Effect of wind on contaminant dispersion in a wetland flow dominated by free-surface effect

Abstract

Flow and environmental dispersion are essential to ecological risk assessment and ecological restoration associated with wetlands. Presented in this paper is an analytical study for effect of wind on contaminant dispersion in a wetland flow dominated by free-surface effect. Based on the momentum transport equation generally adopted for wetland flow, the solution for velocity distribution in a free-surface wetland flow under wind is rigorously derived, with a limiting case covering the known solution of flow in the absence of wind. The thickness of inverse flow layer, maximum velocity, and its location are obtained. By use of Aris's method of concentration moments, the expression for environmental dispersivity in the free-surface wetland flow under wind is derived, and that in the absence of wind can be included as a special case. The direction and intensity of wind can influence greatly the environmental dispersivity at a stable stage. The time scale for environmental dispersivity to approach the stable stage is independent of wind. Analytical solution of mean concentration is derived and illustrated for a pulsed contaminant emission into a wetland flow dominated by free-surface effect under wind. For typical pollutant Pb, the length and duration of influence region with contaminant concentration beyond given standard level of water quality are illustrated.