DEVELOPMENTAL FEATURES AND EVALUATION OF BLOCKING DANGERS OF DASHUI DITCH DEBRIS FLOW IN TANGJIASHAN DAMMED LAKE

Dashui Ditch is located in the upstream side of Tangjiashan Mountain. It was a gully before the May 12 earthquake,however,extremely rich loose sources were formed with all conditions of the occurrence of a debris flow due to the collapses and landslides after the earthquake. It became one of the serious potential dangers of geological disasters after successful discharge of Tangjiashan dammed lake,which controlled the normal operation of Tangjiashan dammed lake as well. Through in-situ investigation,the developmental and dynamic features of Dashui Ditch debris flow was analyzed systematically combining with the developmental situation of debris flow on June 14 on the basis of identifying the distribution and stability of the groove loose sources. In particular,the possible sizes of the debris flow under different rain frequencies were studied,and the possible blocking size, duration and outburst forms were evaluated. The results were confirmed by the once in 100-year debris flow on September 24,2008.