Turbulent open channel flows with large variation of free surface shape and position have been calculated using Reynolds-averaged equations of motion together with a low-Reynolds number turbulence model. The free surface is represented by a height function. The effects of the free surface on the turbulence are incorporated in the model equation through a damping function. Test calculations of flows over a stepped slope and those past a drop with a trench have been compared with recent experimental data obtained by image velocimetry. The results show that the overall flow features can be well computed including mild hydraulic jumps. The detailed distribution of the turbulence parameters such as the-turbulent kinetic energy can be predicted fairly well but the quantitative reproduction will need further improvements of turbulence model.
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