Effects of wind on transient dispersion of active particles in a free-surface wetland flow

Abstract

Mechanisms of active-particle transport in a wetland flow under wind are significant for understanding various biological and ecological processes associated with wetlands. A transport model has been formulated to characterize the transient dispersion of active particles in a typical free-surface wetland flow exposed to wind. The transient evolution of total quantity, centred moving velocity, longitudinal dispersivity, skewness, and kurtosis of the active-particle cloud are analysed, using concentration moment method. It is found that the migration of active-particle cloud can eventually reach a stable status under the combined action of wind, hydrodynamics, and cell motility. The strong reverse wind can result in the negative centred moving velocity and longitudinal dispersivity along each streamline. The strong wind can considerably change the skewness and kurtosis of cell concentration distribution. The analytical solution of depth-averaged and two-dimensional concentration of active particles are derived based on Chatwin’s long-time expansion method, showing a distinct deviation from Gaussian distribution during the initial stage, which is in good agreement with the concentration moment analysis.