International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 03, March 2019, pp. 998-1006, Article ID: IJCIET_10_03_097
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=03
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
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ANALYSIS OF IRRIGATION WATER
REQUIREMENTS IN RICE FIELDS IN SP4,
TANAH MIRING DISTRICT, MERAUKE
REGENCY
Jeni Paresa and Dewi Sriastuti Nababan
Department of Civil Engineering, Faculty of Engineering,
Universitas Musamus, Merauke, Indonesia
ABSTRACT
The purpose of this study was to analyze irrigation water requirements in rice fields
in SP4, Tanah Miring District, Merauke Regency. The method used in analyzing is
discharge measurement by calculating the flow velocity on the channel by using the
Strickler formula. Primary data collection consisting of channel dimension data and
original land elevation using the observation method. From the calculation results, it
is obtained that the available discharge on long storage is 22 liters / second, and the
demand for discharge is 138 liters / second (Qt <Qb). So the total rice fields that are
capable of flowing are 15.17 ha or 14.14%.
Keywords: water requirements, long storage, discharge
Cite this Article: Jeni Paresa and Dewi Sriastuti Nababan, Analysis of Irrigation Water
Requirements in Rice Fields in Sp4, Tanah Miring District, Merauke Regency,
International Journal of Civil Engineering and Technology, 10(03), 2019, pp. 998–1006
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1. INTRODUCTION
Irrigation is an effort to provide and regulate water to support agriculture, which includes types
of surface water irrigation, underground water irrigation, pump irrigation and swamp irrigation,
which are determined by many factors, namely topography, hydrology, climatology, soil
texture, evapotranspiration. The stages of irrigation water management are land preparation,
consumptive use, location, water layer replacement, effective rainfall, and water requirements
in the fields for tertiary plots.
Agricultural land in Tanah Miring SP4 Merauke Regency uses the surface water irrigation
network to use water from long storage so that water can reach the rice fields. In order for the
irrigation network to be used in accordance with its functions, it is necessary to have an
effective and efficient management of irrigation networks. The management of irrigation
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Analysis of Irrigation Water Requirements in Rice Fields in Sp4, Tanah Miring District, Merauke
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networks will affect the system of giving water to rice fields and the level of irrigation services
received by farmers. In the dry season the water needs in the Tanah Miring SP4 rice fields in
Merauke Regency have not been fulfilled, thus affecting farmers' production due to long
storage that cannot function properly.
According to KP-01 Irrigation Planning Standards, Irrigation is a system of providing water
to agricultural land to meet the needs of plants so that the plants grow well. And also according
to Government Regulation No.23 of 1998 irrigation is an effort to provide and regulate water
to support agriculture, and according to Government Regulation No.20 of 2006 is an effort to
provide regulation and disposal of irrigation water to support agriculture whose types include
surface irrigation, swamp irrigation, underground water irrigation, pump irrigation, and pond
irrigation. Each plant must need water in its life cycle (Mangkoedihardjo and April, 2012),
while rain is the main water source for plants. Changes in water supply for plants caused by
changes in certain rainfall conditions will greatly affect plant growth, so this change will cause
a decline in agricultural production.
2. METHODOLOGY
The measurement of discharge in this study was obtained by calculating the flow velocity on
the channel using the Strickler formula. Primary data collection consisting of channel
dimension data and original land elevation using the observation method.
2.1. Effective rainfall
Effective rainfall is estimated for the next stage, which is estimated conservatively from rainfall
to have a probability of 80%, R80. Some of the falling rain water will flow into the surface
water system before it can be used effectively by plants, effective rainfall is assumed to be 70%
of the total rainfall.
Re = 0,7 x R80
where:
Re = effective rainfall (mm/day)
R80 = reliable rain (mm)
2.2. DEFINITION OF IRRIGATION
According to government regulation No.23 of 1998 irrigation is an effort to provide and
regulate water to support agriculture, and according to government regulation No.20 of 2006
is an effort to provide regulation and disposal of irrigation water to support agriculture whose
types include surface irrigation, swamp irrigation, irrigation underground water, pump
irrigation, and pond irrigation.
Irrigation comes from the term irrigaite in Dutch or irrigation in English. Irrigation can be
interpreted as an effort carried out to bring water from its source for agricultural purposes, flow
and distribute water regularly and after use can also be thrown back.
2.3. Alternative cropping patterns
Cropping patterns are general forms of planting schedules which state when to start planting
rice, secondary crops, sugar cane and so on.
The form of the pattern to be applied depends on the conditions of the area and the
availability of water in the Irrigation Area, for example:
1. If there is a lot of water available, a rice-paddy cropping pattern can be done.
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Jeni Paresa and Dewi Sriastuti Nababan
2. If rice with superior variety is used (age <140 days), it is still possible to plant secondary
crops so that the cropping pattern becomes: Paddy-Rice.
3. If the water supply in the dry season is limited, then for paddy fields that get water
difficulties in the dry season, they will apply the planting pattern: Paddy-Palawija-Palawija.
4. If an area is required to plant sugar cane for more than 1 year (ie ± 15 months).
2.4. Estimated monthly plant coefficient
In analyzing our normal water requirements, we will not be separated from the ability of
evapotranspiration plants, therefore an estimate of the monthly plant coefficient is made where
plant growth is based on the type of rice plant and the age at which it starts, the highest need
when the plant has reaching the middle age of the entire production age.
2.5. Water requirements for processing paddy fields
Pre-irrigation is needed to work on land to be planted and to create adequate humid conditions
for newly-grown nurseries.
To calculate the normal water requirements in managing paddy fields, it is usually
influenced by the texture and structure of paddy fields, the effect of the previous land use, soil
treatment process.
The following is the equation formula for estimating irrigation water requirements. Clean
water needs in rice fields for rice:
NFR = Etc + P – Re + WLR
Irrigation water requirements for rice:
IR =
NFR
e
Where:
NFR
= Clean water needs in the fields (l/sec/ha)
IR = Irrigation water needs for rice
Etc
= Consumptive use (mm)
P = Water loss due to percolation (mm/day)
Re = Effective rainfall (mm/day)
e = Overall irrigation efficiency
WLR
= Change the water layer
2.6. Water requirements
Water needs include the problem of water supply, both surface water and underground water.
To find out the amount of water needed / must be provided, it is necessary to know in advance
the functions and properties of water in plant processes. If the water needs of a plant are known,
the water requirements for a larger unit can be calculated.
Water requirements in rice fields are very dependent on land preparation (processing),
evaporation that occurs (evapotranspiration), percolation and seepage, change of water layer,
effective rainfall, puddles of water in the fields.
1. Use of Evaporation land preparation (Eo)
Eo = 1,1 x Eto
where:
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Analysis of Irrigation Water Requirements in Rice Fields in Sp4, Tanah Miring District, Merauke
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Eo = Evaporation
ETo
= Evapotranspiration potential
2. Use of plant consumptions (ETc)
ETc = ETo x Kc
where:
ETc
= Use of plant consumptive
ETo
= Evapotranspiration potential
Kc = Plant coefficient
3. Discharge irrigation water (Q)
Q = A1 x a x e
where:
Q = water discharge (l/sec)
A1 = area of agriculture (ha)
a = amount of water needs (l/sec)
e = irrigation efficiency
2.7. Calculation of hydraulic irrigation canals
In this Planning Criteria, flow rates are used with maximum permissible prices, not shear
forces, as parameters for erosion forces. For hydraulic planning of a channel, there are two
main parameters that must be determined if the required capacity plan is known, namely:
1. Comparison of water depth with a base width
2. The slope extends the channel
In channel planning, there are three conditions that must be distinguished due to the
presence of sediments in irrigation water and embankment material, namely:
1. Irrigation without sediment in the soil channel.
2. Irrigated water is sedimented on the couple's canal.
3. Sediment irrigation flows in the land channel.
For segment planning, the channel flow is considered a fixed flow, and for that the Stricker
formula (DPU 2010) is applied:
V = K ∙ R2/3 ∙ I1/2
Q=V∙A
R = A/P
A = (b + m h) h
2
P  b  2 h (1 m )
N = b/h
where: A = (b + m h) h
Q = Channel discharge, ( m3/sec )
V = Flow speed, (m/sec)
A = Wet cross section area (m2)
R = Hydraulic fingers, ( m )
P = Wet circumference, ( m )
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b = Base width, ( m )
h = Depth water, ( m )
I = Channel slope
K = Strickler coefficient of roughness, (m1/3/sec)
m = Slope of the talud
The cross section of the trapezium channel can be seen in figure 1 below.
Figure 1. Cross Section Parameters
2.8. Long Storage
Long storage is a small water reservoir or reservoir at the location of agriculture that aims to
accommodate excess rainwater in the rainy season and its use in the dry season for various
needs both in agriculture and the interests of the community.
The formula for calculating the amount of long storage, theoretically can be found in
Mangkoedihardjo (2010), but practically can use the following equation:
Vol. =
(B  L  b  l)
2
xT
where:
Vol. = storage volume
B = first parallel side
b = second parallel side
L = first channel length
l = second channel length
T = channel height
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Analysis of Irrigation Water Requirements in Rice Fields in Sp4, Tanah Miring District, Merauke
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3. RESULTS AND DISCUSSION
3.1. Results
Table 1. The Amount of ETo for the First Planting Period
Paramete
r
Unit
ETo
mm/hr
Month / 2 weekly
January
I
II
16
15
4.50
4.22
February
I
II
14
14
3.69
3.69
March
I
II
16
15
3.67
3.45
April
I
15
3.02
II
15
3.02
Table 2. The amount of ETo for the second planting period
Parameter
Unit
ETo
mm/hr
Month / 2 weekly
August
September
I
II
I
II
16
15
15
15
3.69
3.69
3.67
3.45
July
I
16
4.50
II
15
4.22
October
I
II
16
15
3.02
3.02
Eo calculation of land preparation in the first week of the first month: Eo
= 1.1 x ETo
; ETo = 4.50 =1.1 x 4.50 = 4.95 mm/hr
Obtained the same thing for land preparation in the first two weeks and obtained: Eo = 4.64
mm/hr.
Calculation of Eo land preparation in the first week of the first month: Eo = 1.1 x ETo ; ETo
= 2.95 =1.1 x 2.95 = 3.25 mm/hr.
Obtained the same thing for land preparation in the first two weeks and obtained: Eo = 3.05
mm/hr.
Calculation of consumptive use of water for the first week of the second month: ETc = ETo
x Kc =3.69 x 1.1 = 4.06 mm/hr.
Table 3. Calculation of ETc During the First Planting Period
Month
Second
Third
Fourth
Week
First
Second
First
Second
First
Second
ETc
4.06 mm/hr
4.06 mm/hr
3.85 mm/hr
3.62 mm/hr
2.87 mm/hr
mm/hr
Use of consumptive water for the first week of the second month: ETo = ETo x Kc = 4.27 x
1.1 = 4.70 mm/hr.
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Table 4. Calculation of ETc during the second planting period
Month
Week
First
Second
First
Second
First
Second
Second
Third
Fourth
ETc
4.70 mm/hr
4.40 mm/hr
5.89 mm/hr
5.89 mm/hr
6.40 mm/hr
0 mm/hr
3.2. Discharge irrigation water needs (Q)
Table 5. Calculation of Quaternary Channel Discharge During the First Planting Period
Name
No
of
channel
Area
Water needs
Channel
efficiency
(A1 )
(a)
(e)
1
BT 1
2
BT 2
4
BT 3
Total needs
20
38
37
95
1.4
1.4
1.4
0.65
0.65
0.65
Q
(m/
sec)
0.018
0.035
0.034
0.087
Table 6. Calculation of Quarterly Channel Discharge During Second Planting Period
Number
1
2
4
Name of
channel
BT 1
BT 2
BT 3
Total needs
Area
Water needs
Channel
efficiency
( A1 )
(a)
(e)
20
38
37
95
2.23
2.23
2.23
0.65
0.65
0.65
Q
(m/
sec)
0.029
0.055
0.054
0.138
3.3. Long storage capacity
From direct measurements obtained values of b = 18 m, t = 5.5 m, B = 29 m, p = 1789 m, and
P = 1800 m. So that it can use equations:
((29  18000)  (18  1789))
 5,5
2
V =
(46250 27600)
2
=
x 5.5
3
= 232105.5 m
Potential evapotranspiration (Et0) and maximum percolation during the second planting
period.
Et0 + P
= 13,06 + 2
= 15,06 mm/day
= 15,06 x 123 day
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Analysis of Irrigation Water Requirements in Rice Fields in Sp4, Tanah Miring District, Merauke
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= 1852,38 mm/season
= 1,852 m/season
The total maximum storage capacity for long storage is:
Q = 232105,5 – 1,852
= 232103,648
1887,021
= 123 m3/day
=
3070,042
(24  60  60)
= 0.022 m3
3.4. Balance of water needs
Table 7. Comparison Between Qb with Qt
Name of Channel
Tersier 1
Tersier 2
Total
Qavailable
Real
(Long Storage)
0.022 m3
0.022 m3
Qneeds
First
Second
0.053 m3/sec
0.034 m3/sec
0.087 m3/sec
0.084 m3/sec
0.054 m3/sec
0.138 m3/sec
From the table above it can be seen that long storage discharges have a water deficit on
tertiary 1 and tertiary channels 2 for the first and second planting periods taken at 0.116 m3 /
sec = 116 l / sec.
4. DISCUSSION
From the results of the research obtained, it is for consumptive plants during the first planting
period for tertiary channels 1 which is equal to Qb = 0.053 m3 / sec, while the consumptive
needs of plants during the first planting period for tertiary 2 are Qb = 0.034 m3 / sec. For the
consumptive needs of plants during the second planting period for tertiary channels 1
amounting to Qb = 0.084 m3 / sec, while the consumptive needs of plants in the second crop
period for tertiary channels 2 amounted to Qb = 0.054 m3 / sec. So the total requirement for
the first planting period is Qb = 0.087 m3 / sec, and for the second planting period is Qb =
0.138 m3 / sec. To meet the needs of these plants obtained from long storage with discharge
Qt = 0.022 m3 / sec. From long storage discharges, there was a water deficit in tertiary 1 and
tertiary channels 2 and the largest deficit in the second planting period was 0.116 m3 / sec =
116 l / sec.
5. CONCLUSION
Based on the results of the research conducted, it can be concluded that the discharge available
at long storage is 22 liters / second, and discharge needs are 138 liters / second (Qt <Qb). Of
the total area of 95 ha which is capable of flowing using long storage discharges, it is 15.17 ha
or 14.14%. So that other sources are needed to be able to meet the water deficit that occurs
during the first and second planting periods.
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