The Dez dam is located in the Southwest Iran and was constructed in 1963, with a height of 203 m and an underground powerhouse of 520 MW, because of the high rate reservoir sedimentation, in recent years, therefore, performing flushing operations through the three irrigation gates of the dam has received great attention. Due to the release of high concentrations of sediments, on the other hand, performing such operations may cause considerable impacts downstream. The downstream limitations should, therefore, be taken into consideration during the flushing operations. In this paper, it has been tried to identify and introduce the downstream limitations of performing flushing operations for Dez dam, and to determine the most appropriate flushing hydraulic conditions in terms of discharge, concentration, and duration of such operations using model MIKE 11, so that the dam utilization system can perform these operations with the least damage to the downstream. Results show that if we take into consideration every factor involving the decision- making, then the flushing operations along with two stages of opening the irrigation gates (that is the evacuation of sediments) for 6 hours and the discharge of 30 m3/s will be the best option. The interval between the two flushing operations should be at least 6 hours. Based on the results of this paper, appropriate conditions for hydraulic flushing can be determined. These conditions will be manipulated by the responsible administration as these operations would have the least damage and cost.
Key words: Dez dam, environmental impacts, sediment flushing, Mike 11 model.
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