Evaluation of water management after rehabilitation in the Terusan Tengah Swamp Irrigation Area, Kapuas Regency, Central Kalimantan

Abstract The Terusan Tengah Swamp Irrigation Area (TT-SIA) is affected by tides to meet irrigation water needs and drain excess water from rainfall. The Irrigation Network Performance Index (IKSI) for the TT-SIA is 58.69%, indicating poor performance and the need for rehabilitation. The rehabilitation has been carried out by adding culverts to the existing box culverts in the middle of the secondary canals. This study aims to evaluate the effectiveness of the project carried out in 2024, specifically in improving irrigation water supply and drainage capacity, as well as the potential for sedimentation in the secondary canals. HEC-RAS simulations were conducted to describe the existing conditions with canals equipped with box culverts compared to the canals after rehabilitation. Observations focused on 13 rehabilitated canals to determine the cumulative water volume passing through the secondary canals and the potential sedimentation period in those canals. The simulation results show that adding culverts increased the water volume in the secondary canals by 1.65% compared to the initial conditions before rehabilitation. In addition, the average period of bed shear stress below critical shear stress, indicating sedimentation conditions, increased by 0.41%. This condition suggests increased sedimentation, necessitating more routine and periodic operation and maintenance.