The capture of large bottom particles by eddies in a dam break flow

On the base of an experimental study of the boundary layer of the head of a dam break flow it is shown that the thickness of a viscous layer exceeds the bottom particle diameter $d_p$, increases with $d_p$, and decreases with the flow velocity (for ${d_p<1.2}$ cm). Bottom particles are captured by satellite eddies, which originate from main eddies near the bottom. Main eddies periodically appear in the viscous layer if the flow decelerates downstream. If ${d_p>0.045}$ cm the satellite diameter is smaller than $d_p$. Satellites close in and run into one eddy, which can contain the bottom particles if the flow velocity achieves a critical value $U_{\rm dip}$. Particles can be captured when the flow velocity has a higher value${U_{\rm cr}>U_{\rm dip}}$. It is possible under this condition that a particle starts to rotate in the satellite without slippage.