Effects of kinetic sorptive exchange on solute transport in open-channel flow

A theory is presented for the transport in open-channel flow of a chemical species under the influence of kinetic sorptive exchange between phases tha t are dissolved in water and sorbed onto suspended sediments. The asymptoti c method of homogenization is followed to deduce effective transport equati ons for both phases. The transport coefficients for the solute are shown to be functions of the local sediment concentration and therefore vary with s pace and time. The three important controlling parameters are the suspensio n number, the bulk solid-water distribution ratio and the sorption kinetics parameter. It is illustrated with a numerical example that when values of these parameters are sufficiently high, the advection and dispersion of the solute cloud can be dominated by the sorption effects. The concentration d istribution can exhibit an appreciable deviation from Gaussianity soon afte r discharge, which develops into a long tailing as the solute cloud gradual ly moves ahead of the sediment cloud.