cve 471 water resources engineeringusers.metu.edu.tr/bertug/cve471/cve 471 - 7 irrigation.pdfcve 471...

CVE 471 Water Resources Engineering 1/45

Assist. Prof. Dr. Bertuğ Akıntuğ

Civil Engineering ProgramMiddle East Technical University

Northern Cyprus Campus

CVE 471CVE 471WATER RESOURCES ENGINEERINGWATER RESOURCES ENGINEERING

IRRIGATIONIRRIGATION


77. IRRIGATION. IRRIGATION

Overview

IntroductionSustainability of Land for Irrigation

Land ClassificationSoil-Water RelationsClasses and Availability of Soil WaterExtraction Pattern of Soil Water by the PlantFrequency of Irrigation

Determination of Irrigation Water DemandIrrigation Efficiencies

Irrigation Water QualityDesign of Irrigation Systems

Irrigation NetworksIrrigation System Design



Introduction

To increase agricultural outputwise use of land and water resources potentials, anddevelopment of effective irrigation systems.

In Turkey, 28 million hectare of land is irrigable.About 15% is economically irrigable by surface water.About 2% is economically irrigable by groundwaters.

Irrigation is required for productive agriculture in humid areas too.With irrigation

Physical conditions in the soil are improved,The excessive salt in the soil is reached,A variety of crops may grow,Multiple cropping may be achieved.



Overview








Suitability of Land for Irrigation

Arable land is composed of good quality soil, which is suitable for cultivation.Irrigable land is arable land for which sufficient moisture is available by irrigation.Irrigation soil

sufficient depth to allow root developmentability to store water

Suitable soil for irrigation must include certain portions of sand, silt and clay.

Sand: very permeable creates water-retaining problemsSilt and Clay: too dense creates permeability problems

Sandy loam is ideal irrigation soil.




Land Classification




Soil-Water RelationsSoil Texture: The sizes of particles in soil.Soil Structure: The arrangement of soil particles.Soil Tilth: The physical condition of the surface soilReal Specific Gravity, Rs: The ratio of density of a single soil particle to the density of a volume of water equal to the volume of the particle of soil.Apparent Specific Gravity, As: The ration of the weight of a given volume of dry soil, air space included, to the weight of an equal volume of water.Porosity, n: The ratio of volume of voids to the total volume of soil including water and air.The relation between n, Rs, and As:




Soil-Water RelationsSoil Moisture Tension: The tensile for due to suction and capillarity.

Soil Moisture Content, Pw: The ratio of loss of weight of soil specimen in drying in oven to the weight of water-free soil.

Volume Ratio, Pv: Pv = Pw As

The depth of water, d, applied on the surface of soil, which saturates a thickness, D, can be obtained from




Classes and Availability of SoilSoil water can be classified as

Hygroscopic Water exist on the surface of the soil grains in the form of a thin film.Capillary Water is that part in excess of hygroscopic water case. Gravitational Water is that part in excess of hygroscopic and capillary waters which can percolate in the downward direction by the action of gravity.




Classes and Availability of SoilSoil water can be classified as

Field Capacity, F.C., is the moisture content of soil after gravitational water has been removed.Permanent Wilting Point, PWP, is the soil moisture content when plants permanently wilt.Available Moisture, is the difference in moisture content of the soil between filed capacity and permanent wilting point.




The Extraction Pattern of Soil Water by the PlantIn a uniform soil, greater root development takes place in the upper layers of soil than elsewhere.Root development depends on the soil temperature and it does not grow approximately under 5ºC.




Frequency of IrrigationReadily Available Moisture: The portion of the available moisture that is most easily extracted by plants which is 75% of the total available moisture.In practice, for most of the crops, removing not more than 25% of the available water from each sub-root zone will produce maximum yield.Readily Available Moisture, RAM: for any sub-root zone.

RG: Rate of crop growth,SM: Soil Moisture




Frequency of IrrigationRmin will be determine the irrigation frequency, TT: The average time interval in days between two successive irrigations.

uc,daily: the daily water consumption by plants.

Duration of irrigation water application in hours, ta

ic: infiltration rate



Overview








Determination of Irrigation Water Demand

To find irrigation water demand:The consumptive use or the evapotranspiration from the planted area is required for irrigation water demand.Evapotranspiration = Transpiration + Evaporation

There are number of method for evapotranspiration.In Turkey, and in many other countries having semi-arid climate, the Blaney-Criddle (1950) method is widely used for the determination of consumptive use.In Blaney-Criddle Method

The monthly consumptive use value, uc

uc=25.4 k fk: crop coefficient (k= k1k2) Table 10.3f: climatic factor t: mean monthly temperature (ºC)

P: the ratio of monthly daytime hours toannual day time hours. (Table 10.4)




Crop Irrigation Requirement, CIR:

CIR = uc - Peff

where Peff: monthly effective precipitation




Irrigation EfficienciesThe water conveyance efficiency, ec:

where Wf: the water delivered to farm,Wr: the water delivered from the river or reservoir

The water application (farm) efficiency, ef:

where Ws: the water stored in the soil root zone during irrigationThe overall irrigation efficiency, e:




Irrigation EfficienciesThe farm delivery requirement, FDR:

The total delivery requirement, TDR:

The units of CIR, FDR, and TDR are all in mm/month.The irrigation modulus (water duty), q: The water requirement of an average unit area at the maximum demand month on a continuous flow basis from the point of diversion.



Overview








Irrigation Water Quality

The quality of irrigation water is mainly dictated by the amount and type of soluble salts composed of sodium, magnesium and calsium,the presence of industrial wastes, andpresence of silt.

Silt may decrease the porosity of the soil. For soils having lower porosity, silt creates an unsuitable medium for water intake.

High sodium percentage of salt causes binding of soil particles and decrease in air and water ventilation in the root zone (pH value ↑).




The soluble salt concentration is measured by the electrical conductivity of the saturated soil.The alkalinity (sodium) hazard is due to the presence of high amount of exchangeable sodium salts.The amount of exchangeable sodium salts is measured by the sodium adsorption ratio, SAR,

where (Na)c, (Ca)c, and (Mg)c are the soluble sodium, calcium, and magnesium concentrations in irrigation water, respectively.




Irrigation water quality guidelines: High quality irrigation water




Lack of precipitation in arid zones and high evaporation causes the accumulation of soluble salts in soils.Soils having excess soluble salts may have injuries effects on plants.Gypsum, CaSO4, can be added to water or soil to leach away the sodium salts from the soil.The leaching requirement:

Dd: the depth of drainageDi: the depth of irrigation waterECi: the electrical conductivity of irrigation waterECd: the electrical conductivity of drainage water



Example 10.2

Solution:

Table 10.3 and 10.4



Overview








Design of Irrigation Systems

In the design of any irrigation project, followings are considered jointly:

the operational requirements,types of network, andwater application methods.

It is relatively difficult to establish standardized and universally acceptable design procedures.Use of method depends on

the local conditions,farming habits,availability of water,availability of technology, andlabor.




Irrigation NetworksIrrigation water is distributed to the project area by means of one of the networks such as

open channel,canalet,pipeline, and sprinklers.

After economic analysis of each type, considering the available technology,labor,materials,water quality problems, andthe operational requirements

The alternative, which gives the greatest benefit, is chosen.




Irrigation Networks – Open Channel NetworksLined irrigation canals:

main,secondary, andtertiary

Unlined drainage canals:interceptors,collectors, andmain collector.




Irrigation Networks – Open Channel NetworksWater is usually withdrawn from tertiary canal.The desired rate of water is given from a tertiary canal to adjacent land by means of a turnout.

Weir box turnout(http://www.usbr.gov/pmts/hydraulics_lab/pubs/wmm/chap07_13.html)




Irrigation Networks – Open Channel Networks




Irrigation Networks – Canalet Networksa semi-elliptical flume,made of prefabricated plain concrete,length 5 m,prestressed concrete length 7 mwater is withdrawn from a canalet by portable siphon.

http://www.irrig8right.com.au/Irrigation_Methods/Surface_Irrigation/Picture_Folder_Surface/Furrow_siphons_pics.htm




Irrigation Networks – Canalet Networks




Irrigation Networks – Canalet NetworksAdvantages of canalets:

may be constructed in a short time,required slope can easily be adjusted,defective elements can be changed rapidly, andnot affected from the flooding of the area.

Disadvantages of canalets:there are many appurtenances used in the system,expensive through out the cut areastability problem in deep depressions.




Irrigation Networks – Pipe NetworksAdvantages

do not occupy a spacewater losses eliminatedagriculture area is not wastedevaporation and seepage losses are minimumLess appurtenance less maintenance

Disadvantagesmaintenance is difficult.




Irrigation Networks – Sprinkler Networkscomposed of a pressurized feeder.pressure head of 3.5 – 7.0 m.

Advantages:the form of natural precipitation.a wider area may be irrigated with a limited quantity of water.a drainage system may not be required.good for rolling terrains having steep slopes and permeable soils.

Disadvantages:excessive wind may restrict the uniform water application. installation of pumping stations and additional appurtenances may be expensive




Irrigation Networks – Sprinkler NetworksSprinkler system may be applicable to two different situations:1. The main network is composed of open channel, canalets or pipes and

water is applied to the field by means of sprinkler.2. Irrigation network is composed of pressurized pipes, which are

connected to sprinklerspressurized main line

pressurized secondary line




Irrigation System DesignIn Turkey following methods have been used for the design of irrigation systems:

Rotation MethodDemand MethodLimited Demand MethodUnit Area – Unit Water MethodSprinkler Method




Irrigation System DesignRotation Method

After the irrigation, the next irrigation is delayed by a duration equal to the irrigation frequency.The area is divided into sub-zones according to the rotation number.

For example: number of the secondary canal, N = 2number of the tertiary canal, n = 32 x 3 rotation can be applied.Irrigation frequency, T = N x n = 6 daysAt the end of 6th day all the area will be irrigated.




Irrigation System DesignRotation MethodThe irrigation schedule:

Day 1: S1, Area1Day 2: S1, Area2Day 3: S1, Area3Day 4: S2, Area1Day 5: S2, Area2Day 6: S2, Area 3The discharge in irrigation canals:Q = (N x n) qmax AT

where qmax: irrigation modulusAT : largest tertiary area in one group




Irrigation System DesignRotation Method

Discharge is directly proportional to the tertiary area.

In order to transmit almost same discharge for every day during the rotation, summation of tertiary areas in one group should be as close as possible to summation of tertiary areas in other groups

ΣAT(1) = ΣAT(2) = . . . = ΣAT(n)

The design based on rotation method is not economical.




Irrigation System DesignDemand Method

In Turkey, demand method is used for the determination of design discharge in lined irrigation canals.

It is base on continuous watering to supply the necessary amount of water to every point in the project area.

The capacity of the main, secondary, and tertiary canals are determined on the bases of the assumption that max. water demand in the field is continuously available in these canals.

However, in the operation of the system only the desired amount is given to the field.




Irrigation System DesignDemand Method

The canal capacity:Q = A F qmax

where Q: canal capacity (lt/s)A: size of the irrigation area (ha)F: flexibility coefficientqmax: irrigation modulus (lt/s/ha)

F reflects the probability of meeting the demand in the filed, its value depends upon A and qmax.




Irrigation System DesignDemand Method Solution:




Irrigation System DesignLimited Demand Method

In practice it is impossible to meet all demands at the same time in a definite tertiary.If (the amount of water requirements) > (the supply) : farm turnouts are then put in an operation and water is delivered in rotation.

Each day a different parcel receives irrigation water.

In this system, water is given in a limited amount with a delayed schedule.

More area is irrigated with the limited quantity of water.




Irrigation System DesignLimited Demand Method

The max. crop yield is achieved at an optimum depth of water.Because crops require not only water but also some air and nutrient for their growth. If the amount of water is considerably reduced, the corresponding decrease in the yield is relatively small.Operation of the irrigation area by the limited demand method gains importance when the area to be irrigated is very large and the water is scarce.

Cotton

cve 471 water resources engineeringusers.metu.edu.tr/bertug/cve471/cve 471 - 7 irrigation.pdfcve 471...

Documents