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The Impact of Niatak Lateral Spillway Performance on Process of Erosion and Sedimentation of Sistan River of Iran Original Article, D81 Motallebian M, Hassanpour F. J. Civil Eng. Urban. 4(5): 540-545. 2014 ABSTRACT: Sistan River Being located on the tail water of Helmand’s very extensive basin, it is prone to deposition of fine sediments, particularly in times of flood. The diversion structures on this river are Zahak and Sistan Dams. In this research the HEC-RAS model which has the ability to calculate the hydraulic parameters, is used to study of Niatakk spillway located in the upstream of Zahak dam. In this regard after the calibration model, the Erosion and Sedimentation process of the river during various conditions of utilization of the Zahak and Sistan dams was studied. The results show due to backwater by Zahak dam and giving the opportunity to the settling of suspended sediments, the rate of sedimentation between Niatak spillway and Zahak dam in situation of full utilization of Niatak spillway has become twice greater than situation which the gates are completely open. In situation of full utilization from Niatak spillway, the accumulated sediment in the interval between the Niatak spillway and Zahak dam is about 45% of the whole accumulated sediment and the accumulated sediments weight in this interval is about 20% of the whole accumulated sediment in situation which the gates are completely open. Keywords: Sistan River, Niatak Spillway, Erosion, Sedimentation, HEC-RAS model منبع: [Hidden Content] دانلود: [Hidden Content].,%204%20(5)%20540-545,%202014.pdf J. Civil Eng. Urban., 4 (5) 540-545, 2014.pdf