EVALUATION STUDY OF BANKFULL CAPACITY OF THE CITARUM RIVER IN MAJALAYA DUE TO SEDIMENTATION

• Main Author: Pitriani, Djelia
• Format: Theses
• Language: Indonesia
• Subjects: Teknik (Rekayasa, enjinering dan kegiatan berkaitan)
• Online Access: https://digilib.itb.ac.id/gdl/view/84685
• Institution: Institut Teknologi Bandung

The village of Majalaya has experienced an increasing frequency of floods each year. Notably, on February 22, 2018, floodwaters covered an area of 5.73 km². Considering the significant sedimentation in the Citarum-Majalaya River, an analysis and evaluation of the changes in the river's capacity are necessary. This analysis was conducted using numerical modeling with HEC-RAS 6.3.1, based on 11 years of historical discharge data, comparing the river's condition before and after normalization. The Nakayasu Synthetic Unit Hydrograph (HSS Nakayasu) was used to calibrate the flood discharge for the February 22, 2018, event, where the observed peak discharge was 155.08 m³/s, and the calibrated peak discharge was 154.93 m³/s, with an NSE of 0.84. Hydraulic modeling calibration was performed for Manning's roughness coefficient using water surface elevation data, resulting in a Manning's roughness coefficient of 0.065, indicating a significant presence of vegetation. For sedimentation calibration, the Englund-Hunsen method was chosen due to its suitability for riverbed material composed of sand. The sediment calibration was based on changes in the river cross-section from 2021 to 2022. The comparison of results for river cross-sections RS-1873 and RS-1690 showed similar outcomes. The actual cross-sectional area change for RS-1873 was 2.65 m², while the model's result was 2.97 m², and for RS-1690, the actual change was 3.40 m², compared to the model's 3.61 m². Over 11 years of modeling after the Citarum-Majalaya River was normalized, a decrease in river capacity of 50 m³/s was observed, from the post-normalization capacity of 115 m³/s to 65 m³/s, with a sediment volume of 1,280,536 m³. After normalization, the Citarum-Majalaya River experienced changes for 1.5 years, but then stabilized as no significant changes were observed from the second to the eleventh year. In this stable condition, the Citarum-Majalaya River has a capacity of 65 m³/s, which is below ????1,25 , indicating that flooding will occur if sedimentation is not addressed.