2-Methods of Irrigation (1).pdf also defines as modern methods of orrigation

Instructor: Prof. Dr. Ashfaque A. Memon
Subject: IRRIGATION ENGINEERING
Presentation #: 02 (3 hours)
METHODS OF IRRIGATION:
 Classification of Irrigation methods and factors affecting their choice
 Information collected from proposed irrigation site
 Surface Irrigation Methods: Uncontrolled/Wild/Free flooding, Check
flooding, Border flooding/Border Strip Method, Basin flooding, Contour
laterals, Furrow irrigation method and Raised bed method
 Pressurized/High Efficiency Irrigation Methods: Drip irrigation and
Sprinkler Irrigation
MUET
DEPARTMENT OF CIVIL ENGINEERING
References:
 Irrigation and Water Power Engineering by B. C. Punmia and Pande B. B. Lal
 Irrigation Engineering and Hydraulic Structures by S. K. Garg

IRRIGATION METHODS or
Modes of Application of Water to Crops
There are various ways in which the irrigation water can
be applied to the fields.
a) Surface Irrigation Methods:
Just flooding water. About 90% of the irrigated areas in the world
are by this method.
b) Sub-Surface Irrigation:
Flooding water underground and allowing it to come up by capillarity
to crop roots.
c) Pressurised/High Efficiency Irrigation Methods:
Applying water under pressure.
(i) Drip irrigation and (ii) Sprinkler Irrigation
2
Modes of Application-1

The selection of the irrigation method is based on
the following factors:
1. Soil characteristics of the land to be irrigated
2. Topography of the area
3. Available water supply
4. Type of crop and its requirements
5. Size of the stream supplying irrigation water
6. Amount of water required in each irrigation
Factors affecting choice of irrigation method
October 30, 2018 DR. ASHFAQUE A. MEMON 3

Information to be Collected on Visit to A Proposed Irrigation
Site.
a) Soil Properties: Texture and structure, moisture equilibrium points,
water holding capacity, agricultural potential, land classification, kinds of
crops that the soil can support.
b) Water Source: Water source availability (surface water / boreholes),
hydrologic data, water quantity, water quality, possible engineering
works necessary to obtain water.
c) Weather data: Temperature, relative humidity, sunshine hours and
rainfall.
d) Topography e.g. slope: For determining the layout of the irrigation
system and method of irrigation water application
e) History of People and Irrigation in the area: Past exposure of
people to irrigation and land tenure and level of possible re-settlement or
otherwise.
f) Information about crops grown in the area: Preference by people,
market potential, water demand, growth schedules and planting periods.
4

Surface Irrigation Methods
Their main classification of surface methods is as follows:
(1) Uncontrolled/Wild/Free flooding
(2) Check flooding
(3) Border flooding / Border Strip Method
(4) Basin flooding
(5) Contour laterals
(6) Furrow irrigation method
(7) Raised bed method
5

(1) Uncontrolled/Wild/Free Flooding
 Wild flooding method is the earliest and
the primitive method of application of
water to the land
 In this method the water is applied by
spreading it over the land.
 Prior to the application of water, no land
preparations are done in the form of
border or field ditches
 The water is allowed to flow the natural
slope of the land
 Most suitable for close growing crops,
pastures, etc., particularly where the
land is steep.
 Depending upon the slope, texture of soil, crops to be grown, etc. spacing
between contour ditches / laterals / subsidiary ditches is kept 20 to 50 m

(2) Check Flooding
 Check flooding is similar to
ordinary flooding except that
the water is controlled by
surrounding the irrigated area
with low and flat levees
 Levees are generally
constructed along the
contours, having vertical
interval of about 5 to 10 cm
7
 These levees are connected with cross-levees at convenient places
 The confined plot area varies from 0.2 to 0.8 hectare
 In check flooding, the check may be filled with water quickly/slowly
depending upon the infiltration of soil

(3) Border Flooding or Border Strip Method
Land is divided into a number of strips, separated by low levees called
borders.
Strip size: 10 to 20 m wide, and 100 to 400 m long.
To prevent water from concentrating on either side of the border, the
land should be leveled perpendicular to the flow.
8

The supply ditch / irrigation stream may either be in the form
of an channel (earthen/lined) or underground concrete pipe
having risers at intervals.
The size of the supply ditch depends upon the infiltration
rate of the soil, and the width of the border strip.

If
Q =Discharge through the supply ditch; A =Area of land strip to be
irrigated;
y =Depth of water flowing over the border strip; f =Rate of infiltration of soil;
Then
Time required to cover the given area is given by the equation
And, maximum area that can be irrigated in a border strip, is given by the
equation
𝐴𝑚𝑎𝑥 =
𝑄
𝑓










fA
Q
Q
f
y
t 10
log
3
.
2
10

Example:
Determine the time required to irrigate a strip of land of 0.04 hectares in area from a
tube-well with a discharge of 0.02 cumec. The infiltration capacity of the soil may be
taken as 5 cm/hr, and the average depth of flow on the field as 10 cm. Also determine
the maximum area that can be irrigated from this tube well.
Solution:
A = 0.04 hectares = 0.04 x 104 m2= 400 m2.
Q = 0.02 cumecs = 0.02 m3/sec = 0.02 x 60 x 60 m3/hr = 72 m3/hr.
f = 5 cm/hr = 5/100 m/hr= 0.05 m/hr.
y = 10 cm = 0.1 m.
Using the equation,
Putting the values,
i.e. Ans-1
Maximum area that can be irrigated is computed as
Ans-2
11

(4) Basin Flooding
This method is a special type of check
flooding and is adopted specially for
orchard trees.
One or more trees are generally placed
in the basin, and the surface is flooded
as in check method, by ditch water
12

(5) Contour Farming
 Contour farming is practiced in hilly areas with slopes
and with falling contour.
 The land is divided into series of horizontal strips called
terraces.
 Small bunds are constructed at the end of each terrace
to hold water up to equal height.

(6) Furrow Irrigation Method
Furrow irrigation avoids flooding the entire field surface by
channeling the flow along the primary direction of the field using
‘furrows,’ ‘grooves’, ‘lines’.
Only one-fifth to one-half of the land surface is wetted by water,
hence results in less evaporation and percolation losses
Spacing of furrows is determined by the proper spacing of the
plants. Furrows vary from 8 to 30 cm deep and may be as much
as 400 m long.
14

Siphons/hose pipes:
It prevents the necessity of breaking the
ditch bank, and provides a uniform flow
into the furrow.
Cutting the ridge:
Direct gravity flow whereby water is
diverted from the head ditch to the
furrows by cutting the ridge or levee.
Gated pipes:
Large portable pipe (up to 450 mm)
with gate openings can be used to
deliver water to the furrows.

Horizontal movement
due to capillarity
Vertical movement
due largely to gravity
Gravity vs. Capillarity

Furrows
Raised bed
(7) Raised Bed Method
 Raised bed method of irrigation is modified version of furrow
method
 In this method ridge is widened to provide more space under
cultivation and consequently less area is submerged with water

The conventional irrigation methods like flooding, furrows, etc. are
inefficient, resulting:
 loss of valuable irrigation water (particularly the loss of costly
pumped water)
 loss of applied nutrients
 getting poor crop yield
Whereas, in raised-bed planting method, plantation is prepared on
raised-bed/ridges:
 To save the valuable water and increase the crop-production
 To do inter-cropping pattern such as wheat with sugarcane
Why Raised-bed /Ridge Planting is preferred
over Furrows and Flooding Methods?
Januray 22, 2015
Dr. Shafi M. Kori 18

Benefits of Raised Bed Method
 Improves crop yields up
to 25%
 Saves water up to 40%
 Less weeds and less
lodging of the standing
crop
 Easy to drain rain water
 Low effect of standing
rain water
 Saves up to 40% energy
used for pumping water
 Easy for sugarcane inter
cropping with wheat
Additional benefits of
Sugarcane inter cropping with
wheat :
 Increase in crop intensity
 Less fertilizer requirement
 Water saving for both
crops
 Less cost for crop growth
 Less weed infestation in
sugarcane crop

Pressurized/High Efficiency Irrigation Methods:
(1) Drip Irrigation Method
20
Drip irrigation, also called
trickle irrigation, is the latest
field irrigation technique, and
is meant for adoption at places
where there exists acute
scarcity of irrigation water and
other salt problems.
In this method, water is slowly
and directly applied to the root
zone of the plants, thereby
minimizing the losses by
evaporation and percolation.

• Slow, frequent, precise application of water
• Most efficient – highest yield
• Water used – 10% of Flooding/Border strip method
• Irrigation efficiency – 80%
• Popular in Arid or Semi-arid areas where water is scarce
21

Main components Basic Parts
 pumps
 filters
 meters
 valves
 automatic timers
 mainlines
 submain lines
 laterals
 emitters, etc.
Components of a drip irrigation
system

This system involves laying of a system of head, mains, sub-mains,
laterals, and drop nozzles.
24

Water oozes out of these small drip nozzles uniformly and at a very small
rate, directly into the plant roots area.
The head consists of a pump to lift water, so as to produce the desired
pressure of about 2.5 atmosphere, for ensuring proper flow of water
through the system.
The lifted irrigation water is passed through a fertilizer tank, so as to mix
the fertilizer directly in the irrigation water, and then through a filter, so
as to remove the suspended particles from the water, to avoid clogging of
drip nozzles.
The mains and sub-mains are the specially designed small sized pipes,
made of flexible material like black PVC.
These are generally buried or laid on the ground, as shown in Fig.
Their sizes should be sufficient to carry the design discharge of the
system. 27

The laterals are very small sized (usually 1 to 1.25 cm dia.), specially
designed, black PVC pipes, taking off from the mains or sub-mains.
Laterals can usually be up to 50 m long, and one lateral line is laid for
each row of crop. The drip nozzles, also called emitters, or valves, are
fixed on laterals, at regular intervals of about 0.5 to 1 m or so,
discharging water at very small rates of the order of 2 to 10 liters per
hour.
These pressurized methods involves specialized knowledge, and are not
being adopted by our ordinary farmers.
28

Where we can apply?
Onion
Cotton
Cucumber
Banana

(2) Sprinkler Irrigation Method
In this farm-water application method, water is applied to the soil in the
form of a spray through a network of pipes and pumps.
It is a kind of an artificial rain and, therefore, gives very good results.
Water under pressure is supplied to the laterals through mains and sub-
mains.
The water jet comes out through Revolving sprinkler heads usually
mounted on rising pipes attached to the laterals.
32

It is a costly process and widely used in U.S.A.
It can be used for all types of soils, different topographies and slopes.
It can advantageously be used for many crops, because it fulfils the
normal requirement of uniform distribution of water.
This method possesses great potentialities for irrigating the areas, where
other types of surface or sub-surface irrigation are very difficult.
This method has not become popular in Pakistan for the simple reason of
cost and a lot of technical requirements.
The correct design and efficient operation are very important for the
success of this method.
33

Special steps have to be taken for preventing entry of silt and debris,
which are very harmful for the sprinkler equipment.
Debris choke the nozzles, interfere with the application of water on the
land, while the abrasive action of silt causes excessive wear on pump
impellers, sprinkler nozzles and bearings.
The system is to be designed in such a way that the entire sprayed water
seeps into the soil, and there is no run off from the irrigated area.
34

Conditions Favoring the Adoption of Sprinkler Method
(i) Irregular topography
(ii) Gradient is steeper, and soil is easily erodible.
(iii) Excessively permeable soil
(iv) When the water table is high.
(v) Near the coasts where seasonal water requirement is low
(vi) When the crops:
(a) require humidity control, as in tobacco;
(b) having shallow roots; or
(c) require high and frequent irrigation.
(vii) Water scarcity
35

Types of Sprinkler Systems.
A) Conventional Systems;
B) Mobile Systems
Conventionally, sprinkler system can be classified under three
heads, as:
1. Permanent system;
2. Semi-permanent system; and
3. Portable system.
36

In permanent system, all components are fixed in field, which are:
1. Electric motor of required hp
2. Pump of required capacity and head
3. Suction line from the sump
4. Main line
5. Check valves and main gate valves
6. Laterals with risers and sprinklers
37
In the semi-permanent system, sump, pump and main line are fixed,
laterals with sprinklers are moveable.
In the portable system:
All components are transported from one to another position
There are highest labor requirement and lowest Initial cost
Suitable for low growing corps but
Impractical for tall corn or sugar cane

B) Mobile Sprinkler Types
These include:
1. Raingun Irrigation System
2. Linear Move
3. Center Pivot System
38

Raingun is a mobile machine with a big sprinkler.
The speed of the machine determines the application rate.
The sprinkler has a powerful jet system.
39

Raingun Sprinkler Irrigating from Lagoon
11/27/2013 43
Dr. S. M. Kori

Lateral Move System is a long mobile boom in which many
sprinklers are attached.
As the machine moves, it collects water from a canal into the
sprinklers connected to the long boom.
44

In Centre Pivot system the source of water is stationary e.g. a
bore hole.
The boom with many sprinklers rotates about the water source.
46

Pivot of a Centre Pivot System

Center Pivot System with Spray Pad
Sprinklers
11/27/2013 48
Dr. S. M. Kori

Side-Roll Sprinkler Lateral in Peanuts
11/27/2013 50
Dr. S. M. Kori

Water Infiltration Rates and Soil Texture
Surface seal is defined as the orientation and packing of dispersed soil particles which
have disintegrated from the soil aggregates due to the impact of rain drops. OR
Surface seals are formed at the very surface of the soil, rendering it relatively
impermeable to water. (Courtesy: http://www.fao.org/docrep/t1696e/t1696e06.htm)

Soil Infiltration Rate vs. Constant Irrigation
Application Rate

Soil Infiltration Rate vs. Variable Irrigation
Application Rate

Advantages of Sprinkler Irrigation
(i) Seepage losses, which occur in earthen channels of surface
irrigation methods, are completely eliminated. Moreover, only
optimum quantity of water is used in this method.
(ii) Land leveling is not required, and thus avoiding removal of top
fertile soil, as happens in other surface irrigation methods.
(iii) No cultivation area is lost for making ditches, that results in
increasing about 16% of the cropped area.
(iv) In sprinkler system, the water is to be applied at a rate lesser than
the infiltration capacity of the soil, and thus avoiding surface run off,
and its bad effects, such as loss of water, washing of top soil, etc.
54

Advantages of Sprinkler Irrigation (contd.)
(v) Fertilizers can be uniformly applied, because they are mixed
with irrigation water itself.
(vi) This method leaches down salts and prevents water-logging or
salinity.
(vii) It is less labor oriented, and hence useful where labor is costly
and scarce.
(viii) Up to 80% efficiency can be achieved, i.e. upto 80% of
applied water can be stored in the root zone of plants.
55

Limitations of Sprinkler Irrigation
(i) High winds may distort sprinkler pattern, causing. non-uniform
spreading of water on the crops.
(ii) In areas of high temperature and high wind velocity, considerable
evaporation losses of water may take place.
(iii) They are not suited to crops requiring frequent/constant and larger
depths of irrigation, such as paddy.
(iv) Initial cost of the system is very high, and the system requires a high
technical skill.
(v) Only sand and silt free water can be used to avoid damage to pump
impellers.
(vi) It requires larger electrical power.
(vii) Heavy soil with poor intake cannot be irrigated efficiently.
(viii) A constant water supply is needed for commercial use of
equipment. 56

Sub-surface Irrigation Method
 A system by which elevation of the groundwater
table is regulated by artificially adding water to the
sub-soil through sub-surface pipes laid under ground.
 Water flowing in the pipes, infiltrate into the sub-soil
through the joints of these pipes. In this way the
water table is maintained at a pre-determined depth,
most beneficial to the crop.
57

 Sub-surface irrigation is limited to the areas where:
• soil is relatively permeable for a considerable depth;
• surface slopes are gentle;
• natural drainage is restricted; and
• it is practical to hold groundwater table at a
particular depth.
58

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