Study of the Scour Hole Geometry in Downstream Plunge Pool of Siphon Spillway

One of the economical energy dissipater structures applying in high spillways is flip-bucket which falling flow causes scouring in plunge-pool at downstream. In this research, the bed variation as a scour hole at the downstream of a siphon spillway has been investigated. Dimensions and position of the scour hole were analyzed both experimentally and theoretically. The experimental results showed that the maximum scour hole depth was a function of discharge rate and downstream tail water depth. Also, flip-bucket angle had the most significant effect on distances of upstream hill and scour hole bottom from the spillway. It was found that the scour hole length, distances of downstream hill end point and maximum scour from the spillway were affected by the hydraulic conditions but they were less effected by the flip bucket angle and bed particle size. Also, it was seen that the flip bucket angle had a significant effect on upstream hill height. The height of downstream hill height was a function of flow discharge and tail water. Applying Buckingham π-theory, three variable linear equations were extracted to predict the dimension and situation of the scour hole and hills. The comparison between the measured versus the predicted values showed a good agreement between them.