Assessment of equilibrium pressure-flow scour depth by using jet flow theory

https://authors.elsevier.com/a/1fxjA3ZlciVEiV

Abstract

Most models for predicting pressure-flow scour depth are based on using continuity and energy equations. The present study presents a model to predict pressure-flow scour depth using the momentum equation considering the jet flow deflected by the bridge deck. By approaching the bridge deck, the upstream flow acts as a jet flow that deviates toward the bed. Below the bridge deck, a combined jet-flow is created as a result of merging the initial jet-flow and the pressure-flow. The continuity equation is used to determine the thickness of the separated zone and the combined jet-flow angle. Equations are presented to estimate the combined jet-flow velocity and the thickness of the combined jet-flow. The results reveal that the flow intensity, submergence ratio, and relative separated zone thickness are principal parameters affecting the pressure-flow scour depth. The proposed equation of this study shows sufficient precision to predict the equilibrium pressure-flow scour depth for the relative opening height of the bridge deck greater than 0.25. For the relative opening height of the bridge deck less than 0.25, insufficient duration of tests of the available data is a setback to verify the proposed equation.