Micro-geomorphology and characteristic of Zhatai Gully debris flow hazard,Butuo County,Sichuan Province

Zhatai gully is located in Butuo County of Sichuan Province,and on the right bank of Xixi River,one of the tributaries of Jinsha River.Zhatai gully is an old debris flow gully,where several debris flowevents occurred in history.Based on field investigation,laboratory test and photograph measurement,it is found that Zhatai gully has five sub-gullies with a drainage area of 4.86km~2,where the main channel length is 4.53km and the mean gradient is 42%.The drainage density in the area is 2.19km/km~2.The head of the gully is 3100 m above sea level,and the toe of the gully is 1197 m above sea level,so the drainage relief is 1903 m.Zhatai gully enters Xixi River with an angle of 62°. Zhatai gully may generate middle/high frequency-moderate/large magnitude debris flows.Field survey demonstrates that the gully occurred at least three times debris flow during the last 1000 years.The densities of the debris flows were about 2.0 t/m~3,and the blocking coefficient of the gully bed is 1.5.Based on hydrologic calculation,the debris flows discharge every 50-year and 100-year 155.77m~3/s and 178.19m~3/s respectively and the debris flow deposits is 16.39×10~4m~3 and 18.14×10~4m~3 respectively.The gully is a moderate hazardous debris flow gully,and has some threat to the planned dam of a hydroelectric station the lower reach.If it is difficult to avoid the negative influence on the dam construction,countermeasures against the debris flow are necessary.