Environmental transport in wetland channel with rectangular cross-section: Analytical solution by Chatwin's asymptotic expansion

摘要

Predicting the evolution of concentration distribution of environmental transport in wetland flows has a broad range of applications in ecological engineering practice. By extending a previous study, the spatial concentration distribution of solute transport due to an instantaneous environmental emission in a wetland channel with rectangular cross-section is presented in this work by means of Chatwin's long-time asymptotic technique. To account for the effect of high order moment, skewness of the transverse mean concentration distribution is analyzed. Two important parameters, i.e., aspect ratio (depth to width) and damping factor, on the dispersion process are discussed. Four studied cases illustrated that the transverse concentration distribution is nonuniform even at large time and the aspect ratio can affect the transverse concentration distribution greatly. The cross-sectional mean concentration distribution is asymmetrical in the initial stage and shows an asymptotic Gaussian distribution at large time. The dispersion process in a thick (width equals depth) wetland channel is quicker than that in a thin wetland channel. The spatial concentration distribution is dominated by the lateral-sidewall-effect on a large time scale for environmental transport in a thin wetland channel.