Solid transport measurements through image processing

Abstract

The paper describes a novel technique which enables evaluation of sediment fluxes on the upper layer of a granular bed by means of separate measurements of concentration and velocity of the moving particles. Specific elaboration techniques based on digital image processing were applied to films of the solid fluxes, allowing for automatic measurement. Sediment concentration was measured via a technique based on image subtraction and following proper filtering procedures, while grain velocity was measured by Particle Image Velocimetry. The method was applied in laboratory experiments of one dimensional bed load; the solid discharges measured by the proposed image processing technique were compared to those obtained by manual count of the grains passing over a fixed plate used as a sight. After calibration of the automatic technique, dimensionless solid discharges ranging from 1.0 · 10–3 to 1.2 · 10–1 were measured with a maximum error as large as 25%. The technique proposed also enables measurement of the time variation of the quantities and the two dimensional direction of sediment motion, for a complete characterization of grain kinematics in solid transport processes

Particle velocity and concentration profiles in bedload experiments on a steep slope

“…Concerning comparable velocities, it has already been reported that particle velocity is only weakly dependent on the bed shear stress at least for saltation (Niño et al, 1994) or low concentration bedload (Radice et al, 2006), which is consistent with our conditions in the upper part of the profile. Above y* = 1, a reverse trend occurs, the velocity values are comparable while the concentration of N10-20 becomes much higher than that of N10-6.…”

Application of image subtraction data to quantify suffusion

“…Keshavarzy & Ball, 1999;Spinewine et al, 2003;Radice et al, 2006). In this study of suffusion, the velocity of the mobile particles is of secondary importance.…”

“…Such techniques are used to investigate movement of individual particles, for example colloid transport in porous media (Ochiai et al, 2006) and entrainment from a sediment bed (Radice et al, 2006;Wang et al, 2009), as well as the movement of collections of particles using particle image velocimetry (PIV) (e.g. White & Bolton, 2004;Slominski et al, 2007).…”

Image processing for the study of bedload transport of two-size spherical particles in a supercritical flow

“…Progress has been made in suspended sediment turbulencerelated issues and more recently in bedload research. Image analysis has been used in laboratories, more rarely in the field (Drake et al 1988), to measure for instance concentrations or number of particles (Radice et al 2006), grain size distributions and mass flux (Frey et al 1993Graham et al 2005;Zimmermann et al 2008), and particle velocities or trajectories. Tracking a single detected particle is relatively easy, and a number of authors have used image analysis to measure the trajectory of a particle in saltation (Hu and Hui 1996;Niño et al 1994, Lee et al 2000Ancey et al 2002) or in the rolling regime (Ancey et al 2003).…”

“…Drake et al (1988) performed field tests with natural sediments, extracting information from the images by hand. Radice et al (2006) evaluated sediment fluxes from above. The concentration was measured by segmenting subtracted images, a technique already used by Keshavarzy and Ball (1999).…”