Hamed Heidary - Department of Water Engineering, Zabol University, Sistan and Baluchestan, Iran
Farzad Hassanpour - Department of Water Engineering, Zabol University, Sistan and Baluchestan, Iran.

Sistan River, which is located in the downstream of the vast Helmand’s basin, is a suitable place for the deposition of fine sediments especially in times of flood. On the other hand, the occurrence of prolonged drought periods in the region, raises the riverbed level due to the deposition of sediments and the impact of these two processes transforms the river sections thus, reducing its flood discharge. Identifying the sedimentation problems due to the construction of hydraulic structures in rivers, is an efficient tool to better exploit such structures. The HEC-RAS model was used in the current study that has the ability to estimate the annual sediment load and to do hydraulic calculations under moving bed conditions. After the modeling of erosion and sedimentation, with the help of 6002-00 flood hydrograph, the maximum flood discharge of Sistan River if Sistan and Zahak dam were not existed was about 58858 tons per day at the upstream of Nyatak spillway less than current operational conditions

flood, river, sediment, HEC-RAS, Zahak dam, Sistan dam