Analisa Kapasitas Penampang Sungai dengan Hec-Ras (Studi Kasus Sungai Bengkalis)

The Bengkalis River serves as a water drainage channel; however, its limited crosssectional capacity can cause river overflow and flood inundation. This study aims to determine the design flood discharges for return periods of 5, 10, and 25 years, analyze the capacity of the existing river cross-sections to accommodate the design discharges, and identify the distribution of flood-affected areas based on HEC-RAS simulations. The research method involved hydrological analysis using rainfall data and calculating design flood discharge using the Rational Method. Hydraulic analysis was then conducted using HEC-RAS through steady flow and unsteady flow simulations to evaluate the cross-sectional capacity and flood inundation distribution. The results showed that the design flood discharges were 11.43 m³/s for the 5-year return period, 13.44 m³/s for the 10-year return period, and 15.73 m³/s for the 25-year return period. The simulation results indicated that the river cross-sectional capacity at several locations, particularly STA 0+380 and STA 0+000, was insufficient to accommodate the design discharges. The simulations also showed overflow and inundation in several areas surrounding the river, with the affected area increasing as the design discharge increased. In conclusion, the existing cross-sectional capacity of the Bengkalis River is insufficient at several locations, requiring capacity improvement and flood control measures.