Hazard Zonation and Risk Assessment of a Debris Flow under Different Rainfall Condition in Wudu District, Gansu Province, Northwest China

Debris flows induced by heavy rainfall are a major threat in Northwest and Southwest China, due to its abrupt occurrence and long runout. In light of this, this work presents the runout simulation and risk assessment of the Boshuigou debris flow under different rainfall conditions in Wudu district, Gansu Province, Northwest China. Based on field reconnaissance, the geomorphological feature and main source of the Boshuigou debris flow were described. With the application of the FLO-2D simulation, the potential flow depth and flow extent of the Boshuigou debris flow under 100-year return-period rainfall and 50-year return-period rainfall were calculated. The maximum flow velocities of the Boshuigou debris flow under the 100-year return-period rainfall and 50-year return-period rainfall were 5.46 and 5.18 m/s, respectively. Accordingly, the maximum flow depths were 5.85 and 5.57 m. Then, the hazard zonation was conducted in combination of the construction and other properties within the potential impact zone, and the risk assessment of the Boshuigou debris flow under the 100-year return-period rainfall and 50-year return-period rainfall was finally completed. This work presents a method for debris flow risk assessment considering the solid source and water flow, which can provide a basic reference for mitigation and reduction of geohazards induced by torrential rainfall.