Experimental study on the effect of bottomless structure in front of a bottom outlet on a sediment flushing cone

One of the main problems in reservoirs is sedimentation which reduces the operating life of dams if a proper plan and analysis method are not in place. The techniques to manage sediment in reservoirs include several sustainable management techniques that route sediment through or around the reservoir. One of the main economical methods in arid and semi-arid regions is pressurized flushing using moderate drawdown of the water level of the reservoir to evacuate sediment deposited behind dams. In the current study, the effect of a new structure called a dendritic bottomless extended (DBE) outlet structure at three angles of 30°, 45°, and 60° on pressurized flushing efficiency was investigated. Consequently, 45 experiments were designed for three discharge rates (Qo), three sediment levels (Hs), four types of structure, and a no-structure condition (reference test). The results indicated that the DBE structure with a 30° angle between the branches, a sedimentary dimensionless index of Hs/Do=4.59, and a flow dimensionless index of Qo/gDo5=1.43 (where g is the acceleration of gravity and Do is the diameter of the bottom outlet) lead to 10-fold increase in the sediment flushing cone dimensions and sediment removal efficiency compared to the results of the reference test. Finally, according to a statistical analysis of the results, a dimensionless equation for calculating the sediment flushing cone dimensions was developed for the tested sediment characteristics.