An experimental and theoretical analysis of floating wood diffusion coefficients

Abstract

Wood transport during high flow events is here treated as an advective–diffusive phenomenon. A theoretical definition of the governing equation is first provided, highlighting the dependence of floating wood diffusion on the adoption of adequate diffusion coefficients. To estimate these coefficients, an experimental investigation on large wood debris was carried out in a channel presenting a weakly sinusoidal plant, employing regular cylinders with various sizes under different flow conditions. For each configuration, a consistent number of trajectories for the floating wood were acquired and processed through imaging techniques, allowing for a statistical analysis of the wood dynamics. The tests showed that floating logs travel at a velocity lower than the water surface one, not completely aligned to the flow direction and tend to disperse streamwise and transversely. Under the assumption that wood dispersion can be derived from the analysis of wood trajectories fluctuations, the longitudinal, transversal and angular diffusion coefficients were computed. Finally, a preliminary dimensional analysis is presented discussing the relevant spatial and temporal scales for these coefficients.