Equilibrium Scour Downstream of Three-Dimensional Grade-Control Structures

Abstract

To promote grade-control, bank stability, and fish habitat enhancement, three-dimensional structures installed within river channels are becoming increasingly popular choices for rehabilitation. A-, U-, and W-shaped rock weirs are commonly used in streams, yet three-dimensional scour holes develop downstream of the weir crest and often undermine the weir foundation. Current approaches for the prediction of scour depth and geometry are generally extrapolated from the case of two-dimensional flow. Furthermore, data from the literature regarding structures inciting significant lateral flow components are sparse. A series of laboratory experiments were conducted in which data from A-, U-, and W-shaped weirs were collected and evaluated using scour-prediction methodologies, focusing on their applicability to predict maximum scour depths. New dimensionless expressions were developed for the prediction of scour depth downstream of A-, U-, and W-shaped weirs on the basis of laboratory data that incorporate specific parameters accounting for weir geometry. The dimensionless expressions were compared with the most accurate relationship found within the literature, as applied to the compiled database, and mean error was reduced from 37.12 to 10.45%.