Suspended Sediment Changes Under the Influence of Rainfall Erosivity Cycle in Sorkhab Watershed

One of the most important consequences of soil erosion is sedimentation. The detection and surveying the type and amount of sediment is important because of its effects on irrigation networks, environment, and reservoirs. This study was performed in order to investigate the suspended sediment changes under the influence of rainfall erosivity cycle in Sorkhab- Keshvar watershed in the Lorestan province. For estimating the suspended sediment, we used a combination of sediment rating curve of mean loads within discharge classes and average daily discharge data. Monthly and semi-monthly EI30-based erosivity indices were calculated in 13 rain gauging stations inside and around of the watershead. In the next stage, erosivity maps based on kriging interpolation were produced in order to calculate the average monthly and semi-monthly rain erosivities. After calculating monthly and semi-monthly sediment loads, their correlations with corresponding erosivities were investigated. The results show that the maximum and minimum of suspended sediment occured in Azar and Shahrivar (Iranian month equal to Nov. 22 to Dec. 21 and Agu. 23 to Sep. 22) with the values of 246216 and 1272 ton, respectively. Also, the maximum and minimum of rainfall erosivity occured in Dey (Iranian month equal to Dec. 22 to Jan. 20) and summer respectively with the values of 182 and 0.01 MJmm ha-1 h-1.The highest values of semi-monthly erosivity and sediment observed in second half of Dey and Azar (Iranian month equal to Dec. 22 to Jan. 20 and Nov. 22 to Dec. 21) with the values of 104 MJmm ha-1 h-1 and 148241 ton, respectively.Sediment and erosivity showed two peaks in the watershed, two peaks of sediment occured in Azar and Farvardin (Iranian month equal to Nov. 22 to Dec. 21 and Mar.21 to Apr. 20) and for the reosivity occurred in Dey and Farvardin (Iranian month equal to Dec. 22 to Jan. 20 and Mar.21 to Apr. 20).