Kamyab habibi - Master of water and hydraulic structures, Behbahan Khatam Alanbia University of Technology.
Farinaz Erfani fard - Postgraduate student of water and hydraulic structures, Behbahan Khatam Alanbia University of Technology.
Seyed Amin Asghari pari - Associate Professor of Civil Engineering, Behbahan Khatam Alanbia University of Technology

The simple structure and great amount of energy dissipation in the stepped spillways have made them be used in great amounts in dams. Due to the dissipation of a significant amount of energy along the spillway, we usually do not need to build stilling basin downstream of the dam. In this research, the effect of continuous obstacle with the identical relative height of ۰.۱۹, ۰.۳۸, and ۰.۵۵ on the edge of ۴-steps stepped spillway in all the three flow regimes of Nappe, transitional, and skimming has been studied and compared to the similar modes of ۸-steps ones. The results show that the continuous obstacle on the edge of the steps can generally make the flow change into a skimming state with a passing flow lower than the flat step. For the dissipation of energy, we only saw the positive effect in the Nappe flow comparing the flat step, and this effect is negative for the other regimes. This effect has been increased along with the increment of the identical relative height.

stepped spillways, energy dissipation, natural airing, continuous obstacle, the identical relative height of the obstacle