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IRRIGATION ENGINEEERING5th Semester III YearDepartment of Civil Engineering Lecture Slides by SARAVANAN.J B.E Anna University UNIT I INTRODUCTIONIrrigation Need & mode of irrigation Merits & demerits of irrigation Crop & crop seasons Consumptive use of water Duty Factors affecting duty Irrigation efficiencies Planning and development of irrigation projects2IRRIGATIONGeneral: Its the process of artificially supplying water to soil for raising corpsScience: Its a science of planning and designing an efficient, low-cost, economic irrigation system that suits to the natural conditionsEngineering: Its the engineering of controlling and utilizing of various natural sources of water by constructing dams-reservoirs; canals-headworks and finally distributing the water to agricultural fields 33NEED OF IRRIGATIONLess rainfall (Rajasthan canal-100mm to 200mm) Non-uniform rainfall (Most of Indian projects)Growing a number of crops during a yearGrowing perennial crops (sugar cane)Commercial crops with additional waterControlled water supply

4MODES OF IRRIGATION

5FLOW IRRIGATIONIts the type of irrigation in which the supply of irrigation water available is at such a level that it can be conveyed on to the land by the gravity flow.Two different classifications exists:General classification:Perennial Irrigation: Required water is supplied according to crop requirement throughout the crop period.Inundation Irrigation: Deep flooding is carried out to the cultivating land and after complete saturation, drained off prior to planting. 6Its the type of irrigation in which the supply of irrigation water available is at such a level that it can be conveyed on to the land by the gravity flow.Classification upon the source:Direct Irrigation (or) River canal irrigationStorage Irrigation (or) Tank IrrigationCombined storage & direct Irrigation

FLOW IRRIGATION7

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11LIFT IRRIGATIONIts practised when the water supply is at too low a level to run by gravitation on to the land. The lifting is done by mechanical means.(e.g.) Irrigation from wells.

Choice between the systems:Direct irrigation = Perennial riversStorage irrigation = Partially insufficient riversCombined irrigation = Multistage river valley project 12

13MERITS OF IRRIGATIONGeneral development of the countryIncrease in food productionElimination of mixed croppingAddition to the wealth of the countryIncrease in prosperity of peopleGeneration of Hydro-electric powerImprovements of communicationInland navigationCanal plantationImprovement in the ground water storage

14DEMERITS OF IRRIGATIONBreeding places for mosquitoesWater-LoggingDamp climate15CROPS Crops can be classified as follows:

Agricultural Classification:

Field crops: Wheat, rice, maize, barley, oatsCommercial crops: Sugar cane, cotton, tobaccoOil seed crops: Mustard, ground nut, sesameHorticulture crops: Fruits-vegetable-flowerPlantation crops: Tea, coffee, cocoa, coconutForage crops: Fodder, grass

16CROPSClassification based on crop seasons:

Rabi crops (winter crops) :Sown in autumn, harvested in March.(e.g.) gram, wheat, barleyKharif crops (monsoon crops):Sown in monsoon beginning, harvested in October. (e.g.) rice, maize, ground nutPerennial crops: Which needs irrigation water throughout the year(e.g.) sugar cane, fruits, vegetables8 month crops: (e.g.) cotton

17CROPSClassification based on irrigation requirements:

Dry crops: No need of irrigation water.

Wet crops: Cannot exist without irrigation water.

Garden crops: Which requires irrigation throughout the year.18

19CONSUMPTIVE USE OF WATEREvapo-transpiration (or) consumptive use of water by a crop is the depth of water consumed by evaporation and transpiration during crop growth, including water consumed by accompanying the weed growth.

Evaporation: Its the transfer of water from the liquid state to vapour state. The rate of evaporation from water surface is proportional to the difference between the vapour pressure at the surface and the vapour pressure in the overlying air Daltons law.20Transpiration: Its the process by which plants dissipate water from the surface of their leaves, stalks and trunks in the process of growth. Transpiration is associated with photosynthesis of plants.

Transpiration Ratio: Its the ratio of the weight of water transpired by the plant during its growth to the weight of dry matter produced by the plant exclusive of roots. The average values of transpiration ratio for wheat and rice are 560 and 680.CONSUMPTIVE USE OF WATER21FACTORS AFFECTING CONSUMPTIVE USE OF WATEREvaporation, which depends upon humidity.Mean monthly temperature.Growing season of crop & cropping pattern.Monthly precipitation in the area.Irrigation depth (or) the depth of water applied for irrigation.Wind velocity in the locality.Soil and topography.Irrigation practices and method of irrigation.

22PET - AETPET: If sufficient moisture is always available to completely meet the needs of the plants, the resulting evapo-transpiration is called potential evapo-transpiration.AET: The real evapo-transpiration occurring in a specific situation is called actual evapo-transpiration.At the moisture content in the soil corresponding to field capacity, the water supply to the plant is adequate and hence AET/PET = 1.AET/PET reduces with respect to the reduction of moisture content available.

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24MEASUREMENT OF CONSUMPTIVE USE OF WATEREquation Methods:Blaney-Criddle methodPenman methodHargreaves class A pan evaporation methodPrincipal Methods:Tank and lysimeter methods. (10m2 and 3m deep)Field experimental plots. (break point)Soil moisture studies.Integration method.Inflow and outflow studies for large area.

25DUTY & DELTADuty: Its the irrigating capacity of a unit of a water.It gives a relationship between . . . .- Area of a crop to be irrigated - Required irrigation water for growing of a cropDelta: Its the total depth of water required by a crop during its growing in the field.Crop period: Its the time, (in days) that a crop takes from the instant of its sowing to that of its harvesting.Base period: For a crop, its the time from the first supply of irrigation water for the ground preparation to the last supply before the harvesting.

26Relationship b/w Duty & Delta27FACTORS AFFECTING DUTYMethods and systems of irrigationMode of applying water to the cropsMethod of cultivationTime and frequency of tillingType of the cropBase period of the cropClimatic conditions of the areaQuality of waterMethod of assessment of irrigation methodCanal conditionsCharacter of soil and sub-soil of the canalCharacter of soil and sub-soil of irrigation fields28METHODS OF IMPROVING DUTYSuitable method of applying water to the crops should be used.The land should be properly ploughed and leveled before sowing.The land should be cultivated frequently.The canals should be lined.The rotation of crops should be practiced.The alignment of the canals in sandy soils and fissured rocks should be avoided.

29SOME TERMSKor depth: During subsequent watering, the quantity of water needed by crops gradually decreases and is least when crop gains maturity. The first watering is known as kor-watering and the depth applied is kor-depth.Kor period: The portion of base period in which kor-watering is needed is known as kor-period.Outlet factor: Its defined as the duty at the outlet.

30Time factor: Its defined as the ratio of the number of days, the canal has actually run to the number of days of irrigation period.Capacity factor: This is the ratio of the mean supply to the full supply of a canal.Cumec-Day: The quantity of water flowing for one day at the rate of 1 Cumec is known as a cumec-day. Its equal to 8.64 hectare-metres. SOME TERMS31Paleo: Its the first watering before sowing the crop. This is done in order to add sufficient moisture to the unsaturated zone of the soil and is required for the initial growth of crops.Full supply coefficient: Its defined as the area estimated to be irrigated during the base period divided by the design full supply discharge of the channel at its head during maximum demand. This is also known as duty on capacity.Nominal duty: Its the ratio of the area of which the permit has been granted for the period divided by the mean supply for the base periodSOME TERMS32Open discharge: Its the ratio of number of cumec-days to the number of days the canal has actually been used for irrigation.

Root zone depth: Its the maximum depth of soil strata in which the crop spreads its root system and derives water from the soil.SOME TERMS33IRRIGATION EFFICIENCIESIts the ratio of water output to the water input and is expressed as %. Various irrigation efficiencies are:Water Conveyance EfficiencyWater Application EfficiencyWater Use EfficiencyWater Storage EfficiencyWater Distribution EfficiencyConsumptive Use Efficiency

34Water Conveyance EfficiencyIt takes into account the conveyance or transit losses.

c = ( Wf / Wr ) * 100

c = Water conveyance efficiencyWf = Water delivered to the farm or irrigation plotWr = Water supplied or delivered from the river / reservoir.

35Water Application EfficiencyIts the ratio of the quantity of water stored into the root zone of the crops to the quantity of water delivered to the field.

a = ( Ws / Wf ) * 100 a = Water application efficiencyWs = Water stored in the root zone during the irrigationWf = Water delivered to the farm36It should be atleast 60% for a well designed irrigation system.Factors causing low application efficiency:Irregular land surfacesShallow soils underlain by gravels of light permeabilityEither large or small irrigation streamsNon-attendance of water during irrigationLong irrigation runsWrong irrigation methodsImproper preparation of landWater Application Efficiency37Water Use EfficiencyIts the ratio of water beneficially used to the quantity of water delivered.

u = ( Wu / Wd ) * 100u = Water use efficiencyWu = Water used beneficiallyWd = Water delivered38Water Storage EfficiencyThe concept of water storage efficiency gives an insight to how completely the required water has been stored in the root zone during irrigation. s = ( Ws / Wn ) * 100

s = Water storage efficiencyWs = Water stored in root zone during irrigationWn = Water needed in the root zone prior to irrigation39Water Distribution EfficiencyIt evaluates the degree to which water is uniformly distributed throughout the root zone. d = 100 [1 y/d ]d = Water distributed efficiencyy = Average numerical deviation in depth of water stored from average depth stored during irrigationd = Average depth of water stored during irrigation40Consumptive Use EfficiencyIt evaluates the loss of water by deep percolation and by surface evaporation following an irrigation.cu = ( Weu / Wd ) * 100cu = Consumptive use efficiencyWeu = Normal consumptive use of waterWd = Net amount of water depleted from root zone of soil41Planning and Development of Irrigation ProjectInitially we need to know what all are the purposes for which an irrigation development project shall be started.Then, we have to have the basic knowledge about the ways ( or classification) in which we can development of projects.Next, we have to finalize our objectives for which we are developing our water resource project.Then, list out the functional requirements in multi-purpose projects.Finally, the process of project formulation shall be carried out.42Irrigation:Crop growth including cultivation of cash cropsLand reclamationSalinity controlPollution Control:Prevention of salt water intrusionWaste water dilutionSoil Conservation:Erosion controlSedimentation controlWatershed managementWater Transport:NavigationPort or harbor

Purposes of Water Resource Development 43Purposes of Water Resource Development Flood Control:Reservoirs and detention basisEmbankments (or) dikesFlood diversionRiver channel improvementsWatershed managementFlood zoningFlood forecasting and warningHydropower Generation:Run-of-river and storage projectsHydropower from pumped storageTidal powerMunicipal and Industrial water supply:Surface water developmentGround water developmentWater desalination44Classification of Water Resource Development ProjectSingle purpose project: Irrigation Power generation Flood controlMultipurpose project: Serves 2 or more purposes. Such as storage and irrigation; storage and industrial uses; storage and power generation; inland navigation; flood control; preservation and cultivation.Objectives of Multipurpose projects:To enhance national economic development by increasing the output of goods and services.To enhance regional development through increase in regions income, employment, economic base.45Functional Requirements in Multi-Purpose ProjectsRequirements for Irrigation

Requirements for Domestic supply

Requirements for Industrial uses

Requirements for Hydro-electric power

Requirements for Flood control

Requirements for Navigation46Process of Project FormulationThe development process for water resources projects comprises of formulation, construction and operation of a project. Its the dynamic process that includes,

Problem identification and statement of objectivesSolution identificationProjection for planningDefinition of alternativesEvaluation of alternative projectsComparison of alternative projectsSelection of a project47