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The formation of bed topography is the result of a complicated interaction between flow and sediment particles along the bed. Bed form and the geometry of ripples are also a function of bed roughness, median diameter of sediment particles and flow characteristics for example shear stress, separation and Froude number (Mogridge et al. 1994). Ripple geometry and its interaction with flow structure has been studied by many investigators; for example, Bagnold (1946), Carstens et al. (1969), Mogridge et al. (1994), Yalin (1977), Khelifa and Ouellet (2000), Miller and Komar (1980), and Nielsen (1992). In these studies, the geometry of bed ripples was found to be a function of turbulent shear stress parameters. Raudkivi (1997) pointed out that the ripples and vortices within the shear layer are affected by the flow depth, velocity distribution and shear stress on the bed. Despite more than three decades of investigation, there is still insufficient information to characterize ripple-flow interaction in adequate detail and over a range of turbulent flow conditions. One area where this lack of information exists is the application of image processing for particle entrainment and analyze of the turbulence characteristics and flow over ripples. To study the flow structure over the ripples, Sajjadi et al. (1996) found that the vortices that form in the lee of ripples are important for the entrainment of sediment particles. Keshavarzi and Ball (1999) used image processing technique to record entrained and deposited particles over flat bed and found that there is an intermittent nature for particles entrainment and deposition over the bed. Jeremy et al. (2005) used high resolution superVHS video system to monitor the development of the sand bed over a flat bed and observed that initiation occurs at relatively low flow strengths, where sediment transport is patchy and sporadic. Lajeunesse et al. (2010) used high speed video imaging system to record the trajectories of the moving particles over flat bed and observed that entrained particles exhibit intermittent motion composed of the succession of periods of flight and rest. Bennett and Best (1996) conducted a series of experiment over fixed bed ripples and compared the

Stochastic Nature of Flow Turbulence and Sediment Particle Entrainment Over the Ripples at the Bed of Open Channel Using Image Processing Technique