Flow boundary effects on scour characteristics upstream of pipe intakes

Abstract

Intakes are used to take water from reservoirs, lakes, and oceans. Depending on flow and geometrical conditions in which the intakes are located, sediment particles may also be entrained by the intake flow, resulting in a scour hole. Characteristics of scour hole are affected by the bed sediment properties, intake discharge, and intake position with respect to flow boundaries (i.e., dead-end wall, channel bottom, channel side walls). In this study, experiments were conducted to investigate the effects of the intake discharge, sediment size, and intake position relative to flow boundaries on scour hole characteristics. Entrainment conditions of sediment particles at the bed of the channel were also examined. Experimental results indicated that the maximum scour depth along the centerline of the channel was mostly affected by the sub-surface vortices extending from the channel bed to the intake. As the distance between the dead-end wall and the intake center decreased, the strength of the sub-surface vortices also decreased due to the effect of the friction imposed by the dead-end wall on the sub-surface vortices. Furthermore, the width and length of the scour hole decreased as the distance between the intake center and the dead-end wall increased.