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Abstract The developmental state and activity level of debris flow can be reflected by its drainage system pattern. A quantitative description of drainage system is very important to the study of debris flow activity intensity. The three-dimensional data of debris flow are extracted by a computer program based on Matlab software which is written according to fractal theory to calculate the fractal dimensions of three-dimensional drainage system along Jinsha River. The quantitative indicators of drainage system were determined to analyze the debris flow in the study area，considering the amount of loose material and length ratio of sediment supply segment. The law between the factors and the activity intensity is summarized. With the activity intensity of debris flow increasing，the index values of factors also increase. What is more，when the activity intensities are 15 and 21，respectively，the curves of the relationships between factors and activity intensities all bend sharply which prove that there is an internal link in the amount of loose material，length ratio of sediment supply segment and fractal dimensions. New judgments to define the activity intensity of debris flow are proposed to supply new method and evidence for debris flow hazard assessment. The typical debris flows along Jinsha River are studied by above-mentioned method. From the results，it can be seen that the activity intensity of Aiba groove is the largest which proves that the activity intensities of debris flows determined by new judgments are consistent with the reality. The new judgments are scientific and rational.
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Received: 25 February 2010
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