Experimental and numerical investigations of spatially-varying dispersion tensors based on vertical velocity profile and depth-averaged flow field

The dispersion coefficient is the most crucial parameter that governs the model prediction of pollutant mixing in rivers. However, the spatial variability of dispersion coefficient associated with velocity structures has not yet been thoroughly investigated. In this study, two types of spatially varying dispersion tensors were considered using both the vertical velocity profiles (DF) and the depth-averaged flow fields (DA), and the pollutant transports using DF and DA were compared with tracer test results in a meandering channel. The results showed that the peak concentration and arrival time were more accurately predicted by using DF than DA, because the flow properties associated with the shear induced dispersion were explicitly incorporated in the DF. The spatial distributions of the DF showed variations in both stream-wise and span-wise directions due to the creation and destruction of secondary flow in the meandering channel. In contrast, the DA only changed in the stream-wise direction. Therefore, the DF is advantageous to reproduce shear dispersion processes.