APPLICATION OF HEC-RAS MODEL FOR EVALUATING EROSION AND SEDIMENTATION OF KARKHEH RIVER, IRANFarhang Azarang, Abdol Rasoul Telvari, Hossein Sedghi and Mahmoud Shafai Bajestan
Using numerical models is an adequate tool for simulating erosion phenomenon and sediment transport conditions of the rivers that can be the basis for planning and implementation of water and environmental engineering projects. Karkheh Basin is one of the most important watersheds of Iran which belongs to Karkheh River (the third biggest river of Iran). However, the Karkheh River has strategical and environmental importance for design and implementation of large hydrological projects and supplying water for agricultural, industrial and municipal units but, there is no reliable and academic documentation about its erosion and sediment transport especially after the reservoir dam construction. Hence, the famous model of HEC-RAS has been utilized for simulating the sediment transport and erosion of Karkheh River during 12 years (2001-2013) downstream of the reservoir dam. Therefore, Thalweg and cross section alternations were estimated and the total sediment load of Karkheh River was determined at the study site. The results indicate increasing of erosion at the river post-dam which would be reduced in the middle and distal portion. The model outcomes showed that Sediment transport equations such as Ackers-White, Laursen and Engelund-Hansen have been provided the most accurate predictions of changes in erosion and sedimentation of the river. Moreover, the results from morphology section of model present that reservoir dam construction has failed to prevent displacement of Karkheh River central axis. Our survey would be a basic reference for future engineering experiments on Karkheh River and effects of dam construction on alluvial rivers.
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