Analysis Of Initiation Condition And Characteristics Of Wenjia Gully Debris-flow In Qingping Town, Wenchuan Earthquake Area

On13Augest2010, a total of20debris-flows were triggered by heavy rainfall aroundthe town of Qingping, located in the area of the Wenchuan earthquake. Among thesedebris-flows,Wenjia Gully debris flow was the most truly catastrophic. It traveledacross Mianyuan river and produced a debris-dam and then formatted a barrier lake,which then rosed the water river and changed the course of the river. Many buildingswere destroyed by the barrier lake, and causing huge casualties and economic loss.The safety of people’s life and property were seriously threated by Wenjia Gully.The Wenjig Gully landslide,triggered by the May12,2008Wenchuan earthquakeand then transformated Wenjia Gully debris flows under the condition of rainstorm.Rainstorm-induced debris flows had large amounts of loose material in theMeizoseismal area. Especially the Wenjia Gully debris flow in Qingping Town onAugust13,2010. Large amounts of loose materials deposited in the catchment ofWenjia Gully,And five debris flows had happened in this catchment in the past fourrain season.In this paper, the development environment and development characteristics ofWenjia Gully were systematically elaborated from geographical position and traffic,topography, rocks, geological structure and earthquake,meteorological hydrologicaland other aspects. The characteristics of Wenjia Gully catchment were descripedfrom valleys features, forming region(catchment area), forming region(provenance),deposited area, because Wenjia Gully have no typical circulation area. This paper mainly analysed the initiation conditions and typical characteristics of Wenjia Gullydebris flow. The initiation condition of debris flow mainly from the provenanceconditions, water conditions, terrain conditions, and geotechnical characteristics andentrainment effect. Provenance conditions included the number of the materials andthe position of the materials. Water conditions included antecedent rainfall, criticalrainfall and intensity of rainfall. Terrain conditions included basin morphology, valleycharacteristics and the slope of both sides. Geotechnical characteristics andentrainment effect include resistance to erosion, hydraulic permeability and resistanceto corrosion. The analysis of critical characteristics of Wenjia Gully debris flowmainly from larger scale of debris flow and the debris flow’s process of hazard.By comparision the scale of the debris flow before and after the earthquake,wefound that the scale after the earthquake is2.5times than before.The debris flowdisaster chain can be described as:Earthquake-Landslide debris flow-Gully dambody-plug type debris flow-lake.In this paper,the analysis of initiation conditionand characteristics of Wenjia gully debris-flow has important signification to theQingping town of reconstruction.