ARID ZONE JOURNAL OF ENGINEERING, TECHNOLOGY & ENVIRONMENT
AZOJETE, March, 2019. Vol. 15(1):124-132

Published by the Faculty of Engineering, University of Maiduguri, Maiduguri, Nigeria.
Print ISSN: 1596-2490, Electronic ISSN: 2545-5818

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124

ORIGINAL RESEARCH ARTICLE
EFFECT OF DIFFERENT RISER HEIGHTS ON SPRINKLER IRRIGATION PERFORMANCE

UNDER CONSTANT OPERATING PRESSURE
I. A. Kuti1, T. A. Ewemoje2, B. A. Adabembe3, J. J. Musa1, S. C. Nwosu1

(1Department of Agricultural and Bioresources Engineering, Federal University of Technology, Minna, Nigeria
2 Department of Agricultural and Environmental Engineering, University of Ibadan, Ibadan, Nigeria

3 Department of Water Resources Management and Agro meteorology, Federal University Oye -Ekiti, Nigeria)
*Corresponding Author: abykuti6@futminna.edu.ng

ARTICLE INFORMATION

Submitted 15 April 2018
Revised 15 September 2018
Accepted 19 September 2018

Keywords:
Riser Height
Operating Pressure
Coefficient of Uniformity (CU)
Distribution of Uniformity
(DU)
Sprinkler Irrigation

ABSTRACT
The study assessed the effect of different riser heights on the sprinkler
irrigation performance to cater for the cultivation of taller crops and
reduce water losses. A layout of 144 m2 was designed according to the
length of mainline and lateral lines, and 36 catch cans were positioned
in a grid of 2 m apart. The water caught in Cans were subjected to
One-way ANOVA using the Tukey method in Minitab 17 Environment.
The risers 4m, 3m and 2m, were significantly different because the
means without any letter in common and concluded that some of the
riser height have the different mean value of water caught in the catch
cans. The results showed that as the riser height increased the mean
application rate decreased. Also, the Coefficient of Uniformity (%) for
riser height 2 m and 3 m were rated excellent. The Distribution of
Uniformity (%) for 2 m and 3 m were rated excellent and fair. The study
concluded that riser heights 2 m and 3 m had the optimum CU and DU
at 1.6 bar (operating pressure) reduce water losses. The study
suggested that sprinkler irrigation should be carried out in Gidan
Kwano campus between 5:06 pm and 11:35 am. Also, wind direction
should be established before the installation of sprinkler irrigation.

© 2019 Faculty of Engineering, University of Maiduguri, Nigeria. All rights reserved.

1.0 Introduction
Irrigation is viewed as the application of water to the soil to supply moisture for plant
development and crop production (Yahaya, 2002). The need for irrigation arises when the
frequency and amount of rainfall are insufficient to replenish the water required by the crop. In
more arid regions, drought periods last longer in a year, and the seasonal rainfall is unable to
meet crop needs during their growth period (Onwualu et al., 2006). Irrigation systems are
classified as surface, sub-surface, sprinkler and drip irrigation (Onwualu et al., 2006). Sprinkler
irrigation method is a pressurised irrigation system that consumes water from a different source
and sprays it to the cultivated ground or earth as in the shape of rain using an enclosed system
and under pressure (Nakayama and Bucks, 2012). Sprinkler irrigation is an adaptable means of
supplying crops with common and uniform application of water over a broad range of
topography and ground conditions (Nakayama and Bucks, 2012; Fanadzo et al., 2010; Evans and
Sadler, 2008). Water distribution application in a sprinkler system is rich and more coherent than
surface irrigation system (Yazar et al., 1999). A riser is one of the essential elements of a solid set

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125

sprinkler system that influence the performance indicators of the Coefficient of Uniformity (CU)
and Distribution Uniformity (DU) under specified environmental conditions. The CU has either a
positive or negative effect on crop production (Okasha and Pibars, 2016). In summation, the
weak CU and DU reduce the efficiency of sprinkler irrigation system. Water losses in sprinkler
irrigation system occur due to evaporation and wind movement. Thus, there is a need to
improve the functioning of the sprinkler irrigation system to bring down the cost of irrigation
and water losses (Okasha and Pibars, 2016).

Various surveys have indicated that the two common methods of determining sprinkler water
uniformity are the coefficient of uniformity (CU) and distribution uniformity (DU). CU is the
average deviation of the catch compared to the depth of the catch can, while DU compares the
driest quarter of the field to the rest (Kara, 2008). Magagula (2013) reported that a catch-can test
is a safe method of assessing the efficiencies of the existing sprinkler irrigation system. Bishaw
and Olumana (2015) said that increase in riser heights between 2.5 m and 4.0 m lead to increase
in sprinkler water uniformity and riser height 4 m produced optimum CU and DU at low wind
speed. In view of this, the study aims at assessing the effect of different riser heights on the
sprinkler irrigation performance to cater for taller crops and reduce water losses.

2 Materials and Methods
2.1 Study Area
The study area is located within the Federal University of Technology, Minna, Gidan Kwano,
Minna, Nigeria. It lies on latitude 9°32'04.1 N and longitude 6°26'53 E. The study was carried out
on the land adjacent to the Department of Agricultural and Bio-resources Engineering
Laboratory of the University. Gidan Kwano has two seasons namely rainy and dry. The annual
maximum and minimum rainfall in the area is 1086 mm and 1309 mm, respectively, which occurs
in May and ends in October. The yearly maximum and minimum temperature in the area is 37
°C and 19.3 °C respectively (Galadima, 2014).

2.2 Materials and Equipment
2.2.1 Water Pump
The water pump moves water by pressure or suction from the reservoir to field, and its
specification was presented in Table 1.
Table 1:Water Pump Specifications
Item Description
Water pump model WP20X
Type DF1
Connection diameter 50 mm
Delivered volume 600 L/min
Total head 26 m
Power speed 3600 rpm

2.2.2 Sprinkler Irrigation system
The sprinkler irrigation system has a main line of 6 m long with 50 mm diameter. Two lateral
lines have 25 mm diameter with 3 m long each. It has different riser heights such as 1.5 m, 2 m, 3

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126

m, and 4 m with 2.5 mm diameter. Sprinkler irrigation system conveys water from the reservoir
through the main and lateral line to the nozzle which sprays the water in the form of rain to the
field.
2.2.3 Sprinkler Heads
The sprinkler head sprays the water in the form of raindrops to the area. The specifications,
characteristics and manufacturers details of the pressure, spraying radius, nozzle diameter and
discharge of the four sprinkler heads were shown in Table 2.

Table 2: Sprinkler Head Manufacturers’ Specifications
Specification Comments/remarks
Pressure 0.5 – 4.0 Bar
Spraying Radius 3.0 – 16.5 m
Nozzle Diameter 5.0+2.5 mm (7.5 mm)
Flux/ Discharge 6.8-32.4 L/min
Size ¾ inches
Operation Capacity 360º full circle coverage
Model RC130 zinc/brass

2.2.4 Catch Cans
The diameter, height and volume of the catch cans were 84 mm, 130 mm and one litre
respectively.
2.2.5 Water Hose and Siphon Tube
Siphon tube sucks water from the tank to the pump impeller. Water hose conveys water from
the pump to the mainline. The hose connected at the other end of the impeller to the main line
which was held firmly by a clip to prevent leakages.
2.2.5 Tape
A 50 m tape was used to measure the layout and the spacing of the catch cans.
2.2.6 Volumetric cylinder
The cylinder was used to measure the water caught in the catch cans. It has a capacity of
500 cm3.
2.2.7 Marking pegs
Pegs were used to map out the area and grid system.
2.2.8 Stopwatch
A stopwatch was used to measure the time it takes the sprinkler head to fill the container.
2.2.9 Pipe Wrenches
Pipe Wrenches was used to screw in the laterals into the main line and the risers into the laterals.
2.2.9 Cup Anemometer
Cup anemometer was used to measure wind speed and direction.

2.2.9 Portable Thermo-hygrometer
Portable Thermo-hygrometer was used to measure the temperature and humidity of the area

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2.3 Methods
2.3.1 Experimental description and Design Layout
Field evaluation was carried out at Agricultural and Bio-resources Department, Federal University
of Technology, Minna. The field had an area of 144 m2 (12 m by 12 m). The vegetation of the
field was cleared in line with Osie (2009) and mapped out with pegs to form a grid as shown in
Figure 1. Sprinkler compositions used were different riser height (such as 1.5 m, 2.0 m, 3.0 m and
4.0 m), pump, siphon tube, rubber hose, 36 catch cans, four sprinkler nozzles (model RC130), one
main line (6 m in distance and 50 mm in diameter) and two laterals (6 m in length and 25 mm in
diameter). The water pump has two impeller hoses which included a siphon tube and a rubber
hose. The rubber hose was attached or connected to the mainline while the siphon tube was
attached water tank as shown in Figure 1. These components assembled such that the laterals
were spaced 3 m apart on the main line. In summation, the catch cans were spaced 2 m apart
along the grid. The 36 Catch Cans estimated according to the area of the field

Figure 1: Experimental view of sprinkler set up, the arrangement of catch cans on the grid and
design layout

2.3.2 Operation of Sprinkler System Performance
The operating pressure of the water pump adjusted via a pressure gauge and pitot tube. The
Pitot tube was held at 3 mm from the nozzle head and recorded with the operating pressure. In
the trial test, the operating pressure and flow rate were adequately controlled in this experiment.
The speed and direction of the wind are measured every 15 minutes at height 2m with cup
anemometer. At the end of the trial, the amount of water accrued in each catch cans was
measured with cylinders (mL), and the procedures were repeated for each sprinkler nozzle as
described by Kara et al. (2008).

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128

2.4 Calculation of Basic Parameters
2.4.1 Evaporation and wind drift losses
In sprinkler irrigation, water losses came from the nozzle to the irrigated areas due to the wind in
the form of water drift and direct evaporation from the nozzle to the soil (Molle et al., 2012).
Because of this, it is essential to determine evaporation and wind drift losses as described by
Bishaw and Olumana (2015).

E =[1.98 (D)−0.72 + 0.22 (Es – Ea)0.63 + 3.6 x 10−4(H)1.16 + 0.14 (U)0.7]4.2 (1)

where:
E = Evaporation and wind drift, per cent
D = Nozzle diameter, m
H = Riser height, m
U = Wind velocity, m/s

= Vapor pressure deficit, kPa

Vapour pressure deficit is a predominant factor that affects evaporation from the sprinkler
sprays. It is important to determine the vapour pressure deficit affecting the evaporation of the
water from the nozzle (Bavi et al., 2009). The vapour pressure deficit was determined as follows:

Es – Ea = 0.61 exp [17.27 �
�+237.3

] (1 − RH) (2)

where,
T = Air temperature, °C
RH = Relative humidity, fraction.

The evaporation and drift losses were determined for different riser height as recommended by
Smajstrla and Zazueta (1994).

(3)
where,
E = Evaporation and drift losses, %
D = Nozzle diameter, m
H = Riser height, m
U = Wind velocity, m hr-1
RH = Relative humidity, %
T= Air temperature, °C

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129

2.4.2 Christiansen’s Coefficient of Uniformity (CU)
The coefficient of uniformity (CU) was determined as follows:

CU % = 100(1 − the standard deviation of the water in the catch can
mean of water in the catch can

) (4)

2.4.3 Distribution Uniformity (DU)
The distribution uniformity (DU) was calculated as follows:

DU % = 100 × ( an average low quarter of water in the catch can
the average total of water in the catch can

) (5)

2.4.4 Mean Application Rate (MAR)
The mean application rate (MAR) was determined as follows:

I = q
Sm × Sl

× 100 (6)

I= mean application rate is (m hr-1)
q = Sprinkler discharge (m3 hr-1),
Sl = Sprinkler spacing (m),
Sm = lateral spacing (m).

2.5 Data Analysis
The quantity of water measured in each riser were subjected to One-way ANOVA with multiple
comparisons in Minitab 17 Environment. The amounts of water caught in the Cans were used to
compute the Coefficient of Uniformity, Distribution Uniformity and Mean Application Rate of the
sprinkler irrigation system. The results are presented in Tables and charts.

3. Results and Discussion
3.1 Determination of the volume of water Caught in the Catch Cans
The evaporation and wind drift losses range between 5.22% to 10.2% which was in line with the
work of Okasha and Pibars (2016). The amount of water determined in each riser was shown in
Table 3. In a riser 1.5, the amount of water computed in the catch-can equal 799 ml. Also, the
amount of water estimated in riser 2 was 632 ml. The amount of water calculated at riser 3m was
745 ml. The riser 4m has a total amount of 874 ml. The mean application rate for each riser 1.5,
2, 3 and 4 was 8.56 mm hr-1, 7.76 mm hr-1, 7.56 mm hr-1 and 6.76 mm hr-1 respectively as shown
in Table 3. The study revealed that as the riser height increases the mean application rate
decreases because the evaporation and drift losses also increase as indicated in Table 3. This
study agrees with the work of Bishaw and Olumana (2015). The riser heights 4.0 m, 3.0 m and
1.5 m have the highest depth of water, whereas 2.0 m has the lowest volume of water caught in
the catch cans as shown in Table 3. The practical implication is that more water was well
distributed on the land at riser height 2 m while risers 4.0 m, 3.0 m and 1.5 m were not. Thus,
riser (2 m) generates less runoff.

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130

Table 3: Determination of the Volume of water Caught in the Cans under constant operating
pressure

Date Time

Riser
Height
(m)

Total Volume
of Water in the
Cans (ml)

Evaporation
and Drift
Losses (%)

Wind
Direction Mean Application

Rate (mm hr-1)
29/72016 5:06 PM 1.5 799 5.22 NW 8.56
30/7/2106 9:32 AM 2 632 5.7 NE 7.76
30/7/2106 10:27 AM 3 745 8.21 NE 7.56
30/7/2106 11:23 AM 4 874 10.2 SE 6.76

3.2 Effect of Riser Height on Water Caught in the Catch Cans under Constant Operating
Pressure
The analysis of variance for the water determined in the catch cans was shown in Table 1. The
factor riser 1.5m, 2m, 3m and 4m do bring significant information to the model since the
computed p-value is less than alpha (0.05). The risers 2 and 3 were significantly different because
their means do not have any letter in common (Table 1), and concluded that the riser height has
the different mean value of water caught in the catch cans. Besides, the Tukey pairwise
comparisons show that riser heights 1.5 m, 2 m, 3 m and 4 m have different water trapped in the
catch cans because the Means that do not share a letter are significantly different.
Tukey simultaneous tests for differences of means for water caught were shown in Table 3. The
difference in level between riser height 4 m and 2 m have a higher effect on the water found in
the catch-can be followed by the riser 2m and 1.5m, 4m and 3m and 3m and 2m since their p-
values were 0.000, 0.001, 0.016 and 0.046 respectively. Thus, the risers have a different effect on
the volume of water caught.

Table 1: Analysis of Variance
Source DF Adj SS Adj MS F-value P-value
Riser 3 863.9 287.97 11.28 0.000
Error 140 3575.4 25.54
Total 143 4439.3

Table 2: Tukey Pairwise Comparison
Risers Mean Grouping
4 24.28 A
1.5 22.19 AB
3 20.694 B
2 17.556 C
Means that do not share a letter are significantly different

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131

Table 3: Tukey Simultaneous Tests for Differences of Means (volume of water)
Difference in
Level

Difference of
Means

SE of
Difference

95% CI T-Value Adjusted P-
value

2.0 - 1.5 -4.64 1.19 (-7.74, -1.54) -3.89 0.001
3.0 - 1.5 -1.50 1.19 (-4.60, 1.60) -1.26 0.590
4.0 - 1.5 2.08 1.19 (-1.02, 5.18) 1.75 0.303
3.0 - 2.0 3.14 1.19 ( 0.04, 6.24) 2.64 0.046
4.0 - 2.0 6.72 1.19 ( 3.62, 9.82) 5.64 0.000
4.0 – 3.0 3.58 1.19 ( 0.48, 6.68) 3.01 0.016

3.3 Determination of Coefficient of Uniformity (CU) and Distribution Uniformity (DU) under
different Riser Heights at Constant Operating Pressure (1.6 bars)
The uniformity coefficient and the distribution coefficient of the sprinkler irrigation system were
shown in Table 4. At riser height 1.5 m, the Coefficient of Uniformity (CU) and distribution
uniformity (DU) were 70% and 61% respectively. The CU and DU values at 2 m riser height were
89% and 85% respectively. At riser 3.0 m, CU and DU values were 85% and 78% respectively. The
CU and DU at 4 m riser height were 72% and 70 respectively. This study found out that the riser
height 2.0 m had the highest CU (89%) and DU (85%) values. Also, the riser height of 1.5 m had
the lowest CU (70%) and DU (61%) values. CU for riser height 4.0 m and 1.5 m were classified
unsatisfactory while the CU for riser height 2 m and 3 m were rated good (Little et al., 1993). Also,
the DU for 2 m and 3 m were rated excellent and fair while the DU for 1.5 m and 4 m were rated
poor (Bloomer, 2006). The study revealed that riser heights 2 m and 3 m have optimum CU and
DU.

Table 4: Coefficient of Uniformity and Distribution of Uniformity of different Risers

Riser Height (m) CU (%) DU (%)
1.5 70 61
2 89 85
3 85 78
4 72 70

4 Conclusion
The effect of different riser heights on the performance of sprinkler irrigation at constant
operating pressure was assessed to provide water for the cultivation of high crops and reduce
water wastage. The study revealed that as the riser height increases the mean application rate
decreases. The riser heights 2 and 3 m were significantly different because their means do not
have any letter in common, and concluded that some of the riser height have the different mean
value of water found in the catch-can. This study reveals that as the wind direction changes the
volume of water trapped in catch cans also increases which in turn cause weak CU. The study
concluded that riser heights 2m and 3m have the highest CU and DU at 1.6 bars and these riser
heights can provide water for taller crop and reduce water losses on the field.

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