Environmental dispersion in a three-layer wetland flow with free-surface

•To give a velocity profile of the effective flow through the three-layer wetland.•To present an environmental dispersion model by the extension of Taylor’s classical analysis.•To determine the environmental dispersivity by concentration moments method.•To analyze the effects of characteristic parameters on the velocity profile and environmental dispersivity.•To illustrate the evolution of contaminant cloud in terms of critical length and duration of an influenced region.

To further address the characteristic of contaminant transport in wetlands of a multi-layer structure, environmental dispersion of a pulsed contaminant emission into a steady flow is analytically explored in this paper for the typical case of a respectively vegetated or packed three-layer wetland dominated with free-water-surface-effect. The hierarchical structure for the critical length and duration of the contaminant cloud is illustrated for the dispersion of typical contaminant constituents.