Modeling the Runout Behavior of the July 23rd, 2015 Cancia Debris-Flow Event Using Two Numerical Models

On 23 July 2015, a typical volume-enlarging debris flow was triggered by heavy rainfall that occurred a few days before the event. The available data corresponding to this event is obtained from detailed field investigations conducted before and after the event, as well as the monitoring station installed in June 2014. This study aims to reproduce the July 23 debris-flow event using two different numerical methods, analyse the influence of entrainment on the runout behavior of the debris flow and compare the performance of different numerical methods when simulating the same debris-flow event. The results showed the following: (1) The expanded inundated area and unrealistic overflowing were observed in the scenario without entrainment while the simulation that takes entrainment into account presented more perfect results. It illustrates that entrainment is a non-negligible factor for the simulation of these volume-enlarging debris flows. (2) Two models considering the entrainment performed a good match between the simulation and the field survey. However, some noticeable differences can be observed in terms of the erosion-deposition distribution because different numerical schemes were adopted in the two models. Specifically, the DAN3D code always gives higher mobility and larger lateral spreading relative to the Shen model.