Applying fuzzy logic to mapping susceptibility of landslide in Chardavel watershed in Ilam province

One of the slopping processes which created much damage in many locations of Iran and the world is Landslide phenomenon. Making landslide susceptibility map provides the possibility to recognize susceptible areas and to verify them in the environmental programs. Purpose of this research is mapping susceptibility of landslide in Chardavel watershed in Ilam province by establishing informational layers and effective factors in occurrence of landslide via geographical information system (GIS) and fuzzy logic theory which involves operators fuzzy subscription، algebraic Sum، algebraic product and gamma fuzzy. The location of the landslides was determined by using regional photographs and satellite images and LSM. In this work، input information set in assessment of potential hazardous landslide includes nine factors: slope، aspect، elevation، precipitation، distance from road، distance from fault، distance from drainage، land use، and lithology. For comparing maps resulted from landslide susceptibility mapping by quadruple operators in fuzzy logic، density ratio (Dr) index is used. Based on this index، the map obtained by fuzzy gamma operator is more appropriate than other operators in separating suitably between casts of landslide risk. Thereby، more than 57 percent of landslides in this region occurred in 52. 7 percent of the lands and in two cast of high or very high danger. Finally، to estimate the amount of the precision and efficiency of fuzzy quadruplet operators، the evaluation generated maps compared with real zoning maps of basin. Results show that fuzzy gamma map has high overlay with real maps، the highest percent of the overlay of two maps in fifth class (Very High) is 43. 3 % and the lowest percent of overlay in third class (Moderate) is 12. 1 %.