Of Trickle Irrigation Subunits
F. S. Zazueta, A. G. Smajstria, and D. S. Harrison
orida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean
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
PRELIMINARY DESIGN OF TRICKLE IRRIGATION SUBUNITS
(c) IFAS, University of Florida, 1982,1983
PRELIMINARY DESIGN OF TRICKLE IRRIGATION SUBUNITS
Fedro S. Zazueta, Allen G. Smajstrla and Dalton S. Harrison\l
This program is executed by typing DESIGN.
This program computes the necessary pipe diameters of
trickle irrigation subunit components to insure that the flow
variation within the subunit is within prespecified bounds.
A trickle irrigation subunit is defined as a single manifold
with its corresponding laterals and emitters. A trickle irriga-
tion system is composed of a set of one or more subunits (see
Figure 1-1). The different subunits that form the irrigation
system need not be of the same geometry.
The diameters of pipe given by the computations performed in
this program are a first approximation to the design of the
system. Diameters in this preliminary design may be changed as
necessary, depending on a series of practical considerations such
as pipe availability and cost. The changes made to the prelimi-
nary design should be reviewed using the SPEC program to assure
that the -required uniformity of water application is still
This program handles only rectangular subunits. For
irregular subunits the HAZEN program must be used.
Each one of the data items necessary for the computations
done by this program is described below. The data item descrip-
tions given below are in the same order as the program requests.
1) Percent of total losses that occur in the lateral.
This is the ratio, expressed as a percentage, of the fric-
tion head losses allowed to occur in the lateral to the
total head losses due to friction allowed to occur in the
\l Visiting Assistant Professor, Associate Professor and
Professor respectively, Agricultural Engineering Department,
IFAS, University of Florida.
FIGURE 1-1: TYPICAL LAYOUT OF A TRICKLE IRRIGATION SYSTEM
subunit. If a carriage return is entered, the system
defaults to a value of 60%'of the total head loss allowed in
the lateral and 40% of the losses allowed in the manifold.
2) Maximum percent flow variation allowed in the system.
This is the maximum emitter flow variation allowed in the
subunit. It is the difference between the maximum flow and
the minimum flow expressed as a percentage of the average
flow. If a carriage return is entered, the system defaults
to a value of 10%. The program will not allow a variation
greater than 10% as a valid data input.
3) Outflow per tree.
This is the design outflow per tree. It is the product of
the number of emitters per tree and the emitter design dis-
charge. This data item should be given in gallons per hour.
4) Average emitter pressure.
This is the pressure that corresponds to the average emitter
discharge. The average emitter discharge is obtained by
dividing the number of emitters per tree into the discharge
5) Flow characteristics of the emitter.
These data define the pressure-discharge relationship of the
emitter. They consist of a pair of pressures and their
corresponding discharges for the type of emitter used in the
system. Pressure values should be given in pounds per square
inch and discharge values in gallons per hour. These data
are available from the manufacturer of the emitter used in
6) Number of emitters per tree.
The number of emitters per tree. In laterals where emitters
are spaced equally without being assigned to a specific tree
this number can be computed as the total number of emitters
along a lateral divided by the number of trees irrigated by
7) Number of trees along lateral.
This is the number of trees irrigated by a single lateral. A
lateral is defined as a section of pipe connected to the
manifold and used to convey water to the emitters. Notice
that there may be more than one lateral and, typically two,
at the same location along the manifold. The idea of a
"center fed" lateral is not used here. In figure 1-2 there are
two laterals at each connection along the manifold, for a
total of 22 on the manifold. There are five trees per
3) Tree spacing.
This refers to the spacing of the trees along the lateral in
feet. In figure 1-2 the tree spacing along the lateral is 40
9) Hazen-Williams constant.
This data item is the hydraulic constant of the lateral. This
constant is used in the computations of head losses in the
subunit and it depends only on the pipe's material. The
value of this constant is 140 for Polyethylene pipe and 150
for PVC pipe.
10) Number of tree rows along the manifold.
This is the number of tree rows that the manifold feeds.
In figure 1-2 there are 11 tree rows along the manifold.
11) Number of laterals per connection.
This data item refers to the number of hydraulic lateral
connections at a given point along the manifold. When a
manifold is located at one side of the grove there is
typically one connection per tree row. When a manifold goes
through a grove there are typically two laterals, one on each
side of the manifold. These are two laterals per connection
shown in figure 1-2.
The results obtained from this program are as described
below. Each item is followed by the output heading when
1) For the lateral:
a) The nominal diameter of the lateral. Nominal diameters
here are given for flexible PE pipe.
b) The head loss in the lateral. The head loss is computed
using the internal pipe diameter corresponding to the
nominal diameter given in the previous item.
2) For the manifold:
a) The number of the section. This number corresponds to
the pipe between two tree rows. As shown in figure 1-2
numbering starts at the section feeding the last lateral
in the system and ends at the section where the manifold
is fed from the main or submain. (SECTION).
b) The flow rate in gallons per minute in each pipe section.
c) The head loss in feet occurring at each pipe section.
This value is computed using the internal pipe diameters
corresponding to the nominal diameters for each section.
Class 160 rigid PVC pipe is assumed. (HEAD LOSS).
d) The cumulative head loss in feet occurring in the mani-
fold from the first section to the current section.
(CUM. H. LOSS).
e) The theoretical diameter in inches that would cause the
head distribution along the manifold to be linear. This
value is useful when making adjustments to the prelimi-
nary design. (THEOR. DIAM.).
f) The nominal diameter in inches to be used for each
section. With these pipe diameters the head distribu-
tion will be as nearly linear as possible when using
commercially available pipe. (NOM. DIAM.).
The following is an example of a preliminary design for a
trickle irrigation subunit. User input is underlined. The field
layout of the subunit is shown in Figure 1-2.
The percent of the total losses to occur in the lateral is
60%. The maximum flow variation allowable in the system is 10%.
In this design, two red base 360 degree microjets* per tree will
be used at an average emitter discharge of 14.8 gallons per hour
and at a design pressure of 20 pounds per square inch. The out-
flow per tree is 29.8 gallons per hour. The hydraulic character-
istics of the emitter obtained from the manufacturer's specifica-
tions are as follows:
Pressure (psi) Discharge (gpm)
The proposed subunit distribution shows 5 trees along each
lateral. Trees are spaced at 40 feet along the lateral. Tree
rows are spaced 40 ft.along the mainfold. Finally, 10 tree rows
are fed by the manifold supplying water to 20 laterals. A sample
of the interactive session using these data is shown in CRT 1-1
and CRT 1-2.
* Trade names are used for illustrative purposes only, and do not
A A A-- A- --
MANIFOLD SECTION 10
I ^ -- -- _----_---- -
5J SJ *s~
%5 NJ NJ NJ \y. V NJ NJ -- -
IN 7N 7s IN IN 7N 7\ 7N 7N 7\
A\ AN /\ AN IN 7\ A\ ,N A
' 5 X "5 v y Y--y y- - '5
%. '%/ 1 %/ \/ V v J '-- / .v
AN A\ AN AN /* A A\ / /N A>
V/ V V N / V V v V V
fN IN IN rN IN
,/\ 1 \
IN y \.
~N ~ IN
'57 'NJ xi\
\ \ N, /\ 7SECT\ 7 ONI 7 7 TREE
kAMAN /F L S TREE
40 MANIFOLD SECTION I
FIGURE 1-2: LAYOUT OF THE SUBUNIT USED IN THIS EXAMPLE
Number of trees rows aloi
Average tree spacing alo
Hazen Williams constant
Number of laterals per c
Send results to the s5
Send results to the p
ng manifold: 10
ng manifold: 40
of manifold: 150
FLOW HEAD LOSS CUM. H. LOSS THEOR. DIAM
4.93 .32 .32 1.19
9.87 .34 .66 1.53
14.80 .72 1.38 1.53
19.73 .64 2.01 1.75
24.67 .32 2.34 2.19
29.60 .45 2.79 2.19
34.53 .60 3.40 2.19
39.47 .30 3.70 2.65
44.40 .38 4.08 2.65
49.33 .46 4.54 2.65
Lateral pipe is flexib
Manifold pipe is PVC c
)le polyethylene tub
lass 160 IPS plastic
The following is a brief statement of the basic equations
used in the program.
1) Head loss.
Head losses are computed using the Hazen-Williams equation:
H = 10.536 L ---
( CH H
is the head loss in feet.
is the length of the pipe in feet.
is the Hazen Williams constant.
is the pipe flow in gallons per minute.
is the internal pipe diameter in inches.
2) Multiple outlet reduction factor.
The multiple outlet reduction factor was calculated using
Zazueta's (1978) modification of the Christiansen (1942) equation.
is a reduction factor that can be used to
compute the head loss at outlet j in a
multiple outlet pipe with n outlets.
is the distance from the entry point of the
multiple outlet pipe to the first outlet.
is the average outlet spacing along the
multiple outlet pipe.
1942 Irrigation by Sprinkling. Agr. Exp. Station Bul.
670. University of California, Berkeley.
Zazueta F.S. y Trevino H.
1978 Un metodo simplificado para el
de sistemas de riego por goteo
Nacional de Riego por Goteo.
con emisores hi-
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-
tional 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 4-H and Youth publications) are available free to Florida
residents from County Extension Offices. Information on bulk rates or copies for out-of-state 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.