Dams are often operated in a way to discharge over the spillways,which would cause a high dissolved concentration of air and be harmful to fish.The bubble transfer and the water surface transfer play an important role in affecting the concentration of the Total Dissolved Gas（TDG）.Based on recent numerical simulations of the total dissolved gas saturation,in this article,a two-phase TDG transport equation is adopted to develop an unsteady three-dimensional（3-D） two-phase flow Computational Fluid Dynamics（CFD） model,including a number of parameters such as water depth,pressure and air volume entrained.This model is used to predict the hydrodynamics and the TDG distribution under unsteady discharge conditions.Good agreement between measured and numerical results is obtained for a case study.
