Investigation on the Effect of Sediment Level on Pressurized Flushing Performance from Reservoirs using Physical Model

In the Pressurized Flushing method، the previously settled sediments at the bottom of the reservoir will be cleaned up and flushed by the downstream water after opening dam’s bottom outlets. The volume of the flushed sediments can be affected by various factors such as the reservoir water surface elevation، flow rate، and sediment elevation at the dam. This study investigates the laboratory scale “Pressurized Flushing” method as well as the impacts of sediment elevation on the efficiency and the dimensions of scour funnel. A physical model was built in Tarbiat Modarres University in order to assess the effects of the aforementioned factors. All the tests were performed at 3 sediment levels and in each sediment level with 3 water depths and 3 flow rates. According to the measured data، there is a direct correlation between the flushing cone dimensions and the sediment elevations. Based on the measured cone dimensions; the greater the sediment discharge at the higher sediment elevations، the greater the dimensions of the flushing cone will be. Furthermore، increasing of the accumulated sediments elevations at the reservoir leads to a higher efficiency of the pressurized flushing. An average increase of 29 percent in sediment elevation leads to 2 percent increase in the efficiency. Moreover، it has been observed that the flushing cone shape in plan view closely resembles a semicircle. Finally، based on the experimental data، dimensionless equations were developed in order to determine the dimensions of the scour funnel. There was a good correlation between the equations and the experimental data.