International Journal of Ocean System Engineering 2(2) (2012) 71-81 http://dx.doi.org/10.5574/IJOSE.2012.2.2.071 International Journal of Ocean System Engineering Investigation of Dimension Changes in Under Pressure Hydraulic Sediment Flushing Cavity of Storage Dams Under Effect of Localized Vibrations in Sediment Layers Asgar Ahadpour Dodaran 1 , Sang Kil Park 1* , Asadollah Mardashti 2 and Masoud Noshadi 2 1 Department of Civil Engineering, Pusan National University, Busan, Korea 2 Assistant Prof, Department of Water Engineering, University of Shiraz, Shiraz, Iran (Manuscript Received March 22, 2012; Revised April 4, 2012; Accepted May 25, 2012) Abstract Several methods have been proposed to control the sedimentation process. These include catchment manage- ment, flushing, sluicing, density current venting, and dredging. Flushing is used to erode previously deposited sediments. In pressurized flushing, the sediment in the vicinity of the outlet openings is scoured and a funnel shaped crater is created. In this study, the effect of localized vibrations in the sediment layers on the dimensions of the flushing cone was investigated experimentally. For this purpose, experiments were carried out with two bot- tom outlet diameters, five discharge releases for each desired water depth, and one water depth above the center of the bottom outlets. The results indicate that the volume and dimensions of the flushing cone are strongly affected by localized vibrations. Keywords: Pressure Fushing, Local Scouring, Bottom Outlet, Sediment, Localized Vibrations 1. Introduction Sustaining the storage capacity of existing res- ervoirs has become an important issue rather than building new reservoirs which is difficult be cause of strict environmental regulations, high construction costs, and the lack of suitable dam sites (Shen, 1996). Several methods have been proposed to control the sedimentation process. These may include catchment management, flushing, sluicing, density current venting, and dredging. Flushing is used to erode previously deposited sediments (Brandt, 2000). One of the most effective techniques is flushing by hydrau- lically removing the deposited sediment by the flow. The oldest known method of flushing, practiced in Spain in the 16th century, was re- ferred to by D’Rohan (Brown, 1943). The excess shear force of accelerated flows created by the sudden opening of the bottom outlets of dams loosens and re-suspends the sediment. The flow will then wash them from the system. If flushing takes place under pressure, it is called pressure flushing and has only local effects around the outlet. In pressurized flushing, the sediment in the vicinity of the outlet openings is scoured and a funnel shaped crater is created. Figure 1 illus- trates the longitudinal view of the flushing cone in the vicinity of the bottom. This is only an op- tion in reservoirs with a small reservoir capacity compared to the water inflow, and a large sluice capacity (Qian, 1982). Pressurized flushing has been studied extensively in the literature (White, 1984-; Shen and Lai, 1993-; Fang and Cao, 1996-; Scheuerlein, 2004-; Emamgholizadeh, 2005 and 2006). In spite of advances in the in- vestigation of pressure flushing techniques at * Corresponding author. Tel.: +82-51-510-2427, Fax.: +82-51-513-9596 E-mail address: sakpark@pusan.ac.kr Copyright © KSOE 2012.