This PH.D dissertation aims to develop a 3-D numerical model of dam-break flows on movable beds. Three tasks are defined to accomplish the goal of this study. The first task is developing a 3-D hydrodynamic model to simulate dam-break flow on fixed beds with simple geometry and test the water surface tracking technique. This model solves the Reynolds-averaged Navier-Stokes (RANS) equations using a finite-difference method on rectilinear, staggered grids. The volume-of-fluid (VOF) technique with SOLA-VOF advection scheme is used to capture the free surface motion. The developed model is tested using several experimental dam-break flows and the VOF technique is found to be able to effectively treat the rapidly-varying water surface boundary of dam-break flows. As the second task of this dissertation, a 3-D finite-volume model is developed to simulate dam-break flows on irregular fixed beds. Developing this model is necessary to accomplish the major goal of this dissertation since the finite-difference model explained above, which uses the rectilinear staggered grid, is not convenient to extend to the case of irregular and movable beds and integrate with sediment transport calculations. This model solves the RANS equations using a finite-volume method on irregular hexahedral, collocated meshes and adopts the compressive interface capturing scheme for arbitrary meshes (CICSAM) as the VOF advection method. The model is tested by means of experimental dam-break flows on fixed beds with simple and irregular geometries. The final task is extending the 3-D finite-volume model to a dam-break flow model applicable on movable beds. Therefore, it is integrated with a sediment transport model developed in this study. The sediment transport model solves the non-equilibrium transport equations of suspended load and bed load separately and in turn calculates the resulting bed change, based on the flow properties calculated by the hydrodynamic model. Since the time evolution of bed topography affects the hydrodynamic calculations, the model uses a moving grid technique to update the computational grid to fit on the calculated bed topography at every time step. The grid moving velocity and the computational cell volume change generated by the moving mesh are taken into consideration when the governing equations of the hydrodynamic and sediment transport models are discretized. The integrated model is tested using several experimental dam-break flows on movable beds. The calculated spatial and temporal variations of water and bed surfaces are generally in good agreement with the measured data
