FRANK KWAKU BOAKYE OSEI.pdf
106
EVALUATION OF SPRINKLER IRRIGATION SYSTEM FOR IMPROVED MAIZE SEED PRODUCTION FOR FARMERS IN GHANA BY FRANK KWAKU BOAKYE OSEI BSc. (Hons.) Agricultural Engineering, Kumasi A Thesis submitted to the Department of Agricultural Engineering, Kwame Nkrumah University of Science and Technology, Kumasi in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE IN SOIL AND WATER ENGINEERING DEPARTMENT OF AGRICULTURAL ENGINEERING FACULTY OF MECHANICAL AND AGRICULTURAL ENGINEERING COLLEGE OF ENGINEERING SCHOOL OF GRADUATE STUDIES MARCH 2009
Transcript of FRANK KWAKU BOAKYE OSEI.pdf
EVALUATION OF SPRINKLER IRRIGATION SYSTEM FOR IMPROVED
MAIZE SEED PRODUCTION FOR FARMERS IN GHANA
BY
FRANK KWAKU BOAKYE OSEI
BSc. (Hons.) Agricultural Engineering, Kumasi
A Thesis submitted to the Department of Agricultural Engineering, Kwame
Nkrumah University of Science and Technology, Kumasi in partial fulfillment of the
requirements for the degree of
MASTER OF SCIENCE IN SOIL AND WATER ENGINEERING
DEPARTMENT OF AGRICULTURAL ENGINEERING
FACULTY OF MECHANICAL AND AGRICULTURAL ENGINEERING
COLLEGE OF ENGINEERING
SCHOOL OF GRADUATE STUDIES
MARCH 2009
~ i ~
DECLARATION
I hereby declare that this work is the result of my own original research towards the award
of a Master of Science degree and as far as I know, this has not been accepted in whole or
in part, in any previous publication or application for a degree here or elsewhere, except
where other people’s work and observations have been duly acknowledged in the text by
means of referencing.
Frank Kwaku Boakye Osei Signature……………………… Date:…………….
CERTIFIED BY
Ing Prof. N. Kyei-Baffour Signature………………………… Date……………..
(Supervisor)
Dr. E. Ofori Signature…………………………. Date……………..
(Co-Supervisor)
Mr. A. Bart-Plange Signature…………………………. Date……………..
(Head of Department)
~ ii ~
ABSTRACT
Irrigation is the greatest user of water in Ghana, but diminishing water resources, requires
that efficient and effective methods of water application in irrigation is adopted to realise
maximum returns and conserve water resources while eliminating the leaching of plant
nutrients and possible pollution of other groundwater resources. In order to obtain
commensurate yields for a given land area, uniform water application is paramount. This is
only achievable through effective design, maintenance and management of irrigation
systems. Consequently, an existing movable solid-set irrigation system was evaluated to
ascertain the major measures of performance with the view to ensuring the application of
water in an efficient and uniform manner. The suitability of the irrigation system for the
existing soil parameters was also investigated. In this study, field (outdoor)
tests/evaluations were performed for both single-sprinkler and block irrigation
configurations, based on the American Society of Agricultural and Biological Engineers
standards. Results indicated that the average Christiansen’s coefficient of uniformity (CU)
for the 12m×12m and 18m×18m sprinkler spacings were 91% and 87% respectively. The
mean application rates for the 12m×12m and 18m×18m spacing were 10.4mm/h and
4.7mm/h respectively and the average soil infiltration rates observed was 28.5mm/h. The
pattern efficiencies of the 12m×12m and 18m×18m spacing were 86.1% and 82.8%
respectively. The sprinklers had an average discharge of 1.5m3/h and average discharge
efficiency of 83.2% under the prevailing operating and environmental conditions for this
study. The results of the study indicated that the sprinkler irrigation system as designed
was suitable for the soil at the study site and its performance was satisfactory under the
existing environmental conditions.
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TABLE OF CONTENTS
Declaration ........................................................................................................................... i
Abstract ............................................................................................................................... ii
Table of Contents ............................................................................................................... iii
List of Figures .................................................................................................................... vi
List of Tables ......................................................................................................................... vi
Abbreviations/Symbols ...................................................................................................... ix
Acknowledgement ............................................................................................................... x
CHAPTER ONE: INTRODUCTION ......................................................................................... 1
1.1 Background ................................................................................................................... 1
1.2 Justification ................................................................................................................... 3
1.3 Aim and Objectives ....................................................................................................... 4
1.4 Scope of Study .............................................................................................................. 5
CHAPTER TWO: LITERATURE REVIEW ........................................................................... 6
2.1 Introduction .................................................................................................................. 6
2.2 Irrigation ........................................................................................................................ 6
2.3 Types of Irrigation Systems .......................................................................................... 7
2.4 Components of Pressurised Irrigation Systems ............................................................. 8
2.5 Sprinkler Irrigation ...................................................................................................... 11
2.6 Irrigation Efficiency .................................................................................................... 13
2.7 Irrigation Uniformity ................................................................................................... 15
2.8 Quantitative Measures of Irrigation Uniformity ......................................................... 18
2.9 Sprinkler Irrigation Factors Affecting Uniformity ...................................................... 21
2.10 Critical Determinants of Irrigation System Performance .......................................... 27
2.11 Types and Operation Mechanisms of Impact Sprinkler Heads ................................. 28
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2.12 Losses in Sprinkler Irrigation Systems ...................................................................... 29
2.13 Sprinkler Irrigation System Design ........................................................................... 30
2.14 Design Procedure ...................................................................................................... 31
2.15 Effects of Improper Irrigation Design ....................................................................... 32
CHAPTER THREE: MATERIALS AND METHODS ........................................................... 34
3.1 Introduction ................................................................................................................. 34
3.2 Study Area ................................................................................................................... 34
3.3 Climate ........................................................................................................................ 35
3.4 Soils ............................................................................................................................. 35
3.5 Vegetation ................................................................................................................... 36
3.6 Farm Area .................................................................................................................... 37
3.7 Materials ...................................................................................................................... 38
3.8 Methods ....................................................................................................................... 39
3.9 Single Sprinkler Test ................................................................................................... 46
3.10 Block Test ................................................................................................................. 47
3.11 Analyses of Data ....................................................................................................... 47
CHAPTER FOUR: RESULTS AND DISCUSSIONS ............................................................. 50
4.1 Introduction ................................................................................................................ 50
4.2 Results ........................................................................................................................ 50
4.3 Single Tests ................................................................................................................ 51
4.4 Block Tests ................................................................................................................. 55
4.5 Current Irrigation Practice ......................................................................................... 56
4.6 Proposed Design ......................................................................................................... 56
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CHAPTER FIVE: CONCLUSIONS AND RECOMMENDATIONS .................................... 59
5.1 Introduction ................................................................................................................ 59
5.2 Conclusions ................................................................................................................ 59
5.3 Recommendations ...................................................................................................... 60
REFERENCES ............................................................................................................................ 61
APPENDICES ............................................................................................................................. 67
APPENDIX A: Test Results and Computations .............................................................. 66
APPENDIX B: Infiltration Test Results and Graphs ....................................................... 82
APPENDIX C: Statistical Analysis Results ..................................................................... 89
APPENDIX D: Irrigation Plan for a 3-acre field ............................................................. 92
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LIST OF FIGURES
Figure 1: Schematic of a Pressurised Irrigation Network Layout ...................................... 8
Figure 2: Effect of Pressure on Droplet Size and Wetted Diameter ................................ 22
Figure 3: Relative Effects of Different Pressure on Precipitation Profiles for a
Typical Double Nozzle Sprinkler ............................................................................. 24
Figure 4: The Effect of Wind on a Sprinkler Pattern ....................................................... 25
Figure 5: Parts of the Impact Sprinkler Head ................................................................... 28
Figure 6: Map of Ghana indicating location of Afraku near Kumasi .............................. 34
Figure 7: Vegetation map of Ghana ................................................................................. 36
Figure 8: Layout of Foundation Seed Production Farm at Afraku .................................. 37
Figure 9: Catch-can and sprinkler layout for block test ................................................... 40
Figure 10a: Components of an impact-driven sprinkler ................................................... 43
Figure 10b: Length, Width and Height of a Sprinkler Head ............................................ 43
Figure 11: Pitot Tube and Bourdon Gauge used for Pressure Measurement ................... 44
Figure 12: Sprinkler-Collector Layout for Single Sprinkler test ...................................... 46
Figure 13: Simulation of 12m×12m Block Configuration from Single Sprinkler
Test Data…………………………………………………………………. 52
Figure 14: Sprinkler precipitation profiles ....................................................................... 54
Figure A1: Field Sprinkler Distribution Depths for Single Test 1 ................................... 68
Figure A2: Field Sprinkler Distribution Depths for Block Test 1 .................................... 70
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Figure A3: Simulation of 12m × 12m Sprinkler Spacing from Single Test Data ............ 73
Figure A4: Sprinkler Precipitation Profile for Test 1 ....................................................... 76
Figure A5: Sprinkler Precipitation Profile for Test 2 ....................................................... 77
Figure A6: Field Sprinkler Distribution Depths for Single Test 2 ................................... 79
Figure A7: Field Sprinkler Distribution Depths for Block Test 2 .................................... 81
Figure B1: Cumulative Infiltration Curve for Test 1 ....................................................... 86
Figure B2: Infiltration Rate Curve for Test 1 ................................................................... 87
Figure B3: Cumulative Infiltration Curve for Test 2 ....................................................... 88
Figure B4: Infiltration Rate Curve for Test 2 ................................................................... 89
Figure D1: Proposed Irrigation Plan for a1.2ha (3 acre) Field at Afraku ........................ 93
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LIST OF TABLES
Table 2.1: Losses in spray irrigation systems................................................................... 29
Table 4.1: Environmental Conditions During Field Measurements ................................ 50
Table 4.2: Test Outcomes During Sprinkler Precipitation Measurements ....................... 50
Table 4.3: Summary of Computed Results ...................................................................... 51
Table A1: Time and Environmental Conditions during Single Sprinkler Test 1 ............. 67
Table A2: Time and Environmental Conditions during Block Sprinkler Test 1 ............. 69
Table A3: Computation of CU and PE for 18m×18m Block Test 1 ................................ 72
Table A4: Computation of CU and PE for Simulated 12m×12m Block Test1 ................ 74
Table A5: Sprinkler Distribution Profile Data for Test 1 ................................................. 76
Table A6: Sprinkler Distribution Profile Data for Test 2 ................................................. 77
Table A7: Time and Environmental Conditions during Single Sprinkler Test 2 ............. 78
Table A8: Time and Environmental Conditions during Block Sprinkler Test 2 ............. 80
Table B1: Soil Infiltration Test 1 Results ......................................................................... 83
Table B2: Soil Infiltration Test 2 Results ......................................................................... 84
Table B3: Summary of Infiltration Test 1 Results ........................................................... 85
Table B4: Summary of Infiltration Test 2 Results ........................................................... 85
Table C1: t-Test for Means of the 12m ×12m Simulated Data ........................................ 90
Table C2: z-Test for Means of the 18m ×18m Block Data .............................................. 91
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ABBREVIATIONS/SYMBOLS
ASAE American Society of Agricultural Engineers
CU Christiansen’s Coefficient of Uniformity
DE (Ed) Discharge Efficiency
DU Distribution Uniformity
ET Evapotranspiration
FAO Food and Agriculture Organisation
HDPE High Density Polyethylene
I Sprinkler Application Rate
LR Leaching Requirement
MAD Management Allowable Depletion
MAR Mean Application Rate
PAES Philippines Agricultural Engineering Standards
PE Pattern Efficiency
psi pound square inch
PVC Polyvinyl Chloride
q Sprinkler Discharge
Sm Lateral Spacing
Sl Sprinkler Spacing
SS Single Sprinkler
UNESCO Unite Nations Educational Scientific and Cultural Organisation
USDA United State Department of Agriculture
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ACKNOWLEDGEMENT
The writer wishes to thank, the Grains and Legumes Development Board (GLDB) for the
opportunity offered for him to undertake this MSc. programme and the immense inputs
made in the performance of the field trials. Staff of the Afraku farm who made the field
trials possible, especially, Mr. Kofi Appiah, Mr. Paul Yampohekya, Mr. Francis Moro and
Mr. Ayariga Grushiare are acknowledged.
Special gratitude is extended to Thomas Atta-Darkwa for his selfless assistance during all
the field trials. Commendations also go to my colleagues who in diverse ways contributed
to this study.
Special thanks also go to Mrs. Bless Omane-Achamfuor, for her immeasurable assistance
in the acquisition of the Pitot tube and Bourdon gauge (both pivotal to the study) from the
USA to facilitate the smooth take-off of this project.
Dr. Ahmad Addo is also commended for his advice and assistance for this project.
The writer is also indebted to Ing. Prof. Nicholas Kyei-Baffour and Dr. Emmanuel Ofori,
for supervising this project from its inception to completion.
Finally, thanks and praises be to God for his guidance and protection throughout the
project period and his deliverance from the motor accident which occurred on the last day
of the field trials. To God be the glory for great things he has done.
67
APPENDIX A
DATA MEASUREMENTS, RESULTS AND COMPUTATIONS – DAY 1 & 2
SINGLE TEST
Distance from dam to field=100m
Sprinkler operating pressure: 352kPa or 51psi
Average rotational speed= 45s
Wetted diameter measured at three points: 26.4m, 26.3m and 25.8m; average=26.2m
Cross-sectional area of catch can = 55.4cm2
Volume of graduated cylinder= 500ml or 500cm3
Discharge time for 15litres: 37s, 38s, 36, 37; average=37s
Average Discharge rate: 0.41l/s or 1.48m3/h
Relative humidity= 64%
Table A1: Time and Environmental Conditions During Single Sprinkler Test 1
Time (am/pm) Wind speed (m/s) Temperature db (oC) Temperature db (oC) 10:45 1.2 26 32 10:55 1.3 27 33.5 11:05 2.0 26 32 11:15 1.6 26 32 11:25 2.2 24 31 11:35 2.2 27.5 34 11:45 2.0 28 38 11:55 3.0 28 38.5 12:05 1.2 27 36.5 12:15 1.0 27.5 37.5 12:25 1.2 27 38.5 12:35 1.4 28 37.5 12:45 1.6 27 37
Average 1.7 27 35 Standard Deviation 0.57 1.13 2.85
68
Figure A1: Field Sprinkler Distribution Depths for Single Test 1
1 0 3 4 5 5 4 2
4 4 5 7 7 5 2 0
0 4 8 14 12 5 5 10
2 5 10 14 12 12 8 5
5 6 39 10 12 10 5 2
1 3 5 9 10 8 5 3
1 3 4 5 5 3 1 0
0*m
0 0 1 2 1 0 0
0
0
30 10
10
4
0
0 0 0 5 10 5 0 0
7
15
30
56
24
10
0
15
25
25
45
55
29
25
58
15
25
65
30
21
66
16
47
3
25
50 55 45 15
50 25 65
65
4
35
77
38
25
55 75
24
25
30
20
20
20 40
25 10
# Catch-can readings in cm3
*- Catch-can readings in mm
69
BLOCK TEST
Pressure measured at the sprinklers 1-6 (psi)
P1=52, P2=51 P3=51 P4=52 P5=51, P6=51
Average pressure =352 kPa (51psi)
Average discharge for the 6 sprinklers=0.41l/s
Relative humidity= 68%
Table A2: Time and Environmental Conditions During Block Sprinkler Test 1
Time (am/pm) Wind speed( m/s) Temperature (wb)(oC) Temperature (db)(oC) 11:20 1.2 23 30 11:30 1.4 23 30 11:40 1.2 24 31 11:50 1.5 24 31 12:00 1.8 24 31 12:10 1.0 25.5 32 12:20 1.0 25 32 12:30 1.0 25 32 12:40 0.4 24 30.5 12:50 1.0 24 30.5 13:00 1.8 24 30.5 13:10 1.4 24 31 13:20 1.2 24 31
Average 1.2 24 31 Standard Deviation 0.37 0.71 0.69
70
6 3
5
Sprinkler positions
18m
18m
* Catch-can readings in mm (cm3) measured after 2 hours operation
1
2
3
4
5
6 12 18 24 30 36
35
34
33
32
31
11
10
9
8
7
17
16
15
14
13
23
22
21
20
19
29
28
27
26
25
12* (65)
13 (70)
10 (53)
9 (50)
12 (65)
14 (75)
9 (50)
14 (75)
7 (40)
9 (50)
7 (40)
9 (50)
10 (56)
10 (56)
12 (66)
8 (45)
9 (48)
10 (55)
9 (50)
9 (50)
9 (50)
9 (50)
9 (50)
8 (45)
7 (37)
8 (45)
8 (42)
9 (52)
9 (48)
8 (42)
9 (50)
9 (50)
10 (55)
9 (50)
14 (76)
12 (64)
2
1 4
Figure A2:Field Sprinkler Distribution Depths for Block Test 1
71
( )
( )
( )
( )1-
1-
1-
1-
1-
1-
13
l
m
13
1-
lm
mmh9.6
mmh 10008112
1.48 I
ion,configurat 18m12m for the
mmh3.10
mmh 10002112
1.48 I
ion,configurat 12m12m for the
mmh6.4
mmh 10008118
1.48 I
ion,configurat 18m18m for thehm 1.48 test during recorded dischargesprinkler Average
min spacing lateral theis S min spacing mainline theis S
hmin dischargesprinkler theis q where
.mmh 1000SS
q I Raten Applicatio The
=
××
=
×
=
××
=
×
=
××
=
×=
××
=
−
−
The Christiansen Coefficient of Uniformity
100xn
xx1CU
n
1ii
×
×
−−=∑=
∑=
−n
1ii xx - sum of absolute deviations from the mean
n – number of samples
x - mean of the samples
APPLICATION RATE COMPUTATIONS
72
Table A3: Computation of CU and PE for 18m×18m Block Test 1 Can no. Vol (cm3) Depth xi(mm) |xi -x|
1 65 12 2 2 70 13 3 3 53 10 0 4 50 9 1 5 65 12 2 6 75 14 4 7 76 14 4 8 64 12 2 9 50 9 1 10 50 9 1 11 50 9 1 12 75 14 4 13 55 10 0 14 50 9 1 15 50 9 1 16 45 8 2 17 40 7 3 18 50 9 1 19 50 9 1 20 50 9 1 21 37 7 3 22 45 8 2 23 40 7 3 24 50 9 1 25 48 9 1 26 42 8 2 27 42 8 2 28 52 9 1 29 56 10 0 30 56 10 0 31 50 9 1 32 50 9 1 33 48 9 1 34 55 10 0 35 66 12 2 36 45 8 2
346 55
mean 10
CU 83.95
PE 80.21
73
PATTERN EFFICIENCY
%100samples measured all ofmean
sample measuredlowest thenearest to samples theof 25% ofmean PE ×=
Figure A3: Simulation of 12m × 12m Sprinkler Spacing from Single Test Data
0 2
2 12
0 1
5 12
0 0
10 8
1 0
14 5
5 1
14 5
9 3
7 4
12 5
4 2
3 3
8 5
1 4
4 10
0 5
0 12
1 10
0 7
3 8
2 5
5 5
5 4
10 6
3 4
5 9
1 5
2 10
0 5
16
17
18 18 19
25
23
23
19
19
23
19
18 18
17 20
74
Table A4: Computation of CU and PE for Simulated 12m×12m Block Test1
Can No. Depth xi(mm) Deviation |xi -x| 1 16 3.1 2 18 1.1 3 19 0.1 4 19 0.1 5 16 3.1 6 19 0.1 7 19 0.1 8 23 3.9 9 18 1.1 10 18 1.1 11 18 1.1 12 22 2.9 13 17 2.1 14 20 0.9 15 23 3.9 16 22 2.9
307 27.6
mean 19.2
CU 91.0
PE 87.3
75
SPRINKLER DISCHARGE EFFICIENCY (DE)
DE=Mean Water Depth observed/measured
Mean Water Depth Discharged× 100% =
1𝑛∑ 𝑥𝑛
𝑖=1𝑞𝑡
𝑛. 𝑠𝑙. 𝑠𝑚× 100%
SINGLE TEST 1
Where 1𝑛 ∑ 𝑥𝑛𝑖=1 is mean depth measured in single test = 4.8mm
q is the measured discharge = 1.48m3/h
t is the test duration= 2h
n is the number of catch cans =64
sl .sm is the catch can spacing =3m×3m
DE1=164∑ 30764
i=1 mm1.48(2)
64(3)(3)
×100%=4.8mm
5.14mm×100%=93.3%
Using actual measured coverage area ((539.m2) with wetted diameter 26.2m,
DE1a=164∑ 30764
i=1 mm1.48(2)
π(13.1)(13.1)
×100%=4.8mm
5.49mm×100%=87.4%
SINGLE TEST 2
1𝑛∑ 𝑥𝑛𝑖=1 is mean depth measured in single test = 3.6mm
q is the measure discharge = 1.51m3/h
t is the test duration= 2h
n is the number of catch cans =80
sl .sm is the catch can spacing =3m×3m
DE2=180∑ 285.680
i=1 mm1.51(2)
80(3)(3)
×100%=3.6mm
4.19mm×100%=85.9%
Using actual measured coverage area (556m2) with wetted diameter 26.6m,
DE2a=180∑ 285.680
i=1 mm1.51(2)
π(13.3)(13.3)
×100%=3.6mm
5.43mm×100%=66.3%
76
SPRINKLER DISTRIBUTION PATTERNS
Table A5: Sprinkler Distribution Profile Data for Test 1
Distance from sprinkler (m) Average depth
(mm) 21 0 18 1.3 15 2.3 12 4.3 9 7 6 10.8 3 12 0 13 -3 12 -6 10.8 -9 7
-12 4.3 -15 2.3 -18 1.3 -21 0
Figure A4: Sprinkler Precipitation Profile for Test 1
0 1.3
2.3
4.3
7
10.8 12
13 12
10.8
7
4.3
2.3 1.3
0 0
2
4
6
8
10
12
14
21 18 15 12 9 6 3 0 -3 -6 -9 -12 -15 -18 -21
Aver
age
Dept
h of
Pre
cipi
tatio
n (m
m)
Distance From Sprinkler (m)
77
Table A6: Sprinkler Distribution Profile Data for Test 2
Distance from sprinkler (m) Average depth
(mm) 21 0 18 1 15 2 12 3.3 9 5.4 6 9.1 3 13.3 0 14.3 -3 13.3 -6 9.1 -9 5.4
-12 3.3 -15 2 -18 1 -21 0
Figure A4: Sprinkler Precipitation Profile for Test 1
0 1
2 3.3
5.4
9.1
13.3 14.3
13.3
9.1
5.4
3.3 2
1 0 0
2
4
6
8
10
12
14
16
21 18 15 12 9 6 3 0 -3 -6 -9 -12 -15 -18 -21
Aver
age
Dept
h of
Pre
cipi
tatio
n (m
m)
Distance from Sprinkler (m)
78
APPENDIX A: DATA MEASUREMENTS, RESULTS AND COMPUTATIONS – DAY 3
SINGLE TEST
Distance from dam to field=100m
Pressure: 51psi or 352kPa
Wetted diameter measured at three points: 26.6m, 26.5m and 26.6m; average=26.6m
Area of catch can = 55.4cm2
Volume of graduated cylinder= 500ml or 500cm3
Discharge time for 15litres: 36s, 37s, 36s, 36s; average=36s
Average Discharge rate: 0.42l/s or 1.51m3/h
The relative humidity= 55%
Table A7: Time and Environmental Conditions During Single Sprinkler Test 2
Time (am/pm) Wind speed (m/s) Temperature wb (oC) Temperature db (oC) 10:20 1.5 27 34 10:30 1.2 28 35.5 10:40 1.8 25 36.5 10:50 1.8 26 36.5 11:00 2.0 27 36.5 11:10 2.0 27 37 11:20 2.2 28 37 11:30 2.2 27 37 11:40 1.8 28 38 11:50 1.8 28 38 12:00 1.6 28 37.5 12:10 1.6 26 37.5 12:20 1.6 27 38
Average 1.8 27 37 Standard Deviation 0.28 0.95 1.13
79
Figure A6: Field Sprinkler Distribution Depths for Single Test 2
0 0 1 2 3 2 1
4 5 6 5 3 1 0
1 1 6 11
8 4 8
1 2 9 13 14 10
6
6 56
13 13 9 4 1
1 2 3 6 10
9 5
4 5 5 5 4 2 0
2 3
0
6
12 8
4
4
0 10
10
24
48
8
8
0
20
16
14
32
52
16
30
72
6
30
44
3
30
56
20
32
3
56 48
56 72
76
0
32
72
30
30
44 60
1
24
20
8
3
10
# Catch-can readings in 3
*- Catch-can readings in mm
0*
0 4 2 1
0 0 1
16 20 10 6
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
4
4
5
4
3
2
10
2
16
2
30
20
0
0
0
0
0
1
2
2
2
0
0
8
10
1
10
0
0
0
0
80
BLOCK TEST
Pressure measured at the sprinklers 1-6 (psi)
P1=52, P2=51 P3=50 P4=51 P5=50, P6=51
Average pressure = 51psi or 352kPa
Average discharge for the 6 sprinklers=0.41l/s
The relative humidity= 50%
Table A8: Time and Environmental Condition during Block Sprinkler Test 2
Time (am/pm) Wind speed( m/s) Temperature (wb)(oC) Temperature (db)(oC) 13:00 1.6 28 37 13:10 1.6 28.5 37 13:20 1.4 28 37 13:30 1.4 27.5 36.5 13:40 1.6 27.5 36.5 13:50 1.5 28 38 14:00 2.0 28 38 14:10 2.2 28 38 14:20 2.0 29 38.5 14:30 1.8 29 38 14:40 1.8 29 38 14:50 1.8 28 37 15:00 1.8 29 37
Average 1.7 28 37.5 Standard Deviation 0.24 0.56 0.67
81
Sprinkler positions
* Catch-can readings in mm (cm3) measured after 2 hours operation
3
5
18m
18m
1
2
3
4
5
6 12 18 24 30 36
35
34
33
32
31
11
10
9
8
7
17
16
15
14
13
23
22
21
20
19
29
28
27
26
25
12* (65)
11 (60)
11 (60)
12 (65)
11 (60)
12 (64)
9 (52)
10 (55)
9 (48)
9 (50)
7 (40)
9 (50)
9 (50)
9 (50)
8 (45)
9 (50)
8 (45)
7 (40)
9 (48)
8 (45)
9 (50)
9 (50)
9 (50)
9 (48)
9 (48)
7 (40)
8 (46)
8 (46)
9 (50)
9 (52)
9 (52)
9 (50)
11 (60)
10 (54)
11 (60)
10 (55)
2
1 4
6
82
APPLICATION RATE COMPUTATION
( )
( )
( )
( )1-
1-
1-
1-
1-
1-
13
l
m
13
1-
lm
mmh0.7
mmh10008112
1.51 I
ionconfigurat 18m12m for the
mmh5.10
mmh10002112
1.51 I
ionconfigurat 12m12m for the
mmh7.4
mmh10008118
1.51 I
ionconfigurat 18m18m for the thush1.51m test during recorded dischargesprinkler Average
min spacing lateral theis S min spacing mainline theis S
hmin dischargesprinkler theis q where
.mmh1000SS
q I Raten Applicatio The
=
××
=
×
=
××
=
×
=
××
=
×=
××
=
−
−
Figure A7: Field Sprinkler Distribution Depths for Block Test 2
83
83
APPENDIX B: SOIL INFILTRATION TEST RESULTS Site location:…………………………………… Soil type:………………………………….. Test date:…………………………
1 Reading on the clock
hr min sec
2 Time difference
min
3 Cumulative time
min
4 Water level reading before after filling (mm) filling mm
5 Infiltration
mm
6 Infiltration rate
mm/min
7 Infiltration rate
mm/h
8 Cumulative infiltration
mm
Start= 0 Start=0 Start =0
10:31:00
10:33:00
10:36:00
10:41:00
10:51:00
11:01:00
11:11:00
11:31:00
11:51:00
12:11:00
12:31:00
2
3
5
10
10
10
20
20
20
20
2
5
10
20
30
40
60
80
100
120
92
89
85
75
80
84
82
88
91
91
100
100
100
100
100
100
100
100
100
100
8
11
15
25
20
16
18
12
9
9
4.0
3.7
3.0
2.5
2.0
1.6
0.9
0.6
0.45
0.45
240
220
180
150
120
96
72
36
27*
27*
8
19
34
59
79
95
113
125
134
143
Table B1: Soil Infiltration Test 1 Results
*Basic infiltration rate = 27mm/h
AFRAKU Sandy Loam 4TH APRIL 2008
84
Table B2: Soil Infiltration Test 2 Results
*Basic infiltration rate = 30mm/h
1 Reading on the clock
hr min sec
2 Time difference
min
3 Cumulative time
min
4 Water level reading before after filling (mm) filling mm
5 Infiltration
mm
6 Infiltration rate
mm/min
7 Infiltration rate
mm/h
8 Cumulative infiltration
mm
Start= 0 Start=0 Start =0
13:05:00
13:07:00
13:10:00
13:15:00
13:25:00
13:35:00
13:45:00
14:05:00
14:25:00
14:45:00
15:05:00
2
3
5
10
10
10
20
20
20
20
2
5
10
20
30
40
60
80
100
120
94
92
88
82
88
92
88
90
90
90
100
100
100
100
100
100
100
100
100
100
6
8
12
18
12
8
12
10
10
10
3.0
2.7
2.4
1.8
1.2
0.8
0.6
0.5
0.5
0.5
180
160
144
108
72
48
36
30
30*
30*
6
14
26
44
56
64
76
86
96
106
85
Table B4: Summary of InfiltrationTest 2 ResultsCum Time(min) Cum infil (mm) Infil Rate(mm/min)
0 02 8 45 19 3.710 34 320 59 2.530 79 240 95 1.660 113 0.980 125 0.6
100 134 0.45120 143 0.45
Table B3: Summary of Infiltration Test 1 ResultCum Time(min) cum infil (mm) infil Rate(mm/min)
0 02 6 35 14 2.710 26 2.420 44 1.830 56 1.240 64 0.860 76 0.680 86 0.5
100 96 0.5120 106 0.5
86
Figure B1: Cumulative infiltration curve for test 1
y = -0.0073x2 + 1.6621x + 6.5346
0
20
40
60
80
100
120
0 20 40 60 80 100 120 140
Cum
ulat
ive
Infil
trat
ion
(mm
)
Cumulative Time (min)
87
Figure B2: Infiltration rate curve for test 1
y = 6.0591x-0.525
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
0 20 40 60 80 100 120 140
Infil
trat
ion
Rate
(mm
/min
)
Cumulative Time (min)
88
Figure B3: Cumulative infiltration curve for test 2
y = -0.0125x2 + 2.575x + 6.659
0
20
40
60
80
100
120
140
160
0 20 40 60 80 100 120 140
Cum
ulat
ive
Infil
trat
oin
(mm
)
Cumulative Time
89
Figure B4: Infiltration rate curve for test 2
y = 9.575x-0.581
0
1
2
3
4
5
6
7
0 20 40 60 80 100 120 140
Infil
trat
ion
Rate
(mm
/min
)
Cumulative Time (min)
Infiltration Rate Curve 2
90
APPENDIX C – STATISTICAL ANALYSIS Table C1: t- Test for Means of the 12m ×12m Simulated Data
Test 1 Depth (mm)
Test 2 Depth(mm)
16 19 18 14 19 17 19 21 16 14 19 17 19 17 23 22 18 17 18 17 18 14 22 18 17 17 20 16 23 18 22 19 Total 307 277
t-Test: Paired Two Sample for Means
Variable 1 Variable
2 Mean 19.1875 17.2875 Variance 5.095833 4.953167 Observations 16 16 Pearson Correlation 0.537919
Hypothesized Mean Difference 0
df 15 t Stat 3.526692 P(T<=t) one-tail 0.001526 t Critical one-tail 1.75305 P(T<=t) two-tail 0.003052 t Critical two-tail 2.13145
Ho : μ1=μ2 H1 : μ1≠μ2 P values less than α=0.05 hence Decision: Ho is
rejected Conclusion: There is significant difference between the two means
91
Table C2: z- Test for Means of the 18m ×18m Block Data
Vol(cm3) Test 1 Depth (mm) Vol(cm3) Test 2 Depth (mm) 65 12 65 12
70 13 60 11 53 10 60 11 50 9 65 12 65 12 60 11 75 14 64 12 76 14 60 11 64 12 55 10 50 9 50 9 50 9 50 9 50 9 52 9 75 14 55 10 55 10 60 11 50 9 54 10 50 9 50 9 45 8 48 9 40 7 48 9 50 9 50 9 50 9 52 9 50 9 50 9 37 7 48 9 45 8 40 7 40 7 40 7 50 9 50 9 48 9 50 9 42 8 52 9 42 8 46 8 52 9 46 8 56 10 50 9 56 10 50 9 50 9 48 9 50 9 45 8 48 9 45 8 55 10 40 7 66 12 45 8 45 8 50 9
Total 346
334 Variance 3.3
1.5
92
Hypotheses
Ho : μ1=μ2
H1 : μ1≠μ2
P values for both tail tests>α
Decision: Do not Reject Ho.
Conclusion: There is no significant difference between the means
z-Test: Two Sample for Means
Variable 1 Variable 2 Mean 9.601885279 9.291014842 Known Variance 3.3 1.5 Observations 36 36 Hypothesized Mean Difference 0
z 0.851353755 P(Z<=z) one-tail 0.197286436 z Critical one-tail 1.644853627 P(Z<=z) two-tail 0.394572873 z Critical two-tail 1.959963985
93
APPENDIX D: DESIGNED IRRIGATION SYSTEM FOR A 1.2 HECTARE (3 ACRE) FIELD
POND
PUMP
ML Ø75mm
10m
110m
18m
10
m
18m 10m 10m
110m
1 1 2 3 3 2
LL1 Ø50mm LL2
METER
Figure D1: Proposed Irrigation Plan for a 1.2ha (3 acre) Field at Afraku
94
KEY
Sprinkler Position
75mm-50mm Reducer Position with Lateral Move Positions in numerals
ML – Main Line
LL – Lateral Line
Valves
1
CHAPTER ONE
INTRODUCTION
1.1 Background
Irrigation is the artificial application of water to the soil or plant, in the required quantity
and at the time needed. Irrigation is thus a risk management tool for agricultural
production. The risk of yield reduction due to drought is minimised with irrigation,
because moisture can be added to the soil to meet the water requirements of the crop. The
art of irrigation can be achieved using watering cans, sprinklers, emitters, surface systems
and many others. Irrigation is widely carried out through surface and pressurised systems,
characterised by the mode of transport of the water onto the point of application (Keller
and Bliesner, 1990).
Irrigation efficiency is an essential component of any irrigation system management due
to its relationship with the energy and the labour requirements for implementing a
sustainable irrigation scheme. According to Huck (2000), any sprinkler irrigation system
with distribution uniformity (DU) of 85%, in the field, is excellent and acceptable. This
means that even the best sprinkler irrigation system may begin with some 15%
inefficiency. The current stress on water resources, escalating energy cost and threat to
groundwater resource and the environment, at large, further accentuate the essence of
irrigation efficiency. Yoshida et al (2004) wrote that irrigation efficiency, together with
adequacy, equity and reliability constitute one of the major objectives in the management
of water transport and distribution systems for irrigation purposes.
2
Sprinkler irrigation is a class of pressurised irrigation method in which water is carried
through a pipe system to a point near where it will be utilised/consumed. A pressurised
piped irrigation system is a network installation consisting of pipes, fittings and other
devices properly designed and installed to supply water under pressure from the source of
water to the irrigable area (Yoshida et al, 2004). Sprinkler irrigation is suitable for most
crops and adaptable to nearly all irrigable soils (and terrains) due to the availability of
different range of discharge capacities. With the aid of sprinklers, water is sprayed
through the air onto the soil surface or crop and the pattern of the spray simulates rainfall.
The delivery of the water to the soil/plant through the air, however, introduces some
degree of uncertainty as wind and other atmospheric conditions, such as temperature and
relative humidity affect the water application efficiency. Furthermore, variation in
rotational speed of sprinklers, differences in discharges and irregularity of the trajectory
angle caused by riser straightness contribute to the non-uniform application problem
(Keller and Bliesner, 1990). Moreover, no irrigation system, or even ‘Mother Nature’,
applies water in a ‘perfectly’ uniform way, so wet and dry spots always occur (Solomon,
1992). The presence of such bottlenecks leads to under- or over-irrigation on the same
field. Non-uniform application also leads to surface redistribution and eventually
leaching of nutrients on over-irrigated areas whilst under-irrigated portions end up as
dead spots, unable to support plant growth and also create non-uniform crop stands.
These negate the usual goal of sprinkling, which is uniform watering of an entire field
(Keller and Bliesner, 1990).
3
1.2 Justification
Evaluating the uniformity of a sprinkler irrigation system is of significance to realising
the basic aim of efficient application of water to eliminate wastage and the overall
improvement in potential irrigation system efficiency. Moreover, it is essential to
evaluate the performance of new systems because they should be operating at the
designed specification and old systems because their performance deteriorates with time
due to wear. With current developments in agriculture, fertiliser is even applied with
irrigation water (fertigation) and so non-uniform application has both economic and
environmental consequences. Some inherent benefits of the study according to Wilson
and Zoldoske (1997) are:
- Improved soil-moisture uniformity,
- Lower water or energy requirement,
- Easier irrigation system scheduling and management,
- Reduced runoff and deep percolation and
- Healthier plant growth for optimum yields.
Furthermore, fewer specific sprinklers sold in Ghana, have the requisite manufacturer’s
supporting data regarding their basic operational characteristics. The most commonly
used brass impact sprinklers, which are affordable to farmers, do not come with any
performance data (Dawson, 2007). Thus field evaluation is inevitable to obtain essential
data needed to determine the suitability of the sprinkler packages for a given field
condition.
The Grains and Legumes Development Board (GLDB) is the body, established by Act of
Parliament of Ghana (1970), mandated to produce foundation seeds of grains and
4
legumes in Ghana and this study would be of immense benefit to the day-to-day practice
of irrigation for the production of foundation seed of crops like maize, legumes, citrus
and other planting materials. As a seed production agency, with limited budget, the
GLDB’s production is geared towards meeting demands of farmers in an established
chain and hence uniformity of water application is critical to realising yield targets and
maintaining the seed production chain in Ghana. Unfortunately, there is no data on the
sprinklers being used on GLDB’s farms.
The study has the potential benefit of improving irrigation efficiency and reducing stress
on water resources and losses of water and nutrients to groundwater and surface water
resources. Furthermore, findings from the study would serve as a guide in the
implementation of future sprinkler systems for irrigating larger areas with a given volume
of water. This study would also contribute to knowledge in the field of irrigation practice
in Ghana at large.
1.3 Aim and Objectives
The aim of this research was to examine the performance of an existing sprinkler
irrigation system with a view to designing an optimal system for production of
foundation seeds at the GLDB’s farms at Afraku. The specific objectives were to
determine:
• The distribution pattern and pattern efficiency (PE) of the sprinklers
• The mean application rates (MAR) of the sprinklers
• The coefficient of uniformity (CU) of water application
• The efficiency of the system and finally
• To re-design the system for optimal performance
5
1.4 Scope of Study
This thesis is divided into 5 chapters. Chapter 1 contains the introduction, the objectives
and the justification for the study. Chapter 2 discusses relevant literature on irrigation and
parameters utilised in the evaluation of the sprinkler irrigation system. The materials and
method used to conduct field trials are presented in Chapter 3, which also describes the
characteristics of the study area. Chapter 4 presents the results of the research and
discusses these results in comparison with available literature. The derived conclusions
and recommendations are finally presented in Chapter 5.
6
CHAPTER TWO
LITERATURE REVIEW
2.1 Introduction
This chapter discusses the subject of irrigation and the major types of irrigation.
Emphasis is laid on pressurised irrigation systems and sprinkler irrigation in particular
with a review of the main components of the system. The advantages and disadvantages
of sprinkler irrigation have also been enumerated. Irrigation efficiency and the major
measures of irrigation system performance are highlighted. Furthermore, the major losses
associated with sprinkler irrigation have also been outlined. Finally, the design of
sprinkler irrigation system and the adverse effects of poorly-designed systems are
discussed.
2.2 Irrigation
Irrigation is the artificial application of water to the land to provide adequate moisture for
crop production (Solomon, 1990). Phocaides (2000) also defined irrigation as the
application of water, supplementary to that supplied directly by precipitation, for the
production of crops. Indisputably, agriculture is the greatest user of water resources in the
world totalling 70% of total withdrawals and over 80% of the consumptive use of water
(Baudequin and Molle, 2003). Stockle (2001) also wrote that agriculture is the major user
of freshwater, with a world’s average of 71% of the water use. It was added that there are
large regional variations, from 88% in Africa to less than 50% in Europe. Ascough and
Kiker (2002) also stated that irrigated agriculture is the largest user of water resources in
South Africa accounting for 53% of the total annual amount used.
7
World Politics Archives (2000) stated that in Ghana, agriculture accounts for 52% of
water resources withdrawn annually.
Irrigation includes the development of the water supply, the conveyance system, the
method of application, and the waste water disposal system, along with the necessary
management to achieve the intended purpose. In more arid areas, rainfall during the
growing season falls short of most crop needs and thus irrigation makes up for the
shortage. Even in areas of high seasonal rainfall, crops often suffer from lack of moisture
for short periods during some part of the growing season (USDA, 1984). These therefore
underline the importance of irrigation in attaining crop production targets.
Notwithstanding the foregoing potentials, irrigation systems have inherent application
limitations that make field calibration and irrigation scheduling critical for proper use of
the applied water.
2.3 Types of Irrigation Systems
There are two basic types of irrigation systems namely open canal systems and
pressurised piped systems (Phocaides, 2000). Irrigation is thus implemented through
surface and pressurised systems, characterised by the mode of transport of the water onto
the point of application (Keller and Bliesner, 1990). Scherer (2005) expands it further
that there are four basic methods, of water application, which are subsurface irrigation,
surface/gravity irrigation, trickle/drip irrigation and sprinkler irrigation. A pressurised
irrigation system is a network installation consisting of pipes, fittings and other devices
properly designed and installed to supply water under pressure from the source of the
8
water to the irrigable area (Phocaides, 2000). Pressurised piped systems generally consist
of sprinkler and trickler/drip irrigation systems.
2.4 Components of Pressurised Irrigation Systems
The main components of all pressurised irrigation systems (as shown in Figure 1)
according to Phocaides (2000) are:
• the control station (head control unit)
• the mains and submains (pipelines)
• the hydrants
• the manifolds (feeder pipelines) and
• the laterals (irrigating pipelines) with the emitters/sprinklers
Figure 1 - Schematic of a pressurised irrigation network layout (Phocaides, 2000)
9
2.4.1 Head Control
This consists of a supply line (rigid PVC, or threaded galvanised steel) installed
horizontally at a minimum height of 60 cm above ground. It is equipped with an air
release valve, a check valve, 50 mm (2”) hose outlets for connection with the fertiliser
injector, a shut-off valve between the two outlets, a fertiliser injector and a filter. Where a
gravel filter or a hydrocyclone sand separator is required, it is installed at the beginning
of this unit complex. A pump is needed in a sprinkler system, at the head control, to
deliver water against gravity.
2.4.2 Main Pipeline
It is the largest diameter pipeline of the network, capable of conveying the flow of the
system under favourable hydraulic conditions of flow velocity and friction losses. The
pipes used are generally buried permanent assembly rigid PVC, black high density
polyethylene (HDPE), layflat hose, and quick coupling galvanised light steel/PVC pipes
in sizes ranging from 50 to 150 mm (2-6”) depending on the area of the farm.
2.4.3 Submains
These are smaller diameter pipelines which extend from the main lines and to which the
system flow is diverted for distribution to the various plots. These pipes are the same type
as the mains.
10
2.4.4 Offtake Hydrants
These are fitted on the submains or the mains and equipped with a 50-75mm (2-3”) shut-
off valve. They deliver the whole or part of the flow to the manifolds (feeder lines).
Furthermore, hydrants serve as controls for switching between sets and the isolation
and/or correction of defective feeder lines.
2.4.5 Manifolds (Feeder Lines)
These are pipelines of a smaller diameter than the submains and are connected to the
hydrants and laid, usually on the surface, along the plot edges to feed the laterals. They
can be of any kind of pipe available (usually HDPE) in sizes of 50-75 mm (2-3”).
2.4.6 Laterals (Irrigating Lines)
These are the smallest diameter pipelines of the system. They are fitted to the manifolds,
perpendicular to them, at fixed positions, laid along the plant rows and equipped with
water emitters at fixed frequent spacing.
2.4.7 Emitters
A water emitter for irrigation is a device of any kind, type and size which, fitted on a
pipe, is operated under pressure to discharge water in any form: by shooting water jets
into the air (sprinklers), by small spray or mist (sprayers), by continuous drops (drippers),
by small stream or fountain (bubblers, gates and openings on pipes, small diameter
hoses), and so on (Phocaides, 2000).
11
2.5 Sprinkler Irrigation
Sprinkler irrigation systems are broadly categorised into set and continuous-move
systems (Keller and Bliesner, 1990). In set systems, the sprinklers are stationary while
irrigating, whereas sprinklers move, in either straight or circular paths, while irrigating in
the case of continuous-move systems. The set-move or solid set system is sub-divided
into portable and periodic-move systems. The portable systems are either hand-moved or
tractor-moved (end-tow, side-row, side-move, gun and boom). In these systems the
sprinkler laterals are moved manually or mechanically between irrigation sets (Merkley
and Allen, 2004). The periodic-move category, also called the self-propelled or ‘wheel
lines’, are suitable for low to medium height crops.
In solid set systems, the sprinklers may be attached directly to the pipe lines in the case of
low growing crops or attached to a riser for vegetables and taller crops such as citrus and
grains. The fixed/permanent set systems consist of sprinklers attached to buried laterals
which are installed to cover the entire field. Usually, a line/lateral or a block of laterals is
irrigated at once and the next irrigation set is the adjacent lateral or block of laterals
(Merkley and Allen, 2004). In both solid and permanent set systems, movement within
set irrigation events is facilitated by valves which are strategically installed in the pipe
network. Continuous-move systems include travelers, centre pivot and linear move
systems.
12
2.5.1 Advantages of Sprinkler Irrigation Systems
Sprinkler irrigation has advantages according to Keller and Bliesner (1990) regarding:
• Adaptability to various land topographies, problem soils with intermixed textures,
and the amount of water applied because of the wide ranges of sprinkler discharge
available
• Labour requirements which reduce relative to the system being employed; from
hand-moved to fixed systems down to automated systems
• Achieving other special tasks such as modifying/controlling extreme weather
conditions, supplementing erratic rainfall and leaching of salts from saline soils an
• Water savings for systems with high application efficiency.
2.5.2 Disadvantages of Sprinkler Irrigation Systems
• The system requires high initial capital and pumping cost compared to surface
irrigation systems
• The quality of water has effect on both the quality of crops produced and the
system itself. For instance saline water has the potential of corroding metal parts
employed in many irrigation systems
• The sprinkle system is not well-suited to soils with intake rate (infiltration rate)
less than 3mm/h
• The system is greatly affected by windy and excessively dry conditions, which
cause low irrigation efficiencies and
• Field shapes other than rectangular are not suitable for the system, especially for
mechanised sprinkler systems
13
2.5.3 Limitations of Sprinkler Irrigation Systems
Irrigation systems have inherent application limitations that make field calibration critical
for efficient use of water resources. Irrigation systems are normally designed to satisfy
equipment specifications provided in manufacturers’ charts. However, information
presented in manufacturers’ charts is obtained under controlled or still wind conditions
and is based on average operating conditions for relatively new equipment. The discharge
rates and precipitation rates, and therefore performance, change over time as equipment
ages and components wear due to rust caused by the use of saline water sources.
Sprinkler irrigation designs that neglect prevailing field/crop characteristics and
environmental factors can lead to poor system performance. Consequently, equipment
should be field calibrated regularly to ensure that application rates and uniformity are
consistent with values used during the system design and those given in manufacturers’
specifications. Moreover, sprinkler irrigation design and management rules are very site
specific, change with the irrigation materials, and most often rely on unstructured
experiments and life-long professional experience. Hence, regular evaluation of irrigation
systems is of essence to the maintenance of the systems for optimal performance at the
designed parameters (Ascough and Kiker, 2002).
2.6 Irrigation Efficiency
Irrigation efficiency can be defined in many ways, with over 30 definitions currently in
use (Landwise Inc., 2006; Dalton and Raine, 1999). For example, Dalton and Raine
(1999) defined efficiency as the ratio of useful work done to the energy expended. This is
due to the numerous water management sub-systems existing on most irrigated farms.
14
These sub-systems include supply systems, on-farm storage systems, on-farm distribution
systems, application systems and recycling systems (Dalton and Raine, 1999). Efficient
on-farm irrigation depends on water use, energy use, labour, capital investments and how
these aspects relate to production and profitability, and there is no single definition that
covers all aspects of irrigation efficiency. Although there are variant definitions of
irrigation efficiency, they can be grouped into three main categories: irrigation efficiency,
application efficiency and distribution efficiency (Landwise Inc., 2006).
Irrigation efficiency relates to the fraction of water applied to a field that is really utilised
beneficially by the crop. The measurement of ‘beneficial use’, however, is only attainable
on long term basis rather than a single event. So in defining ‘beneficial use’ the boundary
area is very critical (Burt and Styles, 1994 as in Landwise Inc., 2006). Beneficial uses of
irrigation include replacing crop evapotranspiration (ET) (the primary reason for
irrigating), crop cooling, frost protection, crop germination and metabolism, leaching
requirement and pest control. Although frost protection results in the highest peak use in
terms of litres per second per hectare, meeting crop ET requires the highest volumetric
use over an irrigation season (Landwise Inc., 2006).
Where the expected performance index is to be obtained from a single event then
application efficiency, which is generally understood as irrigation efficiency, is used
(Brennan and Calder, 2006). Keller and Bliesner (1990), wrote that the most often used
irrigation efficiency term is the ‘Classical Application Efficiency’, which is defined as
the ratio of the average depth of irrigation water available for evapotranspiration to the
gross depth of irrigation water delivered to the field. Distribution efficiency is a measure
15
of uneven application and it is usually defined in terms of distribution
uniformity/coefficient of uniformity and has a significant effect on the application
efficiency (Landwise Inc., 2006).
2.7 Irrigation Uniformity
Irrigation uniformity is how evenly water is distributed to different areas of the field.
Solomon (1992) wrote that irrigation uniformity actually refers to the variation, or non-
uniformity in the amounts of water applied to locations within the irrigated area.
Therefore, Kelley (2004) asserts that irrigation uniformity is a concept that all areas
within an irrigated field received the same amount of water. Solomon (1990) stated that
specific quantitative study of sprinkler irrigation uniformity started with the work of J. E.
Christiansen in 1942. High irrigation uniformity connotes water being applied adequately
with little excess and low uniformity indicates that some portions of the field would be
deprived of water while other locations will become over-irrigated. Unfortunately, no
irrigation system or even mother nature, applies water in a perfectly uniform way, so wet
and dry spots always occur (Solomon, 1990).
Montero et al (2002) stated that low values of CU are usually indicators of a faulty
combination of factors such as nozzle sizes, working pressure and spacing of sprinklers.
Keller and Bliesner (1990) linked the performance of sprinkler irrigation systems to the
sprinkler physical characteristics (i.e. jet angle, number and shape of nozzles and mode of
operation), nozzle size and pressure. It was recommended that the CU values used for the
final design of a system should be based on actual field or test facility data.
16
Hachum (2006) wrote that the principal indices for evaluating the performance of farm
irrigation systems are:
• Uniformity of water distribution (the key index in the evaluation)
• Adequacy of irrigation, and
• Efficiency of irrigation
According to Dalton and Raine (1999), an important component of the evaluation of in-
field irrigation system performance is the assessment of irrigation uniformity. Irrigation
uniformity is thus an important management factor necessary for achieving high
irrigation efficiency.
King et al (2000) also stated that to maximise production efficiency, two irrigation
management issues required attention, that is, irrigation scheduling and uniformity. The
evaluation of sprinkler systems typically involves an assessment of the volumetric
discharge rate and the uniformity of the discharge (Dalton and Raine, 1999). Huck (2004)
also wrote that for existing irrigation systems, irrigation audit or catch-can test is a good
method for evaluating sprinkler system efficiency. It has been found that raising the
irrigation uniformity from 70% to 90% allows half as much area to be irrigated
adequately with a given volume of water (Davoren, 1995). Irrigation uniformity is thus
affected by the sprinkler characteristics and layout, operating pressure, environmental
conditions and management practices. Assessing irrigation system uniformity is therefore
pivotal to the design of an effective irrigation system.
17
2.7.1 Methods of Determination of Sprinkler Water Distribution
The procedures for determining water distribution and hence sprinkler uniformity are:
• Applying the catch can grid to the existing irrigation system according to Merriam
and Keller (1978) as in Keller and Bliesner (1990)
• Placing a catch can grid around a single sprinkler head in no-wind conditions and
establishing the corresponding overlapping for any sprinkler spacing (Solomon,
1979 as in Montero et al, 2002)
• Reducing the catch cans grid to a single-leg in a radial pattern, in no-wind and
with high relative humidity conditions. The application rate can be calculated by
rotating the radial pattern around the sprinkler (Vories and von Bernuth, 1986 as
in Montero et al, 2002).
2.7.2 Agronomic Significance of Irrigation Uniformity and Performance
Irrigation uniformity is linked to crop yield through the effects of under or over irrigation.
Inadequate water results in high soil moisture tension, plant stress and reduced crop
yields, whilst excess water may also reduce crop yield through mechanisms such as
leaching of plant nutrients, increased disease incidence or hindered growth of
commercially valuable parts of crops (Solomon, 1990). The uniformity and performance
of an irrigation system are inherently associated with the manner in which agricultural
resources are utilised. So that non-uniformity and under performance result in excess
pumping costs and fertiliser loss either through fertigation or leaching by the excess
water. Capital losses are also incurred due to the extra capacity put into the irrigation and
drainage systems to convey the excess water from the field (Solomon, 1990).
18
2.7.3 Irrigation Uniformity and Water Requirement
To conserve water resources, the performance of irrigation systems needs serious
attention. This demands the evaluation of systems on a regular basis and the
implementation of corrective measures to keep the system operating according to design.
The Resource Conservation District of Monterey County (2001) in USA had proven that
a better uniformity can lead to better crop yield, fertilizer application and irrigation
efficiency.
2.7.4 Coefficient of Uniformity
Coefficient of uniformity is a measure of non-uniformity of water application for a given
sprinkler head, nozzle type, operating pressure and sprinkler spacing combination. It is
thus an index of irrigation uniformity. The main stream agricultural industry has long
used a calculated coefficient of uniformity to measure the non-uniformity of water
application (Solomon, 1992).
2.8 Quantitative Measures of Irrigation Uniformity
2.8.1Christiansen’s Coefficient of Uniformity (CU)
Dalton and Raine (1999) found CU as the most commonly used quantitative measure of
irrigation uniformity. This coefficient measures the average deviation from the mean
application depth. Hence, for a perfectly uniform application the CU is 100%, which is
impossible to achieve on a field scale due to equipment deficiencies and limiting
environmental factors. CU values of 80-90% is attainable for set-move systems which are
19
properly designed and maintained, operating under moderate wind speeds less than
16km/h. It has been found that CU values as low as 60% can occur with systems on
undulating topography, with worn or plugged nozzles, and/or under windy conditions
(King et al, 2000). Sprinkler uniformity is generally affected by the combination of wind
speed/direction, operating pressure and sprinkler spacing, in the case of set-move
sprinkler system. Dalton and Raine (1999) found that a wide range of irrigation
uniformity coefficients are used when evaluating performance of irrigation systems and
that one of the basic measures of any irrigation system’s performance is Christiansen’s
uniformity coefficient (CU). Smith (1995) as in Dalton and Raine (1999) indicated that
the uniformity of application is acceptable for CU values greater than 0.84 or 84%. Keller
and Bliesner (1990) also wrote that in general CU of at least 85% is recommended for
delicate and shallow-rooted crops such as potatoes and most other vegetables, whilst
values between 75% and 83% is acceptable for deep-rooted crops like alfalfa, corn,
cotton and sugar beets. In cases where chemicals are applied through the irrigation water,
the CU should be at least 80%.
The mathematical expression for CU is:
( )ax
MCU 1..................................................................................................................1100
−=
Where M is the main absolute deviation of the applied depths, xi, and is given as:
nxx
M i −= ∑
Where x is the mean applied depth and n is the number of catch-can measurements.
20
Alternatively, CU is expressed as:
( )1b..........................................................................................100.......xn
xx1CU
n
1ii
×
×
−−=∑=
Where x is the mean water depth collected in all catch-cans, n is the number of cans and
xi is the water depth collected by a catch-can, i.
2.8.2 Pattern Efficiency (PE) /Distribution Uniformity (DU)
Distribution uniformity is usually defined as a ratio of the smallest accumulated depths in
the distribution to the average depths of the whole distribution (Ascough and Kiker,
2002). This uniformity measure is also called low-quarter distribution uniformity and it is
often used to quantify irrigation uniformity of surface systems (King et al, 2000). The
DU coefficient takes into account the variation of can readings from the mean but
concentrates on the lowest 25% of readings. A commonly used fraction is the lower
quarter, which has been used by the USDA since the 1940s (Ascough and Kiker, 2002).
( ) 100% 25 ×=M
MDU …………………………………………………………………..(2)
Where M is the mean of all the can readings and M25 is the lowest 25% of all the can
readings.
Wilson and Zoldoske (1997) stated that the disadvantage of the DU coefficient is that it
treats under-watering as the critical element but does not indicate how big or severe the
dry spot really is.
21
2.9 Sprinkler Irrigation Factors Affecting Uniformity
Sprinkler irrigation uniformity is affected significantly by:
• Equipment and design factors such as sprinkler characteristics (that is number of
nozzles, size and shape), operating pressure and sprinkler spacing
• Environmental factors such as humidity and more importantly wind condition and
• Management factors such as length of irrigation time, time of day irrigation is
performed, practising of offsetting laterals (alternate sets) and irrigating blocks of
several adjacent laterals at once (Solomon, 1992).
2.9.1 Operating Pressure
The pressure of the irrigation system is the maximum water pressure required for normal
operation and it includes the friction losses in the piping network from the control station
to the distal end of the system, the difference in elevation and the pressure required at the
emitter/sprinkler. Operating pressure used in this work refers to the pressure measured at
the emitter, in this case the sprinklers. Sprinkler irrigation systems can be classified by
the operating pressure as follows (Phocaides, 2000):
• Low pressure systems, where the pressure required are 200-350 kPa;
• Medium pressure, where the pressure required is 350-500 kPa;
• High pressure, where the pressure required exceeds 500 kPa.
The operating pressure of sprinklers has significant impact on irrigation uniformity and
the overall performance of the irrigation systems. The optimum operating pressure of
impact sprinklers, with standard straight bore nozzle is 310.5 kPa to 414 kPa (45 to 60
psi). Armstrong et al (2001) give the common operating pressure range for overhead
22
impact sprinklers as 240 – 400 kPa. Under low pressures less than 276 kPa (40 psi), the
water jet leaving the nozzle does not break up adequately and this results in concentrated
water application. Conversely, pressures above 483 kPa (70 psi) break the jet excessively
(misting) resulting in concentrated water application near the sprinklers (King et al,
2000). This also creates fine mist in the sprinkling zone resulting in excessive wind drift
and evaporation. The operating pressure controls the wetted diameter and the mean water
droplet size (Kranz et al, 2005) as depicted in Figure 2.
To achieve acceptable uniformity, the pressure variation along a lateral is not to exceed
20% of the design pressure. Excessive pressure variation, however, is prevalent on
undulating or sloping topographies and this problem is best rectified with the use of
pressure compensating nozzles or pressure regulators. With rocketing energy cost, the
Too high Pressure
Normal Pressure
Too low Pressure
Wetted diameter
Wetted diameter
Figure 2 Effect of pressure on droplet size and wetted diameter (Source: Kranz et al, 2005)
23
tendency has been to reduce the operating pressure so as to make savings on fuel. To
achieve this, special nozzles (with non-circular orifices) which use mechanical means to
provide extra breakup of the water jet at low pressures are utilised. Such nozzles operate
at pressures that are 1 bar lower than the traditional nozzles (Solomon, 1990).
2.9.1.1 Pressure Measurement
The operating pressures of sprinklers are in the range of 150-250 kPa for low pressure
sprinklers and 400-900 kPa for high pressure sprinklers. Most agricultural sprinklers,
however, have hammer-driven slow-rotating or revolving mechanism and use low-
medium operating pressures i.e. 200 – 350 kPa (Phocaides, 2000). Merkley and Allen
(2004) also wrote that the medium pressure sprinklers operate between 200 and 410 kPa.
For satisfactory sprinkling with impact rotating conventional sprinklers, the minimum
operating pressure should be at least 200 kPa.
According to King et al (2000), a Pitot tube attached to a pressure gauge can be used to
check a pressure regulator’s operation. There are three categories of pressure
measurement, namely, absolute pressure, gauge pressure and differential pressure.
Moreover, there are two types of fluid systems, which are static and dynamic systems. In
dynamic systems, typical of flow through a nozzle, pressure is defined using three terms:
static pressure, dynamic pressure and total pressure. The Pitot tube measures the total
pressure, which is the sum of the static and dynamic pressures. The total pressure is
obtained when the flowing fluid decelerates to zero in an isentropic (frictionless) process.
24
Hence the energy of the fluid is converted to pressure in the Pitot tube and the magnitude
is registered by the pressure gauge attached to the tube (Heeley, 2005).
2.9.2 Sprinkler Precipitation Profile
The extent of uniformity achievable by a set irrigation system is greatly affected by the
water distribution pattern. Each type of sprinkler has its characteristic precipitation
profile which varies with nozzle size and operating pressure. Figure 3 gives typical
precipitation profiles for sprinklers operating at different pressures.
Figure 3: Relative effects of Different Pressure on Precipitation Profiles for a Typical Double Nozzle Sprinkler (Source: Keller and Bliesner, 1990)
Figure 3A depicts a sprinkler operating at too low a pressure. Under such conditions, the
water from the nozzle concentrates in a ring a distance away from the sprinkler resulting
in a poor precipitation profile. At satisfactory/optimum pressure range the precipitation is
symmetrical around the sprinkler as shown in Figure 3B. At excessive pressure ranges,
the water from the nozzle breaks into fine drops and settles around the sprinkler (Figure
25
3C). The fineness of the droplets makes them susceptible to wind movement (Keller and
Bliesner, 1990).
2.9.3 Wind
The performance of sprinkler irrigation systems is greatly affected by both the direction
and magnitude of the prevailing wind. Wind is the chief modifier that reduces the
diameter of throw and changes the profiles of sprinklers as depicted in Figure 4.
Figure 4: The effect of wind on a sprinkler pattern. Top: Sprinkler working under ideal conditions. Bottom: The same sprinkler under windy conditions (Source: Calder, 2005)
Wind speed in combination with sprinkler spacing has significant impact on the
uniformity of set-move sprinkler irrigation systems. The problem is pronounced
especially when wind speed exceeds 8 km/h. The changes in wind speed and direction,
however, tend to increase the cumulative irrigation uniformity calculated over multiple
26
irrigation events. Another phenomenon associated with the wind condition is ‘wind
skips’, which occurs when there is a large difference in wind speed and/or direction
between adjacent irrigation sets. This creates temporary dry zones adjacent to the
sprinkler laterals on the upwind side. It is, however, not cumulative and successive
irrigations/moves correct this effect (King et al, 2000). Notwithstanding these limiting
effects, Merkley and Allen (2004) wrote that occasionally, wind can help improve
uniformity as the randomness of wind turbulence and gusts contribute to smoothening out
the distribution pattern/profile.
2.9.4 Sprinkler Spacing
There are three main types of sprinkler spacing patterns and a number of variations to
adapt these patterns to special situations. These spacing are the square, rectangular and
triangular patterns. The square pattern has equal distance running between the four
sprinkler positions and it is suitable for irrigating square-shaped areas. The limitation of
this pattern is the diagonal distance between sprinklers in the corners and this is usually
susceptible to wind effects. To minimise wind effects, closer spacing is recommended
depending on the severity of the wind. The rectangular sprinkler spacing has sprinkler
positions forming a rectangle with the shorter side of the rectangle across the wind and
the longer side with the wind, so as to obtain a good coverage. This pattern has the
advantage of fighting windy situations and it is suitable for areas with defined straight
boundaries and corners. In the triangular pattern, sprinklers are arranged in equilateral
triangle formats so that the distance from each other is equal. This pattern allows for
lengthy spacing and therefore requires fewer sprinklers compared to the square spacing,
27
for a specified area. Furthermore, two of the above patterns can also be combined on the
same site to achieve optimum sprinkler coverage (Phocaides, 2000).
2.10 Critical Determinants of Irrigation System Performance
Four factors critical to achieving high levels of performance for any irrigation system
are:
• Irrigation timing
• Depth of application
• Uniformity, and
• Water supply characteristics
Irrigation system design is to create the potential for high performance and it must result
in an application system that farmers can use to irrigate uniformly, in the right amount
and at the right time. The performance of an irrigation system is significantly affected by
the interactions between the application system characteristics and water supply
characteristics. Irrigation system design must take into account the water supply
characteristics to ensure that farmers have sufficient flexibility to irrigate at the right time
and apply the right amount of water (Lincoln Environmental, 2000).
28
2.11 Types and Operation Mechanisms of Impact Sprinkler Heads
There are three types of impact sprinkler heads used in agricultural applications. These
are the spoon-driven, wedge-driven and precision jet sprinkler heads.
Figure 5: Parts of the impact sprinkler head
In operation, pressurised water jet from the body passes through the nozzle past the
sloping vane, through the window and into the curve of the spoon (Figure 5). In the
spoon, the reactionary force of the water exiting the spoon drives the arm out of the
stream and away from the nozzle. The tension in the arm spring then restores the arm to
its original position while impact on the bridge causes the sprinkler to turn. Wedge-driven
spinklers, have the same mechanism as the spoon-driven but use a wedge instead of a
spoon to force the arm into or out of the water stream. These sprinklers prevent excessive
deposition of water just below the spinklers. Precision jet sprinklers have similar
operation as the spoon-driven with a precision jet tube in place of the spoon. As the arm
enters the stream, the water is directed through the tube. The reactionary force of water
leaving the tube is along a line away from the fulcrum and thus the arm is kicked back
out of the stream. The advantage of precision jet sprinkler is that the occurrence of side
splash is eliminated (Rain Bird Int. Inc., 2000).
Body
Nozzle
Sloping vane
Window
Spoon Arm spring
29
2.12 Losses in Sprinkler Irrigation Systems
There are many inefficiencies associated with sprinkler irrigation systems including
leakages in pipes, evaporation, wind drift, canopy interception, surface runoff and
uneven/execessive application depths. These losses and their typical values are presented
in Table 2.1.
Table 2.1: Losses in spray irrigation systems
Loss Component Range Typical values
Leaking pipes 0-10% 0-1%
Evaporation in the air 0-10% <3%
Wind drift 0-20% <5%
Interception 0-10% <5%
Surface runoff 0-10% <2%
Uneven/excessive
application depth and rates
5-80% 5-30%
(Source: Davoren, 1995)
It is therefore clear from Table 2.1 that, the greatest losses in sprinkler irrigation is as a
result of uneven application, i.e. uniformity of application. Keller and Bliesner (1990)
wrote that other losses encountered on field scale included evaporation from wet soil
surfaces, transpiration from unwanted vegetation and field border losses. Thus studying
the uniformity of a system is of vital importance to the effectiveness and efficiency of a
sprinkler irrigation system.
30
2.13 Sprinkler Irrigation System Design
The 4 basic steps for designing sprinkler irrigation systems are:
• Site information
• Selection of sprinkler
• Pipe system design and
• Installation
2.13.1 Site Information
Site information encompasses the water resources, the crops ET, site map, pressure,
obstacles on the site, soils and topography, farm schedules, climate, energy and labour.
Soil and crop limitations must be accounted for to reduce runoff and deep percolation by
mismanagement of the irrigation system. Soil water holding capacity, maximum
application rate and climatic data must be used to select the correct irrigation system
design.
2.13.2 Selection of Sprinkler
The selected nozzle, operating pressure, discharge rate and sprinkler spacing must be
shown on the plan. Irrigation interval, set time, application rate and net amount applied
must also be calculated.
2.13.3 Pipe System Design
This involves determining mains, laterals and valves sizes and setting up zones. A zone
includes all the sprinklers that are operated at one time.
31
2.14 Design Procedure
Typical outline of sprinkler design procedure according to Merkley and Allen (2004) and
Keller and Bliesner (1990) are:
• Compute a preliminary value for the maximum net irrigation depth, dx
• Obtain values for peak evapotranspiration (ET) rate, average daily crop water
requirement or use rate during the peak-use month (mm/day) and the cumulative
ET, U from standardised tables.
• Compute the maximum irrigation frequency and the nominal frequency. This
procedure is not applicable for automated fixed systems and centre pivots.
• The required system capacity is then calculated
• Determine the optimum (or maximum) water application rate, which is a function
of the soil type and ground slope and obtainable from tables (Keller and Bliesner,
1990).
• Determine the sprinkler spacing, sprinkler discharge and pressure for optimum
application rate which are available in tables. Determine the number of sprinkler
required to operate simultaneously to meet system capacity
• Decide on the best layout of laterals and mainline
• Size the lateral pipes
• Calculate the maximum pressure required for individual laterals
• Calculate the mainline pipe size(s) and select from available sizes
• Adjust mainline pipe sizes according to the ‘economic pipe selection method’
• Determine the extreme operating pressure and discharge conditions
32
• Select the pump and power unit for maximum operating efficiency within the
expected range of operating conditions and
• Prepare plans, schedules, and instructions for proper layout and operation.
2.15 Effects of Improper Irrigation Design
The potential consequences of poor irrigation design are classified as those affecting:
• Public health
• Waste of natural resources
• Water pollution
• Operator safety and
• Economic factors.
Public health is affected in cases where fertigation is practised without the appropriate
backflow prevention equipment. Thus, there is the backflow of chemicals into public
water supplies. Natural resources are often wasted by poorly designed systems with poor
application uniformity resulting in water and chemical wastage. For non-uniform
irrigation systems, applying sufficient water during irrigation to assure that none of the
crop is under-irrigated rather results in most portions becoming over-irrigated. This
increases the waste of water and chemicals with the attendant waste of fuel used for
pumping the excess water/chemicals. Water pollution results from systems applying
excess water which leaches the chemicals into surface and groundwater resources.
Although it is difficult to quantify the economic and environmental effects of water
pollution, it can be minimised by proper design and prudent management practices. For
instance, irrigation systems which are designed for chemical applications by injection
33
with the irrigation water, have great potential for reducing water pollution from irrigated
land.
The safety of operators and others in the area should be factored into the design process.
This requires that electrical circuits are properly designed and shielded to eliminate the
occurrence of shock hazards in a wet environment. Chemical injection systems must also
be properly designed and installed to avoid operator contact with chemicals. Pressure
relief valves and safety equipment must be installed where required to protect the system
from pressure surges.
Irrigation system cost is directly affected by the quality of design. Well-designed systems
have greater initial cost than poorly-designed systems. This is so because larger
components such as larger pipe sizes are required to minimise pressure losses and
achieve uniform water application. However, the operating costs of well-designed system
are usually lower. On the contrary, pumping, labour and other operating costs need to be
increased to compensate for under-designed irrigation systems. Therefore the total annual
costs are always greater for poorly-designed systems. Moreover, poorly-designed systems
do not provide the necessary soil-water-nutrient environment for optimum crop growth
resulting in poor yield, reduced quality, or high cost per unit of production when
compared to well-designed systems.
The life expectancy of an irrigation system is also dependent on the design. Poorly-
designed systems have shorter life span as components utilised are not properly pressure-
rated and are susceptible to chemical attack and thus result in early failures (Smajstrla et
al, 2002).
34
CHAPTER THREE
MATERIALS AND METHODS
3.1 Introduction
This Chapter describes the materials utilised for the field trials necessary for obtaining
the requisite data presented in this study. The methods adopted for the field trials, have
also been described. The study area characteristics, relevant equations and statistical tools
and measures of performance of sprinkler irrigation systems have also been presented.
3.2 Study Area
N
The study area (Fig. 6) was the Foundation Seed Farm of the Grains and Legumes
Development Board, located at Afraku, a village in the Ejisu-Juaben District of the
Ashanti Region of Ghana. Afraku lies on longitude 06o, 43’W and latitude 01o, 36’N and
at 278m above sea level. The topography of the area is mostly gently sloping towards
River Oworam and its tributaries.
Figure 6: Map of Ghana indicating location of Afraku near Kumasi (Source: Adjei, 2006)
35
3.3 Climate
The climatic data from the nearest meteorological station in Kumasi (30km south) and
Mampong (25km North) indicates that the area is characterised by two rainfall regimes.
The major rainfall season occurs from mid-March to July ending, while the minor regime
begins in September and ends in mid-November. The gross annual rainfall of Kumasi
recorded over 55 years is around 1488.92mm while that for Mampong for 35 years is
1457.91mm. The area has uniformly high mean temperature values between 24-27oC
occurring from December to mid-March for Mampong and Kumasi. Monthly means of
24oC and 22oC are recorded at Kumasi and Mampong respectively during the wet season
(March to July). The highest relative humidity prevalent in the area occurs in the morning
with values of 90% in July-September and 78% in January-February. The relative
humidity is usually around 50% at midday (Dwomoh and Kyei, 1998).
3.4 Soils
The predominant soil in the area is the Bomso-Ofin soil compound association (Ghana
Soil Classification) or Ferric Acrisol-Dystic Fluvisol (FAO/UNESCO soil Classification),
with predominant soils of the Bomso, Kotei, Akroso, Nta, Ofin and Densu series
(Dwomoh and Kyei, 1998). Bomso series are deep well-drained, clay loam with abundant
frequent quartz gravel and iron stone nodules in the subsoil found on the upper slopes and
summits. The top soil is dark brown sandy loam, humus-stained to a depth of 10-15cm.
The subsoil is sandy clay loam which grades to red with depth and the preponderance of
the mica flakes at a depth of about 2m before entering into the partially decomposed rock
at several metres below (Dwomoh and Kyei, 1998).
36
3.5 Vegetation
The natural vegetation of the area is the semi-deciduous forest, inferring from Figure 7,
however, repeated farming has reduced the vegetation to mosaics of secondary forest.
Figure 7: Vegetation map of Ghana [Source: (Menz and Bethke, 2000) as in
(Nyarko, 2007)]
37
3.6 Farm Area
The farm has two sizeable dams which are the sources of water for irrigation. The current
area of land under cultivation is approximately 24 hectares (60 acres), with the layout as
shown in Figure 8. The test area (shaded) on Figure 8 was selected with due
consideration for its proximity to the dams and logistical constraint with respect to the
quantity of main pipes required for the field tests.
Figure 8 Layout of Foundation Seeds Production Farm at Afraku (Source: Adjei,
2006)
UNCULTIVATED FIELD
K 4.0 ha (10 acre)
G 2.4 ha (6 acre)
J 2.0ha (5 acre)
I 1.2ha (3 acre)
H1.6ha (4acre)
A 2.8ha (7 acre)
E 1.6ha(4 acre
B 2.8ha (7 acre)
F1.2ha (3acre)
Test Site C 1.2ha (3 acre)
D 2.0ha (5 acre)
38
3.7 Materials
The materials used were as follows:
• 12kW (16 hp) centrifugal water pump with a head of 54m
• Irrigation pipes, pipe connector fittings, flow control devices and filters
• 8 Rotating impact sprinkler heads
• Pressure gauge with Pitot tube
• 3 m × 14 mm flexible water hose
• 50 m tape measure
• 500 cm3 graduated cylinder
• Marking flags
• 80 Catch cans (1 litre each)
• Stop watch
• Portable anemometer (Maximum speed = 30m/s)
• Portable thermohygrometer
• Double ring infiltrometer (Ø300mm and Ø600mm)
All sprinkler and trickle irrigation systems require energy to move the water at the
desired pressure, through the pipe distribution network and discharging it through the
sprinklers or emitters (Keller and Bliesner, 1990). The centrifugal pump lifted the water
and imparted the required energy to the water to attain the desired pressure necessary to
rotate the sprinkler heads. The water pump was a portable diesel-powered engine, with
impeller diameter of 20 cm, head of 54 m and discharge of 20-110 m3/h (110,000 l/h).
The irrigation unit, a solid-set hand-move type, was made up of PVC quick-coupling
main and lateral pipes with fittings, as well as strainers, to convey the pumped water to
39
the sprinkler heads mounted on risers. The height of risers used for the test was 1627 mm.
The ASABE S398.1 (1985 R2006) recommends that for sprinkler inlet size ≥38mm the
maximum nozzle height allowable above the collector is 1830mm. The Philippine
Agricultural Engineering Standard (PAES) 126, (2002) recommended a maximum nozzle
height above the catch cans to be 1830mm for nominal pipe diameter of 38mm and
above. The riser height used for the tests was therefore within these standards.
3.8 Methods
3.8.1 Site Selection and Preparation
The test plot (Marked C and shaded in Figure 8) was cleared or the vegetation growth
was less than 8mm in height and the slope of the field was less than 2% (PAES 126,
2002). The ASABE S398.1 (1985 R2006) recommended that the vegetation on the testing
site should not exceed 150mm in height.
3.8.2 Catch-can Description and Set-up
Cans of identical measurement were used for the test and they had diameter and height of
84mm and 130mm respectively, with a volume of about l litre. Most irrigation experts
recommend 16-20 cans per test zone for collection of data (Wilson and Zoldoske, 1997).
The Irrigated Crop Management Centre (2002) also recommended at least 30 cans, of
minimum height of 100mm, for the evaluation of sprinkler irrigation uniformity. For this
study, 80 catch-cans were used for the determination of the sprinkler water distribution
pattern involving a single sprinkler head and 36 catch-cans for the block tests. These
were therefore within recommended standards. In field and laboratory tests, catch-cans
40
are most often arranged in either a rectangular grid or in one or more radial ‘legs’ of cans.
The catch-can setup for this test was the full rectangular grid because it provides more
representative data especially when there is significant wind during test. When radial legs
are used, there should only be one sprinkler operating, otherwise the analysis would not
be representative of the actual conditions. Furthermore, the radial legs configuration is
best suited to the evaluation of centre pivot sprinkler systems.
For the purpose of evaluating sprinklers, the typical catch-can spacing used should be 2m
or 3m (Merkley and Allen, 2004). The catch-can spacing (centre to centre) used for this
study was 3m × 3m, considering the radius of throw of the sprinklers >12m and sprinkler
spacing >10m (ASABE S398.1 (1985, R2006)). The rectangular grid arrangement was
thus adopted in this study. The layout for evaluating the block system is depicted Figure
9.
Figure 9: Catch-can and sprinkler layout for block test
3m
3m
18m
18m
Catch-can positions
Sprinkler positions
41
3.8.3 Sprinkler Head and Spacing
The sprinkler heads used for this study were of the full circle rotating impact sprinkler
type with both range and spray nozzles. An impact sprinkler is a water application device
equipped with one or two nozzles and an impact arm to cause sprinkler rotation and water
stream breakup (Kranz et al, 2005). The range nozzle, often larger in diameter, shoots
water jet and covers the area distant from the sprinkler, while activating the rotating
mechanism at the same time. The spreader/spray nozzle sprays water in the vicinity of the
sprinkler. Sprinklers are generally made of brass or engineering/heavy-duty plastics with
internal or external threaded connections.
The sprinkler spacing common with low-medium pressure systems are 6m, 9m, or 12m
along the laterals (sprinkler spacing) and 12m or 18m between laterals on the main line
(lateral spacing). These spacing had initially been adopted considering the standard
length of quick-coupling pipes (6m), but they have proved to be the most practicable as
their closeness, low discharge and precipitation gave better result. Sprinkler spacing (on
and between laterals) can be in square, triangular or rectangular configurations.
Triangular spacing is more common under fixed-system sprinklers (Merkley and Allen,
2004). When testing sprinklers, it is common to have only a single operating sprinkler. In
practice, however, it is most typical to have multiple overlapping sprinkler positions.
Consequently, a single sprinkler test was performed to ascertain the distribution pattern
of the sprinklers. Data so obtained was used to simulate other overlapped configurations.
Moreover, a block test, which is representative of multiple sprinkler positions, was
42
conducted. The sprinkler spacing used was the 18m × 18m, involving six sprinklers
operating simultaneously, with 36 catch-cans set-up among the last four sprinklers.
3.8.4 Sprinkler Head and Specification
The physical characteristics of the sprinkler head used for this study (see Figure 10)
according to COMETAL (2007) were:
Make: COMETAL
Type: AGROS 40®
Nozzles: 2 (Ø4.8mm × Ø2.5mm)
Nozzle bore: circular
Jet angle: 27o
Material: Brass
Overall length: 183mm
Overall width: 26mm
Overall height: 140mm
Mass: 450g
Mode of operation: Circular, 360o
Connection: 19mm threaded unto riser
43
Figure 10a: Components of an impact-driven sprinkler
Figure 10b: Length, width and height of a sprinkler head [Source: PAES 126,
(2002)]
3.8.5 Pressure Measurement
A pressure gauge with Pitot tube was used for the measurement of the nozzle operating
pressure during the test. During the measurements, the Pitot tube (Figure 11a) was held
3mm from the nozzle to record the operating pressure of the nozzle, for the single
sprinkler test. This was to ensure the flow was not disrupted so that a representative
pressure was obtained. In the case of the block test, where more than one sprinkler was
44
operating on one pipe line or lateral, the curved end of the Pitot tube was inserted into the
nozzle to obtain the nozzle pressure (Rain Bird, 2000). The operating pressure used for
both single and block tests was approximately 350 kPa (51psi). Measurements were taken
for all sprinklers in the block test zone. All pressure measurements were taken before the
catch-cans were overturned to start the collection of precipitations.
a. Pitot tube-gauge assembly b. Measuring nozzle pressure
Figure 11 – Pitot tube and Bourdon gauge used for pressure measurement [Sources: (PIR, 2000), (Rain Bird, 2000)]
3.8.6 Sprinkler Discharge Measurement
The volumetric discharge was measured with the aid of a flexible water hose and a 17
litre bucket. The time taken to fill the bucket was recorded and used to determine
discharge using Equation 3:
Discharges were determined for all the sprinkler heads in operation and the averages
obtained were used to represent discharge of sprinklers used for the block test.
( )
l/s.in dischargesprinkler theis qand (s) timefillcontainer theist
(l) litresin collected water of volume theis vwhere,
3.......................................................................tvq =
45
3.8.7 Wind Measuring Equipment and Location
The direction and magnitude of the prevailing wind, during the test, was determined with
the aid of a potable anemometer. The device was mounted at a height of 2m and at a
distance of 5m, from the wetted area taking into consideration, the proximity of
windbreaks (PAES 126, 2002). Zoldoske and Wilson (1997) recommended that the test
be rescheduled if wind speed exceeded 12.8km/h (8mph). ASAE S398.1 (1985, R2006)
also recommends continuous measurement of wind velocity during the test with a chart
recorder. However, in the absence of such equipment velocity can be measured at the
beginning and end of the test and at intervals not exceeding 10% of the test period or at 3
minute intervals. In this study, the wind velocity was measured at intervals of 10 minutes
representing less than 10% of the test period of 120 minutes. The wind speed data is
presented in Appendix A.
3.8.8 Sprinkler Rotation Speed
The speed of rotation of a sprinkler varies with nozzle size, stator size, operating pressure
and condition of the impact drive mechanism. To achieve good water distribution,
rotation speed is to be consistent between sprinklers. Huck (2004) stated that impact
sprinklers should complete one revolution in 2 minutes (±15 seconds) and that under no
circumstance should a sprinkler complete a revolution in less than 105 seconds. However,
ISL (2007) asserts that the ideal rotation speed of a 19mm impact sprinkler is 1 rpm and
that tighter spring tension increases the number of beats per minute and speed of rotation.
46
3.8.9 Test Conditions
Humidity was determined using a portable thermohygrometer by measuring the ambient
dry bulb temperature and the ambient wet bulb temperature. The test conditions are
presented in Table 4.1.
3.8.10 Irrigation Equipment Conditions
The sprinkler system evaluated had been in normal use except for the rotating impact
sprinklers which were new.
3.9 Single Sprinkler Test
To determine the sprinkler water distribution pattern, a single sprinkler located at the
centre of a 3m square grid of catch-cans, was operated at the design pressure under the
prevailing wind speed and direction. The sprinkler was sited equidistant from the four
surrounding catch-cans and a continuous grid of 8 columns by 10 rows of collectors
surrounded the sprinkler as depicted in Figure 12:
Catch-can positions Sprinkler position
Figure 12– Sprinkler-collector layout for single sprinkler test
47
The catch-cans were identical and of diameter 84mm and height 130mm, with volume of
approximately l litre. The sprinkler was run for two hours and the catch volumes were
measured with a 500cm3 graduated cylinder and recorded, starting with the outermost
part of the wetted pattern and ending with the central part, as suggested by Ortega et al
(2003). The run time took into consideration the volume of the catch-can. Montero et al
(2002) used a 16cm diameter and 15cm high collector and the run-time was one hour,
even though it had been shown that 45 minutes was sufficient for the collector size used
(Fischer and Wallender, 1988 as in Montero et al, 2002). The depth of water caught was
obtained by the division of the volume by the catch-can cross-sectional area.
3.10 Block Test
Block irrigation test was conducted with two laterals consisting of four sprinklers per
lateral installed in a square configuration of 18m × 18m (Figure 9). This spacing
corresponded to 65% of the sprinkler coverage diameter under light to moderate wind
conditions in square or rectangular patterns as recommended by Phocaides (2000). A 3m
square grid of catch-cans (made up of 6 rows and 6 columns) were arranged between the
last four sprinklers and the system was run for 2 hours to obtain catch-can data (Ascough
and Kiker, 2002).
3.11 Analyses of Data
Data recorded for both single and block tests were used to determine the distribution
patterns, discharge efficiencies and uniformity parameters presented in the succeeding
sections.
48
3.11.1 Discharge Efficiency
Discharge efficiency, Ed, is the relationship between the water collected by the catch-
cans and water discharged by the sprinkler. The difference between the actual discharge
and the water collected is attributed to evaporation and drift losses during the irrigation
event, mainly as a result of environmental conditions (Montero et al, 2002):
( )2.................................................................100dischargeddepth mean waterobserveddepth mean waterEd ×=
3.11.2 Mean Application Rate (MAR)
The mean application rate (mm/h),
( )4.....1000.)(s spacingsprinkler )(s spacing lateral
(q) dischargesprinkler Ilm
××
=
Where q in mm3/h; sm and sl in m
3.11.3 Christainsen Coefficient of Uniformity (CU)
( )1...........................................................................100.......xn
xx1CU
n
1ii
×
×
−−=∑=
Where, x is the mean water depth collected in all catch-cans, n is the number of cans and
xi is the water depth collected by a catch-can, i (Christiansen, 1942 as in Keller and
Bliesner,1990).
49
3.11.4 Pattern Efficiency/Distribution Uniformity
The pattern efficiency (PE), is the ratio of the mean of 25% of the samples nearest to the
lowest, M25, to the mean of all the measured samples,M. This parameter is also known as
the distribution uniformity (DU):
( ) 100% 25 ×==M
MDUPE ……………………………………………………………..(5)
Sample computations of the mean application rate I, CU, PE/DU and DE are presented in
Appendix A.
3.11.5 Statistical Parameters Analysis
Two statistical parameters the z-test and the t-test were used to test for any difference that
existed between the mean depths obtained for both the single and block tests. The z-test
was applied in the case of the two independent blocks with sample size greater than 30.
For the simulated 12m×12m data, with sample size less than 30, the t-test was applied
(Bluman, 2004). The Microsoft Excel and Microsoft Word were used for statistical
analysis and compilation of results.
50
CHAPTER FOUR
RESULTS AND DISCUSSIONS
4.1 Introduction
In this Chapter, the summarised results are presented in tables or presented in graphs and
the relevant interpretations given. The values of parameters studied have also been
explained vis-à-vis standard values and reasons given for any deviations. Table 4.1
contains a summary of the environmental parameters measured during the field tests.
Table 4.2 is a summary of the depths of water caught during the sprinkler tests and Table
4.3 presents a summary of the computed measures of irrigation system performance.
4.2 Results
Table 4.1 Environmental Conditions during Field Measurements
Table 4.2 Test Outcomes during Sprinkler Precipitation Measurements
TEST TYPE
NUMBER NO. OF CATCH CANS
WATER DEPTH CAUGHT(mm)
AVERAGE DEPTH (mm)
SINGLE 1 64 307.0 4.8 2 80 285.6 3.6
BLOCK 1 36 346.0 10.0 2 36 334.5 9.3
DAY TIME OF DAY AVERAGE WIND SPEED (m/s)
WIND DIRECTION
RELATIVE HUMIDITY (%)
TYPE OF TEST
1 10:45am-12:45pm 1.7 SOUTH-EAST 64 SINGLE 2 11:20am-13:20pm 1.2 NORTH-WEST 68 BLOCK 3 10:20am-12:20pm 1.8 NORTH-WEST 55 SINGLE 3 13:00am-15:00pm 1.7 NORTH-WEST 50 BLOCK
51
Table 4.3 Summary of Computed Results
4.3 Single Tests
The single sprinkler (SS) tests were conducted with operating pressure of approximately
350kPa for a riser height of 1.6m and runtime of 2 hours. In the study, the average
rotational speed measured for the sprinkler was 45 seconds. The wetted diameters
measured for the two tests were 26.2 m and 26.6 m respectively. An average wetted
diameter of 26.4 m and an average sprinkler discharge of 1.5 m3/h were obtained for the
sprinklers working at the operating pressure of 350 kPa. These values fell short of the
28.2 m and 1.72 m3/h respectively stated in the manufacturer’s catalogue. Manufacturer’s
data were, however, obtained under no wind conditions and on fairly level terrains.
The mean application rates (MAR) for the sprinkler spacing of 12m×12m and 18m×18m
were found to be 10.4 mm/h and 4.7 mm/h respectively. The optimum MAR, from
manufacturer’s specification, are 11.8 mm/h and 5.2 mm/h. The average infiltration rate
COMPUTED PARAMETER
Spacing (m) 12×12 18×18
Mean 12×12m 18×18m
Discharge (m3/h)
Test 1 Test 2 Test 1 Test 2 1.48 1.51
1.5
MAR (mm/h)
10.3 10.5 4.6 4.7
10.4 4.7
CU (%)
91 91 84 90
91 87
PE (%)
87.3 85 80.2 85.3
86.1 82.8
DE(%) 87.4 66.3 93 86
76.9 89.5
52
obtained from two tests, performed on the associated field, was 28.5mm/h. Thus, this
particular sprinkler could perform without runoff. The detailed results of the infiltration
tests are presented in Appendix B.
It was observed that the average wind speed recorded during the first SS test was 1.7m/s
at relative humidity of 64%. The second SS test recorded an average wind speed of
1.8m/s at relative humidity of 55% (Table 4.1). The minimum and maximum wind speeds
recorded during the test were 1.0m/s and 3.0m/s respectively. The average ambient
temperatures observed during the two tests were 35oC and 37 oC respectively.
The total depth of water caught in the first SS test was 307mm whilst that for the second
test was 285.6mm. The mean depths of water caught were 4.8mm and 3.6mm
respectively (Table 4.2). The difference could be attributed to the relatively higher wind
speed and lower relative humidity recorded on the second test day. Applying the t-test at
0.05 significant level to the two sets of data, a p-value of 0.003052 was obtained
indicating that there was significant difference between the mean depths (Appendix C).
Detailed data obtained from these single sprinkler tests are shown in Appendix A. From
these sets of data, a 12m×12m sprinkler spacing data were derived and are shown in
Figure 13. Results from the first SS were used.
0 2 2 12
0 1 5 12
0 0 10 8
1 0 14 5
5 1 14 5
9 3 7 4
12 5 4 2
3 3 8 5
1 4 4 10
0 5 0 12
1 10 0 7
3 8 2 5
5 5 5 4
10 6 3 4
5 9 1 5
2 10 0 5
16
17
18 18 19
25
23
23
19
19
23
19
18 18
17 20
Figure 13 Simulation of 12m×12m Block Configuration from Single Sprinkler Test Data
53
Consequently, the Christiansen's uniformity (CU) coefficients were computed from the
derived data to represent 12m×12m sprinkler arrangement on a field. Data from both tests
1and 2 had CU of 91%. Hence the average CU for the 12m×12m spacing was 91% which
was above standard value of at least 85% stated by Keller and Bliesner (1990) for
agricultural sprinklers.
The pattern efficiency (PE) also known as the distribution uniformity DU, was also
computed for the two sets of data. Test 1 had a PE of 87.3% whilst test 2 had 85%
averaging 86.1%. This average PE is observed to be above the standard value of 75%
stated for agricultural sprinklers (Ascough and Kiker, 2002). As shown in Figure 14, the
precipitation profiles obtained were almost symmetrical about the sprinklers and thus
contributed to the excellent CU values obtained. The profiles also indicated that the
sprinklers were operating at a satisfactory pressure. T-test for difference in data obtained
for the two profiles at a significance level of 0.05 (α=0.05) gave a p-value of 0.176> α
indicating that there is no significant difference between the two profiles shown in Figure
14.
54
Figure 14: Sprinkler Precipitation Profiles
The discharge efficiencies computed with the actual measured wetted area covered were
87.4% and 66.3% respectively averaging 76.9%. Using the entire area covered by the
catch-cans for the computation of the discharge efficiency, the outcomes were 93% and
86% respectively with an average of 89.5%. Thus 23% and 10% of the water discharged
were lost through evaporation and drift losses respectively during the irrigation events.
0
2
4
6
8
10
12
14
21 18 15 12 9 6 3 0 -3 -6 -9 -12 -15 -18 -21
Dept
h (m
m)
Distance From Sprinkler (m)
0
2
4
6
8
10
12
14
16
21 18 15 12 9 6 3 0 -3 -6 -9 -12 -15 -18 -21
Dept
h (m
m)
Distance from Sprinkler (m)
Figure 14B: Precipitation Profile of Single Sprinkle Test 2
Figure 14A: Precipitation Profile of Single Sprinkle Test 1
55
The standard ranges for evaporation and drift losses are stated as 0-10% and 0-20%
respectively (Davoren, 1995). These values obtained indicated that the amount of losses
observed during the test were within acceptable limits.
4.4 Block Tests
The block tests were conducted with 18m×18m sprinkler spacing with operating pressure
of approximately 350 kPa for a riser height of 1.6 m and runtime of 2 hours.
From Table 4.1, the average wind speed recorded during the first block test was 1.2 m/s
with a relative humidity of 68%. The second test recorded an average wind speed of 1.7
m/s with a relative humidity of 50%. The minimum and maximum wind speeds recorded
during the test were 1.0 m/s and 3.0 m/s respectively. The average ambient temperatures
observed during the tests were 31oC and 37.5 oC respectively.
From Table 4.2, 346 mm and 334.5 mm water depths were recorded for the first and
second block tests respectively. The mean depths of water caught were 10 mm and 9.3
mm respectively. The difference in depths may be attributed to the relatively higher
average wind speed and lower relative humidity recorded on the second test day.
Statistical observation using the z-test, at a significance level of 0.05, a p-value of
0.39457 was obtained indicating that there was no significant difference between these
mean depths (Appendix C).
From Table 4.3, the CU computed for the two tests were 84% and 90% respectively with
an average of 87%. It was observed that although the average wind speed recorded for the
second block test was higher, a higher CU was obtained relative to the first test. This may
have buttressed the assertion by Merkley and Allen (2004) that, occasionally wind can
56
help improve uniformity as the randomness of wind turbulence and gusts contribute to
smoothening out the distribution pattern/profile.
The pattern efficiencies obtained for the two tests were 80.2% and 85.3% respectively,
with an average of 82.8%. This value was also above the standard pattern efficiency/DU,
of 75%, quoted for agricultural sprinklers by Ascough and Kiker (2002).
4.5 Current Irrigation Practice
The present practice of irrigation on the farm does not depend on any designed
parameters. The operation of irrigation system follows no irrigation interval or schedule.
The application rate and sprinkler spacing combinations are not utilised and thus the
occurrence of runoff is prevalent after a short operation of the system. Moreover the
sprinkler layout used cuts across all the crops planted overlooking crop characteristics.
Thus the current irrigation practice is based on intuition.
4.6 Proposed Design
The design follows that by Keller and Bliesner (1990):
Crop: Corn/Maize (Zea Mays / Obaatanpa)
Root Depth (z) – 0.6-1.2m; Average Root Depth =0.9m
Maturity Period/Growing Season: 105 – 110 days
Crop Water Use Rate (Ud): 7.6mm/day
Seasonal water use (U) up to the physiological maturity stage (90days): 684mm
57
Soil: Bomso-Ofin Compound Association (Ferric Acrisol-Dystric Fluvisol),
(Area=1.2ha)
Surface Texture /depth: Sandy Loam/30cm
Moisture Capacity Wa: 125mm/m
Subsurface Texture/depth: Sandy clay loam/70cm
Moisture Capacity Wa: 183mm/m
Moisture capacity 𝑊𝑎 = 0.3(125)+0.6(183)0.9
= 163.7𝑚𝑚 𝑜𝑓 𝑤𝑎𝑡𝑒𝑟 /𝑚 𝑑𝑒𝑝𝑡ℎ 𝑜𝑓 𝑠𝑜𝑖𝑙
Allowable Depletion MAD: 50%
Maximum Application Depth, dx: = 𝑀𝐴𝐷100
𝑊𝑎𝑍 = 50100
163.7(0.9) = 74𝑚𝑚
Average Soil Intake Rate (from infiltration test presented in Appendix B) = 28.5mm/h
Irrigation Factors
Maximum Irrigation Interval, fx= 𝑑𝑥𝑈𝑑
= 747.6
= 9.7𝑑𝑎𝑦𝑠
Nominal Irrigation Interval, f = 10days
Net Depth dn= f×Ud= 10𝑑𝑎𝑦𝑠 × 7.6𝑚𝑚/𝑑𝑎𝑦 R= 76mm
Operating Time per Irrigation
For irrigation water with salt problems, leaching requirement to control salt build-up,
𝐿𝑅 = 𝐸𝐶𝑤(5𝐸𝐶𝑒−𝐸𝐶𝑤)
Assumed ECw= 2dS/m
𝐿𝑅 =2.0
5(2.5) − 2 = 0.2
For LR>0.1, Gross application Depth d= 0.9 𝑑n(1−𝐿𝑅)� 𝐸𝑎100�
= 0.9(76𝑚𝑚)(1−0.2)(0.83)
= 102.4𝑚𝑚
Where, Ea is the application efficiency, in this case, average DE=83% (Table 4.3)
For the determined application rate, I, of 4.7mm/h for 18m ×18m spacing,
The nominal set operating time Ta =102.4𝑚𝑚4.7𝑚𝑚/ℎ
= 22ℎ
58
Using manunfacturer’s data with I of 5.2mm/h, nominal set operating time, Tm= 20h
For LR<0.1, Gross application Depth d= 𝑑n�𝐸𝑎100�
= (76𝑚𝑚)(0.83)
= 92𝑚𝑚
For the determined application rate, I, of 4.7mm/h for 18m ×18m spacing,
The nominal set operating time Ta =92𝑚𝑚
4.7𝑚𝑚/ℎ= 20ℎ
Hence using the manunfacturer’s data with I of 5.2mm/h, Tm= 18h
Pump flow capacity= 110,000l/h
Manufacturer’s determined discharge of AGROS-40 Sprinkler at 350kPa was 0.47l/s or
1692l/h but field determined average discharge of AGROS-40 Sprinkler at 350kPa was
0.41l/s or 1476l/h.
Maximum number of sprinklers operable by the pump = 65
For the 1.2 hectare (3 acre) field, maximum number of sprinklers required at 18m×18m
spacing, as per the irrigation plan (Appendix D)= 36
For 36 sprinklers, pump flow required = 60912l/h (36×1692l/h)
Total volume of water per application= pump flow × time/shift × no. of shifts=
60912l/h×4h
Total volume per application= 243648 litres
For a critical growth period of 90 days and irrigation interval of 10 days, the number of
irrigation events per season is 9.
Thus seasonal water use would be 2.2 million litres or 1.83l/ha
Number of sprinklers available = 24
Number of main pipes =20
Number of lateral pipes= 36
Irrigation events are to be carried out in sets due to the limited equipment.
59
CHAPTER FIVE
CONCLUSIONS AND RECOMMENDATIONS
5.1 Introduction
The chapter summarises the findings of the study and provides recommendations for
future work in this field. The following conclusions and recommendations can be drawn
from the study:
5.2 Conclusions
From the determined sprinkler mean application rates (MAR) (10.4mm/h and 4.7mm/h)
and the basic soil infiltration rate (28mm/h), the impact sprinkler tested in this study was
suitable and could therefore be used satisfactorily without runoff. Both the 12m×12m and
18m×18m sprinkler configurations could also be employed satisfactorily without any
runoff.
The sprinkler operating pressure used in the study was satisfactory inferring from the
wetted diameter (26.2m) and discharges (1.5m3/h) recorded which deviated marginally
from the standard values (28.2m and 1.72m3/h) quoted by the manufacturer. The average
sprinkler precipitation profiles obtained were also consistent with established profiles of a
double nozzle sprinkler operating at a satisfactory pressure.
Relative humidity and wind had effect on the evaporative and drift losses associated with
sprinkler irrigation systems. This was deduced from the drop in the mean depth of water
observed for the days in which the relative humidity was lower and the wind speed was
higher, indicating greater losses under those conditions.
60
The losses recorded for the sprinklers (10.5-23.1%) were within acceptable range as
indicated by the satisfactory average discharge efficiency (83.1%) obtained under the
prevailing field conditions.
The 12m×12m spacing produced higher/better results than the 18m×18m spacing for all
the parameters studied i.e. MAR, CU and PE/DU. This notwithstanding, the 18m×18m
spacing gave very good results as regards, the CU and PE/DU which were above standard
values stated in literature.
5.3 Recommendations
The following are recommended:
Further elaborate studies may be conducted on the subject by considering the effects of
different pressures on the performance of sprinkler irrigation system.
Different riser heights may also be studied to observe their effect on the measures of
sprinkler irrigation system performance, to cater for the cultivation of other crops.
61
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