Effect of Rainfall Type on Runoff and Sediment Yield in Plot Scale

Investigation of the relationship between rainfall characteristics with runoff and sediment yield is a fundamental study in designing and operating soil and water conservation practices. In this research, the effect of rainfall types on runoff and sediment yield was studied in the plot scale in the Khamsan Watershed located in Kurdistan province. Time to reach the storm maximum intensity was considered as a rainfall type index, based which all rainfalls divided into two types. Runoff, sediment concentration, sediment load and runoff coefficient were also measured in the 22.1 meter length and 1.83 meter width plot for each storm. The results showed that there was a significant difference between rainfall types at the level of 99 percent. In addition, there were significant differences at level of 99% in the runoff, sediment concentration and sediment load between different types of rainfalls. So those, the mean of runoff volume in the type 1 were significantly more than that of type 2 at the significant level of 5 percent. Also, the sediment load and sediment concentration were significantly more in type 2 storms at the level of less than 5 percent. Moreover, bivariate and multivariate modeling of runoff and sediment yield with rainfall characteristics were done and the results showed that the storm runoff could be predicted by the height of precipitation in type 1, the sediment yield of each storm could be predicted by maximum intensity in ten minute of type 1 storm and the maximum intensity in ten minute and runoff of type 2 storm by maximum value of R2 while minimum values of relative errors of estimation and verification.