Transient dispersion of an initial point pollutant concentration in wetland flows

Initial point pollutant transport in wetland flows acts as a typical form in various applications. Accurate determination of the basic characteristics for dispersion fundamentally supports the predication of pollutant transport especially in the transient stage. This work analytically studies the transient dispersion of an initial point pollutant concentration in wetland flows through the phase average technique and the method of concentration moments. The characteristics including the vertical mass distribution, longitudinal displacement, dispersivity, skewness, and kurtosis corresponding to the zeroth- to fourth-order concentration moments are accurately illustrated in their full-time dependance for the first time. Present results show to be distinctive from those of initial uniform concentration in the transient dispersion process. The temporal evolutions of the five characteristics are all dependent of the initial point release position. The results further demonstrate that the timescale 3.0 as measured by the skewness, rather than 0.5 as measured by the dispersivity, should be characterized as the transient period for the dispersion of initial point concentration in comparison with that of initial uniform. Furthermore, the longitudinally distributed mean concentration is as well analyzed through the Hermite polynomials. The results imply that strict criteria for environmental and ecological implications should be established by further accounting for the five characteristics.