UNIVERSITY OF NAIROBI
SCHOOL OF ENGINEERING
DEPARTMENT OF ENVIRONMENTAL AND BIOSYSTEMS ENGINEERING
FEB 540: DESIGN PROJECT
Title: DESIGN PROJECT OF SPRINKLER IRRIGATION SYSTEM FOR
KOMBE FARM IN NANDI COUNTY
A Project concept submitted in partial fulfillment for the Bachelor of
Science (Environmental and Biosystems Engineering) at the
Department of Environmental and Biosystems Engineering at the
University of Nairobi
Compiled by: DANIEL K. TARBEI
Reg No: F21/0040/2008
Supervisor: Mr. E. B. K MUTAI
APRIL, 2013
DECLARATION
I DANIEL TARBEI do declare that the work done and the material presented in this project is my work to
the best of my knowledge and has never been presented for a degree or any other academic award in
any other institution or university.
Signature…………………………………….
Date………………………………………….
This project has been submitted for examination with my approval as a university supervisor
Signature…………………………………….
E.B.K MUTAI
Date………………………………………….
DEDICATION
I dedicate this project to my parents, brothers and sisters for their constant great support always.
God bless.
ABSTRACT
In Kenya at the present, a lot of land is unproductive in terms of agriculture. This could be attributed to a
number of reasons including inaccessibility, lack of equipments, poor agricultural practices and mostly
insufficient water for agriculture. This hassled to the need for irrigation. While some areas have
adequate supply, they end up with low quality yields due to poor and unplanned irrigation practices and
choosing ineffective type of irrigation, and thereby translating to loss in income. It is therefore necessary
to apply irrigation efficiently in order to prevent such cases. Excessive application efficiency, reduction in
quality of crops and ultimately drainage problems. And again under irrigation will result crop water
stress and therefore reduction in crop quality. The aim of the project was to propose an optimal
irrigation water allocation in the farm through sprinkler system of irrigation.
To achieve this, the area and crops under irrigation were considered. The soil type was also considered.
The soil type was red clay loam and its properties such as moisture content, field capacity, wilting point
and its specific gravity were determined.
The rainfall, temperature and evaporation data of the area was also taken into. And finally the
properties of each crop planted in the area were also determined. This is included the evapotranspiration, growth patterns, planting dates and the water requirements were then established.
The design of the system was carried out based on the conditions of the field. The sizes of the pipes and
sprinklers were then selected from the design manual.
The diameters of the laterals were chosen to be three inches for all the plots in the field while the submains had varying diameters according to the flow required by the field.
The diameter of the mainline was determined based on the system capacity as 200mm steel pipe to
deliver the required discharge capacity of 42.1 l/s to the whole field.
TABLE OF CONTENTS
Declaration………………………………………………………………………………………………………..i
Dedication………………………………………………………………………………………………………….ii
Abstract………………………………………………………………………………………………………………iii
Table of contents………………………………………………………………………………………………..iv
Chapter one
Introduction………………………………………………………………………………………………………..1
Problem statement…………………………………………………………………………………2
Overall objective…………………………………………………………………………………….3
Specific objectives…………………….…………………………………………………………….3
Scope……………………………………………………………………………………………………..4
Literature review………………………………………………………………………………………………..5
Methodology………………………………………………………………………………………………………13
Design process…………………………………………………………………………………………………….24
Discussion, recommendation and conclusion………………………………………………………34
Appendix…………………………………………………………………………………………………………….37
References …………………………………………………………………………………………………………43
CHAPTER ONE
1.0 INTRODUCTION
Irrigation is the artificial application of water to the soil usually for assisting in growing crops. In
crop production, it is mainly used in dry areas and in periods of rainfall shortfalls and also to
protect crops from frost.
Additionally, irrigation helps to suppress weeds growing in rice fields. In contrast, Agriculture
that relies only on rainfall are referred to as rain fed farming. Irrigation is usually studied
together with drainage, which is the natural or artificial of surface or sub-surface water from a
given area.
Irrigation scheduling is the term used to determine the procedure by which an irrigator
determines the timing and quantity of water application. When available water is limited,
production is determined by the extent to which full water requirement can be met by the
available water during the entire growing period. When water supply does not meet the crop
water requirements, actual evapo-transpiration (Eto) will fall below maximum evapotranspiration (Etm). Under this condition, water stress will develop which will adversely affect
the crop growth and ultimately the crop yield. The effect of water stress on growth and yields
will depend on the crop species and variety on one hand and the magnitude and time of the
occurrence of water deficit on the other hand. This is the major problem in irrigation scheduling.
(Hillel 1973)
To establish a better irrigation schedule, the following factors are considered:-
Design
Soil plant
Micro-climate
These will help to determine the irrigation amount, the irrigation depth, the irrigation duration
and the irrigation frequency. The most important factor to consider is the crop water use, which
is mostly determined by the growth stage. This is achieved by determining the crop coefficient at
each stage of growth and using it to determine the water requirement.
A universal yield calibration for transferability among sites is unobtainable. However, site
calibration is useful in evaluating crop yield response to different irrigation schedules.
1.1 Problem statement
In most areas in Kenya, people are experiencing food shortages and harsh weather conditions
that cannot support agriculture. It is therefore necessary to create more land for local farming
through irrigation.
1.2 Problem analysis
In an irrigation system, a lot of water is wasted as a result of poor irrigation scheduling mostly
based on estimates and past experiences.
1.3 Site analysis
Kombe farm is located in Nandi County, in Rift Valley and it is 17 km from Kapsabet town.
On the field to be irrigated, the total area under irrigation is 15 hectares and the crops under
irrigation are:Cabbages
3 ha
Kales
2 ha
Potatoes
3 ha
Maize
3 ha
Onions
2 ha
Tomatoes
2 ha
1.4 Overall objectives
To design a sprinkler irrigation system that will satisfy the crop water requirements of each crop
species grown in the farm and the irrigation requirements of the farm.
1.5 Specific objectives
•
To determine the seasonal water requirements of each crop grown in the farm.
•
To minimize cases of over-irrigation and under-irrigation by recommending the seasons
and schedule for irrigation in the plot thus improving crop yields.
•
To reduce water loss along the delivery system of the irrigation set up.
1.6 Scope
The project mainly focuses on an irrigation system that will ensure continuous farming
throughout the year.
2.0 CHAPTER TWO
2.1.0 LITREATURE REVIEW
2.1.1 Sprinkler irrigation
In sprinkler or overhead irrigation, water is piped to one or several central locations within the
field and distributed by overhead high pressure sprinklers or guns. A system utilizing sprinklers,
sprays or guns mounted overhead on permanently installed risers is often referred to as a solidset irrigation system. High pressure sprinklers that rotate are called rotors and are driven by a
ball drive, gear drive or impact mechanism. Rotors can be design to rotate in a full or partial
circle usually with nozzles diameters in range of 0.5 to 0.9 inches (10 – 15 mm).guns are used
not only for irrigation but for industrial applications such as dust suppression and logging.
Sprinklers may also be mounted on moving platforms connected to the water source by a hose.
Center pivot irrigation is a form of sprinkler irrigation consisting of several segments of pipe
(usually galvanized steel or aluminium) joined together and supported by trusses, mounted on
wheeled towers with sprinklers position along its length. The system moves in a circular pattern
and is fed with water from the pivot point at the center of the arc. These systems are common in
parts of the United States where terrain is flat. Most center pivot systems now have drops
hanging from u-shaped pipe called a gooseneck attached at the top of the pipe with sprinkler
heads that are positioned a few feet (at most) above the crop, thus limiting evaporative losses.
2.1.2 Operation of a sprinkler system
a correctly designed sprinkler system will supply water throughout including periods of
maximum water demand by crops. Over irrigation will occur if the irrigation system is operated
at full capacity when the water demand of the crop is less than maximum. Excessive application
will lead to:leaching of soluble nutrients
low water application efficiency
reduction in quality of crops
damage of crops
drainage problems
2.1.3 Principle components of a sprinkler system
I.
pumping station
This is an important part of the design. The pump produces energy and power to pump
the required discharge of the field
II.
mainline pipe
This is the largest pipe of the system that links the pump to the laterals.
III.
Lateral pipes
These pipes links the sprinkler to the main pipe and then to the risers
IV.
Controllers, zones and valves
Most irrigation systems are divided into zones. A zone is a single irrigation valve and one
or a group of sprinklers that are connected by pipes. Irrigation systems are divided into
zones because there is usually not enough pressure and available flow to run the
sprinklers for an entire field or yard at once.
Each zone has a solenoid valve on it that is controlled via wire by an irrigation controller.
The controller determines current conditions by means of historic weather data for the
local area, a moisture sensor (water potential or water content), weather station or a
combination of these.
V.
Sprinklers
When a zone comes on, the water flows through the lateral lines and ultimately ends up at
the irrigation sprinkler heads. Most sprinklers have pipe thread inlets on the bottom of
them which allows a fitting and the pipe to be attached to them.
2.1.4 Water source and piping
The beginning of sprinkler system is the water source. This is usually a tap into an existing water
line or a pump that pulls water out of a well or pond. The water travels through pipes from the
water source through the valves to the sprinklers.
Most pipes used in irrigation systems today are HDPE and UPVC, MDPE or PVC or PEX plastic
pressure pipes due to their ease of installation and resistance to corrosion. This prevents water in
the irrigation system from being pulled back into and contaminating the clean water supply.
2.1.5 Pipe specification
Types of pipes used are;
Galvanized steel
Aluminium
Polyvinyl chloride
Polyethylene
Soft plastic
2.1.6 Sprinkler system design
Preliminary study
Topographical study
Soil texture
Soil water holding capacity
Soil intake rate
Crop planting pattern
Crop depth of rooting and height of growth
Climatic conditions (precipitation, temperature, consumptive use)
Available materials and equipment
Economic viability
Design parameters
The parameters considered for sprinkler irrigation system are;
Maximum daily requirement for peak crop water use
The system application efficiency
Peak use/efficiency = the depth of water that the irrigation system must achieve
Frequency of irrigation. This is determined by the amount of water present in the root
zone. When water in the root zone is depleted by 50% by plant consumption, it needs to
be replenished by irrigation.
Irrigation duration. The time required to irrigate is directly related to the rate of water
infiltration into the soil.
The pumping station is located near the water source and lifts water making it available
under pressure to the system.
The mainline delivers water from the water source to the field. It may either be
permanent or movable.
The lateral pipes deliver water to the mainline to the different sections of the field. This is
usually movable
The riser delivers water from the laterals to the sprinkler. The length of the riser depends
on the height of the crops being irrigated. However a minimum of 30 cm is recommended
for a good distribution pattern.
The sprinkler is the unit that sprays the pressurized water through an orifice an rotates to
distribute water throughout the field
The accessories (e.g. tees and unions are parts of the system that generally connects all
the other units to form a watertight system. These parts are very important to an efficient
system and should be installed whenever possible.
2.1.7 Conventional systems
Irrigation systems using rotary sprinklers operating together were the first to make sprinkler
irrigation popular in the 1930’s. the sprinklers operate at low to medium pressures of about 2-4
m wide up to 300m long at one setting. Application rates vary from 5-35 cm/hr
2.2.0 Types of systems
Portable systems
Solid or permanent systems
Semi-permanent systems
2.2.1 Portable systems
In most cases, only the laterals are moved but the mainline is permanent or fixed. The laterals are
usually between 50mm to 125mm in diameter so that they can be moved easily and remain in
place until irrigation is complete. In some cases, the whole system is moved including the
mainline. This system however has its shortcomings which include:
•
The equipment has to be moved regularly
•
Requires large labour force
•
Working in wet, muddy and uncomfortable condition
•
Skilled operators are needed
2.2.2 Solid set or permanent system
Most solid set systems are buried underground to avoid damage from farm vehicles.
Occasionally they are laid out on the posts over crops. There is need to have sufficient laterals
and sprinklers to cover the whole irrigated area. Most solid set systems have only part of the
system irrigating at one time. This depends on the size of the pipe and the water available. The
initial cost of this system is high due to extra pipes, sprinklers and fittings required while less
labour is needed. They can be automated in areas where labour is hard to find or expensive.
2.2.3 Mobile sprinkler system
This type reduces the need for labour and allow for automation to take place. They are used
extensively in large scale farming popular in Europe and USA. Most of these machines are a
form of portable irrigation and the only difference is that they are motor driven. The examples
include:∗
Self moved side wheeled system
∗
A boom sprinkler system
∗
Center pivot sprinkler system
2.3.0 Problems in irrigation
Competition for surface water rights
Depletion of underground aquifers
Ground subsidence
Under irrigation gives poor soil salinity control which leads to increased soil salinity with
consequent build up of toxic salts on soil surface in areas with high evaporation.
Over irrigation because of poor distribution uniformity or management wastes water,
chemicals and may lead to water pollution.
Deep drainage (from over irrigation) may result in rising water tables which in some
instances will lead to problems of irrigation salinity.
Irrigation with saline or high-sodium water may lead to damage of soil structure.
2.4 Flows in pipes
Pipes are used to supply water to the sprinkler. Their size, wall thickness and strength depend on
the discharge they must carry and pressure required in the system.
CHAPTER THREE
3.0 METHODOLOGY
3.1 ADOPTION OF SOIL PARAMETERS
The soil parameters required are:•
Soil texture
•
Field capacity
•
Permanent wilting point
•
The infiltration capacity
•
Available moisture in the profile depth and its fraction
Soil texture
Infiltration
Total pore
Apparent
Field
Permanent
and
space %
specific
capacity %
wilting point
permeability
(N)
gravity %
(FC)
% (Pwp)
35.6
22
rate cm/hr
(As)
(Ir)
Red clay
0.8
48
1.35
loam
The above data was obtained from the measurement of the soil properties in Nandi area.
3.1 Computations
The dimensions of the irrigated plots were determined. The diameters and discharges
respectively of the sub mains, laterals, and the number of sprinklers required for each plot were
also determined.
Lateral discharge and flow rate were obtained by the following equation;
Q=AΧV
3.2 Water requirements
The water requirements for each plot at each development stage were determined. Water supply
was given by the following equations;
TAW = (FC – PWP)Drz
AW = MAD Χ TAW(depth of application)
II = AW ÷ Etc
Etc = Eto Χ Kc
NIR = II Χ Etc
GIR = NIR/Ea
Where
TAW = total available water
FC = field capacity
PWP = permanent wilting point
Drz = root depth
MAD = manageable allowed deficit
Etc = crop water requirement
II = irrigation interval
Eto = potential evapo-transpiration
Kc = crop coefficient which varies with growth stage of crops.
NIR = net irrigation requirement
GIR = gross irrigation requirement
Ea = application efficiency
3.3 Cropping patterns
The following is the table of the crop growing pattern of each crop in the field.
plant
Days to
20%
Max
Maturity Harvest
Max
Planting
Max
emerge
cover
Cover
(days)
rooting
depth
rooting
(Days)
(days)
(days)
(m)
depth
(days)
Cabbage
3
30
80
85
90
80
0.01
0.50
Onions
5
35
80
85
95
80
0.01
0.35
Spinach
3
30
80
90
95
80
0.01
0.40
Tomatoes 4
30
85
90
95
90
0.20
Potatoes
10
40
100
110
120
100
0.15
0.5
kales
14
30
85
80
90
80
0.01
0.5
From the table, it is seen that potatoes takes the longest time to mature (4 months) and kales and
cabbages takes the shortest time to mature (3 months)
And from the graph of average rainfall, the crops should grow around December and January
since the crops then require less water.
180
160
140
120
100
80
60
40
20
0
jan
feb
mar
apr
may
jun
july
aug
sept
oct
nov
dec
Average rainfall for 20 years.
When the crop reaches maturity, it will need more water and most of which will be
supplemented by the rainfall reducing the irrigation requirement.
3.4 Climatic conditions
Using the pan evaporation method, class A pan of coefficient 0.85 was used and the values of
daily evaporation converted to potential evapo-transpiration.
Monthly data for evaporation and rainfall were obtained from the meteorological station in
Dagorreti for the last two years.
Eto was determined for each month for the last two years using the pan evaporation for the
period of three years.
Graph of evapo-transpiration for the last three years
9
8
7
6
5
year 2005
year 2006
4
year 2007
3
2
1
0
jan
feb
mar
apr
may
jun
Eto = kpan x Epan over the period considered
july
aug
sept
oct
nov
dec
Where
Epan =evaporation in mm/day from an evaporation class A pan
Kpan = pan coefficient
After establishing inputs such as climate, soil data, crop data, irrigation crop and irrigation plan,
they were fed into computer simulation program to obtain varying scenarios of responses of
crops to planting dates and irrigation water requirements. The water requirement for each crop
was determined and the crop with maximum irrigation requirement was considered in order to
determine the overall water requirement for the field to be irrigated.
The laterals and sprinkler spacing were chosen from the design manual according to the
discharge required.
3.5 The system and pump capacity
The following formula was used to determine the capacity:-
=
=
Where
A = area under irrigation
Y = application depth
R = rotation period
T = irrigation time
3.6 Application rate
From the infiltration capacity of the soil, the water application rate from individual sprinkler was
determined by;
=
×
×
Where
Q = required discharge
Sm = spacing of laterals along the mainline in meters
Si = spacing of the sprinklers along the laterals in meters
I = optimum application rate in cm/hr
I ≤maximum infiltration rate
The laterals and sprinkler spacing was obtain from the design manuals according to the discharge
required
3.7 Determination of the pipe diameters
The following formulas were applied;
Q=AΧV
=
(
=√
D=
)
3.8 Total head required by pump
The total length of the mainline from the pump to the end of the field were determined
=
+ =
= minor losses which are normally ignored. h" along the mainline using Darcy’s
equation is given by;
=
Re =
#
$%
$
The frictional loss along the sub-main was also be obtained. The maximum length and the
laterals of sub-main were obtained and using Hazen – Williams equation;
=
& '.)*
+ '.)* ×,-.).**
The sprinkler operating head was given by the formula
P = hρg
Storage tank
pump
mainline
sand separator
Hydro-cyclone
water source
CHAPTER FOUR
4.0 THE DESIGN PROCESS
Taking cabbage crop into consideration,
The maximum rooting depth = 50 cm
From the table of available moisture, and where;
Max crop coefficient of cabbage = Kc
Potential evapo-transpiration = Eto
Max crop water requirement = Etc
Irrigation interval = II
Net irrigation requirement = NIR
Gross irrigation requirement = GIR
Max allowable depletion = MAD = 30%
4.1 sample calculations
TAW = 65 + 50
= 115 mm
AW= TAW Χ MAD
= 115 Χ 30%
=34.5 mm
Kc = 1.1
Max Eto for the last two years = 8.5mm/day
Etc = Eto Χ kc
=8.5 X 1.1
=9.35 mm/day
II = aw/ Etc
=34.5/9.35
= 3 days
NIR = II X Etc
= 3 X 9.35
= 28.05 mm
GIR = NIR/Ea
= 28.05/0.9
= 31.2 mm
Minimum rainfall recorded = 3.65 mm
Therefore the maximum irrigation requirement taking effective rainfall into considerations was;
31.2 – 3.65 = 27.55mm
Volume per ha =
(/0.11234444)
3444
=275.5 cubic meters
Total volume for the cabbage plot = 275 X 3
= 826.5 cubic meters
Application rate =
/01.153444
657844
= 19.2 l/s/ha
4.2 Pipe specification
Taking the plot under cabbage into considerations;
Dimensions;
Length =400m
Width = 70m
Max spacing of laterals = 18 m
Operating pressure 4 bar
Number of laterals per sub main pipe = 70/18
= 4 laterals
Max length of laterals = 120 m
No. of sprinkler per lateral = 120/18
=7 laterals
So four laterals will have 28 sprinklers
1 pipe section = 6m
Pipe section per lateral =
3/4
8
= 20 sections
Required discharge of one sprinkler,
=
=
×
×
9: 9: .9
0.72 l/s per sprinkler
Total discharge per lateral per second
=7 X 0.72
=5.04 l/s
= 0.00504 ;7 /s
The laterals used are 3 inch in diameter (75 mm) UPVC KSO6-149; 1999 class A
4.3 Determination of flow velocity along the laterals
No. of laterals per sub-main = 4
Total discharge per lateral per second = = 0.00504 ;7 /s
Discharge in sub main per second = 0.00504 X 4
= 0.0202 ;7 /s
Design flow velocity = 1.5 m/s
Q= 0.0202 ;7 /s
A = 0.0202 / 1.5
0.0135 ;/
D=
=√
(
)
= 0.13 m
Select UPVC 125mm diameter class A
Flow velocity based on the selected pipe.
A=
V=
4.3/1/5<
6
&
=
=
4.4/4/
4.43/7
= 1.6 m/s
4.4 Determination of system capacity
crop
Area to be
Application
Rotation
Period of work
irrigated (ha)
depth (cm)
periods (days)
(hours)
Cabbage
3
3.5
10
4
Onions
2
3.5
10
4
Spinach
3
3.5
10
4
Tomatoes
2
8.2
20
10
Potatoes
3
4.6
10
6
kales
2
3.5
10
4
4.5 Determination of system pump capacity.
Q = 27.78
>
?@
= 27.78
(/57.1)
((757.1)
+
+
(6534)
(6534)
= 42.09 l/sec
= 0.0421 ;7 /sec
(757.1)
(6534)
+
(/5A./)
(6534)
+
(756.8)
(8534)
+
(/57.1)
(6534)
)
4.6 Determination of mainline diameter
Flow velocity in the sub-main was taken as 2m/s
Q=AXV
A=
=
B
C
4.46/3
/
=0.02105 sq meters
D = √ (4A/π)
= √ {(4 x 0.02105)/π}
= 0.1637 m
Steel pipe of diameter 20 cm is chosen from table No. 13.8 BS 534; 1981
UPVC pipe of diameter 20 cm is chosen from table KS06-149; 1999
4.7 Total head required by the pump
The total length of mainline from the pump to the end of the field is 390 m (assuming the field is
square
And the highest point from the pump is 50 m
=
+ =
= minor losses which are normally ignored. h" along the mainline using Darcy’s
equation is given by;
#
=
Re =
=
$%
$
/D4./
34E.
= 4000
=
F
G
=
3
/4
= 0.005
From moody diagram, f = 0.03
Using Hazen – Williams equation;
=
h" = & '.)*
+ '.)* ×,-.).**
0.03x390x4
2x9.81x0.2
= 11.95 m
4.8 Frictional loss along the sub-main
Maximum length of sub-main = 19m with 10 laterals
And from the Hazen-williams equation
= 1.19Q103/ & '.)*
+ '.)* ×,-.).**
C= 150
Q = 20.2 l/s
D = 25
= 1.19Q103/ /4./'.)*
314'.)* ×3/1-.).**
=18.3m
Friction factor f, for 10 laterals = 0.2
h" = 0.2 x 18.3m = 3.6m
4.9 Head loss along the laterals, with 7 outlet points
3/
h" = 1.19Q10 1.46'.)*
314'.)* ×01-.).**
= 17 m
Friction factor, f = 0.38
h" = 0.38 x 17 = 6.46 m
4.10 Sprinkler operating head
Sprinkler operating pressure = 4bar
P = hρg
H=
R
ST
=
6D344444
3444DU.A3
= 40m
Therefore total head required by pump
Total head = 50 + 11.95 + 6.46 + 40 + 3.6 = 112.01 m
CHAPTER FIVE
5.0 DISCUSSION, RECOMMENDATIONS AND CONCLUSIONS
5.1 Discussion
The project was intended to optimize irrigation water allocation, which is obtained by
determining the crop water requirement s at each stage of growth. To acquire this, the different
crops cultivated under different areas were considered and the design made on different water
requirements.
Since the design is made on the maximum water which is not always the case, a computer
simulation program was introduced to the water needs by different growth stages of the crops.
The rainfall for each month was accounted for and the irrigation requirement computed for each
month.
The graph of rooting depth against time indicates that application depth varies with stage of
growth. The climatic data of Nandi area for the past 2 years gave value of irrigation amount for
the driest month 27.55 which amounts to a figure of 4680 m3 for 15 ha irrigated. This is the
maximum amount of water that is needed therefore the storage reservoir should not be a lesser
volume.
Having determined the diameters of the piping system, the construction process would be
smooth. It is expected to run efficiently since there will be no pressure overloads thus chances of
leakages and malfunctioning are reduced sufficiently.
The result of zero rainfall gave the highest amount of irrigation period, ranging closer to the
value obtained manually. The amount required reduces from the highest being zero to rainfall by
30% of the actual rainfall and 50%of the actual climate data.
5.2 Recommendations
A computer simulation program could be introduced to improve on the irrigation scheduling by
feeding it with an already existing data for the past, (say 10 years). The simulation program
requires a wide range of parameters on scheme which requires enough time to establish in order
to obtain less varying observations. Optall program (optimum allocation program) can be applied
to already existing schemes to improve on the irrigation efficiency.
To ensure maximum efficiency, the source of water could be a river or dam and the water can be
pumped to reservoir elevated to an adequate height that would produce the water at the highest
pressures to run the irrigation system by gravity rather than by pump.
5.3 Conclusion
From the observation results, it was establish that for some parts of the year, the crops could be
cultivated without irrigation this result is based on the observation of the last three-year events of
the areas.
Irrigation water should be applied as indicated by the plant growth characteristics curves in order
to save water.
It is therefore important for the irrigator to have an effective irrigation scheduling to minimize
again the water wastage and avoid over irrigation of the crops.
The results from the computer program will prove a lot of water saving when the trend of plant
growth and adjusted to rainfall contribution are accurately made.
CHAPTER SIX
APPENDIX
Q = discharge
Sm = spacing of laterals along the mainline in meters
Si = spacing of the sprinklers along the laterals in meters
I = optimum application rate in cm/hr
A = area under irrigation
Y = application depth
R = rotation period
T = irrigation time
TAW = total available water
FC = field capacity
PWP = permanent wilting point
Drz = root depth
MAD = manageable allowed deficit
Etc = crop water requirement
II = irrigation interval
Eto = potential evapo-transpiration
Kc = crop coefficient which varies with growth stage of crops.
NIR = net irrigation requirement
GIR = gross irrigation requirement
Ea = application efficiency
Available moisture in mm profile depth up to 180 cm
Moisture (mm)
Profile depth (cm)
65
0-25
50
25-50
35
50-75
25
75-120
15
120-145
10
145-170
5
170+
Depth of full-grown crops on loam soil
crops
Rooting depth (cm)
Fraction of available soil
moisture
Cabbage
60
0.45
Onions
40
0.25
spinach
50
0.25
Tomatoes
100
0.25
Potatoes
50
0.20
kales
50
0.30
Distribution of different crops in the field
plot
crop
Area (ha)
1
Cabbage
3
2
Onions
2
3
spinach
3
4
Tomatoes
2
5
Potatoes
3
6
kales
2
Crop data
plant
Days to
20%
Max
Maturity Harvest
Max
Planting Max
emerge
cover
cover
(days)
rooting
depth
rooting
(days)
(days)
(days)
(m)
depth
(days)
(m)
Cabbage
3
30
85
85
90
80
0.01
0.50
Onions
5
35
85
85
95
80
0.01
0.35
spinach
3
30
90
90
95
80
0.01
0.40
Tomatoes 4
30
90
90
95
90
0.20
0.45
Potatoes
10
40
110
110
120
100
0.15
0.50
kales
14
30
80
80
90
80
0.01
0.50
Graph of rainfall for the last three years
200
180
160
140
120
2005
100
2006
80
2007
60
40
20
0
jan
feb
mar
apr
may
june
july
aug
sept
oct
nov
dec
Average rainfall for 20 years
average rainfall for 20 years
180
160
140
120
100
80
60
40
20
0
average rainfall for 20 years
Rainfall data for the last 20 years
month
Average rainfall
Jan
43.6
Fe
38.0
March
75.7
April
141.6
May
93.95
June
96.17
July
164.5
Aug
163.4
Sept
72.0
Oct
75.5
Nov
62.7
Dec
45.0
CHAPTER SEVEN
REFERENCES
Daniel Hillel 1973. Efficient use of water during irrigation
FAO irrigation and drainage number 33, number 24 and 1 rev 1
Herman J. Finkel 1982. Handbook of irrigation technology volume 2
Michael A. M. 1972 design and evolution of irrigation methods
Michael A. M. 1978 irrigation theory and practice
Community development library CDL
Tsiourtis, N. X. (ed) water resource management under drought or water shortage conditions
proceedings, EWRA 1995 symposium 14-18 march 1995, Nicosia.
Isralcson O. W. 1962. Irrigation principles and practice. 3rd Edition
Internet www.irrigationtutorials.com