Abstract: Despite many research results of debris flow deposit and its influences on the evolution of main river bed and sediment characteristics, analysis on the specific evolution process based on field observational data are rarely seen. Taking the topographic monitoring data of the cross-section and samples of Xiaojiang river reach of the Jiangjia Ravine from 2008 to 2010, in association with the observation data of debris flow, we analyzed the characteristics of deposit and re-start transport of sediment after the Jiangjia Ravine debris flow converged into the main river. Results showed that solid sediment from the debris flow mainly deposited in the range of 500m lower of the confluent entrance (less than 10 times the width of the main river). The amount of the accumulation was related to the amount of the original deposit eroded and transported by the Xiaojiang River. During the transport, the sediment blocked the riverway and frequently changed the route of the main river. Deposit of the debris flow sediment gave rise to nodes at the confluent entrance. Although the riverbed of Xiaojiang River near the confluent entrance exhibited a trend of erosion in recent years, erosion in the downstream was faster than that in the upstream, which led to gradient increase of the riverbed in the downstream whereas decrease in the upstream, showing prominent node features at the confluent entrance. 

Key words: Jiangjia Ravine, debris flow, reach of the confluence, deposit, transport