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Asian Journal of Engineering, Social and Health

Volume 4, No. 1 January 2025

Volume 4, No. 1 January 2025 - (xx-xx)

p-ISSN 2980-4868 | e-ISSN 2980-4841

https://ajesh.ph/index.php/gp

Rule Curve of Meninting Reservoir in West Lombok Regency,

West Nusa Tenggara

Natasya Ainun Nisya1*, Ery Setiawan2, M. Bagus Budianto3, Hartana4

Universitas Mataram, Indonesia

Email: natasyaan2001@gmail.com

ABSTRACT

Meninting Reservoir in West Lombok Regency is essential for addressing uneven water distribution on

Lombok Island. It reallocates water from the Sesaot, Penimbung, and Ketapang Irrigation Areas, covering

1,490 hectares, and supplies 150 liters/second of raw water while generating 2×0.4 MW of electricity. To

ensure equitable water distribution, an optimal rule curve is needed. This study analyzes water demand

and availability using the continuity equation. Water availability was assessed based on discharge data

from the Orong Atas AWLR station, while demand was evaluated under various scenarios, including

different planting schedules and Micro Hydro Power Plant (MHP) integration. Results show that irrigation

demand ranges from 1,082,648.92 m³ to 1,496,415.21 m³ per half-month period, while raw water and

MHP demands are 197,100 m³ and 2,857,950 m³, respectively. The optimal rule curve is achieved with the

October II planting schedule without MHP, ensuring 100% reliability. However, with MHP, the best rule

curve occurs under the November I schedule, reducing reliability to 54.2% and increasing failure risk to

45.8% in dry years. These findings emphasize the need for strategic planting schedules and reservoir

management to balance irrigation, raw water supply, and hydropower generation. The study provides a

scientific basis for optimizing reservoir operations to ensure sustainable water use in West Lombok

Regency.

Keywords: Meninting Reservoir, Rule Curve, Water Balance.

INTRODUCTION

Water resources play a crucial role in human life and survival, as nearly all human activities

require water (Ardana et al., 2021); (Pratama Nataniel, 2022). Without water, humans cannot

survive. Over time, the use of water resources for daily needs has increased alongside population

growth and its associated activities (Ardana et al., 2021); (Rosandi et al., 2023). Therefore, efforts

in water management are necessary to ensure its optimal utilization.

A policy to ensure the sustainability of water resources is the development of water

infrastructure, such as reservoir construction (Mulyawati & Fazhar, 2020). In principle, a reservoir

functions as a place to store and hold water during the rainy season when rainfall is high, so that

it can be used during the dry season when rainfall is low (Shiamah, 2020); (Farida & Andajani,

Natasya Ainun Nisya, Ery Setiawan, M. Bagus Budianto, Hartana

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Volume 4, No. 1 January 2025

2019). It is expected that the water stored in the reservoir can meet various needs, including

irrigation water, raw water, hydroelectric power generation, or other uses, depending on

whether the reservoir serves a single or multiple purposes in accordance with competing

interests (Swastika et al., 2022).

The Ministry of Public Works and Housing is currently completing the construction of

Meninting Reservoir. Meninting Reservoir is located in West Lombok Regency and is part of the

Meninting River Basin. The construction of Meninting Reservoir was motivated by the uneven

distribution of water on Lombok Island. The western part of Lombok Island, which includes the

Meninting River Basin, has sufficient water potential to meet its own needs. However, the

southern part of Lombok Island, particularly the Mujur Complex area, which has significant

agricultural potential, faces water scarcity. To balance water potential and agricultural potential

on Lombok Island, Meninting Reservoir will supply water to the southern part of Lombok Island

by reallocating some of the water from the Sesaot Irrigation Area, covering 1,000 hectares. The

Meninting Reservoir will also irrigate the Penimbung Irrigation Area and Ketapang Irrigation Area,

covering 450 hectares and 40 hectares, respectively, with a planting intensity of 300% for each

irrigation area (1, 2017).

In addition, the decreasing discharge of springs and the increasing demand for drinking

water due to population growth have exacerbated the water balance crisis. Therefore, with the

presence of Meninting Reservoir, the supply of raw water to the northern part of West Lombok

Regency, amounting to 150 liters/second, will be more secure. The outflow from Meninting Dam

for irrigation water supply to southern Lombok Island and for drinking water supply to northern

West Lombok Regency can also be used to generate electricity with a capacity of 2 x 0.4

Megawatts (Wiyasri et al., 2022).

Reservoir management and operational guidelines are essential not only during the

construction phase but also after completion (Anggraheni et al., 2017). In addition to the

increasing demand for water, inefficient water use and fluctuations in Meninting River discharge

contribute to the instability between water availability and demand, especially during the dry

season. Therefore, the rule curve of Meninting Reservoir is crucial to ensure that the water stored

and held in the reservoir can be distributed accurately, meeting all water needs fairly and

equitably.

In this study, water distribution is conducted using a simulation method, by simulating the

reservoir rule curve based on its storage capacity. This aims to determine the water demand and

availability based on the continuity equation or mass balance equation. The continuity equation

relates inflow, outflow, and changes in storage across three conditions: wet year, normal year,

and dry year. For the outflow, several alternatives were tested in this study, including MHP

sharing a channel with irrigation or MHP on a separate channel from irrigation, which were also

simulated at different planting schedules. This way, the optimal reservoir rule curve be

determined, ensuring its role as both a water storage and supply system.

Rule Curve of Meninting Reservoir in West Lombok Regency, West Nusa Tenggara

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RESEARCH METHOD

The research location is the Meninting Reservoir, situated in West Lombok Regency. It lies

within the Meninting River Basin, covering a river basin area of 32.77 km² and an inundation area

of 53.60 hectares. The reservoir has a maximum water surface elevation of 198.72 meters and a

minimum elevation of 169 meters. Its gross volume is 9.91 million m³, with an effective storage

volume of 8.19 million m³.

Figure 1. Map of Meninting Reservoir location

The Meninting Reservoir plays a critical role in water resource management on Lombok

Island and requires a rule curve for effective use. Reservoir operation refers to the control of

water flow from a river into a reservoir and the subsequent release of stored water for various

purposes. The rule curve acts as a reference point to maintain the reservoir's water levels

according to the design, ensuring that outflow meets demand (Soetopo, 2010).

One commonly used method for reservoir operations is the continuity equation, which links

inflow, outflow, and changes in reservoir storage. This simulation model, known as behavior

analysis, calculates water availability and demand based on mass balance principles. The

continuity equation expresses the relationship between inflow, outflow, and changes in storage,

as shown in the following equation (McMahon, 1978):

St+1 = St + Qt + Dt – Et – Lt

For 0 ≤ St+1 ≤ C

Where t is the time period, St+1 is the reservoir storage at the end of period t (m3), St is

the reservoir storage at the beginning of period t (m3), Qt is the inflow during period t (m3), Dt

is the demand during period t (m3), Et is evaporation during period t (m3), Lt is represents water

losses due to leakage and seepage during period t (which can be neglected) (m3), C is the

reservoir's active storage capacity (m3).

The reservoir's storage capacity can be determined from the reservoir capacity curve,

which depicts the curve relationship between water surface area, storage volume, and water

surface elevation (Susanto & Yosananto, 2017).

Natasya Ainun Nisya, Ery Setiawan, M. Bagus Budianto, Hartana

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Volume 4, No. 1 January 2025

Figure 2. Capacity curve of Meninting Reservoir

The inflow to the reservoir, as outlined in the Reservoir Operation Module from the Water

Allocation Training Module 8 by the Training Center for Water Resources and Construction of the

Ministry of Public Works and Housing, is classified into three reliability conditions: a wet year

with 35% reliability, a normal year with 50% reliability, and a dry year with 65% reliability

(Kementerian, 2017).

The water requirements are aligned with the functions of the reservoir, including raw

water, irrigation water, and MHP generation. This study explores several alternatives, including

integrating the MHP with the irrigation system and separating it from the irrigation system, while

also considering the reservoir's function as a source of raw water. These scenarios are simulated

across different planting schedules.

The irrigation water requirements for paddy and secondary crops, according to Planning

Criteria, are based on the principle of water balance, which can be expressed using the following

equations (Sudirman et al., 2021):

NFRpaddy = Etc + WLR + LP + Pe - Reff

NFRsecondary crops = Etc - Reff

Where NFR is the net field water requirement (mm/day), Etc is the crop evapotranspiration

(mm/day), LP is land preparation (mm/day), WLR is water loss replacement (mm/day), Pe is

percolation (mm/day), and Reff is effective rainfall (mm/day).

One of the most important factors in calculating irrigation water requirements is

evapotranspiration, which represents the amount of water lost through evaporation from land

surfaces and transpiration by plants. Evapotranspiration is equivalent to the consumptive water

requirement, defined as the total evaporation from the land and the water needed by the plants.

In this calculation, evaporation and transpiration are considered simultaneously (Triatmodjo,

2009). To determine the evapotranspiration value, the Penman method, modified by the FAO, is

used. This method involves extensive use of climatological data, making the calculations more

accurate and logical. The Penman equation (FAO modification) is expressed as follows (Strahler

& Chow, 1964):

Rule Curve of Meninting Reservoir in West Lombok Regency, West Nusa Tenggara

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ETo = Cf (W. Rn+(1-W).f(u).(ea-ed)

Where Eto is the reference crop evapotranspiration (mm/day), Cf is the wind speed and

humidity correction factor, W is the temperature and altitude factor, Rn is net radiation

(mm/day), f(u) is the wind speed function, ea is saturated vapor pressure (mbar), ed is actual

vapor pressure (mbar).

To determine water demand at the intake, the net field requirement (NFR) is converted

from mm/day to liters/second/hectare using a factor of 0.116 and divided by irrigation efficiency.

Additionally, water loss due to evaporation is a significant factor in reservoir operations.

Evaporation refers to the loss of water from the surface of the water body, land, or plant surfaces

(interception). It is influenced by solar radiation, temperature, humidity, and wind speed. Various

methods can be used to measure evaporation, including evaporation pans, water balance in the

reservoir, mass transfer methods, and energy balance techniques (Triatmodjo, 2009).

RESULT AND DISCUSSION

To determine the average rainfall over the area affecting the catchment of the Meninting

Reservoir, the Thiessen Polygon method is employed, which requires a minimum of three

Automatic Rainfall Recorder (ARR) stations to create the polygon. The rainfall stations impacting

the catchment area of the Meninting Reservoir are the ARR Gunung Sari, with an influence area

of 18.95 km², and the ARR Sesaot, with a sequential influence area of 13.82 km².

Figure 3. Map of the catchment area, location of rainfall stations,

and thiessen polygon for the Meninting Reservoir

Based on the Thiessen polygon above, the average rainfall in the catchment area of the

Meninting Reservoir can be analyzed by multiplying the area of each influential rainfall station by

the respective rainfall data from each Automatic Rainfall Recorder (ARR). The resulting average

rainfall for the Meninting Reservoir is presented in the following table:

Table 1. Half-Monthly Rainfall Data in the Catchment Area of Meninting Reservoir (mm)

Year

Jul

Aug

Sep

Oct

Nov

Dec

2013

104.57

10.24

1.89

10.93

1.75

0.51

16.37

149.98

116.55

111.26

262.21

244.04

2014

29.80

14.88

7.23

1.14

1.01

0.42

5.69

12.55

183.26

76.75

111.51

223.48

2015

0.88

1.79

0.42

1.10

0.00

0.47

9.87

0.93

37.41

66.90

113.68

149.71

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Year

Jul

Aug

Sep

Oct

Nov

Dec

2016

50.14

47.24

43.56

22.70

93.70

117.50

191.95

108.23

197.01

229.44

300.10

133.44

2017

25.71

15.76

6.89

1.99

1.43

34.33

260.00

93.10

167.92

156.95

50.36

177.01

2018

1.56

6.25

0.13

21.22

16.58

31.51

1.43

1.35

259.11

49.86

72.17

55.13

2019

2.60

0.00

2.08

0.00

0.29

0.00

33.53

170.08

176.28

149.94

2020

60.46

1.69

53.16

19.52

22.12

50.99

88.77

226.55

139.80

134.73

192.27

34.48

2021

23.83

0.00

123.10

86.60

74.18

54.48

122.51

165.18

316.20

148.46

295.59

130.67

2022

48.18

1.14

23.00

9.44

218.46

132.21

280.70

190.70

209.46

114.26

114.53

234.90

Subsequently, an analysis of effective rainfall was conducted. Effective rainfall refers to the

portion of precipitation that falls in a specific area and is utilized by plants for their growth. The

analysis of effective rainfall aims to determine the effective precipitation for rice and secondary

crops. In this study, the calculation of dependable rainfall employs the basic month method, using

data spanning a period of 10 years.

Figure 4. Curve of effective rainfall in Meninting catchment area

After analyzing effective rainfall, the next step is to analyze evapotranspiration using the

Modified Penman method, employing average climatological data from 2013 to 2022 obtained

from the West Nusa Tenggara Meteorology, Climatology, and Geophysics Agency (BMKG) station

located in Kediri, West Lombok. This climatological data encompasses information on

temperature, wind speed, humidity, and solar radiation. The recap of water requirements for

evapotranspiration using the Modified Penman method for the Meninting Reservoir can be seen

in the curve in Figure 5 below.

Figure 5. Evapotranspiration curve for the Meninting Reservoir

Rule Curve of Meninting Reservoir in West Lombok Regency, West Nusa Tenggara

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This information helps determine the irrigation water requirements in the irrigation areas

of Meninting Reservoir, which include the Sesaot, Penimbung, and Ketapang irrigation regions.

The cropping patterns used in this analysis are rice, rice-corn, and corn for the Sesaot irrigation

area, and rice, rice, and rice-corn for the Penimbung and Ketapang areas, which reflect the

existing cropping patterns. The planting intensity in the Meninting Reservoir irrigation area is set

at 300%, with each planting schedule allocated equally at 100%. The beginning of the planting

schedule is evaluated with several alternatives, specifically in the first and second weeks of

October (Oct I and Oct II), the first and second weeks of November (Nov I and Nov II), and the

first and second weeks of December (Dec I and Dec II). Based on the analysis results, the irrigation

water requirements in Meninting Reservoir for different planting schedules can be seen in the

curve in Figure 6 below.

Figure 6. Curve of the total irrigation water requirements for Meninting

Reservoir at the beginning of different planting schedules

Meanwhile, the requirements for raw water and MHP generation from the Nusa Tenggara

1 River Basin Center are 150 liters per second for raw water and 2.175 cubic meters per second

for the MHP, with a capacity of 2 x 0.4 MW.

In addition to the water requirements for the reservoir functions, evaporation data is also

needed to determine water loss due to evaporation in the reservoir. For Meninting Reservoir,

the evaporation value is based on the data recorded at the West Nusa Tenggara Meteorology,

Climatology, and Geophysics Agency Station located in Kediri, West Lombok Regency.

Figure 7. Evaporation value curve

Natasya Ainun Nisya, Ery Setiawan, M. Bagus Budianto, Hartana

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Another important factor for simulating reservoir rule curves is the analysis of water

availability. In this study, the discharge data used is the semi-monthly discharge data from the

Automatic Water Level Recorder station at Orong Atas from 2013 to 2022. To obtain the inflow

for the catchment area of Meninting Reservoir, routing needs to be performed using the area

ratio between the catchment area of the Automatic Water Level Recorder at Orong Atas and the

catchment area of Meninting Reservoir. The inflow discharge data for Meninting Reservoir can

be seen in Table 3 below.

Table 2. Inflow discharge of Meninting Reservoir (m³/s)

After obtaining the inflow discharge of the reservoir, the reliability discharge is then

calculated using the basic month method. The reliability used in this study is 35% for wet years,

50% for normal years, and 65% for dry years. The selection of these reliability conditions is based

on Module 8 of Reservoir Operations. The results of the reliability discharge calculation using the

basic month method for Meninting Reservoir can also be seen in the curve in Figure 8 below.

Figure 8. Curve of reliable discharge for Meninting

Reservoir using the basic month method

Rule Curve of Meninting Reservoir in West Lombok Regency, West Nusa Tenggara

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Simulation of reservoir operation is conducted to review the reliability levels or failures that

occur in the operational behavior of the reservoir system in meeting its service needs. In this

study, the rule curve simulation uses a 15-day period, experimenting with several alternatives

based on different planting schedule starts, namely in October I, October II, November I,

November II, December I, and December II. The simulations include a MHP in a single channel

with an irrigation channel (simulation without a MHP) or a MHP in a different channel from the

irrigation channel (simulation with a MHP).

Example of reservoir operation simulation calculation with planting patterns used for rice,

rice-secondary crops, and secondary crops with a planting intensity of 300%, planting schedule

in October, first week of January, 2013, with one channel between the mhp and the irrigation

channel as follows:

1. Inial Reservoir Storage (Eecve)

= 8,190,000.00 m3

2. Inow

= 2.59 m³/second

= 3,357,750.01 m³/half-month

3. Water Availability

= Inial storage + inow

= 8,190,000 + 3,357,750.01

= 11,547,750.01 m³/half-month

4. Irrigaon Water Demand

= 1,813,585.96 m³/half-month

5. Raw Water Demand

= 0.15 m³/second

= 194,400.00 m³/half-month

6. Total Water Demand

= Irrigaon demand + raw water demand

= 1,813,585.96 + 194,400.00

= 2,007,985.96 m³/half-month

7. Evaporaon

= 4.56 mm/day

= 36,662.40 m³/half-month

8. Total Oulow

= Total water demand + evaporaon

= 2,007,985.96 + 36,662.40

= 2,044,648.36 m³/half-month

9. Final Reservoir Storage (Eecve)

= Water availability – total oulow

Natasya Ainun Nisya, Ery Setiawan, M. Bagus Budianto, Hartana

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= 11,547,750.01 – 2,044,648.36

= 9,503,101.65 m³

10. Since the nal reservoir storage exceeds the reservoir's capacity, spillover occurs from the

spillway, commonly referred to as spillout. As a result, the nal reservoir storage equals the

maximum reservoir capacity, which is 8,190,000.00 m³.

11. Spillout

= 9,503,101.65 - 8,190,000.00

= 1,313,101.65 m³

12. Remarks

= Successful

The results of the reservoir storage simulation analysis for the year 2013, at the beginning

of the planting schedule in October I, without the need for the MHP, are presented in Table 3

and figure 9-10 below.

Table 3. Reservoir Simulation of Meninting in 2013 at plant

schedule October I without MHP (m³)

Water Availability

Irrigation Water

Demand

Total Water Demand

Total (m3) Effective (m3) m3/sec m3/half a month m3/half a month m3/half a month m3/sec m3/half a month m3/half a month

I 9,910,000.00 8,190,000.00 2.59 3,357,750.01 11,547,750.01 1,813,585.96 0.150 194,400.00 2,007,985.96

II 9,910,000.00 8,190,000.00 3.82 5,285,201.38 13,475,201.38 - 0.150 207,360.00 207,360.00

I 9,910,000.00 8,190,000.00 6.26 7,569,793.98 15,759,793.98 - 0.150 181,440.00 181,440.00

II 9,910,000.00 8,190,000.00 2.91 3,776,594.55 11,966,594.55 1,448,029.37 0.150 194,400.00 1,642,429.37

I 9,910,000.00 8,190,000.00 2.53 3,276,090.24 11,466,090.24 1,364,577.62 0.150 194,400.00 1,558,977.62

II 9,910,000.00 8,190,000.00 2.61 3,611,710.35 11,801,710.35 1,653,286.59 0.150 207,360.00 1,860,646.59

I 9,910,000.00 8,190,000.00 3.07 3,976,962.45 12,166,962.45 1,419,955.78 0.150 194,400.00 1,614,355.78

II 9,910,000.00 8,190,000.00 2.30 2,987,206.46 11,177,206.46 1,642,664.96 0.150 194,400.00 1,837,064.96

I 9,910,000.00 8,190,000.00 1.18 1,526,682.46 9,716,682.46 1,710,668.13 0.150 194,400.00 1,905,068.13

II 9,501,148.74 7,781,148.74 1.31 1,812,934.78 9,594,083.51 1,931,886.13 0.150 207,360.00 2,139,246.13

I 9,143,247.10 7,423,247.10 1.18 1,530,903.82 8,954,150.93 771,166.74 0.150 194,400.00 965,566.74

II 9,682,468.09 7,962,468.09 2.12 2,744,810.40 10,707,278.49 570,272.40 0.150 194,400.00 764,672.40

I 9,910,000.00 8,190,000.00 0.69 890,199.20 9,080,199.20 147,577.22 0.150 194,400.00 341,977.22

II 9,910,000.00 8,190,000.00 0.47 646,218.68 8,836,218.68 836,228.66 0.150 207,360.00 1,043,588.66

I 9,483,013.76 7,763,013.76 4.47 5,789,815.63 13,552,829.39 1,277,312.46 0.150 194,400.00 1,471,712.46

II 9,910,000.00 8,190,000.00 3.94 5,440,678.12 13,630,678.12 1,363,762.48 0.150 207,360.00 1,571,122.48

I 9,910,000.00 8,190,000.00 3.42 4,432,586.67 12,622,586.67 1,555,208.25 0.150 194,400.00 1,749,608.25

II 9,910,000.00 8,190,000.00 3.25 4,213,504.55 12,403,504.55 292,544.94 0.150 194,400.00 486,944.94

I 9,910,000.00 8,190,000.00 0.00 0.00 8,190,000.00 3,517,249.74 0.150 194,400.00 3,711,649.74

II 6,162,068.50 4,442,068.50 0.00 0.00 4,442,068.50 3,774,640.95 0.150 207,360.00 3,982,000.95

I 2,151,766.69 431,766.69 5.42 7,018,436.93 7,450,203.61 2,410,263.64 0.150 194,400.00 2,604,663.64

II 6,551,641.01 4,831,641.01 5.69 7,372,202.06 12,203,843.06 2,309,687.85 0.150 194,400.00 2,504,087.85

I 9,910,000.00 8,190,000.00 11.38 14,753,015.41 22,943,015.41 1,883,727.63 0.150 194,400.00 2,078,127.63

II 9,910,000.00 8,190,000.00 11.30 15,626,564.42 23,816,564.42 2,219,667.44 0.150 207,360.00 2,427,027.44

JAN

FEB

No.

Month

Initial Reservoir Storage

Inflow

Raw Water Demand

JUN

JUL

AUG

MAR

APR

MAY

DEC

SEP

OCT

NOV

Figure 9. Simulation curve of Meninting Reservoir at plant

schedule October I without MHP

Rule Curve of Meninting Reservoir in West Lombok Regency, West Nusa Tenggara

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To calculate the conditions for wet, normal, and dry years, reliability levels of 35% for wet years,

50% for normal years, and 65% for dry years were used. These reliability conditions were chosen

based on Module 8 of Reservoir Operation (14).

Figure 10. Rule curve of Meninting Reservoir at

planting schedule on October I without MHP

The same process was also carried out for the planting schedules of October II, November

I, November II, December I, and December II, resulting in the following rule curve:

Table 4. Recapitulation rule curve of Meninting Reservoir

Failure Reliability Failure Reliability Failure Reliability Failure Reliability Failure Reliability Failure Reliability

PS I 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0%

PS II 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0%

PS III 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0%

Raw Water 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0% 0.0% 100.0%