Impacts of topographical factors on debris flows and weight analysis at the Gansu segment of the Bailongjiang River Basin

The Gansu segment of the Bailongjiang River is one of the four major debris flow disaster areas in China. Topography is the key factor for the formation of debris flows. In this paper, the impacts of topographical factors on debris flows at the Gansu segment of the Bailongjiang River Basin are examined based on a statistical analysis of the relationship between the main topographical factors, such as the groove gradient, gully slope, relative elevation difference, drainage area and the debris flows' types, and the susceptibility by investigation of 1 008 debris flows in the study area. The contribution degree to the formation of debris flows is analyzed by ranking the weights of the 4 factors which are calculated by the entropy method. The results show that the groove gradient in the range of 200‰-400‰, slope greater than 30 degrees, relative elevation difference greater than 300 m, less than 10 km²of drainage area are beneficial to the formation and movement of debris flows. The greatest contribution degree to the formation of debris flows is the groove gradient, followed by the relative elevation difference and drainage area, and the smallest is the gully slope. The results of this study are of guided significances for the monitoring, warning and prevention of debris flow disasters in this area.