Flood Mapping using HEC-RAS and GIS: A Case Study of Palembang Watersheds

Flooding is a significant issue in Palembang City, affecting areas such as Gandus, Lambidaro, Boang, Sekanak, Bendung, Kidul, Buah, Juaro, Selinca, Nyiur, Aur, Sriguna, Kedukan, Keramasan, Kertapati and Jakabaring watershed. This research contributes to flood control measures by providing flood mapping and modelling for decision-makers and local authorities. The main objective of this paper is to perform a steady flow analysis to study the hydraulic characteristics of flow; velocity and water surface profile of the adjacent research areas. There are three processes involved in the data analysis: hydrological, hydraulic and spatial. The calculation of average rainfall is performed using the Isohyet method with the assistance of the IDW 3D Analyst tool in ArcGIS and the design discharge is calculated using the HSS Nakayasu method. The hydraulic analyses involve river morphology extraction using RAS Mapper tools in HEC-RAS. Steady flow simulations are conducted for normal water depth conditions and the highest tidal conditions. The simulation result is then reclassified and the flood location points are verified with observed data. For normal water depth conditions, the maximum water level in the Lambidaro watershed reaches 2,09 meters, which covers a flood area of 721,53 ha. Meanwhile, based on the highest tidal simulations, the maximum water level in the Selinca watershed reaches 3,21 meters, covering a flood area of 209,36 ha.