Abstract:

The Liziwa Ditch and Huajiaopo Ditch are 2 tributary ditches in middle reaches of the Jiangjia Ditch,a famous ditch having debris flow of high frequency.These two ditches are extremely similar in conditions of drainage area,with high frequency of outbreaks of debris flow and rapid development of deposit fan.These two ditches were studied in this paper,process of movement,ceasing and accumulation of debris flow on deposit fan were observed,deposit body of debris flow with different features were sampled and analyzed,and terrain of deposit fan was measured before and after rainy season annually as well as its vertical and lateral section.By analysis of development process,planar shape,longitudinal and transverse section,accumulation rate of deposit fan in the 2 tributary ditches during 2006~2008,the following conclusions were obtained.Huajiaopo Ditch was larger in volume weight and grain size,and its accumulation was holistic and Lung Kongshaped.Whereas Liziwa Ditch was smaller in volume weight and grain size,and debris flow overflowed on deposit fan and its accumulation was linguiform.Further development of deposit fan was completed by Lung Kongshaped accumulationcourse changing.On accumulation condition of the main channel,deposit fan in tributary ditch had mainly accretion,and extent of accretion was uniformly distributed at top and bottom of the fan.When debris flow fan developed to a certain extent,its vertical gradient was stable and smaller cross slope showed at the upstream direction of the trunk channel.〖