Numerical study of river sediment venting during flood from the reservoir of dams (Case study of Rudbar dam)

Sedimentation in dam reservoirs is known as an effective factor of reducing dams’ life-time and reservoir capacity, disruption of dam operation, blockage and corrosion in intake structures, drain valves and other sediment venting structures and consequently increase costs of maintenance and other related damages. This proves the importance of understanding the hydraulic behavior of density current in dam reservoirs. In this study, the trend of density current moving in Lorestan Roudbar reservoir has been investigated by Mike 3 model. The aim of this study is to withdraw maximum gravity current concentration in flood time period from bottom outlets in order to decrease sedimentation in reservoirs active volume. Therefore, three-dimensional hydrodynamics simulation of density current in this reservoir has been done. The modeling scenarios have been designed to calculate how much mass can be vented from bottom outlet to save more capacity in reservoir when flood with various return time period occur. The results show that increasing the return period of the flood the sediment discharge efficiency, increases. Sediment venting efficiency is increasing with a two-year return period and reaches a maximum in floods with a 20-year return period when the maximum efficiency of sediment venting is roughly 17%.