Flow Characteristics and Energy Dissipation Over Traditional and Stepped Spillway with Semicircular Crest 1

Abstract-- The main purpose of traditional spillway with semicircular crest is to rise and control upstream (U/S) water level. In this study a new performance was added to this spillway, by making it as an energy dissipater. In order to study the energy dissipation percent (∆E/E0) %, the face of traditional spillway was making stepped three times as (Ns = 3, 5 and 7). Twenty four experiments were performed in a laboratory horizontal channel of 12 m length, 0.5 m width and 0.45 m depth for a wide range of discharge. Water surface profile and piezometric head distribution were studied over a traditional and stepped spillway of semicircular crest. The experimental results of the study of flow on traditional spillway show that an increase in (d0/dc) and (Fr1) value causes an increase in (∆E/E0)%, furthermore an increase in (d1/dc) value causes decreasing in (∆E/E0) % value. While, the experimental results of the study on stepped spillway show that an increases in (d0/dc) and (Y1/HC) value causes an increase in (∆E/E0) % , and an increase in the roughness Froude number (F*) value causes decreasing in (∆E/E1) % value. Two empirical equations were established for calculating the dissipation energy. Index Term-- Hydraulic structures; Traditional and stepped spillway; Energy dissipation. 1