The Tamblang Dam break analysis using HEC-RAS 5.0.7 and PenRis hazard classification in Indonesia

Tamblang Dam is one of the dams, north of Bali Island, with a capacity of 7.6 million m3,  and the downstream areas are in the form of agricultural land, citizen settlements, schools, offices, and other public facilities for approximately 10 km2. Considering such a downstream and its large capacity, the Tamblang Dam would have a significant damage impact if it is a failure. Therefore, it is necessary to analyze the failure of the Tamblang Dam. The study aims to analyze the areas affected by floods due to the dam’s failures and to measure the damage risk. The failures were simulated using HEC-RAS 5.0.7 with four scenarios, such as overtopping, upper-piping, middle-piping, and bottom-piping. The simulation result showed that the Tamblang Dam’s failure with the overtopping scenario had the worst impact as it has the highest velocity and discharge compared to the other scenarios. The overtopping scenario inundated 355 ha areas along the river. Six villages would become the victims, namely, Bengkala, Bila, Menyali, Jagaraga, Bungkulan, and Kubutambahan. Tamblang Dam failures’ danger level was figured out in this research according to the PenRis Hazard Classification of Dams in Indonesia. For this case, it is found that 2527 residents are at immediate risk of flooding caused by the failures. Therefore, following the Danger Classification from the Public Work and Housing Guidelines of Indonesia, it can be stated that the Tamblang Dam is a 4-class dam with an extremely high danger status level.