Evaluation of irrigation channels in the dry season at Dadahup swamp irrigation area to strengthen food security

Dadahup swamp irrigation area is included in the food estate project location. The government has rehabilitated irrigation networks to support the program in 2020. A good agricultural system should be supported by water availability to fulfill irrigation water needs. The obstacle often faced in agriculture is usually the water deficit that occurs in the dry season. Corn is usually cultivated in the dry season to reduce water irrigation demand and cannot be inundated with water for long. This study aims to determine the water availability in the irrigation channels to supply water needs for corn. The Storm Water Management Model is used to perform hydraulic analysis in irrigation channels. The results showed that the water levels ranged from +0.04 m to 0.49 m in irrigation channels, while the ground elevations ranged from +1.12 m to 1.74 m. Due to water levels in the irrigation channels below the ground elevation, the Blok A5 Kanan can be proposed for corn cultivation in the dry season. This study’s outcome will be increased crop productivity, achieving sustainable agriculture.


Introduction
The Indonesian government is planning a food estate program in 2020-2024 to increase national food security in Indonesia [1].Dadahup swamp area irrigation is included in the food estate project location.It was one of the mega rice project locations in 1995.The project failed due to the lack of development planning without considering water availability, flood hazard, farmer capabilities, government regulation, and land conflict [2].There were damaged peat domes in land development that caused overdrainage that led to carbon emissions and became an issue of climate change [3].In addition, the decreased precipitation in the dry season will cause lower water table depth.It has caused drained peat and exposure to the air, which increases carbon emissions [4].
Conversely, the reclamation area has a water pH of 2.9 to 3.7 and a soil pH of 4.0 to 4.5 due to pyrite oxidation [5].Therefore, Dadahup swamp area irrigation is abandoned by the government and farmers.However, there is some potential for the area's development, such as wide land availability, flat topography, water sources affected by tide and precipitation, and convenient access [6].Because of that, it is necessary to rehabilitate the existing irrigation network and water management for development for agricultural use [7].In order to increase the irrigation network's efficiency in supplying the water required for agriculture, the government rehabilitated the irrigation network system in 2020.
In developing land for agriculture, not only the well-built infrastructure but also the potential availability of water to achieve a good irrigation network system.Water availability usually faces water 1311 (2024) 012046 IOP Publishing doi:10.1088/1755-1315/1311/1/012046 2 shortage due to low precipitation in the dry season [8].On peatlands in West and Central Kalimantan, climate change events like El Nio and the Indian Ocean Dipole occurred, contributing to the low precipitation and rise inspots [9], [10].It also can lead to peat fire [11].Low precipitation can cause drought and crop failure [12].
Mitigation is needed to prevent crop failure, such as selecting crops that require less water than paddy, such as corn [13].Corn is usually cultivated in swampland areas in the dry season [14].The maximum water needed for paddy is 4.48 m 3 /s, while the water for secondary crops is 1.98 m 3 /s in the Dadahup swamp irrigation area [15].In addition, corn cannot be inundated by water for long [16].Because of that, corn is more suitable than rice for cultivation in the dry season.Therefore, this study intends to evaluate the ability of irrigation channels in order to supply water for corn in the dry season.

. Description Area
This study was conducted at the Dadahup swamp irrigation area in Dadahup Regency, Central Kalimantan Province, especially in Blok A5 Kanan (Figure 1).This location was chosen because it was a pilot project area.The area of Blok A5 Kanan is 872 ha.This area has a length of a secondary channel of 3.3 km, and the length of the five tertiary channels ranges from 2.4 to 2.5 km (Figure 2).The ground elevation of Blok A5 Kanan varies from +1.12 to +1.74 m (Figure 3) [17].

. Material
The data used are land use map, type of soil, seven-day precipitation (Figure 4), seven-day water level in outfall (Figure 5), channels long, and cross-section collected from BWS Kalimantan II.The trapezoidal tertiary channel has a 1.5 m bottom width, 1.5 m height, and 1:1 side slope, while a secondary channel has an 8 m bottom width, 2.5 meight, and 1:2 side slope [17].SWMM is a model that simulates rainfall runoff from urban areas and flow routing in the channel [18].
Based on the modelling results, there were 42 sub-catchments, 41 junctions, 41 conduits, and one outfall without a gate in the irrigation channel.(Figure 6).The simulation was conducted seven days from August 1-7, 2023.The infiltration model used in the simulation was curve number and dynamic wave flow routing.

Result and Discussion
Based on the simulation results, the water elevation profile of the upstream secondary (in simulation as Sek1) (Figure 6) is shown in Figure 7.The secondary's water level ranges from +0.04 m to +0.49 m. (Figure 8).Then, the water elevation profile of upstream the tertiary channel 5 (in simulation as C29) (Figure 6) is shown in Figure 9.The channel's water level ranges from +0.04 m to +0.49 m while the ground elevation on the left side was +1.39 m and on the right side was +1.52 m.Therefore, the tertiary channel's water level is below the ground level (Figure 10).The water elevation profile of downstream tertiary channel 1 (in simulation as C6) (Figure 6) is shown in Figure 11.The channel's water level ranges from +0.04 m to +0.49 m, while the ground elevation is +1.20.Therefore, the tertiary channel's water level is below the ground level (Figure 12).4).A lack of precipitation during the dry season can cause the channel's water levels to drop [19].Low corn production can affect the low precipitation [20].In comparison, ground elevation ranges between +1.12 m to 1.74 m.It turned out that the water level of the entire channel in Blok A5 Kanan is below the ground elevation.It is the same as the previous study in Blok A5 Kanan, where the tertiary channel's water level is below the ground elevation, which is the water level of the channel was descended to +0.48 m in the dry season while the ground elevation ranged from +1.00 m to + 1.30 m [21].In addition, in another previous study, the secondary channel's water level ranged from +0.06 m to +0.77 m while the ground elevation was at +0.8 m, so the secondary channel's water level was below the ground elevation in the dry season [15].Therefore, the determining factor in the development of land for agriculture in Blok A5 Kanan is ground elevation.Figure 13 shows that green-colored land on the Blok A5 Kanan indicates that the ground elevation is above the irrigation channel's water level, so the land is suitable for corn cultivation.Therefore, Blok A5 Kanan, with an area of 872 ha, can be proposed as corn cultivation in the dry season.

Conclusions
The irrigation channel's water level ranged from +0.04 m to +0.49 m.In comparison, the ground elevation ranged from +1.12 m to +1.74 m.It is shown that the irrigation channel's water level is below the ground elevation of Blok A5 Kanan.Therefore, Blok A5 Kanan, with an area of 872 ha, can be considered for corn cultivation in the dry season.