Environmental dispersion in a tidal flow through a depth-dominated wetland

Presented in this paper is a theoretical analysis for longitudinal evolution of mean concentration of an environmental emission into a tidal wetland flow. The velocity distribution of the periodic flow through the wetland is derived, with that for a fully developed steady wetland flow included as a special case. The zero-th, first and the growth of the second order moments of the concentration are rigorously obtained by applying Aris’s method of concentration moments to derive the environmental dispersivity. The necessary time needed for the environmental dispersivity to attain a steady oscillating status is analyzed. The effects of some characteristic parameters, especially one representing the impact of vegetation in the wetland on both velocity profile and environmental dispersivity, and another identifying the effect of flow oscillation on the environmental dispersivity, are illustrated in detail. To reflect the dispersion enhancement by the flow oscillation, a typical example is given to characterize the critical length and duration of the contaminant cloud.