Statistical Assessment of Sediment Change and the Effective Factors (Case Study: Menderjan Station)

Suspended sediment is the major part of total sediments transported by rivers. Suspended sediment measurement is an important issue for erosion and sedimentation، water resources engineering and watershed management studies. The sediment yield of the watersheds is also a major problem of watershed management activities. Statistical analysis of sediment yield is an important method for trend assessment. In this study، sediment yield of Menderjan Watershed for the period of 1979-2004 is considered. Descriptive statistics and trend of observed series (with mean and standard deviation of 59. 66 and 348. 47 mg/lit، respectively) showed a decreasing trend which is significant at 5% level. However، the cumulative standardized plot shows three different periods with Kendall test values of 0. 265، -0. 119 and -0. 166 which are significant at 1، 5 and 10% levels، respectively. Comparison of three nonparametric tests of mean، variance and distribution functions showed significant difference of mean، standard deviation and frequency distribution for the studied periods. This significant difference، especially for standard deviation، shows the reduction of sediment yield in the third period due to watershed management practices in 7135 hectares area، 174 mechanical structures with 3815 cubic meter volume، and 275232. 3 cubic meter sediment storage volume in the basin and its importance.