CVE 471 WATER RESOURCES ENGINEERING
IRRIGATION
Assist. Prof. Dr. Bertuğ Bertuğ Akıntuğ ntuğ Civil Engineering Program Middle East Technical University Northern Cyprus Campus
7 . 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
7 . 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
7 . 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 economically irrigable irrigable by surface water.
About 2% is economically economically irrigable irrigable by groundwaters. groundwaters.
Irrigation Irrigation is required required for productiv productive e agriculture agriculture in humid 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.
7 . 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
7 . IRRIGATION
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, R s: 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, A s: 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, R s, and As:
7 . IRRIGATION
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 a thickness, D, can be obtained from
7 . IRRIGATION
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 the downward direction by the action of gravity.
7 . IRRIGATION
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 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.
7 . IRRIGATION
Suitability of Land for Irrigation The Extraction Pattern of Soil Water by the Plant
In 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.
7 . IRRIGATION
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, 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
7 . IRRIGATION
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, t a
ic: infiltration rate
7 . 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
7 . IRRIGATION
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, u c uc=25.4 k f k: crop coefficient (k= k 1k2) Table 10.3 f: climatic factor
t: mean monthly temperature (ºC) P: the ratio of monthly daytime hours to
7 . IRRIGATION
Determination of Irrigation Water Demand
Crop Irrigation Requirement, CIR: CIR = uc - Peff where Peff : monthly effective precipitation
7 . IRRIGATION
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:
7 . IRRIGATION
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 demand month on a continuous flow basis from the point of diversion.
7 . 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
7 . IRRIGATION
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, 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 ↑).
7 . IRRIGATION
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.
7 . IRRIGATION
Irrigation Water Quality
Irrigation water quality guidelines:
High quality irrigation water
7 . IRRIGATION
Irrigation Water Quality
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 drainage Di: the depth of irrigation water ECi: the electrical conductivity of irrigation water ECd: the electrical conductivity of drainage water
7 . IRRIGATION
Example 10.2
Solution:
Table 10.3 and 10.4
7 . IRRIGATION
Determination of Irrigation Water Demand
7 . IRRIGATION
Determination of Irrigation Water Demand
7 . 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
7 . IRRIGATION
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 universally acceptable design procedures. Use of method depends on
the local conditions,
farming habits,
availability of water,
availability of technology, and
labor.
7 . IRRIGATION
Design of Irrigation Systems Irrigation Networks
Irrigation water is distributed to the project area by means of one of the networks such as
After economic analysis of each type, considering
open channel, canalet, pipeline, and sprinklers. the available technology, labor, materials, water quality problems, and the operational requirements
The alternative, which gives the greatest benefit, is chosen.
7 . IRRIGATION
Design of Irrigation Systems Irrigation Networks – Open Channel Networks
Lined irrigation canals:
main,
secondary, and
tertiary
Unlined drainage canals:
interceptors,
collectors, and
main collector.
7 . IRRIGATION
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)
7 . IRRIGATION
Design of Irrigation Systems Irrigation Networks – Open Channel Networks
7 . IRRIGATION
Design of Irrigation Systems Irrigation Networks – Canalet Networks
a semi-elliptical flume,
made of prefabricated plain concrete,
length 5 m,
prestressed concrete Æ length 7 m
water is withdrawn from a canalet by portable siphon.
http://www.irrig8right.com.au/Irrigation_Methods/Surface_Irrigation/Picture_Folder_Surface/Furrow_siphons_pics.ht m
7 . IRRIGATION
Design of Irrigation Systems Irrigation Networks – Canalet Networks
7 . IRRIGATION
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.
7 . IRRIGATION
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 appurtenance
Æ
less maintenance
Disadvantages
maintenance is difficult.
7 . IRRIGATION
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 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
7 . IRRIGATION
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
7 . IRRIGATION
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
7 . IRRIGATION
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.
7 . IRRIGATION
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
7 . IRRIGATION
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.
7 . IRRIGATION
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 watering to every point in the project area.
Æ
to supply the necessary amount of water
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.
7 . IRRIGATION
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 meeting the demand in the filed, its value depends upon A and q max.
7 . IRRIGATION
Design of Irrigation Systems Irrigation System Design Demand Method
Solution:
7 . IRRIGATION
Design of Irrigation Systems
7 . IRRIGATION
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.
