Optimization Balongganggang Reservoir Capacity for Irrigation

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Introduction
Indonesian agriculture is characterized by unstable growth patterns, particularly in Lamongan Regency, with significant fluctuation in rice production over the last 5 years [1][2].This fluctuation is often experienced in areas such as Balongganggang, where approximately 2256 Ha of land is not fully irrigated due to lack of water supply.Balongganggang is an irrigation area that depends on water supply from Embung Balongganggang, a small reservoir of the entire Gondang Irrigation Area.However, the main source of water in this area is derived from the Gondang Reservoir network.To address the issue of limited irrigation, there is a need to enhance rice productivity by ensuring a consistent water supply.A good irrigation network and constant water supply can provide water demands for agricultural land throughout fferent periods [2][3] [4].Therefore, empowering the construction and maintenance of irrigation systems is essential to maximize crop yields [5] [6].Based on the background above, this research aimed to optimize planting patterns in the Balongganggang Irrigation Area with a linear programming method.
The main objectives of this research consist of three point, first to determine the impact of Gondang Reservoir scharge on Embung Balongganggang inflow discharge.Second, to determine the right planting pattern by the capacity of Balongganggang Reservoir, and the last to determine the impact of the use of reservoir capacity volume on water requirements in planting patterns.

Research Method
The first stage of this research included a comprehensive review of relevant literature such as scientific books, journals, reports, laws, and regulations.After understanding several theoretical frameworks, data collection was carried out based on the theory's requirements that have been investigated [7] [8], which included: a. Irrigation area b.Rainfall data c.Climatological data d.Hydrological data e.Data on the volume of reservoirs and the area of reservoir inundation.
The calculation and analysis process was carried out after data collection, which included: a. Climatological analysis [9] b.Hydrological analysis [10] c. Analysis of irrigation water needs [11] Further analysis was carried out to determine water requirements for each type of plant, assessing the discharge availability in the irrigation area.Subsequently, the linear programming method was optimized to obtain optimal planting patterns.

Hydrology Analysis a. FJ Mock Analysis
Hydrological data from FJ Mock analysis included rain stations and watershed areas [6][12].The stations used included: 1. Gondang Station 2. Girik Station 3. Mantup Station Subsequently, the weight factors of the three stations were calculated as shown in Table 1 [7].In this research, reservoir outflow indicates discharge from the reservoir door.As shown in Figure 3, the graph of recapitulation of the total discharge used at the reservoir door has been added with the incoming discharge due to rain falling directly to the surface of the reservoir and the use of water reserves [14]

Climatology Analysis
Climatological calculations were used to determine the amount of plant evapotranspiration, which included several data such as wind speed, air temperature, humidity, and solar irrigation [9][16].This value served as a crucial input for analyzing runoff discharge using FJ Mock analysis and determining water needs for irrigation.The graph of recapitulation of the results obtained from evapotranspiration calculation is shown in Source: Research Data (2024).

Analysis of Irrigation Water Needs
Analysis of irrigation water needs was carried out in several stages a.Average Rainfall Average rainfall was calculated using the same method as FJ Mock analysis [6][14], which included two stations, namely Sukodadi Station and Pucuk Station [7].
ASukodadi  Effective rainfall is the probability of water adequately meeting the plant's needs, with a reliability threshold set at 80%.Moreover, Figure 6 shows recapitulation of the effective rainfall values for rice, corn, and mung beans [2] In this research, land preparation is carried out for 1.5 months, playing an essential role in effective growth by proving optimal soil and environmental conditions.However, when land has not been cultivated for more than 2.5 months, the irrigation process becomes more prolonged.The water requirements required before rice planting are described in the book "Planning Criteria for the Irrigation Section," where the equation was developed by Van de Goor and Ziljstra (1968) based on a constant water rate in liters per second during the land preparation period [17].A summary of the calculation of water requirements for land preparation is presented in Source: Research Data (2024).: At the beginning of the planting period in December I Alternative 5 : At the beginning of the planting period in December II Alternative 6 : At the beginning of the planting period in December III Recapitulation of water needs in 1 year for alternative 4 is shown in Figure 8.

Optimization of Crop Patterns
The results of agricultural business are determined by subtracting production costs from the net profit.This calculation details multiplying the net profit per area of rice fields by the total paddy land produced.Subsequently, the results are analyzed as a function of goals in optimization [19], as shown in Table 3.

Optimization Model
The inequality planning for optimization process was based on the discharge requirements for each type of plant, along with limitations such as maximum land area.In the Balongganggang Irrigation Area, there is a maximum area of 2256 Ha and limitations in the form of availability of water discharge in the Balongganggang Reservoir.Therefore, this research aimed to maximize land area in one year of growing season and profits from agriculture [14][20].The mathematical model that used for optimization is presented below.
-      Both tables show the same intensity value for each alternative, with the maximum total intensity produced being 130.55% in alternative 4.Moreover, a comparison of alternative 4 with existing contions is shown in Figure 12.Based on the analysis results, the income in one year for alternative 4 was IDR 33,967,000,000.

Suggestions
Based on the results, several suggestions were made for further research, focusing on Balongganggang Irrigation Area and Balongganggang Reservoir: a.The method used in this research was F. J. Mock's analysis of Gondang Reservoir, which was the primary reservoir of Balongganggang Reservoir.The analysis suggested that energy loss along the channel between the two structures could be neglected.Therefore, the use of inflow discharge according to the records available at the Balongganggang Reservoir was recommended.b.Before conducting optimization, there is a need to investigate the existing land conditions.
Additionally, collaboration with farmers and local institutions is essential to understand plant varieties, appropriate water usage according to regulations, and annual planting patterns c.The network efficiency used in this optimization is based on worst-case scenario assumption.Consequently, further research is expected to calculate efficiency correctly for accurate results.d.Optimization of mung bean plants can be replaced with other grains or crops.The decision to include mung beans in this optimization is based on historical data recorded by the Badan Statistik Indonesia (BPS).However, a better approach can be made by analyzing current agricultural product trends.

Figure 1 .
Map of the Gondang watershed and Polygon Thiessen Method subdivision FJ Mock analysis was carried out to determine the price of actual evapotranspiration (Ep), water surplus (WS), base flow, and DSO to obtain the final value as the total runoff R. Subsequently, each analysis results from 10 years was ranked to obtain a discharge value with 80% reliability[5][6], and the final discharge, as shown in Error!Not a valid bookmark selfreference..

Figure 2
Figure 2 shows illustrates the water flow from Gondang Reservoir to Balongganggang Reservoir.

Figure 2 .
Water Flow diagram The inflow value in Embung Balongganggang was [13]: QBalongganggang = A Downstream/(A Upstream+ A Downstream) x 100% x Q80 = 2256/(992 +2256) x 100% x 4,54 = 69,46% x 4,54 = 3,15 m3/dt b.Calculation of Reservoir Outflow discharge I II III I II III I II III I II III I II III I II III I II III I II III I II III I II III I

Figure 5 .
Thiessen Polygon vision in Rice Field Areas b.Effective Rainfall 0

Figure 8 .
Chart of Water Needs of paddy fields in 1 year

Figure 9 .
Input in POM-QM for Windows V5 Program After inputting the entire mathematical model, the program was run and the final result of optimization was shown inError!Reference source not found.Error!Reference source not found.(Based on Discharge Limit) Source: Research Data (2024).

Figure 10 .
Optimization Results Graph Based on Discharge as a Constraint (Based on Area Limit) Source: Research Data (2024).

Figure 11 .
Optimization Results Graph Based on Areas as a ConstraintAnalysis of Optimization ResultsThe equations formulated in POM-QM for Windows V5 program would be run and iterated automatically by the program.Consequently, the output results are obtained in the form of numbers in the coefficient X, representing the area of each type of plant and the value of the destination function Z. Recapitulation of the output results by POM-QM for Windows V5 are shown inError!Reference source not found.and Error!Reference source not found..

Figure 12 .
Irrigation Intensity Chart Between Existing and AnalysisThe calculation results exceeding 9.98% of the existing conditions suggest greater optimality, leading to the conclusion that the optimal planting patterns were Rainy Season : Rice -Grains Dry season I : Paddy -Grains -Grains Dry season II : Grains-Grains The total planted area of each plant was Rice

Table 3 .
The Agricultural Product of Lamongan Regency

Table 4 .
Recapitulation of Optimization Results Based on Land Area Source: Research Data (2024).

Table 5 .
Recapitulation of Optimization Results Based on Profitability In conclusion, the results obtained from the calculation and research analysis are as follows: a. F. J. Mock analysis showed that the reliable discharge used for Gondang Reservoir inflow ranged from 5659.57lt/s to 175.80 lt/s, with a reliability of 80%.Due to the presence of paddy fields along the route to Balongganggang Reservoir, the inflow into the reservoir was only 69.46% of the total discharge.Consequently, the largest and smallest discharges for Balongganggang Reservoir inflow were 3931.03lt/s and 122.11 lt/s, respectively.b.Optimization calculations considered alternative initial planting periods as well as area limits for corn and mung beans of 150 Ha and 50 Ha per planting season.Based on optimization results from alternatives 1 to 6 by the POM-QM for Windows V5 program iteration, the optimal planting pattern was found in alternative 4, in terms of land area and profit.For land area-based optimization results, the planting patterns during rainy season (RS), dry season I (DS I), and dry season II (DS II) were Rice (2106 Ha) -Grains (Corn -150 Ha), Rice (197.15Ha) -Grains (Corn -150 Ha) -Grains (Mung Beans -50 Ha), and Grains (Corn -241.96Ha) -Grains (Mung Beans -50 Ha), respectively.Meanwhile, regarding profit-based optimization, the planting patterns during rainy season (RS), dry season I (DS I), and II (DS II) were Rice (2106 Ha) -Grains (Corn -150 Ha), Rice (197.15Ha) -Grains (Corn -150 Ha) -Grains (Mung Beans -50 Ha), and Grains (Corn -241.96Ha) -Grains (Mung Beans -50 Ha).The maximum profit obtained based on land area and profit optimization was Rp 33,967,000,000.00 in alternative 4. c.The use of Balongganggang Reservoir storage water occurred in several periods due to high water needs and low rainfall.However, the smallest volume was observed in October period III, at 0.85 million cubic meters.