Journal of Watershed Management Research

Studies related to erosion and soil conservation of litho logical and geological characteristics of catchments have particular importance, Due to their effects. Erosion and sediment production are related to many factors, in which, the sensitivity of geological formation to erosion is the most important parameter. In this study, formations sensitivity to erosion in two sub-basins of Doviraj River located in Ilam Province is compared and their role in erosion and sediment yield has been investigated. In order to study the sensitivity of geological formations the Faiznia (1996) method is used. Results showed that the erodibility of the geological formations has a significant role in the erosion and sediment production, so that, the erosion and sediment yield of the first catchment is 2.5 times as much as the second catchment, because 92.4%of the sub-basin 1, is classified as sensitive to erosion and 7.45% the average class of sensitivity, but in the sub-basin 2, the above amounts are 65.01% and 34.99% respectively. Also, in the sub-basin 1, the Gachsaran formation which covers 6304 hectares (82.09% of the catchment) has the highest frequency and the above figure in the sub-basin 2, is 2166.86 hectares (49.07% of the catchment). Higher erosion and sediment yield of the sub-basin 1 compared to the sub-basin 2 is due to the existence of sensitive formation to erosion, especially Gachsaran formation which has the highest frequency in the study area.