In this study, to evaluate the effects of geometry parameters on the dissipation rate in flows over the stepped spillways, a numerical model is provided and validated by using a physical model. A type of Fuzzy Inference System (FIS) is used to study the control of the rates of dissipation. It is used to measure the estimated energy dissipation under different scenarios, and the results are compared with prepared numerical database. An error criterion is used to examine the prediction accuracy of the FIS measurements. The realization of these kinds of considerations may, in turn, lead to a remarkable reduction in the dimensions of stilling basins. The results indicate that proposed FIS can be used as a valuable tool for operational control of dissipater structures with consideration of different geometric parameters. The method is proposed somehow to consider the uncertainty problems with consideration of the benefits, and some shortcomings noted in the literature.

Hydraulic jump is one of the rapidly varied flows that different elements can be employed to control it in stilling basins. The purpose of this study is optimal design of obstacles at USBR II stilling basin of Nazloochay dam model. For this purpose, the obstacles at the end chute with thicknesses and heights of 0.5, 1, 1.5 and 2 m and 2, 3 and 4 steps at the end USBR II stilling basin have been considered. Then for the most optimal state, the pressure, water surface profile, turbulent kinetic energy, and turbulent kinetic energy dissipation investigated for discharging 830 m 3 /s by using K-ε and RNG turbulence model and VOF method. According to changes in water height, obstacles selected with heights of 1 and 1.5 equal of standard state at the end chute and 3 steps at the end stilling basin. The comparison of numerical and experimental values of water surface and pressure profiles showed that numerical model has good agreement with experimental results. Also, hydraulic jump on adverse steps at the end stilling basin increase energy dissipation and stability of hydraulic jump. In addition, numerical model can be used to model stilling basins and measuring non-measurable parameters in laboratory.