A Simulation of Sediment Transport of Floods and its Temporal Variation Using HEC RAS: A Case Study of Poldokhtar Station of Kashkan River, Lorestan Province

Knowing the amount of sediment transport in rivers and the effectiveness of protective measures is necessary. Due to the proliferation of dams on rivers, knowledge of sediment volume estimation and how and when sediment moves is so important.Kashkan watershed is located in Lorestan province with an area of 9287.39 km2. This watershed is one of the main subbasins of large Karkheh river basin in western Iran. Kashkan watershed usually experiences bigfloods with high sediment. In this research, different aspects of sediment transport were assessed using HEC RAS software. In this study, during 31 years (1980 to 2010), geometeric data of Poldokhtar station and 200 meters of its upstream were used and assessed for simulating sediment transport and its temporal changes. The main purpose of this research was to analyze sediment transport in flooding months and to select the best method for estimating sediment transport rates in the study area. The evaluation of sediment transport by the HEC RAS 4.1showed a good agreement between measured and simulated sediment based on Nash Sutcliffe efficiency criteria (72% for the calibration and 78% for the validation period). Moreover, most floods with high sediment transport occur in the winter especially in December.