Lateral concentration distribution of contaminant transport in tidal wetland flows

Abstract

Tidal flows, in addition to the vegetation, introduce considerable complexity into the transport of contaminants in wetland flows. Under the hypothesis that wetlands can be treated as porous media, we apply the phase averaging technique to obtain the apparently continuous concentration distribution at the macro phase-average scale in tidal wetland flows, rather than the extremely complex concentration distribution at the micro plant scale. To meet the requirements of precise concentration in terms of peak concentration position and value for strict environmental and health risk assessments, this work studied the lateral concentration distribution rather than the generally studied approximate longitudinally distributed mean concentration. The lateral concentration functions for tidal wetland flows are concretely derived to support the first-order series expansion of the generalized dispersion model. We show that the lateral concentration nonuniformity can be qualitatively altered as the contaminant cloud is carried back upstream by tidal flows. The peak concentration position periodically appears at the center line or at the wall depending on the tidal flows, and the peak concentration value can even be increased in the transport process. Due to its analytical features, this work provides a model with low computational cost for effective environmental management.