Stepped spillways have a wide range of applicability as a hydraulic structure in large dams to dissipate energy of high-velocity flows at a downstream area of dams as well as release overflows into the downstream. In this study, the numerical simulation of the flow over the stepped spillway was investigated by using Flow3D software as an analytic flow field. The RNG k-ε model was applied as the turbulence model, and Volume of Fluid (VOF) model was used to determine the free surface flow profiles. At the first stage, the model was verified by reliable experimental data. Then, in order to investigate the various features of skimming flow regime, 112 numerical spillway models was designed, which 96 models were stepped spillway models and 16 models were smooth spillway models (i.e., WES profile). In these numerical experiment, two step sizes, six configuration, four passing discharge and four profile slopes (15, 30, 45 and 60 degrees) with various relative discharges were considered to investigate the energy dissipation and discharge coefficient rates. The results indicated that discharge coefficient rate and energy dissipation rate have inverse relationship. Also it was observed that when relative discharges increased, energy dissipation rate decreased and discharge coefficient rate increased.
