Abstract: The dispersion of the contracted jet from a spillway with flaring gate piers for high arch dams depends on the distribution of the velocity at the exit section of the jet.In this research,a 3-D numerical simulation of spillway with flaring gate piers is presented with the volume of fluid (VOF) method for the free surface flow in order to find out the hydraulic features.The results show that four kinds of flow patterns emerge,depending on the water heads over the weir and the geometrical meters of the flaring gate piers.The discharges and water surface profiles from the numerical modeling agree with the experimental results from different flow patterns,including free over-fall,shockwave,hydraulic jump and subcritical flow,which verifies that the model is suitable in this situation.