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Subsurface irrigation of turf: An examination of current
methods
Schmoll, Timothy Jon, M.L.Arch.
The University of Arizona, 1991
UMI
300 N. Zeeb Rd.
Ann Arbor, MI 48106
Subsurface Irrigation of Turf An Examination of Current Methods
by
TIMOTHY JON SCHMOLL
A Thesis Submitted to the Faculty of the
SCHOOL OF RENEWABLE NATUREL RESOURCES
In Partial Fulfillment of the Requirements
For the Degree of
MASTER OF LANDSCAPE ARCHITECTURE
In the Graduate College
THE UNIVERSITY OF ARIZONA
19 9 1
2
STATEMENT BY AUTHOR
This thesis has been submitted in partial fulfillment of requirements for
an advanced degree at the University of Arizona and is deposited in the University
Library to be made available to borrowers under rules of the Library.
Brief quotations from this thesis are allowable without special
permission, provided that accurate acknowledgement of source is made. Requests for
permission for extended quotation from or reproduction of this manuscript in whole or
in part may be granted by the head of the major department or the Dean of the
Graduate College when in his or her judgement the proposed use of the material is in
the interests of scholarship. In all other instances, however, permission must be
obtained from the author.
SIGNED:
APPROVAL BY DEGREE COMMITTEE
lichael T. Deeter
Professor of
Landscape Architecture
/Date'
Dr. Donovan C. Wilkin
Professor of
Landscape Architecture
Dr. James Sell
Assistant Professor of
Geography
mtmi
Date
APPROVAL BY THESIS DIRECTOR
This thesis has been approve^ on the date shown below:
Thqrfs Director
Michael'T. Deeter
4L
/ Daj^
3
ACKNOWLEDGEMENT
As you consider the sentiments expressed in this acknowledgement, remember that limitations
of the written or spoken word are great.
I can't come close to expressing the depth or intensity of feelings of gratitude that I feel
towards you, mother, for believing that I could accomplish my goals. You never gave up and your
steadfastness kept me from giving up many times. I would have not even started the process that lead
to this accomplishment if it were not for you.
Professor Mike Deeter, thank you for assuring me that 1 could do it and somehow making me
believe it. Your confidence in my abilities relieved my personal pressure and actually made the project
fun!
A further expression of gratitude must be made to the other members of my graduate
committee. Dr. Donovan Wilkin, Professor of Landscape Architecture and Dr. James Sell, Assistant
Professor of Geography. Gentlemen, your suggestions, comments and critiques proved invaluable in
keeping me on track during the rocky start and preparation of this study.
4
TABLE OF CONTENTS
LIST OF FIGURES
6
LIST OF TABLES
8
ABSTRACT
9
CHAPTER 1
INTRODUCTION
Scarcity of Potable Water
Water Awareness in the Southwest
Relevance of Turf to the Arid Southwest
CHAPTER 2
IRRIGATION
Crop Irrigation
Landscape Irrigation
Micro-Irrigation
Characteristics of Micro-irrigation
Benefits and Disadvantages of Micro-Irrigation
CHAPTER 3
PROBLEM STATEMENT
Realization of Potential Advantages
Need for Further Research
Objectives
CHAPTER 4
METHODOLOGY
Literature Review
Case Studies
CHAPTER 5
LITERATURE REVIEW
Academic Studies
Summary
Popular Journal Articles
Summary
10
10
12
13
16
16
17
18
19
20
24
24
25
26
n
27
28
29
30
34
37
39
5
Technical Literature
Summary
Conclusions
CHAPTER 6
CASE STUDIES IN MICRO-IRRIGATION OF TURF
Residential Site
Overview
Design
Installation
Scheduling
Maintenance
Evaluation
Governmental Site
Overview
Design
Installation
Scheduling
Maintenance
Evaluation
Conclusions
CHAPTER 7
SUMMARY
Objective 1
Academic Studies
Popular Journal Articles
Technical Literature
Summary
Objective 2
Objective 3
Objective 4
Questions for the Designer
Questions for the User
Other Recommendations
APPENDICES
Appendix A Glossary
Appendix B Vita
REFERENCES
42
56
58
6i
61
61
62
64
64
64
65
65
65
67
68
70
70
71
72
74
74
75
75
75
76
79
81
84
85
85
86
88
89
92
93
6
LIST OF FIGURES
1
Effect of Water Mining on Groundwater Table
14
2
Water Movement in Various Soil Classes
46
3
Chemical Injection Devices
47
4
Cut Away View of Ram Tubing
48
5
Ram Tubing Depth and Connection to PVC Lateral
51
6
Ram Tubing Layout for Turf
52
7
Automatic Line Flushing Valve
52
8
Baseball Field Layout
53
9
Component Layout from Water Source to Irrigation Zones
54
10
Emitter Tubing Layout Showing Lateral and Flush Valves
55
11
Valve Manifold Assembly
56
12
Vibrating Plow Attachment
61
13
Residential Site Front Yard
62
14
Residential Site Rear Yard
62
15
Residential Site Valve Manifold
63
16
Residential Site Soil Wetted Pattern
64
17
Governmental Site Layout
66
7
18
Governmental Site Equipment Enclosure
67
19
Governmental Site Backflow Prevention Device
68
20
Governmental Site Screen Filter
68
21
Governmental Site Master Valve
69
22
Governmental Site Chemical Injector
69
23
Governmental Site Showing Vibrating Plow
70
24
Governmental Site Showing Emitter Lines Following Contours
70
25
Governmental Site Showing Accuracy of Trenching
71
8
LIST OF TABLES
1
Sources of Water on Earth
11
2
Design Summary, Jorgenson & Solomon
33
3
Design Summary, Academic Studies
34
4
Design Summary of Popular Journal Articles
40
5
Potential Evapotranspiration Loss by Climate
49
6
Time Required to Apply One Inch of Water with .6 GPH Emitters
49
7
Time Required to Apply One Inch of Water with .9 GPH Emitters
50
8
Comparison of Irrigation System Costs
53
9
Technical Literature Tubing Spacing and Depth Summary
57
10
All Cited Literature - Data Summary
58
11
Emitter Spacing Value Guide
83
12
Emitter Spacing selector
84
9
ABSTRACT
This study examines literature on subsurface irrigation of turf using published and unpublished
sources to determine its relevance for the designer of irrigation systems. It looks at two installed sites
to determine current industry practices and then develops a model to assist the designer of these
systems. Finally areas in need of further research and technical development are suggested.
Literature is not readily available to the designer and it is sometimes contradictory. Case
studies show that subsurface irrigation is an effective method of irrigating turf, especially in arid parts of
the world. A model to select tubing and emitter spacing is developed by summarizing existing literature
and case studies.
Virtually all areas of design, installation and management need further research. Two primary
areas that need further investigation are specific design issues and benefits to the end user such as cost,
water savings and maintenance procedures.
10
INTRODUCTION
Scarcity of Potable Water
"it is virtually beyond the comprehension of today's
American to realize it is possible that some day water may not flow
from the tap as simply as it does now (Oklahoma Water Resources
Board,
1973, p. 7)."
For too long, Americans have taken for granted that water is an inexhaustible commodity. It
has only been in the last decade or so that they, as a whole, have begun to realize that the natural
resources of the earth are not infinite. Finally attention is being focused on ways to conserve this finite
supply of clean water.
Fresh water is derived from snow or rainfall runoff. So, it follows that these supplies are
linked to the weather. Seasonal variations in precipitation make it difficult to estimate future supplies.
If the use of present water supplies is limited to ensure future supplies, then some water must go
unused. If too much available water is used, the risk of future shortages is high. "The problem facing
the world today is that because of the variability of flow, some water can never be put to use (Leopold,
1974, p. 132)." Additionally, there is a spatial variability to the supply of water. Majopr world regions
are characterised by water deficites, while other regions suffer from extreme over supply.
Table 1 shows that extremely small percentages of unfrozen fresh water, which could
potentially be available for use by humans, are contained in lakes, rivers, ground water and the
atmosphere.
11
WATER ON EARTH
LOCATION
Percentage
SURFACE WATER
Fresh Water Lakes
Saline lakes and inland seas
Average in stream channels
0.009
0.008
0.0001
SUBSURFACE WATER
Water in unsaturated aerated zone
(includes soil moisture)
Ground water within depth of 1/2 mile
Ground water, deep lying
0.005
0.30
0.3!
OTHER WATER LOCATIONS
Ice caps and glaciers
Atmosphere (at sea level)
World ocean
2.15
0.001
97.20
TOTALS (rounded)
100.00
Table 1. Sources of Water on Earth (Leopold, 1974, p. 120).
Ever increasing quantities of water are required for irrigation of newly developed farm lands to
support a growing population. The United States receives an average of approximately 30 inches
precipitation annually. Three quarters of this is returned to the atmosphere as evaporation and
transpiration. The balance infiltrates to the water table or runs off to the oceans. There are
approximately 7,500 gallons of water per day available for use by every person in the United States. Of
this available water, 1500 gallons is actually used (Leopold, 1974, p. 133).
Since the distribution of irrigation water is normally uneven, its efficient use is not only
desirable, but economically imperative. Unfortunately, many present methods of irrigation are not
especially efficient. For this reason, a great deal of research is being conducted in methods of
increasing irrigation efficiencies.
The United States has an abundant and generally dependable supply of fresh water. But major
problems are associated with unequal distribution of precipitation. The western United States receives
only one-third of the nation's average rainfall, yet uses enormous quantities of water, especially for
12
irrigation. This inequitable distribution and location of water supplies, distant from where they are
needed, has given rise to social, economic and legal problems, which will become more complicated and
more critical in the coming decades. Each year, approximately six times the annual flow of the
Mississippi river is used to irrigate the world's crops. By 1990, 230 million hectares of land were
irrigated to produce crops. Each year farming accounts for approximately 70 percent of global water
use (Postel 1990, p. 39).
Certainly water will cost much more in the future. And as the pressures resulting from
increasing population and expanding technological and agricultural needs become more intense, the need
to conserve and wisely use the nation's supplies of fresh water will increase.
Water Awareness in the Southwest
Throughout the Western United States, water is an important resource upon which are placed
multiple demands. One major demand is agricultural use, another is industrial and a third, rapidly
growing demand, is urban. In the low deserts of Arizona, urban growth has been tremendous.
Aggravating this problem are the large areas of turf associated with major income sources such as
tourism, golf and the resort industry (Kneebone, 1979). One area in which people have been most
destructive to the Southwest's environment has to do with overusing the natural water supply. The
results can be seen in water depletion and shortages, as well as destruction of the desert ecosystem.
Rapid population growth and concentrated development in many areas are placing critical demands on
the water supply (Paylore, 1976, p. 4).
The worst nightmare the green industry could have is now coming true in Santa Barbara, Ca.,
where lawn irrigation has been banned by the City Council because of a prolonged drought. In fact,
golf courses were allowed to irrigate greens and tees only until a reclaimed water system could be
installed. California's El Dorado County, Southwest of Lake Tahoe, instituted a moratorium on all new
water connections and landscaping of new homes until the end of the drought. In effect all construction
13
of new buildings in El Dorado County has been stopped (Santa Barbara Bans Lawn Irrigation, 1990,
p. 124).
For several decades, water use in Arizona has exceeded its renewable supply (Steiner,
1985, p. 1). Groundwater supplies, which comprise the major water source in many areas, are being
depleted at an alarming rate. In some of the arid parts of the western United States, water is being
pumped that fell as rain during the Ice Age, at least 10,000 years ago (Leopold, 1974, p. 28). Figure 1
shows the effect of this groundwater mining on the water table. In forty years, the water table depletion
in some areas has almost doubled. The direct effect of this lowering of the water table is an increase in
the cost of the pumped water.
The supply of water available for landscape irrigation is limited and becoming more so each
year. Some Southwestern states are now passing regulations on water use in landscaping (Hurst, 1990,
p. 94). Arizona, recently adopted a comprehensive Groundwater Code. It establishes Active
Management Areas that contain 80 percent of the population of the state. Its goal is to eliminate
groundwater depletion by the year 2050. To accomplish this goal, all water users must participate in
strict conservation measures (Steiner, 1985, p. 1).
Relevance of Turf to the Arid Southwest
A landscape style common to the Southwest contains large canopy trees to shade the residence,
with turf to reduce reflected heat and provide a softer, more usable ground plane. As previously noted,
this type of landscape must be supported by supplemental irrigation. Typically, the additional irrigation
is supplied by a traditional spray irrigation system, an inefficient method of irrigation in hot, arid
climates. Using high pressure sprinklers under hot windy conditions wastes large quantities of water
due to distortion of the spray pattern and evaporation of the fine water droplets in the air (Solomon,
1990, p. 12).
14
So, why bother with turf and lushly planted landscapes?
From a purely water conservation point of view, a minimalist
approach to landscaping would seem appropriate. Aside from
personal preferences, which are a matter of style and could
probably be affected by education if necessary, there are some
strong economic, and ecological, reasons for a more lush
landscape style.
Research at the University of Arizona has shown that the
total electrical usage for a residence can be reduced through the
250
use of effective landscape planting practices. Total electrical
usage for two-week long periods (one in August and one in
October) was similar for turf and shade models, and 7 - 10% more
for the model surrounded by only rock. Results indicated that
cooling energy savings in October would be greater than increased
water costs compared to the unirrigated rock model for all
40 YEARS DEPLETION
Figure 1. Effect of Water Mining
on the Groundwater Table
(Johnson, 1985, p. 5).
landscape treatments with vegetation (McPherson. 1988, p. 2).
Commercial applications can also make a strong case for lush landscapes from a marketing
point of view. In 1988, there were 191 golf facilities in Arizona. They provided an economic benefit
to the state in the form of an annual revenue of $270 million and as annual payroll of $110 million paid
to 8,000 employees and. These direct benefits do not include substantial, and possibly greater benefits
from the tourism industry supported by destination resorts (Barkley, 1989, p. 9).
In Scottsdale, Arizona, the Princess Hotel makes the most of its water supply without
sacrificing an atmosphere of glamour and luxury. In addition to trees, shrubs and drought tolerant
ground covers, the landscape includes 85,000 square feet of lawn. Because of water restrictions in
Arizona, the irrigation system will eventually be converted to tertiary effluent water (Water-Thrifty
Landscape Blends Turf and Desert, 1988, p. 127).
Any method or technique that could increase the effectiveness of the limited water supply
should be welcome. Government agencies, as already noted, will continue to legislate the amount of
water available to the landscape (Hurst, 1990, p. 94). There will be less water available for turf
irrigation in the future, so the "green industry" must take the lead and get its house in order. Subsurface
drip irrigation of turf is one such method that potentially offers a substantial savings in water use.
16
IRRIGATION
Crop Irrigation
Historical and archaeological findings show that crop irrigation has played a major role in the
development of ancient civilizations. The oldest civilizations with irrigation developed along the Nile,
Tigris, Euphrates, Indus, and Yellow Rivers (Nakayama 1986, p. 1). Gravity irrigation began along the
Nile about 6,000 B.C.
These crude systems were based on overflow of flood waters into valley
bottoms and delta lands. By 3,500 B.C., the practice of "bailing up," drawing water from wells using a
counterbalanced pole and dumping it into irrigation canals, was in use (Irrigation History: From Buckets
and Crossbeams to Computers, 1989, p. 94).
The ancient Chinese tried to use bamboo to transport water from streams to crop areas. They
were unsuccessful because they couldn't solve the problem of leakage. Since 800 A.D., and continuing
to the present, sophisticated irrigation practices have been carried on by Pueblo Indians in New Mexico,
Colorado and Arizona. In 1847, Brigham Young and the Mormon settlement in Utah built irrigation
systems in the American south west. The first federal irrigation project was begun in 1868, to irrigate
land on the Mojave Indian reservation in Arizona. By 1948, more than 30 million acres of land were
under public or private irrigation in the United States (Irrigation History: From Buckets and Crossbeams
to Computers, 1989, p. 96).
A surge in irrigated crop lands has taken place since 1950. Today approximately 625 million
hectares of cropland are under irrigation. And one third of the global harvest comes from the 17
percent of the world's cropland that is irrigated (Postel, 1990, p. 39).
Landscape Irrigation
While ancient civilizations were built on flood irrigation, it is not very practical. Efficient
irrigation systems using pipes are more serviceable for larger systems. In 1897, "Farmer Skinner," as he
is remembered, invented the first sprinkler irrigation system.
He borrowed a drill from his local
dentist, took a length of galvanized steel pipe, and made holes in the pipe at three-foot intervals.
Resting the pipe six feet overhead in a Y-shaped piece of pipe set in the ground, Skinner attached a
garden hose and turned 011 the faucet. The crude device worked (Irrigation History: From Buckets and
Crossbeams to Computers. 1989, p. 100).
Prior to World War II and the shortage of strategic melals, copper and aluminum were used for
irrigation piping. However, these metals were easily corroded by the minerals in the water. Although
prone to corrosion, galvanized pipe was found to be acceptable in price and longevity and remained in
use until the early 1980's.
Used in Europe as early as 1937, polyvinylchloride (PVC) was introduced to the American
market in 1952 (Irrigation History: From Buckets and Crossbeams to Computers, 1989, p. 100). In the
early 1960's, the American Society for Testing Materials (ASTM) set standards for PVC strength and
sizes. Due to its long life, ease of installation and low cost, this material has become the standard for
the irrigation industry.
The commercial irrigation industry, as we know it today, developed after World War II when
the returning veterans moved to the suburbs in the early 1950's. Lightweight, corrosion resistant and
low cost materials became available and speeded the growth of the modern commercial irrigation
industry. So, despite its 8,000 year history, modern irrigation is only approximately forty years old.
18
Micro-Irrigation
Micro-irrigation lias no universally acccpted definition. It includes several characteristics,
which may 01 may not all be present in any particular installation. However, its most widely acccpted
characteristic is that it delivers water to the plant at a slow rate. A more specific discussion of microirrigation can be found in the next section of this study.
Early experiments with subsurface irrigation began in the late 1800's (Nelson, 1971, p. 1). The
first work in subsurface trickle irrigation in which water was applied to the root zone without raising the
water table was conducted in the United States at Colorado State University in 1913 by E. B. House,
who concluded that it was too expensive for practical use (Nakayania, 1986, p. 2). Various materials,
including porous clay pipe, canvas hose, reclaimed rubber and plastic products were tested. By the
1980's modem materials had been developed to the point that subsurface, or drip irrigation, as it came
to be known, was reasonably successful.
The observation of Simha Blass. an engineer who developed the first patented surface trickle
irrigation emitter, has been quoted describing greater vigor of a large tree near a leaking faucet in an
orchard (Netafim Irrigation Equipment & Drip Systems, 1986, p.l). From Israel the concept of surface
trickle irrigation spread to Australia, North America and South Africa by the late 1960's and eventually
throughout the world. In 1971, the first International Drip Irrigation Conference was held in Tel Aviv,
Israel, where 24 papers on drip irrigation were presented (Nakayama, 1986, p. 2).
Early application of micro-irrigation to turf was generally unsuccessful, the most common
problem being plugging of the pipe or tubing. Most experiments centered around the use of porous pipe
of one kind or another. However, one of the major disadvantages of porous pipe was its propensity to
plug. With porous pipe, the inside wall of the pipe is, by nature, rough in texture and thus more likely
to trap particles suspended in the water. This method was generally not successful and subsurface
irrigation has suffered in reputation since.
19
In the early 1960's, plastic pipe with a very smooth inner wall and individual emitters at
various spacings was tried. The smooth inner wall allowed the suspended and dissolved particles in the
water to flow through the pipe without adhering to the inner surface of the pipe. Reducing the points of
emission, from essentially the entire inner surface of the pipe to one emitter every few feet, allowed
them lo be individually engineered to greatly reduce plugging. The use of smooth wall pipe in now
becoming the industry standard.
Characteristics of Micro-Irrigation
Micro-irrigalion is an umbrella term used to describe a family of irrigation methods. This
technique of irrigation is also known as drip irrigation, trickle irrigation, micro-spray and sometimes
subsurface irrigation. It has been defined as follows:
"Trickle irrigation is the slow application of water on, above, or beneath the soil by
surface trickle, subsurface trickle, bubbler, spray, mechanical-move, and pulse systems
(Nakayama 1986, p. 1)."
"Micro-irrigalion is used to describe micro-spray, line source (porous pipes, etc.) and
point source (drip) irrigation systems (Micro-Irrigation: Good Things Come in Small
Packages 1989, p. 96)."
"Drip irrigation is the frequent, slow application of water to the soil for the purpose of
sustaining plant growth (Drip Irrigation Systems 1985, p. 1)."
"Drip irrigation is the frequent, slow, application of water to the specific root zone area
of the plant material (Shepersky 1984, p. 4)."
"Drip irrigation is the slow application of water to plants, usually with plastic pipe
lines and either emitters or drip irrigation tubing to deliver water to the desired
location (Drip or Trickle Irrigation for Ornamentals, 1978, p. 1)."
So. micro-irrigation can be said to have the following characteristics:
A.
Water is applied at a low flow rate.
B.
Water is applied over a long period of time.
20
C.
Water is applied at frequent intervals.
D.
Water is applied via a low-pressure delivery system.
E.
Water is applied directly into the plant root zone.
For this study then, micro-irrigation is defined as the application of water directly to the plant
root zone, at a slow rate, over a long period of time, at frequent intervals, under low pressure. The
most significant difference, from a design point of view, between standard irrigation methods and microirrigation is that, with micro-irrigation systems, the water is applied at a slow rate. That is, water is
applied at a rate no faster than the soil can absorb it. Micro-irrigation is really a "system" of delivery
incorporating many methodologies. But low volume delivery is a trait common to all micro-systems.
Benefits and Disadvantages of Micro-Irrigation
The characteristics that set subsurface, or micro-irrigation apart from traditional spray irrigation
systems provide certain advantages to the user, the turf and the designer. These characteristics and
benefits can be described as follows:
A.
Water is applied at a slow flow rate (gallons per hour vs. gallons per minute). Water
is applied at a rate at which it can easily be absorbed by the soil. Sprinkler, or spray,
irrigation systems normally apply water at a rate of 1 gallon per minute or greater for
each sprinkler. That is. each sprinkler head in the circuit passes this quantity of water
to the turf. Micro-irrigation systems, however, operate at much lower volumes,
normally at rates of .5 to 2.0 gallons per hour. The following advantages are realized
by applying water at low flow rates:
21
1.
Soil erosion is easier to control with low flow rates because the puddling of
surface water is eliminated. Thus, sloping terrain can be irrigated with less
concern for runoff that could cause erosion.
2.
With a decrease of puddling, evaporation from the soil surface is greatly
reduced.
3.
Precise control of water location and volume is possible.
4.
A saturated soil condition is easier to avoid with lower flow rates. As water
is applied, the welted front moves through the soil by capillary action,
reducing saturation.
B.
Water is applied over long periods of time (hours vs. minutes). Since the rate of
application is less, longer run times are required in order to apply the amount of water
needed by the plant. Normally, spray irrigation systems apply water for five minutes
to thirty minutes per run cycle. Since micro-systems apply water at much lower flow
rates, they typically run from thirty minutes to a day or longer per cycle. The
following advantages are realized by applying water over long periods of time:
1.
A more desirable soil moisture profile is maintained with frequent water
applications of several hours, instead of weekly applications of short duration.
Fluctuations between the soil saturation/wilting point are reduced.
2.
Deeper watering is possible, allowing poor soils to be utilized more
effectively. Applying the water over a long period of time, allows it to
migrate deeper into the soil.
3.
Salt accumulations can be more easily leached from the root zone area. They
are pushed along the wetted front beyond the root zone.
22
C.
Water is applied at frequent intervals (daily vs. weekly). Applying water at frequent
intervals reduces the variation in soil moisture. Spray irrigation systems normally
apply water between one and three times per week, allowing the soil to dry between
waterings. Depending on seasonal requirements, micro-irrigation systems are generally
run every day, even or odd numbered days or three times per calendar week. The
following advantages are realized by applying water at frequent intervals:
1.
Less plant stress is experienced due to reduced soil saturation/wilting point
cycles.
2.
Plant cooling can be achieved by watering plants on a daily basis and
allowing evaporation from the soil surface to cool the foliage. Heat tolerance
of cool season grasses and ground covers can be increased with this
technique.
D.
Water is applied directly to ihe plant root zone. Spray irrigation systems broadcast
water in the form of small droplets through the air to the leaf surface of the turf.
These droplets arc highly susceptible to wind drift. Sufficient water must fall on the
leaf surface before it can penetrate through the thatch material and begin soaking into
the soil. Micro-irrigation systems can apply water below ground level, exactly where
needed. The following advantages are realized by applying water directly to the plant
root zone:
1.
Wasteful evaporation is reduced.
2.
Runoff and erosion are reduced.
3.
Efficient herbicide, pesticide and fertilizer application is possible directly to
the root zone through the use of in line chemical injection devices.
23
E.
Water is applied under low pressure (15 lo 50 psi vs. 30 to 150 psi). Traditional
sprinkler irrigation requires high head pressures in order to eject the water stream from
the spray head the required distance. Micro-irrigation allows the capillary action
within the soil to move the water. So pressure is only required to force the water
through the emitter. The following advantages arc realized by applying water under
low pressure:
1.
Installation costs are reduced. Components such as pipes, valves, pumps etc.
can be downsized due to low pressures and reduced flow rates.
2.
Fewer components can be used because larger areas can be irrigated with the
same size components.
3.
F.
Pumping costs can be reduced.
Other Characteristics of micro-irrigation:
1.
Tolerance to water and soil salinity is increased through micro-leaching. Due
to low water tension in the root zone, the turf takes up fewer salts.
2.
Vandalism can be substantially reduced because the components are not
visible.
3.
There is no over spray on cars, buildings, windows or sidewalks. Liability is
reduced, therefore insurance rates can also be reduced.
4.
Maintenance costs can be reduced. Mowing, edging and fertilization times
can be greatly reduced. Since no sprinkler heads are located above ground in
the turf area, damage from mowing and the necessity of edging around heads
is eliminated. Fertilizer, soil amendments and insecticides can be applied
through the system rather than being applied to the surface of the soil.
5.
Irrigation need not interfere with activities on the site, so scheduling is
simplified. Since there is no above ground water spray, irrigation can take
place any time, day or night, even during active use of the area.
24
PROBLEM STATEMENT
Realization of Potential Advantages
Although potentially great, the advantages of micro-irrigation systems have not been realized,
nor has research conclusively determined that these advantages actually exist. Literature on the subject
makes varying claims of potential water savings. In practice, water savings have more often been
negligible. This may be due, at least in part, to inefficient design, poor system management and
generally a piecemeal approach to the design and installation of these systems.
Subsurface irrigation of turf has its own specific set of design issues that must be identified and
controlled. Material and component engineering have recently been developed to the point where there
is now little reason not to utilize this method of turf irrigation. But it is not in wide use today. In fact
it is seldom used, and only then after considerable effort on the part of the designer to overcome
resistance of other professionals involved. Subsurface irrigation of turf, like any other irrigation system,
will not serve the needs of every turf variety, land situation or end user objective.
In 1985. while at a landscape architectural firm in Phoenix, the author was charged with
designing a state of the art irrigation system that would demonstrate modern water conservation methods
of turf irrigation. Subsurface irrigation techniques were examined and it was determined that they
offered a possible answer to the client's request. However, information on the subject was scattered and
many times contradictory.
25
Design information was scattered among many sources and incomplete at best Justification for
the use of such a system was sketchy or nonexistent. It appeared to the author that subsurface irrigation
of turf offered many advantages, but this was difficult to document for the client and city officials who
would have to eventually approve the system.
With considerable guess work and difficulty, the project was designed. It was impossible,
however, to receive the required city approvals. The city engineer refused to give the needed approvals
on the grounds that it had not been demonstrated that the system was dependable and so could not be
used in the city right-of-way, one of the requirements of the project. The lack of solid, unbiased
research seems to be hampering the adoption of what could be a very useful, water efficient technique.
Need for Further Research
Many arguments can be made for further investigation into the subject of subsurface irrigation
of turf. Water is scarce, especially in the Southwest. In periods of extreme scarcity many governing
bodies have been considering water rationing. Some are beginning to consider turf and its attendant
irrigation to be a luxury that can be eliminated. Literature is unconvincing, unscientific and suffers from
a lack of consolidation. Subsurface irrigation shows great promise for alleviating water shortages, but it
is not generally accepted by the industry. Presently, there is no place a designer can go for assistance.
The experts in the field tend to be the few contractors who install these systems. Since there are no text
books for subsurface irrigation of turf, the designers of these systems who are competent must have
learned through trial and error.
Objectives
This paper serves four academic and personal goals. They are to:
1.
Review existing literature using published and unpublished sources to
determine its relevance for the designer of subsurface irrigation systems;
2.
Examine selected installed sites to determine current industry practices.
3.
Develop a model to assist the designer of subsurface irrigation systems for
turf; and to
4.
Determine the areas of greatest need for further research and technical
development.
27
METHODOLOGY
The methods used in this paper to examine subsurface irrigation of turf include a review of
current literature and an examination of two case studies. Each method provides an alternative source
of information for determining the answers to the objectives being addressed by this paper.
Literature Review
Literature dealing with design issues of subsurface irrigation of turf is scattered among many
sources and seldom directed toward assisting the designer of such a system. To simplify analysis,
existing literature is divided into three general categories: academic studies, popular journal articles and
technical literature.
This categorization is imprecise because some scientific studies and much of the manufacturer
generated technical literature is presented in popular journals. Even though there is a crossover in the
categories where the material can be found, this classification is appropriate because the writings for
each of these categories are directed to very different audiences, and written for different purposes.
The academic studies reviewed include dissertations, theses, conference proceedings and
extension publications. Popular journals articles are from industry journals that contain advertising and
could be considered promotional in nature, although much technical information is included. The term
"technical literature" is used loosely. As used here, it does not infer accuracy. It is meant only to
include irrigation design manuals and published manufacturer's installation handbooks, which tend to be
of a more technical nature.
28
Case Studies
Although there are studies dealing with many of the elements involved in such a design, critical
issues such as cost comparisons with conventional irrigation systems, specific design techniques,
installation procedures, fertilization and maintenance are difficult to uncover. It is hoped that an
examination of installed projects will give some insight into the accuracy and applicability of present
writings on the subject. For this reason, two case studies will be examined in this paper.
The sites chosen, a residence and a city park, represent very different scales, uses and
management regimes. They are located in the greater Phoenix area and include a small privately owned
residence and a city park. It is hoped that comparing two quite different sized projects will provide the
model with greater applicability and give insight into advantages of the methodology in relation to the
size of the project.
29
LITERATURE REVIEW
An examination of current literature yields few studies that deal specifically with microirrigation of turf. Information is dispersed and of little use to the designer. To simplify the study, this
literature review is divided into three categories: academic studies, popular journal articles and technical
literature. Categorization of the literature is difficult and no clear division is apparent. A topical
segregation, such as emitter spacing or depth or potential water savings, is difficult because of the
different purposes for which the material is written. Popular journal articles tend to be promotional in
nature and broad in scope, while academic studies are more narrow in extent. The technical literature is
product specific, but does contain some valuable information on general design principles.
Most of the academic studies deal with the application of micro-irrigation of agricultural crops
(Nelson, 1971 and Minner, 1987) or with some other consideration of turf irrigation such as water
requirements of turf (Gassmin, 1987; Kneebone, 1979; Morgan, 1987 and Ratledge, 1987). However
several studies are directly applicable to the design of subsurface irrigation systems (Snyder et. al.,
1974; Devitt & Miller, 1988 and Jorgenson & Solomon, 1990). Popular journal articles such as (Stroud,
1987) deal explicitly with the topic, but in a more informal or promotional manner. Technical literature
includes irrigation design text books designed for the classroom, of which Handbook of Landscape
Architecture Construction (Weinberg, 1988) is an excellent example, and manufacturer's installation
handbooks such as Leaky Pipe by Entek.
30
Academic Studies
A study dealing most with the design issues of emitter spacing, tubing depth and the effect of
soil type on water movement within the soil was done at the Agricultural Research Center in Fort
Lauderdale, Florida (Snyder et. al., 1974).
The study analyzed various 10 foot square plots of turf with
seven different soil classifications. Emitters were spaced 20 inches apart on the tubing and the tubing
was spaced 24 inches apart in the ground and laid at a depth of 4 inches. Observations were made on
the width of the bands of turgid turf over the irrigation lines. Several conclusions were drawn from the
study. From a design standpoint, emitter spacing should be no more than 24 inches and as shallow as
practicable, within four inches of the surface if possible. Because of the sandy soil used in the study,
the system should be operated at relatively high emission rates with 1.8 to 2.8 gph/emitters. Three
additional factors discussed in the study are worth noting. First, it was suggested that because of the
low operating pressures involved with this type of system, variations in land elevations will cause
uneven water flow and thus uneven turf appearance. Second, a coarse textured layer of soil beneath a
finer textured layer has the potential to improve lateral water movement and thus allow wider tubing
spacings, reducing system cost. Finally, fertilizer and pesticide application through the subsurface
irrigation system might cause localized concentrations of nutrients causing undesirable turf conditions.
The observation was made that ". . . when one emitter fails, the turf served by that emitter suffers
noticeably (Snyder et. al., 1974, p. 37)."
A second study directly applicable to micro-irrigation of turf in a landscape situation was done
in 1988 (Devitt & Miller, 1988). The purpose of this study was to determine what effect water salinity,
soil type and emitter spacing had on turf appearance. The effects of three different emitter spacings (24,
35.8. and 48 inches) were compared. The most common Southwest turf species, common bermuda
grass (Cynodon dactvlon) was used in the study. A saline water was used for irrigation (Devitt, 1988,
p. 134). The results of the study showed that in the sandy soil, turf quality decreased as water salinity
31
increased. In the clay soil, the most important factor in turf quality was emitter spacing, with the 24
inch spacing the maximum effective. There were several conclusions drawn from the study. First, the
selection of a turf grass species, or subspecies that is salt tolerant is important to the overall success of a
subsurface drip system when using saline water. Many of the bermuda hybrids in wide use today are
very salt tolerant, and at the same time drought tolerant; common "midiron" being one of the more salt
and drought tolerant varieties. For the sandy soil, a 24 inch spacing and 6 inch depth is suggested. For
clay soil, a shorter spacing is recommended.
The author discourages the use of subsurface irrigation in
clay soils because emitter spacing would have to be greatly reduced, thus driving up installation costs by
suggesting that "the appropriate drip line spacing interval will be a Irade-off between desired level of
turf response and the cost of materials and installation" (Devitt. 1988 p. 142). And, "The canopy
temperature data suggest that the bermuda grass was being subjected to greater stress via the subsurface
drip systems than by the surface irrigated controls (Devitt, 1988, p. 140)."
A third study (Gibeault & Meyer, 1988) examined the effect of sprinklers and subsurface
irrigation under water stress conditions. Research was conducted on several warm season and cool
season turf grass varieties, watering them at 100%, 80% and 60% of the turf evapotranspiration
requirements, with no difference in turf quality found. It was shown that considerable water can be
saved by watering at less than the evapotranspiration rate, while maintaining turf appearance. With the
warm season species there was no significant difference in appearance when irrigated by spray or
subsurface irrigation. However, the cool season species, performed significantly better when irrigated
by sprinklers. It was noted that when the tubing was installed at the manufacturer recommended
spacing of 23 inches and emitter spacing of 18 inches at a depth of 8 inches, the cool season grasses did
worse than the turf irrigated with spray systems. It was acknowledged that the subsurface-irrigation
system "was apparently too deep and/or too widely spaced to provide adequate amounts of water
(Gibeault, 1988, p. 17)." It was also suggested that subsurface-irrigation offered no probability of
saving water.
A fourth study (Rauschkolb, 1991) is being conducted by the Maricopa Agricultural Experiment
Station, affiliated with the University of Arizona. It is presently involved in research that should
provide important design data for designers. This study is evaluating tubing spacings of 12, 24 and 36
32
inches at depths of 4, 8 and 12 inches. Two soils are being used in the study, a sandy loam common to
lawns and parks throughout Arizona and river bottom sand, of a quality commonly used in golf greens.
The study is not complete, but preliminary studies indicate optimum tubing spacing and depth of 24
inches and 8 inches respectively. An initial conclusion is that emitter and tubing spacings should be
reduced in high traffic conditions (Rauschkolb, 1991).
A fifth study, (Jorgenson & Solomon, 1990) is being conducted by the Center for Irrigation
Technology al California State University in Fresno, California. It shows great potential benefit for the
designer of subsurface irrigation systems. Begun in 1990, the study will last for three years. Its goals
are to determine the viability of subsurface irrigation of turf, conduct product evaluations and identify
management techniques particular to this type of irrigation. Seven different brand products are being
evaluated, both point source emitters and continuous line source tubing. Irrigation tubing is installed at
a depth of five inches. Three horizontal spacings are used - the manufacturer's recommendation, one
third narrower and one third wider than recommended. Turf quality and the presence of pests are being
evaluated. The soil used for the tests is Hanford Fine Sandy Loam, with a more broad based
applicability to landscape situations than the sandy soil used in some other studies. The study has
already yielded several observations. Turf on the edges of the plots was dryer than other areas,
probably due to heating of the soil caused by the concrete near the edge of the plot. An automatic air
vent/vacuum relief valve is recommended for each remote control valve to prevent water and solids
from being drawn back into (he tubing when the valve is turned off. Even though the grass was not
washed by water from traditional sprinklers, the surface did not become dusty or dirty as expected.
The quality ratings for the line source tubing remained high further into the summer season than those
for the point source emitters. Table 2 is a summary of the emitter spacing, emitter depth and the flow
rate used in the study.
33
DESIGN SUMMARY - JORGENSON AND SOLOMON
Product
Nominal
Flow
Emitter/Tubing
Spacing
Tatting
Deptb
Drip-in subsurface
irrigation
0.5 GPH
18"
5"
Netafim Ram
0.6 GPH
12"
5"
Agrifim Subflo
1.0 GPH
12"
5"
Agrifim Inline
1.0 GPH
15"
5"
Pepco Laser Tubing
1.0 GPH
12"
5"
CTA
2.1 GPM/100'
Continuous
5"
Irri-Namic
1.6 GPM/100'
Continuous
5"
Aquapore
0.5 GPM/100'
Continuous
5"
Range
Point Source
0.5 CPH/1.0 GPH
12"
5"
Mean
Point source
.8 GPM
14"
5*
Range
Line Source
0.5-2.1 GI'M/
100'
18"
5*
Mean
Line source
1.4 GPM/100'
Continuous
Sn
Table 2. Design Summary, Jorgenson and Solomon (Jorgenson and Solomon. 1990, p. 2).
A sixth study (Krans and Johnson, 1974) evaluated the merits of subsurface irrigation of turf
during periods of heat stress. Two soil types were used in the experiments: a mixture of sand, Lomite
and natural soil, and an unamended sandy soil. Treatments included sprinkler irrigation and subsurface
irrigation using a lysimeter to saturate the soil from below. Several findings of interest here were
determined. Recovery from heat stress was significantly greater for the subsurface irrigated plots than
for the sprinkler irrigated plots. There was significantly greater root mass with the subsurface irrigated
plots than for the sprinkler irrigated plots. Soil moisture content tended to be more consistent over time
for the subsurface irrigated plots. Moisture stress was more apparent on the sprinkler irrigated plots. A
34
final conclusion was "Subirrigation appears (o have potential for improving the maintenance of bentgrass
during periods of prolonged stress" (Krans and Johnson 1974, p. 530).
Summary
Table 3 shows a comparison of the emitter spacing, tubing spacing and tubing depth of the
academic studies. It shows a range of emitter spacing of 12 to 24 inches, a tubing spacing of 8 to 48
inches and a tubing depth of 4 to 8 inches.
DESIGN SUMMARY OF ACADEMIC STUDIES
Emitter
Spacing
Tubing
Spacing
liiiiiii
Theory and Experimentation for Turf Irrigation
from Multiple Subsurface Point Sources
Snyder et. al., 1974
20"
24"
4"
Subsurface Drip Irrigation of Bermudagrass With
Saline Water
Devitt, 1988
24"
24"
6"
Irrigation and Water Conservation
Gibeault, 1988
18"
23"
8"
Maricopa Agricultural Experiment Station,
University of Arizona
Rauschkolb, 1991
16"
24"
8"
Evaluating Subsurface Drip Irrigation for
Turfgrass: an Intrum Report.
Jorgensen, and Solomon, 1990
8"
5"
Table 3. Design Summary, Academic Studies.
Tubing
to
48"
oo o w
Source
13"
Range
12" to 24"
8" to 48"
Mean
18"
23"
to
4" to*"
35
It is possible to summarize the design recommendations from these studies. It should be
realized that any summary, drawn from different sources, must be general in nature. These
recommendations could not be used by a designer without applying them to the conditions particular to
the site in question. But, by drawing recommendations from a spectrum of sources, a picture of the
issues involved in the design of a subsurface irrigation system can be drawn. Design recommendations
from the academic studies are summarized as follows:
A.
Emitter spacing should be no more than 24 inches, preferably less.
B.
Emitter spacing should be reduced in heavy, clay soils.
C.
Emitter spacing should be increased in high traffic areas.
D.
Tubing spacing should be no more than 24 inches.
E.
Tubing depth should be no more than 6 inches.
F.
Tubing should be placed closer to the edge of the turf when it comes into contact with
concrete, preferably within 6 inches.
G.
An automatic air vent/vacuum relief valve is recommended at each remote control
valve.
H.
As soil texture becomes more coarse, emission rates should increase to 1.8 to 2.8
gallons per hour.
I.
A layer of coarse textured soil beneath a finer textured layer has the potential to
improve lateral water movement.
J.
Salt tolerant turf species is important to success.
K.
A pressure compensating system should be used if there are elevation differences on
the site or if the tubing is used in excessively long runs.
L.
Emitter and tubing spacings should be reduced in high traffic conditions.
36
Several value judgements are made with respect to subsurface irrigation of turf in the academic
studies. The studies each have a different approach to the topic and consider different variables
important. So, even though the conclusions may differ, they are relevant under varying conditions
found in the field. These valuations can be summarized as follows:
A.
Considerable water can be saved by watering at less than the evapotranspiration rate.
B.
Turf appearance does not become dusty or dirty as a result of subsurface irrigation.
C.
Cool season grasses perform less well with subsurface irrigation than warm season
grasses.
D.
Cool season grasses require that the tubing be placed closer to the soil surface.
E.
The visual quality may be higher with line source emission systems than point source
emission systems.
F.
Subsurface-irrigation may offer little or no water savings.
G.
Recovery from heat stress is greater for subsurface irrigated turf.
H.
There is significantly greater root mass with the subsurface irrigated turf.
I.
Soil moisture content tends to be more consistent over time for subsurface irrigated
turf.
J.
Moisture stress is less apparent on subsurface irrigated turf.
K.
Fertilizer and pesticide application through the subsurface irrigation system could cause
localized concentrations of nutrients.
37
Popular Journal Articles
Many applications, including residential and commercial lawns, athletic fields and ornamental
plantings are suggested by Stroud for low volume, low pressure irrigation systems (Stroud, 1987, p. 80).
This article describes installation procedures and lists advantages and disadvantages of subsurface
irrigation of turf. Among the advantages listed are reduced maintenance costs, elimination of over
spray, water savings, energy savings, simplified chemical application, use of the site while it is being
watered, reduced disease problems and short payback period. Disadvantages are higher initial cost, poor
quality of turf immediately after system installation, high accuracy required at installation and problems
with defective equipment. Stroud recommends the injection of 10% sulfuric or muriatic acid through
the system to prevent root intrusion into the system. In describing installation of the tubing, she
suggests 24 inch to 32 inch spacing for the emitter lines and 24 inch spacing of the emitters. Stroud
infers that the 32 inch spacing was chosen to reduce installation costs. The article suggests that the
amount of trenching required for this spacing causes the initial installation cost to be up to 20% higher
than spray systems. Stroud also claims a water savings of 50 to 60% if the system is properly installed
and conscientiously operated.
A second article. (Subsurface Irrigation: Made for the Challenge of Drought, 1988) goes into
great detail about design, installation procedures and advantages of this type of system. It also claims a
water saving potential of 25 to 40% for the system. One of the most important advantages discussed is
that of reduced liability. The reduced potential of lawsuits from wet sidewalks and streets is noted
(Subsurface Irrigation: Made for the Challenge of Drought, p. 72). Other advantages discussed are a
reduction of splash-transmitted diseases, ease of fertilizer application, cost comparable to conventional
systems and uniform water distribution on slopped areas. An important point the article makes is the
necessity for good design and installation practices. Spacing between rows must be exact and
38
consistent. It is also important that the designer be familiar with this type of system since design and
installation of subsurface systems is not forgiving of error. This is one of the few articles that
recommends an emitter line spacing of less than 24 in. This is also the only popular journal article that
describes modern vibrating plow installation of the tubing. The article says that installation costs no
more, and probably less than conventional irrigation systems. To reduce the chance of root intrusion
into the system, a regular watering schedule is suggested. It is thought that a dry soil condition will
promote "hunting" by the roots and they will seek out water within the system (Subsurface Irrigation:
Made for the Challenge of Drought, p. 80). This is the only article to address the issue of coefficient of
uniformity, a measure of the evenness that the irrigation system is applying the water to the turf.
Traditional surface irrigation systems are not very even in their application of water. But because the
emitters are placed within two feet of each other throughout the lawn an extremely high coefficient of
uniformity is obtained with subsurface irrigation.
A third article, (Micro-Irrigation: Good Things Come in Small Packages, 1989), is a
comprehensive article that discusses a wide range of drip irrigation issues. The thrust of the article is
that the quality, reliability and dependability of the components have recently been developed to the
state where drip irrigation components are as dependable as any other type of irrigation components. It
discusses several components that would be included in a typical system. A filtration system should be
included in any drip system. A pressure regulator should be used on all systems, regardless of elevation
changes on the site. A chemical injector will allow fertilizers, herbicides and insecticides to be applied
through the system. A tensiometer should be used to monitor soil moisture and can even take charge of
the irrigation controller. The use of pressure compensating emitters greatly simplifies the design and
cost of the system by eliminating flow differences between emitters of different elevations. When
considering total cost of the system, initial cost, installation cost, operating cost and maintenance cost
must be considered. Operating costs are considerably less than conventional irrigation systems. One
manufacturer has developed an emitter constructed of a plastic with an herbicide molded into the emitter
39
orifice. This emitter has been highly successful in reducing root intrusion into the emitter (MicroIrrigation: Good Things Come in Small Packages, 1989, p. 104).
A fourth article, (Cloud, 1980) was especially forward looking, considering that it was written
eleven years ago. It suggested that
. . no previous development will have the impact of the new,
subterranean, injected irrigation systems (Cloud, 1980, p.36)." The article discussed the concept of
"pulse watering," periodically cycling the system on and off to increase lateral movement of the water in
the soil. It notes that extreme accuracy is needed in installing the system. Among the advantages listed
were the elimination of trimming around sprinkler heads, reduced liability, no over spray on buildings,
elimination of evaporation, the option of watering while the site is being used. Of interest is a comment
that
"Compaction is also not a problem with this form if irrigation, since the water is
injected at a relatively high pressure into the substructure. Tiny channels are created
when the water escapes to the surface and these become air ducts straight to the root
zone (Cloud, 1980. p. 37)."
Summary
Table 4 shows a comparison of the emitter spacing, tubing spacing and tubing depth of the
popular journal articles. It shows a range of emitter spacing of !2 inches to 32 inches, a tubing spacing
of 12 inches to 24 inches and a tubing depth of 4 inches to 6 inches. Two of the articles, (MicroIrrigation: Good Things Come in Small Packages, 1989 and Cloud, 1989) are not included in the table
as they make no specific recommendations as to emitter spacing, tubing spacing or tubing depth.
Again, this summary is general in nature and sometimes contradictory. These design
recommendations have been tried in the field and worked for the specific sites involved.
40
DESIGN SUMMARY OF POPULAR JOURNAL ARTICLES
% Water
Savings
Emitter
Spacing
Tubing
Spacing
Tubing
Depth
Subsoil Irrigation Systems
Stroud, T., 1987
50%-60%
24 inches/
32 inches
24"inches
4 inches/
6 inches
Subsurface Irrigation: Made for
the challenge of drought
25%-40%
12 inches/
18 inches
12 inches
None
Given
2S%-60%
13 inches/
32 inches
24 inches
4 inches/
6 inches
Source
Landscape & Irrigation
Range
Table 4. Design Summary of Popular Journal Articles.
The recommendations from the popular journal articles are summarized as follows:
A.
Water filtration is required with subsurface irrigation of turf.
B.
A pressure regulator is needed to provide even flow at all parts within the system.
C.
Tensiometers should be used to monitor soil moisture.
D.
Chemical injectors can be used to apply chemicals through the system.
E.
Pressure compensating emitters can be used simplify the design and improve
performance.
F.
The total cost of the system from design, installation, operation, maintenance to repair
should be considered when evaluating subsurface irrigation of turf.
G.
Pulse watering can be used to increase lateral water movement in the soil.
H.
A solution of 10 per cent sulfuric or muriatic acid, when injected through the system,
can prevent root intrusion.
I.
The designer and installer must be familiar with this type of system because subsurface
irrigation of turf is not forgiving of error.
J.
Modern vibrating plow equipment should be used for installation of the emitter tubing.
K.
Regular watering is recommended to reduce root intrusion into the emitters.
41
Popular journal articles tend to make more value judgements respect to subsurface irrigation of
turf than the academic studies. These positive valuations can be summarized as follows, realizing that
most of them may be undocumented.
A.
Component quality has improved in recent years.
B.
Operating costs are less with subsurface irrigation when compared to conventional
irrigation.
C.
Maintenance costs are reduced with subsurface irrigation.
D.
Liability may reduced considerably with subsurface irrigation.
E.
Scheduling is simplified because watering can take place while the site is in use.
F.
Soil compaction is reduced with subsurface irrigation.
G.
Energy saving, in the form of pumping costs, are great because of the low pressures
used with subsurface irrigation.
H.
Splash transmitted diseases are eliminated with subsurface irrigation.
I.
Water savings of 50 per cent to 60 per cent are possible with subsurface irrigation.
J.
Efficient installation procedures can keep costs comparable to conventional irrigation
systems.
K.
A better coefficient of uniformity can be achieved on sloped areas with subsurface
irrigation.
There are also some negative comments or cautions about subsurface irrigation of turf. They
are summarized as follows:
A.
There are still problems with poor quality products.
B.
Installation must be more exact with subsurface irrigation than with conventional
irrigation systems.
42
C.
Initial costs can be higher with subsurface irrigation of turf.
D.
High trenching costs can cause installation costs to be up to 20 per cent higher for
subsurface irrigation systems.
Technical Literature
Irrigation design manuals, published manufacturer's installation handbooks and unpublished
manuals are included here. The great majority of design manuals deal exclusively with spray irrigation.
Only those publications that are produced by manufacturers of components used in subsurface irrigation
of turf, deal with the topic in any detail.
The long time industry standard design handbook. Turf Irrigation Manual, (Watkins, 1983)
makes no mention of subsurface irrigation of turf. It was first published in 1959, before subsurface
irrigation was widely used in this country, and, surprisingly, does not include reference to it in its latest
edition.
A second publication, Trickle Irrigation For Crop Production (Nakayama, 1986), is a complete
technical reference on the subject of subsurface irrigation. The text is broad and includes a discussion
of design, operation and management principles. Each topic is covered thoroughly, with considerable
mathematical justification when required. Of considerable interest to subsurface irrigation of turf are the
sections on soil water distribution, soil salt distribution, emitter clogging, filtering systems, fertilization
and irrigation scheduling. It is noted that due to recent advances in material and design,". . .
maintenance requirements of subsurface systems are similar to surface trickle systems (Nakayama, 1986,
p. 12)." Among the potential advantages listed for trickle irrigation are (Nakayama, 1986, pp. 16-18):
43
A.
Enhanced plant growth
B.
Reduced salinity hazard to plants
C.
Improved fertilizer and other chemical application
D.
Decreased energy requirements.
Also listed are several potential disadvantages (Nakayama, 1986, pp. 18-19):
A.
Higher maintenance requirements
B.
Salt accumulation near plants
C.
Restricted plant root development
D.
High system costs
The system designer must consider many variables, more than with conventional systems, when
designing a subsurface irrigation system. These design and installation suggestions are given below
(Nakayama, 1986, pp. 19-20):
E.
Lateral tubing should be run flat, downhill or along the contour for noncompensating
emitters.
F.
Lateral lines can be run regardless of slope if pressure compensating emitters are used.
G.
System capacity must be designed to meet peak plant evapotranspiration (the worst
possible case).
H.
Filtration units must meet the water quality and flow capacity of the system.
I.
Backflow prevention devices must be installed to protect the water supply from
chemicals injected through the irrigation system.
44
J.
Air, or vacuum relief valves should be installed to prevent debris from being drawn
into the system.
Nakayama suggests that the primary goal of any trickle irrigation maintenance program should
be to control emitter clogging, thus providing the required amount of water to the plant. He suggests
the following maintenance requirements for trickle irrigation systems (Nakayama, 1986, pp. 20-21):
K.
Filters should be cleaned and inspected regularly.
L.
Automatic flushing devices should be used where the water is high in silt and clay.
M.
Chemical injectors and time clocks should be checked weekly.
N.
The entire system should be inspected for malfunctioning emitters and leaks at least
monthly.
O.
Chemical water treatment should be used when chemical or biological hazards are
present.
P.
Inject only chemicals that have been approved for trickle irrigation systems.
Q.
Soil moisture should be checked regularly.
R.
Maximum chemical injection efficiency is achieved by allowing the system to run long
enough to establish flow equilibrium, or evenly wet the soil, before the chemicals are
injected into the system (Nakayama, 1986, p. 236).
Apart from the maintenance points just mentioned, Nakayama also suggests several
management techniques or considerations to insure the best subsurface irrigation system performance.
They are as follows (Nakayama, 1986, p. 21):
A.
Automation of the system can save labor, water and chemical expense, however it may
increase maintenance problems.
45
B.
Use field measurements and observations to assist in irrigation scheduling.
C.
More frequent irrigation scheduling can benefit soil or water salinity problems.
D.
Fertilizer applications should be more frequent during the early stages of plant growth
A third publication is Handbook of Landscape Architectural Construction (Weinberg, 1988). It
is the most current, complete irrigation design text available. It deals with irrigation master planning,
components, design process, contract documents, specifications, bidding and drip irrigation design for
shrubs and trees. As complete as it is, it makes only one reference to subsurface irrigation of turf.
"When used to irrigate turf, the turf surface is usable at all times, even during irrigation (Weinberg,
1988, p. 206)." This is a major omission of an otherwise complete text. Reference is made to modern
vibrating plow installation of drip tubing for shrubs and trees.
A fourth publication that deals exclusively with drip irrigation of trees, shrubs and ground
covers is Landscape Drip irrigation Design Manual (Shepersky, 1984). It does not mention subsurface
irrigation of turf. However, it is of value for its guidance in the hydraulic design of drip systems in
general.
A fifth publication, of particular value, is Micro-irrigation Design Manual (Boswell, 1986). It
does not address subsurface irrigation of turf, but it covers all other aspects of design. Soil wetting
patterns ar discussed and It is noted that "Water movement in soils will be affected by the condition of
the topsoil, the permeability of the subsoil, layers of soil with varying properties and the presence of a
plow pan (Boswell, 1986, p. 2-6)." Figure 2 illustrates the relative shapes of wetting patterns as they
are affected by soil. The article notes that "In addition to soil type, the application rate will affect the
shape of the wetted pattern ... a higher application rate tends to produce a wider zone of saturation
under the emitter, assisting in horizontal movement. Thus for increased lateral movement, light sandy
soils require water applications at higher rates. Heavy clays and clay loams, on the other hand, often
46
Fine Textured Soils
Poorly Prepared Cloddy Soils
Coarse Textured Soils
<?
5<?.VflVol
w
v'1* v
V*'/;
f-
Figure 2. Water Movement in Various Soil Classes (Boswell, 1986, pp. 2-7).
benefit from a lower application rate (Boswell, 1986, p. 2-7/2-8)." Considerable treatment is given to
chemical injection through the system. It is recommended that bacterial slime and algae be controlled
with intermittent chlorination of 10 to 20 ppm for between 30 and 60 minutes (Boswell, 1986, p. 4-2/45). It is also suggested that chlorine treatment may be beneficial as a preventive to control biological
growth in all parts of the system if used on a regular basis. Acid treatment of the system is also
recommended to lower the Ph as a control mechanism to discourage microorganic growth and the
precipitation of dissolved solids in the water. Phosphoric, hydrochloric and sulfuric acid are
recommended. A procedure to adjust the Ph of the irrigation water is described (Boswell, 1986, p. 414). The author starongly recommends the application of fertilizer through the system. Among the
advantages claimed are reduced fertilizer use, elimination of leaf burn and elimination of inhalation
hazards. The three primary fertilizers, nitrogen, phosphorus and potassium, can easily be injected
through the system (Boswell, 1986, p. 5-2/5-6). Several methods of injecting chemicals are described.
Figure 3 shows three such chemical injection devices.
A sixth unpublished work by Netafim Irrigation, an Israeli company involved with drip
irrigation since its inception, is a manual dealing with general subsurface irrigation design principles
47
Venturi
Injector
=ft
Injection
Pump
Figure 3. Chemical Injection Devices (Boswell, 1986, pp. 5-11).
(Netafim Irrigation Equipment & Drip Systems, 1986). Netafim produces an emitter tubing, called Ram
tubing, used in agriculture applications and subsurface irrigation of turf. The emitter is built into the
inside of the polyethylene tubing. The advantage of the emitter being built into the tubing is that a
vibrating plow can be used to install the tubing without fear of damaging the emitter. Figure 4 shows a
cut away section of Ram tubing with the emitter inside.
Among other advantages listed for subsurface irrigation of turf are (Netafim Irrigation
Equipment & Drip Systems, 1986, p. 1):
A.
Near 100 per cent coefficient of uniformity can be achieved.
B.
Reduction or elimination of runoff on sloped sites is possible.
C.
Narrow or irregularly shaped areas, such as those found in road medians and parking
lot medians, can easily be irrigated.
D.
Vandalism can be greatly reduced, if not eliminated.
E.
Due to the low pressure nature of the systems, large expanses of turf can be irrigated
at one time.
F.
Modification of existing systems is simplified if the turf area is modified.
48
Figure 4. Cut Away View of Ram Tubing (Netafim Irrigation Incorporated, Specifications Sheet, 1991).
Subsurface irrigation of turf presents several hazards or areas of caution which are listed below
(Netafim Irrigation Equipment & Drip Systems, 1986, p. 3):
A.
Use only the highest quality materials and equipment.
B.
Allow for regular flushing of drip lines.
C.
Preventive maintenance is very important.
D.
Because subsurface irrigation systems operate with low pressures, problems can go
unnoticed.
Considerable attention is given to irrigation scheduling. It is recommended that watering be
scheduled several times a week instead of a short watering every day. Several formulas and tables are
given to help plan watering needs and scheduling. Once the soil moisture is brought to its optimum
level for the turf, then only water that is lost through evapotranspiration need be replaced (Netafim
Irrigation Equipment & Drip Systems, 1986, p. 13). Table 5 shows the evapotranspiration loss for
different climate zones.
49
POTENTIAL EVAPOTRANSPIRATION LOSS BY CUMATE
Average
Average Rei.
High Temp. F.
Humidity %
P. E, ?.
Inches/Day
P.&T.
Indies/Wk.
Cool Humid
Below 70
Above 50
.10
0.70
Cool Dry
Below 70
Below 50
.15
1.05
Moderate Humid
70-85
Above 50
.17
1.19
Moderate Dry
70-85
Below 50
.20
1.40
.25
1.75
8
Above 50
Warm Dry
86- 100
Below 50
.28
1.96
Hot Humid
Above 100
Above 50
.32
2.24
Hot Pry
Above 100
Below 50
.36
2.52
ON
1
N*
Warm Humid
00
Climate
Table 5. Potential Evapotranspiration Loss by Climate (Netafim Irrigation Equipment & Drip Systems,
1986, p. 13)
Once the evapotranspiration is established for a climate area. Table 6 and Table 7 can be used
to determine the length of time the irrigation system must be run to supply that much water.
TIME REQUIRED TO APPLY ONE INCH OF WATER
Drip Mae Spacing
.fiGPH
Emitter
12"
14"
W
18"
20"
24"
Minutes
63
73
84
94
104
125
Hour
1.0
1.2
1.4
1.6
1.7
2.1
Minutes
94
110
125
141
157
188
Honrs
1.6
1.8
2.1
2.4
2.6
3.1
Minutes
125
146
167
188
209
251
Hours
2.1
2.4
2.8
3.1
3.5
4.2
Emitter
Spacing
12 laches
18 Inches
24 Inches
Table 6. Time Required to Apply One Inch of Water with .6 GPH Emitters (Netafim Irrigation
Equipment & Drip Systems, 1986, p. 15).
They give the length of time required to apply one inch of water. By multiplying tlie
evapotranspiration rate from Table 5 by the number of minutes or hours from Tables 6 or 7, the run
time for the system can be determined.
TIME REQUIRED TO APPLY ONE INCH OF WATER
I>r ip Line Spiicing
3 GPH
Emitter
lilllllll
12"
14"
16"
18"
20"
24*
Minutes
40
46
53
59
66
79
Hours
0.7
.8
0.9
1.0
1.1
31.3
Minutes
59
69
79
89
99
119
Hours
1.0
1.2
1.3
1.5
1.6
2.0
Minutes
79
92
106
119
132
158
Moors
1.3
1.5
1.8
2.0
2.2
2.6
Emitter
Spacing
12 Inches
IS Inches
24 Incites
Table 7. Time Required to Apply One Inch of Water with .9 GPH Emitters (Netafim Irrigation
Equipment & Drip Systems, 1986, p. 15).(Netafim Irrigation Equipment & Drip Systems, 1986, p.15)
Simple formulas to calculate water requirements are also given. Equation 1 can be used to
determine the gross or total amount of water needed to maintain a certain area of turf. It shows the
volume of water in gallons needed to replace the loss due to evapotranspiration.
V = .623 x A x Et.
Equation 1. (Netafim Irrigation Equipment & Drip Systems, 1986, p. 14)
V
= Volume of water that needs to be applied, in gallons
.623 = Constant
A
= Area in square feet to be irrigated
Et = Evapotranspiration rate
51
Equation 2 shows the amount of water applied in inches per hour based on the flow of the
emitter, the space between emitter lines and the space between emitters. It can also be used to calculate
the time required to apply the needed water.
Equation 2. Netafim Irrigation Equipment & Drip Systems, 1986, p. 14)
Q = Quantity of water applied in inches per hour
1.6
= Constant
f
= Emitter flow in gallons per hour
d
= Space between drip lines in feet
e
= Space between emitters on the drip lines in feet
Netafim also suggests a deep watering several times a week instead of a short watering every
day (Netafim Irrigation Equipment & Drip Systems, 1986, p. 13). Netafim includes two construction
details of emitter tubing installation. Figure 5 shows a recommended tubing depth of four inches to six
inches and a typical connection to a PVC lateral pipe.
4" to 6 *
Elbow
Ram Tubing
8" to 10"!
Ram ConnectoR
c\r
Polyethylene
Tubing
X" PVC Tee
-
*
PVC Pipe
Figure 5. Ram Tubing Depth and Connection to PVC Lateral (Netafim Irrigation Equipment & Drip
Systems, 1986, p. 6).
52
Figure 6 shows a Ram tubing layout for turf. It shows that the Ram tubing is run parallel and
serviced by a PVC lateral pipe, or manifold, to which each Ram tube is connected. There is another
PVC manifold, to which the outlet end of each Ram tube is connected.
Figure 6. Ram Tubing Layout for Turf (Netafim Irrigation Equipment & Drip Systems, 1986, p. 8).
Netafim produces an line flushing valve, shown in Figure 7 that automatically flushes a
predetermined quantity of water from the emitter tubing at the start and Finish of each irrigation cycle.
The automatic nature of the device is ideal for homeowner applications where maintenance may be
erratic.
Figure 7. Automatic Line Flushing Valve (Netafim Irrigation Incorporated, Product Specification Sheet,
1990).
53
A seventh design manual that deals specifically with subsurface irrigation of turf, is from Intek
Corporation (Leaky Pipe Subsurface Dispersal Systems, 1990). Intek produces porous pipe that emits
water along its entire length. The manual is promotional in approach, but is a reasonably complete
design manual. It deals with movement of water within the soil, saturation/wilting point cycles, cost
comparisons, detailed installation procedures and includes simplistic installation plans. For a
comparison of installation costs between conventional and subsurface irrigation systems, see Table 8.
LABOR REQUIREMENTS AND CAPITAL COSTS FOR INSTALLATION
OP VARIOUS TYPES OP IRRIGATION SYSTEMS
Systetd Type
Labor llr/At
Capital $/Ac
Surface
0.15 to 1.00
120 to 500
Sprinkler
0.05 to 0.10
400 to 1200
Moving
0.20 to 0.70
200 to 400
Subsurface
0.14 to 0.16
250 to 1000
Table 8. Comparison of Irrigation System Costs (Leaky Pipe Subsurface Dispersal Systems, 1990. p. 31)
Figure 8 shows a typical baseball field lay out. The manual provides simple plans for football
and baseball fields and suggests that "The savings on water and maintenance should pay for the field in
Baseball Field
Leaky
Lateral
Lines
PVC Header
FLOW METER
WATER SOURCE
Figure 8. Baseball Field Layout (Leaky Pipe Subsurface Dispersal Systems, 1990, p. 34).
54
less lhan three years (Leaky Pipe Subsurface Dispersal Systems, 1990. p. 31)." This claim, however, is
not substantiated, nor is the type of field being considered given.
Intek recommends emitter tubing spacing of two feet and tubing depth of between eight inches
and twelve inches. The manual discusses the concept of "old soil" and "new soil".
"In the process of laying or burying the Subsurface Delivery System,... at the point
of installation, the old soil is disturbed or wounded. That portion becomes more
permeable than the old soil until the disturbed soil settles down to again become old
soil (Leaky Pipe Subsurface Dispersal Systems, 1990. p. 15)."
The eighth and ninth manuals examined are by Aquapore (Installation, Operation and
Maintenance Instructions for Aquapore Subsurface Irrigation Systems, 1989 and Aquapore Installation
Specifications and Construction Details, 1989). Aquapore also produces a type of porous pipe used in
subsurface irrigation of turf. The manuals cover water movement within the soil, system components,
installation methods, necessary equipment, turf water requirements and maintenance. Aquapore has
written the most complete installation manuals available, that are designed for the general public.
Figure 9 shows a typical Aquapore system component layout, from the water source to each irrigation
zone.
The Manual covers irrigation components, soil preparation, installation methods, system layout,
scheduling and maintenance.
It recommends a tubing spacing of 12 to 36 inches and a depth of 4
inches. A typical emitter tubing layout is shown in Figure 10.
ZONE 1
ZONE 2
ZONE 3
Figure 9. Component Layout from Water Source to Irrigation Zones (Installation, Operation and
Maintenance Instructions for Aquapore Subsurface Irrigation Systems, 1989, p. 3-4).
55
«
Header Line
AQUAPORE
LATERAL LINES
«
< ^ Flush Port
^ ) Flush Port
1
Flush Line
( ) Flush flat
Figure 10. Emitter Tubing Layout Showing Lateral and Flush Valves (Installation, Operation and
Maintenance Instructions for Aquapore Subsurface Irrigation Systems, 1989, p. 6-2).
It is suggested that an application rate of .5 GPM per 100 foot of pipe in loam soil and .75
GPM to 1.0 GPM per 100 foot of pipe in sandy soils is sufficient for most turf species (Installation,
Operation and Maintenance Instructions for Aquapore Subsurface Irrigation Systems, 1989, p. 4-2). An
entire chapter is devoted to soil preparation. The most important point made is that
"The most ideal soil conditions for the installation of Aquapore are found when the
soil has just recently been tilled and has a high moisture content without being too wet
for the proper operation of the installation equipment. Rototilling is a must on all new
installations (Installation, Operation and Maintenance Instructions for Aquapore
Subsurface Irrigation Systems, 1989, p. 4-5)."
Considerable detail is also given as to layout of the emitter tubing. Specifically,
"The first and last runs of Aquapore in each area or zone which parallel the edge
should be laid only 6 inches from the edge of the zone. This is especially true when
the zone is bordered by a cement sidewalk, driveway or other hard surface. These
hard surfaces collect the heat from the sun and transfer the heat into the bordering
lawn at a higher rate than normal, thus drying out that part of the lawn. At the
bottom of a slope they can be 16 inches away from the driveway or sidewalk
(Installation, Operation and Maintenance Instructions for Aquapore Subsurface
Irrigation Systems, 1989, p. 4-6)."
In discussing trenching for the porous pipe, Aquapore considers conventional methods of trenching and
vibrating plow methods. Aquapore provides a complete set of installation specifications and
construction details. A filter/backflow/chemical injector assembly is shown in Figure 11.
56
11OVAC\i
-y
FERTILIZER INJECTOR
FLOWMETER/ PULSER
REDUCED PRESSURE
BACKFLOW PREVENTER'
FILTER
•PRESSURE
BALL
yi
SOLUTION TANK
UNION-
UBSfca
Figure 11. Valve Manifold Assembly (Aquapore-Installation Specifications and Construction Details,
1989, p. 7),
Aquapore also produces a "de-clogging" chemical specifically designed for subsurface irrigation
systems. It contains phosphoric acid and is designed to dissolve iron, magnesium and calcium salts. If
used regularly, it is claimed to inhibit slime deposits in the system. Aquapore has written a reasonably
complete manual. Its primary drawback is that it is written specifically for an installation using porous
pipe. Application to designs using point source emitters, such as Netafim, would have to be approached
with caution.
Summary
Table 9 summarizes the tubing spacing and tubing depth recommendations from the technical
literature. It shows a range for tubing spacing of 12 to 36 inches and a range for tubing depth of 4 to
12 inches. Only Intek and Aquapore are summarized in the table, as only they give depth or spacing
recommendations.
57
TECHNICAL LITERATURE
TUBING SPACING AND TUBING DEPTH SUMMARY
Source
Leaky Pipe Subsurface Dispersal Systems
Tubing
Spacing
Tubing
24"
8"-12"
12"*36"
4"
12"-36"
4"-12"
Depth
Entek Corporation, 1990
Aquapore - Installation Specifications and Construction Details
Aquapore, 1989
Range
Table 9. Technical Literature Tubing Spacing and Depth Summary.
A general summary of the recommendations of the technical literature can be drawn. Again, it
should be realized that the summary is drawn from many sources, but consistent, recurring
recommendations should carry weight. Without reiterating all recommendations and suggestions firom
the technical literature, several important points can be emphasized here:
A.
Emitter spacing should be reduced for coarse, sandy soils. Spacing can be increased
for heavy, clay soils.
B.
Pressure compensating emitters simplify the system design. Emitter lines can be run
without regard for land contours.
C.
Good filtration is important for satisfactory operation.
D.
Backflow prevention devices are required because many chemicals can be run through
the system.
E.
Air relief valves will help keep the system free of debris by eliminating back suction
when the system is turned off.
F.
Automatic flush valves will simplify maintenance and help keep the system clean.
G.
Chemical injectors can be used to supply many types of chemicals through the system.
H.
Several scheduled waterings per week are preferable to daily waterings.
I.
Coarse, sandy soils require higher emission rates from the emitters than heavy, clay
soils.
J.
Ideally, the soil should be uniform in texture throughout the site.
K.
A vibrating plow can simplify installation.
58
Conclusions
Table 10 is a summary of water savings, emitter spacing, tubing spacing and tubing depth for
all literature cited. As can be seen, there is considerable variability in the four categories shown.
ALL CITED LITERATURE
DATA SUMMARY
% Water
Savings
Source
Emitter
Spacing
Spacing
Tubing
Tubing
Depth
Academic Studies
Irrigation and Water Conservation
Gibeault, Meyer, 1988
Not
Mentioned
18"
23"
8"
Subsurface Drip Irrigation of
Bermudagrass With Saline Water
Devitt, Miller, 1988
Not
Mentioned
24"
None
None
Theory and Experimentation for
Turf Irrigation from Multiple
Subsurface Point Sources
Snyder et. at. 1974
Not
Mentioned
20"
24"
4"
Maricopa Agricultural Experiment
Station, University of Arizona
Rauschkolb, Roy S.
Not
Mentioned
None
24"
8"
Popular Journal Articles
Subsoil Irrigation Systems
Stroud, T., 1987
S0%-60%
24"-32"
24"
4"-6"
Subsurface Irrigation: Made for the
Challenge of Drought
25%-40%
13"-18"
None
None
Landscape & Irrigation
Technical Literature
Not
Mentioned
None
24"
12"
Not
Mentioned
None
12"-36"
4"
Range
25%-60%
13"-32"
12"-36"
4"-12"
Mean
44%
21"
24"
7"
Leaky Pipe Subsurface Dispersal
Systems,
Entek Corporation, 1990
Aquapore, Installation Specifications
and Construction Details
Aquapore, 1989
Table 10. All Cited Literature - Data Summary
59
Academic studies tended to deal with sandy soils that are not typically found in Southwest
residential or commercial landscaping situations. These soils are used in golf course greens and funding
may be more readily available for this type of study (Rauschkolb, 1990). These studies would not have
wide application in residential and commercial landscape uses as far as system design, but may be
helpful in specific situations. Emitter spacings of 20 inches to 24 inches were recommended along with
tubing depths of 4 to 8 inches. An interesting concept introduced by Snyder (Snyder, 1974) is that a
course textured layer of soil beneath a finer textured layer has the potential to improve lateral water
movement.
Several potential disadvantages or problems were addressed. They included problems with
slope conditions, fertilizer and pesticide application, poor performance in clay soils and emitter
plugging. Appearance, not biomass is the controlling factor in landscape turf. So, academic studies that
place a premium on turf growth (Krans, 1974; Devitt, 1988 and Rauschkolb, 1991) may not be as
relevant as those that recognize turf appearance as more important (Jorgenson, 1990).
Popular journal articles claim a water savings of 25% to 60%. It could be expected that these
might be inflated since they are written for a potentially consuming audience and could be promotional
in nature. Only one article mentioned reduced liability potential with subsurface irrigation methods
(Subsurface Irrigation: Made for the Challenge of Drought, 1988). This may turn out to be a very
important consideration in the future economics of micro-irrigation of turf. Presently this advantage is
not being realized and may be an educational issue (Ilercil, 1990). These articles suggested a wide
range of emitter spacing, ranging from 13 to 32 inches. It is presumed that wide spacings are chosen to
reduce installation costs.
Irrigation text books offer virtually no help to the subsurface irrigation designer. Technical
literature, with two exceptions, also offers little help for the designer. It deals with subsurface irrigation
only peripherally. When subsurface irrigation of turf is alluded to, it is only considered as a possibility.
60
Design issues are not addressed. Aquapore has written a design manual that deals specifically with
subsurface irrigation of tuif. It is acceptable as an overview of design principles, but lacks sufficient
explanation for design flexibility. It also addresses only one method of subsurface irrigation turf, the
use of porous pipe.
For design criteria to be more usable by the designer, they will need to be directly related to
subsurface irrigation of turf and deal with both porus tubing and point source emission systems.
Presently, all design parameters are not brought together in a logical form or in one location. Specific
applications to subsurface irrigation of turf must be inferred and gathered from a multitude of sources.
61
CASE STUDIES IN MICRO-IRRIGATION OF TURF
The sites are chosen to represent a cross section of possible design scenarios for subsurface
irrigation of turf. They also reflect different maintenance or management regimes. They are located in
the greater Phoenix area and include a city park and a small privately owned residential site.
Both were new projects, as opposed to conversions of existing spray irrigation systems, and
both were installed by the same irrigation contractor.
Both projects were installed using drip tubing
with point source emitters built into the tubing at selected intervals. To simplify installation, the
contractor used a small tractor with an attachment capable of feeding emitter tubing through a vibrating
plow blade. A metal plow blade designed to aid
in installing the tubing is attached to the tractor
as is shown in Figure 12.
Residential Site
Overview
The residential site is located in
northwest Phoenix. It was installed in the
summer of 1986 and has been in continual
operation since. The design includes subsurface
irrigation of the turf in the front and rear yards
and conventional drip irrigation of the shrubs and
Figure 12. Vibrating Plow Attachment.
62
trees. The front turf panel is
approximately 700 sq. ft. and
the rear panel is approximately
900 sq. ft. The owner
contracted with Aqua Tech for
design and installation of the
system (Ilercil, 1990). Figures
13 and 14 show the front and
rear yards respectively.
Figure 13. Residential Site Front Yard.
Design
The system was designed with an automatic controller for scheduling and includes an
atmospheric backflow prevention device at the point of connection to the potable main line leading to
the house. A valve manifold is
located in the front yard to
control the turf and shrubs in
that area and a one inch PVC
main line runs to a similar
manifold in the rear yard to
service the turf and shrubs in
the rear. This part of the
design is consistent with a
traditional spray irrigation
Figure 14. Residential Site Rear Yard.
63
system. Figure 15 shows the
valve manifold assembly in the
rear yard.
The manifolds consist
of brass remote control valves
with built in anti-siphon devices
as additional protection for the
system. Each valve is followed
by a plastic screen filter to
Figure 15. Residential Site Valve Manifold.
collect particulate matter before
it passes to the emitter tubing. A pressure regulator then reduces the water pressure to the 30 PSI
working pressure of the emitters. The emitter tubing is then attached to valve manifolds as shown.
A collector manifold, at the end of each tubing run, is used to equalize pressures within the
lines and provide a single flush valve for cleaning the lines. The emitter tubing for this project is
supplied from the factory with the emitters buill in the tubing spaced one foot apart. The tubing is
installed four inches deep, two feet apart, giving a two foot by one foot grid pattern for the emitters.
Along the edges of all turf panels that come in contact with concrete, such as sidewalks, pool
decking or concrete walls the emitter tubing is installed 6 inches from the edge. This is done to
compensate for the heat transferred to the soil by the concrete edges. This added heat promotes
evaporation near the edges of the lawn, stressing this area (Ilercil, 1990).
64
Installation
The contractor. Aqua Tech of Phoenix, Arizona, has been installing subsurface irrigation
systems for seven years. A vibrating plow, as shown in Figure 12, was used to install the emitter
tubing. This attachment allows for installation of the emitter tubing at the spacing and depth desired to
within a fraction of an inch (Ilercil, 1990). After installation of the tubing, the turf bed was raked to
remove rocks and a root stimulating fertilizer was applied to the top of the soil. The system was turned
on to wet the soil prior to laying a hybrid bermuda sod. Figure 16 shows the wetted pattern on the soil
as the emitters begin to wet the surface. The project took three days to install.
Scheduling
The irrigation
controller is scheduled to run
the system for a total of five
hours per week. The run time
is divided into two cycles of 2
'/i hours each. With the emitter
spacing used on this project,
five hours of run lime provides
approximately 2 inches of
water per week for the turf.
Figure 16. Residential Site Soil Wetted Pattern.
Normal praclice for spray irrigalion systems in Phoenix in the summer is 2.25 in. per week. Thus, the
turf is receiving .25 inches per week less, approximately 11% less, water than would be provided by a
spray system.
Maintenance
The homeowner mows the lawn every seven to ten days during the growing season. The
mower is set at a height of I 3/4 to 2 inches depending on the appearance desired by the owner. The
grass clippings are collected and removed during mowing.
65
Fertilizer is applied manually every other month during the growing season, approximately four
times. Fertilization is done with a broadcast spreader using ammonium phosphate and applied at
manufacturer's recommended rate. The fertilizer is then watered in with an oscillating sprinkler. The
contractor recommends manual fertilizing to simplify maintenance procedures for residential home
owners.
The irrigation system is flushed, using the previously described flush valves, twice a year in the
spring and fall. The flush valves are opened and (he system is turned on for several minutes until the
water flows clean. In the four years of operation, there has been no noticeable plugging of the emitters.
Evaluation
An interview with the homeowner indicates very high satisfaction with the system. Aside from
periodic line flushing and seasonal changes in the controller program, there has been virtually no
maintenance. A visual examination of the turf shows very high color quality and an even density.
Governmental Site
Overview
The second case study is a six acre site located in Glendale, Arizona, at 5850 W. Glendale
Avenue. It is part of the Sahuaro Ranch Park - Phase Four, a division of the Glendale city park system.
The site is within the northwest corner of the Sahuaro Ranch park, bounded by 63rd Avenue on the
west. Cheryl Drive and Brown Street on the north and east, and the remainder of the park on the south.
Figure 17 shows the site layout.
The site is a retention basin for the park area. The soil is a loamy-clay, relatively uniform
throughout. There is little slope on the site, except for a 30 foot to 50 foot wide strip around the edge.
The maximum slope on these edges is the angle of repose for the soil, approximately 3:1. Some sloped
areas are graded at 4:1 and 5:1. There is little rock in the soil, which simplified the use of the vibrating
plow (Ilercil, 1990).
66
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SAHUARO RANCH PARK
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PARKING LOT & PARK IMPROVEMENTS
CITY PROJECT « NI7S024.11
IRRIGATION PLAN
Figure 17. Governmental Site Layout.
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67
Mr. Randall Sprcilzer, Ihe Glcndale Parks Supervisor, was interviewed for this study and
supplied considerable information about management of the system. The Glendale city park system has
embarked on an informal testing program to evaluate various turf irrigation systems. They are now in
the process of testing subsurface irrigation of turf on several of their city parks. Present tests have
been successful and additional test projects are scheduled for the future (Spreitzer, 1990).
Design
The project was
designed by Dames & Moore
Planning and Design Services
of Phoenix, Arizona. They
were contracted by the City of
Glendale to design the system
and then observe construction.
Figure 18 shows an
equipment enclosure built to
house the primary controls for
the system. Figures 19, 20, 21
Figure 18. Governmental Site Equipment Enclosure.
and 22 show the valve manifold with reduced pressure backflow prevention device, screen filter, master
shut off valve and chemical injector. Water for the system is supplied by a six inch main line coming
from within the park. It is directed to an equipment enclosure, where it is reduced to a four inch line.
A flow meter and a manual shut-off valve are also included to complete the system.
From the manifold, a four inch main line runs to nine remote control valves located on the site.
The remote control valves range from 2 inches to 2 'A inches in size. PVC sub-main lines extend from
the valves to service the emitter tubing.
68
On the horizontal
areas, the tubing is laid two
feet on center. Emitter spacing
is also two feet on center,
giving a 2 feet by 2 feet grid
for the emitters. Emitter
spacing on the slopes is one
foot on center, giving a 2 feet
by 1 feet grid. The designer
determined that a closer
Figure 19. Governmental Site Backflow Prevention Device.
spacing is necessary on slope conditions to offset the effects of gravity on water movement within the
soil (Teal, 1990). One gallon per hour emitters are used throughout the design.
Installation
Installation of the
system took thirty five days
during June and July of 1988.
The site was first soaked to
soften the soil for the vibrating
plow. The following day,
when the soil surface had dried
sufficiently, trenching was
begun.
Figure 20. Governmental Site Screen Filter.
69
Figure 23 shows
installation of the emitter tubing
with the vibrating plow. The
plow operator followed a string
line to insure accuracy of line
spacing. Using the vibrating
plow, it was possible to lay
2400 feet of tubing per hour.
Figures 24 and 25
show the emitter tubing
Figure 21. Governmental Site Master Valve.
following contours and the accuracy of installation on level ground. With one foot emitter spacing
running parallel with the contours, and a two foot tubing spacing, gravity tends to assist in the lateral
movement of the water within the soil (Teal, 1990). Glendale city inspectors verified design tolerances
throughout installation of the system. Tubing spacing and depth were required to be held to plus or
minus one inch.
After the tubing was
laid and connected to the sub
main lines, it was buried with a
gannon attached to a tractor.
The site was then smoothed to
finished grade. When
installation was complete.
common bermuda grass was
hydro seeded.
Figure 22. Governmental Site Chemical Injector.
70
Scheduling
An automatic
controller cycles the system in
order to apply a total of (wo
inches of water per week
during the summer. The
scheduling for the flat areas is
twice that for the sloped areas
because of the difference in
emitter spacing. The flat areas
Figure 23. Governmental Site Showing Vibrating Plow.
run a total of five hours and the sloped areas run a total of 2 'A hours. All water is applied in one
application, as opposed to two applications per cycle for the residential site. A complete watering cycle
requires 40 hours to run through all nine valves.
Maintenance
Parks department
maintenance crews were
originally apprehensive about
learning to maintain a new type
of system. But, they have
since come to appreciate the
reduced time required to
maintain this subsurface
irrigation system. Normal
maintenance practices on spray
Figure 24. Governmental Site Showing Emitter Lines Following
Contours.
irrigation systems require
weekly visits to check on
system operation. However,
crews have been able to
maintain the subsurface
irrigation system by visiting the
site once every three weeks
(Spreitzer, 1990).
The major difference
Figure 25. Governmental Site Showing Accuracy of Trenching.
in maintenance practices is the
virtual elimination of repairs necessitated by vandalism. With spray irrigation systems, irrigation is
normally carried on at night to reduce evaporation and so that activities of the park are not disrupted.
However, high rates of vandalism occur at night (Spreitzer, 1990).
At present, fertilization is done with conventional methods by broadcasting over the surface. It
was felt that maintenance crews should learn operation of the system on a sequential basis. In the
future, experiments will be conducted using the fertilizer injector installed at the manifold.
Evaluation
On a scale of six acres or larger, the size of this project, the relative cost of the subsurface
irrigation system and a traditional spray system is S.15 per sq. ft. for a spray system and $.21 per sq. ft
for a subsurface irrigation system or approximately 40 % greater for the subsurface system.
Considering savings in maintenance and repairs only, the estimated payback on the additional cost of the
system is two to three years (Spreitzer, 1990).
72
The system is less efficient than a spray system for up to one month after installation. This is
due to less compaction of the soil in the trenches where the tubing is installed.
As compaction
equalizes due to normal settling, foot traffic and lawn mowers, lateral movement of the water increases
to design limits (Ilercil, 1990).
Approximately the same amount of water is applied per square foot of turf with the subsurface
irrigation system as would be with a spray system. From the standpoint of the quality of the turf,
however, the advantage of a subsurface irrigation system is that better quality, healthier turf is realized
for the same amount of water. In the summer of 1991, experiments will be conducted to determine the
advantages of other scheduling regimes (Spreitzer, 1990). It is expected that applying 60% of the water
at one time and then 30% a day or so later, a 10% savings is possible with no degradation of turf
quality.
The reduction in liability afforded a public agency with the use of subsurface irrigation systems
may greatly overshadow any savings in water or costs. Litigation costs today provide great incentive to
adopt subsurface irrigation of turf on public properties (Spreitzer, 1990). The city of Glendale is
presently studying this issue, but it has yet to be documented.
Conclusions
The use of a vibrating plow is essential if costs of subsurface irrigation systems are to compare
favorably with spray irrigation systems. They provide the contractor the advantages of precise
placement of the tubing both in spacing and depth, to within plus or minus one inch. The contractor has
found (hat this level of accuracy is required to insure proper water coverage (Ilercil, 1990). Second, the
plow can install up to four lines of tubing at one time, greatly reducing installation cost.
The case studies suggest different management regimes are needed for different size projects.
On larger projects, considerably less maintenance and repairs are required. On smaller projects, the
savings in maintenance costs, while still substantial, are not as significant as those on a larger project.
Client satisfaction with the systems was very high, but for different reasons. The homeowner
was pleased with the quality of the turf and the elimination of sprinkler repairs experienced with
previous systems. The Glendale Parks Supervisor was pleased with reduced vandalism and maintenance
costs. Cost savings were sufficient on this first generation system to warrant additional testing
(Spreitzer, 1990).
The advantages of subsurface irrigation of turf need to be documented. Savings in water,
maintenance costs, liability costs and repairs due to vandalism are difficult to accurately judge. Other
advantages, such as better turf quality and reduced interruption of site activities need investigation also.
74
SUMMARY
At the root of this study is the desire to see subsurface irrigation of turf utilized more in water
sensitive areas of the world. As an irrigation designer experienced in both spray and subsurface
irrigation systems, the author has found it difficult to utilize this promising technology. It is hard to
convince a client to allow anyone to experiment with his money. Without explicit design principles,
adaptable to varying conditions, the designer is forced to do just that. This paper has examined the
application of subsurface irrigation technology to turf in the landscape and has been directed by four
objectives as expressed in the section titled "Problem Statement". A response to those objectives can
best summarize this paper.
Objective 1
Review existing literature using published and unpublished sources to determine its relevance
for the designer of subsurface irrigation systems.
The first objective of this study has been accomplished. It has been shown that the
information is not centralized and not directly applicable to design questions. In its present form,
existing information is of little value to the designer.
With a few exceptions, the literature does not deal specifically with subsurface irrigation of
turf. Few studies would be helpful to the designer of a project. Existing literature is spread among
many sources, sometimes contradictory, and of little use to the irrigation designer. In its present form,
it is neither easily available, nor particularly useful to those who need it. Much of the knowledge of
these systems is not in the literature, it is in the minds of a small group of practitioners.
75
Academic Studies
Much of the academic research on subsurface irrigation revolves around the application of this
technology to agricultural crops. One application found in the literature that would be helpful to the
landscape designer related to sandy soils, typically used in golf course greens.
For design criteria to be useful to the designer, they must be directly related to subsurface
irrigation of turf. Issues such as emitter spacing, emitter tubing lay out, filtering and scheduling must be
dealt with specifically.
Popular Journal Articles
Popular journal articles deal more explicitly with the topic, but typically in a promotional
manner with undocumented claims. These articles are many times written by manufacturers and contain
exaggerated claims about their product. Several articles draw conclusions that conflict with findings
from field installations. The most conspicuous of these claims is that of high water savings achieved for
subsurface irrigation (Stroud, 1987). These claims are highly suspect because they are not well
documented, sometimes not at all.
One article mentioned reduced liability potential with subsurface irrigation methods (Cloud,
1980). For public projects, this aspect of the technology may prove to be more important than any other
(Spreitzer, 1990).
These articles do present many design and management recommendations that are consistent
with other sources. They seem to be backed by a reasonable amount of trial and error and should be
quite valid because they relate directly to a field situation, as opposed to experimental data that would
have to be adjusted to fit field conditions.
Technical Literature
Irrigation text books are little help to the subsurface irrigation designer. Most reference to the
topic deals with soil water relationships, salt distribution, emitter clogging, filtering systems, fertilization
76
and irrigation scheduling (Nakayama, 1986). The Nakayama book contains background information
required for hydraulic design of subsurface irrigation systems, but it is much too theoretical and
technical in nature and does not deal specifically with turf applications.
Manufacturer's publications are more helpful. They seem to be backed by more
experimentation than other sources. There are several recommendations that remain consistent between
authors. Some manufacturers have developed formulas to aid in the design. Two manufacturers
provide simplified plans of sports fields and smaller sites. These plans may give the designer the
concept for a design, but they are not complete enough to be of assistance in the actual design of a site.
Summary
Along with considerable disagreement, agreement from many sources can be found in the areas
of advantages, disadvantages, design, installation and maintenance. Very little information of value to
the designer appears to be universally accepted. But, as more sources agree on certain principles or
practices, they achieve a certain validity and become less risky for the designer to rely on. These areas
of agreement can be summarized as follows:
A.
Advantages when compared with traditional spray irrigation are as follows:
1.
Considerable water can be saved by watering at less than the
evapotranspiration rate.
2.
Turf appearance does not become dusty or dirty from lack of overhead spray.
3.
Recovery from heat stress may be greater.
4.
There is significantly greater root mass.
5.
Soil moisture content tends to be more consistent over time.
6.
Moisture stress is less apparent.
7.
Component quality has improved in recent years.
8.
Maintenance costs appear to be significantly less.
9.
Liability is considerably reduced.
10.
Scheduling is simplified because watering can take place while the site is in
use.
11.
Soil compaction is reduced.
12.
Energy saving, in the form of pumping costs are reduced.
13.
Splash transmitted diseases are reduced.
14.
Fertilizer and other chemical application is simplified.
15.
Nearly 100 per cent coefficient of uniformity can be achieved.
16.
Reduction or elimination of runoff on sloped sites is possible.
17.
Narrow or irregularly shaped areas, such as those found in road medians and
parking lot medians, can easily be irrigated.
18.
Vandalism can be greatly reduced, if not eliminated.
19.
Larger expanses of turf can be irrigated at one time.
20.
Modification of existing systems is simplified if the turf area is changed.
Disadvantages when compared with traditional spray irrigation are as follows:
1.
Cool season grasses perform less well than warm season grasses.
2.
The designer and installer must be familiar with this type of system because
subsurface irrigation of turf is not forgiving of error.
3.
There may offer little or no water savings if the system is not properly
designed.
4.
Installation procedures must be more exact.
5.
Initial costs can be higher.
6.
Maintenance procedures may be more difficult to learn.
7.
Because the systems operate with low pressures, problems can go unnoticed.
8.
Fertilizer and pesticide application could cause localized concentrations of
nutrients.
Design Parameters
1.
All systems should include pressure regulators, chemical injectors, automatic
flush devices and water filtration systems.
2.
Emitter spacing should be less in heavy, clay soils than in sandy soils.
3.
Tubing spacing should be no more than 24 inches.
4.
Tubing depth should be between 4 and 6 inches.
5.
Tubing should be placed closer to the edge of the turf when it comes into
contact with concrete, no farther than 6 inches from the edge.
6.
Emitter spacing should be reduced in sloped conditions.
7.
An automatic air venl/vacuum relief valve should be used at each remote
control valve.
8.
As soil texture becomes more coarse, emission rates should increase to 1.8 to
2.8 gallons per hour.
9.
A layer of coarse textured soil beneath a finer textured layer can improve
lateral water movement.
10.
Pressure compensating emitters should be used if point source emitters are
utilized.
11.
Emitter and tubing spacings should be reduced in high traffic conditions.
12.
Salt tolerant turf species are important to success.
13.
Cool season grasses require that the tubing be placed closer to the soil
surface.
14.
The total cost of the system from design, installation, operation, maintenance
to repair should be considered when evaluating subsurface irrigation of turf.
15.
Efficient installation procedures must be used to keep costs comparable to
conventional irrigation systems.
79
D.
Installation Methods
1.
Modern vibrating plow equipment should be used for installation of the
emitter tubing.
2.
E.
The soil should be slightly moist to assist with installation of the tubing.
Maintenance Practices
1.
Fertilizer and pesticide application must be properly managed.
2.
Pulse watering should be used to increase lateral water movement in the soil.
3.
Acid solutions, herbicides and insecticides can be injected through the system,
to prevent emitter plugging.
4.
Regular watering is recommended to reduce root intrusion into the emitters.
5.
Filters, controllers, drains and other components should be checked regularly.
6.
Maximum chemical injection efficiency is achieved by allowing the system to
run long enough to establish flow equilibrium before the chemicals are
injected into the system.
7.
More frequent irrigation scheduling can benefit soil or water salinity
problems.
8.
Fertilizer applications should be more frequent during the early stages of plant
growth
Objective 2
Examine installed sites to determine current industry practices.
The two installed sites, even though they are quite different in scale, have essentially the same
components. They also were installed using virtually the same equipment. The components included in
each system, in order of their assembly, beginning with the point of connection at the water main is as
follows:
80
A.
Main Line - It connects the system to the water source.
B.
Backflow Prevention Device - It protects the water source from contamination from
chemicals used in the system.
C.
Sub Main - It extends from the backflow prevention device to the valve manifold.
D.
Valve Manifold - It is an assembly that contains the valves and other components.
E.
Filter Device - It removes particulates from the water to help prevent emitter clogging.
In smaller, residential sites, it also serves as a chemical injection device.
F.
Master Valve - It is used in large sites where additional control of the water supply is
desired.
G.
Chemical Injector - In larger systems, it is a stand alone device used to inject various
chemicals into the system.
H.
Pressure Regulator - It reduces the water supply pressure to a level usable to the
emitters.
I.
Header or Lateral - It carries the water to the turf area and the emitter tubing.
J.
Emitter Tubing - It supplies water to the soil at a predetermined rate and may have
internal point source emitters or it may be a line source emitter.
K.
Collector Manifold - It collects water from the emitter tubing and helps equalize
pressure among the emitter lines.
L.
Flush Valve - It is an automatic valve that flushes water and debris from the collector
manifold.
Regardless of the size of the project, all the functions accomplished by these components must
be performed in order for the system to operate properly. Leaving out even one function for the sake of
81
money or design simplicity will cause problems (Ilercil, 1990). The area of most concern to the
designer of each site was the layout of the emitter tubing in both spacing and depth. This area of
design requires the most experimentation by a novice in subsurface irrigation, at least until a level of
competence is achieved. The clients for each system expressed a very high level of satisfaction, but
both for different reasons. The homeowner liked the very low maintenance and high visual quality of
the turf. And the city park manager appreciated the savings in maintenance and reduced liability.
Objective 3
Develop a model to assist the designer of subsurface irrigation systems for turf.
This objective points out the condition, expected by (he author, that much additional research
and testing remains to be done on the topic. It is apparent that every area examined would benefit from
additional research and experimenting. Information, when it can be found, is suspect With each
project undertaken, the designer is left to make many decisions for which he has no justification .
Information that might benefit the end user, such as maintenance procedures, operating costs or pay
back periods is almost nonexistent. As previously noted, tubing and emitter layout is a critical question
for the designer. Yet, little information on the subject is definitive. Almost every site variable, client
need and maintenance regime affects the designer's choices.
By using these variables it is possible to develop a matrix to help the designer with system
design. But the qualitative values applied to the variables must be informed guesses at best. Only an
extended use and subsequent adjustment of values in such a matrix could validate it. With that in mind,
the following matrix is suggested. Its purpose is to assist in tubing and emitter spacing.
The matrix is composed of an Emitter Spacing Value Guide, Table 11 and an Emitter Spacing
Selector, Table 12. The designer first enters the Emitter Spacing Value Guide and determines an
82
adjusted value for each design variable found in the project. The spacing factors related to each design
variable affect the spacing for that design variable. When a spacing factor is selected, it is multiplied by
the spacing value associated with it. The spacing value is an indication of the emitter relative emitter
spacing required by that variable. A smaller number indicates a closer emitter spacing. The spacing
value is then multiplied by the weighting factor to give an adjusted value. The weighting factor relates
to the relative importance or sensitivity of the factor to the spacing of the emitters. The adjusted vales
are added and then divided by the sum of the weighting factors to give the weighted adjusted value, or
spacing value. The weighted adjusted value is then compared to those shown in the Emitter Spacing
Selector matrix to arrive at the final tubing and emitter layout. An on center spacing grid, either square
or rectangular is then selected from the matrix. Emitter coverage in square feet is also given.
The values assigned to the variables in both charts are estimates only. They are meant to
provide a framework for further study and experimentation. The values used in the charts are estimates
and must be tempered with the designer's experience. They are not meant to be used without further
study.
83
Decision
Module
EMITTER SPACING VALUE GUIDE
rv/'m' "trnfi v > tyi,'
Value
Factor
High coarse sand
fine sand
1.00
Medium Sandy loam
Loam
1.25
Low Clay loam
Clav
1.75
ShaIlow<12"
or Hardpan
3.00
Depth > 12"
1.00
Level < 10%
2.00
Slope 10-20%
1.50
Slope > 20%
1.00
Turf
Variety
Cool Season
1.00
Warm Season
1.50
Mainte­
nance
Intense
Management
2.00
Regime
Minimal
Management
1.00
High
1.00
Medium
1.25
Low
1.50
High
1.00
Medium
1.25
Soil
Infil­
tration
Rate
Soil
Depth
Slope
Desired
Appearance
Quality
Site
Use
Intensity
Low
1.50
«
* t ..
. .
Sum of A
djusted
3
•k^sssmI
1
2
|||
3
13tp
2
1
1
''Wv,
1
.
Values
Sum of Weighting Factor*
Weighted
Table II. Emitter Spacing Value Guide.
Adjusted
Value
'
*•*
13
->\ "Wt
84
r
EMITTER SPACING SELfiCTOk' v '
|^
I '-11^
I
h-
18
21
/
' " '
MillH
18x18 o r
12x24
2.25
Square
3.06
Only
24
Square
4.00
Only
Table 12. Emitter Spacing Selector.
Objective 4
Determine the areas of greatest need for further research and technical development.
At the root of this study is the desire to see subsurface irrigation of turf utilized more in water
sensitive areas of the world. As an irrigation designer experienced in both spray and subsurface
irrigation systems, the author has found it difficult to utilize this promising technology. It is hard to
convince a client to allow people to experiment with his money. Without explicit, proven design
principles, adaptable to varying conditions, the designer is forced to do just that.
It would be accurate to suggest that all areas of the subject need additional investigation. One
area that stands out as in more need of research than others is that of tubing and emitter layout. It
seems unlikely that subsurface irrigation will progress until a data base is developed that will give the
designer confidence that he can design a system that will work without experimenting. The selection
matrix presented here is derived from many different sources and personal experience. The value and
weighting factors used in the matrix need to be experimented with and adjusted as necessary.
Future investigations naturally fall into two categories. The designer will be served by an
examination of specific design issues that are needed to make the system work. The end user, on the
other hand, needs answers to a different set of questions. Before he can justify selecting a new
technology, financial and performance questions must be answered.
85
If subsurface irrigation of turf is to become more widely used, the guesswork must be taken out
of design. To be of value to the designer, information must be in the form of universal principles that
are adaptable to varying situations. But, researching these questions is not enough. The information
must then be made available to those who need it, the designers and the end users. One of the
difficulties encountered while doing this study was the gathering the information from widely dispersed
sources. It should be compiled in a design manual for subsurface irrigation that would relate directly to
the design of an operating a system and include answers to the following questions:
Questions for the Designer
Included here is the component layout for the design such as valve manifold, valve layout,
emitter and tubing spacing and depth. Emitter plugging and filtering requirements are vital to long term,
problem free operation. Even though it has been demonstrated that plugging is not a problem with a
properly designed and operated system, it is perceived as a problem. Issues affecting emitter plugging
that need investigation include maintenance practices, requirements for filtering different qualities of
water and long term use of the system. Different methods of irrigation scheduling should be
investigated. Pulse watering, soil structure, turf variety and emitter spacing should be examined.
Questions for the User
System cost is very important to the end user. In evaluating system cost, a long term approach
is necessary. For an accurate picture, the complete life cycle of the project should be considered.
Larger projects can cost much more than conventional systems. However, large projects offer the
greatest potential for saving when operational costs are considered. On large projects, where an
inventory of repair costs must be carried, interest savings can be substantial.
Water savings have not been sufficiently documented. As the technology is improved,
substantial water savings should be realized. If it is found that subsurface irrigation consistently can
86
save water, demand will increase substantially. Answers to this question should be realized with
research in other areas.
Maintenance costs are important to the weekend gardener and vital to the large site manager.
The questions of chemical injection, system scheduling and normal maintenance need to be answered.
Other Recommendations
Subsurface irrigation of turf is a reality. It has been suggested by the case studies that it works
well and can be cost effective. The problem seems to be a general lack of knowledge and
misconceptions about the technology. It is important to think of subsurface irrigation of turf as a
distinct product, not a group of technologies performing a function. Therefore, an educational effort is
needed to inform the user, designer and installer of the advantages of the system. This educational
function could be performed by professional societies such as the American Society of Landscape
Architects, the American Society of Irrigation Consultants and the Irrigation Association.
One complaint the author has heard many times is that a subsurface irrigation system is
difficult to install because so much trenching is needed for the emitter tubing. It has been demonstrated
by the case studies that this need not be so if modern equipment is used. Equipment, even larger than
that shown in the case studies, and with devices to feed the tubing from rolls could bring installation
costs in line with conventional spray systems. Again, education and experimentation is needed.
Landscape design on (op of structures using turf has always been difficult. This type of
application is generally pedestrian intensive and a method of preventing over spray should be welcome.
The weight of the soil and over spray from irrigation systems present significant problems to the
designer. Subsurface irrigation would seem a natural solution to the over spray problem. It is possible
that substantial weight and water savings are possible with soil stratification techniques.
Soil stratification or layering entails engineering the soil bed with individual layers suited to
specific purposes. The top layer of suitable thickness would be used as the turf rooting medium. A
87
fibrous soil separation blanket would be used to isolate the top layer from a lower drainage layer. The
author believes this technique could improve lateral water movement and thus allow wider tubing
spacings, reducing system cost. For on-structure applications the lower, drainage layer could be
composed of a weight reducing material.
Investigation into the potential savings in insurance costs need to be undertaken. This area
should prove to be a strong deciding factor for public entities trying to reduce litigation costs. It may
require an educational effort to inform insurance companies of the possible savings. Even though this
could be a strong factor in favor of subsurface irrigation, it will take some time for insurance companies
to develop actuary tables in order to develop a rate structure. A larger, and more immediate savings
may be a reduction in claims.
The marketing of subsurface irrigation of turf is sadly lacking. It has been demonstrated to
work well and be cost effective. The problem seems to be a general lack of knowledge and
misconceptions about the technology. It is important to think of subsurface irrigation of turf as a
distinct product, not a group of technologies performing a function. Therefore, an educational effort is
needed to inform the user, designer and installer of the advantages of the system. This educational
function could be performed by professional societies such as the American Society of Landscape
Architects, the American Society of Irrigation Consultants and the Irrigation Association.
Above all, a larger number of installed projects need to be studied. The only way to prove the
technology is to document its success in the field. Scientific studies will help quantify some variables,
but actual sites must be examined to work out the fine points of design. Both small and large scale
sites should be studied. Variables such as cost comparisons, maintenance practices and water savings
should be studied along with the various design issues.
APPENDICES
89
GLOSSARY
Important or widely used terms whose meanings may not be clear are included here. It should
be noted that many terms dealing with the topic of this paper are used interchangeably by the industry.
Every effort has been made to use the most common or typical terminology employed in the irrigation
industry. To clarify the terms used in this paper, the following definitions are included:
Air vent/vacuum relief valve - An automatic valve placed just after the remote control valve in a
system that prevents a vacuum from being produced in the line. Prevents soil slurry and other
contaminants from being drawn back into the line.
Drip irrigation • The most commonly used term to describe a form of micro-irrigation, usually applied
above ground so the water drips onto the soil near the base of the plant. Same as trickleirrigation or micro-irrigation.
Emitter - Component of a drip irrigation system that dissipates pressure within the irrigation line and
discharges water to the plant. Ideally it passes a specific amount of water at a constant
discharge rate that does not vary significantly throughout the system.
Evapotranspiration - The total loss of water by both transpiration through the plant leaf material and
evaporation from the soil surface. Because little or no water is at the soil surface, the
evaporation component is greatly reduced by drip irrigation.
Lateral pipe - An irrigation pipe, downstream of the control valve, to which other pipes are connected.
Line source emission - A method of discharging water in which water is emitted along the entire
surface of the pipe (see porous pipe).
Lysimeter - A device used to test water consumption of plant material. Consists of a box in which the
plant is grown that can receive measured amounts of water from a tube attached to the bottom.
90
Manifold - A grouping into a single assembly of irrigation valves. Assembly and maintenance is
simplified by placing valves together.
Micro-irrigation • A blanket term used to describe several methods of irrigation. Generally refers to
technologies utilizing low volumes of water (includes drip irrigation, micro-spray, trickleirrigation).
Micro-spray - A form of micro-irrigation that utilizes small, low volume spray heads for above ground
use.
Plant cooling - The creation of a micro-climate around the base of a plant by the evaporation of surface
moisture. Effective in preventing sun scalding and heat desiccation of ground covers and low
shrubs.
Point source emission - A method of discharging water in which water is emitted at specific points
along the delivery pipe. Emission points can be holes in the pipe or highly engineered emitters.
Polyethylene - The major component in modern flexible irrigation pipe. Uses simple compression
connections. Not susceptible to ultraviolet degradation.
Polyvinyl chloride (PVC) - The major component in modem rigid irrigation pipe. Uses simple
cemented connections. Susceptible to ultraviolet degradation.
Porous pipe - A type of micro-irrigation pipe with a permeable surface. Contains many microscopic
pores per meter of pipe. Water is emitted along the entire surface of the pipe (see line source
emission).
Pulse scheduling - Scheduling the irrigation system to be turned on repeatedly for short periods of time
instead of running the system for the required length of time in one cycle. Total run-time of
the system is the same in both cases. Lateral movement of water is increased in the soil with
pulse scheduling.
PVC (polyvinylchloride) - A type of rigid plastic pipe used for irrigation systems. The most common
material used in landscape irrigation pipe.
Rizosphere - The zone within and just above the soil that contains the roots of the plant. This area
must supply the water and nutrients that the plant needs for growth.
Root intrusion - The tendency of plant roots to grow into an underground emitter. Water flow from
the affected emitter is then reduced or stopped entirely.
91
Root zone - The area within the soil that contains the plant root system. Must be supplied with all the
water and nutrients the plant needs for growth.
Saturated/wilting point cycle - The cycle caused by traditional irrigation techniques in which the soil is
first saturated and then allowed to dry to the wilting point between applications of water.
Saturation point - The point at which the soil cannot hold further water. Gravity drains additional
water from the soil.
Soil moisture profile - The ratio between the moisture content in the driest part of the soil and that in
the wettest part of the soil. In a desirable soil moisture profile, the soil moisture content is
relatively uniform throughout.
Splash transmitted disease - Plant diseases caused by water sprayed or splashed onto plant material.
Water sitting on plant leaves can provide ideal conditions for disease and fungus growth,
especially in warm, shady locations.
Spray irrigation - The traditional above ground method of irrigating crops and turf. Water is dispersed
over the plant material in the form of droplets. Water droplets are highly susceptible to wind
drift. Very difficult to achieve uniform coverage of the surface area.
Subsurface irrigation - A form of micro-irrigation in which the emission point is below ground and
located within the root zone of the plant.
Tensiometer - A device that measures the moisture content of the soil. Can be used to override the
irrigation controller to prevent over watering.
Trickle-irrigation - A form of micro-irrigation, usually applied above ground so the water drips onto
the soil near the base of the plant. Same as drip irrigation.
Wetted front - The face of the wetted area caused by water movement through the soil. It moves away
from the point of emission in an ellipsoidal shape. Soil and water salts are translocated by the
wetted front and moved away from the point of emission.
Wilting point - Soil moisture content at which the plant cannot draw water from the soil and wilting
occurs. A prolonged soil wilting point will cause plant death.
Xeriscape - A concept in which landscape water consumption is reduced by the use of appropriate
design techniques. Three primary components are design, plant selection and efficient
irrigation.
92
VITA
Personal Data
Date of Birth:
Affiliations:
Military:
Education
July 10, 1942
American Society of Landscape
Architects,
American Society of Irrigation
Consultants,
Lt. J.G. U.S. Navy
Honorable discharge 1969
UNIVERSITY OF ARIZONA: Tucson, Arizona
Major: Landscape Architecture
Degrees in Progress:
Master of Landscape
Architecture,
Bachelor of Landscape
Architecture
ARIZONA STATE UNIVERSITY: Tempe, Arizona
Major: Marketing
Degree: Bachelor of Science
Year:
1968
PHOENIX COLLEGE: Phoenix, Arizona
Major: Engineering
Professional
Experience
1990 - Present, Oklahoma State University: Stillwater,
Oklahoma, Instructor - Landscape Architecture.
1988 - 1990, University of Arizona: Tucson, Arizona
Instructor - Site Engineering, Landscape Construction.
1988 - 1989, Harlow's Landscaping: Tucson, Arizona
Landscape Designer/Draftsman, Construction
Observation.
1986 - 1978, Lendrum Design Group: Phoenix, Arizona
Landscape Designer-Draftsman, Construction
Observation, CADD Operator.
1984 - 1986, Leisure World: Mesa, Arizona
Landscape Foreman, Construction Supervisor.
1975 - 1984, Prescott Landscape Systems: Prescott, Arizona
Owner/Operator, Landscape Design-Build Firm.
93
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