Accurate prediction of water flow and transport is important to hydraulic and coastal engineering. Over the last several decades, continuing efforts have been made to construct a numerical model that can predict complex environmental flow phenomenon with the requirement of generality, accuracy and efficiency. In order to simulate complex flow, hydrodynamic models based upon the three dimensional Navier?CStokes equations seems a promising approach with the development of computation technology.

There are two ways to describe the moving air?Cwater interface, the first is Eulerian method, while, free surfaces are captured by using marker and cell method, volume of fluid? method, and level-set method; the second is the arbitrary Lagrangian?CEulerian method. Although capturing methods can deal with complicated free surfaces (e.g. breaking waves), dense or adaptive grid should be used in order to compute moving free surface accurately, which limit practical applications of these kinds of models. The main problem for the arbitrary Lagrangian?CEulerian method is rezone process when fluid undertakes large deformation. For free-surface elevations with a single-valued function of horizontal positions, varying grid and free-surface can be effectively treated? with relatively small computational cost,? For example, the method of σ-transformation in computation domain.

To insure the quality of the simulation results, a computational model of flow and Numerical modeling should be verified and validated before application in solving practical problems. Model verification and validation usually follow three steps :(1) Verification by Analytic Solutions. The agreement between analytic and numerical solutions certifies the correctness of the mathematical formulation, numerical methods, and computer programming. It can also determine errors of numerical solution quantitatively. (2) Validation by Laboratory Experiments. Because laboratory experiments conducted in controlled environments can eliminate many unnecessary complications, the numerical model should be able to reproduce the same physical phenomena measured in laboratories. (3) Validation by Field Measurements. One portion of the field data should be used to calibrate the physical parameters in the model, and the remaining data can be used to determine whether the computational model can simulate the real-life ??problem. Researchers must realize that the numerical results may only approximately agree with the measured data, because the computational model only represents a simplified version of the physical processes in natural rivers. How ever, the realistic trend of spatial and temporal variations should be predicted correctly.

In order to simulate complex flow, hydrodynamic models based upon the three dimensional Navier?CStokes equations seems a promising approach with the development of computation technology. In the present article, a conservative unstructured collocated grid scheme is employed to solve the three-dimensional, non-hydrostatic Navier-Stokes equations. Comparisons with analytic solutions, laboratory experiments and field measurements were given also.