Io r
ovember 1983
Circular 584
Hydraulic Specifications
Of Trickle Irrigation Subunits
COMPUTER SERIES
F. S. Zazueta, D. S. Harrison, and A. G. Smajstrla
rida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean
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mk'
MAWA
Trade names are used liberally in this documentation. Their
mention is for illustrative purposes only and does not reflect
any preference, support or relationship by or to the authors, The
University of Florida, and The Cooperative Extension Service, in
any explicit or implicit manner.
FLORIDA COOPERATIVE EXTENSION SERVICE
INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES
Department of Agricultural Engineering
University of Florida
HYDRAULIC SPECIFICATIONS OF TRICKLE IRRIGATION SUBUNITS
(c) IFAS, University of Florida, 1982,1983
SECTION IV
HYDRAULIC SPECIFICATIONS OF TRICKLE IRRIGATION SUBUNITS
by
Fedro S. Zazueta, Dalton S. Harrison and Allen G. Smajstrla \1
INTRODUCTION
This program is executed by typing SPEC.
Trickle irrigation consists of the frequent application of
small quantities of water on or below the soil surface as dis
crete or continuous drops, tiny streams or miniature spray
through an extensive hydraulic network.
The purpose of the irrigation system is to maintain a zone
of adequate dimensions and water content in order to achieve high
levels of productivity. Water and the nutrients in solution that
are necessary for plant growth are available to the plants only
if they are within the active root zone of the crop. If water
moves beyond the root zone, it cannot be used by the crop thereby
causing a reduction in the efficiency of the system.
In general, poorly designed systems will have portions of
the system which are overirrigated and other portions that are
underirrigated. In order to compensate for the sections that are
underirrigated it is necessary to operate the system for longer
periods of time which may result in severe overirrigation in a
significant portion of the system. Ultimately, poor design leads
to a system that may be difficult to manage and that may not
produce the expected benefits.
The criteria used in evaluating the hydraulic performance of
trickle irrigation systems are uniformity coefficients. Whatever
the mathematical expression of a uniformity coefficient might be,
it is an indicator of how equal (or unequal) the application
rates from the emitters are. It is an overall measure of how much
the emitter discharges in the system differ from the average
emitter operating discharge due to: 1) changes in pressure due to
energy losses and, 2) manufacturing variation.
Uniformity coefficients are difficult to interpret. Thus, it
is convenient also to know the average, the minimum and the
maximum discharges that occur within a concurrently operating
\1 Visiting Assistant Professor, Professor and Associate
Professor, IFAS, Agricultural Engineering Department, University
of Florida, Gainesville, FL.
section of the system. The computations of the uniformity coeffi
cients, pressures, and discharges are time consuming and are
greatly simplified by the use of this computer program.
INPUT DATA
Three types of information are necessary to run this program:
information relative to 1) the lateral, 2) the manifold and, 3)
the emitter.
Lateral Data.
The necessary input is:
1) The discharge per tree in gallons per hour.
2) The number of emitters per tree.
3) The lateral's internal diameter in inches.
4) The tree spacing along the lateral in feet.
5) The number of trees along the lateral.
6) The HazenWilliams constant of the pipe.
7) The slope of the lateral in feet per one hundred feet.
(This is equivalent to % slope.)
Manifold data.
1) The number of laterals along the manifold.
2) The Hazen Williams constant of the pipe.
3) The slope of the manifold.
4) The pipe diameter in inches and the length in feet of
each section of pipe along the manifold.
Emitter Data.
1) The emitter trademark.
2) The manufacturing coefficient of variation.
3) The discharge relationship of the emitter. This item
consists of two points along the pressuredischarge
relationship of the emitter. Pressure should be given
in pounds per square inch and discharge in gallons per
hour.
4) The average design operating pressure in pounds per
square inch.
OUTPUT
The output from this program is suitable for printing. Two
pages of output are generated (see listing 1). In the first page
all input data are echoed with an option to send to the printer.
The second page displays the values of:
1) Head losses expressed in feet of water occurring in the
lateral and in each section of the manifold.
2) The average lateral discharge and the total discharge
entering the manifold expressed in gallons per minute.
3) The minimum and maximum pressures occurring in the sys
tem expressed in pounds per square inch and the varia
tion in percent from the average design pressure.
4) The minimum and maximum emitter discharge expressed in
gallons per hour and the variation in percent from the
average design discharge.
5) The subunit and absolute design emmission uniformities.
Emission uniformities may be interpreted using the values in
table 41.
SSAMPLE RUN
An example of how to interpret the data and run the program
are described here. This system was designed for demonstration
and research purposes by IFAS irrigation specialists (Harrison,
1981) The system is a 40 acre trickle (spray jet) irrigation
system. Notice that the review of specifications using this
program refers to a subunit in the system. A subunit is defined
as a single manifold with its corresponding pressure regulators
(if any),laterals and emitters. The example of the 40 acre citrus
irrigation system will be explained below in detail.
From Figure 41, a reduction of the blueprint of the 40 acre
citrus irrigation system, note that the system is composed of: 1)
four identical subunits (sets) of 744 trees each and, 2) two
subunits (sets) of 768 trees each. The subunits with the larger
number of trees are the ones on the upper part of the plan. In
the irrigation subunits with 744 trees, half of the laterals
supply water to 15 trees while the other half supply water to 16
trees. In the subunits with 744 trees all laterals supply water
to 16 trees. Otherwise, the subunits are identical, having the
same lateral diameter and pipe diameters and lengths of the
manifold. The subunit with the 768 trees will be used as an
example. Data input is illustrated in CRTs 41, 42 and 43.
LATERAL DATA
1) Discharge per tree:
This is the the average volume per unit time in gallons
per hour applied at each tree. Notice that it is not
the discharge per emitter but the sum of all the
emitter discharges at a given tree. The irrigation
design plan of the 40 acre citrus grove specifies that
a single microjet operating at a discharge of 14.8 gph
will be used per tree, thus the value corresponding to
this data item is 14.8 as is shown in the sample form.
2) Number of emitters per tree.
Average number of emitters per tree computed from the
emitters per lateral divided by the number of trees.
In the 40 acre citrus grove example a single emitter
per tree was used, thus this data item is 1.
3) Diameter of lateral.
This is the internal pipe diameter in inches. Internal
diameters differ from nominal diameters ad may differ
from manufacturer to manufacturer. This value should
be obtained from the pipe manufacturer's specifica
tions. The design plan of the 40 acre citrus irriga
tion grove specifies that the pipe to be used has an
internal diameter of .700 inches, thus this data item
is 0.700
4) Tree spacing along lateral.
Average spacing in feet of trees along the lateral
pipe. In the 40 acre citrus grove example the trees
along the lateral line are spaced at an interval of 14
feet. Thus, this data item has a value of 14.
5) Number of tree rows along lateral.
This is the number of trees that are irrigated by a
single lateral. For this subunit each lateral irri
gates 16 trees. Thus, this data item is 16. If the
laterals are not all of the same length, computations
should be made using the HAZEN program with the
corresponding correction for multiple outlet pipes.
6) HazenWilliams constant
This value depends only on the material that the late
ral is made of. In trickle irrigation systems the pipe
materials used are polyvinyl chloride (PVC), Polyvinyl
dichloride (PVDC), Polyethylene (PE), Acrylonitrile
butadiene styrene (ABS). Mostpipe is PVC or PE with
corresponding values of 150 and 140. In the 40 acre
citrus grove the lateral is specified as PE with a
corresponding value for the HazenWilliams constant of
140.
7) Slope of the lateral.
The average change in elevation of the ground surface
along the lateral expressed in feet/100 feet. Specify
44
if it is upwards (+) or downwards () in the direction
of flow. The topography in which the example is set is
flat with no change in elevation, thus this data item
is 0.
MANIFOLD DATA
1) Number of laterals along manifold.
This is the number of laterals that are fed by a single
manifold. A lateral is the distribution pipe that
feeds the emitters. Notice that each lateral is
connected at one end to the manifold and that more than
one lateral may be connected to the manifold at any
point along the manifold. (Rather than using the idea
of a 'center fed' lateral the lateral is defined as
stated above.) In the 40 acre citrus grove there are
24 laterals on each side of the manifold. Therefore
this data item is 24 x 2 = 48.
2) Hazen Williams constant.
This value depends only on the pipe material as
explained above for the lateral. The plan for the 40
acre citrus grove specifies that the manifold be con
structed from PVC pipe. Thus, this data item is 150.
3) Slope of manifold.
The average change in elevation of the terrain along
the manifold expressed in feet/100 feet. Specify if it
is upwards (+) or downwards () in the direction of
flow. The topography in which the example grove is set
is flat with no significant changes in elevation, thus
this data item is 0.
4) Laterals on both sides of the manifold?
Sometimes the manifold is set at the side of the grove,
having laterals only to one side, in which case answer
NO. When the manifold supplies water to laterals on
both of its sides, answer YES. In the example given
here the answer is YES.
5) Pipe diameters and lengths.
These are the lengths and the internal diameters of the
different sections of pipe that make up the manifold.
If the manifold is not tapered, there will be only one
diameter and length. If it is tapered there will be
several diameters and lengths. A close analysis of the
irrigation plan will yield the following data items:
Internal Diameters (inches)
4.15 322
3.23 168
2.65 112
1.53 56
Once again notice that the pipe diameter values refer
to internal diameters. These values are obtained from
the manufacturer and are usually available in most
commercial literature.
EMITTER DATA
1) Coefficient of variation.
This coefficient is sometimes available from the manu
facturer. If not available answer N/A. In the
example this datum was not available from the
manufacturer.
2) Discharge relationship.
These data are available from the manufacturer in
the form of a table or a graph. Two pairs of pressure
discharge are necessary. It is not critical what two
specific values are used, although it is desirable that
they be close to the system's design operating
pressure. The values for the 40 acre citrus grove are
taken from the manufacturer supplied data shown in
table 1, and are as follows:
Pressure (psi) Discharge (gph)
15 13
20 14.8
3) Average design operating pressure.
The pressure in pounds per square inch corresponding to
the average discharge per emitter, for which the system
is designed. In the 40 acre citrus grove the design
discharge per tree was selected to be 14.8 gph using
one spray jet. Notice that this discharge from the
emitter will occur at a pressure of 20 psi. Therefore
the value of this data item is 20 psi.
4) Date and System Location.
These data are given for identification purposes only.
They are not used in any computations. They are echoed
to the output as they are input by the user.
46
Length (feet)
The results of using the computer program for the 40 acre
citrus grove data are shown in Listing 1. The design uniformity
is well above the recommended 90% for uniform topography. (See
Table 41). Thus, if the necessary pressure at the head of the
subunit is maintained, and good management techniques are
practiced to avoid clogging, the hydraulic performance of the
irrigation systems used in these groves will be excellent. Both
of these groves have been installed as part of research and
extension demonstration projects.
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DATA FOR LATERAL
Outflow per tree (GPH) 14.8
Number of emitters per tree 1
Diameter of lateral (in) .70
Tree spacing along lateral (ft) 414.
Number of trees along lateral 16
HazenWilliams constant 140
CRT 41
:1
~___
DATA FOR MANIFOLD
Number of laterals along manifold 48
HazenWilliams constant for manifold 150
Number of laterals per connection 2
Number of different pipe sizes 4
Diameter (in) and length (ft) pairs
D: 4.15
L: 322
D: 3.23
L: 168
D: 2.65
L: 112
D: 1.53
L: 56
CRT 42
410
J
I
Enter two pressure
Pressure in PSI ar
P1: 20
Ql: 14.8
P2: 15
Q2: 13
Enter coefficient
Enter average ope
Enter today date
Enter location of
Enter Selection:
i, discharge pairs for
id discharge in GPH
of variation .05
rating pressure 20
May 5 ,1983 1983
system La Belle, Florida.
Send output to screen 1
Send output to printer 2
Selection?
1
CRT 43
411
emitter
_I
FLORIDA COOPERATIVE EXTENSION SERVICE
INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES
Department of Agricultural Engineering
University of Florida, Gainesville.
HYDRAULIC SPECIFICATIONS OF TRICKLE
IRRIGATION SYSTEM SUBUNITS
Version 1.04.01
University of Flo'rida
June 8, 1983
LATERAL DATA:
Discharge per emitter:
Discharge per tree:
Number of emitters per tree:
Diameter of lateral (in):
Tree spacing (ft) :
Number of trees per lateral:
HazenWilliams constant of lateral:
Slope of the lateral (ft/100ft):
14.80 gph
14.80 gph
1
.70
14.00
16
140.00
0.00
MANIFOLD DATA
Number of tree rows along manifold: 24
Number of laterals per connection: 2
Hazen Williams constant of manifold: 150.00
Slope of the manifold (ft/100ft): 0.00
Diameter and lengths of pipes:
Diam (in) Length (ft)
4.15 322.00
3.23 168.00
2.65 112.00
1.53 56.00
EMITTER CHARACTERISTICS
Design pressure (psi): 20.00
HeadDischarge relationship:
Pressure (psi) Discharge (gph)
15.00 13.00
20.00 14.80
Listing 41
412
 2 
University of Florida
HEAD LOSSES
Lateral head loss (ft):
Manifold losses:
Section Diam (in)
1 4.15
2 3.23
3 2.65
4 1.53
June 8, 1983
6.32
Length (ft) Head loss (ft)
322.00 3.08
168.00 1.51
112.00 .62
56.00 .46
DISCHARGES
Average lateral discharge (gpm) : 3.95
Manifold discharge (gpm): 189.44
SYSTEM PRESSURES AND
Minimum pressure (psi):
Maximum pressure (psi):
Pressure variation (%):
DISCHARGES
19.33
21.31
9.92
Miminum discharge (gph):
Maximum discharge (gph) :
Discharge variation (%) :
SYSTEM UNIFORMITIES
Subunit design emission uniformity (%): 96.65
Absolute design emission uniformity (%): 95.24
Listing 41 (continued)
413
14.57
15.23
4.43
TABLE 41 : RECOMMENDED RANGES OF DESIGN
EMISSION UNIFORMITY (EU)

Emitter Type Soil Topography EU 

Point source on Uniform @ 90 to 95
permanent crops Steep or undulating & 85 to 90
Point source on Uniform 85 to 90
permanent or Steep or undulating 80 to 90
semipermanent crops +
Line source on Uniform 80 to 90
annual row crops steep or undulating 70 to 85

* Spaced > 4 m (13.1 ft) apart
+ Spaced < 2 m (6.6 ft) apart
& Slope > 2%
@ Slope < 2%
# These values may be reduced up to 10% for humid climates
and high water retention deep soils.
414
TECHNICAL NOTES
The following is a list of the basic equations used in the
computation performed by this program.
1) Head loss.
These are computed using the HazenWilliams equation.
1.852
Q
H = 10.536 L 
CH
4.866
Where:
is the
length
is the
is the
is the
head loss in feet.
of the pipe in feet.
HazenWilliams constant.
pipe flow in gallons per minute.
internal pipe diameter in inches.
2) Reduction factor for the head loss in multiple outlet pipe.
1.852
(ni+l)
+
2.852
2.852
Sl
n Se
is a reduction
tiansen factor
at outlet j in
outlets.
factor analogous to the Chris
that will yield the head loss
a multiple pipe with n
is the distance from the entry point of the
multiple outlet line to the first outlet.
is the average emitter spacing along the
lateral.
415
F
n,k,j
Where:
i=n
i=2
3) Emitter discharge relationship.
The emitter discharge Q as a function of pressure P is
given by:
x
Q = C P
The values of the fitting constants C and x are obtained
from two pressuredischarge pairs as follows:
x = ln(Ql/Q2)/ln(Pl/P2)
C = Ql/( Pl
Where:
Q1, Q2 emitter discharges corresponding to pressures Pl
and P2 respectively.
4) Minimum and maximum discharge ratios, and uniformity coeffi
cients are computed using Keller and Karmeli's (1975) method.
416
REFERENCES
Harrison,
1981
D.S.
40 acre citrus irrigation system demonstration grove.
blueprint 1470. Agricultural Engineering Department,
University of Florida.
Keller, J. and Karmeli D.
1974 Trickle irrigation design.
Rainbird Sprinkler Manufacturing Corporation.
Glendora, CA.
Zazueta, F.S. and Trevino H.
1978 Un metodo simplificado para el diseno hidraulico de
sistemas de riego por goteo con emisores controlables.
3er. Seminario Nacional de Riego por Goteo. CENAMAR,
Region Lagunera.
417
COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OF FOOD AND AGRICULTURAL
SCIENCES, K. R. Tefertiller, director, In cooperation with the United States Department of Agriculture, publishes this Infor
mation to further the purpose of the May 8 and June 30, 1914 Acts of Congress; and Is authorized to provide research, educa
tlonal Information and other services only to Individuals and Institutions that function without regard to race, color, sex or
national origin. Single copies of Extension publications (excluding 4H and Youth publications) are available free to Florida
residents from County Extension Offices. Information on bulk rates or copies for outofstate purchasers Is available from
C. M. HInton, Publications Distribution Center, IFAS Building 664, University of Florida, Gainesville, Florida 32611. Before publicizing this
publication, editors should contact this address to determine availability.
