Effect of sedimentation behind Ogee spillways on the flow characteristics

In this study, the effect of sedimentation behind Ogee Spillway on the characteristics of flow including upstream head and velocity, discharge coefficient, water surface profile, critical depth position and flow conditions downstream of a spillway, are investigated experimentally. The experiments were carried out by using an Ogee spillway with height of 25 cm and different upstream side slopes as 1H: 3V, 2H: 3V and 3H: 3V. The used sediment had a diameter of 0.4 mm and sedimentation heights in the range of 0-24 cm were considered. The results showed that the upstream flow depth and upstream flow velocity are increased by increase of sediment level upstream of spillway. As a result, the design head (He) will be increased. A change in He decreases the discharge coefficient of spillway. It was also found that the discharge coefficient changes from 2.25 for no sediment deposition (first stage of operation) to 1.69 for full sediment deposition in upstream reservoir. Thus, these results showed that the design of diversion weirs based on initial conditions is not accurate and causes major problems during operation of diversion weir.