Hydraulic simulation on the extensification area of the Katingan I swamp irrigation area, Central Kalimantan Province

Abstract

The Katingan I Swamp Irrigation Area (DIR Katingan I) is projected as one of the Food Estate areas in Indonesia. The food sector development program at DIR Katingan I has been implemented since 2021 through the Strategic Irrigation Modernization and Urgent Rehabilitation Project (SIMURP) programs, including extensions of irrigation networks and structures. This study aims to evaluate flow patterns in DIR Katingan I, particularly in the extensification areas with higher elevation than the existing area and has not undergone the leaching processes. The flow pattern of the macro irrigation system is modelled and simulated using Hydrologic Engineering Center’s River Analysis System (HEC-RAS) 6.4.1 software. The modelling is based on channel geometry data and water level elevation recorded in the Katingan River as a downstream boundary condition. Calibration with measured data in the primary channel resulted in a Manning’s coefficient of 0.03, closest to field conditions (R = 0.81, error = 6.63%). Simulation results show that without control structures, the flow in the irrigation network cannot reach the extensification area with the elevation above +3.9 m. Additionally, the primary channels function as a supply channel and the collector channel as a drainage channel cannot be achieved, allowing water from the leaching process to re-enter the rice fields. Thereafter, it is recommended to operate control structures so that the flow can reach the entire extensification area and the supply and drainage flows can be completely separated. Thus, leaching intensity is expected to increase and the soil ripening process will occur more quickly.