The present study findings indicated that the sedimentation problem is severe. The most obvious impact of sedimentation in a reservoir is the cumulative loss of its storage capacity, affecting both the operational plan and economic investments based on reservoir use, especially in the drinking sector. To determine the most appropriate method for estimating suspended sediment in the Kardeh Dam reservoir located in a semi-arid region, measured flow discharge and suspended sediment load data at two hydrometric stations (Kardeh and Koshakabad) were investigated. To select an optimal model (with the best adaptation to hydrography operation results), the amount of suspended sediment transport by applying 6 models based on sediment rating curve equations and 14 individual and compound error criterias were estimated. By combining error criterias, 6 methods and 8 sub-methods were examined. It was found that the use of numerous individual or compound error criterias approximately has the same results, but using mean scores of individual/compound error criterias or only compound error criterias can improve the results. According to the results of statistics and hydrographic operations, a model of sediment rating curve equation is determined as the optimal model (model F). In this model, sediment discharge data can be divided into four categories according to hydrological conditions, and for each category, the equation of sediment rating curve was determined. It is suggested to conduct similar research in different climatic areas in order to investigate the effects of climatic conditions on data classification and selection of the most suitable sediment transport estimation model.

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