An Evaluation of Bias Correction Factors in Sediment Rating Curves: A Case Study of Hydrometric Stations in Kalshor and Kashafroud Watershed, Khorasan Razavi Province, Iran

Complex and variable nature of the river sediment yield caused many problems in estimating the long-term sediment yield and problems input into the reservoirs. Sediment rating curves are generally used to estimate the suspended sediment load of the rivers and drainage watersheds. Since the regression equations of the sediment rating curves are obtained by logarithmic retransformation and have a little independent variable in this equation, they also overestimate or underestimate the true sediment load of the rivers. In order to evaluate the bias correction factors in Kalshor and Kashafroud watersheds, 7 hydrometric stations of this region with suitable upstream watershed and spatial distribution were selected. Investigation of the accuracy index (ratio of estimated sediment yield to observed sediment yield) and the precision index of different bias correction factors of FAO, QMLE, Smearing, and MVUE with LSD test showed that FAO coefficient increase the estimated error in all of the stations. Application of MVUE in Linear and Mean load rating curves has not statistically meaningful effects. QMLE and Smearing factors increased the estimated error in mean load rating curve but that does not have any effect on linear rating curve estimation.