Behavioural analysis and dynamic simulation of the debris flow that occurred in Ganluo County (Sichuan, China) on 30 August 2020

On August 30, 2020, a high-intensity storm that dropped 45.4 mm of rain in 5 hours hit the Heixiluo basin and triggered a landslide-generated debris flow event, causing fatalities and damage. The original source of the debris flow was a large slope collapse on a steep hillside. The fallen debris mass was enlarged through sediment entrainment and slope collapse and ultimately buried a bridge at the gully entrance. Approximately 6.9×10⁵ m³ of material, including sediments and collapsed slope deposits in the gullies, was entrained, and the maximum erosion depth reached 17 m. A geomorphological analysis was initially performed based on a detailed field investigation to recognize the liquid and solid sources of the debris flow and the areas subjected to deposition and erosion. A map of the erosion-deposition distribution was obtained based on pre- and post-event DEMs. Using the rainfall estimated by the nearest rain gauge and the solid source estimated by the DEMs, runoff and debris flow propagation was simulated using a liquid-solid two-phase model that considers the effects of runoff and entrainment. The similarity between the estimated and simulated deposition-erosion volumes was satisfactory. The behaviour of debris flows captured in the simulation is broadly in line with the main features of the observed event.