Environmental dispersion in a two-layer wetland: Analytical solution by method of concentration moments

For the most typical two-layer wetland with free-water-surface-effect, analytically explored in this paper is the environmental dispersion in terms of the longitudinal evolution of the depth-averaged concentration. Taylor’s classical analysis for soluble matter dispersion in a single phase fluid flow is rigorously generalized for the two-layer case of a wetland flow to develop the dispersion model. The velocity profile of the fully developed flow through the wetland is derived, with that for the single-layer wetland flow included as a special case. Aris’s method of concentration moments is applied to determine the dispersivity with an asymptotic time variation. For typical contaminant constituents of chemical oxygen demand, biochemical oxygen demand, total phosphorus, total nitrogen and heavy metal, the process of dispersion is shown characteristic of a hierarchical structure in the critical length and duration of the contaminant cloud.

► To give the velocity profile of superficial flow through the two-layer wetland. ► To determine the environmental dispersivity in the two-layer wetland. ► To analyze the effects of characteristic parameters. ► To illustrate the evolution of contaminant cloud by critical length and duration of an influenced region.