Hec-ras 6.6 Dam Break Analysis With InaSAFE Disaster Impact Assessment Approach of Bili Bili Dam

Abstract

Bili Bili Dam is a zoned rockfill embankment dam that plays a critical role in water supply, hydropower, and flood control for the Jeneberang River Basin. However, with an effective reservoir volume of 346 million m3 , the dam possesses a high hazard potential to the downstream area. In accordance with Permen PUPR No.27/PRT/M/2015, every dam is required to develop and periodically review its emergency action plan, particularly when changes occur in hydrology conditions, environmental factors, or the social conditions of the downstream. Therefore, a dam break analysis is essential to support emergency compilation and disaster-risk reduction for the Bili Bili Dam. This study performs a comprehensive dam break analysis using HEC‐RAS 6.6 through an integrated 1D-2D unsteady flow modelling approach. The 1D model represents the river channel hydrodynamics, while the 2D domain captures the floodplain propagation and inundation behaviour. Breach parameters were determined using the empirical equations of Froehlich (2016), and three piping‐failure scenarios were simulated at breach-initiation elevations for both the Main Dam and the Right‐Wing Dam. Hazard and exposure data processed in QGIS and analyzed using InaSAFE 5.0.7 to quantify potential impacts. Numerical stability was achieved through stepwise calibration of steady and unsteady simulations. The simulation revealed that the highest peak discharge reached 30,635.40 m3/s under the Right‐Wing Dam top‐piping scenario, while the most extensive inundation of 238.336 km2 occurred in the middle‐piping scenario. The results further showed that flood waves arrived in downstream settlements in less than 3 hours, with maximum depths in Makassar occurring within 3–6 hours. InaSAFE impact assessment indicated that up to 143,100 buildings, 2,017 km of road network, and 12,800 ha of farmland may be affected.