Estimation of Longitudinal Dispersion Coefficient in Ice-Covered Rivers

Flow structure and dispersion characteristics change significantly in ice-covered channels and rivers, and the longitudinal dispersion coefficient is an important parameter for water pollution control and environmental protection. Considering the secondary flow in ice-covered channels and based on the Shiono and Knight method (SKM), the lateral distribution of the depth-averaged velocity in ice-covered channels is solved in this study by adopting a power series. The result agrees well with the original analytical solution and experimental data. The longitudinal dispersion coefficient caused by nonuniform distribution of transverse velocity is derived using Fischer's triple integral formula, and the longitudinal dispersion coefficient formula in a rectangular experimental ice-covered channel is obtained by regression analysis, which coincides with the experimental results. The computational formula of longitudinal dispersion coefficient in natural ice-covered rivers is obtained by logarithm linear regression of the longitudinal dispersion coefficient in an experimental ice-covered channel based on the mapping relationship between the data obtained from experiments and natural rivers. The measured data and the corresponding dispersion formula in natural ice-covered rivers show a mean error rate of 28.4%, which verifies the correctness and the rationality of the proposed formula. The proposed formula can be used to estimate pollutant transport in broad and shallow ice-covered channels and natural ice-covered rivers. The comparison with ice-free rivers shows that the longitudinal dispersion coefficient of ice-covered rivers is considerably smaller than that of ice-free rivers. (C) 2018 American Society of Civil Engineers.