Investigation of Gully Erosion by using the Analytical Hierarchy Process Model Case study: Roudbar, Gilan Province, Iran

  Gully erosion is one of the geomophological phenomenon that causes numerous losses to farmland, rangeland, roads, and increased sediment rate. Recognition of the causes and modeling gully erosion has an important role in watershed management, which aids in preventing the destruction of lands in sustainable development. In this research, a gully erosion map was prepared with the use of airphotos at a scale of 1:40000, IRSsatellite  images, and a field survey with the use of GPS. Initially, with respect to the lack of comprehensive research and an investigation of prior research,factors such as lithology, slope, land unit, aspect and landuse were studied. Then, by using the analytical hierarchy method, the impacting factors were binary compared with each other. A weighted coefficient for each factor was computed. Finally,we prepared a gully hazard zonation map and watershed model. The results of this investigation showed that marl silt and old Makhroot Afkana (100%) and land type Tapa Mahoor (57%) are effected by gully erosion. In the investigated area, this study showed that the majority of gully erosion influenced:i) land that had a slope of 5%-20%(which consisted of approximately 92% of the entire land area)ii) land that had a southern slope (82%) and iii) poorly covered range land (100%). The analytical hierarchy method is a suitable model for determining gully erosion susceptibility in the Aliabad catchment.