Reattachment Length of Flow at the Lee Side of a Vertical Spur Dike in an Open Channel

Abstract

Spur dikes are deployed to regulate the flow in an open channel for navigation and bank protection as well as protection of beaches against erosion. The spacing between spurs is a crucial design parameter. The reattachment length at the lee side of a single spur dike may be viewed as the maximum spacing between consecutive spurs, as a larger spacing may result in propagation of the recirculation flow toward the bank between them. This paper presents a physically based approach to characterize and compute the reattachment length in the lee side of a vertical spur dike under both fixed and mobile beds. A new model is introduced based on the principles of momentum and energy. The reattachment length is inversely proportional to the scour depth, resulting in approximately a 4%‒38% reduction when reaching the equilibrium scour compared to no scour condition, and the relative reattachment length ranges from 8.5 to 13.5b for the scoured bed. The model is applied to the field data, and the predicted reattachment length is compared with the spacing between two consecutive spurs. This formula performs better in estimating the reattachment length than other reported formulas. It proves useful for hydraulic engineers to decide the efficient design spacing between spurs during bank protection and navigation channel regulation design.