cve 471 - 7 irrigation
TRANSCRIPT
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Assist. Prof. Dr. Bertuğ Akıntuğ
Civil Engineering Program
Middle East Technical University
Northern Cyprus Campus
CVE 471CVE 471
WATER RESOURCES ENGINEERINGWATER RESOURCES ENGINEERING
IRRIGATIONIRRIGATION
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7 7 . IRRIGATION . IRRIGATION
Overview
Introduction
Sustainability of Land for Irrigation
Land Classification
Soil-Water Relations
Classes and Availability of Soil Water
Extraction Pattern of Soil Water by the Plant
Frequency of Irrigation
Determination of Irrigation Water Demand
Irrigation Efficiencies
Irrigation Water Quality Design of Irrigation Systems
Irrigation Networks
Irrigation System Design
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7 7 . IRRIGATION . IRRIGATION
Introduction
To increase agricultural output
wise use of land and water resources potentials, and development 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.
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7 7 . IRRIGATION . IRRIGATION
Overview
Introduction
Sustainability of Land for Irrigation
Land Classification Soil-Water Relations
Classes and Availability of Soil Water
Extraction Pattern of Soil Water by the Plant
Frequency of Irrigation
Determination of Irrigation Water Demand
Irrigation Efficiencies
Irrigation Water Quality Design of Irrigation Systems
Irrigation Networks
Irrigation System Design
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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 development
ability to store water
Suitable soil for irrigation must include certain portions of sand, silt
and clay. Sand: very permeable creates water-retaining problems
Silt and Clay: too dense creates permeability problems
Sandy loam is ideal irrigation soil.
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Suitability of Land for Irrigation
Land Classification
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Suitability of Land for Irrigation
Soil-Water Relations
Soil Texture: The sizes of particles in soil. Soil Structure: The arrangement of soil particles.
Soil Tilth: The physical condition of the surface soil
Real Specific Gravity, Rs: The ratio of density of a single soil particleto 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 equalvolume 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:
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Suitability of Land for Irrigation
Soil-Water Relations
Soil 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 athickness, D, can be obtained from
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Suitability of Land for Irrigation
Classes and Availability of Soil
Soil 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 thedownward direction by the action of
gravity.
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Suitability of Land for Irrigation
Classes and Availability of Soil
Soil 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 thesoil moisture content when plants
permanently wilt.
Available Moisture, is the difference in
moisture content of the soil betweenfiled capacity and permanent wilting
point.
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Suitability of Land for Irrigation
The Extraction Pattern of Soil Water by the Plant
In a uniform soil, greater root development takes place in theupper layers of soil than elsewhere.
Root development depends on the soil temperature and it does
not grow approximately under 5ºC.
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Suitability of Land for Irrigation
Frequency of Irrigation
Readily 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, removingnot 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
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Suitability of Land for Irrigation
Frequency of Irrigation
Rmin will be determine the irrigation frequency, T T: 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
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7 . IRRIGATION G O
Overview
Introduction
Sustainability of Land for Irrigation
Land Classification Soil-Water Relations
Classes and Availability of Soil Water
Extraction Pattern of Soil Water by the Plant
Frequency of Irrigation
Determination of Irrigation Water Demand
Irrigation Efficiencies
Irrigation Water Quality Design of Irrigation Systems
Irrigation Networks
Irrigation System Design
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Determination of Irrigation Water Demand
To find irrigation water demand:
The consumptive use or the evapotranspiration from the planted area isrequired 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, theBlaney-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 f
k: crop coefficient (k= k1k2) Table 10.3
f: climatic factor t: mean monthly temperature (ºC)P: the ratio of monthly daytime hours to
annual day time hours. (Table 10.4)
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Determination of Irrigation Water Demand
Crop Irrigation Requirement, CIR:
CIR = uc - Peff
where Peff : monthly effective precipitation
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Determination of Irrigation Water Demand
Irrigation Efficiencies
The 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 irrigation
The overall irrigation efficiency, e:
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Determination of Irrigation Water Demand
Irrigation Efficiencies
The 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 demandmonth on a continuous flow basis from the point of diversion.
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Overview
Introduction
Sustainability of Land for Irrigation
Land Classification Soil-Water Relations
Classes and Availability of Soil Water
Extraction Pattern of Soil Water by the Plant
Frequency of Irrigation
Determination of Irrigation Water Demand
Irrigation Efficiencies
Irrigation Water Quality Design of Irrigation Systems
Irrigation Networks
Irrigation System Design
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Irrigation Water Quality
The quality of irrigation water is mainly dictated by
the amount and type of soluble salts composed of sodium, magnesiumand calsium,
the presence of industrial wastes, and
presence 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 ↑).
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Irrigation Water Quality
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.
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Irrigation Water Quality
Irrigation water quality guidelines:High quality irrigation water
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Irrigation Water Quality
Lack of precipitation in arid zones and high evaporation causes theaccumulation of soluble salts in soils.
Soils having excess soluble salts may have injuries effects onplants.
Gypsum, CaSO4, can be added to water or soil to leach away thesodium salts from the soil.
The leaching requirement:
Dd: the depth of drainage
Di: the depth of irrigation water
ECi: the electrical conductivity of irrigation water
ECd: the electrical conductivity of drainage water
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Example 10.2
Solution:
Table 10.3 and 10.4
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Determination of Irrigation Water Demand
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Determination of Irrigation Water Demand
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Overview
Introduction
Sustainability of Land for Irrigation
Land Classification Soil-Water Relations
Classes and Availability of Soil Water
Extraction Pattern of Soil Water by the Plant
Frequency of Irrigation
Determination of Irrigation Water Demand
Irrigation Efficiencies
Irrigation Water Quality Design of Irrigation Systems
Irrigation Networks
Irrigation System Design
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Design of Irrigation Systems
In the design of any irrigation project, followings are considered
jointly:
the operational requirements,
types of network, and
water application methods.
It is relatively difficult to establish standardized and universallyacceptable design procedures.
Use of method depends on
the local conditions,
farming habits,
availability of water,
availability of technology, and
labor.
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Design of Irrigation Systems
Irrigation Networks
Irrigation 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, and
the operational requirements
The alternative, which gives the greatest benefit, is chosen.
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Design of Irrigation Systems
Irrigation Networks – Open Channel Networks
Lined irrigation canals: main,
secondary, and
tertiary
Unlined drainage canals:
interceptors,
collectors, and
main collector.
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Design of Irrigation Systems
Irrigation Networks – Open Channel Networks
Water 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)
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Design of Irrigation Systems
Irrigation Networks – Open Channel Networks
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Design of Irrigation Systems
Irrigation Networks – Canalet Networks
a semi-elliptical flume, made of prefabricated plain concrete,
length 5 m,
prestressed concreteÆ length 7 m
water is withdrawn from a canalet by portablesiphon.
http://www.irrig8right.com.au/Irrigation_Methods/Surface_Irrigation/Picture_Folder_Surface/Furrow_siphons_pics.ht m
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Design of Irrigation Systems
Irrigation Networks – Canalet Networks
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Design of Irrigation Systems
Irrigation Networks – Canalet Networks
Advantages of canalets: may be constructed in a short time,
required slope can easily be adjusted,
defective elements can be changed rapidly, and
not affected from the flooding of the area.
Disadvantages of canalets:
there are many appurtenances used in the
system,
expensive through out the cut area
stability problem in deep depressions.
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Design of Irrigation Systems
Irrigation Networks – Pipe Networks
Advantages do not occupy a space
water losses eliminated
agriculture area is not wasted
evaporation and seepage losses are minimum
Less appurtenanceÆ less maintenance
Disadvantages maintenance is difficult.
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Design of Irrigation Systems
Irrigation Networks – Sprinkler Networks
composed 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 limitedquantity 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 additionalappurtenances may be expensive
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Design of Irrigation Systems
Irrigation Networks – Sprinkler Networks
Sprinkler 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 sprinklers
pressurized main line
pressurized secondary line
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Design of Irrigation Systems
Irrigation System Design
In Turkey following methods have been used for the design of irrigation systems:
Rotation Method
Demand Method
Limited Demand Method Unit Area – Unit Water Method
Sprinkler Method
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Design of Irrigation Systems
Irrigation System Design
Rotation 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 = 2
number of the tertiary canal, n = 3
2 x 3 rotation can be applied.Irrigation frequency, T = N x n = 6 days
At the end of 6th day all the area will be irrigated.
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Design of Irrigation Systems
Irrigation System Design
Rotation Method
The irrigation schedule:
Day 1: S1, Area1
Day 2: S1, Area2
Day 3: S1, Area3
Day 4: S2, Area1
Day 5: S2, Area2
Day 6: S2, Area 3
The discharge in irrigation canals:
Q = (N x n) qmax AT
where qmax: irrigation modulus
AT : largest tertiary area in one group
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Design of Irrigation Systems
Irrigation System Design
Rotation 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
Σ AT(1) = Σ AT(2) = . . . = Σ AT(n)
The design based on rotation method is not economical.
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Design of Irrigation Systems
Irrigation System Design
Demand Method
In Turkey, demand method is used for the determination of design discharge
in lined irrigation canals.
It is base on continuous wateringÆ
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 iscontinuously available in these canals.
However, in the operation of the system only the desired amount is given to
the field.
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Design of Irrigation Systems
Irrigation System Design
Demand Method
The canal capacity:
Q = A F qmax
where Q: canal capacity (lt/s)
A: size of the irrigation area (ha)
F: flexibility coefficient
qmax: irrigation modulus (lt/s/ha)
F reflects the probability of meetingthe demand in the filed, its value
depends upon A and qmax.
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Design of Irrigation Systems
Irrigation System Design
Demand MethodSolution:
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Design of Irrigation Systems
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Design of Irrigation Systems
Irrigation System Design
Limited 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.
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Design of Irrigation Systems
Irrigation System Design
Limited 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