Flood hazard assessment of overtopping dam break case at tailing dam using debris and non-debris flow

Abstract Tailing dam failure can result in flash floods, not only infrastructure damage and potential loss of life but also environmental and economic impacts. The flow resulting from a tailing dam failure is typically classified as debris flow (mud) with high solid content. This study examines a hypothetical tailing dam failure at a confidential site in Java by comparing non-Newtonian debris (mud) and Newtonian non-debris (water) flow conditions under sunny and rainy days. Flood inundation from this tailing dam failure is simulated using the HEC-RAS 2D. The embankment breach of the tailing dam is modeled at both the left and right sides to compare the worst-case impacts. The results show that non-Newtonian debris flow creates a larger inundation area than non-debris flow, while the maximum flow velocity is lower in debris flow than in non-debris flow. The largest flood inundation occurs when the right embankment fails under rainy conditions. The flood extends to the river estuary, with the downstream area modeled using the Highest High-Water Level (HHWL) as the worst-case scenario. Maximum flow depths range 4–5 meters in residential areas, decreasing to 1–2 meters towards the downstream. Flow velocities at the breach point reach more than 5 m/s, decreasing to 0–1 m/s as it moves toward the estuary and beach. These findings contribute to a more comprehensive flood hazard assessment for overtopping dam break cases at tailings dams, helping identify high-risk zones and critical mitigation priorities.