Abstract: According to historical records and the evidence of accumulation area, Dadu River blocking due to Moxi River debris flow happen easily and frequently in history, it's a typical case of debris flow blocking the river. For analyzing the movement of debris flow confluence with the main river and the effect of key parameters deeply, in this paper, the physical simulation experiment was carried out by using 1:500 geometric similarity. And some conclusions are drawn as the followings. Firstly, the bulk density and flow rate of debris flow is the major impact on the debris flow blocking the main river,and there is a critical point for the occurrence of the river blocked. Secondly, the influence of the speed ratio is small. Secondly, the main factor for the debris flow blocked the Dadu River is bulk density, flow ratio, and there is a critical point for the occurrence of the river blocked. And finally, the early identification index of Dadu River blocking due to Moxi River debris flow is obtained. When the Moxi River debris flow is greater than 2 000 m³/s, material composition is medium-coarse sand mixed with drifting pebbles and thick, Dadu River is blocked easily due to Moxi River debris flow. The experiment and conclusion has practical significance to secondary disaster chain disaster prevention and mitigation of Moxi River debris flow. It also provides a technical method for the early identification of debris flow confluence with the main river and the experimental research.

Key words: Moxi River, debris flow, physical modeling, early identification