Plunge pools are economic means to dissipate hydraulic energy of high speed flows. Plunge pools are usually at the end of either spillways or bottom outlets. The flood discharge is directed into an air water jet and travels through the atmosphere and eventually strikes the plunge pool in which the hydraulic energy is dissipated. Many scour problems result from those free falling jets downstream of the hydraulic structures. In recent years various researchers have investigated scour problems downstream hydraulic structure such as spillways and bottom outlets and numbers of empirical and semi-empirical equations have been developed for predicting the length and depth of scour hole resulting from the jet.