The effects of flushing operation in Sefidrud reservoir on the downstream river

The sefidrud Dam was constructed and made operational in Iran in 1962. The reservoir lost a considerable amount of its storage capacity in the first two decades of its operation when about 800 MCM sediment deposited in it and by considering the total capacity, 1800 MCM, the live storage capacity was reduced by 45 percent in 1980. The Gilan Project Authorities have attempted to recreate the reservoir capacity by removal of deposited sediments through flushing operation. Thus, they have started this process in 1980 and still it is being practiced every year. In this research, the effects of flushing operation on the river reach downstream of the reservoir have been studied. For this purpose the HEC-6 model was adopted. The results of the model application show that the releases during flushing operations are inadequate to transport silt and sand particles, consequently, these settled sediments are being transported to irrigation canals and agricultural lands. In the prevailing situation in Sefidrud River, the Yang’s method can perform better that the other sediment transport equations being used in HEC-6. Finally, it is concluded that higher releases during flushing operations are required to reduce sedimentation and its consequences in Sefidrud river.