CE2301-NOL

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CE 2301-Irrigation Engineering (Notes)Importance of Irrigation

Definition the supply of water to crops and landscaping plants by

artificial means Estimates of magnitude

world-wide: 544 million acres (17% of land 1/3 of food production)

Purpose Raise a crop where nothing would grow otherwise (e.g., desert areas) Grow a more profitable crop (e.g., alfalfa vs. wheat) Increase the yield and/or quality of a given crop (e.g., fruit) Increase the aesthetic value of a landscape (e.g., turf, ornamentals)

Reasons for yield/quality increase Reduced water stress Better germination and stands Higher plant populations More efficient use of fertilizer Improved varieties

Other Benefits of Irrigation Leaching of salts Frost protection Plant/soil cooling



Chemical application Wind erosion control Waste disposal

Types of Systems Sprinkler

pressurized irrigation through devices called sprinklers (water isdischarged into the air and hopefully infiltrates near where itlands)

used on agricultural and horticultural crops, turf, landscapeplants

Surface Irrigation water flows across the field to the point of infiltration primarily used on agricultural crops and orchards

Micro (drip, trickle) frequent, slow application of irrigation water using pressurized

systems used in landscape and nursery applications, and on high-value

agricultural and horticultural crops

Water Measurement Volume

Quantity of water; Water at rest Gallon, cubic foot, etc. V = A d (units: acre-inch, acre-foot, hectare-meter etc.)

Depth Rainfall measured as depth; Useful for irrigation applications as

well Inch, foot, millimeter, centimeter, etc. D = V / A (units: usually inches or millimeters)

Flow Volume of water per unit time; Water in motion Gallons per minute, cubic feet per second, acre-inches per day,

liters per second, cubic meters per second etc. Q = V / t (units must be consistent)



Soil Water Relationships Texture

Definition: relative proportions of various sizes of individualsoil particles

USDA classifications Sand: 0.05 2.0 mm Silt: 0.002 - 0.05 mm Clay:



Soil water content

Mass water content (m) m = mass water content (fraction) Mw = mass of water evaporated, g (24

hours @ 105oC) Ms = mass of dry soil, g Equivalent depth of water (d) d = volume of water per unit land area = (v A L) / A = v L d = equivalent depth of water in a soil layer L = depth (thickness) of the soil layer

Soil Water Potential Description

Measure of the energy status of the soil water Important because it reflects how hard plants must work to

extract water Units of measure are normally bars or atmospheres Soil water potentials are negative pressures (tension or suction) Water flows from a higher (less negative) potential to a lower

(more negative) potentialIrrigation SchedulingGeneral Approaches

Maintain soil moisture within desired limits direct measurement moisture accounting

Use plant status indicators to trigger irrigation wilting, leaf rolling, leaf color canopy-air temperature difference

Irrigate according to calendar or fixed schedule Irrigation district delivery schedule Watching the neighbors

sw

m MM



Canals: Conveyance of water, open and closed conduits. Canals and tunnelsfunctions and classification of canals, canal alignment, balancing depth.design of lined canals, design of unlined canals, critical velocity, regimecanals, Kennedys and Laceys theories, advantages of lines canals, methodof lining. Design of lines canals..Lining of Irrigation CanalsMost of the irrigation channels in Iraq are earthen channels. Themajor advantage of an earth channel is its low initial cost, these sufferfrom certain disadvantages, like the following:-1- Maximum velocity limited to prevent erosion.2- Seepage of water into the ground.3- Possibility of vegetation growth in banks, leading to increased friction.4-Possibility of bank failure, due to erosion.5-More maintenance requirement.Types of Canal LiningTypes of lining are generally classified according to the materialsused for their construction. Concrete, rock masonry, brick masonry,bentonite-earth mixtures, natural clays of low permeability, and differentmixtures of rubble, plastic, and asphaltic materials are the commonlyused materials for canal lining. The suitability of the lining material isdecided by:A- Economy.B- Structural stability.C- Resistance to erosion.E- Durability.F- Hydraulic efficiency.[A] Concrete Lining[B] Precast concrete lining[C] Shotcrete Lining[D] Bricks, Tiles and Stone lining[E] Asphaltic Lining[F] Earth Linings1- Stabilized Earth LiningsSub-grade is stabilized using either clay for granular subgrade or byadding chemicals that compact the soil.



2- Loose Earth BlanketsFine grained soil is laid on the sub grade and evenly spread. However,this type of lining is subject to erosion, and requires a flatter side slopesof canal.3- Compacted Earth LiningsThe graded soil containing about 15 percent clay is spread over thesubgrade and compacted.4- Buried Bentonite MembranesBentonite is a special type of clay soil, found naturally, which swellconsiderably when wetted.5- Soil-cement Linings:These linings are constructed using cement (15 to 20 per cent byvolume) and sandy soil (not containing more than about 35 per cent of siltand clay particles). Cement and sandy soil can be mixed in place andcompacted at the optimum moisture content. This method of constructionis termed the dry-mixed soil-cement method.3- Failure of Canal LiningThe main causes of failure of lining are the water pressure thatdeveloped behind the lining material due to high water table, saturationof the embankment by canal water, sudden lowering of water levels in thechannel, and saturation of the embankment sustained by continuousrainfall. When the water level in canal was raised and lowered the bankssuffering from instability due to erosion and seepage through the banksmay be occurs. In order to minimize the seepage, a secondary berms wereconstructed along the length of bank at various locations.Diversion head works: Weirs and Barrages, Layout of diversion headworks and components, failure of hydraulic structures on previousfoundations, Blighs Creep theory, Lanes weighted theory and Khoslastheory, concept of low net, u/s and d/s cutoffs and protection measures,design of vertical drop weir.Canal Structures: Types of falls and their location, design principles andTrapezoidal notch fall, siphon well drop, straight glacis fall. Canal regulationworks, alignment of off taking canal. Distributary head regulators and crossregulation and their design. Canal escapes, types of metering flumes, typesof canal modules and proportionality, sensitivity, flexibility.



Cross Drainage Works: Definition, classification, design principles ofaqueducts, siphon aqueducts, canal siphons, super passages and inlet andoutlets, selection of cross drainage works.Bridges and Culverts: Discharge, Waterway and sour depth computations,Depth of Bridge foundation, spans and vertical clearance, effluxcomputations, pipe culverts and box culverts.Water Power: Classification of Hydropower plants, definitions pf terms,load, head, power, efficiency, load factor, installed capacity, utilizationfactor, capacity factor, use of mass curve and flow duration curve.Components of power plant-intakes, fore/bay, penstocks, functions and typesof sewage tanks, General arrangement of power house, sub-structure andsuper-structure..Design of Hydraulic StructuresDesign of Hydraulic StructuresCOURSE Contents1. Introduction2. Gravity Dams Site selection, Forces,Stability analysis.3. Diversion Works Weirs and Barrages4. Canals Design and Canal Falls.5. Cross Drainage Works6. Head Regulators and Cross regulatorsIS CodesIS Code 6512: Criteria for Design of Solid Gravity DamsIS Code 1893: Criteria for Earthquake Resistant Design of StructuresIS Code 7784-Cross-Drainage Works: Part 1 - GeneralIS Code 7784- Cross-Drainage Works: Part 2 - AqueductIS Code 7784- Cross-Drainage Works: Part 2 Syphon AqueductIS Code 7784- Cross-Drainage Works: Part 2 Canal SyphonIS Code 7784- Cross-Drainage Works: Part 2 SuperpassageIS Code 7784- Cross-Drainage Works: Part 2 Level CrossingCEL351: Design ofWhy study Hydraulic Structures?INTRODUCTIONDevelopment of water resources of a region



RequiresConceptionPlanningDesignConstructionOperationof various facilities to utilise and control water, andto maintain water quality.Utilize/Need waterDomestic & Industrial usesIrrigationPower generationNavigationOther purposesWater Resources EngineeringUtilisation of waterControl of waterWater quality managementWater is controlled and regulatedFlood controlLand drainageSewerageBridgesNot cause damage to property, inconvenience to thepublic, or loss of lifeWater-quality managementRequired quality of water for different usesPreserve Ecological balanceContamination of Groundwater/Surface waterWater Resources development projects are plannedto serve various purposesMain PurposesDomestic & Industrial uses, IrrigationPower generation, Navigation, Flood controlSecondary PurposesRecreational, Fish and wild life, Drainage control,Watershed management, Sediment control,Salinity control, Pollution abatementMiscellaneous Purposes



Employment, Accelerate development etcSingle-purpose andMulti-purposeWater Resources projects Two Main StepsFirst step How much water is available?Knowledge of HydrologyPrecipitation averageAbstraction LossesRunoff, Yield of basinFlood Peak runoffReservoir sizing Mass curveSecond step How to utilise and control water?Require various structureHydraulic StructuresTypes of Hydraulic StructuresStorageDiversionTransportationRegulationControlMain source of water is PrecipitationPrecipitation is not uniform over space and timeMonsoon, North East, Himalaya, W. GhatStore water at surplus location during surplusperiod Storage structures ReservoirsDam and Reservoir coexistDam solid barrier across riverReservoir artificial lake u/s of damReservoirDamReservoirDam SpillwayRESERVOIRS RESERVOIRSTypes of Reservoirs Single-purpose and Multi-purposeStorage (or conservation) reservoirsFlood control reservoirsMultipurpose reservoirDistribution reservoirsBalancing reservoirs



Flood Control runoff exceeding safe capacity ofriver is stored in the reservoir. Stored water isreleased in controlled mannerDetention Reservoirs regulated by GATESAdv: More flexibility of operation and better control ofoutflow; Discharge from various reservoirs can be adjustedDisadv: More expensive; Possibility of human errorRetarding Reservoirs UNGATESAdv: Less expensive; Outflow is automatic so possibility ofhuman errorDisadv: No flexibility of operation; Discharge from variousreservoirs may coincide heavy floodMultipurpose ReservoirsServe two or more purposes. In India, most of the reservoirsare designed as multipurpose reservoirs to store water forirrigation and hydropower, and also to effect flood controlDistribution ReservoirsSmall storage reservoirs to tide over the peak demand ofwater. The distribution reservoir is helpful in permittingthe pumps to work at a uniform rate. It stores waterduring the period of lean demand and supplies the sameduring the period of high demand. As the storage islimited, it merely helps in distribution of water as perdemand for a day or so and not for storing it for a longperiod. Distribution reservoirs are mainly used formunicipal water supply but rarely used for the supply ofwater for irrigation.RESERVOIRS RESERVOIRSMultipurpose ReservoirsServe two or more purposes. In India, most of the reservoirsare designed as multipurpose reservoirs to store water forirrigation and hydropower, and also to effect flood controlDistribution ReservoirsSmall storage reservoirs to tide over the peak demand ofwater. The distribution reservoir is helpful in permittingthe pumps to work at a uniform rate. It stores water



during the period of lean demand and supplies the sameduring the period of high demand. As the storage islimited, it merely helps in distribution of water as perdemand for a day or so and not for storing it for a longperiod. Distribution reservoirs are mainly used formunicipal water supply but rarely used for the supply ofwater for irrigation.RESERVOIRS RESERVOIRSBalancing ReservoirsA balancing reservoir is a small reservoir constructed d/s ofthe main reservoir for holding water released from themain reservoir.RESERVOIRS RESERVOIRSStorage Capacity of ReservoirsStorage capacity of a reservoir depends upon the topography ofthe site and the height of dam.Engineering surveysThe storage capacity and the water spread area at differentelevations can be determined from the contour map.In addition to finding out the capacity of a reservoir, thecontour map of the reservoir can also be used to determinethe land and property which would be submerged when thereservoir is filled upto various elevations.To estimate the compensation to be paid to the owners of thesubmerged property and land. The time schedule,according to which the areas should be evacuated, as thereservoir is gradually filled, can also be drawn..RESERVOIRS RESERVOIRSStorage Capacity of a ReservoirBoth the elevation-area curve and the elevation- storage curve onthe same paper. Abscissa - areas and volumes - oppositedi tiArea-Elevation Curve from contour map Anelevation-area curve isthen drawn betweenthe surface area asabscissa and theelevation as ordinate.



Elevation-CapacityCurve: is determinedfrom elevation-areacurve using diffformulae.Storage Capacity calculation formulae1. Trapezoidal formula2. Cone formula3. Prismoidal formula4. Storage Volume from cross-sectional areasBasic Terms and Definitions1. Full reservoir level (FRL): is the highest water level to whichthe water surface will rise during normal operatingconditions. Also called the full tank level (FTL) or thenormal pool level (NPL).2. Maximum water level (MWL): is the maximum level to whichthe water surface will rise when the design flood passes overthe spillway. Also called the maximum pool level (MPL) ormaximum flood level (MFL).3. Minimum pool level: is the lowest level up to which the wateris withdrawn from the reservoir under ordinary conditions.It corresponds to the elevation of the lowest outlet (orsluiceway) of the dam. However, in the case of a reservoir forhydroelectric power; the minimum pool level is fixed afterconsidering the minimum working head required for theefficient working of turbines.Basic Terms and Definitions4. Useful storage: volume of water stored between the fullreservoir level and the minimum pool level. Also known asthe live storage.5. Surcharge storage: is the volume of water stored above thefull reservoir level upto the maximum water level. Thesurcharge storage is an uncontrolled storage which existsonly when the river is in flood and the flood water is passingover the spillway. This storage is available only for theabsorption of flood and it cannot be used for other purposes.



6. Dead storage: volume of water held below the minimum poollevel. The dead storage is not useful, as it cannot be used forany purpose under ordinary operating conditions.7. Bank storage: If the banks of the reservoir are porous, somewater is temporarily stored by them when the reservoir isfull.8. Valley storage: The volume of water held by the natural riverchannel in its valley upto the top of its banks before theconstruction of a reservoir is called the valley storage. Maybe important in flood control reservoirs.9. Yield from a reservoir: Yield is the volume of water whichcan be withdrawn from a reservoir in a specified period oftime. The yield is determined from the storage capacity ofthe reservoir and the mass inflow curve.10 Safe yield (Firm yield): is the maximum quantity of waterwhich can be supplied from a reservoir in a specified periodof time during a critical dry year. Lowest recorded naturalflow of the river for a number of years is taken as thecritical dry period for determining the safe yield11. Secondary yield: is the quantity of water which is availableduring the period of high flow in the rivers when the yield ismore than the safe yield. It is supplied on as and when basisat the lower rates. The hydropower developed fromsecondary yield is sold to industries at cheaper rates.12. Average yield: is the arithmetic average of the firm yieldand the secondary yield over a long period of time.13. Design yield: is the yield adopted in the design of a reservoir.Fixed after considering the urgency of the water needs andthe amount of risk involved. The design yield should be suchthat the demands of the consumers are reasonably met with,and at the same time, the storage required is not undulylarge.

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CE2301-NOL