Relation between transverse dispersion and diffusion at meandering channel in two-dimensional mixing based on tracer tests

Abstract

It is fundamental task to reveal the mechanism of the dispersion and the diffusion on solute transport in open channel flow. In this study, the dispersion and the diffusion coefficients were observed and compared with each other based on the tracer tests at a prototype channel in the Andong experimental site, South Korea. The channel has sinuosity of 1.2 and can control the flow rate. For each experimental condition, measurements of average velocity by wading and the turbulence intensity were performed with a fixed device. The dispersion and diffusion coefficients were calculated using a dissolved tracer (Rhodamine WT) and a surface particle tracer (GPS floater), respectively. For each channel section, based on the tracer experiments, the transverse dispersion coefficient and transverse diffusion coefficient were calculated. The observed diffusion and dispersion coefficients were laid on the reliable ranges. The relation between dispersion and diffusion was analyzed by comparing the transverse diffusion coefficient, calculated by the diffusion of surface particles, and the transverse dispersion coefficient, determined by the surface flow velocity, which was calculated using the vertical distribution equation. Based on the analysis, the results that the turbulent diffusion coefficient is proportional to the turbulence intensity, and the transverse turbulence intensity is proportional to the transverse flow velocity. Also, the transverse flow velocity is relative to the transverse dispersion coefficient. Thus, the correlation between dispersion and diffusion is confirmed by the experimental results, and a formula that could be converted based on the relation is proposed.