Jalal Attari - Assistant Professor, Power and Water University of Technology, Iran
Mohammad Sarfaraz - Graduate Student, Department of Civil Engineering, Sharif University of Technology, Iran

Construction of large dams, using roller compacted concrete (RCC) technique, allows for steeply stepped spillways to form part of the dam body which leads into cost and time saving. If the ogee spillway crest and stepped chute profile are joined without a transitional stepped zone, the flow behavior would be unfavorable for low discharges. The flow falls on the bottom of first steps, springs out like a jet and impinges on some steps further downstream. This process of flow separation from the stepped bottom and successive impingement may cause significant damage on the steps. This paper presents the importance and need for the transition steps to join the ogee crest profile and the stepped chute. For this purpose, physical as well as numerical modeling was employed on a case study. The original design was modified by introducing a transitional stepped zone, in accordance with the CEDEX profile, and results showed a favorable flow pattern. Furthermore, the good agreement of the numerical results with physical modeling observations highlights the advantage of hybrid modeling for hydraulic structures

Stepped Spillways, RCC dams, Transitional Steps Zone, Physical modeling, Numerical Modeling