Modeling and mapping the environmental impact of debris flow hazard on alluvial fans for sustainable development in Bangga and Poi Villages, Sigi, Central Sulawesi

On September 28, 2018, an Mw 7.5 Palu earthquake triggered massive landslides upstream, followed by 24 debris flood events that spread to 15 villages in Sigi from September 2018 to December 2021. Debris flow and flash floods on alluvial fans inundated lowland communities, causing severe property destruction and structural damage to bridges and roadways and resulting in an estimated 900 damaged houses. Understanding their historical occurrence is essential to sustainable fan development and minimizing their threat to infrastructure and human life due to their severe geohazard potential. Poi and Bangga Villages were affected by the disastrous debris flood in Sigi Regency, Central Sulawesi. This study aimed to create a landslide inventory map, a back-analysis model, and a damage and loss assessment (DaLAs) to evaluate the potential hazard and environmental impacts of debris flow on Sigi’s alluvial fans. The result of landslide mapping showed more than 400 mapped landslides within Bangga Village in various sizes and a massive landslide within Poi Village were digitized. Then, the back-analysis model overpredicted flow direction due to vegetation, infrastructure, and road information not covered by the digital elevation model (DEM). Finally, DaLAs shows the losses caused by damaged buildings were estimated at around 65.7 and 7.4 billion rupiah in Bangga and Poi Villages, respectively.