Analysis of Mini Polder Performance for Improved Water Management in the Dadahup Swampy Irrigation Area

The Indonesian government has chosen the Dadahup Swampy Irrigation Area as one of its Food Estate regions to address food security concerns. Following the rehabilitation of the irrigation network and the construction of gates from 2020 to 2022, block A5 is chosen as a pilot project using a mini polder as its water system management. In the right block A5, mini polders small-scale embankments are designed to regulate water flow and optimize land utilization. This research comprehensively evaluates the mini polder’s effectiveness in right block A5 in improving water control within the swampy landscape, considering the influence of rainfall patterns. Our study aims to comprehensively evaluate how mini polders effectively improve water control in the Dadahup Swamp Irrigation Area. To achieve this, we consider the influence of rainfall patterns, which play a significant role in the region’s hydrological dynamics. In addition to traditional data analysis, we integrate hydraulic simulations into our study using HEC-RAS software. These simulations allow us to model and visualize how mini polders interact with the complex water flow patterns in the Dadahup Swampy Irrigation Area. By combining empirical data with hydraulic simulations, we can better understand how mini-polders function in response to varying rainfall scenarios. Based on the simulation results, it was found that without the polder system, the water level would be on dry land during the dry season. The simulation provides direction or guidelines for polder operations to maintain the water level as long as possible during the dry season and prevent flooding during the rainy season. This research can provide valuable insights into sustainable agriculture practices in this unique and challenging environment.


Introduction
In the global context of climate change, agricultural initiatives take on crucial significance, given the profound challenges posed to food security worldwide [1].Climate change has far-reaching impacts, influencing crop yields, water availability, and agricultural productivity [1].The triumph of the Food Estate Program, initiated by the Indonesian government in 2020 to enhance food security, is intricately linked to its ability to navigate and adapt to the effects of climate change on the Dadahup Swamp and its surroundings.This ambitious project, centered around revitalizing the Ex-PLG area to establish it as Indonesia's primary food stock region, recognizes the designated Dadahup Swampy Irrigation Area in the Kapuas Regency of Central Kalimantan Province [2].The Indonesian government's 1323 (2024) 012004 IOP Publishing doi:10.1088/1755-1315/1323/1/012004 2 acknowledgement of the Dadahup Swamp as a valuable resource underscores its commitment to securingfood resources amid the challenges posed by climate change through the rehabilitation program.The rehabilitation and construction of gates in the Dadahup swampy irrigation area were carried out as an extensive effort, demonstrating the Indonesian government's commitment to addressing food security.Implemented between 2020 and 2022 to rejuvenate the ageing irrigation network to harness this potential.Simultaneously, new gates were constructed to facilitate water management.These initiatives underscore the government's commitment to transforming the Dadahup Swamp into a productive contributor to the nation's food security objectives.A total of 2,195.21kilometers of irrigation canals underwent rehabilitation.This included 507.41 kilometers of primary canals, 41.97 kilometers of auxiliary primary canals, 444.82 kilometers of secondary canals, 80.18 kilometers of collector canals, 338.86 kilometers of tertiary canals, and 781.95 kilometers of quarter channels [3].Additionally, 226 built sluice gates were included in this extensive rehabilitation effort.The Dadahup Swampy Irrigation Area encompasses a total of 17 land blocks.One of the Dadahup Swampy Irrigation Area's blocks, Block A5, has been chosen as the designated site for trialling an irrigation system, specifically for a demonstration rice planting plot.Block A5 has come to the forefront as a testing ground for implementing mini polders, representing an innovative approach to managing water.Considering variances in ground elevation and operational convenience, it is imperative to partition the water management system into smaller segments or blocks [3].A polder is a low-lying land that constitutes an artificial hydrological unit [4].It is encircled and protected by embankments, commonly known as dikes, to prevent flooding from surrounding water bodies [4].Mini polders, characterized as compact embankments, are purposefully designed to regulate water flow and enhance land utilization within the swampy landscape [5].These mini polders constitute the focal point of our study, as they serve as a blueprint for improved water control and the promotion of sustainable land usage practices.The water management within tidal irrigation schemes should strive to achieve at least three primary goals.The initial objective is to ensure an ample water supply for leaching and diluting acidic water.The second goal involves efficiently managing the excess water during storms.The third objective is to sustain the potential acidic sulfate soils under reduced conditions, thus preventing excessive oxidation [6].Many studies have been conducted on the water management system in DIR Dadahup, both at the macro and micro levels.The most recent research on the micro water management system in DIR Dadahup focused on a hydraulic study regarding using gates to enhance drainage performance [3].Based on previous research, it is believed that one of the significant challenges in agricultural development in DIR Dadahup is the issue of inundation [3] and water management, particularly during the dry season [7].Based on the same idea, in this research, it is deemed essential to analyze the performance of the existing mini-polder system in Block A5 under its current conditions.A notable gap in the existing body of research pertains to the micro-level water management system in DIR Dadahup, particularly in Block A5.It occurred during the initial phase of gate construction, thus providing a snapshot of conditions specific to that time.Moreover, the hydraulic study was limited to the geometry of tertiary channels and comprehensive 2D analysis exclusively in the form of tertiary plots.Introducing quarter channels in Block A5 necessitates a more detailed investigation at the quarter plot level.Additionally, it is crucial to acknowledge that the terrain data in these studies originated from the initial 2019 planning, introducing the potential for significant disparities compared to the current onsite conditions.This incongruity between the existing data and the present field reality underscores a critical research gap in the study of DIR Dadahup's micro water management system.Our primary objective is to thoroughly assess the effectiveness of mini polders within Block A5 in the Dadahup Swampy Irrigation Area, particularly on water control, to approximate the original conditions as closely as possible.Our endeavor is guided by recognizing the significant impact of rainfall patterns on the region's hydrological dynamics.In addition to conventional data analysis, our study extends into the domain of hydraulic simulations using the HEC-RAS software.Flow analysis is greatly facilitated through the utilisation of the HEC-RAS software.This powerful tool provides the means to conduct unsteady flow simulations, which are valuable for understanding how water levels and flows change over time, not just in one dimension (1D) but also in two dimensions (2D).The 2D simulation capability of HEC-RAS is particularly significant because it allows for a more detailed representation of how water inundates and spreads across the landscape.This multifaceted approach allows us to immerse ourselves in an in-depth exploration of how mini polders interface with the intricate patterns of water flow.By thoroughly assessing their impact on water control and striving to replicate original conditions, the study contributes to enhancing the understanding of hydrological dynamics influenced by rainfall patterns in the region.The benefits extend to practical applications in optimizing mini polder functionality, ensuring more resilient water management, and supporting sustainable agricultural practices.Moreover, the study's findings could have broader implications for similar swampy areas, providing valuable guidance for stakeholders involved in water resource management, agriculture, and sustainable development.

Study Area
The Dadahup Swamp Irrigation Area is in the Kapuas Regency of Central Kalimantan Province.It encompasses a vast potential area of 21,226 hectares, with a functional site covering 6,111 hectares [2].The water system in this region is primarily influenced by three major rivers: the Barito River to the east, the Mangkatip River to the west, and the Kapuas Murung River to the south.It is important to note that the Dadahup Swamp Irrigation Area, specifically DIR Dadahup, is in zones II-b and III [3].In these areas, parts of the region experience the influence of tides in freshwater without any saltwater intrusion [3].The central focus of our study lies within the Right A5 Block.This block serves as a pilot project and a demonstration plot for water management trials within the food estate program of DIR Dadahup.The Right A5 Block covers approximately 875 hectares and features secondary canals extending over approximately 3,300 meters.It also includes five right tertiary canals, each with a length of about 2,500 meters.Additionally, there is a quarter channel with a length of around 3,300 meters.The land elevations within Block A5 Right vary, ranging from +0.5 to +1.3 meters.The water management system in the Right A5 Block operates as a controlled closed water system on the secondary and tertiary channels.The irrigation in Block A5 Right relies significantly on rainfall.During the rainy season, the tertiary and secondary channels function as drainage or discharge channels.Conversely, the precipitation collected in these channels is stored for future use during the dry season.For further geographical context, the location of Block A5 Right is visually represented in Figure 1.Data for the current research project were gathered from various sources, as detailed in Table 1, encompassing both primary and secondary data.There is some adjustment to the data used in this study.One of the adjustments made pertains to terrain data.The terrain data was generated by collecting elevation data points for Block A5 Right.Based on the elevation map of Block A5 Right, it was determined that the elevation range of the land in Block A5 Right was from 0.83 to 1.74 meters Fig. 2a).However, field checks revealed that land-clearing activities had changed elevation values.Based on this situation, an assumption was made to adjust the land elevation by subtracting 0.5 meters from the existing elevation values.As a result, the new range of land elevation for Block A5 Right now falls between 0.33 and 1.34 meters, aligning more closely with the current field conditions (Fig. 2b)  better understanding of how water flows and interacts with agricultural land within the context of this research.To connect the quarter-field plots with the quarter channels, lateral structures in the form of adjustable-covered pipes were employed, as shown in Figure 5. Due to limitations in field data regarding the actual quantity, it was assumed that each quarter-field plot is connected to three pipe-shaped lateral structures with a diameter of 0.5 meters and adjustable gates.There are 122 lateral structures throughout the Block A5 Right area.This paper simulates the network system's state during the rainy and dry seasons.The differentiating factor in each simulation lies in the data employed, specifically the rainfall data and stage hydrograph during the rainy (Fig. 5) and dry seasons (Fig. 6).Additionally, the scenarios and gate pattern settings also play a pivotal role in determining the success of modelling and evaluating the polder system.Stage Hydrograph data were applied as boundary conditions in the downstream area in this simulation.Furthermore, a rainfall event was modeled using a 2D Flow Area, with precipitation as a boundary condition.It is important to highlight that the stage hydrograph and precipitation events within this model were based on actual conditions measured during the period from February 11 to February 20, 2023 (Figure 5).The hydraulic simulation was carried out using two scenarios: without gates (open channel) and the mini polder with gates in the secondary and tertiary channels, as shown in Figure 3.
The first scenario involves hydraulic simulation without gates.In contrast, the second scenario is a simulation of the mini polder by the existing conditions, which include secondary (Fig. 7) and tertiary gates (Fig. 8).The results from each scenario will be compared to obtain insights and data to analyze the performance of existing mini polder in Blok A5 Right.

Hydraulic simulation in the dry season
The HEC-RAS analysis involved a roughly ten-day simulation from February 11 to August 20, 2023.Stage Hydrograph data were applied as boundary conditions in the downstream area in this simulation.Furthermore, a rainfall event was modeled using a 2D Flow Area, with precipitation as a boundary condition.It is important to highlight that the stage hydrograph and precipitation events within this model were based on actual conditions measured during the period from February 11 to February 20, 2023 (Figure 6).Based on the data in Figure 6, the water level dropped to +0.1 to +0.5m, and there was no rainfall in ten days of simulations.The hydraulic simulation was carried out using two scenarios: without gates (open channel) and the mini polder with gates in the secondary and tertiary channels, as shown in Figure 3.

Hydraulic simulation result on rainy season
The analysis was simulated for ten days (240 hours) from February 11 to February 20, 2023.This simulation incorporated Stage Hydrograph data as boundary conditions for downstream areas.We also used a 2D Flow Area to model a rainfall event, with precipitation as a boundary condition.Based on the flow simulation, Figure 9 illustrates the area that experienced inundation.Flooding affected nearly all areas of Block A5 Right in the absence of the gate.The utilization of gates in the secondary and tertiary channels leads to a decrease in the inundation area, surpassing the improvements observed in the previous scenario.
In the scenario without a gate, it is evident that the highest inundation levels reach approximately 0.3 to 1 meter.The implementation of secondary and tertiary gates reduces the inundation height to around 10 cm in each plot within Block A5 Figure 10, significantly improving micro water management and mitigating the impact of tides-the tertiary gates scenario yields similar results to the secondary gates scenario in the right area.Based on the simulation results, it is believed that using pumps is necessary to enhance the drainage capacity of the polder system on the right in Block A5.Since there was no rainfall during the simulation period, the results showed that almost the entire plot area remained free from water inundation.Furthermore, water could not flow into the fields because the water level was only 0.5 meters, and the average levee height was 1.422 meters.Even though there are areas with elevations of +0.3 meters, water still could not flow directly into the fields.Based on the results from the mini polder, it was found that water could flow into a portion of the plot area, specifically in Block T1.Although not substantial, the presence of gates in the secondary and tertiary channels did, indeed, raise the water level in the field.In the case of the dry season, it appears necessary to use pumps to convey water to the fields.

Managing Seasonal Challenges for Effective Water Control
The hydraulic simulation results presented in the study demonstrate a clear connection between climate change, specifically seasonal variations, and the findings regarding the effectiveness of mini polders in the Dadahup Swampy Irrigation Area.In the simulation during the rainy season, which aligns with the impact of climate change on intensified rainfall patterns, the study reveals that flooding significantly affects almost all areas of Block A5 Right in the absence of gates.The implementation of secondary and tertiary gates, however, proves instrumental in decreasing the inundation area and mitigating the impact of tides.This insight is crucial in the context of climate change, where increased rainfall and potential extreme weather events can lead to heightened flooding risks.On the other hand, the simulation during the dry season provides insights into the challenges posed by climate change-induced variations, such as reduced rainfall.The findings suggest that, despite the absence of rainfall during the simulation period, the entire plot area remains free from water inundation.However, the study highlights the need for pumps to convey water to the fields, indicating that even in the dry season, climate-related factors can affect water availability in the region.This underscores the importance of adaptive measures, such as the use of pumps, in response to changing climate conditions.

Conclusions
The analysis of mini-polder performance in the Dadahup Swampy Irrigation Area has provided valuable insights into the crucial aspects of water management.This study revealed the significance of addressing inundation and water management challenges, especially during the dry season, to enhance agricultural development.The research highlighted the necessity of evaluating the existing mini-polder system in Block A5 under its current conditions.Considering ground elevation disparities and operational ease, the study emphasized the importance of segmenting the water management system into smaller blocks for more efficient control and optimization of water resources.The findings indicate that employing gates can effectively decrease the inundated area while regulating the water level in the channel in alignment with cultivation requirements.The absence of rainfall during the simulation period underscored the challenges of water availability, particularly in maintaining the desired water levels for agricultural purposes.It was observed that the existing infrastructure, with some regions of higher elevation, did not effectively facilitate the direct water flow to the fields, further emphasizing the need for improved water management strategies such as using pumps.In summary, the study's hydraulic simulations offer valuable insights into the dynamic relationship between climate change and the effectiveness of mini polders, emphasizing the need for adaptive strategies to address both heightened flood risks during the rainy season and water conveyance challenges in the dry season.

Figure 2 .
Figure 2. Data terrain of A5 Block Right.a. Terrain before land clearing b.Terrain after land clearing2.3Hydraulic Simulation ProcessHydraulic simulation is conducted using the HEC-RAS software.This simulation requires various data inputs for the HEC-RAS model, including longitudinal and cross-sectional channel profiles, the layout of hydraulic control structures, boundary conditions (upstream and downstream), hydrological data, and terrain data.The water system layout for hydraulic simulation represents the existing mini polder in Block A5 Right, as shown in Figure3.Furthermore, the 2D flow area feature was employed in modelling the paddy fields.The 2D flow area of 36 quarter-field plots is depicted in Figure3.The selection of the 2D flow model in this simulation allows for a more detailed consideration of the interaction between water flow and paddy fields.Accurate topographical data is paramount in ensuring the precision of simulation results, especially in environments with limited satellite image resolution.Consequently, this process enables a

Figure 3 Figure 4
Figure 3 Water system layout of Mini Polder in Blok A5 Right

Figure 5 Figure 6
Figure 5 Water level and precipitation in the rainy season

7 Figure 7 Figure 8
Figure 7 Geometry of secondary gate

Figure 9 Figure 10 2
Figure 9 Inundation area of flow simulation: a. without gate, b. mini polder

Figure 11
Figure 11 Inundation area during the dry season: a. without gate, b. mini polder

Table 1 .
Sources of materials and data for the study area MaterialsSources/process/references Rainfall Bureau of Kalimantan River Basin Region II (BBWS Kalimantan II) Geometry of channel and hydraulic gates Bureau of Kalimantan River Basin Region II (BBWS Kalimantan II) Topography map Bureau of Kalimantan River Basin Region II (BBWS Kalimantan II) Water level data Telemetry data of DIR Dadahup, Bureau of Kalimantan River Basin Region II (BBWS Kalimantan II)