Solute transport in turbulent open-channel flows and porous beds

The pore-water flow inside the sediment bed resulting from water flow in the overlying river channel can control the mass and momentum transfer across the channel-bed interface. Furthermore, the presence of a boundary layer in the top part of the sediment bed where flow characteristics are non-linear due to inertia effects can result in higher mass flux across the porous surface. Two analytical models were developed to investigate the pore-water velocity field and study the effects of non-linear flow on solute transport. It was shown that advective transport dominates diffusion for the problems studied, and that diffusive exchange between a channel and its sediment bed cannot capture all the significant processes. To account for flow in porous beds, a two-layer, coupled transport problem was developed and the Aris method of moments was used to derive analytical solutions for the dispersion and effective velocity of the solute cloud. The role that an underlying flow and transport play in trapping the contaminant in the river channel, as well as the release of contaminant from the porous bed into the river channel were studied. The dispersion in the bed relative to dispersion in the channel was found to greatly influence the transport and dispersion of solutes in the river.