THE EFFECT OF SPECIFICATIONS OF COHESIVE AND NON-COHESIVE SEDIMENT ON PRESSURE FLUSHING EFFICIENCY IN DAM RESERVOIRS

Nowadays, a plenty of dam reservoirs are encountered to several problems regarding high volume of sediments in their reservoirs. Pressure flushing is a type of hydraulic flushing technique. As the bottom outlet is opened in pressure flushing method, a flushing cone is formed at the front. The dimension of this cone is affected from several parameters such as outlet discharge flow, water depth of reservoir, and kind of sediments accumulated in the reservoir. Since the flow pattern near the outlet discharge is three dimensional in the pressure flushing method, its behaviour is too complicated to consider. In this research, scientists use one physical model with specific dimensions for study about the effect of cohesive and non-cohesive sediment on the form of flushing cone. The result of this research show that the plan was Retrogressive Erosion in non-cohesive sediment and while experiments done with at least high water depth(40 cm) and maximum discharge(8 lit/s),the flushing cone be balance after 9-11 minutes. Also about cohesive sediments the result of this research show that the plan was Retrogressive Erosion and the slope of flushing cone in the longitudinal direction was slightly higher than Side slope. In average longitudinal slope 5.2% was greater than the transverse slope. Generally the slope of flushing cone of cohesive sediment much bigger than non-cohesive sediments.