STUDY ON REGIONALIZATION OF DEBRIS FLOW DANGER DEGREE UNDER GIS SUPPORT——TAKING THE AREA ALONG G212 IN LONGNAN AS AN EXAMPLE

Longnan in is one of the most famous areas for debris flow. The disaster has greatly hampered the economic development of Longnan and the construction of highway. Through detailed geological and environmental investigation of the area, the research area locates in the northeastern fringe area of hai-Tibet plateau, Complicated geological structure, intense structural activities, high and steep slopes, mass and concentrative rainfall and improper human activities provide necessary preconditions for debris flow disaster. Then we analyze spatial and temporal characteristics of the debris flow distribution synthetically. Debris flows mainly exist in the Bailong River, Min River(the first-level branch of Bailong River) and Beiyu River and appear in July and August. Finally, we filtrate eight regionalization factors and ascertain their proportion by considering factual condition, these factors include: rock and soil characteristics, the distance from falutages, seism, gradient, relative altitude, rainfall from May to August, soil using and vegetation coverage, then we use GIS to finish the regionalization result of debris flow danger degree and achieve a good result. The study will have some instructional meaning on how to choose route and establish approaches and measures to deal with a geological disaster.