FORMATION, CHARACTERISTICS AND PREVENTION ON DEBRIS FLOW HAZARDS IN LUDING COUNTY, SICHUAN

As located at the transition terrain between Tibet Plateau and Sichuan Basin,Luding county is typical of complex geological envirnonment and 127 debris flow gullies are distributed in this county with a formation density of 054 gully10km-2. On the basis of RS interpretation and field investigation,the forming,characteristics,damages,developing trend were discussed and corresponding prevention advices were put forward.(1)Complex geological,steep geomorphology and intense rainfall supply enough loose solid materials and advantageous potential and kinetic energy to debris flows. Whats more,an obvious powerlaw relationship is existed between the intraday rainfall and former sixday antecedent effective rainfall.(2)Debris flows are typical of groupoccurrence(including 2005-06-30 event, 2005-08-11 event and 2006-07-14 event)as occurrence space is concerned and nightoccurrence as occurrence time is concerned.(3)Burying,bursting,eroding and blocking consist of the main damage mode of debris flows and 74 residents had lost their lives because of debris flows in history.(4)Most debris gullies are at the forming stage and developing stage(113 gullies, 89%)and the annual period has been shorting from 20 years to less 10 years but the occurrence times have been increasing from 4 to 44 on the contrary.(5)Town debris flows,blocking of debris flows,scenic spot debris flows and ravine debris flows are four main prevention problems in Luding county and corresponding prevention advices were put forward including scientific planning,constructing of riskmitigation system,engineering,monitoring and warning. 