ANALYSISOF TURBIDITY CURRENTS MEASURED IN DEZ RESERVOIRMehdi Ghomeshi, Mohammad Reza Zayrie and Houshang Hasounizadeh
Turbidity currents may play an important role on reservoir sedimentation as they are capable of transport-ing large quantities of fine sediments over long distances towards the dam wall.Prediction of the behavior of turbidity currentsis of great interest to many reservoir engineers. Sediment deposition by turbidity cur-rents will contribute to reservoir loss of water storage capacity, obstruction of the bottom outlets, or inter-fere with the operation of the intake structures and affect the reservoir ecology. DezDam is located in North westof province of Khouzestan, Iran, and it is a large hydroelectric dambuilt on upstream of the DezRiver.The dam was built in 1963 with a total storage of 3.340 million cubic meters. It has 203 meters(666 ft.) in height, whichis the highest dam in Iran.To find the characteristics of turbidity current that occur inthe reservoirand its effectsonsedimentation, measurement are madein this reservoir in two time in years2003 and2007.inthese period all togethertwelveturbidity currents events are recorded.The main purpose of this paper is to ana-lyze the measured turbidity currents and tofindappropriate criteria to manage such currents in this reser-voir. The results showed when the mean daily discharge was over 600 mr/s, or sediment concentration was over 1.2 gr/lit, theestablished turbidity current was relatively strong and have brought sediment particlesnear to wall ciam.In the case the mean daily discharge was over 1380 /s, or sediment concentration was over 4 gr/lit, the turbidity currents have acted as self-accelerate mode. In this condition,when the turbidity current moves from frontal part of deltaregion of sediment deposited, the current eroded the sediment particles from the bed and therefor the sediment concentration in the turbidity currents were increased and transported toward the dam wallit can be say, if the accelerated turbidity currents are kept in the reservoir then the sediment deposition will increase highly near dam wall in compare with past.
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