This paper reports a quasi 3D numerical simulation in a reach of the Yangtze River near The Nanjing City, China, aiming to develop a numerical tool for modeling turbulent flows and pollutant transport in natural waters. The recently built depth-integrated twoequation turbulence  ~ ~  k model, together with  ~ ~ k  and k w~ ~  models, were used to close non-simplified quasi 3D hydrodynamic fundamental governing equations. The discretized equations were solved by advanced multi-grid iterative method under non-orthogonal body-fitted coarse and fine two-levels’ grids with collocated variable arrangement. Except for steady flow and transport computation, the processes of contaminant inpouring and plume development, caused by the side-discharge from two tributaries, also have been investigated numerically. The used three closure approaches are suitable for modeling strong mixing turbulence. The established  ~ ~ k  model with higher order of magnitude of transported variable provides a possibility to elevate the computational precision. Based on the developed hydrodynamic model, a CFD (Computational Fluid Dynamics) software, namely Q3drm1.0, was developed. This tool focuses on the refined simulations of the steady and unsteady problems of flow and temperature/contaminant transports in complicated computational domains with the strong ability to deal with different types of discharges: side-discharge, point-source discharge/point-sink, and area-source discharge from the slope along bank. In this paper, only the study of side-discharge is presented.

Keywords: depth-integrated turbulence models; contaminant transport; numerical modeling; river modeling; multi-grid iterative method.