Numerical study of the transport of a pulse load over a bedform

Solute transport in streams and rivers is strongly related to river characteristics, such as mean flow velocity, velocity distribution, secondary currents and turbulence features. In a channel with dunes the separation region downstream the crest affects the transport of a solute. This paper presents the results of a numerical study aimed at understanding how a dune acts as a dead zone modifying the transport of a pulse load of a tracer injected upstream in the water column. The numerical results for the flow field showed a good agreement with the available experimental data both in the prediction of the length of the separation zone downstream the dune crest and of the vertical profiles of the time-averaged velocity. The analysis of the concentration field due to the pulse load of a tracer revealed the role of the different processes, i.e. advection and turbulent diffusion, acting in the transport of the tracer in a flow over a bedform.