12/18/2008
IRRIGATION DESIGN FOR THE REYES AND ROMERO PIPELINES, EL SALVADOR
E.S. Brooks, J. Boll, and the ICUBED Senior Design Team
Reyes and Romero Canals
The Reyes and Romero pipelines were designed to provide irrigation water to 73.55 manzanas
(mz) and 18.7 mz, respectively, in the El Centro/Las Pilas Regions of El Salvador. The irrigated
water for both systems is taken out of the Qda. El Salto, known to the local residents as the Rio
Reyes.
Irrigated Water Demand.
The crop water demands in this region were calculated using monthly weather records from the
Las Pilas weather station. According to the weather records the potential evapotranspiration
(ET) during the dry season (Dec-Jan) is close to 90 mm/month. According to crop coefficients
published by the World Food and Agriculture Organization (FAO) the crop coefficient relating
potential ET to actual ET for cabbage during the peak growth season is 1.05. As a conservative
estimate to account for extreme hot, dry periods when the potential ET will exceed 90
mm/month we used a design crop coefficient of 1.3. Therefore our design irrigated crop water
requirement was set to 117 mm/month (i.e. 117 mm/month = 90 mm/month * 1.3). The total
design flow for the Reyes and Romero systems was determined by multiplying this rate by the
total irrigated area. This design flow rate was 22.98 and 5.84 liters per second for the Reyes
and Romero systems, respectively.
Design Constraints
The pipe sizing was based on several constraints. The smallest sprinklers that our currently
used in the region operate on a design pressure of 28 pounds per square inch (PSI), therefore
one of the constraints of the design was to provide at least 28 PSI wherever water would be
delivered to end users. Another constraint was to limit the pressure in the pipe to a maximum
of 40 PSI less than pressure rating for the PVC pipe to provide some factor of safety to minimize
pipe failure by water hammer. Another related constraint was to limit the water velocity in the
pipes to less than 5 ft/sec to minimize the risk of pipe failure by water hammer.
Inlet:
The pipe inlet should be a ditch in the river, 18 inches wide and 18 inches deep, filled with gravel, where
the lower part of the 6 inch pipe will be 3 inches above the bottom of the ditch and the upper part of
the 6 inch pipe will be 9 inches bellow the water surface, refer to Figure 3. The pipe inlet itself should be
covered with a 2mm, strong, chicken wire to serve as screen for the pipe system avoiding gravel and
other big particles to get inside. The intension is that the pipe inlet will be deep enough in the deepest
part of the river and buried itself on gravel to provide constant water flow. The gravel will serve as
screening system for sediment and the sediment deposited above the gravel will be flushed away during
every big flow event. This gravel might have to be protected to avoid loss by placing a bigger, fix screen
on top of it. Refer to figure 4.
Pipe cover
The top of the pipe must be buried at least six inches bellow the ground surface, including at
pints where pressure regulators, valves and manifolds are placed. Pipes must be buried at least
one foot on gravel roads cross sections and where on risk of damage do to vehicle pass over it.
Pipe cover
The top of the pipe must be buried at least six inches bellow the ground surface, including at
pints where pressure regulators, valves and manifolds are placed. Pipes must be buried at least
one foot on gravel roads cross sections and where on risk of damage do to vehicle pass over it.
Reyes System
The Reyes system design consists of 8 unique pipeline sections, see Figure 1. The pipeline
diameter and design flow for each section was based on irrigated area, length of pipe, and
change in elevation along the pipe. Figures 2 and 3 show the distribution of pipe diameter and
design flow for the Reyes system. Table 1 provides a detailed breakdown of water pressures
and pipe sizing throughout the system. Table 2 lists the size, length and cost of piping for the
Reyes system. Table 3 lists the number and cost of pressure regulators, valves, and fittings for
the Reyes System.
Pressure regulators
The Reyes canal system will require three pressure regulators on the Terciaria Graciela,
Terciaria Armando Ramirez, and Terciaria Arturo Chacon. These pressure regulators will drop
the pressure down to 10 psi in each of these systems. Table 1 identifies the exact distance and
elevation of where these regulators should be installed. These pressure regulators are required
to maintain the design pressure at the outlet of the system and to prevent over-pressurizing the
pipes. The 120-bZ hYflow Pressure Reducing Valves sold by Bermad Water Control Systems
(http://www.bermad.com/) are well suited for this application. In addition to maintaining a
constant downstream pressure during peak flows, these pressure reducing valves also sense
downstream pressure fluctuations and close a valve as the downstream demand for water
decreases or stops for periods of time. The TORO company (http://www.toro.com/index.html)
also sells these pressure regulators as part number B120-XZ-03-Y-NP for the three inch
regulator and B120-XZ-02_Y_NP for the two inch regulator. Both companies list the price of
these regulators at $332 and $278 for the three inch and two inch regulators, respectively. The
Bermad sales associate mentioned that the price of these regulators could be cut in half if we
wanted to set up an account with Bermad. I suspect TORO would offer similar lower prices if
we set up and account with them.
Valves
We recommend installing 6 valves in the Reyes system; one valve for each major branch of the
pipe system. This includes a 6 inch valve at the beginning of the Primaria section, a 6 inch valve
at the beginning of the Upper secundaria Los Chacones, a 4 inch valve at the beginning of the
Secundaria Guillermo Reyes, a 3 inch valve at the beginning of the Terciaria Graciela, a 3 inch at
the beginning of the Terciaria Arturo Chacon and a 2 inch valve should be placed at the
beginning of the Terciaria Armando Ramirez.
Note: Globe valves and needle valves are recommended. Globe valves provide more precise
control of flows and minimize the risk of shutting a valve too quickly which increases the risk of
water hammer. Gate, ball and butterfly valves are not recommended in a location since they
are quick acting valves that are only used to open and close water flow not to regulate the flow.
Fittings
The Reyes System will required two 6 inch and one 4 inch Ts, two 6 inch to 4 inch reducers, one
6 inch to 3 inch reducer, one 4 inch to 3 inch reducer and one 4 inch to 2 inch pipe reducer, see
Figure # 1. We recommend avoiding the use of elbows at all times since they greatly reduce
pressure. Similarly Ys should be used instead of Ts if at all possible.
Note on Manifolds
The required fittings at each manifold location in the system will include a T of the same size as
the pipeline and enough reducer fittings to reduce to 1 inch lines. If the budget allows we
recommend that each farmer is provided with a 1 inch valve to control flow to their farm at the
manifold. At a minimum the design requires one 1 inch T for every irrigation line connected to
the pipe system. If a particular farmer has more than one irrigation line connected at a
particular manifold location then the manifold should be designed such that the 1 inch valve
provided to the farmer by the project controls all his irrigation lines.
Currently, there is not enough information to identify the number of required manifolds and
provide a list of the exact number of irrigation lines attached to the system. This information
will become clearer as the system is installed.
Special Design Notes for Los Chacones Section
Special care should be taken when installing the Los Chacones pipelines. This tributary of the
mainline starts as a 6 inch diameter pipe and continues 313 m where it then converts to a 4 in
line and extends out another 297 m. The topographic map indicates a 9 m drop in elevation for
the 6 inch line and then a 5 m rise in elevation for the 4 inch line. We assumed that since this
line will be installed in an existing diversion ditch and that the elevation difference actually does
not increase in this section. With this assumption the pressure at the end of the end line is at
22 PSI which is below the minimum design sprinkler pressure. However by assuming that
roughly half the flow will be extracted to irrigate fields at the junction between the 6 in and 4
inch line the pressure at the end of the 4 inch line will be equal to minimum design pressure, 28
psi. If this 4 inch line is actually installed to run uphill, then the pressure at the end of the pipe
will drop below the minimum sprinkler design pressure.
Figure 1. Names of each pipe section of the Reyes system.
Figure 2. Pipe diameter and pressure distribution within each pipe section in the Reyes design.
Numbers in yellow boxes represent pressure readings in pounds per square inch (PSI). Black
dots represent locations of pressure regulators which drop the pressure down to 10 psi.
Figure 3. Design flow rate and pressure distribution for each pipe section in the Reyes design.
Numbers in yellow boxes represent pressure readings in pounds per square inch (PSI). Black
numbers next to the pipes represent flow rates in liters per second for each pipe. Black dots
represent locations of pressure regulators which drop the pressure down to 10 psi.
Table 1. Reyes system design by pipe section.
Description
Canal Segment
Cumulative
ID
Length
Length (m)
Number
(m)
Elevation
(m)
Total Flow
In Pipe Q
(l/sec)
Pressure
Diameter Pressure
after
Number of Price per 6
of Pipe
at end of
Total Cost
Regulator
Pipes
m pipe
(in)
Pipe (psi)
(psi)
Main Line: Pipeline ID Numbers 1-3 (Reyes)
At river
Primaria
Secundaria escuela centro
Secundaria Guillermo Reyes
1
2
3
610
480
230
0
610
1090
1320
2007
1989
1983
1976
23.0
23.0
13.3
9.0
6
6
4
0.4
19.0
25.4
31.8
102
80
39
$51.50
$51.50
$29.50
$5,253
$4,120
$1,151
Pipeline ID numbers 4 and 5 (Los Chacones)
Junction with 1
Upper secundaria Los Chacones; End of 4
Lower secundaria Los Chacones; End of 5
4
5
313
297
610
1090
1570
1989
1980
1980
9.7
9.7
5.0
6
4
19.0
30.8
28.0
53
50
$51.50
$29.50
$2,730
$1,475
Pipeline ID number 6 (Graciela)
Junction with 2
Upper Terciaria Graciela; Middle of 6
Lower Terciaria Graciela; End of 6
6
6
202
111
1090
1292
1403
1983
1950
1932
4.2
4.2
4.2
3
3
25.4
70.3
34.7
10.3
34
19
$17.00
$17.00
$578
$323
Pipeline ID number 7 (Armando Ramirez)
Junction with 3
Upper Terciaria Armando Ramirez; Middle of 7
Lower Terciaria Armando Ramirez; End of 7
7
7
170
133
1320
1490
1623
1976
1930
1912
1.7
1.7
1.7
2
2
31.8
95.1
33.4
10.3
29
23
$8.19
$8.19
$238
$188
Pipeline ID number 8 (Arturo Chacon)
Junction with 3
Upper Terciaria Arturo Chacon; Middle of 8
Lower Terciaria Arturo Chacon; End of 8
8
8
428
147
1320
1748
1895
1976
1928
1910
3.1
3.1
3.1
3
3
31.8
97.8
35.1
10.3
72
25
$17.00
$17.00
$1,224
$425
Total Pipe Costs = $17,704
Table 2. Total pipeline costs for the Reyes design.
Pipe Size
Total
Pressure Number of
Length
Rating
Pipes
(m)
Reyes Design
6" PVC
4" PVC
3" PVC
2" PVC
100 PSI
100 PSI
150 PSI
150 PSI
235
89
150
52
1410
534
900
312
Price
per 6 m
pipe
Total Cost
$51.50
$29.50
$17.00
$8.19
$12,102.50
$2,625.50
$2,550.00
$425.88
Total Pipe Costs =
$17,703.88
Table 3. Total valves, regulators, and fittings costs for the Reyes design.
Description
Diameter(in)
Quantity
Unit cost
Total Cost
Valve
2"
1
$7.66
$7.66
Valve
3"
2
$63.82
$127.64
Pressure Regulator
3"
2
$332.00
$664.00
Pressure Regulator
2"
1
$278.00
$278.00
T fitting
6"
1
$35.50
$35.50
Reducer
4"x 3"
1
$1.13
$1.13
Reducer
3"x2"
1
$2.73
$2.73
Reducer
6"x4"
1
$12.16
$12.16
Reducer Y or T
4"x3" x 2"
2
$12.16
$24.32
Reducer Y or T
6"x4"x3"
1
$13.29
$13.29
Valve per farm
1"
TBD
$7.66
TBD
T per irr. Line
1"
TBD
?
TBD
Subtotal
$1,166.43
Romero Canal System
The Romero system design consists of 6 unique pipeline sections, see Figure 4. The pipeline
diameter and design flow for each section was based on irrigated area, length of pipe, and
change in elevation along the pipe. Figures 5 and 6 show the distribution of pipe diameter and
design flow for the Romero system. Table 4 provides a detailed breakdown of water pressures
and pipe sizing throughout the system. Table 5 lists the size, length and cost of piping for the
Reyes system. Table 6 lists the number and cost of pressure regulators, valves, and fittings for
the Romero System.
Pressure regulators
The Romero canal system will require one pressure regulator at the start of Secundaria
Modesto Hueso pipe segment. We recommend putting a 2 inch diameter pressure regulator of
the same model as the 2 inch regulator in the Reyes system. This pressure regulator will drop
the pressure down to 33 psi to maintain the design pressure at the outlet of the system and to
prevent over-pressurizing the pipe.
Valves
We recommend installing 4 valves in the Romero system; one valve for each major branch of
the pipe system. This includes a 6 inch valve at the beginning of the Primaria section, a 3 inch
valve at the beginning of the Secundaria Vicente Romero, a 3 inch valve at the beginning of the
Secundaria Nehemias Upper, and a 2 inch valve before the pressure regulator at the beginning of
the Secundaria Modesto Hueso.
Note: Globe valves and needle valves are recommended. Globe valves provide more precise
control of flows and minimize the risk of shutting a valve too quickly which increases the risk of
water hammer. Gate, ball and butterfly valves are not recommended in a location since they
are quick acting valves that are only used to open and close water flow not to regulate the flow.
Fittings
The Romero System will required one 6 inch T, two 6 inch to 3 inch reducers, two 3 inch to 2
inch reducers, and one 2 inch to 1 inch reducer, see Figure 5. We recommend avoiding the use
of elbows at all times since they greatly reduce pressure. Similarly Ys should be used instead of
Ts if at all possible.
Note on Manifolds
The required fittings at each manifold location in the system will include a T of the same size as
the pipeline and enough reducer fittings to reduce to 1 inch lines. If the budget allows we
recommend that each farmer is provided with a 1 inch valve to control flow to their farm at the
manifold. At a minimum the design requires one 1 inch T for every irrigation line connected to
the pipe system. If a particular farmer has more than one irrigation line connected at a
particular manifold location then the manifold should be designed such that the 1 inch valve
provided to the farmer by the project controls all his irrigation lines.
Currently, there is not enough information to identify the number of required manifolds and
provide a list of the exact number of irrigation lines attached to the system. This information
will become clearer as the system is installed.
Special Design Notes for Los Secundaria Modesto Hueso Section
We recommended using a two inch pressure regulator before reducing to the 1 inch pipe size at
the start of the Los Secundaria Modesto Hueso section. The pressure above the regulator at
the end of the Terciaria Reservorio line will be at 70 psi which is greater than the minimum
design pressure. After the two inch regulator this pressure will be at 33 psi which is much
closer to the 28 psi design pressure and would be an ideal place to put a sprinkler manifold.
If the regulator fails then the pressure at the lowest point during static conditions will be 195
psi, well above the pressure rating of the 1 inch pipe. With a working pressure regulator set at
33 psi this pressure will be 113 psi. Special care should be taken to open valves slowly to
prevent water hammer at this location.
Figure 4. Names of each pipe section of the Romero system.
Figure 5. Pipe diameter and pressure distribution within each pipe section in the Romero
design. Numbers in yellow boxes represent pressure readings in pounds per square inch (PSI).
The Black dot represents and location of a pressure regulator to drop the pressure down to
33.6 psi.
Figure 6. Design flow rate and pressure distribution for each pipe section in the Romero design.
Numbers in yellow boxes represent pressure readings in pounds per square inch (PSI). Black
numbers next to the pipes represent flow rates in liters per second for each pipe. The Black dot
represents and location of a pressure regulator to drop the pressure down to 33.6 psi.
Table 3. Romero system design by pipe section.
Description
Canal ID
Number
Segment
Cumulative
Length
Length (m)
(m)
Elevation
(m)
Total Flow
In Pipe Q
(l/sec)
Pressure
Diameter Pressure
after
Number of Price per 6
of Pipe
at end of
Regulator
Pipes
m pipe
(in)
Pipe (psi)
(psi)
Main Romero Pipeline
At river
Primeria
Secundaria Vicente Romero
Terciaria reservorio
Secundaria Modesto Hueso Pt. 1
Secundaria Modesto Hueso Pt. 2
Secundaria Modesto Hueso Pt. 3
Secundaria Modesto Hueso Pt. 4
1
2
3
4
4
4
4
297
652
173
93
78
225
220
0
297
949
1122
1215
1293
1518
1738
2070
2068
2038
2013
1968
1990
1937
1982
5.8
5.8
3.8
1.6
0.5
0.5
0.5
0.5
6
3
2
1
1
1
1
0.4
3.0
38.1
70.9
94.5
55.4
113.6
28.6
Secundaria Nehemias
Junction with 1
End of 4
End of 4
End of 4
End of 4
End of 5
5
5
5
5
5
6
75
310
24
34
480
297
480
777
960
1257
1440
2068
2049
2048
2030
2049
2030
2.1
2.1
2.1
2.1
2.1
2.1
3
3
3
3
2
3.0
28.5
27.7
51.7
21.5
33.1
36.6
Total Cost
50
109
29
16
13
38
37
$51.50
$17.00
$8.19
$2.71
$2.71
$2.71
$2.71
$2,575
$1,853
$238
$43
$35
$103
$100
13
52
4
6
80
$17.00
$17.00
$17.00
$17.00
$8.19
$221
$884
$68
$102
$655
Total Pipe Costs =
$6,878
Table 4. Total pipeline costs for the Romero design.
Pipe Size
Total
Pressure Number of
Length
Rating
Pipes
(m)
Romero Design
6" PVC
100 PSI
3" PVC
150 PSI
2" PVC
150 PSI
1" PVC
150 PSI
50
184
109
104
300
1104
654
624
Price
per 6 m
pipe
Total Cost
$51.50
$17.00
$8.19
$2.71
$2,575.00
$3,128.00
$892.71
$281.84
Total Pipe Costs =
$6,877.55
Table 5. Total valves, regulators, and fittings costs for the Romero design.
Description
Diameter(in)
Quantity
Unit cost
Total Cost
Valve
Valve
Valve
Pressure regulator
Y reduced
Reducer
Reducer
Valve per farm
T per irr. Line
2"
3"
6"
2"
6" x 3"
3"x2"
2"x1"
1"
1"
1
3
2
1
1
2
1
TBD
TBD
$16.91
$63.82
$326.96
$278.00
$6.34
$2.73
$1.13
$7.66
?
$16.91
$191.46
$653.92
$278.00
$6.34
$5.46
$1.13
TBD
TBD
Subtotal
$1,153.22
Inlet Design
Both the Reyes and Romero systems extract water from the Reyes River using a 6 inch PVC
pipe. Both designs require that the entrance of the pipe remain under at least 0.3 m (1 ft) of
water at all times. In order to ensure that this condition is met during the dry season as well as
the high flow season we recommend using a gravel trench. The 18 inch deep and 18 inch wide
trench should extend out into the stream such that it will allow the water to flow over the
trench even during the driest time of year. The trench will first be filled with 6 inches of
washed rock (i.e. greater than 2 mm diameter rock) then the pipe is then laid into the trench
and should extend to the deepest part of the stream. The end of the pipe should be covered
with strong 2mm chicken wire to prevent the washed rock from entering the pipe. After the
pipe is laid into the trench the trench should then be completely filled with the washed rock.
This washed rock will serve to protect the pipe and act as a filter for the water. In order to
prevent the trench from scouring out during high flows we recommend covering the gravel
trench with a heavy metal screen having approximately 25 mm diameter openings. This screen
should be staked down on each bank to prevent it from being pealed up during high flows.
Securing this fence to larger stable rocks would also be beneficial if available. Diagrams of the
intake trench is provided in Figures 7 and 8.
Figure 7. Front and side view of intake pipe.
Figure 8. Overhead view of intake pipe.