Terrain-Driven Flood Risk Modeling of a Levee Breach Scenario along the Jeneberang River: Implications for Urban Housing in Buyang Village, Makassar, Indonesia

Flooding caused by levee breaches remains a significant hazard in urban environments, particularly in low-lying regions exposed to intense rainfall and characterized by geomorphological vulnerability. This study assesses the flood risk to Buyang Village, Makassar, in case of a hypothetical levee failure at the Patompo Embankment along the Jeneberang River. Using a Probable Maximum Flood (PMF) hydrograph as input, the simulation was carried out with HEC-RAS 1D unsteady flow modeling, enhanced by high-resolution GPS-based topography, DEM generation, GIS integration, and terrain analysis via TOPAZ. The model incorporated a 300-meter lateral breach with outflow peaking at 86 m^³/s. Results indicate that floodwaters are diverted toward Sambung Jawa and Balang Baru due to natural elevation barriers, leaving the Rusunawa housing site in Buyang Village unaffected under worst-case conditions. Model validation was conducted by comparing simulated pathways with known flood-prone areas, while calibration involved sensitivity testing of Manning's roughness coefficients, breach parameters, and inflow variations. These tests confirmed that the protective influence of terrain—and the resulting safety of Buyang Village—remained consistent across all scenarios. The findings highlight the pivotal role of terrain in flood mitigation and underscore the utility of integrating hydrodynamic simulation with geospatial analysis in urban flood risk assessments. This study offers critical input for disaster risk reduction, urban zoning, and infrastructure planning in flood-prone Indonesian cities.