CVE 471 - 7 Irrigation

7/28/2019 CVE 471 - 7 Irrigation

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CVE 471 Water Resources Engineering 1/45

Assist. Prof. Dr. Bertuğ Akıntuğ

Civil Engineering Program

Middle East Technical University

Northern Cyprus Campus

CVE 471CVE 471

WATER RESOURCES ENGINEERINGWATER RESOURCES ENGINEERING

IRRIGATIONIRRIGATION




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





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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Overview

Introduction


Land Classification Soil-Water Relations







Irrigation Networks


7 IRRIGATIONIRRIGATION




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.






Land Classification







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:







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






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.






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.






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.







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

77. IRRIGATION. 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

77 . IRRIGATION. IRRIGATION




7 . IRRIGATION G O

Overview

Introduction









Irrigation Networks







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)






Crop Irrigation Requirement, CIR:

CIR = uc - Peff

where Peff : monthly effective precipitation







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:







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.





Overview

Introduction









Irrigation Networks






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 ↑).






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 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





Example 10.2

Solution:

Table 10.3 and 10.4















Overview

Introduction









Irrigation Networks






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.






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.






Irrigation Networks – Open Channel Networks

Lined irrigation canals: main,

secondary, and

tertiary

Unlined drainage canals:

interceptors,

collectors, and

main collector.







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)












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













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.






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.






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






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







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







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.







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







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.







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.







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.







Demand MethodSolution:












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.







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

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CVE 471 - 7 Irrigation