Predicting Plunge Pool Velocity Decay of Free Falling, Rectangular Jet

Abstract

Plunging jets from overtopping dams have the potential to erode dam foundations and abutments. The erosive potential of the jet is related to the energy of impact and the rate of energy dissipation in the plunge pool. A method was sought to predict the velocity decay of a free-falling, highly turbulent, rectangular jet in a plunge pool. Two types of jets were evaluated: a highly turbulent, fully air entrained developed jet; and a highly turbulent, nonaerated undeveloped jet. A model of a plunging jet was constructed to simulate these free-falling, highly turbulent rectangular jets. Data were collected from 14 tests, from which empirical equations were derived for the two jet classifications to predict jet velocity decay through the plunge pool. The jet velocity decay was determined to be a function of jet impact velocity with the plunge pool surface, jet density at impact with the plunge pool surface, the density of the water, gravity, and plunge depth. An expression was derived to compute jet breakup length to determine the jet condition at impingement with the plunge pool.