Joint Frequency Analysis of River Flow-Suspended Sediment Load Based on Copula Functions in the Zayanderood Sub-Basin

The river flow-suspended sediment load relationship in basins due to the rivers flow and natural and unnatural changes does not lead to providing an accurate relationship, so it is necessary to use new methods for the development of this sector. Multivariate methods and simulation and modeling based on copula functions can be considered in this regard due to the consideration of data distribution. In this study, two-dimensional copula functions were used in the period of 2010-2019 in order to simulate and joint frequency analysis of river flow-suspended sediment load and estimate the conditional probabilities in the sub-basin of Qale-Shahrokh, Zayanderood Dam basin. While examining the dependence of the studied pair-variable and choosing appropriate marginal distributions, Frank's copula was selected as the best copula in joint frequency analysis of the pair-variable of discharge-suspended sediment load according to the RMSE and NSE values. By using the selected parameters, the simulation of the studied pair-variable of river flow-suspended sediment load with the probability of more than 80% was carried out in the selected station. So that with a probability of more than 80%, it is possible to estimate the amount of suspended sediment load given by the river flow in studied station. Finally, with the probabilities of 90-95% and 95-99%, it was suggested that the equation of forecasting suspended sediment load given by the corresponding river flow in the study area, which presented the efficiency of 84% and 82%, respectively, according to the Nash-Sutcliffe statistic.