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Efficiency of Different Irrigation Systems for
Sustainable Management of Water and Nutrient
Flows in the Harvey Irrigation Area
Ainalem Nega
B.Sc. (Civil) UoN, BEng. (Environmental)
Curtin 2007
This thesis is presented in partial fulfillment of the requirement of the degree of
Master of Engineering Science to the University of Western Australia
School of Environmental Systems Engineering
July 2011
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ABSTRACT
Sustainable management of water resources and the mitigation of nutrient flows into the
Peel Harvey inlet from irrigated farmland can be achieved through a combination of
land management practice and the implementation of efficient irrigation systems. A
quantitative understanding of efficiency for individual irrigation systems is required to
determine the efficacy of system employed to grow crops or pastures and improve water
resource and delivery management. An improved understanding is gained through the
evaluation of design and water application methodologies utilized in the Harvey
Irrigation District in Western Australia. Various irrigation system performance
measures are used to evaluate and compare the irrigation systems. Soil moisture
measurements over a 60 mm depth were taken before and after irrigation for each
application system to determine the temporal and spatial variability of soil moisture
within the study area.
The four irrigation systems (floppy, solid set, center pivot and subsurface drip) used in
the Harvey Irrigation District were compared using efficiency and uniformity criteria.
Soil moisture measurements were taken at the Waroona Research Station for each
irrigation system before and after the irrigation cycle, over 60 mm depth using a
thetraprobe. A ten m grid spacing for irrigation performance measures and a five m grid
spacing was used to assess soil moisture retention rates.
The combined water application and irrigation efficiency for each sprinkler system was:
73.4% for floppy; 68% for solid set; 81.2% for center pivot; and 94.4% for subsurface
drip system. The total system efficiency from reservoir to experimental plot was derived
for each system and given as: floppy 59.0%, solid set 54.0%, center pivot 65.0% and
subsurface drip 75.0% irrigation methods. The average low-quarter distribution
uniformity (DUlq) was: 50.0% for floppy: 52.0% for solid set: 56.2% for center pivot;
and 84.4% for subsurface drip irrigation system. The water distribution coefficient was
similar for the sprinkler systems (64.9%, 67.6%, 68.9%) but was significantly improved
for subsurface (89.4%) system.
The comparison of irrigation methods based upon initial water application and soil
moisture retention was implemented using the distribution uniformity (DUlq), soil
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moisture retention and infiltration rate. The initial water application efficiency for each
sprinkler system was: 76.6% for floppy, 82.2% for solid set, 59.4% for center pivot, and
93.3% for subsurface drip system. The soil moisture retention over the 24 hr monitoring
period for each sprinkler system was: 50% for floppy, 50% for solid set, 100% for
center pivot and 30% for subsurface drip system, and infiltration rate ranged between
0.22-8.1, 0.06-6.3, 0.05-6.4 and 0.08-3.1 mm/hr for each sprinkler system in the order
given.
The comparison of the different types of irrigation techniques demonstrated that the
subsurface drip and solid set irrigation methods were more efficient and effective than
the floppy and center pivot sprinkler irrigation methods.
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DEDICATION
To my beloved aunty Annie Macleod, for her love, support and enthusiasm
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DECLARATION
This thesis is wholly my own composition, and where I have used other sources I have
acknowledged their contribution. This thesis has not previously been accepted for any
other degree in this or another institution and has been entirely accomplished during
enrolment in the degree held at the University of Western Australia. This thesis is
largely composed of two papers which are in preparation for submission. The coauthors
of these papers are aware and have given permission for these papers to be included in
this thesis.
Ainalem Nega (Candidate) ________________________________
Keith R. Smettem (Supervisor) ________________________________
Neil A. Coles (Supervisor) ________________________________
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ACKNOWLEDGEMENT
I with great appreciation and recognition that I wish to thank the following people and
institution for the tremendous effort and contributions they made to the completion of
this thesis. The help of many people and resources in generating this thesis must be
acknowledged. The supervisor of the thesis, Professor Keith Smettem, has been a
continuous source of knowledge and support. My relationship with Keith has taught me
a lot about various aspect of life, some of which have included Ecohydrology: the use of
field and laboratory experimentation. My co-supervisor, Professor Neil Coles, for his
time and effort spent on editing and correction of this thesis. Thanks must also go to
other faculty members, staff and students at the School of Environmental Systems
Engineering for providing an interesting and stimulating work environment. It has been
a privilege to work with the various co-authors of my published works, Professor Keith
Smettem, Professor Neil Coles and Dr Kyungrock Paik. In particular my friendship with
Neil was appreciated during the latter stages of my candidature. I also wish to
appreciate and thank Professor Charitha Pattiaratchi for his great comment and advice in
this thesis.
Other individual who have contributed to this work include Mr James Newman, Mr
Todd Stokes and Mr Richard Yates who helped me during my field work. They were
very supportive from the beginning to the end of the field work, and I am very grateful
for my friendship with them. Dr Krystyna Haq played a major role in developing my
research and writing skills. Krystyna‟s assistance (Thesis Writing Workshops for
Masters and PhD students) has been very beneficial. Professor Chris Ford and Professor
Xiaolin Wang, whom I met through participating in the Tutorial Teaching Scheme, also
contributed to the postgraduate learning experience. Mr Ming Wu, a PhD candidate who
shared my office space has also contributed to this work in day-to-day problems. The
UWA Scholars‟ Thesis especially Matthew Simpson who received a Nobel Prize in his
PhD Thesis (1998) and Francis Herbert D‟Emden who also got a Distinction in his
Master Thesis (2006) and others were very helpful to structure my Thesis as a Series of
Papers.
In addition, family and friends have provided a consistent source of encouragement and
normality with a welcome stream of emails, telephone calls and visits since I left them
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to live in Perth, Western Australia. It has been a constant source of comfort to know that
whatever has been happening my life (such as loss of beloved father in mid of research
and loss of beloved mother in the end of the research but pursue research without give
up while trusting God for every things in a foreign land) others so far are interested and
willing to listen and share. Last but not least I wish to thank Sonia Connell and her
family, Samuel Watango for their constant encouragement, concern, care, motivation,
support and guidance all through this study.
In terms of technical support, it should be mentioned that the work presented in the
latter part of the thesis was heavily based upon the comparison of irrigation
performance measures: efficiency and uniformity and comparison of irrigation methods
based upon initial water application efficiency and soil moisture patterns in space and
time.
Finally, I am grateful to the financial assistance provided through the University
Postgraduate Award system. Additionally, the supplementary funding (Ad Hoc
Scholarship) provided through the University of Western Australia was much
appreciated.
“Praise be to the name of the Lord who has helped me with all these difficulties, and I am very
grateful for my beloved brother, Dr Ivan Haigh for his great concern and prayer.”
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CONTENTS
Abstract 3
Chapter 1: Background 11
Research questions 17
Structure 18
Site description 19
Chapter 2: An evaluation of irrigation performance measures:
efficiency and uniformity in the Harvey irrigation area in
Western Australia 24
Appendix 2-A: Composition of soil samples from each irrigation system
in the Harvey irrigation area 75
Chapter 3: Comparison of different irrigation methods based on the initial
water application efficiency and soil moisture retention
in the Harvey irrigation area in Western Australia 90
Appendix 3-A: Composition of soil samples from each irrigation system
in the Harvey irrigation area 117
Chapter 4: Discussion, Conclusions and Future Works 128
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CHAPTER 1: INTRODUCTION
1.1. BACKGROUND
Historically, irrigation was undertaken to meet human needs for food and competition
was limited to neighboring irrigators sharing the same source of water. In the post-
industrial era, population has increased dramatically and economies have diversified
leading to competition for water among different sectors. With increasing competition,
water is now viewed as a limited resource and the notion of water conservation has
emerged.
In modern irrigation systems, crop production with efficient use of water is now a major
goal. Water cost and farm sustainability as well as potential for waste and pollution of
the water resource by over-irrigation and fertilizer application has to be taken into
consideration (Baum, Dukes & Miller 2003; Smajstrla et al. 1991). Users of irrigation
water often have to defend their share of the water resource with the argument that it is
necessary and wisely used (Boland, Bewsell & Kaine 2006). Different methods for
irrigation are available such as surface, sprinkler, micro, subirrigation and hybrid
irrigation. Cost and convenience are often major factors influencing in the choice of one
system over another (Burt et al. 1997).
With an increased demand on water resources, it is becoming difficult to manage
irrigation systems (water delivery, on-farm operations and distribution uniformity)
effectively and efficiently. Water losses from current irrigation systems through several
pathways are not always possible to measure but can be high (Edkin 2006). For
example, the delivery losses from the older concrete channel delivery system once
routinely used in the Harvey irrigation district in Western Australia have been estimated
at over 30% between dam and farm. This results from seepage into ground, leaks in the
channels and structures, evaporation and end of systems outflow. The original concrete
canal delivery systems are now being replaced by pipes in order to minimize this loss.
However, water losses within the farm irrigation remain high and are estimated at 50
percent of delivered water (CSIRO 2007; Moore et al. 2004). The water source for the
Harvey irrigation areas are fully allocated and no additional water is available, placing
constraints on irrigated agriculture unless savings can be made through further
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efficiency gains. Figures 1-1 to 1-4 show the types of irrigation methods in the Harvey
Irrigation Area.
Figure 1-1: Floppy sprinkler irrigation systems in the Harvey Irrigation Area
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Figure 1-2: Solid set sprinkler irrigation system in the Harvey Irrigation Area
Figure 1-3: Center pivot sprinkler irrigation system in the Harvey Irrigation Area
Figure 1-4: Subsurface drip irrigation system in the Harvey Irrigation Area (site plan)
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1.1.1 DETERMING IRRIGATION EFFICIENCY
O.W. Israelsen, a pioneer in irrigation technology, was concerned about the quantity of
water being applied to irrigated land in the USA, and he developed several parameters
for characterizing irrigation performance. He called the first parameter, water
application efficiency, related to the quantity of water that was added to soil ( ) during
irrigation. The second parameter was the ratio of the quantity of irrigation water
consumed in evapotranspiration (ET) relative to the quantity applied called irrigation
efficiency (Ei) (Jensen 2007).
Israelsen et al. (1944) defined water application efficiency (Ea) as “ the ratio of the
amount of water that is stored by irrigation in the soil root zone and ultimately
consumed (transpired or evaporated or both) to the amount of water delivered to the
farm” (Jensen 2007). They reported that a study of water requirements in citrus and
avocados by (Beckett, Blaney & Taylor 1930), “made observation of „irrigation
efficiency‟- a term used by them with the same meaning as the term „water application
efficiency (Ea)‟ used here”. Israelsen et al. (1944) reported measurements of water
applications on 23 farms in Utah and Salt Lake Counties in Utah using gravimetric soil
moisture sampling techniques and calculated the water application efficiency (Ea).
Efficiency is the ratio of system output over system input (Baum, Dukes & Miller
2001). For irrigation, input is the water taken from the water source while output is the
water used for beneficial purposes. For instance, the beneficial purposes include water
used for consumptive use, leaching of salts, freeze protection, seedbed preparation, and
maintenance amongst others and so forth (Baum, Dukes & Miller 2003). According to
Webster‟s Unabridged Dictionary (New World Dictionaries 1979) defined efficiency as
(1) the ability to produce the desired effect with a minimum of effort, expense, or waste;
and (2) the ratio of effective work done to the energy expended in producing it, as of a
machine; output divided by input.
Analysis of efficiency ratings receives a lot of attention. For example, we like efficient
engines, air conditioners, water heaters and furnaces. Conservationists like efficient
water systems that deliver water for its intended use without loss due to leakage, spills
or contamination. Since irrigation is the largest appropriated water user in on-farm
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agriculture in the world, irrigation systems also receive merit based on how efficient
they are reported to be (Rogers et al. 1997). While this might sound straightforward and
simple, there is room for confusion because there are different ways to define
efficiency. Rogers et al. (1997) stated that the derived efficiencies can vary in time and
with management. They also emphasized that very “efficient” systems by some
definitions can have very poor performance by other definitions if distribution
uniformity and delivery amount are inadequate to fulfill crop need.
Rogers et al. (1997) discussed the irrigation efficiency as the combination of several
common efficiency terms in use for irrigation system and showed how these terms
apply to the same common irrigation situations such as water conveyance efficiency
(Ec), water application efficiency (Ea), irrigation efficiency (Ei), water distribution
efficiency (Ed) and distribution efficiency (Ud). Similarly, Kruse, Bucks and von
Bernuth (1990) described many types of efficiency that have been defined for surface,
sprinkler, micro, subirrigation and hybrid irrigation systems. They discussed on their
literature that different writers have given different definitions for the same efficiency
term therefore, anyone considering the efficiencies of irrigation systems needs to define
terms carefully and be sure that the use of all terms are clearly understood. The authors
also noted that effectiveness of an irrigation system cannot be described with any single
efficiency term. For example, an effective irrigation system will store most of the
applied water in the soil root zone where it is available to the crop (high water
application efficiency); each irrigation will replace nearly all the soil moisture deficit in
the soil root zone (i.e. high water storage efficiency) and water will be applied
uniformly to all parts of the field being irrigated (i.e. high coefficient of uniformity)
(Kruse, Bucks & von Bernuth 1990).
The type of irrigation system and its design affect not only efficiency but also the
distribution uniformity of water application. Uniformity refers to how uniformly water
is applied; this affects many parameters that are used to asses irrigation performance.
Efficiency can be measured in a myriad of ways, and what is assessed as efficient by
one measure may not be by another. Also, the highest efficiency may not meet
economic or environmental objectives. For instance, under-irrigation may have a high
efficiency in the short term but can lead to salinization problems in the long term as
salts are not leached below the rootzone (Heermann & Solomon 2002).
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The factors affecting distribution uniformity (Ud) for each irrigation method (surface,
sprinkler, micro, subirrigation and hybrid irrigation method) are different. For example,
most microirrigation (drip) systems are relatively simple to evaluate because most of the
nonuniformity can be directly assessed by measuring the flow from individual emitters
(Burt et al. 1997). However; hand-move sprinklers are more difficult to evaluate
because flow rate differences at the emission point lead to poor sprinkler pattern
uniformity.
It is well known that the uniformity of water application has an effect on crop yield
(Letey 1985; Solomon 1984). Actual field measurements of irrigation uniformity are
both difficult and expensive to make. Molden and Gates (1990) consider that the
success of an irrigation water-delivery system can be measured by how well it meets the
twin objectives of delivering an adequate and dependable supply of water in an
equitable, efficient manner to crops or pastures. The authors point out that water must
arrive at the farm in timely and adequate amount in order to maintain crop yield and
farm net returns. Also, it is important that each farmer receives an amount of water that
is fair and not excessive.
Several papers have highlighted the importance of understanding irrigation efficiency
(e.g. Bos & Nugteren 1974; Burt et al. 1997; Haman, Smajstrla & Pitts 1996; Hart,
Skogerboe & Peri 1979; Heermann & Solomon 2002; Israelsen et al. 1944; Jensen
1967; Kruse 1978; Smajstrla et al. 1991; Solomon 1984). This recognition is, in part, a
response to the realization that irrigation systems need to be efficient and effective over
the entire system performance (i.e. from source to plant deliver system). Heermann et
al. (1990) noted that many irrigators fail to recognize the value of irrigation schedule
control through improved technology and lack a knowledge of efficiency provided
either through self education or by contracting with consultants that can improve their
crop productivity. Burt et al. (1997) provides more detailed information on statistical
distribution uniformity and the accuracy of irrigation efficiency estimates that can be
used to clarify the common point of confusion on the definition of efficiency.
This thesis presents an assessment of efficiency and uniformity in two parts: the first is
largely a theoretical development and comparison of various irrigation performance
measures and techniques; the second is an evaluation of system application efficiency
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through basic field measurement to assess the performance of different irrigation
methods used in the Harvey Irrigation Area (HIA) of Western Australia. The methods
are however, quite general and can be applied to any irrigation system.
1.2. RESEARCH QUESTIONS
This research project is broadly focused on assessing the irrigation efficiency of
delivery and application system in the Harvey Irrigation Area in Western Australia.
Irrigation performance measures evaluate the irrigation water balance and determines
the fate of various fractions of the total irrigation water applied: how much gets to the
crop and how it is distributed among the plants, how much of the remainder is
recoverable, how much enters the ground water and surface drainage (Burt 1999; Burt
et al. 1997). Alternatively an alternate irrigation performance measure evaluates the
water distribution and delivery systems in terms of efficiency, adequacy, dependability
and equity of water delivery (Molden & Gates 1990). It evaluates the irrigation
efficiency of different irrigation methods and recommends the best irrigation method as
defined in terms of efficiency and uniformity for this area or any other region.
These measures provide a quantitative assessment not only of overall system
performance, but contribute to the performance analysis of the design and management
components of irrigation systems (Molden & Gates 1990). In general, the application of
irrigation performance measures provides a method of evaluating: various management-
allowed depletion; frequencies of irrigation; and system capacities (Heermann et al.
1990).
In this research project, field-data is collected and analyzed to evaluate the root zone a
soil-water budget model for irrigation scheduling (i.e. theoretical equation). Data
includes the amount of rainfall and irrigation, meteorological data to estimate ET, soil
water status, and impact on crop production. In addition, the research addresses the
question of irrigation efficiency and uniformity, irrigation methods, design and
operation of on-farm irrigation systems, irrigation (soil-water budget) and economic
constraints. The research is designed to provide insight into these broader questions by
focusing upon the following:
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Can the irrigation performance measures: efficiency and uniformity, and
comparison of irrigation efficiency measures reduce irrigation water losses in
the Harvey irrigation district? Can this assessment provide an unbiased
comparison of irrigation system performance for systems used in this district
and be extended to the other sub-region irrigation districts?
Can the comparison of different irrigation methods based on initial water
application efficiency and soil moisture retention assist in determining and
managing the water loss associated in the Harvey irrigation district? Can this
assessment provide equitable system performance criteria for this district and
others?
How efficient are the current irrigation systems and what is the most efficient
option available to irrigators in the region?
Can the use of resources and irrigation efficiency be optimized?
1.3. STRUCTURE
This thesis is, in accordance with postgraduate and research scholarship regulation 31(1)
of the University of Western Australia, is presented as a series of scientific papers that
resulted from the study. The four main chapters of the thesis consist of an introductory
account of the research, followed by two chapters, which contain expanded versions of
two scientific papers. Therefore, these two chapters can be read either as a part of the
whole thesis, or as separate entities. Each of these chapters contains an independent
introduction, literature review, methods, results and discussion sections, conclusion and
therefore some overlap, especially in the presentation of the comparison of irrigation
methods used in Chapter 2 and 3 is unavoidable since each chapter concerned with a
similar or related research question. In addition, each chapter is independently
referenced to acknowledge the contribution of previous related research. A general
discussion and conclusions chapter close the thesis.
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In the current chapter, the aims, background, scope and purpose of the research are
presented. This chapter provides the basic stimulus for the study and maps out the
fundamental research question to be addressed in the thesis
In the second chapter (Chapter 2, „Irrigation performance measures: efficiency and
uniformity), a general discussion and comparison of the fundamental efficiency and
uniformity equations are used to assess the water losses and compare the different types
of irrigation systems used in the area. The analysis presents an unbiased comparison of
the irrigation systems in terms of efficiencies and uniformity. Also, an analyses of
different types of irrigation efficiency terms evaluate the relative advantage of one
irrigation method over another to determine the best system. Evaluation of irrigation
methods using efficiency terms and uniformity is also used to assess the entire system
performance.
Chapter 3 present a comparison of different irrigation methods based upon initial water
application efficiency-using the uniformity of distribution and soil moisture retention. In
addition, the water application and soil drainage over 24 hr period is used to reveal the
drainage pattern and soil moisture depletion associated with each irrigation method.
Furthermore, the discussion and analysis presented describes the variability in soil water
status (i.e. change in soil water storage) as result of nonuniformity in water application
efficiency. This approach shows for the development of a management decision and
irrigation support tool for scheduling.
The final chapter (Chapter 4) presents the closing discussion and concluding remarks.
This section provides an overall discussion of the issues raised in the thesis and points
to new questions for further research defined as a result of the research undertaken in
this thesis.
1.4. SITE DESCRIPTION
The Harvey Water Irrigation Area (HWIA) is located to the west of the Darling Scarp
on the Swan Coasted Plain, approximately 100 kms south of Perth, Western Australia. It
covers an area of 112,000 hectares (around 75 kms long and 15 kms wide) in three
irrigation zones: Harvey, Waroona and Collie. There are currently around 10,100 ha of
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land under permanent irrigation for dairy farming, beef grazing and horticulture, with a
total potential area for irrigation of approximation 30,000 ha. The irrigatable area and
value of output could be further increased with the introduction of an efficiency delivery
system and improved irrigation technologies. The total gross value of agricultural
production (GVAP) from the irrigation area is estimated at $ 100 million per annum.
This study is focused on the Harvey Irrigation Area (HIA) shown in Figure 1-5.
Figure 1-5: The location of area the Harvey Irrigation Area in which this study was
instigated
The HWIA is different from most Australian irrigation areas because it does not have a
longitudinal river system(s) from which water is diverted or pumped. Water has
historically been supplied by gravity from dam to farm along a network of open
concrete lined and earthen channels. The slopes are quite short and relatively steep and
feed water laterally across the system to farms. Water releases are actively managed
using a computer monitoring system as a Supervisory Control and Data Acquisition
system (SCADA).
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REFERENCES
Baum, MC, Dukes, MD & Miller, GL 2001, Residential irrigation uniformity and
efficiency in Florida, American Society of Agricultural Engineers Meeting
Paper No. 02-2246, St. Joseph, MI.
Baum, MC, Dukes, MD & Miller, GL 2003, 'Residential Irrigation Uniformity and
Efficiency in Florida', ASAE Section Meeting Presentation, FL03-100, Florida.
Beckett, SH, Blaney, HF & Taylor, CA 1930, Irrigation water requirement studies of
citrus and avocado trees in San Diego Country, California Agricultural
Experimental Station, Bulletin. 489, California.
Boland, AM, Bewsell, D & Kaine, G 2006, 'Adoption of sustainable irrigation
management practices by stone and pome fruit growers in the Goulburn/Murray
Valleys, Australia', Irrigation Science, vol. 24, no. 2, pp. 137-145.
Bos, MG & Nugteren, J 1974, On irrigation efficiencies, International Institute for Land
Reclamation and Improvement, Publication No. 19, Wageningen, The
Netherlands, P. 95.
Burt, CM 1999, 'Irrigation water balance fundamentals', in Conference on
benchmarking irrigation system performance using water measurement and
water balances, Irrigation Training and Research Center, California Polytechnic
State University, San Luis Obispo, California, pp. 1-13.
Burt, CM, Clemmens, AJ, Strelkoff, TS, Solomon, KH, Bliesner, RD, Hardy, LA,
Howell, TA & Eisenhauer, DE 1997, 'Irrigation Performance Measures:
Efficiency and Uniformity', Journal of Irrigation and Drainage Engineering,
vol. 123, no. 6, pp. 423-442. Available from: ASCE Research Database [13 May
2008].
22
Commonwealth Scientific and Industrial Research Organisation 2007, Science to
improve Australian's irrigation systems: Irrigation overview and challenges
[Online], Commonwealth Scientific and Industrial Research Organisation
(CSIRO). Available from: http://www.csiro.au.org/Irrigation-Research.html
[Accessed 1 September 2009].
Edkin, R 2006, Irrigation Efficiency Gaps - Review and Stock Take, Report No
L05264/2, Sustainable Farm Fund and Irrigation New Zealand, Aqualinc
Research Ltd, New Zealand.
Haman, DZ, Smajstrla, AG & Pitts, DJ 1996, Efficiencies of irrigation systems used in
Florida Nurseries 1, Bulletin. 312, Institute of Food and Agriculture Science,
University of Florida, Gainesville, Florida.
Hart, WE, Skogerboe, GV & Peri, G 1979, 'Irrigation performance: An evaluation',
Journal of the Irrigation and Drainage Division, vol. 105, no. 3, pp. 275-288.
Heermann, DF & Solomon, KH 2002, 'Efficiency and uniformity ', in Design and
operation of farm irrigation systems, ed. ME Jensen, American Society of
Agricultural Engineers, Michigan, pp. 108-119.
Heermann, DP, Martin, DL, Jackson, RD & Stegman, EC 1990, 'Irrigation scheduling
controls and techniques', in Irrigation of agricultural crops, eds BA Stewart &
DR Nielsen, American Society of Agronomy, Inc., Crop Science Society of
America, Inc. & Soil Science Society of America, Inc, Wisconsin, USA, pp.
509-535.
Israelsen, OW, Criddle, WD, Fuhriman, DK & Hansen, VE 1944, Water application
efficiencies in irrigation, Agricultural Experimental Station. Bulletin 311, Utah
State Agriculture College, Logan, Utah, 55 pp.
Jensen, ME 1967, 'Improving irrigation efficiencies', in Irrigation of agricultural lands,
eds RM Hagon, HR Haise & TW Edminster, American Society Agronomy,
Madison, WI, pp. 1120-1142.
23
Jensen, ME 2007, 'Beyond irrigation efficiency ', Irrigation Science, vol. 25, no. 3, pp.
233-245.
Kruse, EG 1978, 'Describing irrigation efficiency and uniformity ', Journal of the
Irrigation and Drainage Division, vol. 104, no. 1, pp. 35-41.
Kruse, EG, Bucks, DA & von Bernuth, RD 1990, 'Comparison of Irrigation Systems', in
Irrigation of Agricultural Crops, eds BA Stewart & DA Nielsen, American
Society of Agronomy, Inc., Crop Science Society of America, Inc, Soil Science
Society of America, Inc., Wisconsin, USA, pp. 475-508.
Letey, J 1985, 'Irrigation Uniformity as Related to Optimum Crop Production -
Additional Research Is Needed', Irrigation Science, vol. 6, no. 4, pp. 253-263.
Molden, DJ & Gates, TK 1990, 'Performance measures for evaluation of irrigation
water delivery systems', Journal of Irrigation and Drainage Engineering, vol.
116, no. 6, pp. 804-823.
Moore, K, Kuzich, R, Rivers, M, Chester, D & Nandapi, D 2004, Project DAW45:
Changing irrigation systems and management in the Harvey Irrigation Area,
Project DAW45, Department of Agriculture Western Australia, Harvey.
New World Dictionaries 1979, 2 edn, Simon & Schuster, Inc., New York.
Rogers, DH, Lamm, FR, Alam, M, Trooien, TP, Clark, GA, Barnes, LP & Markin, K
1997, Irrigation management series: efficiencies and water losses of irrigation
systems, MF-2243, Cooperative Extension Service, Kansas State University,
Manhattan.
Smajstrla, AG, Boman, BJ, Clark, GA, Haman, DZ, Harrison, DS, Izuno, FT, Pitts, DJ
& Zazueta, FS 1991, Efficiencies of Florida Agricultural Irrigation Systems,
Bulletin 247, Institute of Food and Agricultural Sciences, Cooperative Extension
Service, University of Florida, Gainesville, Florida.
Solomon, KH 1984, 'Yield related interpretations of irrigation uniformity and efficiency
measures', Irrigation Science, vol. 5, no. 3, pp. 161-172.
24
CHAPTER 2: AN EVALUTION OF IRRIGATION PERFORMANCE
MEASURES: EFFICIENCY AND UNIFORMITY IN THE HARVEY
IRRIGATION DISTRICT IN WESTERN AUSTRALIA
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SUMMARY
Irrigated agriculture is the largest user of water in Western Australia. Due to the water
demand and the limited amount of water resources, efficient and uniform distribution of
water and its application, and the equitable use of water is of paramount important for
the optimal performance of any irrigation system. This can only be achieved through
effective design, installation, maintenance, and management of the irrigation system.
The irrigation system uniformity and the water application rates impact the system
efficiency. For instance, uniformity and water application rate affect the stored soil
moisture, water availability (for plant use) and subsurface drainage (below the root
zone). The efficiency and uniformity of an irrigation system needs to be high to ensure
high yields by providing adequate water use to the majority of the crop. Optimal
uniform supply should also minimize water and nutrient losses to deep percolation
below the root zone associated with over-irrigation and saturation of the soil surface.
Irrigation performance measures: efficiency and uniformity of application plays an
important role in determining water allocation and the gross amount of irrigation water
applied in the field. The concept of efficiencies and uniformities are discussed in this
paper and then applied to evaluate the comparative performance of four irrigation
methods.
Result of from the Waroona Research Station in the Harvey Irrigation Area (HIA) in
Western Australia indicate that the average water storage efficiencies (Es) of floppy,
solid set, center pivot sprinklers and the micro (subsurface drip) irrigation systems was
82.4% for each system and water conveyance efficiencies (Ec) were 97% for each
system (i.e. 3% water losses as results of surface tension, pressure and friction losses
from the pipes). The average water application efficiencies (Ea) and irrigation efficiency
(Ei) were 73.4% for floppy, 68.0% for solid set, 81.2% for center pivot and 94.4% for
subsurface systems. The average overall irrigation efficiencies (Eo) and effective
irrigation efficiencies (Ee) of floppy, solid set, center pivot and subsurface methods
were 59.0%, 54.0%, 65.0% and 75.0% respectively. Finally, the average low-quarter
distribution uniformity (DUlq) was 50.0% for floppy, 52.0% for solid set, 56.2% for
center pivot and 84.8% for subsurface irrigation systems. The average water distribution
26
efficiency (Ed) and coefficient of uniformity (Cu) of floppy, solid set, center pivot and
subsurface systems was 64.9%, 67.6%, 68.9% and 89.4% respectively.
The comparison of the different types of irrigation techniques revealed that the
subsurface drip and center pivot irrigation methods were more efficient and effective in
all categories of irrigation performance measures than the floppy and solid set sprinklers
irrigation methods. An irrigation system that is well maintained and correctly operated
generally had a high efficiency and acceptable low-quarter distribution uniformity
(DUlq).
27
2.1. INTRODUCTION
Western Australia is the driest State in the world‟s driest continent and water
availability and use is the State‟s ongoing challenge. Water engineers are being called
on to meet increasing demand and also to manage this demand across industry,
community and environmental (Morony 1980). Agriculture is one of the largest users of
water resources within the Harvey irrigation district in Western Australia. It is estimated
that 520 GL of water is used annually for irrigation in Western Australia. Around 150
GL is used in the Kimberley and Gascoyne regions, and 370 GL in the South-Western
regions. At the State level 55% of the available water resources is used in agriculture,
and in the South West horticulture account for 65% of the water use (SABI 2006).
Irrigated agriculture is the economic and community life of the Harvey Water Irrigation
Area (HWIA) and the economic gross value of agriculture in HWIA is over A$120M
per annum (ABS 2000), the variation of asset values (important component of a
company's total value) between activities and water losses from irrigation systems
implies that the future quality of water used in agriculture will be very sensitive to the
water policies (preparing a future with less water) that affect the perceived scarcity and
demand for water.
In dollar terms, it is estimated that the 200 GL of water used in the south western
regions has a potential asset value of at least A$5,000/ML (Brennan 2006). However,
the water is not used as efficiently and effectively as it could be as: (1) between 10 and
30 percent of water diverted from rivers in to irrigation system is lost before it reaches
the farm gate, (2) up to 20 percent of water diverted to the farm get may be lost in
distribution channels on-farms and around 60% percent of water used for irrigation on
the farms is applied using high volume, inefficient gravity irrigation methods, (3) more
than 15 percent of water applied the crops is lost through over watering and (4)
inaccurate measurement of water diversion from rivers and water uses on farms is
leading to unintentional and intentional over use (CSIRO 2007).
Hence, this study assesses the performance of irrigation schemes to provide information
to assist farmers to improve irrigation efficiency and uniformity. This chapter begins by
outlining the definitions and development irrigation performance measures. It then
28
summarizes the results of performance evaluation techniques applied to assess the
irrigation systems used in the Harvey Irrigation Area (HIA).
Improving irrigation performance is a crucial issue for agriculture and irrigation
development in the Harvey Water Irrigation Area (HWIA). For example, the delivery
losses from the Harvey Irrigation District (HID) in Western Australia have been
estimated over 30% between dam and farm (CSIRO 2007; Moore et al. 2004). This
results from seepage into ground, leaks in the channel structures and end of systems
outflows. To manage these issues original concrete canal delivery systems between dam
and farm have been replaced by pipes in order to minimize this loss. However, water
losses within the farm from irrigation systems are estimated 50 percent (Brennan 2006;
CSIRO 2007; Harvey Water 2009; Powell 1998). The water source for the Harvey
irrigation areas is fully allocated and no additional water is available. Therefore
irrigation efficiency is one the key issues facing irrigation farmers and water managers.
Improving irrigation efficiency has many benefits include both environmental and
economic measures. Improved water distribution uniformity will help farmers use less
water to obtain increased yield while leaving more water for in the ecology and
environment, resulting in improved livelihood in the region (Phengphaengsy &
Okudaira 2008). The benefits of more efficient systems include less stress on water
resources, reduced losses of water and nutrient flows to groundwater and surface water,
improved production and overall profits; and potentially allowing a greater area to be
irrigated with a given volume of water.
Previous investigations using irrigation performance measures (efficiency and
uniformity) for the Harvey Irrigation Area (HIA) are limited. Philosophical discussions
of irrigation performance measures in a general context are available. However, these
are constrained and provide very little insight into the practical use of performance
measures in Harvey irrigation district. For example, Research and Extension Engineers
at Kansas State University (Rogers et al. 1997) have discussed the irrigation efficiency
from an engineering and conservation perspective, the most common efficiency terms
in use for irrigation systems and how these terms apply to some common irrigation
situations. Similarly, (Burt et al. 1997) defined irrigation performance measures so that
29
irrigation professionals and water rights specialists can share a common and solid
technical understanding of the concepts of efficiency and uniformity.
Commonly used definitions of irrigation efficiencies, factors affecting irrigation
efficiencies, and typical values for well-designed and well-managed Florida field-scale
irrigation systems are discussed in literature by (Smajstrla et al. 1991). Irrigation
efficiency is a measure of: (1) the effectiveness of an irrigation system in delivering
water to a crop, or (2) the effectiveness that the irrigation technique has in increasing
crop yields. From definition (1), irrigation efficiency may be expressed as the ratio of
the volume of water used or available for use in crop production to the volume pumped
or delivered for use. From definition (2), irrigation efficiency may be expressed as the
ratio of crop yield or increase in yield over nonirrigated production to the volume of
irrigation water used (Smajstrla et al. 1991).
The ASCE Task Committee on Defining Irrigation Efficiency and Uniformity, the
Irrigation Water Requirements Committee of ASCE on Irrigation and Drainage,
International Commission on Irrigation and Drainage, Scientist, Engineers and
Universities have provided a comprehensive examination of various irrigation
performance indices such as storage efficiency, conveyance efficiency, application
efficiency, irrigation efficiency, overall (farm) irrigation efficiency, effective irrigation
efficiency, irrigation sagacity and distribution uniformity, and other measures (ASCE
1978; Bos 1979; 1980; Bos et al. 1994; Bos & Nugteren 1974; 1990; Burt et al. 1997;
Haman, Smajstrla & Pitts 1996; Haman, Smajstrla & Pitts 2005; Hart, Skogerboe &
Peri 1979; Heermann & Solomon 2002; Jensen 1967; 1974; 1977; 1978; 1983; 2007;
Kruse 1978; Kruse, Bucks & von Bernuth 1990; Kruse & Heermann 1977; Smajstrla et
al. 1991; 2002; Solomon 1983; 1984; 1988; 1990). They demonstrated that the
irrigation performance measures: efficiency and uniformity are the most common
accurate parameters to be used to evaluate or assess the condition of any on-farm
irrigation system.
The objective of this study is to compare the different irrigation systems in the Harvey
irrigation district and recommend the best irrigation method as defined by in term of
efficiency and uniformity for this area or in any other sub region. In particular, each
30
irrigation system will be evaluated using irrigation performance measures so that the
key driver of water losses within on-farm irrigation system can be identified.
2.2. METHODS
In order to assess irrigation performance measures and techniques, it was necessary to
obtain field data on the spatial pattern of water content distribution before and after
irrigation and determine if these patterns resulted primarily from soil heterogeneity or
from irrigation non-uniformity. During an individual irrigation run the average depth of
applied water and the distribution (as applied to the soil surface) across the individual
irrigation system was assessed and compared to the topsoil change in water storage
before and after irrigation. Field and laboratory methods are described in the following
section.
2.2.1. FIELD AND LABORATORY METHODS
Field work was conducted to collect data for evaluating irrigation system efficiency and
uniformity of the irrigation system used in the Harvey Irrigation Area (HIA) in Western
Australia. This data was collected at Waroona Experimental Station between May and
October 2009. Data were collected by the author, staff from the Centre for Excellence
Ecohydrology and the University of Western Australia. The data were collected from
each irrigation system at HIA.
The four irrigation systems (floppy, solid set, center pivot and subsurface) used in the
Harvey Irrigation District were compared using efficiency and uniformity criteria.
Soil moisture measurements were taken from each irrigation system before and after the
irrigation cycle over 0 – 60 mm depth using a thetraprobe. A 10 m grid spacing was
used throughout. The total area evaluated for each sprinkler system and the numbers of
soil moisture readings taken are given in Table 2-1.
For the three surface irrigation system: catch cups were deployed randomly in order to
assess the spatial uniformity. The numbers of catch cups were 10, 10 and 7 from floppy,
solid set and center pivot sprinkler irrigation area in the order given.. Soil samples were
31
taken at each site to correlate the theta probe measures. The number of theta probe soil
moisture measurement and soil samples for each system and percentage of total
irrigated area sampled is given in Table 2-1. Soil samples at 0-60 mm depth were
collected before and after irrigation from each irrigation system (see Appendix 2-A:
Table 2A-(1-7)). The numbers of samples were 10, 7, 14 and 9 from floppy, solid set
and center pivot sprinklers, and subsurface drip irrigation area respectively.
Table 2-1: Numbers of soil moisture measurement, soil samples and area for each
irrigation system
Type of System
Soil Moisture
Measurements (no)
Soil Samples
(no)
Area Covered
(ha)
Floppy 96 10 0.96
Solid set 70 7 0.70
Center pivot 70 14 0.70
Subsurface drip 63 9 0.63
Soil samples were randomly collected from each system as indicated and the soil type
classified, specific gravity, degree of saturation, gravimetric water content, void ratio
and porosity, and bulk density were derived for each samples (see Appendix 2-A).
Finally, this method was used for evaluation whether there was runoff or percolation of
water during the irrigation cycle.
2.2.2. IRRIGATION PERFORMANCE MEASURES AND
TECHNIQUES
The irrigation performance measures and techniques used 10 techniques (water storage
efficiency, water conveyance efficiency, water application efficiency, irrigation
efficiency, overall/farm irrigation efficiency, effective irrigation efficiency, water
distribution efficiency, distribution uniformity, coefficient of uniformity and coefficient
of variation). These techniques/principles used to evaluate and determine the efficiency
and uniformity of each irrigation systems in the HIA using a combination of theoretical
techniques, field work and laboratory analysis.
32
There is volume of international research literature that defines these 10 techniques for
assessing (efficiency and uniformity). However, in Australia application of these
methods and available literature for Australia condition are limited.
Results are presented for each irrigation system and a comparison of irrigation
efficiency and uniformity is detailed and discussed. Figure 2-1 shows the study area and
the placement of the four irrigation systems that are utilized in the HIA in South-
western Australia.
1- Floppy sprinkler irrigation systems 3- Center pivot sprinkler irrigation
systems
2- Solid Set sprinkler irrigation systems 4- Micro (Subsurface) irrigation systems
Figure 2-1: Waroona Research Station study highlighting the placement of the four
irrigation systems used in the Harvey Irrigation Area in South-Western Australia
33
2.3. DEFINITIONS OF EFFICIENCY AND GOVERNING EQUATIONS
2.3.1. WATER STORAGE EFFICIENCY (Es)
Smajstrla et al. (1991) defined the reservoir storage efficiency (Es) as the ratio of the
volume of irrigation water available from an irrigation reservoir to the volume of water
delivered to the reservoir. The definition of reservoir storage efficiency proposed by the
Irrigation Water Requirements Committee of the American Society of Civil
Engineering (Jensen 1974) is similar to that proposed by the International Commission
of Irrigation and Drainage (Bos & Nugteren 1974) and to the Es by (Baum, Dukes &
Miller 2003; Burman et al. 1983; Smajstrla et al. 1991). This ratio is normally less than
100% because of losses. Similarly, (Baum, Dukes & Miller 2003) defined the reservoir
storage efficiency as the percentage ratio of the volume of water available from the
reservoir for irrigation, to the volume of water delivered to the storage reservoir-
surface or underground- for irrigation . This defined as,
(2-1)
where Vr is the volume of water available from reservoir for irrigation and Vdr is the
volume of water delivered to the storage reservoir-surface or underground-for irrigation.
A reservoir may be a pond, lake, tank or other different storage mechanism. The most
common type of reservoir is a pond which can be either natural or manmade. Water
losses can occur due to seepage (through the bottom), evaporation (from the surface
water) and transpiration (from vegetation growing in the reservoir). The reservoir
storage efficiency is variable depending on site conditions and the lowest values can be
attributed to surface reservoir (Baum, Dukes & Miller 2003).
The soil water storage efficiency (Es) is defined by (Hansen, Israelsen & Stringham
1980; James 1988; Warker & Skogerboe 1979) as the ratio of the volume of water
stored in the soil root zone to the volume of water required to fill the root zone to field
capacity. It is expressed as:
34
(2-2)
where Vs is the volume of water stored in the soil root zone from an irrigation event, Vfc
is the volume capacity at field capacity in the soil root zone, and Va is volume of water
in the soil root zone prior to an irrigation event.
Hansen et al. use an alternate definition differs than the one typically used, as it goes
beyond just the simple account of soil moisture deficits. It implies that in order to
minimize deep percolation, the maximum net amount water that should be applied in
the irrigation event is the difference between the field capacity and the average water
content in the root zone at the time of irrigation. The main use of the soil water storage
efficiency is to manage surface and sprinkler irrigation systems where the objective is to
minimize labour and the number of irrigation events, and prevent overirrigation
(Heermann & Solomon 2002).
One problem of using storage efficiency with sprinkler and microirrigation systems is
that even if it is low, frequent irrigation may still provide sufficient water for crop
production, and this management practice leaves some soil water storage room for
rainfall which would otherwise result in deep drainage losses. Sprinkler and
microirrigation system are typically operated on a frequent basis and can supply just the
water needed without waterlogging the soil.
2.3.2. WATER CONVEYANCE EFFICIENCY (Ec)
The conveyance of water from the source to the irrigated field can be through natural
drainage lines, constructed earthen or lined channels or closed conduits. Many
conveyance systems have transmission losses, thus, water delivered to the field is
usually less than the direct diversion from a flowing stream, reservoir, or underground
aquifer.
Rogers et al. (1997) defined the water conveyance efficiency (Ec) as the percentage ratio
of the volume of water delivered to the field boundary to the volume of water diverted
from the source and can be expressed as:
35
(2-3)
where Wf is the water that is now delivered to the field and Wc is the water diverted
from source. Conveyance efficiency is generally a concern for irrigation districts that
supply a group of farmers through either a system canals or open ditches. Since most
HIA irrigation water is carried in closed conduits, conveyance efficiency should be
nearly 100 percent. However, the friction losses from the pipes as a result of relative
roughness should be taken into consideration during calculation of the efficiency. The
velocity pressure of irrigated water flow can be affected be the relative roughness of the
pipes.
Smajstrla et al. (1991) also defined the water conveyance efficiency as the ratio of the
volume of water delivered for irrigation to the volume of water placed in the
conveyance system. According to the authors, this ratio is normally less than 1.0
(meaning less than 100 percent) for open channel conveyance irrigation systems, but it
may be approximately 1.0 (mean approximately 100 percent) for pipeline conveyance
systems. Losses from open channel conveyance systems occur due to seepage,
evaporation, and transpiration. These losses can be reduced by lined channels and
controlling vegetative growth. Some evaporation losses will be unavoidable.
Open channels (surface irrigation methods) are still used in parts of the Harvey
irrigation district where existing high water tables (Harvey river) and restricted soil
layers minimized seepage losses. However, even under such conditions, the water
conveyance efficiency is very site- specific and must be determined by measurements
taken at the site or estimated by an operator experienced with these surface irrigation
systems.
Similarly, the same water conveyance efficiency definition can be found in the literature
by (Baum, Dukes & Miller 2003; Bos 1980; Bos & Nugteren 1974; Bos & Nugteren
1990; Burman et al. 1983; Burt et al. 1997; Edkin 2006; Haman, Smajstrla & Pitts 2005;
Hart, Skogerboe & Peri 1979; Jensen 1967; Kruse 1978; Kruse & Heermann 1977;
Smajstrla et al. 1991; Smajstrla, Clark & Haman 1992; Solomon 1988).
36
Heermann & Solomon (2002) showed that increasing water conveyance efficiency for
efficiency‟s sake may not be economically justified nor is increasing the available water
supply. The entire demand on a given water supply must be examined to determine the
necessity and value of increasing the conveyance efficiency. For example, operational
spills may cost very little and only return high quality water back to the stream for
rediversion downstream. However, when water demands cannot be satisfied, it may
justify decreasing operational spills. Similarly, actual cost and available water supply
must be considered before lining canals or installing pipelines to reduce losses, but this
may be necessary to meet the demand for water and/or to reduce water quality
degradation caused by seepage irrigation systems (Heermann & Solomon 2002).
2.3.3. WATER APPLICATION EFFICIENCY (Ea)
Israelsen et al. (1944) defined water application efficiency (Ea) as “the ratio of the
amount of water that is stored by the irrigator in the soil zone and ultimately consumed
(transpired or evaporated or both) to the amount of water delivered to the farm” (Jensen
2007). They indicated that (Beckett, Blaney & Taylor 1930), in reporting a study of
water requirements of citrus and avocados, “made observations of „irrigation
efficiency‟- a term „water application efficiency‟ is herein used”.
Israelsen et al. (1944) reported measurements of water applications on 23 farms in Utah
and Salt Lake Countries in Utah using gravimetric soil sampling techniques and
calculated water application efficiency (Ea) (Jensen 2007).
Haman, Smajstrla & Pitts (2005) also defined the water application efficiency (Ea) as
the ration of the volume of irrigation water stored in the root zone and available for
plant use (evapotranspiration) to the volume delivered from irrigation system. This ratio
is always less than 1.0 because of losses due to evaporation, wind drift, deep
percolation, lateral seepage (interflow) and runoff which occur during irrigation.
Similarly, Burman et al. (1983) also defined Ea as the ratio of the volume of irrigation
water required for beneficial use in specified irrigation area to the volume of water
delivered to this area.
37
In the broad terms, the water application efficiency (Ea) is the percentage of water
delivered to the field that is used by the crop as by (ASCE 1978; Baum, Dukes & Miller
2003; Bos & Nugteren 1974; Burman et al. 1983; Haman, Smajstrla & Pitts 2005;
Heermann & Solomon 2002; Rogers et al. 1997; Smajstrla et al. 2002). The water
application efficiency (Ea) is defined as
(2-4)
where Wc is water available for use by the crop and Wf is water delivered to the field.
However, Burt et al. (1997) defined the irrigation application efficiency or water
application efficiency (Ea) as
(2-5)
Burt‟s definition differs from the one typically used as it goes beyond simply replacing
soil water deficits. It implies that water contributing to the target will eventually be of
beneficial use. In addition to accounting for evapotranspiration, it considers crop water
needs such as germination, cooling, frost protection, leaching and pest control. Partial
replacement of the soil water deficit to allow more effective use of rainfall is also
considered.
If application depths are normally distributed and the mean depth of water applied is the
same as the mean soil water deficit, Seginer (1987) showed that water application
efficiency can be approximated from Uc as:
(2-6)
Haman, Smajstrla & Pitts (2005) discussed how the water application efficiencies can
also be affected by cultural practices that affect water storage in the plant root zone. For
instance, Ea is reduced by use of plastic mulches which shed water from the production
bed of some sprinkler irrigated field production systems, by nonuniform wetting of
hydrophobic soil (soil that resistant to wetting), and by the plant root zones being
limited by containers in sprinkler irrigated nursery production systems. The effect of
38
site-specific factors such these need to be evaluated to accurately determine application
efficiencies of individual systems.
Water application efficiencies are also affected by irrigation system management
practices. Because it is not possible to measure and apply the exact amount of water
required in the plant root zone at precisely the time that available soil water is depleted,
excess water applications will occur. As a result Ea will be reduced (Haman, Smajstrla
& Pitts 1996).
2.3.4. IRRIGATION EFFICIENCY (Ei)
Irrigation efficiency can be divided into two components: water losses and uniformity
of application. If either the water losses are large, or application uniformity is poor,
efficiency will be low. Although both components of efficiency are influenced by
system design and management, losses are predominantly affected by management,
while uniformity is predominantly affected by system design (Solomon 1988).
Water to satisfy crop evapotranspiration is not the only beneficial water that can be
supplied with an irrigation system. According to (Burt et al. 1997), all water consumed
in order to achieve an agronomic objective is beneficial. The major beneficial uses are
crop ET and water needed either for improving or maintaining soil productivity such as
water for salt removal, water applied for climate control (cooling or frosting protection
of plants), seedbed preparation, germination of seeds, softening of a soil crust for
seedling emergence and water for wind breaks. Rogers et al. (1997) defined the
irrigation efficiency as the percentage ratio volume of water which is beneficially used
to the volume of irrigation water applied as:
(2-7)
where Wb is the water used beneficially and Wf is the water delivered to field. Irrigation
efficiency is more broadly defined than water application efficiency in that irrigation
water may have more uses than simply satisfying crop water requirements as noted
above. However, most Harvey irrigation systems are single purpose, which is to supply
39
water for crop use which allows water application efficiency and irrigation efficiency to
be used interchangeably.
The ASCE On- Farm Irrigation Committee (ASCE 1978) also defined the irrigation
efficiency as the ratio of the volume of water which is beneficially used to the volume
of irrigation water applied, expressed as:
(2-8)
Although the ASCE on- Farm Irrigation Committee‟s definition is the same on the one
typically used is not expressed in term of the percentage, However, it still follows the
same principles and methods for the calculation of irrigation efficiency. The beneficial
uses that are discussed by ASCE Irrigation Committee also include crop water use, salt
leaching, frost protection, crop cooling, and pesticide or fertilizer application
highlighted previously. Excessive deep percolation, surface runoff, weed ET, wind drift
(in part) and spray evaporation are not considered beneficial uses (Heermann &
Solomon 2002).
Burt et al. (Burt et al. 1997) defined the irrigation efficiency (IE) as:
(2-9)
Burt‟s definition differs from the one typically used as it goes beyond simply replacing
soil water deficits. It implies that water contributed to the target will be eventually be
beneficially used. The denominator in the formula represents the total volume
(beneficial plus non beneficial uses) of irrigation water that leaves the boundaries
(outflow = applied - ∆ storage). This volume of water leaves within a specified time
interval (e.g. the interval from just before an irrigation to just before the next irrigation,
or possibly, an entire season). Burt‟s also discussed that if at the end of the time period,
the water contained within the designated region is the same as it was the start, then the
∆ storage of irrigation water shall be equal to zero.
The definition of irrigation efficiency (Ei) by (Burman et al. 1983; Edkin 2006; Hart,
Skogerboe & Peri 1979; Heermann & Solomon 2002; Molden & Gates 1990; Smajstrla
40
et al. 1991; Smajstrla et al. 2002; Smajstrla, Clark & Haman 1992) is the same as by
(ASCE 1978; Rogers et al. 1997).
Determination of irrigation efficiency requires definition of both a boundary and a time
interval. Irrigation water moving into the space defined by the boundary (e.g., field,
farm, irrigation district or river basin) over a given time interval (e.g., one irrigation
cycle, one irrigation season, one year, etc) become the applied volume. If at the end of
the time period the irrigation, the water content within the designated region is the same
as it was at start, ∆ storage = 0. Irrigation Efficiency (IE) may be defined in terms of
depth rather than volume, where depth is defined as the total irrigation water volume
divided by the area enclosed by the boundary (Burt et al. 2000).
2.3.5. OVERALL IRRIGATION EFFICIENCY (Eo)
Burman et al. (1983) defined the overall irrigation efficiency (or farm irrigation
efficiency) as the product of the component terms (Es, Ec, Ea), expressed as ratios.
(2-10)
The overall irrigation efficiency for a farm, project or a river basin can be expressed in a
similar manner. For clarity and comparative purposes, all efficiency estimates or
evaluation should identified as the size of unit, the period of time or number of
irrigation involved, the adequacy of irrigation in meeting net irrigation requirements,
and computational procedure used.
Smajstrla et al. (1991) also defined the overall (irrigation system, project, farm)
irrigation efficiency (Eo), in similar definitions to Burman. Overall irrigation efficiency
is calculated by multiplying the efficiencies of the components. For a system which
includes reservoir storage, water conveyance, and water application, the overall
irrigation efficiency is defined as where all terms are as previously
defined.
41
2.3.6. EFFECTIVE IRRIGATION EFFICIENCY (Ee)
Effective irrigation efficiency of a farm, project, or river basin is necessary to estimate
or evaluate the net depletion of water within a river basin or groundwater system
(Jensen 1977). This estimate is based on the assumption that irrigation efficiency (Ei =
Vc/Vw) as defined by (Israelsen 1950) is the ratio of water consumed (Vc) by the
agricultural crops on a farm project to water diverted (Vw) from a natural source into
farm or project canals and laterals. The net depletion of water, Vdep, specifically used for
irrigation (Burman et al. 1983) is
(2-11)
where Vc is the volume consumed by agriculture crop; Vnc is the volume of diverted to a
farm or project that is not consumed by the crops; and Er is the fraction of Enc that is
recovered for agricultural or other use. The effective irrigation efficiency (Ee) is
expressed as
(2-12)
this also can be expressed as
(2-13)
Smajstrla et al. (1991) defined the effective irrigation efficiency (Ee) as the overall
irrigation efficiency corrected for water which (1) is used, or (2) is restored to the water
source without a reduction in water quality. Tailwater recovery systems allow runoff
from an irrigated field to be recycled or used on the field. These systems increase Ee
above Eo. If seepage from open channel flows into the field being subirrigated, this will
not be lost from the irrigation system. Thus, Ee will be greater than Eo.
Smajstrla‟s also discussed that if irrigation water moves from the crop root zone due to
lateral flow or deep percolation, its quality may be degraded by salts and other
production associated chemicals. If this water cannot be intercepted for reuse in the
same production, it will reduce irrigation efficiencies unless interception drains or
42
ditches are installed to recover this water for reuse. According to (Smajstrla et al. 1991),
the effective irrigation efficiency (Ee) is defined as
(2-14)
where FR is the fraction of the water lost that is recovered and reused. Some of the
water that leaves an irrigated field due to runoff, seepage or percolation might be
recovered in some cases. Losses due to evaporation, wind drift, and transpiration cannot
be recovered.
Smajstrla‟s definition of Ee is slightly different from Burman‟s definition of effective
irrigation efficiency (Ee). The authors discussed both the fraction of water lost that is
recovered in some cases, and evaluated the losses that may be experienced from the
irrigation system. However, Smajstrla discussed the Ee in terms of the overall irrigation
efficiency (Eo) or farm irrigation efficiency corrected for water used or restored to the
water source without reduction in water quality while Burman‟s discussed the Ee in
terms of irrigation efficiency only. The definition of effective irrigation efficiency by
(Haman, Smajstrla & Pitts 2005) is similar to the Smajstrla‟s definitions.
2.3.7. WATER DISTRIBUTION EFFICIENCY (Ed)
Rogers et al. (1997) defined the water distribution efficiency (Ed) as the percentage of
average application depth delivered to the least-watered part of the field and can be
expressed as:
(2-15)
(2-16)
where y is the average absolute numerical deviation in depth of water stored from
average depth stored during the irrigation and d is the average depth of water stored
during irrigation.
43
The water distribution efficiency indicates the degree of uniformity in the amount of the
water infiltrated into soil. It is also defined as the uniformity in depths applied at surface
based on catch-can measures for sprinkler systems. This concept for uniformity was
originally developed by Christiansen in 1942 for sprinkler systems. Generally, high
uniformity is assumed since each plant has an equal opportunity to access applied water.
Non-uniformity results in areas that under-watered or over watered (Rogers et al. 1997).
2.3.8. DISTRIBUTION UNIFORMITY (Ud)
Distribution uniformity is a measure of the uniformity with which irrigation water is
distributed to the plants in a field. The practice of using the least watered 25% of the
area (low quarter) as the reference standard has gained wide acceptance (Burt et al.
1997). The uniformity described by DUlq (and all terms involving the low quarter) is
equivalent to about 1/8 of the area, and is less than the value of the numerator. This
“under irrigation” varies from the zero at the 1/8 point to the minimum depth applied at
the extreme.
The concept of distribution uniformity (Ud) can be applied to all irrigation methods:
surface, sprinkler, microirrigation, subirrigation and hybrid (Burt et al. 2000). The
values of Ud are comparable across the various irrigation methods provided it is
measured accurately and properly (Burt et al. 1997). Although the concept of Ud is the
same for each irrigation method, the spatial distribution of the nonuniformity will be
different for various methods. In addition to the issue of how well the applied water is
used, it is the important how uniformly this water is distributed to the crop. A
nonuniform distribution not only deprives water to portions of the crop, but can also
result in overirrigation of some portions of the field, leading to water-logging, plant
injury, salinization, and transport of chemicals to the ground water (Burt et al. 1997;
Solomon 1983).
Burt et al. (1997) discussed that the distribution itself must be carefully defined before
the distribution uniformity (Ud) is measured in order for it to be truly universally
applicable to all crops. According to Burt, Ud is usually defined as the ratio of some
measure of the smallest accumulated depths in the distribution to the average depth
accumulated. An appreciation of the smallest depths in the distribution is afforded by
44
averaging the smallest depth in that portion of the field containing them (i.e. the lowest
quartile). This average d lowest is then used in numerator of the Ud definition rather than
using the absolute minimum value.
Heermann & Solomon (2002) define the distribution uniformity (DU), as the average
depth infiltrated in the low one-quarter of the field divided by the average depth of
water infiltrated over the entire field, expressed as:
(2-17)
where DU is the distribution uniformity; Dlq is average depth infiltrated on the one-
quarter of the field with the least infiltration; and Dav is the average depth infiltrated
over the entire field. The distribution uniformity is also often applied to microirrigation
and sprinkler irrigation systems including center pivot systems.
Rogers et al. (1997) defined the distribution uniformity (Ud) as the percentage of
average application amount received in the least- watered quarter of the field, expressed
as
(2-18)
where Dlq is the average low-quarter depth of water infiltrated (or caught) and Dav is the
average depth of water infiltrated. The distribution uniformity gives an indication of the
magnitude of the distribution problems. It can be defined as the percentage of average
application amount in the lowest quarter of the field. Ud is less tedious to calculate than
the water distribution efficiency (Ed). Rogers‟s definition differs from the one typically
used, and is presented as a percentage in the formula to solve the magnitude of the
distribution problems. While, according to (Burt et al. 1997) the distribution uniformity
(DU) is not an efficiency terms presented as a percentage, but as a ratio, defined as
(2-19)
45
Further work by (Baum, Dukes & Miller 2003; Hart, Skogerboe & Peri 1979; Rogers et
al. 1997; Smajstrla et al. 1991; Solomon 1983; Solomon 1988) also expresses the
distribution uniformity as a percentage.
The literature contains many definitions for evaluating the irrigation uniformity. Many
of them use the moments of the measured or estimated distribution depths. However, it
has been reported (Hart & Heermann 1976) that many of the uniformity definitions can
be expressed as mathematical functions of each other. Another measure of uniformity
simply assumes a normal distribution and then uses the mean depth and standard
deviation. Warrick (1983) considered a number of population distributions and
summarized the interrelationship of uniformity terms across theses distribution. The
Christiansen uniformity and low-quarter distribution are related mathematically for
normal, log normal, uniform, specialized power, beta, and gamma distribution of water
application (Heermann & Solomon 2002). The low quarter distribution gives the
percentage of average application amount received in the least- watered quarter of the
field as
(2-20)
where Udlq is the distribution uniformity, is the average low-quarter depth of water
infiltrated (or catch) and is the average depth of water infiltrated (or catches). The
distribution uniformity gives an indication of the magnitude of the distribution
problems.
2.3.9. COEFFICIENT OF UNIFORMITY (Uc)
Christiansen (1942) developed Uc to measure the uniformity of sprinkler irrigation
systems, and it is most often applied in sprinkler situation. Though, Uc has been
occasionally applied to other forms of irrigation. Distribution uniformity (Ud) has been
applied to all types of irrigation systems. In trickle irrigation system, it is also known as
Emission uniformity (Eu), and has been applied to sprinkler situation under the name of
Pattern efficiency (Ep) (Solomon 1988).
46
Several mathematical definitions have been proposed and used to describe the
uniformity of the system. Christiansen‟s (1942) uniformity coefficient (Uc) was defined
to evaluate sprinkler irrigation systems and has the strongest historical precedent in the
sprinkler irrigation industry. It is commonly used for evaluating sprinkler system
uniformity. The coefficient of uniformity treats over-irrigation and under-irrigation
equally, and is compared to the mean (Baum, Dukes & Miller 2003). The measure can
be calculated by Christiansen formula as:
(2-21)
where Uc is the Christiansen‟s uniformity coefficient (%); iV is the depth of water in
individual catch can; and V is the average depth of water in all catch cans. In addition to
the coefficient of uniformity and the distribution uniformity, there are other important
factors in evaluation of an irrigation system such as application rates, runoff, wind,
amount of water applied, pump performance, and overall system management must be
considered when evaluating total irrigation system performance (Baum, Dukes & Miller
2003).
The most widely accepted measure of irrigation uniformity in the turf industry is JE
Christiansen‟s uniformity coefficient (Uc). It developed before the computer;
Christiansen‟s Cu can be calculated employing only simple arithmetic procedures
(Zoldosake & Solomon 1988). Uc is given by:
Uc = 100
(2-22)
where Uc is the Christiansen‟s uniformity of coefficient, %; xi is the measured depth
(volume or mass) of water in equally spaced catch cans on a grid; xm is the mean depth
(volume or mass) of water of the catch in all cans. This requires that each catch can
represent the depth applied to equal areas. This is not true for data collected under
center pivots where the catch cans are equally spaced along a radial line from the pivot
to the outer end. For center pivot system it is necessary to adjust and weight each
measurement based on the area it represent (Heermann & Hein 1968).
47
Heermann & Solomon (2002) considered that the efficiency and uniformity of an
irrigation systems is the major factor that must be considered in determining the
irrigation efficiency and be used to manage competition for limited water resources as
well as performance parameters when designing irrigation systems.
The coefficient of uniformity is used to evaluate an individual irrigation, but it may be
more important to evaluate the uniformity of several irrigation events or even over an
entire irrigation season. The uniformity coefficient generally increases if the depths are
accumulated for multiple irrigations because of the random nature of application and
wind effects.
The definition of Ud and Uc require that catch volumes are representative of the depth
applied either to equal areas or the catch volumes are weighted according to the area
they represent. Solomon (1988) mentioned that the coefficient of uniformity (Uc) and
the distribution uniformity (Ud) of the irrigation performance measures can be
approximately related using:
Uc = (0.63) x (Ud) = 37 (2-23)
Ud = (1.59) x (Uc) – 59 (2-24)
2.3.10. COFFICIENT OF VARIATION (Cv)
Statistically based expressions of uniformity have historically been used. The Christian
Uniformity Coefficient (Uc) was the first of such methods and has been widely used in
the sprinkler industry. For normally distributed data it is equivalent to DUlow half and is
not recommended in making comparisons between irrigation systems. The coefficient of
variation (Cv) is an another statistical expression of water application uniformity
requiring a large number of sampling points and has typically been used in the
drip/micro irrigation industry to describe on small component of field uniformity- that
of assessing the manufacturing variation of emitters (Burt et al. 2000). The Cv can be
expressed as:
(2-25)
48
For normally distributed data it has been shown (Hart & Reynolds 1965; Hart 1961) that
Cv is related to DUlq by the following relationships:
(2-26)
2.4. COMPARISON OF IRRIGATION SYSTEMS
The modern pressurized irrigation methods can be divided into two categories: sprinkler
and microirrigation. Sprinkler irrigation systems are those where water is supplied in a
pressurized network and emitted from sprinkler heads mounted on either fixed or
moving supports. Microirrigation irrigation includes drip or trickle irrigation methods
and other low pressure systems. Water is often distributed in plastic conduits and
emitted through drippers, tricklers, bubblers, small misters, foggers or sprayers (Kruse,
Bucks & von Bernuth 1990).
2.4.1. SPRINKLER IRRIGATION
Sprinkler irrigation is the application of water to the soil using a device or system that
direct water through the air onto soil. Water is delivered to the sprinkler device through
a pressurized pipeline. Sprinklers systems are human‟s attempts to duplicate natural
rainfall; water sprayed from a pressurized pipeline into the air break into drops which
fall to the earth like rain. The size of the drops, the uniformity with which they fall, and
the rate at which they fall are all affected by design of the system and external
environmental factors. Consequently, the design of a sprinkler system is important to its
overall success at being efficient and effective irrigation systems (Kruse, Bucks & von
Bernuth 1990; Smajstrla, Clark & Haman 1992). There are a number of different types
of sprinkler irrigation methods but only floppy, solid set (fixed set systems) and center
pivot (mobile systems) are part of this study and have been compared in terms of their
efficiencies and uniformities with micro (subsurface) irrigation systems.
During water applications, sprinkler irrigation systems lose water due to evaporation
and wind drift. More water is lost during windy conditions than calm conditions. More
is also lost during high evaporative demands periods such as hot and dry days than
49
during low demand periods like cool, cloudy and humid days. Thus, sprinkler irrigation
systems usually apply water more efficiently and effectively at night including early
morning and late evenings than during the days (Smajstrla et al. 1991). Although it
depends on the characteristics of a growers production systems as to whether they can
benefit from night-time irrigation. For instance, some crops may suffer from increased
disease due to night-time irrigation, and others may require irrigation more frequently
than once per day or may require cooling by irrigation during plant peak water use
periods of the day (Smajstrla et al. 2002).
More water is lost by sprinklers that discharge water at high angles, over great distance,
and at great heights above the ground surface due to greater time opportunity time for
evaporation as discussed by (Smajstrla et al. 1991; 2002; Smajstrla, Clark & Haman
1992). In addition to this, greater water losses occur from systems which discharge a
greater proportion of small droplet sizes because small droplets are more readily carried
by wind, and they expose more surface area to the atmosphere for evaporation.
Smajstrla et al. (1991) discussed the sprinkler irrigation application efficiencies that are
reduced by nonuniform water application. Nonuniform application can causes some
areas to be over-irrigated which may lose water and nutrients to deep percolation while
other areas can be under-irrigated (reducing crop yield). All these can occur if the
sprinklers are not properly selected, matched and designed to the sprinkler spacing and
operating pressure used. In addition, nonuniformity also occurs if pressure losses within
the irrigation system are excessive due to friction losses or elevation changes. Other
causes of nonuniformity such as clogged nozzles or enlarged nozzles from abrasion by
pumping sand also reduce water application efficiency (Ea) (Hart & Reynolds 1965;
James 1988; Jensen 1983; Smajstrla et al. 1991; 2002).
According to (Smajstrla et al. 1991; 2002) , it is not possible to apply water with perfect
uniformity due to friction losses, elevation changes, manufacturing variation in
components, and other factors. In addition, achieving greater uniformities generally
increases irrigation cost because of the need for larger pipe sizes, pressure compensating
emitter, or other considerations. Similar ideas are discussed in the literature by (Baum,
Dukes & Miller 2001; 2002; 2003; Burt et al. 1997; Clemmens 1991; Heermann &
50
Solomon 2002; Jensen 2007; Kruse, Bucks & von Bernuth 1990; Kruse & Heermann
1977; Seginer 1979; Solomon 1983; 1984; 1988; USDA 1983a).
2.4.1.1. FLOPPY/OVERHEAD CABLE/SYSTEM
Floppy sprinkler system is a new generation irrigation system. It is the only sprinkler in
the world with a built-in flow controller, ensuring super accurate irrigation even on
slope (SABI 2009). A floppy consists of a plastic nipple on which a flexible silicon tube
is mounted. When water is passed through the tube, it snake to and fro while slowly
rotating through 360o, forming uniform droplets similar to raindrops. Each sprinkler is
fitted with a flow controller that regulates flow to 730 liters per hour with pressures
varying from to 2 to 6 bar. The average water application rate is 5 mm per hour
(Lombard 2009).
Floppy sprinkler can be installed as a solid set system with variation according to the
irrigated crop cultivation practice. It can be mounted conventionally on stand pipes or
on an overhead cable system. Substantial amount of water and energy are saved by the
overhead cable system as discussed by (Ascough & Kiker 2002; Lombard 2009;
Simpson & Reinders 1999; SABI 2009). The riser system of the overhead cable system
depends on the irrigated area and location of the irrigation systems but the floppy
sprinkler can be mounted at 2.25 m to 6 m height (SABI 2009).
The required design parameters of the overhead cable system sprinkler may affect the
uniformity of water distribution and water application. For example, incorrect spacing
and or orientation of sprinklers, miss-matched standing times, flow hydraulics and
nozzle wear are some factors that may affect the efficiency and uniformity of these
systems. The application rates and uniformity of the linear system and/ or floppy
sprinkler system may also be affected by pressure and wind drift, sprinkler spacing and
the design capacity (such as flow controller) of irrigation system as mentioned by
(Griffiths & Lecler 2001; King et al. 1999).
51
2.4.1.2. SOLID SET SYSTEMS
Solid set systems are those in which the sprinklers are place on a fixed grid or spacing.
There may be enough sprinklers to covers all the irrigated area, in which case the
sprinklers are not moved. Set systems are often categorized by the materials used in the
pipelines. Aluminum is the most commonly used material for pipelines that are not
moved. If the lines are not moved during the irrigation season the systems is called a
solid set system. A significant advantage of solid set systems is that they can be used to
modify the crop environment; they can used to cool the crop during hot periods or to
prevent damage due to subfreezing conditions. The typical pipe lengths are 2.1 m (21 ft)
(Kruse, Bucks & von Bernuth 1990).
Properly designed solid set systems have sprinklers permanently installed at spacing‟s
that result in optimum uniformity. However, wind, incorrect operating pressure, and
component wear or failure can still distort water application patterns and reduce
uniformity and water application efficiency (Ea). Solid set sprinkler water application
pattern must overlap sufficiently (typically about 50%) to apply water uniformly as
discussed by (Smajstrla et al. 1991; 2002).
2.4.1.3. CENTER PIVOT SYSTEMS
The center pivot is the most used of the mobile systems. A center pivot consists of a
pipeline mounted on a series of wheeled towers. The entire pipeline rotates about a
fixed end through which water is fed. A similar system which moves in a straight line
and is fed water from a ditch, series of hydrants, or flexible host is known as a lateral-
or linear- move system. Sprinkler heads or sprayers apply water from the moving pipe.
Depth of water applied is usually quite uniform, but application rates under
continuously moving systems are usually higher than with set-type systems (Bernstein
& Francois 1973; Kruse, Bucks & von Bernuth 1990; USDA 1983b).
Overlap of sprinkler patterns and uniformity of water application are generally not
problems except at field boundaries. Large changes in elevation, large changes in soil
properties and soil water storage may affect system pressures and infiltration rates, and
also lower water application efficiency (Ea) as highlighted by (Smajstrla et al. 1991;
52
2002). A Center pivot which uses gun sprinklers on the ends of the laterals to expand
the irrigated area will have lower overall application efficiencies (Eo) because of the
greater water losses from the guns.
In recent years, center pivot systems have developed to operate at low pressures and
apply water either with controlled droplets sizes or by dripping near the surface so that
application efficiencies are high even under moderately windy condition (Smajstrla et
al. 1991). However, wind, incorrect operating pressure, and component wear or failure
can still distort water application patterns and reduce uniformity and water application
efficiency (Ea) in the same way as solid set systems.
2.4.2. MICRO IRRIGATION
The term micro irrigation encompasses several method or concepts, chief of which are
drip/trickle, subsurface, bubble, and spray irrigation (ASAE 1988). In microirrigation
systems, water delivered through a network of plastic lateral lines that are fitted with
emitters that dissipate the pressure through narrow nozzles or long flow paths and
discharge water at only a few liters per hour to each unit of field area. The area that can
be watered from each emission point is, therefore, limited by the water‟s horizontal
flow.
Microirrigation systems are low pressure systems which distribute water through low
flow rate emitters. Water is discharged near or within the root zone of the crop being
irrigated. The water application efficiencies (Ea) of microirrigation systems are typically
high. Water losses due to wind drift and evaporation are typically small because these
systems distribute water near or directly into the crop root zone. Wind drift and
evaporation losses can be high if spray or microsprinkler systems are operated under
wind condition on hot and dry days as mentioned by (Haman, Smajstrla & Pitts 1996;
Smajstrla et al. 1991).
According to Haman, Smajstrla and Pitts (1996), and Smajstrla et al. (1991), the
primary losses in efficiency of micro systems occurs from nonuniform water application
due to pressure losses either through friction or elevation change, or management
problems such as over-irrigation or clogged emitters. Compare to the other types of
53
irrigation systems, design standards (resulting from economic prospective) require that
water application from micro systems be made at less than perfect uniformities, and this
results in water application efficiencies that are less than 100% (Smajstrla et al. 1991).
The limitation on the wetted soil volume can be overcome by choosing an application
rate and volume of application that will meet both the evapotranspiration demand of the
crop and the infiltration and water holding characteristic of the soil (Kruse, Bucks &
von Bernuth 1990; Kruse, Willardson & Ayars 1990). Among the types of
microirrigation systems, only the subsurface system is used as part of this study and has
been compared with the sprinkler irrigation methods such as floppy, solid set and center
pivot system in terms of the irrigation performance measures: efficiency and uniformity.
2.4.2.1. SUBSURFACE DRIP SYSTEMS
Subsurface irrigation is the application of water below the soil surface through emitters
that have rates of discharge generally in same range as those for drip/trickle irrigation.
Subsurface irrigation is not to be confused with subirrigation, a method of irrigating the
root zone through water table control. Lately, subsurface systems have gained wider
acceptance on small fruit, row, and vegetable crops. A subsurface system, in
comparison with surface drip/trickle systems, eliminates the need to anchor the lateral
lines at the beginning or to remove them at the end of growing season, reduces
interference with cultivation or other cultural practices, and possibly results in a longer
operational life. In addition, subsurface irrigation is becoming more recognized as an
efficient method for applying fertilizer, fungicides, insecticides, and other chemicals
precisely within the crop root zone. Plugging of subsurface emitters, the greatest single
disadvantage of such system, can be difficult to detect (Kruse, Bucks & von Bernuth
1990; Kruse, Willardson & Ayars 1990).
54
2.5. RESULTS AND DISCUSSION
2.5.1. EFFICIENCY AND UNIFORMITY
The results for the reservoir storage efficiency (Es), water application efficiency (Ea),
conveyance efficiency (Ec), irrigation efficiency (Ei), overall/farm irrigation efficiency
(Eo), effective irrigation efficiency (Ee), water distribution efficiency (Ed), low-quarter
distribution uniformity (DUlq), coefficient of uniformity (Cu) and coefficient of variation
(Cv) are shown in Figure 2-2 and Table 2-2 to Table 2-6. The majority of the irrigation
systems had a DUlq lower than the standard DUlq suggested by (Pitts et al. 1996) (see
Table 2-7). The subsurface drip system evaluated had excellent high DUlq and none of
the floppy, solid set and center pivot irrigation systems tested exceeded the standard
DUlq (Table 2-5). During this study only one system of each type of floppy, solid set,
center pivot and subsurface drip irrigation systems were evaluated; therefore the
excellent DUlq result achieved each of these systems may not be representative of these
systems in general. A possible explanation for the substandard performance of the
overhead irrigation systems could be the system pressure and wind speed. During the
field experiments the wind speed varied from 1 m/s to 7 m/s and the coefficient of
variation (Cv) of nozzle system pressure ranged from 12% to 40% (see Table 2-5 and
Table 2-6). Many of these systems were operating at high a nozzle pressure except
subsurface drip was operating within an acceptable pressure range.
A summary of the water application efficiency (Ea) obtained for overhead irrigation
systems is shown in Table 2-3, Table 2-4 and Table 2-6. From the data presented it can
be seen that the systems that exhibited high uniformity generally had high water
application efficiencies. However, some of the systems that had a poor DUlq also had
high application efficiency. An example of this, the DUlq was 50.0% and Ea was 73.4%
for floppy sprinklers and DUlq was 56.2% and Ea was 81.2% for center pivot systems.
This is due to the definition of water application efficiency where averages are used.
Here the Ea was high because the average depth emitted from the sprinkler compared to
the average depth recorded on the ground was similar. However, the DUlq shows that
the low-quarter received only 50.0% and 56.2% of the average. This means that under-
irrigation has occurred in the test area.
55
The average water application efficiency for different types of irrigation systems is
close to the design norms suggested by the South African Irrigation Institute (SABI
2009). Those design norms represent the average spray and evaporation losses of the
irrigation systems. The average Ea for floppy, solid set, center pivot and subsurface drip
suggested by (Baum, Dukes & Miller 2001; Burt et al. 2000; Haman, Smajstrla & Pitts
2005; Smajstrla et al. 1991) are 70%, 75%, 75% and 85% respectively, and these are
given in Table 2-3.
The overall or farm irrigation efficiency (Eo) and effective irrigation efficiency (Ee) are
given in Table 2-4 and Table 2-6. From the data it has been demonstrated the system
that displayed high uniformity and application efficiency generally had high farm
irrigation efficiency and effective irrigation efficiency. The values of Eo and Ee are the
same for each system because the growers in these areas have not installed a system to
recycle runoff water. Thus, the fraction of runoff, seepage, or deep percolation is not
recovered. As a result of this, the values are the same, and both the Eo and Ee values
ranged from 59% to 75%. The subsurface drip irrigation systems had the best farm
irrigation efficiency. If growers in these areas install a system to recycle runoff water,
there is potential increase in the value of Ee. The United States Bureau of Reclamation
(USBR) conducted farm irrigation efficiency (Eo) studies in the 1960s and 1970s
(USBR 1970; 1971; 1973) and summary resulting of average farm irrigation efficiency
(Eo) for Idaho, Nebraska, Wyoming and Washington were 43%, 45%, 44% and 35%
respectively (Jensen 2007). Keller and Keller (1995) also presented a comparison of
effective irrigation efficiency (Ee) for Grand Valley (pre-intervention and post-
intervention), Imperial Irrigation District in California (per-intervention and post
intervention) and the Nile Valley irrigation system in Egypt and summary of resulting
were 36.8%, 61.7%, 74.6%, 74.6% and 91.3% respectively.
The overall irrigation efficiency or farm irrigation efficiency is the product of reservoir
storage efficiency (Es), water conveyance efficiency (Ec) and water application
efficiency (Ea). The Es and Ec obtained for floppy, solid set, center pivot and subsurface
drip irrigation systems are shown in Table 2-4 and Table 2-6. The Es and Ec values can
be seen in Figure 2-4, Figure 2-5 and Figure 2-7. The Es is 82.4% and Ec is 97% for all
overhead irrigation systems. All the pressurized irrigation systems had only one open
ground reservoir storage dam with a capacity of 56 giga liter and both of them delivered
56
water to the field through pipelines. Typically reservoirs are assumed to be 50% while
groundwater reservoirs (aquifer) are assumed to be 100% efficient as by (Smajstrla et al.
1991). Clemmens (1991) developed statistical performance parameters equation to
water storage efficiency (Es) and a summary resulting of this statistical performance for
Es was ranged from 96% to 100%.
For pressurized irrigation systems Ec is normally close to 1.0 or 100% according to
(Baum, Dukes & Miller 2003; Haman, Smajstrla & Pitts 1996; Smajstrla et al. 1991;
Smajstrla et al. 2002). In this case, the four overhead irrigation systems in terms of
water delivery and storage performance are similar. However, it does not mean that the
reservoir storage and water conveyance did not affect the overall irrigation efficiency as
the Es, Ec and Ea affect the farm irrigation efficiency.
The summary of irrigation efficiency (Ei) obtained for the overhead irrigation systems
are shown in Table 2-4 and Table 2-6. From the data it can be demonstrated that the
systems that exhibited high uniformities had high irrigation efficiencies. Although some
of the systems that had a poorer DUlq also had high irrigation efficiency. For instance,
the DUlq for floppy was 50.0% and Ei was 73.4%, and DUlq for center pivot was 56.2%
and Ei was 81.2% (see Figure 2-29). Here Ei was high because the average depth
emitted from the pressurized irrigation system compare to average depth recorded on
the ground was similar. However, the DUlq shows the low-quarter of the area received
only 50% and 56.2% of the average. This means that more water is lost by sprinklers
that discharge water at high angles, over greater distances, and at great heights above
the ground surface because of greater opportunity of time for evaporation.
In addition, greater water losses occur from systems which discharge a greater
proportion of small droplet sizes because small droplets are more readily carried by
wind and they expose more surface area to the atmosphere for evaporation. Keller and
Keller (1995) presented a comparison of irrigation efficiency (Ei) for Grand Valley (pre-
intervention and post-intervention), Imperial Irrigation District in California (per-
intervention and post intervention) and the Nile Valley irrigation system in Egypt and
summary of resulting efficiencies were 26%, 30.4%, 71.9%, 74.6% and 41.2%
respectively.
57
The variation in soil moisture storage and distribution uniformity for each system before
and after irrigation can be seen in Figures 2-3 to 2-10. The Cu and Ed ranged from
64.9% to 89.4% (Table 2-6), the Cv ranged from 12% to 40%, and DUlq ranged from
49.8% to 84.4% for each system. The micro (subsurface drip) irrigation systems had
some of the best water application uniformities. Center pivot and solid set sprinkler
systems had the most variability in the application uniformities calculated.
The New Zealand Agricultural Engineering Institute carried out tests under a range of
travelling irrigators to determine the coefficient of uniformity (Cu) and the average
results for guns, rotary room, linear boom, low pressure boom and lateral move were
70%, 75%, 80%, 92% and 96% respectively (John, Lees & English 1985). Ascough and
Kiker (2002) also summarized the average low-quarter distribution uniformity (DUlq) of
center pivot, dragline, micro irrigation, floppy and semi-permanent sprinkler systems as
81.4%, 60.9%, 72.7%, 67.4% and 56.9% respectively (see Table 2-8).
2.5.2. VOLUMETRIC SOIL MOISTURE CONTENT
The percent volumetric soil moisture content (%) obtained from each irrigation systems
before and after irrigation cycle over 0-60 mm depth are shown in Figure 2-3 to 2-10.
From the contour plotting profile of each system, it can be seen that subsurface drip
system evaluated had high volumetric soil moisture content with excellent distribution
uniformity (DUlq) all over the irrigation area (see Figure 2-9 & 2-10). Center pivot
sprinkler system had the second best in volumetric soil moisture distribution (see Figure
2-7 & 2-8) although it had an over-irrigation problem. After irrigation cycle, the percent
volumetric soil moisture content obtained for subsurface drip irrigation area ranged
from 32 to 38.7% and its peak of difference was 6.7%. Center pivot sprinkler also had
from 36 to 48.7% with a peak difference of 12.9%.
The other systems: floppy and solid set sprinkler had relatively poor distribution of
volumetric soil moisture content compared to center pivot sprinkler and subsurface drip
system. Before the irrigation cycle, the volumetric soil moisture content (%) for floppy
and solid set sprinklers is similar (i.e., a peak of 15.6% and 18.2% respectively) (see
Figure 2-3 and Figure 2-5). However, the irrigation area for center pivot sprinkler was
wet (i.e., a peak of 27%) even before the irrigation cycle (Figure 2-7). Subsurface drip
58
irrigation area had uniform volumetric soil moisture content (i.e., a peak difference of
0.4%) (Figure 2-9).
2.5.3. SOIL WATER
Soil water (mm) stored in 0-60 mm depth of soil water obtained for each irrigation
systems (i.e. before and after irrigation cycle) are shown in Figure 2-11 to 2-18. From
the contour plotting profile of each system, it can be seen that subsurface drip system
evaluated had high soil water storage with excellent distribution uniformity (DUlq) all
over the irrigation area (Figure 2-17 & 2-18). Center pivot sprinkler system had the
second best soil water stored in 0-60 mm depth of soil water. However, it experienced
over-irrigation problems because of excess water during application (Figure 2-15 & 2-
16). A peak difference of soil water stored for subsurface drip system was 5.4 mm (i.e.
range from 18.1 to 23.5 mm) while 9.4 mm was measured for the center pivot sprinkler
system (i.e. range from 19.2 to 28.6 mm).
2.5.4. CHANGE IN SOIL WATER STORAGE
The change in soil water storage (mm) over 0-60 mm depth of soil water was obtained
for the pressurized irrigation systems (floppy, solid set, center pivot and subsurface drip
systems) and shown in Table 2-9 to Table 2-12. The change in storage contour plotting
profile of each systems evaluated is displayed in Figure 2-19 to 2-22. From the figures
and tables it can be seen that subsurface drip system exhibited the most significant
change in storage with excellent distribution uniformity (DUlq). The change in storage
for the subsurface drip micro irrigation systems ranged from 7.1 mm to 12.4 mm with
an average storage of 9.92 mm (Table 2-12). While the other systems: floppy, solid set
and center pivot that had lower DUlq, and an average water storage of 4.70 mm, 4.22
mm and 7.31 mm respectively (Table 9-11). This may suggest that the type of sprinkler
irrigation systems (floppy, solid set and center pivot) may have lost water due to
evaporation and wind drift (some of the days were very hot and windy during the
experiment so the overheads pressure sprinklers might have lost more water). More
water can be lost during windy hot and dry days than in calm conditions during the
irrigation cycle. Therefore, sprinkler irrigation systems usually apply more efficiently at
59
night (and early mornings and late evening) than during a day (Haman, Smajstrla &
Pitts 1996; Haman, Smajstrla & Pitts 2005).
60
2.6. CONCLUSIONS
For irrigation systems to be efficient and effective in terms of uniformity and water
application, close attention has to be paid to the performance measures. Irrigation
systems should be properly designed, installed, and managed to achieve high
efficiencies. Regular evaluation is also required to ensure that the systems are
maintained and performing according to design. The distribution uniformity of a system
must be as high as possible to ensure the efficient application of water.
An irrigation system should be scheduled so that water application (in timing and
amount) can deliver optimal crop production. An irrigation system can only be efficient
and uniform in distribution when it is both scheduled properly and operated to apply the
desired amount water efficiently and effectively.
The results of the study conducted show that the average water storage efficiencies (Es)
of floppy, solid set, center pivot sprinklers and micro (subsurface) irrigation systems
was 82.4% for each systems and water conveyance efficiencies (Ec) were 97% for each
system. The average water application efficiencies (Ea) and irrigation efficiency (Ei)
were 73.4% for floppy, 68.0% for solid set, 81.2% for center pivot and 94.4% for
subsurface systems. The average overall irrigation efficiencies (Eo) and effective
irrigation efficiencies (Ee) of floppy, solid set, center pivot and subsurface methods
were 59.0%, 54.0%, 65.0% and 75.0% respectively. Finally, the average low-quarter
distribution uniformity (DUlq) was 50.0% for floppy, 52.0% for solid set, 56.2% for
center pivot and 84.8% for subsurface irrigation systems. The average water distribution
efficiencies (Ed) and coefficient of uniformity (Cu) of floppy, solid set, center pivot and
subsurface systems was 64.9%, 67.6%, 68.9% and 89.4% in the order given.
The comparison of the different types of irrigation techniques revealed that a subsurface
drip irrigation method is the most efficient and effective in all categories of irrigation
performance measures than the floppy, solid set and center pivot sprinkler irrigation
methods. Center pivot is the second best effective measure based on the analysis of
performance measures and distribution uniformity.
61
Figure 2-2: Summary of the comparison of efficiency and uniformity for different type
of irrigation systems used in the Harvey Irrigation Area (HIA)
Table 2-2: Summary of uniformity parameters for different type of irrigation systems
Average Types of irrigation systems
Floppy Solid set Center pivot Subsurface
CU (%) [Ed (%)] from the study area 64.9 67.7 (67.6) 69.0 (68.9) 89.4
DUlq (%) from the study area 50.0 52.0 56.2 84.4
Pitts's Standard DUlq (%)
(Pitts et al. 1996)
(from Table 2-21)
75.0
75.0
75.0
85.0
Ascough‟s Standard DUlq (%)
(Ascough & Kiker 2002)
(from Table 2-22)
75.0
75.0
75.0
85.0
62
Table 2-3: Summary of water application efficiency (Ea) for different type of irrigation
systems
Average Ea (%) Type of irrigation systems
Floppy Solid Set Center Pivot Subsurface
Average Ea (%) from study area (HIA) 73.4 67.7 81.2 94.4
Rogers's Ea (%)
(Rogers et al. 1997)
65 - 80
70 - 85
75 - 90
75 - 90
Solomon Ea (%)
(Solomon 1988)
65 -75
70 - 80
75 - 90
75 - 95
Haman‟s Average Ea (%)
(Haman, Smajstrla & Pitts 2005)
70.0
75.0
75.0
85.0
Smajstrla's Average Ea (%)
(Smajstrla et al. 1991)
70.0
75.0
75.0
85.0
Burt‟s Average Ea (%)
(Burt et al. 2000)
70.0
75.0
75.0
85.0
Baum's Average Ea (%)
(Baum, Dukes & Miller 2001)
70.0
75.0
75.0
85.0
Table 2-4: Summary of the Comparison of Irrigation Systems and Irrigation Efficiencies
in the Study Area in the Harvey Irrigation District
Type of System Depth of Water
Contents
(mm)
Type of Efficiencies
Sprinkler Irrigation Es
(%)
Ec
(%)
Ea
(%)
Ei
(%)
Eo
(%)
Ee
(%)
Ed
(%)
Floppy Sprinkler 0-60 82.4 97.0 73.4 73.4 59.0 59.0 64.9
Solid Set Sprinkler 0-60 82.4 97.0 68.0 68.0 54.0 54.0 67.6
Center Pivot Sprinkler 0-60 82.4 97.0 81.2 81.2 65.0 65.0 68.9
Micro Irrigation
Subsurface 0-60 82.4 97.0 94.4 94.4 75.0 75.0 89.4
Table 2-5: Summary of the Comparison of Irrigation Systems and Irrigation
Uniformities in the Study Area in the Harvey Irrigation District
Type of System Depth of Water
Contents (mm)
Type of Uniformity
Sprinkler Irrigation DUlq
(%)
Cu
(%)
Cv
(%)
Floppy Sprinkler 0-60 50.0 64.9 40.0
Solid Set Sprinkler 0-60 52.0 67.7 38.0
Center Pivot Sprinkler 0-60 56.2 69.0 35.0
Micro Irrigation
Subsurface 0-60 84.8 89.4 12.0
63
Table 2-6: Summary of the Comparison of Irrigation Systems, Efficiencies and
Uniformities in the Study Area in the Harvey Irrigation District
Type of System Type of Efficiencies Types of
Uniformities
Sprinkler Irrigation Es
(%)
Ec
(%)
Ea
(%)
Ei
(%)
Eo
(%)
Ee
(%)
Ed
(%)
DUlq
(%)
Cu
(%)
Cv
(%)
Floppy Sprinkler 82.4 97.0 73.4 73.4 59.0 59.0 64.9 50.0 64.9 40
Solid Set Sprinkler 82.4 97.0 68.0 68.0 54.0 54.0 67.6 52.0 67.7 38
Center Pivot
Sprinkler
82.4
97.0
81.2
81.2
65.0
65.0
68.9
56.2
69.0
35
Micro Irrigation
Subsurface 82.4 97.0 94.4 94.4 75.0 75.0 89.4 84.8 89.4 12
Where Es is the reservoir water efficiency; Ec is the water conveyance efficiency; Ea is
the water application efficiency; Ei is the irrigation efficiency; Eo is the overall irrigation
efficiency; Ee is the effective irrigation; Ed is the water distribution efficiency; DUlq is
the distribution uniformity; Cu is the coefficient of uniformity and Cv is the coefficient
of variation.
Table 2-7: Summary of DUlq evaluation & standard for DUlq (Pitts et al. 1996)
Irrigation type
Evaluation
(no)
Average DUlq
(%)
Standard DUlq
(%)
Agricultural sprinkler 159 65 75
Micro irrigation 174 70 85
Surface (Furrow) irrigation 15 70 65
Turf 37 49 75
Table 2-8: Summary of Uniformity Parameter by Irrigation Type (Ascough & Kiker
2002)
System type
Average CU
(EI) (%)
Average
DUlq (%)
Standard
DUlq (%)
With good field
condition DUlq (%)
Center pivot 88.0 81.4 75.0 100.0
Dragline 74.0 60.9 75.0 15.4
Drip & Micro -
spray
81.6 (76.3)
72.7
85.0
30.0
Floppy 74.5 67.4 75.0 0.0
Semi-permanent
sprinkler
70.8
56.9
75.0
14.3
64
Figure 2-3: Percent volumetric soil moisture content (%) for floppy sprinklers before
irrigation cycle
Figure 2-4: Percent volumetric soil moisture content (%) for floppy sprinklers after
irrigation cycle
65
Figure 2-5: Percent volumetric soil moisture content (%) for the solid set sprinklers
before irrigation cycle
Figure 2-6: Percent volumetric soil moisture content (%) for the solid set sprinklers after
irrigation cycle
66
Figure 2-7: Percent volumetric soil moisture content (%) for the center pivot sprinklers
before irrigation cycle
Figure 2-8: Percent volumetric soil moisture content (%) for the center pivot sprinklers
after irrigation cycle
67
Figure 2-9: Percent volumetric soil moisture content (%) for the subsurface drip system
before irrigation cycle
Figure 2-10: Percent volumetric soil moisture content (%) for the subsurface drip
system after irrigation cycle
68
Figure 2-11: Floppy sprinklers: soil water (mm) stored in 0 – 60 mm depth (before
irrigation)
Figure 2-12. Floppy sprinklers: soil water (mm) stored in 0 – 60 mm depth (after
irrigation)
69
Figure 2-13: Solid Set sprinklers: soil water (mm) stored in 0 – 60 mm depth (before
irrigation)
Figure 2-14: Solid Set sprinklers: soil water (mm) stored in 0 – 60 mm depth (after
irrigation)
70
Figure 2-15: Center Pivot sprinklers: soil water (mm) stored in 0 – 60 mm depth (before
irrigation)
Figure 2-16: Center Pivot sprinklers: soil water (mm) stored in 0 – 60 mm depth (after
irrigation)
71
Figure 2-17: Subsurface drip irrigation: soil water (mm) stored in 0 – 60 mm depth
(before irrigation)
Figure 2-18: Subsurface drip irrigation: soil water (mm) stored in 0 – 60 mm depth
(after irrigation)
72
Figure 2-19: Change in storage (mm) over 0-60 mm depth for floppy sprinkler irrigation
systems, and number of randomly catch cups (i.e. in green color) over the irrigation area
Figure 2-20: Change in storage (mm) over 0-60 mm depth for solid set sprinkler
irrigation systems, and number of randomly catch cups (i.e., brown color) over the
irrigation area
73
Figure 2-21: Change in storage (mm) over 0-60 mm depth for center pivot sprinkler
irrigation systems, and number of randomly catch cups (i.e., brown color) over the area
Figure 2-22: Change in storage (mm) over 0-60 mm depth for subsurface drip irrigation
systems
74
Table 2-9: Change in storage (mm) over 0-60 mm depth of soil water for floppy
sprinkler irrigation systems
5.3 6.0 5.5 2.6 5.3 6.9 6.9 6.1 3.8 7.8 2.1 4.1
3.2 3.2 4.5 7.6 8.2 4.3 4.9 7.0 3.8 4.4 10.0 3.6
5.7 1.9 2.4 4.2 5.1 2.9 2.4 7.1 3.6 5.0 6.4 2.2
5.7 7.2 4.9 5.8 1.9 6.7 4.3 5.2 4.2 4.2 4.5 2.9
3.3 4.3 4.2 2.2 3.1 3.2 8.1 3.6 10.2 7.7 3.4 2.4
4.3 6.7 2.5 5.5 6.5 3.8 4.6 3.5 7.9 1.7 6.7 0.2
4.3 5.9 0.3 1.5 5.5 6.2 7.0 2.8 5.6 2.2 6.8 2.8
4.3 3.0 3.0 4.7 3.5 4.1 5.8 7.3 6.9 6.7 4.7 3.0
Table 2-10: Change in storage (mm) over 0-60 mm depth of soil water for solid set
sprinkler irrigation systems
2.0 2.9 3.0 4.0 7.4 3.1 3.5 3.3 5.4 5.6
2.2 3.3 2.8 3.9 5.9 4.5 4.3 4.7 2.2 4.6
2.8 2.2 1.6 3.2 5.4 1.4 3.4 4.0 5.4 6.1
3.7 5.8 2.4 5.6 4.5 1.5 2.6 2.6 6.6 6.0
1.0 4.9 1.2 5.7 3.8 4.5 7.4 3.1 5.2 3.1
5.4 2.0 3.9 5.5 4.1 7.8 4.2 6.2 5.8 6.9
3.6 3.4 4.9 3.4 5.7 4.0 5.3 4.6 4.9 8.4
Table 2-11: Change in storage (mm) over 0-60 mm depth of soil water for center pivot
sprinkler irrigation systems
4.2 4.0 8.1 4.2 4.0 9.7 10.2 10.2 5.4 11.7 6.1 7.6 8.7 8.1
4.3 4.0 8.2 4.3 4.1 9.7 10.3 10.2 5.4 11.7 6.1 7.6 8.7 8.1
4.1 3.9 8.0 4.1 3.9 9.6 10.2 10.1 5.3 11.6 6.0 7.5 8.7 8.1
4.1 3.9 8.1 4.1 3.9 9.6 10.1 10.2 5.9 11.7 6.0 7.5 8.7 8.1
4.3 4.1 8.2 4.1 3.9 9.7 10.2 10.2 4.6 11.7 7.9 7.5 8.7 8.2
Table 2-12: Change in storage (mm) over 0-60 depth of soil water for subsurface drip
irrigation systems
8.9 9.4 9.2 9.7 12.0 8.6
9.6 9.2 9.8 8.8 9.4 8.4
8.2 8.1 9.2 10.9 9.6 9.4
11.9 8.6 9.3 10.4 9.3 10.1
10.5 7.1 12.2 12.4 9.4 9.4
10.7 7.1 10.7 11.5 8.4 11.5
9.3 10.0 10.3 10.8 11.7 9.7
9.9 11.7 12.0 9.8 10.2 7.3
11.5 11.2 11.4 10.7 10.0 9.1
75
APPENDIX 2-A: COMPOSITION OF SOIL SAMPLES FROM EACH IRRIGATION SYSTEM IN THE HARVEY IRRIGATION
AREA
Table 2A-1: Soil samples of floppy sprinkler systems before irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw)
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
23.51 19.12 4.39 22.96 3.38 2.69 4.39-6
1 4.39-6
7.08-6
0.6 38 2056 1681
23.75 20.66 3.09 14.96 2.45 2.71 3.09-6
1 3.09-6
7.65-6
0.4 29 2221 1936
18.16 15.48 2.68 17.31 0.90 2.70 2.68-6
1 2.68-6
5.73-6
0.5 33 2133 1800
33.75 28.82 4.91 17.04 3.90 2.69 4.91-6
1 4.91-6
2.88-5
0.2 17 2408 2241
37.20 31.07 6.13 19.73 4.87 2.71 6.13-6
1 6.13-6
3.11-5
0.2 17 2425 2258
26.52 22.95 3.57 15.56 2.83 2.69 3.57-6
1 3.57-6
2.30-5
0.2 17 2408 2242
32.20 26.82 5.38 20.06 4.27 2.70 5.38-6
1 5.38-6
2.68-5
0.3 23 2307 2077
23.88 20.50 3.38 16.38 2.68 2.70 3.38-6
1 3.38-6
2.05-5
0.2 17 2416 2250
33.03 29.63 3.40 11.47 2.70 2.69 3.40-6
1 3.40-6
2.96-5
0.1 09 2536 2445
27.23 23.69 3.54 14.94 2.81 2.71 3.54-6
1 3.54-6
2.37-5
0.2 17 2425 2258
where W = total weight (g); Ws = weight of solid (g); Ww = weight of water (g); = gravimetric water content ( =Ww/Ws, %); h = depth of water
(mm); Gs = specific gravity of solid (Gs = s/w); Vw = volume of water (m3/m
2); Sr = degree of saturation; Vv = volume of void (Vv = Vw/Sr); Vs =
volume of solid (m3); e = void ratio (e = Vv/Vs); n= porosity (n = e/e+1, %); b = bulk unit of weight (b =w (Gs+eSr/1+e), kg/m
3); d = dry unit
weigh (d = wGs/(1+e)), kg/m3)
76
Table 2A-2: Soil samples of floppy sprinkler systems after irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw)
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
42.72 35.25 7.49 21.25 5.94 2.69 7.49-6
1 7.49-6
1.31-5
0.6 38 2056 1681
43.52 36.38 7.14 20.59 5.67 2.69 7.14-6
1 7.14-6
1.35-5
0.5 33 2127 1793
48.32 40.47 7.85 19.40 6.23 2.70 7.85-6
1 7.85-6
1.50-5
0.5 33 2133 1800
51.74 42.03 9.71 23.10 7.71 2.69 9.71-6
1 9.71-6
1.56-5
0.7 41 1994 1582
47.88 39.27 8.61 21.93 6.83 2.71 8.61-6
1 8.61-6
1.45-5
0.6 33 2069 1694
46.94 37.72 9.22 24.44 7.32 2.69 9.22-6
1 9.22-6
1.40-5
0.7 41 1994 1582
38.69 30.21 8.48 28.07 6.73 2.70 8.48-6
1 8.48-6
1.12-5
0.8 44 1944 1500
48.66 38.39 10.27 26.75 8.15 2.70 1.03-5
1 1.03-5
1.42-5
0.7 41 2000 1588
48.30 39.60 8.70 21.97 6.90 2.69 8.70-6
1 8.70-6
1.47-5
0.6 33 2056 1681
44.52 36.81 7.71 20.95 6.12 2.71 7.71-6
1 7.71-6
1.36-5
0.6 33 2069 1694
Soil composition of each irrigation system in the Harvey Irrigation Area
77
Table 2A-3: Soil samples of solid set sprinkler systems before irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h (mm) Gs
(γs/γw)
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
29.76 24.53 5.23 21.32 4.15 2.69 5.23-6
0.7 7.47-6
9.09-6
0.8 44 1805 1495
34.31 27.18 7.13 26.23 5.66 2.69 7.13-6
0.7 1.02-5
1.01-5
1.0 50 1695 1345
35.61 28.12 7.49 26.64 5.94 2.70 7.49-6
0.7 1.07-5
1.04-5
1.0 50 1700 1350
37.57 32.26 5.31 16.46 4.21 2.71 5.31-6
0.7 7.59-6
1.19-5
0.6 38 1956 1694
28.66 24.17 4.49 18.58 3.56 2.70 4.49-6
0.7 6.41-6
8.95-6
0.7 41 1876 1588
39.18 33.81 5.37 15.88 4.26 2.70 5.37-6
0.7 7.67-6
1.25-6
0.6 38 1950 1688
33.68 29.90 3.78 12.64 3.00 2.69 3.78-6
0.7 5.40-6
5.40-5
0.5 33 2027 1793
Table 2A-4: Soil samples of solid set sprinkler systems after irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw )
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
24.92 20.12 4.80 23.86 3.81 2.70 4.80-6
1 4.80-6
7.45-6
0.6 38 2063 1688
38.48 27.12 11.36 41.89 9.02 2.72 1.14-5
1 1.14-5
1.00-5
1.0 50 1853 1355
41.21 32.56 8.68 26.57 6.87 2.69 8.65-6
1 8.65-6
1.21-5
0.7 41 1994 1582
34.73 28.25 6.48 22.94 5.14 2.69 6.48-6
1 6.48-6
1.05-5
0.6 38 2056 1681
41.86 33.55 8.31 24.77 6.60 2.71 8.31-6
1 8.31-6
1.24-6
0.7 41 2006 1594
41.88 32.03 9.85 30.75 7.82 2.69 9.85-6
1 9.85-6
1.19-6
0.8 44 1939 1494
40.06 37.22 2.48 7.63 2.23 2.70 2.84-6
1 2.84-6
1.38-5
0.2 17 2416 2250
78
Table 2A-5: Soil samples of center pivot sprinkler systems before irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw )
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
30.03 22.56 7.47 33.11 5.93 2.70 7.48-6
1 7.48-6
8.26-6
0.9 47 1895 1421
16.14 10.56 5.56 54.33 4.43 2.70 5.58-6
1 5.58-6
3.91-6
1.0 50 1850 1350
17.64 12.27 5.37 43.77 4.26 2.70 5.37-6
1 5.37-6
4.45-6
1.0 50 1850 1350
34.32 20.66 13.66 66.12 10.84 2.71 1.37-5
1 1.37-5
7.65-6
2.0 67 1565 901
37.48 25.14 12.34 49.09 9.79 2.69 1.23-5
1 1.23-5
9.31-6
1.0 50 1851 1349
32.68 25.12 7.56 30.10 6.00 2.70 7.56-6
1 7.56-6
9.30-6
0.8 44 1944 1500
33.68 23.78 9.90 41.63 7.86 2.70 9.90-6
1 9.90-6
8.81-6
1.0 50 1850 1350
31.00 23.15 9.92 42.85 7.78 2.70 9.92-6
1 9.92-6
8.57-6
1.0 50 1850 1350
20.99 17.31 5.75 33.22 4.56 2.70 5.75-6
1 5.75-6
6.41-6
0.9 47 1895 1421
20.92 18.43 4.51 24.47 3.58 2.70 4.51-6
1 4.51-6
6.83-6
0.7 41 2000 1588
31.34 24.91 8.50 34.12 6.75 2.70 8.50-6
1 8.50-6
9.23-6
0.9 47 1895 1421
27.93 18.99 11.01 57.98 8.74 2.70 1.10-5
1 1.10-5
7.03-6
2.0 67 1568 901
31.46 25.02 8.51 34.01 6.75 2.70 8.51-6
1 8.51-6
9.27-6
0.9 47 1895 1421
23.45 16.76 8.76 52.27 6.95 2.70 8.76-6
1 8.76-6
6.21-6
1.0 50 1850 1350
79
Table 2A-6: Soil samples of center pivot sprinkler systems after irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw )
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
43.11 28.67 10.44 36.41 8.29 2.69 1.04-5
1 1.04-5
1.06-5
1 50 1852 1350
23.30 13.95 10.35 74.19 8.21 2.71 1.05-5
1 1.05-6
5.17-6
2 67 1562 899
21.42 10.73 10.69 99.63 8.48 2.71 1.07-5
1 1.07-5
3.97-6
3 75 1426 677
36.80 21.74 15.06 62.27 11.95 2.71 1.51-5
1 1.51-5
8.05-6
2 67 1566 901
25.73 17.68 8.05 45.53 6.39 2.70 8.06-6
1 8.06-6
6.55-6
1 50 1850 1350
23.59 16.58 7.01 42.28 5.56 2.70 7.01-6
1 7.01-6
6.14-6
1 50 1850 1350
23.84 13.10 10.74 81.89 8.52 2.69 1.07-5
1 1.07-5
4.85-6
2 67 1569 900
26.23 17.59 10.80 61.40 8.57 2.70 1.08-5
1 1.08-5
6.51-6
2 67 1567 900
29.45 21.98 9.54 43.62 7.57 2.73 9.54-6
1 9.54-6
8.14-6
1 50 1847 1352
34.92 24.38 12.61 51.72 10.00 2.69 1.26-5
1 1.26-5
9.03-6
1 50 1846 1346
30.80 21.87 11.00 50.30 7.94 2.70 1.10-5
1 1.10-5
8.10-6
1 50 1850 1350
20.98 13.76 9.30 67.59 7.38 2.70 9.30-6
1 9.30-6
5.10-6
2 67 1567 900
30.28 22.30 10.05 45.07 7.98 2.69 1.00-5
1 1.00-5
8.26-6
1 50 1859 1352
30.51 19.52 13.06 66.91 10.37 2.71 1.31-5
1 1.31-5
7.23-6
2 67 1562 901
80
Table 2A-7: Soil samples of subsurface drip systems before irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw )
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
52.19 41.48 10.71 25.81 8.50 2.69 1.07-5
1 1.07-5
1.54-5
0.7 41 1996 1584
45.46 34.48 10.35 31.81 8.71 2.70 1.10-5
1 1.10-5
1.28-5
0.9 47 1890 1417
46.98 34.92 12.06 34.54 9.57 2.71 1.21-5
1 1.21-5
1.29-5
0.9 47 1894 1422
47.02 35.11 11.91 33.92 9.45 2.70 1.19-5
1 1.19-5
1.30-5
0.9 49 1896 1422
44.01 31.12 13.49 43.35 10.71 2.71 1.35-5
1 1.35-5
1.15-5
1.0 50 1854 1354
50.01 36.08 13.93 38.61 11.06 2.69 1.39-5
1 1.39-5
1.34-5
1.0 50 1849 1348
47.18 36.23 10.95 30.22 8.69 2.72 1.10-5
1 1.10-5
1.34-5
0.8 44 1947 1504
46.51 33.89 12.62 37.24 10.02 2.69 1.26-5
1 1.26-5
1.26-5
1.0 50 1848 1347
48.37 33.79 14.58 43.15 11.57 2.71 1.46-5
1 1.46-5
1.25-5
1.0 50 1852 1353
Table 2A-8: Soil samples of subsurface drip systems after irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw )
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
47.56 36.39 11.17 30.70 8.87 2.68 1.11-5
1 1.11-5
1.35-5
0.8 44 1945 1498
51.45 39.33 12.12 30.82 9.62 2.69 1.21-5
1 1.21-5
1.46-5
0.9 47 1893 1418
49.82 36.16 13.66 37.78 10.84 2.71 1.37-5
1 1.37-5
1.34-5
1.0 50 1850 1351
52.08 37.62 14.28 37.96 11.33 2.71 1.43-5
1 1.43-5
1.39-5
1.0 50 1852 1353
46.98 32.52 14.46 44.46 11.48 2.72 1.45-5
1 1.45-5
1.20-5
1.0 50 1855 1356
50.98 37.17 13.81 37.15 10.96 2.69 1.38-5
1 1.38-5
1.38-5
1.0 50 1846 1346
49.70 36.55 13.15 35.98 10.44 2.72 1.32-5
1 1.32-5
1.35-5
1.0 50 1853 1355
50.76 36.83 13.93 37.82 11.06 2.70 1.39-5
1 1.39-5
1.36-5
1.0 50 1854 1353
53.09 38.15 14.94 39.12 11.86 2.70 1.49-5
1 1.49-5
1.41-5
1.0 50 1855 1354
81
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90
CHAPTER 3: COMPARISON OF DIFFERENT IRRIGATION
METHODS BASED ON THE INITIAL WATER APPLICATION
EFFICIENCY AND A SOIL MOISTURE RETENTION IN THE HARVEY
IRRIGATION AREA IN WESTERN AUSTRALIA
91
SUMMARY
A fundamental question regarding the soil moisture storage in the irrigation systems is
to estimate the accurate fore-casting of water application (in time and amount) for
optimal crop production and to estimate date/time at which the next irrigation volume
should be applied for efficient irrigation using a particular system. The main objective
of this research is to compare different irrigation methods based on the initial water
application efficiency and soil moisture retention in a small representative plot (600
m2) for each irrigation system used in the Harvey Irrigation Area in Western Australia.
The comparison of the different types of irrigation techniques revealed that the solid set
sprinkler and subsurface drip irrigation methods were more effective and efficient than
the floppy and center pivot sprinkler irrigation methods for improving crop
productivity. The results indicated that the subsurface drip system evaluated had
extremely high initial water application efficiency of 93.3%, high soil water storage of
96.4%, low soil moisture retention of 30%, low infiltration rate of 0.08-3.1 mm/hr and
low depletion over the 24 hr monitoring period compared to floppy, solid set and center
pivot sprinkler methods. The second best option in system performance was solid set
sprinkler method that had 82.2%, 67.8%, 50%, 0.06-6.3 mm/hr and 9.3 mm
respectively. Floppy and center pivot sprinkler systems had the following performance
indicator of 76.6% and 59.4%, 63% and 51.1%, 100% and 50%, 0.22-8.1 mm/hr and
0.05-6.4 mm/hr, and 9.5 mm and 11.9 mm respectively. These two system performance
were poor relatively to either subsurface drip or solid set system.
The results demonstrated that by applying subsurface drip irrigation and solid set
sprinkler instead of floppy and center pivot sprinkler methods, the initial water
application efficiency and soil moisture retention has the potential to be improved.
However, it should be noted that there are some inherent difficulties in comparing
subsurface infiltration systems with above ground systems, and the methods of water
application and distribution are obviously different, as demonstrated by the data present
here. The potential efficiency gains would have significant benefits to irrigator in the
HIA. However, significant cost will be incurred to change the irrigation systems and an
economic evaluation is required. In addition, these systems may not be suitable for all
farm operations.
92
3.1. INTRODUCTION
Reduction of crop stress by provision of sufficient water to meet crop demands with
minimal waste of water through runoff and deep percolation below the rootzone is a
major objective of modern irrigation system design.
Accurate water application prevents over or under irrigation. Over-irrigation wastes
water, energy and labour, leaches nutrient below the root zone and can lead to water
logging which reduces crop yield. If a crop is “over-irrigated”, it is likely that excess
water will be lost through run-off and additional soil evaporation or drainage below the
root zone (Dodds, Meyer & Barton 2005). Under-irrigation stresses the plant, resulting
in yield reductions and decreased returns. With irrigation scheduling the problem of
over and under-irrigation can be managed as it modifies when and how much water to
apply to an irrigated crop relative to soil moisture to maximize net returns (Abdel-
Mawgoud et al. 2009; Phene 1999).
The design and operation of efficient irrigation systems require a knowledge of soil
water moment and storage (Skaggs, Miller & Brooks 1983). Adequate knowledge of
soil moisture storage as well as evaporation and transpiration at the land surface is
essential to understand the prediction of reciprocal influences between land surface
processes, weather and climate on design and operation of the farm irrigation system
(Yoo 2001)
The rate soil moisture decrease over time in a soil profile is discussed by (Hewlett &
Hibbert 1963). They highlight problems associated with the collection of soil moisture
data changes in soil compaction, and noted that amount of soil moisture drained and the
rate of drainage appeared to increase with height above the outflow level.
The rate of infiltration is generally limited by physical characteristics of soil, surface
slope, porosity and temperature, and by the hydrostatic pressure that results from
superficial flooding or ponding. Infiltration rate is one the most important soil properties
affecting irrigation systems. Infiltration rates are consistently very low however; it can
increase for a short period following irrigation and can created drainage problems on the
irrigation area as discussed by (Mousavi, Nouri-Emamzadei & Afyuni 2000; Tayel, EI
93
Gendy & Abd EI-Hady 2009). Yapa (1996) discussed the drainage problems in a “very
rapid” and “rapid infiltration rate” during water application, and recommended the use
of overhead irrigation method so that a higher water use efficiency can be achieved.
Improved irrigation technology in which the plant uses a greater fraction of applied
water, has the potential to conserve water with little or no loss of yield. Sprinkler
irrigation, for example, saves from 10-35% of the applied water through increased water
application efficiency (Ea) compared with more traditional surface irrigation systems
(Caswell & Zilberman 1985). However, the application efficiency of an irrigation
system depends not only on the attributes of the system but also on the physical
characteristic of the field such as soil texture, type of crop, topography and climate
(Heermann et al. 1990; Jensen 1977; Jensen 2007; Kruse, Bucks & von Bernuth 1990).
The objective of this study is to compare the irrigation systems using initial water
application efficiency and soil moisture retention. In particular, the entire system
performance of floppy, solid set, center pivot sprinkler and subsurface drip irrigation
systems can be evaluated using the two methods. The comparison of irrigation methods
can highlight areas where the system or the irrigation scheduling can be improved.
In this paper the results are presented for each irrigation system. The average of all
samples for all irrigation methods in the Harvey Irrigation Area (HIA) were used to
compare and evaluate each system in terms of initial water application efficiency (Ea)
and soil moisture retention. Water added by irrigation to each irrigation system was
used to determine the initial water application efficiency and soil moisture retention.
3.2. METHODS
Two methods were used to compare and evaluate the irrigation systems in the Harvey
Irrigation Area (HIA). These were the: Initial water application efficiency (Ea) and soil
moisture retention. Several techniques were used to evaluate these components
including field experiments, soil analysis, irrigation water balance, and Horton‟s
infiltration equation to evaluate the infiltration and soil retention rate of different types
of irrigation systems. This study was conducted in the Harvey Irrigation Area (HIA)
94
which is located at about 100 km south of Perth in Western Australia (Latitude 33o.07
N, Longitude 115o.52 E and 33m high above the sea level).
Field experiments were carried out on small experimental plot at the Waroona Research
Station over two successive growing seasons under four irrigation systems:
floppy/overhead cable sprinkler, solid set sprinkler, center pivot sprinkler and
subsurface drip irrigation systems. Soil moistures reading at the depth of 0-60 mm were
taken from each system. At the cessation of the irrigation cycle, two hundred ten (30 x
7) soil moisture readings were taken from each irrigation system on a 5 m grid over an
area of 20 x 30 m (600 m2) at 0.0hr, 0.5hr, 1.5hr, 2.5hr, 4.0hr, 6.5hr and 24.0hr. The
number of moisture measurement for each system and area covered is given in Table 3-
1.
Table 3-1: Numbers of soil moisture measurement for each irrigation system and area
covered
Type of System
Soil Moisture
Measurements (no)
Soil Samples
(no)
Area Covered
(ha)
Floppy 210 7 0.06
Solid set 210 7 0.06
Center pivot 210 7 0.06
Subsurface drip 210 7 0.06
In addition, soil samples at 0-60 mm depth were collected before and after irrigation
from each irrigation systems (see Appendix 3-A: Table 3A-(1-8)). Soil samples were
randomly collected from each system at the time of theta-probe measurement to
correlate field soil moisture readings with laboratory analysis. Soil moisture
measurements were obtained before and at seven times after an irrigation cycle.
The type of soil under each irrigation system to be assessed was assessed for, specific
gravity and degree of saturation, gravimetric water content, void ratio and porosity, and
bulk density (see Appendix 3-A). A determination of whether runoffs or deep-
percolation was likely to occur under each the irrigation cycle. The study area and site
plan shown is in Figure 3-1.
95
Figure 3-1: The location of floppy, solid set, center pivot and subsurface drip irrigation
systems in the study area in the Harvey Irrigation District of Western Australia
3.3. GOVERNING EQUATION AND TECHNIQUES
3.3.1. INITIAL WATER APPLICATION EFFICIENCY (Ea)
The concept of efficiency is not well established despite being utilized worldwide.
Reviews on various efficiency terms are provided by (Bos et al. 1994; Burt et al. 1997;
Heermann et al. 1990; Jensen 2007; Pereira 1999; Rogers et al. 1997; Smajstrla et al.
1991; Wolters 1992).
The classical definition of irrigation efficiency proposed by Israelsen (1932) is the ratio
between the irrigation water consumed by the crops of an irrigated farm or project
during crop growth and the water diverted from a river or other natural source into
farms or project canals during the same time. Jensen (1996) considered the term
„efficiency‟ as inappropriate and a cause of misinterpretation/misunderstanding, and
proposed to rename it as a consumptive use coefficient. This allows a better
96
understanding of the terms water consumption which includes evaporation (E),
transpiration (T) or embodiment in a product and water use (WUE), which involves
both consumptive and nonconsumptive components (Burt et al. 1997; Pereira 1999).
The concept of potential/initial water application efficiency is useful in measuring the
performance of a system for a single irrigation cycle. The measure is based on the
concept of meeting a target irrigation depth for that application event while Ea is used to
estimate what happens during a single irrigation event even when water has not yet been
used. If deep percolation losses can be minimized, the application efficiency would be
at a maximum without significant underirrigation (Burt et al. 1997; Smajstrla et al.
1991; Solomon 1988). However, irrigation system uniformity and initial water
application efficiency can also affect the application depth and cause variability in
actual soil water status in the field (Heermann et al. 1990). A 5% error in measuring
irrigation volume is typical. This, coupled with uncertainly in determining the initial
water application efficiency, can easily lead to 10% error in deriving the effective
irrigation volume (Heermann et al. 1990).
According to Burt et al. (1997); Rogers et al. (1997) and Smajstrla et al. (1991), the
potential or initial water application efficiency (Ea) for a single event is defined as
(3-1)
where Wc is the average depth of irrigation water (i.e. water available for use by the
crop) and Wf is the average depth of irrigation water applied (i.e. water delivered from
the source to the field).
3.3.2. A SOIL MOISTURE RETENTION
3.3.2.1. IRRIGATION WATER BALANCE
A „water balance‟ is an accounting of all water volume that enters and leaves the field
over a specified period of time (Burt 1999). Burt‟s also discussed that a „water balance‟
is not the same as an „irrigation water balance‟. An irrigation water balance is typically
more difficult to construct than a water balance because the specific portion of ET and
97
Leaching Requirement (LR) that originated as irrigation water must be estimated (Burt
1999). According to Burt‟s discussion, the sub-categories water balance includes such
parameters as rainwater balances, on-farm irrigation water balance, conveyance water
balances, root zones moisture water balance, and groundwater water balance.
(a) (b)
Clemmens and Burt (1997) also derived the hydrologic water balance for defining the
irrigation system performance within defined boundaries. For irrigation purposes the
change in soil water storage ( ) can be calculated from the water balance equation:
ΔS = I + P – ET – RO – DR (3-2)
where I and P are irrigation and precipitation, respectively, and represent inputs to the
system; ET, RO, DR are evapotranspiration, runoff, and drainage respectively, and
generally represent from output the system. All the terms in Eq. (3.2) have dimensions
of length [L] (i.e. depth) with positive water depths for input to the soil and negative
water depths for output (Blonquist, Jones & Robinson 2006).
As mentioned by Blonguist, Jones and Robinson (2006), if the runoff (RO) and drainage
(DR) can be considered negligible, and ΔS can only change as ET removes water while
irrigation (I) and precipitation (P) replenish water, within the system performance (i.e.
no lateral water flow into the soil profile), then the water balance can be rearranged as
98
ΔS = I + P – ET (3-3)
where there is a positive sign in the change in soil water storage, the ΔS can indicate the
net water gain but if it is a negative sign, it shows the loss of water from the soil. Within
the short period of time, the ΔS can increase moderately while a decrease in ET occurs
between irrigation and precipitation events. However, the change in soil water storage
remains relatively constant over long time periods. The volumetric soil moisture content
(θ) is a direct approximation of the change in soil water storage (ΔS) in the water
balance equation (Blonquist, Jones & Robinson 2006) and this can be shown as:
ΔS = Δθ*D = ET (3-4)
where D is the rooting depth of the plant [L]
3.3.2.2. SOIL MOISTURE
Water is the most critical resource in our planet earth. In fact, without it life cannot
exist. About 97.2% of the global water resources are stored in the oceans, 2.15% in the
ice sheets and glaciers, and 0.63% ground water (Strahel 1997). Soil moisture, which is
the water held in the soil within reach of the plant roots constitutes only 0.005%
(Wagner, Lemoine & Rott 1999). Despite the fact that the soil reservoir is relatively
small (in global terms) it exerts a prominent control on the interaction between the
hydrosphere, biosphere and atmosphere. Consequently, soil moisture is very important
for a number of disciplines and research applications.
Soil moisture is a key status variable for understanding many hydrological processes
that are involved in a large variety of natural processes such as geomorphological,
climatic, ecological, and others (Fernandez & Ceballos 2003). Soil moisture determines
the amount of water available for evapotranspiration, and it controls subsurface flow
and the migration of chemicals toward aquifers. In irrigated areas, it can be used to
assess management practices in terms of technical application efficiency, the
optimization of water resources, and agricultural production. Changes in this parameter-
will all largely depend on field condition, ground cover, seasonal variables and
irrigation scheduling.
99
The interaction between crop yield and water availability and the water holding capacity
of the irrigation area is an important dimension of soil performance. In many locations,
rainfall is not sufficient to meet the needs of the crop, so additional water must be
applied through irrigation systems. The effectiveness of an irrigation system as
measured by the fraction of applied water which is actually utilized by the plant is a
function of the water holding capacity of the soil and the method of water application as
discussed on literature by (Caswell & Zilberman 1986). For example, with traditional
irrigation systems, water applied in a short period of time often results in a nonuniform
application of water. Whereas with modern irrigation systems (such as sprinklers and
microirrigation systems), water is applied continuously over a longer period of time and
pressure is used to distribute water uniformly throughout the field.
3.3.2.3. INFILTRATION RATE (f)
The process of infiltration has been widely studied and represents an important
mechanism for movement of water into the soil under gravity and capillarity forces.
Horton (1933) showed that when the rainfall rate (i) exceeds the infiltration rate (f),
water infiltrates the surface soils at a rate that generally decreases with time. For any
given soil, a limited curve defines the maximum possible rates on infiltration vs. time.
The rate of infiltration depends in a complex way on rainfall intensity, soil type, surface
condition, and vegetal cover (Bedient & Huber 1992).
For excess rate of rainfall, the actual infiltration rate will follow the limiting curve
shown in Figure 3-3, called the infiltration capacity curve of the soil. The capacity
decrease with time and ultimately reaches a constant rate. The decline is caused mainly
by the filling of soil pores with water, thus reducing capillary suction. For instance, it
has been shown through controlled tests that the decline is more rapid and the final
constant rate is lower for clay soils than for sandy soils (Bedient & Huber 1992).
100
Figure 3-2: Horton‟s infiltration concept (adapted from (Bedient & Huber 1992; Horton
1933))
The hydrologic concept of infiltration capacity is empirically based on observations at
ground surface. Horton (1940) suggested the infiltration equation, where rainfall
intensity i > f at all times:
f = fc + (fo – fc) e-kt
(3-5)
where f is infiltration capacity (mm/hr), fo and fc are initial infiltration capacity and final
capacity (mm/hr) respectively, and k is empirical constant (hr-1
). Horton‟s observed
curves can be theoretically predicted given the rainfall intensity, the initial soil moisture
conditions, and a set of unsaturated characteristic curves for the soil as discussed in the
literature by (Rubin & Steinhardt 1963; Rubin, Steinhardt & Reiniger 1964). They
showed that the final infiltration rate is numerically equivalent to the saturated hydraulic
conductivity of the soil (Bedient & Huber 1992).
3.4. TYPE OF IRRIGATION SYSTEMS
3.4.1. SPRINKLER IRRIGATION SYSTEMS
Sprinkler irrigation is one of the most extensive irrigation methods used on sloping
fields. Stationary systems such as „hand-moved‟ laterals are widely used in many
irrigated areas of the world. Uniform water distribution under these systems is necessary
to maximise crop returns and reduce deep percolation (Mateos 1998).
101
Sprinkler systems are generally categorized by how they are used in the field. Usually a
sprinkler system is designed so that only a portion of the field is being irrigated at one
time, if the individual sprinklers are stationary for the duration of the time that they are
in use, the system is called a set system. If the lines are not moved during the irrigation
system is called a solid set system. If the lines are mobile around a central fixed point it
is called a center pivot (Kruse, Bucks & von Bernuth 1990; Smajstrla et al. 1991).
3.4.2.1 FLOPPY SPRINKLER IRRIGATION SYSTEM
The floppy sprinkler system is a new generation irrigation system. It is the only
sprinkler in the world with a built-in flow controller, ensuring highly accurate irrigation
even on slope. A floppy consists of a plastic nipple on which a flexible silicon tube is
mounted. When water is passed through the tube, it snake to and fro while slowly
rotating through 360o, forming uniform droplets similar to raindrops. Each sprinkler is
fitted with a flow controller that regulates flow to 730 liters per hour with pressures
varying from to 2 to 6 bar (give pressure in kPa 200 to 600). The average water
application rate is 5 mm per hour (Lombard 2009).
The design parameters of the overhead cable system sprinkler may affect the uniformity
of water distribution and water application. For example, incorrect spacing and or
orientation of sprinklers, miss-matched standing times, flow hydraulics and nozzle wear
are some of the factors that may affect the efficiency and uniformity of the systems.
Another, The application rates and uniformity of the linear move system and/ or floppy
sprinkler system may also be affected by pressure and wind drift, sprinkler spacing and
the design capacity (such as flow controller) of the irrigation system (Griffiths & Lecler
2001; King et al. 1999).
3.4.2.2 SOLID SET SPRINKLER IRRIGATION SYSTEM
A properly designed solid set sprinkler system has sprinklers permanently installed at a
spacing that results in optimum uniformity. However, wind, incorrect operation
pressure, and component wear or failure can still distort water application patterns and
thus reduce uniformity and water application efficiency (Kruse, Bucks & von Bernuth
1990; Smajstrla et al. 1991).
102
As mentioned by Smajstrla et al. (1991), the solid set sprinkler water application must
overlap by about 50 percent in order to achieve and uniformity of applied water.
Nonuniformity can occur at the end (or edges) of the field area where there is no
overlap.
3.4.2.3 CENTER PIVOT SPRINKLER SYSTEM
The center pivot system involves irrigation of circular field using a series of sprinklers
mounted on a pipe supported by a row of mobile of towers and rotated to distribute
water supplied by a center well. Sprinklers are spaced so that the water is applied at
increasing rates with distance outward along the pipe (Kruse, Bucks & von Bernuth
1990; Smajstrla et al. 2002; Solomon 1990; Spilnter 1976).
The advantages are its automatic operation on large tracts (of land) and ability to irrigate
lightly and frequently. It is also more effective on coarse or sandy soil; moisture in the
root zone is replenished sufficiently to allow cropping (Spilnter 1976). Pasture irrigated
by this system has proved dramatically more productive than the other mobile systems
(Solomon 1990). Fertilizer can be injected into the water supply line to administer
nutrients as needed. Some disadvantages are the substantial energy requirements and
possible depletion of underground water reservoirs where aquifers are the main
localized water source (Kruse, Bucks & von Bernuth 1990; Spilnter 1976).
3.4.2. MICRO IRRIGATION SYSTEMS
Micro irrigation is first invented in Israel during 1960‟s and has spread to many other
parts of the world, especially the USA. These systems seem particularly suited to
conditions in water-scare regions such as western and southern India, Northern China
and Australia. The terms micro irrigation includes several methods or concepts and the
main chief of which are drip/trickle, subsurface, bubbler and spray irrigation (ASAE
1988).
In microirrigation systems, water is delivered through a network of plastic lateral lines
that are fitted with emitters that dissipate the pressure through narrow nozzles or long
flow paths and discharge water at only few liters per hours (actually 1.6 l/hr) to each of
103
field area as discussed on literature by (ASAE 1988; Kruse, Bucks & von Bernuth 1990;
Singh et al. 2000; USDA 1984b).
3.4.2.1 SUBSURFACE DRIP IRRIGATION SYSTEM (SDI)
Subsurface drip irrigation is the application of water below the soil surface through
emitters. The rates of discharge are generally in the same range as those for drip/trickle
irrigation. Subsurface drip systems can be much more efficient and effective than
sprinkler irrigation systems if properly managed since only the root zone of the cropped
area is irrigated (Kruse, Bucks & von Bernuth 1990).
Subsurface drip irrigation systems apply water in individual drops or as a small stream
from individual drip emitters on, near, or below the soil surface. Line source systems
apply water from closed spaced orifices and discharge water at a only few liters per
hour (most drippers discharge at about 1.6 liters per hour (Smajstrla et al. 1991).
Kruse, Bucks and von Bernuth (1990) indicated that subsurface irrigation is becoming
more recognized as an efficient method for applying fertilizer, fungicides, insecticides,
and other chemicals precisely within the crop root zone. Similarly, a recent survey
conducted by the International Commission on Irrigation Drainage (Abbott 1984)
indicated that micro irrigation increased beneficial use of available water, enhanced
plant growth and yield production and improved fertilizer and other chemical
application.
104
3.5. RESULTS AND DISCUSSION
It should be emphasized that the results obtained during the study were under the
particular field and climate conditions at the time of the field experiments and data
collection. The excessive or low pipe pressure during the irrigation operations had a
large impact either on water application rate or distribution of irrigation water. Field
experiments conducted in lesser wind condition may have shown better results. In
general, results should therefore be view in the light that the field works were conducted
in conditions that may not have been optimal. Although, the types of soil, type of crops,
topography and climate condition were the same for all irrigation systems but in actual
fact, all systems won‟t be accommodating the same condition in all. Some irrigation
systems are designed for a particular condition and others are not (Heermann et al.
1990; Kruse, Bucks & von Bernuth 1990; Smajstrla et al. 1991). Any rainfall was
included in calculation of the irrigation water balance.
The result for initial water application efficiency (Ea), soil moisture retention, change in
soil water storage , infiltration rate (f), depletion (DP) and total volume of
infiltration rate are shown in Figure 3-3 to 3-10 and Table 3-2 to 3-5.
A summary of the average initial water application efficiency (Ea) obtained for
pressurized irrigation systems: floppy, solid set and center pivot sprinkler, and
subsurface drip irrigation is shown in Table 3-3. The data illustrates which system
exhibited the highest soil water storage, negligible depletion; low infiltration capacity
and soil moisture retention (i.e. low rate decline accompanied with distribution
uniformity) and had the highest water application efficiency. Apart from the center
pivot sprinkler system that had a poor initial Ea of 59.4%, some of the irrigation systems
also had high average initial Ea. The initial Ea was 76.6% for floppy and 82.8% for solid
set system. The average Ea as suggested by (Baum, Dukes & Miller 2001; Burt et al.
2000; Haman, Smajstrla & Pitts 2005; Smajstrla et al. 1991; Smajstrla et al. 2002) for
floppy, solid set, center pivot and subsurface drip are 70%, 75%, 75% and 85%
respectively. Similarly, Rogers et al. (1997) suggested as 60-80% for floppy, 70-85%
for solid set, 75-90% for center pivot and 75-90% for subsurface drip system. The
implication from the data obtained from the center pivot sprinkler system is that it might
have had lost water due to surface runoff, deep-percolation, high wind drift and
105
evaporation. All these might have occurred due to high application pressures during the
operation of the center pivot systems.
The subsurface drip system evaluated had an excellent soil moisture retention
performance over 0-24 hr drain time after the scheduled irrigation. Over this period, the
soil moisture retention of subsurface drip irrigation system was 30%, which was the
slowest of the soil moisture decline or drain the soil moisture compared to floppy, solid
set and center pivot sprinkler irrigation system. This may be attributed to sub-soil
saturation as the sub-surface irrigation method relies on subsoil application at a depth
not measured by the theta probe. The average peak of soil moisture at 0 hour after
irrigation using subsurface drip was 35.8% and the drain or lower after 24 hour was
28.6% (see Table 3-2).
Relatively, the solid set sprinkler system was the second best performer achieving an
average of 37%. The peak soil moisture content and soil moisture retention at 0 hr and
after 24 hr were 37.4% and 29.7% (Table 3-2) respectively. However, center pivot and
floppy sprinkler system had an average of 50% and 100% soil moisture retention
(floppy sprinkler had the fastest drainage and also exposed to wind draft and percolation
compared to the others systems). The average peak and drain of these irrigation systems
were 33.2% and 25.1% for center pivot system and 33.8% and 14.9% for floppy system
respectively. Thus retention of soil water for these two methods was very high compare
to either subsurface drip or solid set. The soil moisture retention for each system over
the 0-24 hr period is shown in Figure 3-4 to 3-7.
The summary of the change in soil water storage ) obtained for the irrigation
systems are shown in Table 3-3. The S of each system evaluated can be seen in Figure
3-8. From the figure, it can be seen that the system that demonstrated the lowest soil
moisture decline generally had high soil water storage. It can also be seen that some of
the systems that demonstrated the highest soil moisture retention (i.e. poor quality and
drains fast) also had high change in soil water storage. For instance, floppy sprinkler
systems had the fastest drainage in soil moisture retention (almost about 100%) (Figure
3-7) but it had high change in soil water storage of 63%. This shows that the irrigation
area had received only 63% of the average. If the surface runoff and drainage are
106
negligible within the entire system performance of floppy, solid set and center pivot
sprinkler system, then the S shall be increased by 17%, 12% and 30% respectively.
The depletion (DP) soil water for each irrigation systems can be seen in Table 3-3. The
DP of each irrigation system evaluated can be seen in Figure 3-9. From the figure, it can
be seen that the system that display high storage and low soil moisture retention had
almost negligible depletion. While floppy, solid set and center pivot sprinkler had a
depletion of 9.5 mm, 9.3 mm and 11.9 mm below the measured depth (60 mm depth of
soil water) respectively. Center pivot sprinkler irrigation system had the highest
depletion relatively compared to floppy and solid set. This shows that the entire pipeline
rotates about a fixed end through which the water is fed could be probably operated
with an excessive high pressure and exposed for depletion (reach the wilting point
where water cannot recover for the plant use). Pressurized irrigation systems do not
have to be operated with either excessively high or low pressure as suggested by
(Heermann et al. 1990; Kruse, Bucks & von Bernuth 1990; Smajstrla et al. 1991;
Solomon 1988) because water that is applied unevenly or in excess can result in deep-
percolating or runoff (Kruse, Bucks & von Bernuth 1990).
The infiltration rate (mm/hr) over 0-60 mm depth of soil water obtained for the
irrigation systems (floppy, solid set, center pivot and subsurface drip) is shown in Table
3-4. The infiltration rate (f) and the total volume infiltrated (Vf) over 24 hr period of
each system evaluated is shown in Figure 3-9 and Figure 3-10. From the figures and
table, it is demonstrated that the subsurface drip system had the best (i.e. low)
infiltration rate relative to infiltration capacity. The infiltration rate for the subsurface
drip ranged from 0.08 mm/hr to 3.1 mm/hr with an average total volume of infiltrated of
10.5 mm over the scheduled period. While the other systems: floppy, solid set and
center pivot that demonstrated high infiltration rate also had an average f that ranged
from 0.22-8.1 mm/hr, 0.06-6.3 mm/hr and 0.05-6.4 mm/hr with an average Vf of 27.8
mm, 19.3 mm and 19.3 mm respectively. This may imply that these sprinkler irrigation
systems, had lost water due to either evaporation or wind drift.
Finally, The specific gravity and degree of saturation of the soils, gravimetric water
content, void ratio and porosity of the soils and bulk density of the soil at each site were
calculated from soil samples (see Appendix 3-A). Each system had a similar average
107
specific gravity and degree of saturation of 2.7 and 1 respectively. Both solid set
sprinkler and subsurface drip system had a similar bulk density of 1851 kg/m3 while
2037 kg/m3 for floppy and 2047 kg/m
3 for center pivot systems. However, the void ratio
and porosity of soil at each site of each irrigation systems were completely different.
From the Appendix 3-A, it can be seen that center pivot and floppy sprinkler systems
had runoffs and percolations of water during the irrigation cycle.
108
3.6. CONCLUSION
The results showed that the subsurface drip system evaluated had extremely high initial
water application efficiency of 93.3%, high soil water storage of 96.4%, low soil
moisture retention of 30%, low infiltration capacity of 0.08-3.1 mm/hr and non
depletion over the 24 hr schedule period compared to floppy, solid set and center pivot
sprinkler methods. The second best option in system performance was solid set
sprinkler method that had 82.2%, 67.8%, 50%, 0.06-6.3 mm/hr and 9.3 mm
respectively. Floppy and center pivot sprinkler system also had 76.6% and 59.4%, 63%
and 51.1%, 100% and 50%, 0.22-8.1 mm/hr and 0.05-6.4 mm/hr, and 9.5 mm and 11.9
mm in the order given.
The comparison of the different irrigation methods based on the initial water application
efficiency and soil moisture retention revealed that the solid set sprinkler and subsurface
drip irrigation methods were more effective and efficient than the floppy and center
pivot sprinkler irrigation methods. In particular, where water supply is limited, and
labour and water are expensive; the other systems cannot compete with subsurface drip
method (note economics of installation are not considered). It increased beneficial use
of available water and has the potential to enhanced plant growth relative to water
inputs and improves plant yields per kilolitre. Subsurface drip is not generally affected
by weather since water is applied directly to soil. Wind typically has little effect on
water distribution or losses. However, initial costs of these systems are high.
The results demonstrated that by applying subsurface drip irrigation and solid set
sprinkler instead of floppy and center pivot sprinkler methods, the initial water
application efficiency and soil moisture retention has the potential to be improved by
75% in Harvey Irrigation Area. The potential efficiency gains would have significant
benefits to irrigator in the HWIA and may provide for increased production per kilo-
liter of water inputs. However, significant cost will be incurred to change the irrigation
systems and an economic evaluation is required. In addition, these systems may not be
suitable for all farm operations.
109
Figure 3-3: Initial water application efficiency of floppy, solid set and center pivot
sprinkler and subsurface drip irrigation systems
110
Figure 3-4: Change to moisture content (%) during drainage over 0-24 hr for floppy
sprinkler irrigation systems (October 28-30, 2009)
111
Figure 3-5: Change to soil moisture content (%) during drainage over 0-24 hr for solid
set sprinkler irrigation systems (October 28-30, 2009)
112
Figure 3-6: Change to soil moisture content (%) during drainage over 0-24 hr for center
pivot sprinkler irrigation systems (October 28-30, 2009)
113
Figure 3-7: Change to soil moisture content (%) during drainage over 0-24 hr for
subsurface drip micro irrigation system (October 28-30, 2009)
114
Figure 3-8: Soil moisture drainage curves for center pivot, floppy, solid set sprinklers
and subsurface drip irrigation methods
Figure 3-9: Soil depth, measured soil water depth (over 0-60 mm) and depletion of
floppy, solid set, center pivot sprinkler and subsurface drip irrigation systems
115
NB. The Soil depth includes any rainfall and irrigation, and percolation that went below
the measured soil water depth which was below 60 mm depth.
Figure 3-10: Drainage rate vs time of floppy, solid set, center pivot sprinkler and
subsurface drip irrigation system
Table 3-2: Volumetric soil moisture contents (%) vs time (hr) for the different type of
irrigation systems after cessation of irrigation
Time
(hr)
Type of System
Floppy Solid set Center pivot Subsurface drip
0.0 33.82 37.41 33.17 35.82
0.5 29.74 37.37 32.20 35.14
2.5 27.52 36.71 32.12 33.67
4.0 25.05 35.10 27.75 34.40
6.5 21.60 32.36 25.23 31.77
24.0 14.91 25.06 25.06 28.57
Average 25.40 34.80 29.30 33.20
St.Deviation 6.60 3.10 3.70 2.70
116
Table 3-3: Change in soil water storage (ΔS), soil depth and measured soil water (SW)
depth, depletion (DP) and initial water application efficiency (Ea) of irrigation systems
Type of
system
ΔS
(%)
Initial Ea
(%)
soil depth
(mm)
Soil water
measure depth
(mm)
Depletion
(mm)
Floppy 63.0 76.6 69.5 60.0 9.5
Solid set 67.8 82.8 69.3 60.0 9.3
Center
pivot
51.1 59.4 71.9 60.0 11.9
Subsurface
drip
96.4 93.3 38.0 60.0 0.0
Table 3-4: Drainage rate (mm/hr) of different type of irrigation systems
Time
(hr)
Type of System
Floppy Solid set Center pivot Subsurface drip
0 8.10 6.30 6.40 3.10
5 1.59 1.14 1.15 0.60
10 0.46 0.25 0.24 0.17
15 0.26 0.09 0.08 0.10
20 0.23 0.07 0.06 0.08
24 0.22 0.06 0.05 0.08
Average 1.81 1.32 1.33 0.69
St.Deviation 3.13 2.48 2.52 1.20
Table 3-5: Daily weather observation around the irrigation area on Harvey Station from
October 28 – 30, 2009
Day Temperature (oc) Rainfall Evaporation Wind Humidity Cloud
Min Max (mm) (mm) Km (h) (%) (Eighths)
28 14.0 20.5 0.0 1.8 x 0.8* 19.0 62.0 8.0
29 7.5 19.0 7.8 2.2 x 0.8* 4.5 60.0 7.0
30 6.8 23.0 0.0 2.6 x 0.8* 9.0 58.0 6.0
Av 9.4 20.8 2.6 1.76 10.8 60.0 7.0
(0.8*) The adjustment factor which is so called pan coefficient
117
APPENDIX 3-A: COMPOSITION OF SOIL SAMPLES FROM EACH IRRIGATION SYSTEM IN THE HARVEY IRRIGATION
AREA
Table 3A-1: Soil samples of floppy sprinkler systems before irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw)
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
23.75 20.66 3.09 14.96 2.45 2.71 3.09-6
1 3.09-6
7.65-6
0.4 29 2221 1936
18.16 15.48 2.68 17.31 0.90 2.70 2.68-6
1 2.68-6
5.73-6
0.5 33 2133 1800
33.75 28.82 4.91 17.04 3.90 2.69 4.91-6
1 4.91-6
2.88-5
0.2 17 2408 2241
37.20 31.07 6.13 19.73 4.87 2.71 6.13-6
1 6.13-6
3.11-5
0.2 17 2425 2258
26.52 22.95 3.57 15.56 2.83 2.69 3.57-6
1 3.57-6
2.30-5
0.2 17 2408 2242
32.20 26.82 5.38 20.06 4.27 2.70 5.38-6
1 5.38-6
2.68-5
0.3 23 2307 2077
23.88 20.50 3.38 16.38 2.68 2.70 3.38-6
1 3.38-6
2.05-5
0.2 17 2416 2250
where W = total weight (g); Ws = weight of solid (g); Ww = weight of water (g); = gravimetric water content ( =Ww/Ws, %); h = depth of water
(mm); Gs = specific gravity of solid (Gs = s/w); Vw = volume of water (m3/m
2); Sr = degree of saturation; Vv = volume of void (Vv = Vw/Sr); Vs =
volume of solid (m3); e = void ratio (e = Vv/Vs); n= porosity (n = e/e+1, %); b = bulk unit of weight (b =w (Gs+eSr/1+e), kg/m
3); d = dry unit
weigh (d = wGs/(1+e)), kg/m3)
118
Table 3A-2: Soil samples of floppy sprinkler systems after irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw)
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
43.52 36.38 7.14 20.59 5.67 2.69 7.14-6
1 7.14-6
1.35-5
0.5 33 2127 1793
48.32 40.47 7.85 19.40 6.23 2.70 7.85-6
1 7.85-6
1.50-5
0.5 33 2133 1800
51.74 42.03 9.71 23.10 7.71 2.69 9.71-6
1 9.71-6
1.56-5
0.7 41 1994 1582
47.88 39.27 8.61 21.93 6.83 2.71 8.61-6
1 8.61-6
1.45-5
0.6 33 2069 1694
46.94 37.72 9.22 24.44 7.32 2.69 9.22-6
1 9.22-6
1.40-5
0.7 41 1994 1582
38.69 30.21 8.48 28.07 6.73 2.70 8.48-6
1 8.48-6
1.12-5
0.8 44 1944 1500
48.66 38.39 10.27 26.75 8.15 2.70 1.03-5
1 1.03-5
1.42-5
0.7 41 2000 1588
Soil composition of each irrigation system in the Harvey Irrigation Area
119
Table 3A-3: Soil samples of solid set sprinkler systems before irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h (mm) Gs
(γs/γw)
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
29.76 24.53 5.23 21.32 4.15 2.69 5.23-6
0.7 7.47-6
9.09-6
0.8 44 1805 1495
34.31 27.18 7.13 26.23 5.66 2.69 7.13-6
0.7 1.02-5
1.01-5
1.0 50 1695 1345
35.61 28.12 7.49 26.64 5.94 2.70 7.49-6
0.7 1.07-5
1.04-5
1.0 50 1700 1350
37.57 32.26 5.31 16.46 4.21 2.71 5.31-6
0.7 7.59-6
1.19-5
0.6 38 1956 1694
28.66 24.17 4.49 18.58 3.56 2.70 4.49-6
0.7 6.41-6
8.95-6
0.7 41 1876 1588
39.18 33.81 5.37 15.88 4.26 2.70 5.37-6
0.7 7.67-6
1.25-6
0.6 38 1950 1688
33.68 29.90 3.78 12.64 3.00 2.69 3.78-6
0.7 5.40-6
5.40-5
0.5 33 2027 1793
Table 3A-4: Soil samples of solid set sprinkler systems after irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw )
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
24.92 20.12 4.80 23.86 3.81 2.70 4.80-6
1 4.80-6
7.45-6
0.6 38 2063 1688
38.48 27.12 11.36 41.89 9.02 2.72 1.14-5
1 1.14-5
1.00-5
1.0 50 1853 1355
41.21 32.56 8.68 26.57 6.87 2.69 8.65-6
1 8.65-6
1.21-5
0.7 41 1994 1582
34.73 28.25 6.48 22.94 5.14 2.69 6.48-6
1 6.48-6
1.05-5
0.6 38 2056 1681
41.86 33.55 8.31 24.77 6.60 2.71 8.31-6
1 8.31-6
1.24-6
0.7 41 2006 1594
41.88 32.03 9.85 30.75 7.82 2.69 9.85-6
1 9.85-6
1.19-6
0.8 44 1939 1494
40.06 37.22 2.48 7.63 2.23 2.70 2.84-6
1 2.84-6
1.38-5
0.2 17 2416 2250
120
Table 3A-5: Soil samples of center pivot sprinkler systems before irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw )
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
34.32 20.66 13.66 66.12 10.84 2.71 1.37-5
1 1.37-5
7.65-6
2.0 67 1565 901
37.48 25.14 12.34 49.09 9.79 2.69 1.23-5
1 1.23-5
9.31-6
1.0 50 1851 1349
32.68 25.12 7.56 30.10 6.00 2.70 7.56-6
1 7.56-6
9.30-6
0.8 44 1944 1500
33.68 23.78 9.90 41.63 7.86 2.70 9.90-6
1 9.90-6
8.81-6
1.0 50 1850 1350
31.00 23.15 9.92 42.85 7.78 2.70 9.92-6
1 9.92-6
8.57-6
1.0 50 1850 1350
20.99 17.31 5.75 33.22 4.56 2.70 5.75-6
1 5.75-6
6.41-6
0.9 47 1895 1421
20.92 18.43 4.51 24.47 3.58 2.70 4.51-6
1 4.51-6
6.83-6
0.7 41 2000 1588
Table 3A-6: Soil samples of center pivot sprinkler systems after irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw )
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
36.80 21.74 15.06 62.27 11.95 2.71 1.51-5
1 1.51-5
8.05-6
2 67 1566 901
25.73 17.68 8.05 45.53 6.39 2.70 8.06-6
1 8.06-6
6.55-6
1 50 1850 1350
23.59 16.58 7.01 42.28 5.56 2.70 7.01-6
1 7.01-6
6.14-6
1 50 1850 1350
23.84 13.10 10.74 81.89 8.52 2.69 1.07-5
1 1.07-5
4.85-6
2 67 1569 900
26.23 17.59 10.80 61.40 8.57 2.70 1.08-5
1 1.08-5
6.51-6
2 67 1567 900
29.45 21.98 9.54 43.62 7.57 2.73 9.54-6
1 9.54-6
8.14-6
1 50 1847 1352
34.92 24.38 12.61 51.72 10.00 2.69 1.26-5
1 1.26-5
9.03-6
1 50 1846 1346
121
Table 3A-7: Soil samples of subsurface drip systems before irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw )
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
45.46 34.48 10.35 31.81 8.71 2.70 1.10-5
1 1.10-5
1.28-5
0.9 47 1890 1417
46.98 34.92 12.06 34.54 9.57 2.71 1.21-5
1 1.21-5
1.29-5
0.9 47 1894 1422
47.02 35.11 11.91 33.92 9.45 2.70 1.19-5
1 1.19-5
1.30-5
0.9 49 1896 1422
44.01 31.12 13.49 43.35 10.71 2.71 1.35-5
1 1.35-5
1.15-5
1.0 50 1854 1354
50.01 36.08 13.93 38.61 11.06 2.69 1.39-5
1 1.39-5
1.34-5
1.0 50 1849 1348
47.18 36.23 10.95 30.22 8.69 2.72 1.10-5
1 1.10-5
1.34-5
0.8 44 1947 1504
46.51 33.89 12.62 37.24 10.02 2.69 1.26-5
1 1.26-5
1.26-5
1.0 50 1848 1347
Table 3A-8: Soil samples of subsurface drip systems after irrigation cycle
W
(g)
Ws
(g)
Ww
(g)
(Ww/Ws)
(%)
h
(mm)
Gs
(γs/γw )
Vw
(m3/m
2)
Sr Vv
(Vw/Sr)
Vs
(m3)
e
(Vv/Vs)
n
(e/e+1)
(%)
γb
(γb=γw
((Gs+eSr))/(1+e))
(kg/m3)
γd
(γd=γwGs/(1+e))
(kg/m3)
51.45 39.33 12.12 30.82 9.62 2.69 1.21-5
1 1.21-5
1.46-5
0.9 47 1893 1418
49.82 36.16 13.66 37.78 10.84 2.71 1.37-5
1 1.37-5
1.34-5
1.0 50 1850 1351
52.08 37.62 14.28 37.96 11.33 2.71 1.43-5
1 1.43-5
1.39-5
1.0 50 1852 1353
46.98 32.52 14.46 44.46 11.48 2.72 1.45-5
1 1.45-5
1.20-5
1.0 50 1855 1356
50.98 37.17 13.81 37.15 10.96 2.69 1.38-5
1 1.38-5
1.38-5
1.0 50 1846 1346
49.70 36.55 13.15 35.98 10.44 2.72 1.32-5
1 1.32-5
1.35-5
1.0 50 1853 1355
50.76 36.83 13.93 37.82 11.06 2.70 1.39-5
1 1.39-5
1.36-5
1.0 50 1854 1353
122
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128
CHAPTER 4: DISCUSSION, CONCLUSIONS AND FUTURE WORK
The focus of this thesis was to compare, evaluate and improve the understanding of
efficiency and uniformity of different irrigation systems for sustainable management of
water in Harvey irrigation area. The key feature of the comparison and evaluation in this
thesis was the ability to use irrigation performance measures: efficiency and uniformity,
and comparison of irrigation methods based upon initial water application efficiency
and soil moisture retention so that irrigation methods would be effective and efficient in
the entire system performance. For an irrigation system to function optimally, the
utilization and measurement of irrigation performance measures are important because
the efficiency of irrigation systems depend on the parameters measured. If these
measures are not included for the analysis of irrigation methods, then the comparison or
evaluation of irrigation systems is ineffective or inefficient. This thesis has given insight
into four main research questions.
Comparing the different types of irrigation systems based on the irrigation performance
measures such as water storage efficiency, water conveyance efficiency, water
application efficiency, irrigation efficiency, overall irrigation efficiency, effective
irrigation efficiency, water distribution efficiency, distribution uniformity, coefficient of
uniformity and coefficient of variation equations demonstrated that the methods mainly
differ in how they behave in irrigation efficiency definitions. The efficiency
performance criteria were assessed before and after irrigation cycles, and how uniformly
water was distributed on the irrigation area was determined. Comparing these irrigation
methods proved that the subsurface drip irrigation system was better able to maintain
the integrity of irrigation systems when using all the irrigation performance measures.
Therefore, micro (subsurface drip) irrigation system can provide a key solution to water
losses in the Harvey irrigation area depending on the economics associated with this
systems. However, the efficiency measure applied did demonstrate that two different
methods Center Pivot and Solid Set have some advantage, as there efficiency as
determined by the methods applied in Chapter 2 and Chapter 3 varied.
This comparison of irrigation methods using the two methods has helped alleviate, to
some degree, a long-standing debate within the agricultural sector community. In the
past, different researchers have given different definitions for the same efficiency term,
129
and for terms having the same name that has lead to confusion because the effectiveness
of an irrigation system cannot be described with a single efficiency term (Jensen 2007;
Kruse 1978; Kruse, Bucks & von Bernuth 1990). For over four decades, the
performance indicators, usually called efficiencies for intuitive appeal and have been
defined differently to account for one factor or another, or in application to one or
another irrigation method. Often given the same names, say, “irrigation efficiency”,
they meant different things to different segments of the profession, and this has lead to
confusion (Burt et al. 1997; Edkin 2006; Haman, Smajstrla & Pitts 1996; Hart,
Skogerboe & Peri 1979; Jensen 2007; Kruse, Bucks & von Bernuth 1990; Kruse &
Heermann 1977; Rogers et al. 1997; Smajstrla et al. 1991).
Needless to say, arguments based on different numerical values for terms having the
same name lead to confusion. According to Burt et al. (1997), another component of
goodness or indicator of performance, was recognized, namely, “uniformity”, reflecting
the need for equal treatment of plants in various portions of a field. The two terms were
sometimes used interchangeably, again leading to confusion within the literature as to
the actual perameter being measured or assessed. It should be acknowledged that there
are obvious situations where the choice between irrigation performance measures and
comparison of irrigation methods are clear. In this case, the surface drip irrigation
systems has a clear advantage over the other irrigation methods such as floppy, solid set
and center pivot irrigation systems.
The pattern of efficiency of different irrigation systems for sustainable management of
water and nutrient flows were compared and analyzed using the irrigation performance
measures in Chapter 2. This work was unique because it relied upon the irrigation
efficiency definitions to represent the efficiency and uniformity of an irrigation system
as standard benchmark for the comparison of irrigation system efficiency. For example,
a major contribution to bring order to the profusion of terms and concepts was provided
by the On-Farm Irrigation Committee of the Irrigation and Drainage Division,
American Society of Civil Engineers (ASCE 1978) in a concise paper of defining
irrigation efficiency and uniformity. The results shown have extended the knowledge
concerning the efficiency and uniformity of an irrigation method. In all irrigation
efficiency definitions, subsurface drip irrigation system outperformed the other systems.
The second best, in whole system performance (as applied in Chapter 3), was solid set
130
sprinkler system, however in terms efficiency (as determined in Chapter 2) the Center
Pivot system was superior. It is very important as a first step to demonstrate the ability
of comparison of irrigation performance to produce independent results in order to
resolve water losses problems.
There are obvious possibilities to extend the work presented in Chapter 2. For example,
there are other issues not addressed in this thesis such as the design, installation and
maintenance, and management of irrigation systems. The irrigation systems efficiency
is dependent these components to maintain the operational efficiency required as
described by (Baum, Dukes & Miller 2001; Baum, Dukes & Miller 2002; Baum, Dukes
& Miller 2003). They discussed that a properly designed and maintained system can be
highly inefficient due to mismanagement, and effective management is also difficult if a
system is not designed properly. Similarly, Burt et al. (1997) also described the
irrigation systems efficiency that depends on management and design. In addition, the
authors discussed the various irrigation system efficiency definitions and distribution
uniformity definitions (ASAE 1996). This is important point for further analysis since
irrigation system efficiency also depend on designs, installation and maintenance.
The comparison of irrigation methods based upon initial water application efficiency
and soil moisture retention was presented in Chapter 3. The results showed that the
subsurface drip system again performed significantly better than the other systems:
performing well in water application efficiency, with almost no soil moisture depletion
during the 24 hr period. Solid set sprinkler system was the second best option in the
entire system performance. However, floppy and center pivot sprinkler systems were
poor in any system performance. The reasons for this occurrence were over-irrigation
(means excess water applied as result of continuous operation), highest ET (which
means added evaporation opportunity with sprinklers) and wind drift (i.e. exposed the
system to evaporation). Poor maintenance and management of two of these irrigation
systems might have made them more inefficient or ineffective in the assessment of
system performance.
These poor performances had created runoff, deep percolation and excessive soil water
depletion (i.e. limited water availability for plant use). Besides, they reduced efficiency
and system performance of the irrigation methods. Incorrect timing or application
131
depths of irrigations can reduce the irrigation efficiency (Heermann et al. 1990;
Heermann, Haise & Mickelson 1976; Heermann, Buchleiter & Dukes 1984; Fereres et
al. 1981). In general, the comparison of the different types of irrigation techniques
revealed that the solid set and subsurface drip irrigation methods were more effective
and efficient over all, than the floppy and center pivot sprinkler irrigation methods for
improving yield productivity in the Harvey irrigation area.
There are obvious possibilities to extend the work presented in Chapter 3. For instance,
there is one further issue not addressed in detail in this thesis such as irrigation
scheduling controls and management techniques applied to the system. Irrigation
systems also need irrigation scheduling controls and techniques so that the irrigation
methods shall deliver water to the plant in a timely fashion and amount of water.
Heermann et al. (1990) summarized that „irrigation scheduling”, is a key element of
proper management and the accurate forecasting of water application (in both timing
and amount) for optimal crop production. Intelligent scheduling knowledge enables the
estimation of the earliest date or time at which the next irrigation should be applied for
efficient irrigation with the particular system as described by (Heermann et al. 1990).
Irrigation scheduling also allows the irrigator to develop a strategy for using the rainfall
expected to occur before the next irrigation. An irrigation system can only be efficient
and effective when it is both scheduled properly and operated to apply the desired
amount of water efficiently (Heermann, Haise & Mickelson 1976; Heermann et al.
1990). A breakdown in either of these can result in poor management and water losses.
According to Heermann‟s, the tools and techniques available for improving irrigation
scheduling is using water budgets, for example, an irrigation scheduling program using
meteorological data to calculate water use and maintain a water budget was developed
by (Jensen 1969; Jensen & Heermann 1970; Jensen, Robb & Franzoy 1970; Jensen,
Wright & Pratt 1971), Computers, an irrigation scheduling models for operation on
centralized main-frame computers was developed by (Jensen 1969; Jensen & Heermann
1970; Jensen, Wright & Pratt 1971) and Field-data Requirements, an irrigation
scheduling program using field-data requirements to estimate ET, soil water status and
crop production was also developed by (Jensen & Haise 1963; Penman 1948). Thus,
this is also important point for further analysis since efficient irrigation systems requires
132
appropriate irrigation scheduling controls and techniques for efficient and effective use
of water in the irrigation area.
This thesis has evaluated the irrigation systems in used in the Harvey Irrigation Area
(HIA) and demonstrated that the subsurface drip and solid set irrigation methods are
more potentially efficient than floppy and center pivot sprinkler irrigation systems. The
basic irrigation performance measures and comparison of irrigation methods used in the
study have provided a significant and novel contribution to understanding of irrigation
systems efficiency. The study has suggested potential key solutions for the management
of water losses from an irrigation system. It is hoped that the contribution to
understanding from this thesis shall be integrated into future body of knowledge so that
some of the problems associated with poor understanding of efficiency of irrigation
systems in the agricultural sector at the present time can be alleviated.
133
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