Evolution of Developing Flushing Cone during the Pressurized Flushing in Reservoir Storage

loss of storage capacity is one of the most serious problems in dam engineering. Pressurized flushing, a way to remove sediments from the reservoir, is flushing under a pressurized flow condition and nearly constant water level. Pressurized flushing has only local effects around the outlet. Sediment in the vicinity of the outlet openings is scoured and a funnel shaped crater is created. In this study, the temporal development of flushing cone under various hydraulic conditions was studied experimentally. Time variations of parameters such as maximum length and width of flushing and also depth of scouring cone was measured. Results indicated that an increase in flow velocity (and consequently in Froude number) established new hydraulically conditions for flushing mechanism and so a sudden growth was observed in the amount of sediment released and also scouring dimenssions. In addition, a set of nondimensional relationships were identified for temporal variations of flushing scour dimenssions, which can eventuallt be used to estimate the development of flushing cone. I. INTRODUCTION HE sedimentation in reservoirs occurs at a rate of about 0.3% per year worldwide. Sedimentation rate in many regions such as Asia is much higher and can be estimated between 0.5 and 1.0 percent annually [1]. Reservoirs sedimentation and its corresponding loss of storage capacity is one of the most serious problems of dams, which was paid more attention in the past few decades.