Th engineered log jams (ELJ) using large woods are widely used in stream and watershed restoration projects. ELJs can create diverse eco-hydraulic and scouring conditions that may benefit aquatic habitat and provide stream bank protection. They are also economical as the materials are usually locally available. The use of ELJs, however, has its challenges; for example, the potential complex shapes (size, shape, placement location, etc.) make their impact on local flow and scour dynamics very difficult to estimate, leading to the lack of good guidelines of their installation for a given restoration site. In this study, a practical, semi-automatic, 3D CFD model is used to simulate complex flows through ELJs. The specific purpose is to examine the ability of CFD model to compute the drag force acting on an ELJ giving a specific condition. Once the CFD model is validated, it is used to simulate various ELJ configurations, so that a better understanding of the ELJ drag force may be gained. Such knowledge is critical in developing a reliable method to represent ELJs in 2D depth-averaged numerical models which are still the practical design tools for stream restoration projects.
