CHARACTERISTICS AND EVOLUTION OF DEBRIS FLOWS IN WENCHUAN COUNTY AFTER "5·12" EARTHQUAKE

The 2008 "5.12" Wenchuan earthquake greatly changed the characteristics of debris flows in the earthquake zone. The earthquake not only enhanced the activity of debris flows,but also made the earthquake area under the threat of debris flows for a long time. During the past 10 years after the earthquake,debris flows occurred frequently. It is of great significance to study the characteristics and development trend of debris flows in Wenchuan County. We analyze the longitudinal gradient,gully density and slope gradient in Wenchuan County by means of remote sensing interpretation and field investigation. We further analyze the rainfall spatial and temporal trends and critical rainfall characteristics of debris flows in Wenchuan County by collecting rainfall data and previous research. According to the study,the average annual rainfall in Wenchuan County increased by 5.17% after the earthquake. The rainfall was mainly in July and September,the amount of rainfall decreased gradually from north to south. The gully density of debris flow gully is between 0.2 and 4,which belongs to the soil erosion area of the micro-degree. The longitudinal gradient of debris flow is large,which is conducive to the occurrence of debris flow. The slope gradient of debris flows is 30°~40°,which is conducive to the occurrence of disasters. The rainfall threshold of the post-earthquake debris flow shows a slow increased in 2008-2013, but declined in 2019. It is expected that it can take a long time to return to the pre-earthquake levels. The provenance of debris flows in Wenchuan County is abundant,and the amount of provenance in the earthquake is decreased in a fluctuating tendency.