Determine the location of Gully erosion occurred based on the ‎Geomorphology threshold and factors affecting it (case study: ‎Cham-e- Zhab of Darrehshahr ‎, Ilam)‎

Gully erosion is the most important water erosion which causes land degradation and imbalance in lands. Land degradation, broken ecological balance of landscapes and sensitive condition of biological resources are among reasons of gully erosion study. This study performed with the goal of determining the topographical threshold of gully erosion and expansion and also predicting sensitive areas to this kind of erosion. Therefore, 36 gully in the study area selected and after data separation, impact of land use factors, various active mechanisms for gully expansion and method of data extraction of area and slop using aerial photographs, field measurement and GIS were investigated. Results showed that R2 coefficient has increased from 0.162 to 0.214 for agricultural land use data. But for abandoned land use, this value was equal to 0.043 and non-significant (P=0.54). R2 coefficient of 0.267 for the field measurements data and 0.162 for the GIS derived data, show that in spite of the significant relationship for both method (at significant level of 5%), use of field methods and direct measurement will lead to better results. In addition, the ability of model about sensitive areas predicting to gully erosion was studied using ROC curve. Area under the ROC curve was equal to 0.748 and indicated that this model is suitable for prediction of sensitive area for gully erosion.