Assessment of the Slop Gradient on the Estimated Erosion and Sediment Delivery Ratio by Using 137Cs in the Khamsan Representative Watershed

The sediment budget has been introduced as a valuable concept and tool for describing the production, transport and deposition of sediment in a watershed. In order to study the effect of slope on sediment budget, the distribution map of erosion and sedimentation of the Khamsan Representative Watershed, located in the south of the province of Kurdistan, was prepared using 137Cs and overlapping with the slope map. The results showed that 15 sub-watersheds with an average area of ​​185.39 ha and an average slope of 31.83% had a mean sediment delivery ratio of 28.43%. Increasing the area to the whole watershed (4098.66 ha without rocky outcrops) with an average slope of 25.26%, the ratio decreased to 12.63%. This finding emphasizes on the impact of internal plain with the average slope of 10.27% on sediment trapping and decrease of sediment delivery ratio by 15.8%. The results of comparing the sediment budgets in slope classes showed that an orchard, irrigated agriculture and rangeland treated with soil conservation activities, the sedimentation is a dominant condition in all the slope degrees, while almost all the erosion caused by rain fed agriculture with the slope gradient degrees of 2-20%, and the rangeland with the gradients slope of more than 30%. Therefore, it is recommended to investigate the sediment delivery ratio with an emphasis on the performance of the low-slope areas as a sediment trap before applying the check dams, if necessary, and only in the most efficient places. Also prevent the conversion of rangeland to dryland and farming, also prevent plowing in the slope direction.