Using fuzzy relations and GIS method to evaluate debris flow hazard

The study area, located in the southeast of Tibet along the Sichuan-Tibet highway, is a part of Palongzangbu River basin where mountain hazards take place frequently. On the ground of field surveying, historical data and previous research, a total number of 31 debris flow gullies are identified in the study area and 5 factors are chosen as main parameters for evaluating the hazard of debris flows in this study. Spatial analyst functions of geographic information system (GIS) are utilized to produce debris flow inventory and parameter maps. All data are built into a spatial database for evaluating debris flow hazard. Integrated with GIS techniques, the fuzzy relation method is used to calculate the strength of relationship between debris flow inventory and parameters of the database. With this methodology, a hazard map of debris flows is produced. According to this map, 6.6% of the study area is classified as very high hazard, 7.3% as high hazard, 8.4% as moderate hazard, 32.1% as low hazard and 45.6% as very low hazard or non-hazard areas. After validating the results, this methodology is ultimately confirmed to be available.