[A-CG37] Water and Sediment Dynamics from Land to Oceans [En]

[ACG37-05] Sedimentation Reaccumulation in the Citarum River, Indonesia: Challenges in Post-Normalization Flood Control

Siti Aisyah Nurul Qolbi¹、*Faizal Immaddudin Wira Rohmat¹、Indratmo Soekarno¹、Siska Wulandari¹、Joko Nugroho¹、Arno Adi Kuntoro¹ (1.Faculty of Civil and Environmental Engineering, Institut Teknologi Bandung)

キーワード：River sedimentation, Citarum, HEC-RAS, Flood mitigation

The Citarum River, especially in the Majalaya Area, experiences frequent annual flooding caused by many factors, including extreme weather, land cover changes, and sedimentation. In particular, sedimented rivers reduce the river's capacity and cause flooding to occur more frequently. Before 2020, the Majalaya Area reported at least six yearly flood events, with the largest being the February 2018 flood that claimed one life. River normalization was carried out and completed in April 2020 to improve the river's capacity. Because of that, the area reported no flood occurred during the 2020–2022 period. Despite such normalization efforts, significant flooding occurred again in 2023 due to sedimentation gradually building up in the river since 2020. This study aims to analyze the sediment transport and deposition pattern in the 1.3 km long Citarum River stretch in the Majalaya area, with a simulation date from May 2020 until January 2022. HEC-RAS is used to model the sedimentation pattern and analyze changes in river morphology. Data included river geometry, satellite-derived DEM data, primary river bathymetry, AWLR discharge data, and primary on-site sedimentation measurements. The analysis also compares river bathymetry data in 2009 (pre-normalization), 2020 (normalization as-built data), and 2022 (recent post-sedimentation data). Comparing the 2009 to 2020 bathymetry, the sedimentation volume excavated calculated from the river was 38,009 m³ or an average of 2.36 m thickness. Two years after normalization, in January 2022, the sedimentation volume reached 17,081 m³ or an average of 1.06 m thickness. This indicates that sedimentation that previously took eleven years to accumulate after normalization only took two years to reach almost 50% of the previous sedimentation volume. The results of this study provide an essential insight into the effectiveness of river normalization in reducing sedimentation in the Citarum–Majalaya River and provide a basis for better management and planning for future flood mitigation.