irrigated entire soil surface through spray heads so that it breaks up into small water drops which fall to the ground.

  39. SPRINKLER IRRIGATION (Cont): The conditions favouring sprinkler irrigation are • Soils too porous for good distribution by surface methods. • Shallow soils, the topography of which prevents proper levelling for surface irrigation method. • Land having steep slopes and early errodable soils. • Undolating land, too costly to level sufficiently for good surface irrigation. • Labour available for irrigation is either not experienced in surface methods of irrigation or is unreliable.

  40. Types of Sprinklers: • Fixed Nozzles attached to Pipes • Perforated Pipes • Rotating Sprinklers

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