Evaluasi Kinerja Saluran Drainase Menggunakan Aplikasi Hec-Ras(Studi Kasus Desa Sei Alam, Kecamatan Bengkalis)

Flood inundation is one of the problems occurring in Sei Alam Village, Bengkalis District, Bengkalis Regency, which is influenced by the relatively low elevation of the area, limited drainage system capacity, and tidal effects. This study aims to analyze the capacity of the drainage system in conveying design flood discharge and to determine the pattern and extent of flood inundation in the study area. Hydrological analysis was conducted to determine design flood discharges using several methods, namely the Rational, Weduwen, Haspers, and Nakayasu methods, with return periods of 5, 10, and 25 years. Furthermore, hydraulic analysis was conducted using HEC-RAS software through 1D Steady Flow and 2D Unsteady Flow modeling. Based on the analysis results, the design flood discharges obtained using the Rational method for 5-, 10-, and 25-year return periods were 44.12 m³/s,51.24 m³/s, and 59.31 m³/s, respectively. The HEC-RAS 2D simulation results indicate that the inundation area increases as the design flood discharge increases. The inundation areas without tidal effects were 1,1765 km² for Q5, 1,2924 km² for Q10, and 1,2895 km² for Q25. The results show that flood inundation mainly occurs in low-elevation areas, following the river and drainage networks, and affecting residential areas and local road networks. Therefore, mitigation measures are required, including increasing drainage capacity, channel normalization and maintenance, developing runoff control infrastructure, and managing tidal effects to reduce the risk of flood inundation in the study area.