Abstract:

The semiarid region is characterized by sparse vegetation and rich source of loose sediments, which is favorable for the development of debris flows. A typical example was selected from the Benzilan-Changbo segment of the upper Jinsha River. Based on field investigation and interpretation of remote sensing images, the distribution of debris flows in this area was studied and six factors were selected as the assessment index, including rock type, structural fault, slope gradient, relative relief, annual average rainfall and normalized vegetation index. GIS technology and AHP (analytical hierarchy process) method are combined to build assessment model of debris flow susceptibility for semiarid region, then the grid map of debris flow susceptibility assessment in the study area was obtained. Dividing the study area into small basins, performing the statistical analysis and classification based on small basin units, the debris flow susceptibility assessment map of the study area was finally obtained. The susceptibility assessment map show that the high susceptibility area mainly distributed in the northeast, central and southwest along the banks of the Jinsha River; the area with high and little high susceptibility accounts for about 1,040.9 km²，occupying 35.7 percent of the study area. In addition, after using test curve to inspect the results of debris flow susceptibility assessment, the area of debris flow in high and slightly high susceptibility accounts for about 651.4 km²，occupying 51.1 percent of the total debris flow area. It indicates that the result is reasonable.

Key words: dry valley, debris flow, susceptibility assessment, analytic hierarchy process, upper Jinsha River