Predicting Equilibrium Scour-Hole Geometry near Angled Stream Deflectors Using a Three-Dimensional Numerical Flow Model

Abstract

Stream rehabilitation projects often involve the installation of instream structures such as flow deflectors. The objective of this study is to use the output of a three-dimensional numerically simulated flow field over a flat, predeformation bed to predict the planform extent of the equilibrium scour hole near stream deflectors of varying angles. It is shown that the upstream extent of the simulated flow separation zone determines the upstream limit of scour, whereas the lateral scour extent at the nose of the deflector is determined by the width of the separation zone. Further, scour depths are greatest in regions where strong downwelling (negative vertical velocity) exists, and the position of the local minimum dynamic pressure point in the simulated flow field defines the downstream limit of scouring. The results have implications for future design of habitat improvement structures where different angles and lengths of structures could potentially be tested prior to their implementation to determine the resultant scour geometry.