Pemodelan banjir Sungai Cibeureum ruas CB.64 – CB.97 menggunakan HEC-RAS 6.5

The Cibeureum River along the CB.64–CB.97 section in Cilacap Regency is highly prone to flooding due to the limited river cross-sectional capacity, particularly during periods of intense rainfall. The flood event on December 5, 2024, caused river overflow with inundation depthhes reaching 60–100 cm, resulting in physical and non-physical losses and disrupting community activities. These conditions indicate that the existing river capacity is inadequate to optimally convey flood discharge, highlighting the need for hydrological and hydraulic analyses to determine flood characteristics and appropriate flood control measures. This study utilized hydrological data in the form of rainfall records to estimate design flood discharges for return periods of 2 years (Q₂), 10 years (Q₁₀), and 25 years (Q₂₅). The hydrological analysis produced design flood discharges of 71.552 m³/s for Q₂, 225.197 m³/s for Q₁₀, and 323.949 m³/s for Q₂₅, with a peak discharge time of approximately 3 hours. Hydraulic modeling under existing conditions using the Q₂ discharge revealed that several river sections were unable to accommodate flood flow effectively, with the most critical condition identified at Station 23 downstream of the Station 23.5 bridge. Model calibration showed a water level difference of approximately ±0.6 m between simulation and field observations, which remains within acceptable limits. Flood control alternatives were then developed based on the technical criteria of Ministry of Public Works and Public Housing Regulation No. 12 of 2014. The simulation results indicated that Scenario 1 was the most efficient solution for Q₁₀, while Scenario 3 was the most suitable alternative for Q₂₅ due to its greater flow capacity improvement through comprehensive cross-sectional adjustments.