CONTAMINANT DISPERSION IN STREAMBEDS

The transport and fate of environmental contaminants in fluvial systems depends on the rate and depth of their penetration into the stream sediments at the base of the channel. We hypothesize that the depth and rate at which environmental contaminants penetrate the bed of a channel depends on both the flow velocity and the characteristic grain size of the bed sediment in much the same way that the transverse dispersion of a contaminant in a porous media depends on these parameters. To test this hypothesis, we measured, as a function of grain size and flow velocity, the transverse dispersion of dye-saturated water into porous media composed of 0.6-.8mm, 1.5mm, 3mm, and 5mm diameter glass beads. The dispersion calculated in these experiments is then compared to the rate and penetration depth, as a function of flow velocity, of both dye saturated water into channel beds composed of uniform diameter glass beads and, for the first time, the short-lived fallout radionuclide 7Be into the bed of a natural channel. We expect that the rate and depth of penetration into the channel beds will increase with increased grain size and flow velocity.