Determination of Friction Head Losses in Trickle
(Bubbler) and Sprinkler Irrigation Systems.
By
ALAWI MOHAMMED ALAWI ALSAQAF
B.Sc. Agric-(Soil and Water)
United Arab Emirates University (1996)
A THESIS
Submitted to the University of Khartoum
in partial fulfillment of the requirements for the
Degree of Master of Science in Agriculture
(Irrigation)
Supervisor: Dr.Amir Bakheit Saeed
External Supervisor: Dr Mahmoud Hassan Ahmed
Department of Agricultural Engineering
Faculty of Agriculture
University of Khartoum
January 2006
‫ﺑﺴﻢ اﷲ اﻟﺮﺣﻤﻦ اﻟﺮﺣﻴﻢ‬
‫) ﻭﻣﻦ ﺁﻳﺎﺗﻪ ﺃﻧﻚ ﺗﺮﻯ ﺍﻷﺭﺽ ﺧﺎﺷﻌﺔ ﻓﺈﺫﺍ ﺃﻧﺰﻟﻨﺎ ﻋﻠﻴﻬﺎ ﺍﳌﺎﺀ ﺍﻫﺘﺰﺕ ﻭﺭﺑﺖ ﺇﻥ ﺍﻟﺬﻱ‬
‫ﺃﺣﻴﺎﻫﺎ ﶈﻲ ﺍﳌﻮﺗﻰ ﺇﻧﻪ ﻋﻠﻰ ﻛﻞ ﺷﻲﺀ ﻗﺪﻳﺮ (‬
‫)ﺻﻮﺭﺓ ﻓﺼﻠﺖ – ﺍﻵﻳﺔ ‪(39‬‬
Dedication
TO THE TRUE MEANING OF SACRIFICE AND LOVE,
TO MY FATHER AND MOTHER
TO MY BROTHERS AND SISTERS
TO MY WIFE AND CHILDERN.
Acknowledgment
Thanks God the most gracious and most merciful.
The author would like to express his deep thanks and gratitude to Dr.
Amir Bakheit Saeed, the supervisor of the study for his guidance,
invaluable suggestions and constructive criticism. Deep thanks and
gratitude are also extended to Dr. Mahmoud Hassan Ahmed, the
external-supervisor of the study for the encouragement and help he
provided during the execution of the experimental work. Special thanks
are extended to the staff of the computerized irrigation unit, Al-Ain
Central District of the Directorate of the General Gardens, Al-Ain
Municipality for the help they provided during the fieldwork. The author
is indebted to many individuals and institutions in the United Arab
Emirates and Sudan for the assistance provided during the preparation
and execution of the study.
To my parents, wife and beloved children, I wish to offer my deep thanks
for their encouragement and patience during the extended periods I stayed
away from them in Sudan.
Abstract
Field experiments were conducted at Al-Ain Central District of the
General Public Gardens Directorate, Al-Ain Municipality, Abu Dhabi
Emirate, United Arab Emirates. The experiments were run to determine
the friction head losses along the laterals of the trickle (bubbler) and
sprinkler irrigation systems within the automated (computerized)
irrigation system of the Central District.
The results of the experiments indicated that there were no significant
differences between the practically measured head losses and head losses
as calculated by using friction head losses equations namely : the HazenWilliams and Darcy-Weisbach when factor (G), as suggested by Anwar
(1999) was used. The average measured head losses for trickle (bubbler)
and sprinkler systems were 4.36 m and 4.18m, whereas their respective
values as calculated by using Hazen-Williams equation and introducing
Anwar's(G) factor were 4.20m and 4.64m.
Factor (G) is a sequel to the widely used Christiansen's factor (F). It has
the advantages to allow for an outflow at the downstream end of the
pipeline beyond the last outlet. It can, therefore, be used for computation
of frictional head losses and eventually designing of system such as
trickle (bubblers) and sprinklers systems in which the pipelines have
multiple diameter sizes and equally spaced outlets.
‫ﺧﻼﺻﺔ اﻟﺪراﺳﺔ‬
‫أﺟﺮﻳﺖ هﺬﻩ اﻟﺪراﺳﺔ ﺑﺎﻟﻘﺴﻢ اﻷوﺳﻂ ‪ -‬اﻻدارة اﻟﻌﺎﻣﺔ ﻟﻠﺤﺪاﺋﻖ‪ -‬ﺑﻠﺪﻳﺔ اﻟﻌﻴﻦ‪-‬ﻣﺪﻳﻨﺔ اﻟﻌﻴﻦ‬
‫–اﻣﺎرة أﺑﻮﻇﺒﻲ‪-‬دوﻟﺔاﻻﻣﺎرات اﻟﻌﺮﺑﻴﺔ اﻟﻤﺘﺤﺪة ‪ -‬ﺑﻬﺪف ﺗﺤﺪﻳﺪ ﻓﻮاﻗﺪ اﻻﺣﺘﻜﺎك‬
‫ﺑﺎﻟﺨﻄﻮط اﻟﻔﺮﻋﻴﺔ ﻷﻧﻈﻤﺔ اﻟﺮي ﺑﺎﻟﺘﻨﻘﻴﻂ )ﻧﻈﺎم اﻟﺒﺒﻠﺮ( واﻟﺮي ﺑﺎﻟﺮش‪.‬‬
‫وﻗﺪ أﺟﺮﻳﺖ اﻟﺘﺠﺎرب اﻟﻌﻤﻠﻴﺔ ﻓﻲ ﻣﻨﻄﻘﺔ ﻧﻈﺎم اﻟﺮي اﻷﺗﻮﻣﺎﺗﻴﻜﻲ)ﺑﺎﺳﺘﺨﺪام اﻟﺤﺎﺳﺐ‬
‫اﻻﻟﻲ( ﻓﻲ اﻟﻘﺴﻢ اﻷوﺳﻂ‪.‬‬
‫وﻗﺪ أوﺿﺤﺖ ﻧﺘﺎﺋﺞ اﻟﺪراﺳﺔ أﻧﻪ ﻻﺗﻮﺟﺪ ﻓﺮوﻗﺎت ﻣﻌﻨﻮﻳﺔ ﺑﻴﻦ اﻟﻨﺘﺎﺋﺞ اﻟﻌﻤﻠﻴﺔ ﻟﻠﺪراﺳﺔ‬
‫ﻓﻲ ﻣﺎﻳﺨﺘﺺ ﺑﻔﻮاﻗﺪ اﻻﺣﺘﻜﺎك ﻓﻲ ﺧﻄﻮط اﻟﺮي ﺑﺎﻟﺘﻨﻘﻴﻂ واﻟﺮي ﺑﺎﻟﺮش وﺗﻠﻚ اﻟﺘﻲ ﺗﻢ‬
‫ﺣﺴﺎﺑﻬﺎ ﺑﺎﺳﺘﺨﺪام ﻣﻌﺎدﻻت اﻟﻔﻮاﻗﺪ)ﻣﻌﺎدﻟﺔ هﻴﺰن – وﻟﻴﻢ وﻣﻌﺎدﻟﺔ دارﺳﻲ ‪ -‬وﻳﺴﺒﺎج(‬
‫ﻋﻨﺪ اﺳﺘﺨﺪام ﻣﻌﺎﻣﻞ أﻧﻮر )‪.(1999) (G‬ﻓﻘﺪ آﺎﻧﺖ ﻣﺘﻮﺳﻄﺎت ﻓﻮاﻗﺪ اﻻﺣﺘﻜﺎك اﻟﻤﻘﺎﺳﻪ‬
‫ﻟﻨﻈﺎﻣﻲ اﻟﺮي ﺑﺎﻟﺘﻨﻘﻴﻂ واﻟﺮي ﺑﺎﻟﺮش ‪4.36‬م و‪4.18‬م ﻣﻘﺎرﻧﺔ ﺑﻘﻴﻢ ‪4.20‬م و‪4.64‬م‬
‫واﻟﺘﻲ ﺗﻢ ﺣﺴﺎﺑﻬﺎ ﺑﻤﻌﺎدﻟﺔ هﻴﺰن وﻟﻴﻢ ﻣﺼﺤﺤﺔ ﺑﻤﻌﺎﻣﻞ أﻧﻮر)‪(G‬‬
‫وﻗﺪ وﺿﺢ أن‬
‫ﻣﻌﺎﻣﻞ )‪ (G‬ﻳﻤﻜﻦ أن ﻳﻌﻄﻲ ﻧﺘﺎﺋﺞ ﻣﺒﺎﺷﺮة ﻋﻨﺪ اﺳﺘﺨﺪاﻣﻪ ﻓﻲ ﺣﺴﺎب اﻟﻔﻮاﻗﺪ ﻣﻊ‬
‫ﻣﻌﺎدﻻت ﺣﺴﺎب ﻓﻮاﻗﺪ اﻻﺣﺘﻜﺎك وذﻟﻚ ﻋﻨﺪﻣﺎ ﺗﻜﻮن اﻟﻤﺴﺎﻓﻪ ﺑﻴﻦ ﻣﺪﺧﻞ ﻣﺎء اﻟﺮي ﻣﻦ‬
‫اﻟﺨﻂ اﻟﻔﺮﻋﻲ وأول )ﻣﺨﺮج( ﻳﻌﺎدل ﻣﺴﺎﻓﻪ ﻣﺴﺎوﻳﻪ ﻟﻠﻤﺴﺎﻓﺎت ﺑﻴﻦ اﻟﻤﺨﺎرج ﻋﻠﻰ ﻃﻮل‬
‫اﻟﺨﻂ اﻟﻔﺮﻋﻲ‪.‬‬
‫ﻣﻌﺎﻣﻞ )‪ (G‬ﻳﺘﻮاﻓﻖ ﻣﻊ ﻣﻌﺎﻣﻞ آﺮﻳﺴﺘﻴﺎﻧﺴﻦ)‪ ( F‬اﻟﺸﺎﺋﻊ اﻻﺳﺘﺨﺪام وﻟﻜﻨﻪ ﻳﻤﺘﺎز ﻋﻠﻴﻪ‬
‫ﺑﺈﻣﻜﺎﻧﻴﺔ اﺳﺘﺨﺪاﻣﻪ ﻟﺤﺴﺎب ﻓﻮاﻗﺪ اﻻﺣﺘﻜﺎك ﺣﺘﻰ ﻓﻲ ﺣﺎﻟﺔ وﺟﻮد ﺗﺼﺮف ﻓﻲ ﻧﻬﺎﻳﺔ‬
‫ﺧﻄﻮط اﻟﺮي آﻤﺎ ﻳﻤﻜﻦ اﺳﺘﺨﺪاﻣﻪ ﻟﺘﺼﺎﻣﻴﻢ ﻧﻈﻢ اﻟﺮي ﺑﺎﻟﺘﻨﻘﻴﻂ )اﻟﺒﺒﻠﺮ( واﻟﺮي ﺑﺎﻟﺮش‬
‫ﻣﺘﻌﺪدة اﻟﻤﺨﺎرج واﻷﻗﻄﺎر‪.‬‬
TABLES OF CONTENTS
Dedication
i
Acknowledgment
ii
Abstract
iii
Arabic Abstract
iv
Table of contents
v
List of Abbreviations
vi
Chapter one
INTRODUCTION
1. Background of the U.A.E
1
1.1. Geographical location of U.A.E
1
1.2. U.A.E Soil
1
1.3. Water Resources in U.A.E.
2
1.3.1. Ground Water
2
1.3.2. Ground Water Elevation
2
1.4. Performance of the Irrigation systems
4
1.5. The Study Objectives
7
Chapter Two
Literature Review
2.1. Introduction
8
2.2. Friction Head Loss in laterals
10
2.3. Minor Head Losses
13
2.4. Blasius Friction Factor
14
2.5. Hazen-William formula
18
2.6. Darcy-Weisbach formula
18
2.7. System Design
20
2.7.1. Sprinkler System
20
2.7.2. Trickle (Drip) system
22
2.7.3. Hydraulics of drip irrigation
22
Chapter Three
MATERIALS AND METOHDS
3.1 Concepts
25
3.2. The irrigation system
25
3.2.1. Central control station
26
3.2.2. Pump station
28
3.2.3. Weather station
28
3.2.4. Layout of the Remote Terminal units on sites
31
3.2.5. RTU (Remote Terminal Units) Hardware parts
31
3.2.6. RTU Function
31
3.2.7. Schedu
31
3.2.8. Reports
33
3.3. The Experimental site
33
3.4. Layout of the Experiment
34
3.5. Data Analysis
34
Chapter Four
Results and Discussion
4.1. Data Acquisition
36
4.1.1. Trickle (Bubbler) system data
36
4.1.2. Sprinkler system data
36
4.2. Data Analysis
39
4.2.1. Data Analysis for Bubbler system
42
4.2.2. Data Analysis for Sprinkler System
42
4.2.3. Measured friction losses in Bubbler system
42
4.2.4. Measured friction losses in Sprinkler system
44
4.2.5. Comparison between measured head losses and calculated
Head Losses by using Hazen-William equation and Anwar (G) factor.
45
4.3. Concluding remarks
47
4.4. Figures for Bubblers and Sprinklers
49
Chapter Five
Conclusions and Recommendations
5.1. Conclusions
78
5.2. Recommendations
79
Tables for Bubblers and sprinklers
80
Appendices
109
References
114
List of Abbreviations
C = Hazen- Williams resistance coefficient.
c = a coefficient of retardation based on the pipe material.
D = diameter of the pipe in (mm).
f = a resistance coefficient.
fn = friction factor related to Qn .
G = factor defined by Anwar (1999).
g = gravitational acceleration (m/s2).
Hf (100) = friction loss per 100 m of pipe.
Hf (L) = friction loss in(L) length of lateral.
K = a constant based on the dimension used in the formula.
Ks = Scobey resistance coefficient.
m = velocity exponent.
N,n = number of outlets on the lateral (Hazen-William formula).
P = pressure at sprinkler or trickle nozzle.
Q = Discharge of Water in the line,(liter per second).
Qn = total flow through the pipe.
Qr = the residual outflow at the downstream end.
R = the hydraulic radius (m).
S = slope (m/m).
V = mean velocity (m/s).
υ = viscosity of the fluid (m2 /s).
ε = roughness of pipe.
Abstract
Field experiments were conducted at Al-Ain Central District of the
General Public Gardens Directorate, Al-Ain Municipality, Abu Dhabi
Emirate, United Arab Emirates. The experiments were run to determine
the friction head losses along the laterals of the trickle (bubbler) and
sprinkler irrigation systems within the automated (computerized)
irrigation system of the Central District.
The results of the experiments indicated that there were no significant
differences between the practically measured head losses and head losses
as calculated by using friction head losses equations namely : the HazenWilliams and Darcy-Weisbach when factor (G), as suggested by Anwar
(1999) was used. The average measured head losses for trickle (bubbler)
and sprinkler systems were 4.36 m and 4.18m, whereas their respective
values as calculated by using Hazen-Williams equation and introducing
Anwar's(G) factor were 4.20m and 4.64m.
Factor (G) is a sequel to the widely used Christiansen's factor (F). It has
the advantages to allow for an outflow at the downstream end of the
pipeline beyond the last outlet. It can, therefore, be used for computation
of frictional head losses and eventually designing of systems such as
trickle (bubblers) and sprinklers systems in which the pipelines have
multiple diameter sizes and equally spaced outlets.
‫ﺧﻼﺻﺔ اﻟﺪراﺳﺔ‬
‫أﺟﺮﻳﺖ هﺬﻩ اﻟﺪراﺳﺔ ﺑﺎﻟﻘﺴﻢ اﻷوﺳﻂ ‪ -‬اﻻدارة اﻟﻌﺎﻣﺔ ﻟﻠﺤﺪاﺋﻖ‪ -‬ﺑﻠﺪﻳﺔ اﻟﻌﻴﻦ‪-‬ﻣﺪﻳﻨﺔ اﻟﻌﻴﻦ‬
‫–اﻣﺎرة أﺑﻮﻇﺒﻲ‪-‬دوﻟﺔاﻻﻣﺎرات اﻟﻌﺮﺑﻴﺔ اﻟﻤﺘﺤﺪة ‪ -‬ﺑﻬﺪف ﺗﺤﺪﻳﺪ ﻓﻮاﻗﺪ اﻻﺣﺘﻜﺎك‬
‫ﺑﺎﻟﺨﻄﻮط اﻟﻔﺮﻋﻴﺔ ﻷﻧﻈﻤﺔ اﻟﺮي ﺑﺎﻟﺘﻨﻘﻴﻂ )ﻧﻈﺎم اﻟﺒﺒﻠﺮ( واﻟﺮي ﺑﺎﻟﺮش‪.‬‬
‫وﻗﺪ أﺟﺮﻳﺖ اﻟﺘﺠﺎرب اﻟﻌﻤﻠﻴﺔ ﻓﻲ ﻣﻨﻄﻘﺔ ﻧﻈﺎم اﻟﺮي اﻷﺗﻮﻣﺎﺗﻴﻜﻲ)ﺑﺎﺳﺘﺨﺪام اﻟﺤﺎﺳﺐ‬
‫اﻻﻟﻲ( ﻓﻲ اﻟﻘﺴﻢ اﻷوﺳﻂ‪.‬‬
‫وﻗﺪ أوﺿﺤﺖ ﻧﺘﺎﺋﺞ اﻟﺪراﺳﺔ أﻧﻪ ﻻﺗﻮﺟﺪ ﻓﺮوﻗﺎت ﻣﻌﻨﻮﻳﺔ ﺑﻴﻦ اﻟﻨﺘﺎﺋﺞ اﻟﻌﻤﻠﻴﺔ ﻟﻠﺪراﺳﺔ‬
‫ﻓﻲ ﻣﺎﻳﺨﺘﺺ ﺑﻔﻮاﻗﺪ اﻻﺣﺘﻜﺎك ﻓﻲ ﺧﻄﻮط اﻟﺮي ﺑﺎﻟﺘﻨﻘﻴﻂ واﻟﺮي ﺑﺎﻟﺮش وﺗﻠﻚ اﻟﺘﻲ ﺗﻢ‬
‫ﺣﺴﺎﺑﻬﺎ ﺑﺎﺳﺘﺨﺪام ﻣﻌﺎدﻻت اﻟﻔﻮاﻗﺪ)ﻣﻌﺎدﻟﺔ هﻴﺰن – وﻟﻴﻢ وﻣﻌﺎدﻟﺔ دارﺳﻲ ‪ -‬وﻳﺴﺒﺎج(‬
‫ﻋﻨﺪ اﺳﺘﺨﺪام ﻣﻌﺎﻣﻞ أﻧﻮر )‪.(1999) (G‬ﻓﻘﺪ آﺎﻧﺖ ﻣﺘﻮﺳﻄﺎت ﻓﻮاﻗﺪ اﻻﺣﺘﻜﺎك اﻟﻤﻘﺎﺳﻪ‬
‫ﻟﻨﻈﺎﻣﻲ اﻟﺮي ﺑﺎﻟﺘﻨﻘﻴﻂ واﻟﺮي ﺑﺎﻟﺮش ‪4.36‬م و‪4.18‬م ﻣﻘﺎرﻧﺔ ﺑﻘﻴﻢ ‪4.20‬م و‪4.64‬م‬
‫واﻟﺘﻲ ﺗﻢ ﺣﺴﺎﺑﻬﺎ ﺑﻤﻌﺎدﻟﺔ هﻴﺰن وﻟﻴﻢ ﻣﺼﺤﺤﺔ ﺑﻤﻌﺎﻣﻞ أﻧﻮر)‪(G‬‬
‫وﻗﺪ وﺿﺢ أن‬
‫ﻣﻌﺎﻣﻞ )‪ (G‬ﻳﻤﻜﻦ أن ﻳﻌﻄﻲ ﻧﺘﺎﺋﺞ ﻣﺒﺎﺷﺮة ﻋﻨﺪ اﺳﺘﺨﺪاﻣﻪ ﻓﻲ ﺣﺴﺎب اﻟﻔﻮاﻗﺪ ﻣﻊ‬
‫ﻣﻌﺎدﻻت ﺣﺴﺎب ﻓﻮاﻗﺪ اﻻﺣﺘﻜﺎك وذﻟﻚ ﻋﻨﺪﻣﺎ ﺗﻜﻮن اﻟﻤﺴﺎﻓﻪ ﺑﻴﻦ ﻣﺪﺧﻞ ﻣﺎء اﻟﺮي ﻣﻦ‬
‫اﻟﺨﻂ اﻟﻔﺮﻋﻲ وأول )ﻣﺨﺮج( ﻳﻌﺎدل ﻣﺴﺎﻓﻪ ﻣﺴﺎوﻳﻪ ﻟﻠﻤﺴﺎﻓﺎت ﺑﻴﻦ اﻟﻤﺨﺎرج ﻋﻠﻰ ﻃﻮل‬
‫اﻟﺨﻂ اﻟﻔﺮﻋﻲ‪.‬‬
‫ﻣﻌﺎﻣﻞ )‪ (G‬ﻳﺘﻮاﻓﻖ ﻣﻊ ﻣﻌﺎﻣﻞ آﺮﻳﺴﺘﻴﺎﻧﺴﻦ)‪ ( F‬اﻟﺸﺎﺋﻊ اﻻﺳﺘﺨﺪام وﻟﻜﻨﻪ ﻳﻤﺘﺎز ﻋﻠﻴﻪ‬
‫ﺑﺈﻣﻜﺎﻧﻴﺔ اﺳﺘﺨﺪاﻣﻪ ﻟﺤﺴﺎب ﻓﻮاﻗﺪ اﻻﺣﺘﻜﺎك ﺣﺘﻰ ﻓﻲ ﺣﺎﻟﺔ وﺟﻮد ﺗﺼﺮف ﻓﻲ ﻧﻬﺎﻳﺔ‬
‫ﺧﻄﻮط اﻟﺮي آﻤﺎ ﻳﻤﻜﻦ اﺳﺘﺨﺪاﻣﻪ ﻟﺘﺼﺎﻣﻴﻢ ﻧﻈﻢ اﻟﺮي ﺑﺎﻟﺘﻨﻘﻴﻂ )اﻟﺒﺒﻠﺮ( واﻟﺮي ﺑﺎﻟﺮش‬
‫ﻣﺘﻌﺪدة اﻟﻤﺨﺎرج واﻷﻗﻄﺎر‪.‬‬
Chapter one
Introduction
1. Background of United Arab Emirates (U.A.E):
1.1. Geographical location and climate
The United Arab Emirates (U.A.E) lies along the coast of the Arabian
Gulf between longitudes 52° and 56°E and latitudes 22° and 26°N.
The total area is approximately 83000 square kilometer. It lies in the
arid region. Its climate is characterized by high temperature and low
relative humidity in summer season which extends from early April to
the end of September. The average maximum temperature in summer
season is around 46° C. The winter season is characterized by mild
temperature; average mean daily temperature is around 13°C. Winter
season extends from mid-November to early March. March and
October are considered as transitional months with temperature
relatively high during daytime and mild during night. The average
evaporation is relatively high and varies according to location relative
to the Gulf Coast. The average annual evaporation reaches about
980mm in the coastal areas while inland it reaches about 400mm. The
United Arab Emirates receives the highest solar radiation worldwide.
The average solar radiation ranges between 14 MJm-2 per day during
September and 22 MJm-2 per day in June.
1.2. United Arab Emirates soil:
U.A.E. is characterized mainly by light sandy soils, but in some areas,
the soil consists mainly of coarse sand with high percentage of quartz.
1.3 Water resources in the U.A.E:
Water is the most important determinant factor of agricultural
production in United Arab Emirates. The main water resources are
groundwater, treated sewage water and desalinized sea water. Treated
sewage water data is shown in Appendix (2). Desalinized water is
very limited and it is not used in agriculture due to its high cost. It is
mainly for domestic use.
1.3.1. Ground water:
The surface aquifer system of the ground water in United Arab
Emirates is composed of a number of hydro-geologic units. The units
include alluvium of Quaternary age, altered late tertiary rocks
composed of elastic and non-elastic sediments, evaporate, tertiary and
cretaceous limestone that contains secondary fractures and solution
cavities. The major aquifer in the region is the alluvium deposited by
the Quaternary-age fluvial systems, which carries sediment westward
from the Oman Mountains. Groundwater enters the surface aquifer
system at the base of the Oman Mountains as subsurface inflow in
burial alluvial channels and as recharge along wadi beds.
1.3.2. Ground water Evaluation:
In 1988 the National Drilling Company of Abu Dhabi, in cooperation
with the United States Geological Survey, started a ground water
research program to evaluate the water resources of the Emirates. The
survey conducted by the program covered an area of 1200 square
kilometer in north eastern Abu Dhabi Emirate about 50 kilometers
north of the oasis city of Al-Ain. The research results showed that
heavy pumping from the surface aquifer system has resulted in
ground-water level decline of 9 meters in parts of the area. Some fresh
ground water moving westward with the regional flow regime escapes
the pumping and is wasted to evaporation in inland sabkhas (salty
areas). During 1996 over 200 ground water samples were collected
from private wells tapping different aquifers in U.A.E. Filed
measurements of ground water levels and ground-truth information
were gathered for remote-sensing studies (Rizk et.al, 1997).
The water samples were analyzed for major, minor and trace dissolved
constituents. Primary results of the study indicated presence of local,
intermediate and regional ground water flow systems, which affect
salting, quality and type of ground water.
Excessive ground water pumping has created cones-of-depression
ranging in compute at Abu Dhabi, Hatta, Al-Ain and Liwa areas.
These cones have caused decline of ground water levels, dryness of
several shallow wells and salt-water intrusion problems (Rizk et.al,
1997)they also found that ground water salinity of 1000-3500 mg/l
was measured at Al-Ain, Diba, Hatta, and Al-Fujairah areas the
analysis of the ground water samples indicated that the calculated
sodium adsorption ratios (S.A.R) of the ground water in the northern
and eastern parts has little harmful effect on plants and soil (S.A.R.
<10).On the other hand the ground water along the western coast, west
of Al-Ain and coast of Liwa has high S.A.R. values and can be very
harmful to plants and soils when used for irrigation (S.A.R. >26).
Silva and Fatima Alnaumi (1997) using a ground water model for Abu
Dhabi Emirate reported that if 1995 pumping rates continued, several
areas would be depleted within 20 years.
1.4. Performance of Irrigation Systems:
In order to determine the performance of irrigation systems, pressure,
wind, temperature and water quality should be studied. The hydraulic
specification and properties of the irrigation delivery system are
critical to being able to deliver water in a known and consistent
pattern. System pressure, in particular, must be maintained because it
is directly related to the required application rate and irrigation
uniformity. Drippers, sprinklers and bubblers, each differ in their
water application characteristics and performance. Sprinkler system
operated at lower than recommended pressure will produce poor
distribution or cover, and when operated at higher pressure than
recommended will produce a fine spray and this will result in poor
distribution because of wind-direct effect and high level of
evaporation loss prior to drops landing on the soil surface.
The uniformity of application is more vital when using high salinity water
than low salinity water because poor uniformity will result in moisture
variation in the plant root-zone.
Pressurized pipelines with multiple outlets are used extensively in
modern irrigation systems such as sprinkler, bubbler and drip (trickle)
systems.
A detailed hydraulic analysis of multiple outlet pipelines is essential for
irrigation system design and evaluation.
Head losses along lateral lines substantially affect the available head at
outlet nozzles of pressurized irrigation systems. The head losses are
estimated by adding the frictional losses along a uniform pipe section
between consecutive outlets to singular minor losses.
The estimation of the frictional head losses along a lateral with multiple
outlets needs a stepwise analysis starting from the downstream-most
outlets, moving upstream and computing the head loss in each part of the
lateral. The hydraulic analysis for frictional losses in a lateral with
multiple outlets is more complex than for a straight length of pipe. The
analysis for a lateral must account for the fact that water is removed at
each outlet and volumetric flow rate is decreasing along the lateral.
A number of friction head loss formulae may be applied to compute the
equivalent head loss for a flow pipe. Examples are the Scobey, HazenWilliams and Darcy-Weisbach equations.
One formula that is generally accepted is the Hazen-Williams:
⎛Q⎞
H f (100) = K ⎜ ⎟
⎝C ⎠
1.852
D −4.87 L.........................(1.1)
Where: Hf (100) = friction loss per 100 m of pipe, C= a coefficient of
retardation based on the pipe material, Q= the flow of water in the line in
liters per second (l/s), D = the diameter of the pipe in (mm), K = a
constant which is 1.22*1012 for metric units.
When water is being removed at intervals from the lateral the friction loss
for a given diameter and length of the lateral will be less than if the flow
is constant for the entire length. As mentioned above, to accurately
determine friction losses in the lateral start at the last outlet on the line
and work backwards to the supply line, and computing the friction loss
prior to each outlet. This complex tedious process has been simplified by
a procedure developed by Christiansen (1942). Christiansen developed an
adjustment factor (F) to correct the friction loss calculated from the
several formulae that assume all the water is carried to the end of the line,
thus:
FK (L 100)(Q C )
H f (L ) =
.........................(1.2 )
D 2 m+ n
m
Where
Hf (L) = friction loss in a lateral of length (L) with multiple
outlets
having
equal spacing and discharge, m and n = velocity
exponent.
For the first outlets along the lateral the value of F is computed using the
following equation:
F=
m −1
1
1
+
+
.............................(1.3)
m + 1 2N
6N 2
For N >10, the last term
m −1
can be omitted.
6N 2
Several subsequent improvements have been made notably by Jensen and
Fratini (1957) and Scaloppi (1988). Jensen and Fratini (1957) derived an
adjusted factor F, which allows for calculating head loss in a singlediameter pipe lines with multiple equally spaced outlets, when the first
outlet is one-half an outlet spacing from the pipe line inlet.
Scaloppi (1988) derived an adjusted factor Fa which allows for direct
calculation of head loss caused by friction in a single-diameter pipe line
with multiple equally spaced outlets and the first outlet at any distance
from the pipe line inlet. Scaloppi (1988) and Jensen and Fratini (1957),
both assume zero outflow past the most downstream outlet. For a singlediameter pipeline with multiple outlets, factor F as suggested by
Christiansen, or the adjusted factor Fa as suggested by Scaloppi, allows
rapid calculation of head loss caused by friction. However in case of a
multiple-diameter pipe line, both the F factor and the adjusted Fa factor
cannot be used directly to the entire length of the pipe line. Keller and
Bliesner (1990) developed a factor G that can be used in pipeline with
multiple equally spaced outlets and any out flow at the downstream end
past the last outlet and for any multiple-diameter pipeline. The DarcyWeisbach formula expresses head loss of turbulent flow in pipelines on a
rational basis:
fL V 2
.........................(1.4 )
HL =
D 2g
Where HL= the loss of head in equivalent height of water in a length of
Pipe L.
D = inside diameter of the pipe.
V= the mean velocity
g = the gravitational acceleration.
f = a resistance coefficient.
Both Hazen-Williams and Darcy-Weisbach equations are used in
determination of friction head losses in irrigation system.
1.5. The study objectives:
This study was conducted with a view to evaluating the performance of
the existing computerized irrigation system in Al-Ain town with the
objective of improving it.
New concepts in hydraulics were followed in determining friction head
losses in the irrigation system network.
Chapter Two
Literature Review
2.1. Introduction:
Irrigation pipeline capacity and head loss in an irrigation pipeline must be
selected according to size to obtain the best operating performance and
economy. The size must be adequate to deliver enough irrigation water to
meet crops needs.
The Darcy-Weisbach's formula expresses head loss of a turbulent flow in
pipelines it is defined as:
fL V 2
...........................(1.4 )
HL =
D 2g
Where HL = head loss, m
L = length of pipe, m
D = inside diameter of the pipe, m
V = the mean velocity, m/s
g = the gravitational acceleration, m/s2
f = resistance coefficient.
The values of the resistance coefficient (f) have been related to boundary
roughness dimensions for certain types of pipe surface and determined
empirically. Two other formulae are used extensively for determining
friction losses in irrigation pipelines. Resistance coefficients for these
formulae are readily available, for tubing commonly used in irrigation.
The first of these formulae is the Hazen’s Williams which can be written
as:
V = 0.849CRh0.63 S 0.54 .........................(2.1)
Where:
R= hydraulic radius, m
S= slope, m/m.
C= Hazen-Williams resistance coefficient.
The other formula is the Scobey's formula, which can be stated as
follows:
S = 10 −3 CV 1.9 D −1.1 ............................(2.2 )
Where
C = 516 Ks
Ks = the Scobey resistance coefficient; the exponents in Scobey's
equation are for aluminum pipes and the equation may have different
values for other pipe materials. Frequently the Hazen-Williams equation
is presented in hydraulics, water supply, and sanitary engineering
together with the Darcy-Weisbach equation. Vennard (1961), Streeter and
Wylie (1985), Streeter
et. al (1996), Potter and Wiggert (1997) and Liou (1998), discussed the
limitations of the Hazen-Williams equation. Despite the limitations
indicated, the Hazen-Williams equation has been used for a long time and
there exists a valuable database for the inner surface roughness of the
older pipes (Hudson, 1966).
Liou (1998) suggested a method for estimation of relative roughness
coefficient for older pipes for the Hazen- Williams (C).
The relative roughness so established by Liou (1998) can then be used to
determine the friction factor in Darcy-Weisbach equation.
According to Liou (1998) analysis, friction head losses can be calculated
correctly for Reynolds number and pipe size ranges wider than those used
in establishing the C values.
2.2. Friction Head loss in Irrigation laterals:
The analytic determination of friction loss is based on the
assumption that the outflow varies continuously in space along the pipe
line (Valiantzas 2002). Head loss determination is one of the main
problems to solve in any lateral design. Vallensquino and LuqueEscamilla (2002) developed a simplified approach based on successive
approximation scheme for solving the lateral hydraulic problem in
laminar and turbulent flows. The analysis they followed led, in the first
stage, to formulation of a constant outflow model leading to a standard
equation that is valid for laminar and turbulent flows, which is used to
calculate friction and local head losses. In this approach Darcy-Weisbach
equation together with a more generic correction parameter FP: N which is
equivalent to Anwar's (1999) Gafactor was developed. The difficulty
arising form the spatially varied friction factor is overcome by means of
equivalent friction factor (fe q n) that can easily be calculated for any
regime of flow. In the second stage of the analysis, Valesquino and
Luque-Escamilla (2002) reached a better estimation of the outflow
distribution along the lateral by using the previous head loss model
results together with a variable discharge model based on Tayler's
polynomials. The approach allowed them to directly calculate some of the
important parameters used in any lateral design, such as the real mean
lateral design, and the real mean lateral outflow. In the final approach
they improved the model taking into account more realistic head losses
approach based on the non-constant out flow distribution model
developed on the previous level. This step is useful if an accurate result is
needed when the relative head loss (∆Hf k n / He1) and outflow variation
(∆q) are great.
Christiansen (1942) developed an adjustment factor (F) to correct the
friction loss calculated from the general formula that assumes all of the
water is carried to the end of the line:
FK (L 100)(Q C )
.......................(1.2 )
H f (L ) =
D 2 m+n
m
Where:
Hf (L) = the friction head loss in a lateral of the length L, and with
multiple outlets having equal spacing and discharge.
K= a constant based on the dimension used in the formula.
L= length of the pipe.
Q = total flow into the lateral.
D = diameter of the pipe.
m , n = velocity exponent.
Computing the head loss in a pipe considering the entire discharge to
flow through the pipe and multiplying by Christiansen (1942) factor F
allows the head loss through a single diameter pipe line with multiple
outlets to be estimated. Christiansen (1942) in deriving factor F made the
following assumptions:
• No out flow at the downstream end of the pipeline.
• All out lets are equally spaced.
• All outlets have equal discharge.
• The distance between the pipe inlet and the first out let is equal
to the outlet spacing.
Factor F is a function of the friction formula used and the number of
outlet along the lateral. However, in many cases, the first outlet cannot be
located in a full spacing from the pipeline inlet. Jensen and Fratini (1957)
suggested an adjusted F factor which allows for the calculation of head
loss in a single-diameter pipeline with multiple equally spaced outlets
where the first outlet is one-half an outlet spacing from the pipeline inlet.
The model or expression suggested by Jensen and Fratini (1957) does not
allow for any outflow at the downstream end of the pipeline. Chu (1978)
suggested a modification for Jensen and Fratini (1957) adjusted F factor
and claimed that this modified factor F could be considered as a constant
for five or more outlets with out introducing any significant error. As
Jensen and Fratini (1957), Chu's work also assumes no outflow at the
downstream end of the pipeline beyond the last outlet sprinkler. Scaloppi
(1988) went further and reached to development of adjusted F factor
which allows for direct calculation of head loss caused by friction in a
single-diameter pipeline with multiple equally spaced outlets and the first
outlet at any distance from pipeline inlet. In developing the adjusted F
factor, Scaloppi (1988) also assumed that no outflow past the most
downstream outlet. On the other hand Blasius (1913) proposed a simple
equation for estimating the friction loss factor for very smooth pipes. The
equation is based on the Reynold's number and is given as:
f = aR b ........................(2.3)
Where (f) = the friction factor; (a) and (b) = empirically determined
coefficients; and (R) = the Reynold's number.
Schlichting (1968) stated that the Blasius equation is very accurate for
smooth pipes and Reynolds number less than 100,000. Watters and Keller
(1978) and Von Bernuth and Wilson (1989) have shown that Blasius
equation works well for small-diameter plastic pipe when the Reynolds
number is les than 100,000; however, as the Reynolds number is less than
4000 in laminar flow or critical zones the Blasius equation will over
estimate the friction factor by as much as a factor of five (Von Bernuth,
1996). For irrigation pipeline purposes, that is in significant because the
losses would be considered negligible. If flow is assumed to be laminar, f
can be estimated by:
f = 64 R ...........................(2.4 )
Design limitation on velocity in irrigation pipeline (1.5 m/s) will limit
Rynolds numbers to 100,000 for pipe 64 mm in diameter or smaller.
Von Bernuth (1996) derived simple and accurate friction loss equation
using a combination of the Blasius and Darcy-Weisbach equation. This
equation is quite similar to Hazen-Williams equation. The derived
equation is:
hl = KIQ1.75 d −4.75 .........................(2.5)
Where:
hl = head loss in a pipe length, (L)
Q = flow rate, ( L3/T)
l = pipe length, (L)
K = unit conversion = 2.458 * 10-2
d = the diameter of the pipe, (L).
2.3. Minor Head losses:
Head losses along lateral lines of drip irrigation systems have a
substantial impact on the available head at emitter nozzles. As a result,
discharge distribution is significantly affected when conventional noncompensating emitters are used. These head losses are frequently
estimated by adding frictional losses along uniform pipe sections between
consecutive emitters, to singular minor losses, resulting in some
resistance at emitter insertions. Since the order of magnitude of both is
similar, they deserve complementary attention (Howell and Barinas,
1980; Al-Amoud, 1995; Losada et al, 1999).
2.4. Blasius's friction factor:
The Blasius factor f = 0.316 R-0.25 ……………..
(2.6), when added to
Darcy – Weisbach equation, provides an accurate estimation of the
frictional losses produced by turbulent flow inside uniform pipes with
low wall roughness and when Reynold’s numbers fall within the range
3000 <R<100000. Most of drip irrigation laterals are usually made of
smooth polyethylene pipes and their flow regime fits these conditions.
Christiansen (1942) related head losses in a sprinkler lateral with a flow
Q0 distributed by N evenly spaced outlets (each distributing to the same
flow q = Q0/N) with those corresponding to the same lateral length (L)
and internal diameter (D), discharging the whole flow Q0 at the
downstream end of the lateral. A reduction factor F should be considered
in the latter to obtain the former. However, the discharge (q) in the rough
conventional (non compensating) emitter nozzles is not constant, but
depends on the pressure head (h) (Juana et.al, 2002).
Considering the head loss equation:
h f = CQ0m D − n .........................(2.7 )
Where C is a constant, and it takes the form:
F=
1
1
m −1
.........................(1.3)
+
+
6N 2
m + 1 2N
The above formula refers to situation where the first emitter is located at
a distance (L /N) from the lateral head (Juana et al, 2002). In general, the
number of emitters is large, and water distribution is assumed to be
continuous and uniform. Wu and Gitlin (1975) suggested that the head
loss at any point (R) located at a distance X from the lateral head (hf x c)
relative to the head losses in the whole lateral (hƒ L c) as follows:
R = (h fxc h flc ) = 1 − (1 − x L ) ..........................(2.8)
m +1
Head losses through local irregularities at emitter insertion of the
irrigation laterals must be included (Juana et.al, 2002). These minor
losses, hƒs , are produced at connections of on-line, in-line and integrated
emitters as if the pipe length was increased by the so-called equivalent
length (Le) which means a length of the same uniform pipe that would
have the same head loss. Minor head losses hƒs , are expressed in the
classical form of the kinetic head multiplied by K as follows:
V2
h fs = K
.........................(2.9 )
2g
Where V = mean water velocity in uniform pipe sections and (g) is the
gravitational constant (9.8 m/s2).
In general the friction coefficient K depends upon the geometric
characteristics at the emitter insertion and upon the Reynolds number R.
Bagarello et al (1997) in experiments with several on-line emitter models
proposed the following relationship:
1.29
⎛1 ⎞
K = 1 − 68⎜ − 1⎟ ..........................(2.10)
⎝r ⎠
The ratio r between the flow cross-section area Ar, where the emitter is
located, and the pipe section A can be determined by measuring both the
area occupied by the emitter insertion and that of the pipe.
Using the Blasuis’ formula, the equivalent length (Le) is related to K as
follows:
Le = K D f .........................(2.11)
Amin (1994) worked on laterals with sealed emitters and presented
results on a log-log chart as f-R diagrams with f values including minor
losses. Line parallelism with Blasuis friction factor was observed by
Amin (1994), indicating the practical validity of constant (Le) values.
Losada et al (1992) and Martinez et.al (1994) used experimental
procedures to determine (Le). Pressures at the inlet and at the downstream
ends of the conventional laterals were measured, as well as the discharge
from each emitter. These data were used to calculate (Le) by an iterative
method.
Friction losses along uniform pipe sections between consecutive emitters
were determined by the Blasuis formula and were added to minor losses,
in order to evaluate the minor losses, a common initial value was
assigned to (Le) which was changed until the pressures calculated at the
inlet and the downstream ends of the lateral matched those observed. The
(Le) values were statistically valid due to the relatively large number of
emitters considered. In most experiments conducted, lateral head losses
were not adequately calculated using Christiansen’s reduction factor F.
So, the energy slope was thus calculated for all uniform pipe section
(Losada et.al, 1992; Martinez et al, 1994).
Kermeli and Keller (1975) expressed that emitter discharge equation
through conventional (non compensating) emitter nozzles as follows:
q = kh x .......................................(2.12 )
Where K and x are coefficients whose values are constants when uniform
geometry of emitters is assumed.
Following and based on Christiansen approach, Anwar (1999) has
developed factor Ga that can be applied for quick estimation of the head
loss in irrigation lateral, with multiple, equally spaced outlets and any out
flow at the downstream end past the last outlet. Factor G which was
suggested by Anwar (1999) will reduce to factor F when the outflow at
the downstream end is set to zero, and hence factor G can be applied
equally well to the most downstream reach of the lateral line. Factor G
can be used in the design of pipeline network with multiple equally
spaced outlets using multiple pipe diameters or one diameter. The head
loss caused by friction at the given segment or length (K) can be
calculated using the following equation, which was suggested by
Christiansen (1942):
H fk =
CKQkm L
..........................(2.13)
D 2 m+ n
Where Hfk = friction loss between the downstream of the pipeline up to
and including section K.
C = units coefficient.
K = friction factor based on friction equation used (Hazen-Williams or
Darcy-Weisbach).
Qk = discharge of the given factor k of the pipe length.
L=length of each pipe section.
m and n = exponents of the pipeline and internal pipeline diameter.
The exponent (m) of the average flow velocity in the pipeline assumes
the value of 1.85 for the Hazen-William friction formula or 2.0 for the
Darcy-Weisbach equation. This developed the following equation when
using Darcy-Weisbach equation using m = 2.0
CKQlm G
..........................(2.14 )
H fk =
D 2 m+n
Where G = factor defined and tabulated by Anwar (1999) for various
ratios of the outflow discharge to the total discharge through the outlets
along the pipe line (denoted by r):
r=
Qο
..........................(2.15)
Nq
Where: Q0 = outflow discharge at the downstream end of the pipeline
beyond the last outlet; N = number of the outlets along the pipeline; q =
the discharge of each outlet.
When using Hazen-Williams friction formula the value of (m) is
considered equal to 1.85. Anwar (1999) suggested that when using m =
1.85, values for factor G >1.0 can be observed and a more accurate
estimate of the factor G can be obtained for m= 1.85.
Using the summations form of factor G rather than its Euler-Mclaurim
expansion.
2.5. Hazen-William formula:
TheHazen-williams formula relates the slope of an energy grade line to
the hydraulic radius and the discharge velocity of water flowing full in a
pipe. Hazen-Williams equation uses a constant to characterize the
roughness of the pipe’s inner surface. Hazen-Williams is used in
computing friction head loss in irrigation pipelines, given as:
⎛Q⎞
H f (100) = K ⎜ ⎟
⎝C ⎠
1.852
D −4.87 L.........................(1.1)
Where:
K =conversion coefficient (1.22*1010 for SI system of units)
L= length of pipe (m)
Q= volumetric flow rate (L /s)
C= Hazen-Williams coefficient (140-150 for PVC and PE pipes)
D= pipe inside diameter, (, mm)
2.6. Darcy-Weisbach formula:
Darcy-Weisbach formula expresses head loss in pipelines as:
fL V 2
.........................(1.4)
HL =
D 2g
Where:
HL = the loss of the head in equivalent height of water in length of
pipe L (m)
D = the inside pipe diameter, m
V = the mean velocity (m/s).
g = the gravitational acceleration, (m/s2 )
f = a resistance coefficient (dimensionless).
This equation is revised to a form applicable to pipe flow as:
Q2
H f = K 2 fL 5 .........................(2.16 )
D
Where:
K2 is a conversion factor (8.2627*1010 using SI units).
The friction factor (f) is a function of the flow regime (laminar or,
turbulent or transitional) and roughness of the pipe material. The head
loss along a lateral is due to friction with the wall pipe (friction losses)
and to disturbance of the stabilized flow in fittings and couplers (local
losses).
The friction head loss (Hfn) produced in the lateral segment between any
two consecutive outlets can be given by the Darcy-Weisbach equation:
8H fn LQn2
.........................(2.17 )
Hf n =
8π 2 D 5
Where:
Qn = nq +Qr
Qn = the total flow through the pipe.
Qr = the residual outflow at the downstream.
q = the discharge flow rate at the outlet.
n = number of outlets over the pipe.
fn = friction factor related to Qn.
L=outlet spacing (m). Darcy-Weisbach equation is more appropriate than
Hazen-Williams (Liou, 1998; Christiansen et al, 2000), but needs
additional effort to calculate
fn.
As stated above the two factors which determine the fn are the flow
regime and the roughness of the pipe. The flow regime is determined by
the dimensionless (Reynolds number RN):
RN =
VD
........................(2.18)
1000ν
Where:
V = flow velocity, m/s
ν = viscosity of the fluid m2 /s (which is 1.0 *10-6 m2 /s for water (20c°).
F = 6 y / RN (when RN ≤ 2000, laminar flow) and 1/f½ = 2 log(3.7 D/ε)
for RN > 4000 (turbulent flow), (where ε is the roughness of pipe). In
this study factor G as developed by Anwar (1999) was used for direct
computation of head loss caused by friction along the irrigation laterals of
sprinkler and bubbler systems, with multiple equally spaced outlets. And
the outflow at the downstream end was assumed to be zero and hence r =
zero (the ratio between the inlet flow and downstream out flow).
2.7 Systems design:
2.7.1. Sprinkler system:
Sprinkler lateral sizes are traditionally selected using hydraulic design in
which frictional head loss plays an important rule. The system designer
determines the number of sprinklers on a lateral line and the size of the
lateral line to meet the field requirements. The manufacturer's
recommendation may be used for deciding the spacing, operating
pressure, and average sprinkler discharge and application rate. The main
criterion of designing a lateral line is to select that diameter with a
pressure variation within the allowable limit. The allowable limit of the
pressure variation is usually taken as 20% of the pressure ratio as a
sprinkler lateral; (p/po) is the ratio of the pressure at any point on the
lateral to the pressure at the end sprinkler (Addnik et.al, 1983). The
discharge ratio is equal to the square root of the pressure ratio
q qο =
p pο Where q is the discharge of any sprinkler whose pressure
is p and qo is the discharge of last sprinkler on a lateral with pressure po.
Thus with 20% variation in pressure along a lateral, the variation in
discharge is about 10%. In a constant diameter, multi-outlet lateral, half
of the pressure loss due to friction will occur in the first 25 percent of the
lateral average operating pressure for achieving an acceptable value of
distribution uniformity (>75%) (Mohar and Singh, 2001).
Sprinkler discharge is a function of the pressure of individual sprinklers
(Addink et.al, 1983).
Q = k p ...........................(2.19)
Where:
Q= sprinkler discharge
K= nozzle discharge coefficient
P= pressure at sprinkler
Because pressure varies along the lateral due to friction and elevation
differences, sprinkler discharge also will vary. However, the ratio of
pressure at any point in the lateral to the pressure at any other point will
be constant for a given flow.
The hydraulic design of sprinkler laterals has been thoroughly discussed
by Benami (1968), Perold (1977), and Wu and Gitlin (1983).
Economic criteria in the design of sprinkler systems were considered by
Mandry (1967), Perold (1974), Chen and Wallender (1984), Gohring and
Wollender (1987) and Kumar et al (1992).
2.7.2. Trickle (Drip) Systems:
Drip or Trickle irrigation is the most recent of all commercial methods of
water application. Originally, drip irrigation was developed as subsurface
irrigation applying water beneath soil surface (Davis, 1974). The first
such experiment began in Germany in 1869, where clay pipes were used
in a combination of irrigation and drainage systems.
2.7.3. Hydraulics of Drip irrigation lines:
Flow in the drip irrigation lines is hydraulically steady, spatially varied
pipe flow with lateral outflow. The total discharge in a drip irrigation line,
lateral, sub main or main decreases with respect to the length of the line
(Howell
et.al, 1983). Friction loss for drip irrigation lines can be determined by
Darcy-Weisbach equation and Hazen-Williams empirical equation.
Hughes and Jepson (1978) compared the two equations using C (the pipe
roughness coefficient) ranging from 130 to 150 depending on Re (Renold
number) in terms of the friction factor. Many pipe manufacturers
recommend a maximum velocity of 1.5 m/s in plastic pipe. At this
velocity the value of C compares best to the Blasuis equation (for the
turbulent and laminar flows when:
F= 0.316 Re-0.2 (4000≤ Re ≤ 100,000) (For turbulent flow) and f= 64/ Re
(Re ≤ 2000) for laminar flow)
This depends on the pipe diameter since C =130 for 14 to 15-mm pipe, C
= 140 for 18- to 19mm pipe, and C = 150 for 25- to 27mm pipe diameter.
Hughes and Jepson (1978) suggested that underestimating C results in
more conservation friction loss for design purposes.
The total specific energy of any section of a drip line can be expressed by
the energy equation:
H =Z+H +
ν2
2g
...........................(2.20)
Where:
H = The total energy
Z= the potential head or elevation
H= the pressure head.
v2
= The velocity head, and all expressed in meters.
2g
As the flow rate in the line decreases with respect to the length because of
emitter discharges from the lateral and lateral outflow from sub mains,
the energy gradient line will not be a straight line but a curve of
exponential type as expressed by Myers and Bucks (1972) and Wu and
Gitlin (1975).
The shape of the energy gradient line for level irrigation lines can be a
dimensionless pressure gradient line, since velocity head changes are
negligible, as derived by Wu and Gitlin (1974):
Ri = 1 − (1 − i ) .........................(2.21)
m +1
Where:
Ri :
∆Hi
(Pressure drop ratio,)
∆H
m= the exponent of the hour rate in the friction equation.
i = ℓ/L
L = is the total length of the line,m
ℓ = is the given length measured from the head end of the line, m.
Chapter Three
MATERIALS AND METOHDS
3.1. Concept:
Many researchers and scientists have studied extensively the hydraulic
design of lateral lines in modern, pressurized irrigation system such as
sprinkler, bubbler and drip system.
In these irrigation systems pressurized pipelines with multiple outlets are
used extensively. A detailed hydraulic analysis of multiple outlet
pipelines is essential for design and evaluation purposes of these systems.
Recently increasing progress in computer technology has resulted in
development of various numerical methods. However, simple but
sufficiently accurate analytical methods remain an alternative solution for
routing engineering application. Head loss determination is a basic
problem to be solved in any irrigation lateral design. Head losses along
lateral lines of drip, sprinkler and bubbler irrigation systems substantially
affect the available head at outlet nozzles. Consequently, discharge
distribution is significantly affected when convectional non-compensating
nozzles, bubbler or sprayers are used.
3.2. The irrigation system:
The irrigation system now in use in Al-Ain town center is characterized
by a number of qualities. The water that is used for the irrigation of AlAin town center is treated sewage water. The system is a real time,
custom made, flexible and has a number of capabilities that make it one
of the best and highest quality-irrigation and water management tool in
the region. The irrigation system consists of a central computerized
station; pump station, water reservoir, weather station, remote terminal
units, solenoid valves, flow sensors, butterfly valves, and the irrigation
network.
Irrigation network: the main irrigation line conveys the water to the
submain and lateral lines, which in turn subdivide into three types of
irrigation emitters:
• Drip lines which are used to irrigate flowers,
• Bubblers which are used to irrigate palm trees and all other types
of trees.
• Sprinklers which are used for the irrigation of grasses and lawns.
Since its installation and use the irrigation system has resulted in:
• Improvement of the irrigation system efficiency, and because it is a
real time system the problems can easily be detected and resolved
at the right time (i.e. less lost time).
• The system has resulted in about 50-60% saving in water use. The
plants including salt leaching requirements.
Less labour is required to run the system, two persons in the control
room, one for irrigation scheduling, one for pump room supervision and
only four skill labour for daily supervision and maintenance at sties.
3.2.1. Central control station:
The central control station consists of two computers: main and backup
computers. The backup computer is used as a monitoring station and as a
backup in case of main computer crash. The two computers have custom
made software that was developed using" In touch Wonder ware
Development Package" to monitor, control, and manage the irrigation in
Al-Ain town center. The computers are controlling thirty one (Remote
Terminal Units, RTUs) in Al-Ain town center through a wire line
communication cable and
Plate (3.1) Main Control Panel
have the capabilities for radio communication to control and monitor
remote areas. The developed software has user-friendly screens that show
all parts connected to the irrigation system for monitoring, control, and
management.
3.2.2. Pump station:
The pump station is connected to the central computerized system and
consists of three pumps with a variable frequency drive feature. The
pump station screen shows the three pumps, filtration system, water
supply volume, water outflow volume, tank , butterfly valves (supply,
discharge, and return). All status of pumps operation, filtration, water
supply, and water discharged, tank water level/volume, and butterfly
valves are real time. A very important feature of the pump station screen
is the ability to give a full cycle of irrigation to all solenoid valves
proportionally in case of water shortage using the "Irrigation Factor
Feature". Another feature is the ability of the system to automatically
close the supply butterfly valve in case of water level in tank reaching a
critical point.
Also, a good feature of the system is the ability of the system to open the
return butterfly valves for water to return to tank in order to reduce the
pressure in site. Incase of any malfunctioning devices, alarm are
generated by the system and logged in the report database.
3.2.3. Weather station:
The software program incorporate the latest FAO evaporanspiration (ET)
determination model (Penman-Monteith). The system is connected to a
weather station that provides the daily weather parameters, which the
software program uses to calculate the potential evapotranspiration (ET0).
Crop and ET-base factors are present in the program to determine that
actual
Plate (3.2) Pump Station
Plate (3.3) Layout of Pump Station
Plate (3.4) Weather Station
evapotranspiration and have the daily crop irrigation requirements. A tenyear database of the weather parameters is collected from a local weather
station and the water requirements for various ornamental plants are
estimated. These estimates are used in the irrigation schedule for summer,
winter, and autumn seasons.
3.2.4. Layout of the Remote Terminal units on sites:
The irrigation control system which is designated Moscada (Motorla
Supervisory Control and Data Acquisition) consists of 31 RTUs (Remote
Terminal Units) all connected to the control station computerized system
by a wire line communication cable. Solenoid valves, Butterfly valves,
Flow meters, Pressure sensors, and fountains are wired to RTUs.
3.2.5. RTU (Remote Terminal Units) Hardware parts:
Remote terminal unit's hardware made by Motorola consists of CPUs,
modules (DO, DI, AI, and Mixed), modems, PCBs, etc.
3.2.6. RTU Functions:
A remote terminal unit shows the solenoid valves/real-time status of
various types (palm, grass, drip and shrubs), butterfly valves, flow
sensors/real-time value and fountain status. Valves and fountains can be
controlled from the irrigation software. A good feature in the RTU screen
is the "RTU water factor" which can be used to increase the vale runtime.
3.2.7. Schedule:
The schedule is the main feature of the irrigation system, which can be
downloaded from the main computer at the control centre to the remote
terminal units to automate the irrigation. The schedule is saved in the
RTUs and applied at the specified time. The schedule can be modified as
required.
Plate (3.5) RTU Functions
3.2.8. Reports:
The irrigation system includes a database that logs all data from the
system such as water supply, water consumption, valve run time, weather
data and alarms.
3.3. The Experimental site:
The experiments of this study were conducted in the Municipality traffic
and parking improvement project at Al-Ain city, Abu Dhabi Emirate,
United Arab Emirates. The project lies in Al-Ain central district garden
directorate. The project encompasses a modernization of the automated or
computerized irrigation system in Al-Ain town center and is
characterized by a number of qualities. It is a real-time, customer-made,
flexible, and has a number of capabilities that make it one of the best and
highest quality irrigation systems in the region. The system consists of a
central computerized control unit, pump station, water reservoir, weather
station, remote solenoid valves, flow sensors, pressure sensor, butterfly
control valves and irrigation network. The irrigation system consists of
bubbler, sprinkler and drip systems. The main irrigation line conveys the
irrigation water (treated waste water) to sub mains and lateral lines all
made of (PVC) and (PE) material. The central control station consists of
two computers; a main computer is used as a monitoring device and a
second computer as a backup when the main computer fails. The software
used is a customer-made that has been developed using “In touchwindow viewer wonderware package” to monitor, control and manage the
irrigation system. The pump station is connected to the central
computerized system via a variable frequency drive features. The pump
screen shows the three pumps, water filtration system, water supply
volume, water outflow volume, and tank water level. The
status of all these parts is real time. The software program incorporates
the latest FAO reference evaportranspiration (ET0) determination formula
Penman-Monteith as stated by Allen et al (1989). The system is
connected to the weather station that provides the daily weather
parameters (air temperature, relative humidity, wind speed and solar
radiation). The software uses these parameters to compute the reference
evaportranspiration (ET0) and using the crop factors, the system
determines the actual evaportranspiration for each plant grown in the
area. Rainfall is also measured and the data is used in the irrigation
requirement.
3.4. Layout of the Experiment:
Three sites for each irrigation system, namely, bubbler and sprinkler,
were selected randomly. The criteria for selection were that the electric
solenoid valve should include a pressure gauge that shows the pressure at
the connection point between the lateral and the main line.
In each selected site these solenoid valves were selected at random
provided that they included pressure gauges.
Then, the pressure head was measured at outlets that were spaced a
distance of 7 meter from downstream up to the end of the lateral. The
collected data were recorded. This exercise was carried out regularly
during the summer season, which is the time of the highest irrigation
water requirements.
3.5. Data Analysis:
The collected data were tabulated (Table 1-29) and the analysis was
conducted using the SPSS (statistic package for science and social
studies) software.
Plate (3.6) Experiment Layout
Chapter Four
Results and Discussion
4.1. Data Acquisition:
The Field experiments were carried out in the randomly selected sites of
the irrigation system. Data for bubbler and sprinkler system were
collected and tabulated as presented in Tables (1 to 29). The experiments
consisted of measuring the pressure in each selected electric solenoid
valve between the most downstream ends at equally spaced outlets to the
first upstream outlet using Burdon pressure gauges.
4.1.1. Trickle (Bubbler) system data:
The data for the ten randomly selected electric solenoid valves of the
trickle (Bubbler) system are shown in Tables (1 to 19), (see Appendix 1)
The outlets along the pipeline were equally spaced at 7 meter each (To
irrigate trees and palm tree).
The tabulated data for the Bubbler system were plotted in the diagrams of
Figure (1) to Figure (19).
4.1.2. Sprinkler system data:
The randomly selected electric solenoid valves of the Sprinkler system
were treated similarly as the bubbler system valves. The pressure along
the pipeline of each solenoid valve was measured using the Bourdon
pressure gauge and the data were recorded in Tables (20-29) and their
respective pattern of the pressure behavior along the pipeline is exhibited
by Figures (20-29). The spacing between the sprinklers was 4 m (to
irrigate grass and ground cover).
Plate (4.1) Bourdon Pressure Gauge
Plate (4.2) Bubbler System in Operation
Plate (4.3) Sprinkler System in Operation
4.2. Data Analysis:
The collected data were tabulated (table 1-29) and the analysis was
conducted using the SPSS (statistic package for science and social
studies) software.
The procedure adopted and followed for the analysis in this study was
based on Anwar’s (1999) G factor for pipeline with equally spaced
multiple outlets and outflow.
Factor G was developed assuming that the first outlet is one outlet
spacing from the inlet of the pipeline. Christiansen (1942) assumed that
the outlets along the pipeline with multiple outlets, there would be energy
losses caused by the coupler and structure of the outlet. However, there is
also gradual decrease in velocity head as the water flow passes the outlet
and this will cause an increase in pressure, which will balance losses due
to couplings as, suggested by Scallopi (1988).
As a result of this an exact procedure to calculate pressure losses in
pipeline with multiple outlets cannot be justified as reported by Pair
(1975).
The assumption also underlines the work in this study.
The pipeline of the bubbler system with equally spaced outlets and inflow
and outflow at the downstream end was assumed to have the flow into the
pipeline given by:
Qi = Nq + Qo
………( 4.1 )
Where
Qi = discharge into the pipeline inlet.
N = number of outlets along the pipeline.
q = discharge of each outlet.
Qo = the outflow discharge at the downstream end of the pipeline beyond
the last outlet.
The ratio of the outflow discharge (Qo) to the total discharge through the
outlets along the pipeline (Nq) is represented by the following
relationship:
r = Qo /Nq
( 2.16)
where: represents the ratio.
Rearranging this relationship will resulte in:
Qo = r Nq
( 4.2)
And by substitution in equation
Qi = Nq + r Nq
( 4.1 )
= Nq (1+r)
or q = Qi /N (1+r)
( 4.3 )
…………( 4.4 )
Using Christiansen" (1942) formula for calculation of head loss caused
by friction at any segment along the pipeline
CKQlm G
..........................(2.14 )
H fk =
D 2 m+n
Where
Qk = represents the discharge in the pipeline at a section of length (k) and
k is an index representing the successive sections of the pipeline length
between the outlets with k = 1 at the most downstream section increasing
up to k = N at the most upstream segment adjacent to the pipeline inlet.
C = unit coefficient.
K = friction factor based on whether Darcy-Weisbach or Hazen-William
equation is used to determine the friction head loss.
D = the internal diameter of the pipeline.
m , n = exponents of the average flow velocity in the pipe line and
internal pipe line respectively, which in turn their value is based on the
friction model used in calculating the friction head loss.
In equation (2.14) the value for the exponent (m) typically assumes 1.85
for Hazen-Williams friction formula or 2.00 for the Darcy-Weisbach
friction formula.
Using the factor G as defined by Anwar (1999) the equation for
determining the head loss in the pipeline:
CKQkm L
..........................(2.13)
H fk =
D 2 m+ n
Appendix (3) Shows the value of factor G for a pipeline with up to 100
outlets for various ratios of outflow r and m=1.85 and m=2.00.
Equation (2.15) was used to calculate the head loss along the pipeline for
both bubbler and sprinkler system in this study, the following
assumptions were made:
1 -The friction coefficient C for the Hazen-Williams formula was
140 for PVC and PE pipes.
2 -The ratio of the outflow discharge to the total discharge through
the outlets along the pipeline (r)=zero i.e. Qo (the outflow
discharge at the downstream end of the pipeline beyond the last
outlet) was negligible (equal to zero).
3 -The internal diameter D of the pipeline was constant(50mm).
4.2.1. Data Analysis for Bubbler system :
The collected data for the bubbler system were analyzed using factor
G in both Hazen-Williams and Darcy-Weisbach formula. In the
former formula the value of the exponent (m) was assumed to be 1.85
while in the latter its value was assumed to be equal to 2.0.
The value of factor G for m =1.85 and m = 2.0 in (Appendix 3)were
used respectively for calculation of the friction headlosses along the
pipeline of the bubbler system with the corresponding number of
outlets. Tables (1-19). (The Appendix 1) Show the results of the
analysais and these results are exhibition in Figures (1-19).
4.2.2. Data Analysis for Sprinkler System:
Similary, the collected data for of the sprinkler system were analyzed
using the same procedure as for the bubbler system. The results of
the analysais are given in tables (20-29) of (Appendix 1) and shown in
their respective Figures (20-29).
4.2.3. Friction losses in Trickle (Bubbler) system using Hazen Williams equation, and applying Anwar G Factor.
(Q C )
×
1.852
H L = 1.212 × 10
12
× L 100
D 4.87
.........................(4.5)
Q = 3.5 L/ s
C = 130 factor coefficient of PVC pipes.
L = 140 m (lateral length of PVC pipes).
D = 50 mm (diameter of lateral of PVC pipes).
(3.5 130) × 140 100
×
(50)
1.852
H L = 1.212 × 10
12
4.87
HL = 11.175 m.
Multiplying by Anwar Factor G (Appendix 3)
HL = 11.175 m * 0.376 = 4.20 m
The actual average measured friction losses in Bubbler system
(Table 1– to 19).
Table
H(m)
Accumulated pressure head(m)
1
14.0
4.3
2
14.0
3.8
3
14.0
6.0
4
12.0
4.0
5
12.5
4.5
6
13.0
4.6
7
12.0
3.8
8
15
4.8
9
12.5
4.2
10
13.5
3.8
11
13.0
4.5
12
14.0
4.7
13
12.5
4.3
14
13.0
4.2
15
13.0
4.0
16
13.0
4.4
17
14.0
4.6
18
12.0
4.3
19
12.0
4.2
Total
249
83
The Average head losses (HL) = 83 /19 = 4.36 m.
4.2.4. Measured friction losses in sprinkler system using Hazen Williams equation, and applying Anwar G Factor.
(Q C )
×
1.852
H L = 1.212 × 10
12
D
× L 100
4.87
.........................(4.5)
Q = 5.625 L/ s
C = 130
factor coefficient of PVC pipes.
L = 60 m (lateral length of PVC pipes).
D = 50 mm (diameter of lateral of PVC pipes).
(5.625 130)
×
(50)
1.852
H L = 1.212 × 10
12
× 60 100
4.87
HL = 11.531 m.
Multiplying by Anwar Factor G (Appendix 3)
HL = 11.531 m * 0.402 = 4.64 m
The actual average measured friction losses in sprinkler system
(Table 20– to 29).
Table
H(m)
Accumulated pressure head(m)
20
27.0
3.7
21
28.0
3.9
22
34.0
4.4
23
38.0
4.3
24
36.0
4.6
25
34.8
4.1
26
28.0
3.7
27
30.5
4.5
28
32.0
4.0
29
36.5
4.6
Total
324.8
41.8
The Average head losses (HL) = 41.8 / 10 = 4.18 m.
4.2.5. Comparison between measured Head losses and calhead
losses by using Hazen-William equation and Anwar G Factor.
System
The Measured Head Calculated Head losses by
losses
using Anwar G Factor.
Bubbler
4.36 m
4.20 m
Sprinkler
4.18 m
4.64 m
Plate (4.4) Measuring the Pressure in Bubbler System
Plate No. (4.5) Measuring the Pressure in Sprinkler System
4.3. Concluding remarks:
Head losses determination is an important factor to be solved in
any pressurized, closed irrigation system design. In this study the lateral
head losses in sprinkler and trickle (bubbler) systems were computed
assuming that the outlet discharge (q) was not discrete and constant.
Actually this assumption is not true in all cases since the outlet discharge
is discrete and spatially varied. However, it can be a good approximation
in cases where the lateral outlet variation is about 10% or less as
suggested by Vallesquino and Luque-Escamilla (2002). Therefore, two
assumptions were used in this study: first, the discharges from the trickle
(bubbler) and sprinkler outlets along the lateral were assumed to be
constant. Secondly, the outflow discharges at the downstream end of the
pipeline, in both systems, beyond the last outlet were assumed to be equal
to zero. Based on these two assumptions and as the outlets along the
lateral in both systems were equally spaced, the friction head losses were
computed using Hazen-Williams equation (2.15), as suggested by Keller
and Bliesner,(1990), and also by introducing the Anwar's
G Factor
(Anwar, 1999) as in the equation:
CK (Q C ) (L 100) * G
.........................(4.5)
Q=
D 4.87
1.852
The velocity (or discharge) exponent in the above equation is taken
as 1.85, which approximately results in a velocity equal to the measured
velocity along the lateral (1.2 m/s).
Factor G as suggested by Anwar (1999) is a more generalized form of
factor F suggested previously by Christiansen, (1942), in that it allows for
outflow at the downstream end of the pipeline beyond the last outlet.
In this study since the outflow at the downstream end was set to zero,
factor G can be reduced to factor F. Factor G when used for calculation of
head losses caused by friction in sprinkler and trickle (bubbler) systems
where the laterals have multiple and equally spaced outlets, would give
calculated head losses very close to the measured ones for both systems.
The calculated head loss for the trickle (bubbler) system was 4.20m
compared to a measured value of 4.36m. For the sprinkler, the calculated
head loss was 4.64m compared to a measured value of 4.18m. Such an
approach allows direct and accurate enough computation of friction head
losses along the lateral with multiple and equally spaced outlets.
The proposed method could be applied to laterals (or sub mains) in trickle
(bubbler or drip) and sprinkler irrigation systems under any situation with
great simplicity and flexibility. The residual outflow allows the
computation of complex laterals when any parameter such as the
diameter, flow regime, outlet spacing or ground slope is varied from one
simple lateral to another as recommended by Vallesquino and LuqueEscumilla (2002).
The same calculation can be performed in a stepwise manner, i.e. starting
the computation at the downstream end and proceeding upstream towards
the inlet of the lateral; however this procedure may be considered tedious
and cumbersome.
Chapter Five
Conclusions and Recommendations
5. Conclusions:
From this study the following conclusions can be drawn:
1. Since the head losses along the laterals of the trickle (bubbler) and
the sprinkler irrigation systems affect the available operating
pressure head at the outlets, the discharge distribution along these
lines will be significantly affected particularly when noncompensating sprinkler heads (sprayers heads) or bubblers and
emitters are used.
2. The head losses caused by friction in a pipeline with multiple
outlets along its length, in trickle (bubbler) and sprinkler systems,
are less than the head losses caused by friction in a pipeline
without outlets, because of the decreasing discharge along the
length of the pipeline.
3. The estimation of head loss caused by friction in pipelines using a
stepwise analysis is tedious and cumbersome.
4. The Christiansen's analytical approach of introducing the concept
of a friction factor to calculate the total friction head drop at the
end of a multiple outlet pipeline, neglecting the effect of velocity,
and assuming equal discharge from outlets, was a first step in
giving good estimation of friction head losses in pressurized
irrigation systems.
5. For a single-diameter pipeline with multiple outlets, factor F
suggested by Christiansen (1942) or the adjusted factor (Fa)
suggested by Scaloppi (1988) will allow rapid calculations of head
losses caused by friction.
6. Factor (G) suggested by Anwar, (1999) will allow friction head
losses along a multiple equally spaced outlets along the trickle
(bubbler) and the sprinkler irrigation systems to be computed
directly using either the Hazen-Williams or Darcy-Weisbach's
friction equations.
7. Application of the Anwar's (G) factor, in this study, using HazenWilliams equation with exponent of velocity term equals to 1.85
gave high precision results. The measured head losses caused by
friction in the trickle (bubbler) and the sprinkler laterals with
multiple and equally spaced outlets have been found to be
comparable with head losses computed using factor (G).
8. This research presents factor (G) as an alternative to the wellknown and widely used Christiansen’s factor (F) for direct
computation of head loss caused by friction in the laterals or sublaterals of the trickle (drip or bubbler) and the sprinkler systems
with multiple equally spaced outlets.
9. When the outflow at the downstream end is set to zero, Anwar's
factor (G) and Christiansen's factor (F) will give similar results.
5.2. Recommendations:
Based on the conclusions drawn from this research the
following points can be recommended:
In designing pressurized irrigation systems, the head losses caused by
friction should be given great concern.
Factor (G) suggested by Anwar (1999), is recommended to be used in
calculation of friction head losses when designing laterals of pressurized
irrigation systems.
More research work is needed to investigate the optimum number of
outlets along a lateral and sub lateral of pressurized irrigation systems, to
achieve better discharge distribution when using the conventional noncompensating outlet nozzles.
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Appendices
Appendix1: Tables of Data for Trickle (Bubbler) and Sprinkler.
Appendix2: Treated Sewage Water.
Appendix3: Tables for G Factor.