An Experimental and Numerical Approach to Modeling Large Wood Displacement in Rivers

Abstract

Large wood (LW) is used for river restoration, aquatic habitat conservation, and flood control; however, it can pose a threat to human life and the built environment. The formation of LW jams, river management strategies, and design of mitigation measures crucially all depend on how the large wood is transported along a river. This paper experimentally analyses at laboratory scale the motion of natural sticks in a long stretch of a straight channel ((Formula presented.) 16 m), when LW is released at different locations and with different flow conditions. Results show that instream large wood, following a transient motion shortly after being released at the water surface, tends to follow preferential patterns along the channel. Froude number and location of large wood input may provide an estimation of the LW location in downstream reaches. Several mechanisms of motion were observed, some of which were very common, including a frequent tendency to assume a tilted position with respect to the direction parallel to the flow. The experiments also suggest that theories on secondary cells responsible for channeling LW in preferential directions are incomplete. A new model, based on acceleration induced by hydrodynamic actions, has been established and proposed in this work, showing promising results and paving the way for the development of a comprehensive model for transport of large wood at the river surface in full-scale applications.