Tracking bed load particles in a steep flume: Methods and results.

In this paper, we present an experimental study about the motion of bed load particles in water. Recent developments in the stochastic theory of bed load transport call for precise experimental data to validate the models. We set up the experiment in a tilted narrow flume, where we could control water discharge. The erodible bed was made of natural rounded particles of mean diameter 8 mm. Two high speed cameras, disposed next two each other, recorded the transport process at 200 frames per seconds over an observation window of approximatively 1 meter and during periods of 150 seconds. Contrasting with previous experimental study that aimed to track moving particles, we imposed ourselves three constraints: (i) all moving particles have to be tracked, (ii) tracking should be fully automatic, (iii) bed load transport rates have to be measured independently. The former constraint is mandatory to correctly compare to theoretical predictions while the second is a condition to be able to get large samples of trajectories in relatively short time periods. The latter is obviously needed to validate the algorithm. After briefly introducing the numerical treatment that allow the particle tracking, we present some interesting results about the bed load particles dynamics.