Ruby Ekit AENG 90 Engr.

Jose Carlo Dizon

BSAE 4 IRRIGATION AND DRAINAGE MAY7, 2018

LABORATORY EXERCISE #7

DESIGN OF SPRINKLER IRRIGATION SYSTEM

INTRODUCTION

An irrigation sprinkler is a device used to irrigate agricultural crops, alwns,

landscapes, golf courses, and other areas. They are also used for cooling and for the

control of airborne dust. Sprinklers provide efficient coverage for small to large areas adn

are suitablefor use on all types of properties. It is also adaptable to nearly all irrigable

soils since sprinklers are available in a wide range of discharge capacity,

Sprinkle irrigation is a method of applying irrigation water which is similar to

natural rainfall. Water is distributed throughh a system of pipes usually by pumping. It is

then sprayed into the air through sprinklers so that it breaks up into small water drops

which will then fall to the ground. It is also the application of water to the surface of the

soil in the form of spray, simulating that of rain. The spray is produced by the flow of

water under pressure through small orifices or nozzles. The pressure is usually provided

by pumping. Some of the major advantages of the system are: runoff and erosion can be

eliminated, application efficiency is high, shallow soils in steep and rolling topography

can be easily irrigated, and can be automated to reduce labor requirements.

The main objective of sprinkler system is to apply water as uniformly as possible

to fill rootzone of the crop with water. In designing a sprinkler irrigation system, there are
important factors that should be given attention. Like the location and size of the pump,

size of mainline (manifold), laterals, and sprinkler head.

Design of the system should provide minimal cost of pipes, low labor

requirements,

and distribute water over the area in the required period of time.

OBJECTIVES

Generally ths laboratory exercise aims to design a sprinkler irrigation system.

Specifically it aims to:

· prepare a layout of irrigation system

· design the sprinklers, lateral and main pipes

· determine the system capacity

· determine the size of pump for the system

METHODOLOGY

In this laboratory exercise students tasked to design a sprinkler irrigation system

including the layout of the system. Compute for the data needed to in order to design the

irrigation system with the given formula below.

1. The student made up an inventory of available resources and operating conditions:

a. Size, shape, and topography of the design area (Use figure 1)

b. Information on soils (infiltration rate, water holding capacity, effective depth,

apparent specific gravity

c. Crops (rooting depth, consumptive use, growing season)

d. Farm operation schedules (hrs of operation per day, day of operations/week)

e. Water supply (source, amount available, seasonal variation)

 f. Power source and costs (electrical, distance from pump location, ICE)

g. Climatic conditions (length of growing season, period of maximum water

consumption

2. The student decided on what type of sprinkler system is to be used among the

following:

a) Permanent Set – mainline and laterals are set/installed for that field for the

whole growing season and not to be moved from one place to another.

b) Periodic Move – system to be either (a) fully portable, (b) portable main and

laterals, and (c) with portable or permanent main and portable laterals.

c) Continuous move - system which continuously moving while in operation.

3. The student planned the layout based on the type of system selected and source of

water supply. The resulting arrangement of main and laterals have:

a) have minimal investment in the cost of irrigation pipes;

b) have low labor requirements; and

c) provide for an application of water over the total area in the required period.

4. Based on the available resources and conditions of the area, the student was able to

determine the following:

a. Net depth of water to be applied per irrigation, dn

dn= WHC x Drz x MAD/100

Where: MAD= management allowed deficit, the moisture between FC

and PWP that can be used by the crop, % (assumed 50%)

WHC= water holding capacity of the soil, L/L (Table 1)

Drz – crop rooting depth, L (Table 2)

b. gross depth of irrigation, Dg

Dg= dn/ Ea

Where: Ea – irrigation application efficiency (Table 3)

dn= Net depth of water

 c. frequency of irrigation, F

F- dn/ Et

F should be maximum allowable irrigation interval during the peak water use

period ET = k x PET

Where: ET = peak daily consumptive use

k = crop factor (Table 4)

PET = Potential evapotranspiration, L/T (Table 5)

 d. Application rate, I

I= Ig/t

Where: t – design application time, T

I ≤ soil intake rate

5. For the selected type of sprinkler system, the following was determined:

a. operating pressure, range of wetted diameter, and sprinkler and lateral spacing

(Tables 7 & 8)

b. required sprinkler discharge

q= I x SL x SM

Where: SL – spacing of sprinklers along lateral, L

Sm – spacing of laterals along the main, L

 c. Select sprinkler head based on the computed q (from manufacturer’s catalog

with average discharge close to computed q)

d. Number of sprinklers per lateral, NS

Ns= Ll/ SL

Where: Ll – length of lateral, L

SL – spacing of sprinklers along the lateral, L

e. Lateral capacity, qL

qL= Ns x q

Where: Ns – number of sprinkler heads along a lateral

f. Main/Manifold capacity, Qm

Qm= NL x qL

Where: NL – number of laterals operating simultaneously

g. System Capacity, Qs

Qs= Nm x Qm

Where: Nm = number of manifold operating simultaneously

6. The student determined the sizes of lateral pipe using Scobey’s equation for friction or

head loss in pipes. The allowable friction losses along the lateral is 20% of the sprinkler’s

operating pressure.
 Recommended values of Ks for design purposes:

Transite pipe 0.32

Steet/Aluminum pipe 0.40

G.I. Pipe 0.42

To obtain the actual loss, Hf was multipled by a factor F. Suggested values of F are given

in Table 9 for friction losses in aluminum pipes with multiple outlets.

7. Then, the maximum total head was computed as follows:

a. Nozzle pressure at the farthest end of the line, Ho, using the equation

b. Pressure or head Hn required at the junction of the lateral and the main

c. Compute the total dynamic head

8. then the student determined the required sizes of manifold and/or mainline pipe. The

pipe diameter is obtained using Scobey’s equation. The allowable total friction losses in

the mainline should be less than 30% of the TDH

9. Lastly, the power requirement was determined and estimated the size of power unit.

RESULTS AND DISCUSSION

A grape is a fruit, botanically a berry, of the deciduous woody vines of the flowering

plant genus Vitis. Grapes can be eaten fresh as table grapes or they can be used for

making wine, jam, juice, jelly, grape seed extract, raisins, vinegar, and grape seed oil.

Grapes are a non-climacteric type of fruit, generally occurring in clusters.

Grape cultivation or farming is one of the most lucrative and profitable farming.

Grape is cultivated under a variety of soil and climatic condition in three distinct agro

climatic zones. Grapes are grown in both temperate and tropical climate. Grapes perform

well where there is no or little rain at the ripening time of the grapes.
 .

Figure1. Contour Map Sample for Grapes

The figure above shows area with a given length of 100 meters and width of 200 meters

in a 2 ha land. The source of water is in deep well.

GIVEN DATA:

Source of Water Deep well

Sprinkler System Permanent Set

Type of Soil Sandy loam

Infiltration Rate 0.9 cm/hr

Water Holding Capacity 1.50 in/ft

Apparent Specific Gravity 1.35

Root Depth 2.25 ft

Consumptive use 6.05 mm/day

Growing season 3 years

Hours of Operation per day 20 hours

Days of Operation per week 7 days

Available Head 50 yr period

Seasonal variation None

Electrical 15 hp

Distance from Pump Location 5m

Length of growing Season 36 months

Type of Sprinkler System Permanent

Calculations:
Net Depth
In = WHC x D x (MAD/100)
= 1.50 in/ft (2.25 ft) x (50%/100)
= 1.69 in
Gross Depth
Sprinkler Irrigation Efficiency for Moderate Climate
Ea = 0.90
Ig = In/Ea
= 1.69 in/0.90
= 1.87 in
Frequency of Irrigation
F = In/ET
ET = k x PET
ET = 1 x 0.175
ET = 0.175
F = In/(k x PET)
F = 1.65 in/(1 x 0.175 in/day)
F = 4.63 days = 5 days
Application Rate
I = Ig / t
= 1.87 in/ 25 hrs
I = 0.0748 in/hr

Sprinkler System
a. Sprinkler with medium pressure
Operating pressure: 200 - 350 kPa (275 kPa)
Range of wetted diameter: 20-30 m (25 m)
b. Wind velocity = 0 km/hr
Sprinkler and Lateral Spacing
Sl = 50% (25 m) = 12.5 m
Sm = 65% (25 m) = 16.25 m
Calculations
Required Sprinkler Discharge
q = I x S l x Sm
= (0.0019 m/hr)(12.5 m)(16.25 m)
= 1.404 m3/hr = 0.39 L/s
Number of Sprinklers per Lateral
Ns = Ll/Sl
Where LL = length of lateral, USE 100 m
SL = spacing of sprinklers along laterals, USE 16.25 m
Ns = 100 m/16.25 m
= 6.25 = 8 sprinklers

Lateral Capacity
QL = Ns x Q
Where NS = no. sprinkler heads along lateral, USE 8
Q = required sprinkler discharge, USE Q = 0.39 L/S
QL = 8(0.39 L/s)
= 3.12 L/s

Main Manifold Capacity

QM = NL x QL
Where NL = no. laterals operating simultaneously, USE 3
QL = lateral capacity, USE q = 3.12 L/s
QM = 2 (3.12 L/s)
= 6.24 L/s
System Capacity
Qs = NM x QM
Where NM = no. of manifold operating simultaneously, USE 6
QM = main/manifold capacity, USE 6.24 L/s
Qs = 6 (6.24 L/s)
= 37.44 L/s
Sizes of Lateral Pipe
Calculations

Friction/Head Loss in Pipes

Hf = 20% of sprinkler operating pressure
= (0.20 x 275 kPa)/ 9.806
= 5.61 m
KS = Scobey’s coefficient of retardation, USE 0.42 for G.I. PIPE
L = length of pipe, USE 100 m
Q = total discharge, USE 2.73 L/s
D = inside diameter of pipe, mm
5.61 m = ((0.42)(100 m)(2.40 L/s)1.9(4.10 x 106))/(D4.9)
D = 55.13 mm (diameter of lateral pipe)
Actual Loss
To solve for the actual loss, Hf is multiplied to correction factor of 0.41 @ 8 sprinkler
heads).
Hf = 3.28 m

Maximum Total Head

Nozzle Pressure at the farthest end of the line, (Ho)
Ha = Ho + 0.25Hf + 0.4He
Where Ha = average pressure at the nozzle,
= (275/ 9.806), USE 28.04m
Hf = friction head loss in the lateral, USE 3.28 m
He = max difference in elevation between the junction
with the main and the farthest sprinkler on the
lateral, USE ± 1.0 m since lateral is mounted downhill
Ho = 28.04m - 0.25(3.28 m) - 0.4(± 1.0 m)
Ho = 26.82 for positive elevation
Ho = 27.62 for negative elevation

Pressure head required at the junction of lateral and main, (Hn)

Hn = Ha + 0.75Hf + 0.6He + Hrp
Where Ha = average pressure at the nozzle,
= (275/ 9.806), USE 28.04m
Hf = friction head loss in the lateral, USE 3.28 m
He = max difference in elevation between the junction
with the main and the farthest sprinkler on the
lateral, USE ± 1.0 m since lateral is mounted downhill
Hrp = the riser height, USE 1 m
Hn = 28.04+ 0.75(3.28) + 0.6(±1.0 m) + 1 m
Ho = 32.1m for positive elevation (Use this)
Ho = 30.9m for negative elevation
Total dynamic head, (Ht)
Ht = Hn + Hm + Hj + Hs
Where Hm = maximum friction loss in main, suction line and
NPSH of pump, m ( 30% of TDH)
Hn = Pressure head required at the junction of lateral and main, USE
32.1m
Hj = elevation difference between the pump and junction of lateral and
main,
= Hf – He = USE 22.88 m
Hs = elevation difference between the pump and the
water supply after drawdown, USE 0.9 m
Ht = 32.1m + 0.30Hm + 5.36 m + 0.9 m
0.70(Ht) = 40.09 m + 5.36 m + 0.9 m
Ht = 66.21 m
Friction/ Head loss in pipes, (Hf)
Where Hm = 30 % of TDH
= 0.30 (66.21 m) = 19.86 m
KS = Scobey’s coefficient of retardation,
USE 0.42 for G.I. PIPE
L = length of pipe, USE 100 m
Q = total discharge, USE 3.12 L/s
D = inside diameter of pipe, mm
• 19.86 m = ((0.42)(100 m)(4.8 L/s)1.9 (4.10 x 106))/(D4.9)
• D = 48.51mm

Power Requirement And Estimation Of Power Unit Size

Where BHP = brake horsepower,
Ep= pump efficiency, USE 75%
γ = specific weight of water, USE 9806 N/m3
CF = CONVERSION FACTOR (1 hp = 0.746 kW)
TDH = 66.21 m
Q = 49.21L/s
• BHP = (0.009806 kN/m3)( 49.21L/s)(66.21 m) / (0.75)(0.746 kW)
• BHP = 57.10 hp engine
= 42.59kW electric motor

CONCLUSION
 Designing an irrigation sprinkler system requires data to be computed for an ideal

sprinkler design. Net depth, gross depth, frequency of irrigation, application rate, lateral

capacity, manifold capacity, system capacity, size of the lateral pipe, total head loss, size

of manifold pipe and power requirement are some parameters needed to compute.

When choosing a sprinkler irrigation system, choose sprinklers that spray water

close to the ground since these are considered more water efficient. Sprinkler irrigation

technology can support farmers to adapat climate change by making more efficient use of

their water supply. This is particularly appropriate where ther is limited or irregular water

supply for agricultural use.The sprinkler use less water than irrigation by gravity and

provides a more even application water to cultivated plot.

Additionally, sprinkler irrigation can reduce the risk of crops freezing due to

colder than usual temperatures. More frequent and intense frosts are already impacting on

crops as a result of climate change. All sprinklers undergo extensive quality testing in our

well equipped state of the art lab. Moreover, performance of the products are also tested

in the field to ensure uniformwater distribution and higher efficienyc.

REFERENCES

· Carriaga,C(Lecture). Design of Sprinkler Irrigation System

· Sprinkler Irrigation Systems (2014). Retrieved from

https://jains.com/irrigation/popupsandsprinklers/

· Sprinkler irrigation. Retrieved from

https://www.climatetechwiki,org/content/sprinkler-irrigation

· FAO(1988). Irrigation Water Management: Irrigation Methods, FAO. Rome