Study On Comprehesive Prevention Of Dagou Debris Flow Of Tianquan County

The Dagou debris flow gully is located in the Tianquan County,Ya'an City,where is the transition section between Chengdu Plain and Western Sichuan Plateau.Because of the strong tectonic erosion,the overall landscape is gorges in high or mid-high mountains with a amount of loosen debris sources.The gradient of the Dagou gully and the both slopes of the valley is steep to provide the favorable condition of gathering the debris sources.The Dagou gully is 5.34 km long,3 to 10 m wide,and the square is 4.4 km2.The highest and lowest points of the gully is 1220.5 m and 750 m asl.,respectively,with the relative relief of 470.5 m.Both banks of the gully are generally gentle with the gradient of 6 to 16 degrees,covering with grass-shrub vegetation.Before "5.12" Wenchuan Earthquake,the geological disasters like landslides and debris flows didn't develop.Since the "5.12" Wenchuan and"4.20" Lushan earthquakes,some new adverse geological phenomenons as landslides and collapses appeared and offered plenty of loosen solid sources in the gully.Various scales of debris flows burst out every rainy season,parts of the farmlands was submerged but nobody injured.According to the geographic and geomorphic conditions,combined with the location of unstable solid sources,we divide the gully area into 3 parts:formation region,transportation region and accumulation region.The distance between the highest point of the mud vestige and the bottom of the Dashi Bridge culvert was only 0.5 m.The old downtown and the planning area of Tianquan County is located in the downstream of the gully,with high-density-population and complicated roadways.The debris flow could cause property loss of 50 million yuan.The total solid source volume is about 5.302×104 m3,and the dynamic reserves is about 5.02×103 m3.According to the damage and economic loss,the Dagou debris flow belongs to mixed-type,intermediate-frequency,and large-scale type.Through the investigation,the possibility of it is great.Based on above-mentioned,the formation mechanism of the Dagou debris flow,and the comprehensive prevention measures combining a general plan for the urban reconstructionwere proposed.