Experimental Investigation of the Effect of a Semi-Cylinderical Structure on increasing Pressurized Sediment Flushing Capacity in Reservoirs of Dams

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Pressurized sediment flushing is one of the methods for removing deposited sediment in reservoirs of dams. In this method, by opening the bottom outlet, deposited sediment in the vicinity of the bottom outlet is flushed out. In this study by performing experiments on a  physical model, the effect of a semi-cylindrical structure in front of a bottom outlet on increasing pressurized sediment flushing capacity was investigated. The Semi-cylinderical structure used in the experimnts was closed at the upper side and had an opening width equal to the bottom outlet diameter at the upstream. Also in the all experiments the height of the structure was six times greather than the bottom outlet diameter and the level of the sediment layer was tangent to the bottom outlet. The experiments were conducted with four different discharges released from the bottom outlet, three water depths above the bottom outlet and four diameters of the semi-cylinderical structure. The results of the Experiments indicated that using a semi-cylinderical structure can increase sediment flushing capacity up to 10 times in contrast to nonstructured case. For a fixed depth of water, an increase in outflow discharge increased scour cone depth. Also for a fixed amount of outflow discharge and structure diameter, changes in water depth had almost no effect on scour cone depth. Also the results indicated that at a constant water level for each outflow discharge there was a proper diameter for the semi-cylinderical structure.

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