Study of kinematic characteristics of a rock avalanche and subsequent erosion process due to a debris flow in Wenjia gully, Sichuan, China

This paper aims to systematically study kinematic characteristics of Wenjiagou rock avalanche triggered by the M8.0 2008 Wenchuan earthquake and one of subsequent debris flows that occurred on August 13, 2010 (8.13 debris flow), using a numerical approach. The kinematic characteristics of the rock avalanche are back-calculated using an energy-based runout model. The erosion process of the subsequent rainfall-induced debris flow is analyzed using a progressive scouring entrainment model incorporated in the energy-based runout model. The results indicate that Wenjiagou rock avalanche traveled farther than most other rock avalanches with a maximum velocity of approximately 73 m/s detected at about 1700 m away from the source zone. The erosion of the 8.13 debris flow mainly occurred right after the dam failure which contributes to more than 97% of the total eroded volume. Besides, four different scenarios, including no blockage of the runoff (scenario I), no dam failure (scenario II), dam failure at the end of precipitation (scenario III), and no erodible material (scenario IV), are supposed to study the effect of the failure of a check dam on the erosion characteristics of the debris flow. The results reveal that the blockage of the channel without failure could reduce 86% of the total volume and the failure of check dams is the main reason for the destructive consequence of the 8.13 debris flow. This paper proposes an approach to explore kinematic characteristics of a rock avalanche and erosion process of the subsequent rainfall-induced debris flows and also innovatively provides a method to indirectly assess mitigation strategies that can be used for the design of mitigation projects.