Flood simulation to determine flood hazard susceptibility of downstream Singkil watershed in Aceh Province

The damage to the Singkil watershed, one of the largest watersheds in Aceh Province, has become a concern for many parties, primarily due to increased flood events in the downstream area of the watershed. Based on previous studies, the problems which cause flooding are watershed damage due to illegal logging and high rainfall intensity reaching 3000-4500 mm/year, and increased erosion of 0.887 tons/ha/year, which causes a decrease in river capacity due to sedimentation. For this reason, this study aims to do 2D flood hydraulic modeling for five return periods of 2, 5, 10, 25, and 50 years which can be a reference for flood management in Aceh Singkil District. The hydrological analysis of the design flood discharge for several return period was carried out using Nakayasu and SCS-CN method. 1D-2D flood simulation generated using GeoHECRAS software to study flood hazard characteristic at downstream by combining tidal effects. The flood event in September 2012, a 10-year return period flood, became the basis for validating and calibrating the simulation model. Based on flood simulation result, it is known the downstream area of the Singkil watershed, Aceh Singkil districts is an area with a high flood potential and frequently occurs.